Peak limiting for driver protection
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Topic: Peak limiting for driver protection
Posted By: Augusts
Subject: Peak limiting for driver protection
Date Posted: 26 December 2022 at 11:39am
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Hey! I have been doing a lot of digging and there are a lot of approaches and its a very complicated process alltogether but to simplify - If a speaker reaches its Xmax at 1000w AES, than, using the XTA dsp with the look-ahead limiter, should I set the peak limiter +6db or + 3db above the RMS limiter. I am asking this because I have almost destroyed a voice coil by hitting it against the backplate, with using just the rms limiter. As I understand RMS limits the speaker at the given rms value and then it lets the music still be dynamic by letting throught what is called the program material. and then there are peaks that are not important in the subwoofer Xmax context because peaks are so fast that the cone does not travel the distance of what 4000w peak power would do if it was not a peak. Do I understand correctly or not? The thermal power rating I understand its aes+3db program plus 3db peak. but I am curious about how these two XTA limiters work together in the coil travel context Thanks A
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Replies:
Posted By: Augusts
Date Posted: 26 December 2022 at 11:43am
| If I have an amp with a peak limiter than should I set it plus 3db above DSP RMS limiter or can I set it plus 6db, thus also raising the amps rms power by 3db. The DSP limiter would still be at 1000w but would not that exceed the Xmax if I raise the amps power by 3db |
Posted By: toastyghost
Date Posted: 26 December 2022 at 5:11pm
I’m afraid it's more complicated than that. The AES power handling value on a driver's spec sheet is for the transducer suspended in free air with a particular filtered pink noise test stimulus. The wattage shown on the spec sheet is a calculated value, based on the RMS voltage and the single-value nominal impedance of the driver, again in free air. The more in-depth Klippel Large Signal Identification testing system reports the measured Real Power applied to the driver over a given test period, but this is not done by all manufacturers or for all transducers. If it is, the values are not often publicly available. They can be very revealing, however; as an example, a top-tier best-in-class 18" driver that is very popular across the world has an AES power rating of 1700 Watts, but the plot of the rise in voice coil temperature, and the measured Real Power dissipated in the driver over a 1-hour period shows a different story:  This chart shows that the thermal rise of this particular driver stabilises after 30 minutes of a continuous signal. We see a 125-degrees C increase in the voice coil temperature during the test, which didn't increase further so long as the Real Power applied did not exceed 300 Watts. During that test, the voltage logged at the driver terminals was 63 Vrms and 201 Vpk, and a little shy of 4 dB power compression was observed in the output SPL. The DC resistance (Re) of the driver had changed from 5.4 to 8.4 Ohm after the test was completed, too. Please understand this does not mean the AES rating is a lie. You just need to understand the conditions of the test and how it applies to real-world usage. These values are unlikely to remain the same when the driver is mounted in your cabinet, as the box loading will not only modify the electrical impedance curve of the driver but also changes the amount of airflow or cooling to various parts of the hardware. All of this means that finding the best thermal, RMS voltage, peak voltage and over-excursion limiter thresholds not only requires an understanding of how the driver behaves in the cabinet but also the types & durations of signal that it is likely to be driven with. Spanking a subwoofer with heavy rolling electronic bass lines for 16 hours, every day for half a week at a festival is going to require a more strict threshold than the same box installed in a church with the odd Christian rock band. For the example driver shown, I'd be comfortable with a thermal limiter threshold of 500 Watts, but know that this will be giving up some headroom for increased safety. I'd also like to do that using a dedicated thermal limiter which tracks the change in current versus the electrical impedance as the driver & coil temperature goes up or down - I'd use separate RMS and Peak voltage limiters, and base those on when the box starts to distort heavily or suffers from other non-linear behaviour. There's a test process described in the AES2012-2 standard to determine the Maximum Input Voltage a given speaker in a given cabinet can handle, before power compression starts to sap the output level down and thermal runaway begins. It's commonly called the "Toaster Test" because you deliberately heat the thing up, but it's non-destructive when done properly. In simple terms, you bypass all DSP processing and measure the frequency response of the output while driving the box with an increasing level signal, using pink noise that has been filtered in a suitable way to prevent applying too much signal way outside of the intended frequency range of the speaker. That’s typically using the curves supplied in either IEC 60268-1 or CTA-2034 for subs & full-range speakers, or a simple second-order Butterworth HPF for HF drivers. Once the level has dropped by 3 dB in comparison to the sensitivity measurement, the input voltage is logged. That goes into GLL or CLF data, and can be used to choose a suitably-sized amplifier to drive the speaker without clipping. The process has been updated a couple of times over the years, but these two links cover the common approach: https://www.prosoundtraining.com/2012/09/20/loudspeaker-maximum-input-voltage-test-results/ https://www.prosoundtraining.com/2013/11/22/the-loudspeaker-toaster-test-revisited/ These days, anyone can do this test at home with: - a powerful amplifier - a cheap two-channel audio interface - dual-channel FFT software - a 1/3 octave band equaliser - a True RMS DMM/voltmeter - a microphone ()ideally a measurement one, but a good condenser or even SM58 will do in a pinch we’re only interested in the relative change in level when compared to an initial measurement) - 30 minutes or so of free time - friendly neighbours (or a large bribe for them to go somewhere else for the afternoon) The IEC 60268-1 curve can be approximated on a graphic equaliser with the following adjustment:  An example of traces taken from the EASE SpeakerLab manual’s guide to the test process:  In general, the MIV obtained in this process might seem to be lower than it you’d expect. That’s because it is an approximate test - to do better, you’d need a lot more kit to monitor the temperature of various bits, the impedance curve and so on. Which is why a Klippel Analyser with the relevant modules costs thousands of dollars. You don’t need those to get in the ballpark though. I could perhaps be persuaded to find time to make an updated step-by-step guide or video on how to do this using the freeware OpenSoundMeter or the free version of ARTA in the new year, if people are keen. The Peak voltage limit threshold is then typically set somewhere between 6 dB and 12 dB above the RMS voltage threshold, but it again depends on the likelihood that the signal applied to the box has a low crest factor or not. Another, and in my opinion much better, method to find the peak voltage threshold is to conduct a distortion-limited stepped level test using a dense multitone stimulus. See Production Partner test for an example. The distortion threshold varies, but 10% for subs and 3% for full-range boxes is common. That way, you ensure the speaker sounds good which is kind of an important goal, although it seems many don’t agree with me from listening to a lot of rigs… Same for the attack and release thresholds; a limiter that engages before completing a single cycle of the lowest frequency the speaker is designed to play will sound bad. For subs, the lower Peak overshoot value might be advised - so long as the system operator will pay attention and back the drive level off to maintain headroom and clarity when the limiters are engaging often. For a 6 dB increase in output you need four times the power, or two times the voltage: http://www.sengpielaudio.com/dB-chart.htm Here are some example limiter threshold values for a ported 18” subwoofer cabinet with a processed response of 30 Hz to 100 Hz. It uses 4 Ohm nominal drivers, each rated at 1700 Watt AES, and the magnets have a clear air path to the outside world via a large opening: RMS: 80 Volts (0.8 seconds attack, 1 second release) Peak: 160 Volts (32 ms Attack, 256 ms release) Thermal: 40 Volts (3.0 Second Attack, 3 Second Release) XMax: 60 Volts at 25 Hz That last one is often overlooked, but it dictates what kind of filtering the box needs to support the peak voltage limiter threshold. 60/160 = 0.375 A voltage ratio of 0.375 is a decrease of ~8.5 dB, so the electrical HPF used on this speaker must produce an acoustic level drop of 10 dB or more by 25 Hz to prevent over-excursion For the sake of head maths, let's assume that the box's unprocessed output frequency response is ruler flat with a -3 dB point of 30 Hz and a natural second-order roll off below there (as for a ported cabinet). In that case, considering port compression and such that makes the large signal frequency response deviate from flat, we may need to add a fourth-order (24 dB per octave) Butterworth HPF at 35 Hz to meet the above condition at all drive levels. The idea is that you should very rarely see the RMS voltage limit engaged in normal use. A well-chosen peak limiter can flick gently on signal peaks. If you're seeing either of these limiters engaged often then you probably should have brought more speakers. If it's on a lot, you're may start to be heat up the coil because the signal's peak-to-average ratio goes down - it's getting compressed. That's when a dedicated thermal limiter (with a very slow attack and release in seconds) can save the day, acting as a last line of defence to avoid burnt coils. There's plenty of reading out there on general practice for limiting. Likewise for simple calculators for various tools. Powersoft provide some useful bits of both, which don't require you to use their amplifiers https://www.powersoft.com/wp-content/uploads/2019/01/powersoft_TN009_LimiterSetup_en_v1.0.pdf https://www.powersoft.com/en/ufaq/how-to-calculate-limiter-values/ If you're after a quick answer, I'm afraid there aren't many of those that don't massively over simplify the situation. Unfortunately, your XTA only features a single RMS limiter, so you're going to have to choose a value that's somewhere between absolute thermal protection and keeping a good amount of headroom in the system. |
Augusts wrote:Posted By: Conanski
Date Posted: 26 December 2022 at 5:16pm
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An RMS limiter offers zero driver excursion protection, it's purpose is to control voice coil heating which occurs over an extended period of time so it completely ignores momentary peaks. As a measurement AES does not equal RMS despite lots of online sources suggesting it does. And if we are being rigid about it RMS is always a voltage measurement, there is no such thing as RMS power, but everybody uses it so we may have to igore that. The AES test signal has a 6dB crest factor(peak - continuous average ratio), that continous average is what heats a voice coil and if we are talking about power in this case it is 25%(-6db) of the peak value. The RMS value of that same test signal would be 0.707 of the peak value or 50%(-3dB) of power. If you want to thermally protect a driver with an RMS limiter then it has to be set at the AES continuous average, if you set it at the calculated RMS value it offers no protection. The peak limiter should be set at the peak voltage that results in driver xmax or maybe xmax+3dB depending how much warmth(distortion) you like to hear. Forget about the published ratings for the drivers, they are calculated(theoretical) and depending on the cabinet design the driver may never be able to handle that much power. So in your example if a driver hits xmax at 1000w that is what the peak limiter should be set at or perhaps +3db as mentioned above, and the RMS limiter should be set at 1/4 of that or 250w. See the link for some actual driver test results.. https://www.aesmelbourne.org.au/wp-content/media/AES-Dec2021-final.pdf" rel="nofollow - PowerPoint Presentation (aesmelbourne.org.au)
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Posted By: Earplug
Date Posted: 26 December 2022 at 5:24pm
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In my experience, the maths here are only a rough guide. There really isn't anything that can be cast in stone - like so much when it comes to sound - or engineering in general, when you are balancing several factors that may be in conflict with each other. It will depend on the processor, amp/s & driver/s. The best is to get levels set by injecting some noise into the system, listening carefully & maybe monitoring the o/p of the amp with a scope, or multimeter to check on the voltages/clipping. And if you can also monitor the temperature of the drivers, even better. There is no point trying to squeeze that extra 1/2 dB from the speakers, when you'll just loose 3/4, or more due to overheating. It makes no sense. If you want louder, take more gear!!  ------------- Earplugs Are For Wimps! |
Posted By: Augusts
Date Posted: 26 December 2022 at 7:26pm
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Ok, so Powersoft suggests RMS or True Power for a woofer that has a 4" voice coil 250W max to not to overheat. Then Hornresp says that my simulated speaker RMS is 1000W@4ohms or 63Volts, that hits the Xmax. So I guess than it does not matter how is it called but I know that at that point it hits Xmax. XTA manual calls the limiter a Program limiter BUT points out that I should be looking for the speaker RMS power rating, and calls the peak limiter - a limiter to protect the speaker from over excursion. So concluding from all this, and what I read from your posts, the XTA peak limiter should be set to 63Volts and the Program limiter should be set to 1/4 of that, being 250w for a 4" voice coil and plus 6db for the peak limiter. And if I would like to be very precise with the power rating I should do the test that you suggested and take that as the limit. I guess my delusion was because in my mind I had calculated that a conventional limiters' treshold is meant to limit the musical material to at say a 1000W and it lets trough only peaks that are shorter in time than for example a 100hz for a subwoofers LP filter that is 10ms. That would mean that the coil would not move further than the treshold set to a 1000W if the attack time is 8ms for example. |
Posted By: Augusts
Date Posted: 26 December 2022 at 7:37pm
| But, in that case, I don't understand how all the manufacturers except for D&B Audiotechnik perhaps, provide insane AES and RMS, Program, Peak Power ratings for their speakers. I cant imagine an 18" subwoofer with a 4" voice coil that the specs would say 250rms (or AES) and 500w Program. Maybe 10 years ago. |
Posted By: Augusts
Date Posted: 26 December 2022 at 7:44pm
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I have done a lot of speaker simulations and in no case it would be possible to have a 4000W RMS speaker that plays 40hz at that power. If we assume that that would be the peak power value that a sim like Hornresp provides. I think its not.
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Posted By: Augusts
Date Posted: 26 December 2022 at 7:57pm
| Ok I get it I think. The simulation simulates 1000W RMS amplifier power. And an amps Vpeak would be 3db more. |
Posted By: Augusts
Date Posted: 26 December 2022 at 8:00pm
| But I still don't get where the big guys get 1500W AES and 6000W peak from a speaker enclosure. |
Posted By: Conanski
Date Posted: 26 December 2022 at 10:01pm
It's theoretically possible with program material that has 12db crest factor or more, that would result in 375w continuous with 6000w peaks.
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Posted By: toastyghost
Date Posted: 27 December 2022 at 5:11am
Edit: double post due to terrible signal halfway up a mountain  To make it not be a complete waste of space… Like most software modelling tools (and real world constant voltage amplifiers and loudspeakers) Hornresp applies a drive voltage to the modelled design, using the value set in the Eg field when defining the model. It calculates the current demand versus frequency based on the predicted electrical impedance curve. The power values shown are then calculated from that. This produces Apparent Power, not Real Power. There are scaling tools on the various plots of data it produces, and some of these allow a wattage value to be entered for convenience. However, this is back-calculated to determine a new drive voltage, before the model’s output values are recalculated. |
Posted By: toastyghost
Date Posted: 27 December 2022 at 5:12am
Like almost everyone else, the spec sheets are written by marketers not engineers. They use the AES power rating for the transducers mounted in the box on the spec sheet, but rarely drive them at this level on their DAP amp platform unless they’re keen to make even more cash selling the operators of their systems spare parts  As I said before, the AES rating for a driver is not a lie. People just seem to rarely check the what the test standard entails and how that applies to their use case.
As the vast majority of music does, for the majority of the 20 Hz to 20 kHz that we are interested in. Even if you're playing modern electronic bass-heavy music which can have a 6 dB crest factor in the lower notes when analysing the full track, the resulting crest factor of the signal the speaker terminals will typically be closer to 9-12 dB due to the use of a high pass and low pass filter on the DSP. It's quite easy to test this out for yourself. Just analyse the electrical signal at the output stage of your DSP's sub channel while playing your heaviest tracks. Either in real-time using an RTA tool such as the one in REW, or by making a recording of it using a direct balanced connection to the input of an audio interface and then analyse that with something like Audacity or Reaper. The M-Noise study that led to the AES75-2022 standard did essentially this process for hundreds of thousands of music tracks across all genres, and of course found that crest factor is actually far higher for the upper HF region, at 16-20 dB. A 20 dB increase in output level to handle those peaks without clipping requires 10 times the voltage and 100 times the power in comparison to the average signal level. If you're not shattering HF diaphragms regularly when using an 8 ohm nominal compression driver rated at 60 Watt AES, and we use the common spec sheet peak power handling of 4 times the AES test value, that means the RMS voltage applied to your compression driver should be just 4.38 Volts, or 2.4 Watts average to ensure you are reproducing the music as it's recorded. That's not such a problem when the driver and waveguide has a voltage sensitivity of 114-116 dB with 2.83 V applied to it. You'll be hitting 135 dB on the peaks with the above values. An arguably bigger problem is that a whole heap of premium loudspeakers are well into harmonic and modulation distortion levels above 5% by that point, which almost every study shows is clearly audible and unpleasant. Some of the peak or max SPL values listed on manufacturer spec sheets are at 10% distortion for full-range speakers, which is almost unlistenable. Look up some of the Production Partner “im test” reviews via Google Translate. They’re quite thorough, and show the average and maximum SPL thresholds achieved for a suitable distortion level when using various test signals that represent music well. There are several subwoofers and full-range speakers of various sizes in their archive. |
Posted By: Augusts
Date Posted: 27 December 2022 at 11:17am
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I might have posed the question inaccurately. I have no questions about MR and HF drivers because they are kinda in their own acoustical environment and I usually trust the manufacturers given power ratings. My concern was with subwoofers where excursion comes into consideration about how to limit everything. It does not matter wether the system goes into limiting or does not, I want my drivers to be safe. For example for a Xilica processor, it has just one limiter, the standart RMS one or some might say that it is an AES value that we input into the limiter calculator (Funktion BTW has updated their calculators section.) So the question would be, if I am designing my own speakers and I know my way around hornresp, I can see the actual driver power at every frequency but I want to choose the right amp and the right treshold for a Xilica limiter - Hornresp power input is 1000W RMS 4 ohms and the driver side of the simulation is under control, everything is fine. Then should I set the limiters treshold to 1000W RMS 4ohms or 500W RMS 4ohms? And would I have to have and amp of 2000W RMS 4ohm or 1000W 4ohm? Because I know that I need at least 3db headroom for the peaks that the limiter lets through for the signal to stay dynamic. All of this that I am talking about is theoretically, what would be the right approach of setting the treshold for a subwoofer to stay in the Xmax zone. If a peak is shorter in time that the most upper frequency in time that the upper LP frequency of the woofer (100hz) then I can safely set the amps Vpeak limiter +3db than the Xilicas dsp treshold.
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Posted By: Augusts
Date Posted: 27 December 2022 at 11:24am
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I have never had problems with overheating. But I have however destroyed quite a few coils by hitting them at the backplate due to feeding excessive power to them. I know I have to have more boxes but that does not mean that they should be limited incorrectly. In my case, I think I am going to go with 1000W treshold for Program limiter and +3db for peaks
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Posted By: toastyghost
Date Posted: 27 December 2022 at 11:48am
I’m not sure why you still think a 3 dB overshoot is sufficient, in any pass band. It suggests you either haven’t read or haven’t understood everything that’s been posted in this thread. For subs, a 6 dB ratio between RMS and Peak voltage limiter values is common for a reason. Also, as I mentioned on the previous page, Hornresp is calculating the Apparent power from the drive RMS voltage and electrical impedance curve. The Wattage power value cannot be a single number for all frequencies; this is why sensitivity and such must be measured by applying a fixed voltage. The vast majority of DSP limiters are also based on an RMS voltage value. This is because you cannot have RMS Power, since it is calculated from the RMS voltage. Only modern “smart amps” which directly integrate the DSP into active monitoring of the amplification stages and load that can use limiters based on the Real Power or current delivered to the drivers. Powersoft have white papers on their TruePower limiter which explain this, and the limitations of a single-value RMS voltage limiters to control thermal rise. If you check the Xilica manual, I believe there is a peak limiter in the signal chain but it’s values are fixed in relation to the pass band’s electrical HPF. Similar to the “Auto” option on a XTA DP series. |
Posted By: Augusts
Date Posted: 27 December 2022 at 12:47pm
Have not understood. This is by applying 1000W@4ohm or 63Volts from the amp, and this is what the driver receives at given frequencies, this is with HPF and LPF applied. But I still dont understand does setting the limiters treshold at a 1000w would protect the driver from over excursion. Just a simple question limit at a 1000W or limit at 1/4of a 1000w to leave space for +3db program material and +3db peaks. I dont care about overheating because this driver is rated 1200w AES and they have been playing in a club with limiters engaged for about 5 years and still are working fine.
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Posted By: Elliot Thompson
Date Posted: 27 December 2022 at 12:50pm
98% of the people in the sound industry have never encountered banging the voice coils on the back plate. So their experience under your circumstance is minimum to none. I have experienced such a phenomenon decades ago so, I know exactly what you are talking about.
Your situation is due to either feeding the driver's voice coil frequencies they are incapable of producing or, the loudspeaker is unloading in the box.
All loudspeaker voice coils have a limitation on what frequencies they can produce from a dB Standpoint. It is relative to the TS Parameters as a whole in addition to your experience level on what the numbers mean as a whole.
As we know xmax has no influence on the calculated TS Parameters. It is the reason why you may see woofers moving back and forth as a piston with no sound being heard. That is due to the limitation of the TS Parameters and/or the Enclosure. The cone will still move back and forth regardless, as it is operating solely as a piston at this point.
Horn Response is not sophisticated enough to give you that answer. To find the answer, you would need a dB measurement microphone. Preferably non-C weighted.
Unloading is when the cabinet loses control of the loudspeaker and the driver is operating at the given frequencies as if it is not in a box. Erratic movement of the cone is a prime example of unloading. Again, Horn Response is not sophisticated enough to give that answer. A dB measurement microphone would give you the answer on where you stand from a sound pressure level.
The above is relative to how much power/wattage you are feeding the drivers and, how the loudspeaker is reacting to the box, based on it's TS Parameters at that given moment and time.
So your method is a good starting point. You must take your experience level of your own sound system into play. Use your own gut feeling. If you feel the drivers can handle more, then increase the limitation higher.
Best Regards, ------------- Elliot Thompson |
Posted By: Augusts
Date Posted: 27 December 2022 at 12:54pm
| I shall be doing a toaster test |
Posted By: Augusts
Date Posted: 27 December 2022 at 1:00pm
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Thanks. After I discovered that the amp has a Vpeak limiter, I set it to RMS +3db and the woofers now are not hitting the backplates even if the limiter is never switching off. I just wanted to clarify what is all this AES, Program and Peak values because my gut feeling is telling me that something is still not right I guess a toaster test without limiters and then with limiters on and cranked all the way up would give me realistic data
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Posted By: Earplug
Date Posted: 27 December 2022 at 1:30pm
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Yes, as I mentioned before, just relying on the maths - or models is not going to do it. And trying to decipher some of the data given out by some manufacturers is a waste of time. The only way is to test, use your ears and definitely measure everything you can. I worked for a while with a carpenter/box builder down here that really made some amazing cabs (I still use several on a regular basis), but I don't think that any came out on the first try. They all needed tweaking (he had SMAART - a great tool if you can get hold of it). Have you looked at this thread:- https://orum.speakerplans.com/sinai-rc1_topic107484_page1.html?KW=paraflex" rel="nofollow - https://forum.speakerplans.com/sinai-rc1_topic107484_page1.html?KW=paraflex An example of why proper measurement can save a lot of pain & wasted resources! And:- "the loudspeaker is
unloading in the box" Definitely something to check. Your filters may need tweaking to avoid that happening again. ------------- Earplugs Are For Wimps! |
Posted By: toastyghost
Date Posted: 27 December 2022 at 3:44pm
Your gut is correct. You need to go back and re-read most of the posts & links here. You’re also misunderstanding the toaster test procedure if you think running it with limiters (or processing) engaged is a good idea. This peak-to-average ratio is still far too low. You may prevent the coil hitting the back of the gap, but have dramatically increased the risk of thermal failure. Sitting in the peak limiter robs the signal of dynamic range or crest factor that is in the original content. This will then raise the average power, regardless of where your RMS voltage limiter sits. The same problem can occur if the HPF is set too high, robbing the cabinet and driver of cooling airflow due to movement at the diaphragm and the exchange of pressure and velocity at the pole piece vent or port(s). Effective loudspeaker limiting is a balancing act between thermal, excursion and distortion limits, and needs to be coupled with sensible use of high pass filtering for excursion and low pass filtering for thermal buildup, particularly in woofers. Really, the combination of empirically derived acoustic and electrical high pass responses plus an absolute zero-attack brick wall soft 'clip' limit is the best way to control excursion damage. The easiest way to achieve this is by choosing a sensibly-sized amplifier in the first place, which can deliver the RMS voltage and unclipped peaks to handle the crest factor of the signal. Which is always going to be greater than 6 dB in practice! https://www.prosoundtraining.com/2016/07/19/power-amplifier-calculator/" rel="nofollow - https://www.prosoundtraining.com/2016/07/19/power-amplifier-calculator/ https://www.prosoundtraining.com/2010/03/10/why-all-the-fuss-about-power-the-equivalent-amplifier-size-part-2/" rel="nofollow - https://www.prosoundtraining.com/2010/03/10/why-all-the-fuss-about-power-the-equivalent-amplifier-size-part-2/ https://www.prosoundtraining.com/2010/03/20/target-spl-and-required-amplifier-size/" rel="nofollow - https://www.prosoundtraining.com/2010/03/20/target-spl-and-required-amplifier-size/ The peak limiter is then used to prevent the speaker from sounding bad or becoming significantly non-linear. https://www.prosoundtraining.com/2010/03/21/using-limiters-to-help-protect-loudspeakers/" rel="nofollow - https://www.prosoundtraining.com/2010/03/21/using-limiters-to-help-protect-loudspeakers/ No limiter system will ever be completely fool-proof, and speakers will fail if they are driven into their limits - electronic or physical - for long periods of time without correction by an operator. This is why it's a good idea to include an additional automatic gain control system with permanent installations where an engineer won't be present. Even better if that is driven from acoustic measurement in the venue, like the higher end DateQ models. Despite what Elliot says, a well-qualified model is quite accurate for predicting a subwoofer's excursion and such, so long as the loudspeaker is driven in such a way that it is linear time-invariant. That generally means small to medium drive voltage signals, which avoid significant nonlinear behaviour. Most of these things can be calculated to get you started, but when it comes to measurements all of the functionality of Smaart (& software tools which are way more appropriate for loudspeaker design) can be had for free, using REW, VituixCAD, OpenSoundMeter, or ARTA. |
Posted By: Augusts
Date Posted: 27 December 2022 at 4:15pm
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Thanks all of you guys for very in depth responses, links, opinions and pointers If we dont meet any time soon - have a happy New Year! A
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Posted By: 4D
Date Posted: 27 December 2022 at 4:19pm
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Beginning of the month we had a visiting engineer confound both a drawmer sp2120 & a xta dp limiter section Thoroughly cooking several 18" drivers that hitherto had survived countless hours of relentless EDM unscathed. How ? Pushing the gain higher but avoiding clipping through the application of heavy compression on the M3 master output.. ------------- DMZ. "The bass was intense. Girls were literally running up to stand next to the subs" |
Posted By: Elliot Thompson
Date Posted: 27 December 2022 at 5:27pm
Which concludes you need to literally Measure. I used many of programs listed above and put some down throughout the years. Horn Response is a Simulator. It predicts things in the ideal situation. All simulators can only predict. They cannot guarantee the results are accurate. Measurement software can show different results among-st one another. However, the results are still a better representation of real world conditions than any simulator in a virtual world can offer.
There comes a time when sound professionals needs to step up to the next level. Searching for articles that may offer a keyword based on their dilemma, is not productive (nor needed) once you have the proper measurement tools at your disposal.
Best Regards,
------------- Elliot Thompson |
Posted By: Augusts
Date Posted: 27 December 2022 at 5:35pm
| Thank you, that is very encouraging |
Posted By: toastyghost
Date Posted: 28 December 2022 at 12:32am
“Make a measurement” - of what, exactly? How? What stimulus? What distance? Where should the mic be placed? How should the room be excluded, or not? Your suggestion is vague and frankly, unhelpful. Measurements are useless if the person making them doesn’t know how to do them properly, or understand what they are looking at, the limitations of the processing and electro-acoustic environment that was used to make the measurement, & what the various elements of the results are caused by. Essentially, to make a measurement useful, you need to know what should appear on the screen before making the sweep. The computer is just answering a question, it's down to the operator to know how to ask the right question and assess whether the answer is correct. This can be as simple as knowing in advance that your ported subwoofer should have a natural fourth-order roll off at the low corner, without any electrical filtering in place. If the plot produced from measurement doesn't show that, then you can try to figure out why: maybe room modes, reflections, driver unloaded, air leak, etc etc etc The vast majority of useful measurements when designing a loudspeaker are also small-signal ones. That’s because you want the speaker to be linear time invariant for the maths to work, both in convolution of the measurement stimulus and to qualify it to electro-acoustic concepts. Funnily enough, most models also work on the same principles. “No models are perfect, but some are useful.” Measurements of non-linear behaviours are absolutely an advanced stage of making measurements, especially in real-world environments. I’d argue that many folks don’t even know how to do them in such a way that the data is even remotely representative of the device under test alone. You know a really great way for people to bridge these gaps in knowledge and experience? Using simulation tools. Same for building what they sim - a huge problem for lots of people - and then measuring that, and qualifying it back to the simulation. Any discrepancy then can be investigated, and used to refine either the model, the build, or the measurement process. Often, there need to be tweaks to all three, and several repeats before the person begins to really understand what's happening. All of the above caveats about knowing what you're looking at still apply, every step of the way. Each of the links I’ve posted are to in-depth articles from my own personal reference manager/research archived, written by hugely respected industry engineers who've worked for many major brands, on a literal professional sound training website... One could argue the benefits in approach to helping people learn the what & the why for themselves by pointing them in the right direction and offering qualified, detailed advice with examples rather than just posting vague suggestions, but that probably wouldn't be very much in the spirit of the season 
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Posted By: Augusts
Date Posted: 28 December 2022 at 9:25am
| I have just one simple question - does the value that reaches Xmax would be considered Program power or AES? |
Posted By: Elliot Thompson
Date Posted: 28 December 2022 at 10:11am
It's unhelpful to you for you do not have any real world experience on the issue August is having! Despite you are trying to be helpful, the information you are copying and pasting is not relevant to a loudspeaker's voice coil hitting the back plate.
As I mentioned in my previous post...
98%
of the people in the sound industry have never encountered banging
the voice coils on the back plate. So their experience under your
circumstance is minimum to none. I have experienced such a phenomenon
decades ago so, I know exactly what you are talking about.
Your
situation is due to either feeding the driver's voice coil
frequencies they are incapable of producing or, the loudspeaker is
unloading in the box. All one needs to do is recreate the same scenario again. You are measuring the behavioral status of the loudspeaker in real time visually (using the same music material that created the problem) and, monitoring the dB level with an SPL Meter. Reducing the gain level on the mixer until the voice coil stops hitting the back plate. Observe the dB Meter throughout the process.
Connect a Multi-meter on the output of the amplifier. Monitor the output Peak voltage at the reduced dB level when the loudspeaker's voice coil is not hitting the back plate. Set the limiter so the output voltage peak does not exceed the peak figure of the Multi-meter. Raise the mixer's gain to confirm the limiter is indeed preventing any overshoots, using your Multi-meter.
An SPL Meter and Multi-meter are basic measuring tools every sound professional should have and, will pay themselves off for years to come.
This test can be done in less than 3 minutes. No simulation needed. All you need is your eyes, ears, hands and, measuring tools.
August has already solved his dilemma following a similar principal. So the above are for those who are curious how it is done without using a computer.
Best Regards, ------------- Elliot Thompson |
Posted By: Elliot Thompson
Date Posted: 28 December 2022 at 10:25am
Your scenario was exceeding the Xmechanical limit. If you want to know how much watts you are encountering, during and prior to the Xmechanical limit, connect a Multi-meter on the output of the amplifier. Multiply the volts times volts and divide it by your impedance load. That will give you the peak wattage your speakers are receiving. For Example: 40 x 40 / 4 = 400 watts You can then, look at the wattage figures of Program Power and/or AES to determine which wattage your figure falls under. Best Regards, ------------- Elliot Thompson |
Posted By: bob4
Date Posted: 28 December 2022 at 10:37am
I suppose the most precise method would be to take an impedance sweep of his cab, and substitute the actual real resistance at the frequency of interest for the nominal impedance? |
Posted By: Elliot Thompson
Date Posted: 28 December 2022 at 10:47am
Yes. That is the benefits of measurement tools over simulations. DATS is the most user friendly software out there. I even have it despite using ARTA. Best Regards, ------------- Elliot Thompson |
Posted By: Augusts
Date Posted: 28 December 2022 at 10:54am
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The question is not about where to limit. The question is how to do that correctly I build my own speakers, I know that the speakers limit is 1000w@4ohm precisely. What I dont know however, what data should I input into a limiter calculator and how does the XTA limiter work. If my speaker hits the Xmax at 1000w, would that be considered AES by using it I would calculate the limiters treshold? And then add+ 6db for peaks on the XTA?
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Posted By: Earplug
Date Posted: 28 December 2022 at 10:58am
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"I suppose the most precise method would be to take an impedance sweep of
his cab, and substitute the actual real resistance at the frequency of
interest for the nominal impedance?" Or sweep through the low end frequencies with a generator and see if there is one - or a band - that is causing the problem, i.e. the speaker becoming "unloaded" and hitting the back plate. If so, it would be a simple matter to set a filter, or adjust the hp/lp filters to avoid it happening. ------------- Earplugs Are For Wimps! |
Posted By: Augusts
Date Posted: 28 December 2022 at 11:08am
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I am telling you guys, the speaker hit the backplate because, the Vpeak was 141Volts for a 4ohm driver. that is 6000w. and from what I concluded that a single rms limiter does not limit the speakers excursion all together , but that there is a relation between the AES( that is used to calculate the RMS limiters treshold), +3db Program Power (which is the dynamic music material and not pure sine waves) and +3db for Peak power which is as I understand a very short peak that cannot do a mechanical damage to a subwoofer because it is very short. If I would be working with factory made speakers I would just input all the data into a limiter calculator and move on. Therefore I thought I would do a power compression test and tweak the limiter settings until everything falls into place.
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Posted By: toastyghost
Date Posted: 28 December 2022 at 11:44am
I give up. You don't seem to have built a speaker in a decade and are advocating using a basic broadband SPL meter, yet you're saying I'm the one lacking in experience developing modern loudspeaker DSP presets? I'm not even going to waste my time trying to justify myself. If you truly think I'm just blindly copy & pasting stuff then you're either deluded or intentionally trolling at this point. Or perhaps simply don’t read what others actually post before weighing in Good luck with your limiting, Augusts. |
Posted By: Augusts
Date Posted: 28 December 2022 at 11:46am
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Thank you Im sorry, it seems people are getting cranky because of my post
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Posted By: Earplug
Date Posted: 28 December 2022 at 12:44pm
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"I am telling you guys, the speaker hit the back plate because, the Vpeak was 141Volts for a 4ohm driver. that is 6000w" R = 4 ohm, nominal resistance! In real life, your speaker becomes a complex impedance that will vary with frequency. Do you understand the difference? Some manufacturers supply an impedance curve with their products, but put the driver in a box and that changes again. The only way to find out is to measure - or get one of those modern, fancy amps that tell you! Like I've already said, do a sweep test with a signal generator and see what going on. ------------- Earplugs Are For Wimps! |
Posted By: Augusts
Date Posted: 28 December 2022 at 12:51pm
| Yes, I know it is a nominal resistance. I know what are you saying, thank you, I have recalculated the resistance to a precise 4ohms for the convenience of using treshold calculators. I think the problem could have been that I had set a too long of an attack time for the limiter. Something must have gone through the limiter. |
Posted By: smitske96
Date Posted: 28 December 2022 at 1:39pm
| What kind of cabinet + driver are we talking about? With some drovers its impossible to hit the backplate due to the spider limiting travel. |
Posted By: snowflake
Date Posted: 28 December 2022 at 2:09pm
| excursion varies with frequency. What about applying dynamic eq or sidechain compression? |
Posted By: Earplug
Date Posted: 28 December 2022 at 4:21pm
Ok, you obviously (now) have it under control. Good luck! ------------- Earplugs Are For Wimps! |
Posted By: Elliot Thompson
Date Posted: 29 December 2022 at 9:29am
Yes, Give up. You do not have any experience on the issue August is facing. It's that simple! Best Regards, ------------- Elliot Thompson |
Posted By: Elliot Thompson
Date Posted: 29 December 2022 at 9:42am
Some drivers that offer dual spiders can have one fail. The end result is one driver moving stronger than the other drivers within the chain. Best Regards, ------------- Elliot Thompson |
Posted By: smitske96
Date Posted: 29 December 2022 at 10:57am
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If you have a spider fail on you due to excursion, you are well passed the limit of something bearable to listen to. I use peak limiting more as the max before it is going to sound crap. |
Posted By: Esc4pe
Date Posted: 29 December 2022 at 12:27pm
Toasty’s posts have been an absolute godsend for me (and I’m sure countless others) while learning throughout the years. This poor attempt of trolling should be considered blasphemy as far as I’m concerned I know who I would take advice from. My simpleminded 2 cents that no one asked for: could you take more kit to the events and run with less power instead of ragging a smaller amount and surely won’t run into this problem then? I never damage drivers and rarely use any limiting at all? To bottom out a driver is quite a task, Elliot does raise a point that they may be becoming unloaded due to improper setup maybe?
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Posted By: bob4
Date Posted: 30 December 2022 at 8:15am
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Interesting topic, and first of all, happy to see that August has found a practical solution to his problem!
However, I don't understand this repeated statement of yours. You probably refer to the impulse peaks of the full range audio signal. Your woofers are acoustically capable of playing back frequencies up to 1- 2 kHz. Yes, if you played a FULL RANGE signal through your woofers, they would roll of somewhere around 1-2 kHz. That part of the signal also contains a lot less energy in relation to the bass, and would be insignificant. So for INPUT limiting of full range signals, your statement is correct. But all that is completely irrelevant to the subject of bass signal lmiting! In your dsp, i suppose you are using a dedicated OUTPUT limiter on the subwoofer channels output that sees a filtered bass signal only. That limiter only sees sub frequencies, lets say 30-120 Hz. That signal still has peaks, obviously. There is no part of that filtered signal that will be "too fast" for the woofer to follow. So you HAVE to consider the peak part of your subwoofer signal. The waveforms will probably be quite close to a sine wave, due to the narrow bandwidth the signal will contain only a fundamental and one or two overtones (e.g. 35, 70, 105 Hz). As toasty quoted, typically 6 dB crest factor. I suppose that the optimum solution would be to set your rms limiters so that your subs stay within xmax most of the time, and set the peak limiter to reign in the cone somewhere between xmax and xmech, before it hits the back plate. Prevention of power conpression could also be considered. As others suggested, reviewing the low corner of your cabs and hpf setting would probably help as well. Frankly, you have not provided enough information. What kind of cabs? What was your test signal in your excursion tests? Music? Bass drums/impulses? Sine waves? In your inquiry, you have also omitted the time constants of the limiter(s). Toasty's replies, as always, thorough and exhaustive  Happy to learn more  |
Posted By: Pasi
Date Posted: 31 December 2022 at 12:11pm
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Posted By: Augusts
Date Posted: 02 January 2023 at 4:28pm
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The problem was too long of an attack time for the Xilica DSP. I had set it to 20ms. I should have been 10ms, as it is crossed at a 100Hz I like to limit everything because you newer know what kind of people are behind the decks and Im not a millionaire, I can't afford 50 L'acoustics subs. I use what I build myself  |
Posted By: spongebob
Date Posted: 02 January 2023 at 8:55pm
Please leave this forum Elliot, otherwise you'll drive others who have intelligent answers away |
Posted By: smitske96
Date Posted: 02 January 2023 at 9:03pm
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@August What was the driver failure?
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Posted By: Father-Francis
Date Posted: 03 January 2023 at 11:11am
 Tell him now Bob ------------- Music is the strongest form of magic.(+45 31879997)blakmanpro@gmail.com, foa@sweetboxaudio.dk |
Posted By: Augusts
Date Posted: 03 January 2023 at 11:56am
| @smitske The problem was with FaitalPro 18HP1030. Thankfully there was no failure but I heard the voicecoil hitting the backplate. Since then I thought that it was because I hadn limited the peak power on the amp which I did thus lowering also the rms. But after reading the articles here and talking to a few people I now know that it was the attack time and not the peaks. I set the peaks +6db as it should be |
Posted By: smitske96
Date Posted: 03 January 2023 at 1:15pm
| Wasn't there any audible distortion before that point? Because it should definately be there. |
Posted By: Augusts
Date Posted: 03 January 2023 at 1:27pm
| It was Muslimgauze his squarewave synth, since they never play something like that in the club, I discovered this while doing mh tests and it happened really fast |
Posted By: bob4
Date Posted: 03 January 2023 at 1:57pm
Which track? Need it for reference  For subbass testing, try to find "Judgement Dub" by Rog Mogale. It contains strong bass down to 30 Hz, and towards the end even deeper, iirc goes down to around 20 Hz
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Posted By: Elliot Thompson
Date Posted: 03 January 2023 at 2:17pm
Haters are going to Hate At least Toastyghost tried to help. You on the other hand.... What did contribute to Augusts dilemma again? Best Regards, ------------- Elliot Thompson |
Posted By: Augusts
Date Posted: 03 January 2023 at 3:20pm
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@Bob4 It could have been something like this but I dont remember the exact track, but he has alot of stuff that could destroy subs. https://www.youtube.com/watch?v=JooFMbEGzdw" rel="nofollow - https://www.youtube.com/watch?v=JooFMbEGzdw Thanks for the Judgement track!
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Posted By: snowflake
Date Posted: 03 January 2023 at 5:24pm
that's not really the issue. And frankly if people don't have a better answer than what others have posted it is better that they contribute NOTHING on that topic. I think you are being called out for persistently acting like a bit of a know-it-all and dispensing advice to new members which doesn't really stand up to scrutiny - and then has to be corrected by others. You do make interesting posts now and then but often you seem to be afflicted by Dunning-Kruger.
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Posted By: jammin75
Date Posted: 03 January 2023 at 5:39pm
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https://easyupload.io/w6c3eu" rel="nofollow - https://easyupload.io/w6c3eu void 30hz test track if anyone wants
 ------------- feel the vibes !!! "Who Feels it Knows it" Strong like Lion |
Posted By: spongebob
Date Posted: 03 January 2023 at 6:17pm
I just read and observe on here unless I know (not believe) any comment would be constructive and helpful For example, I know you not posting such drivel would be helpful, as apposed to believing it to be true |
Posted By: Augusts
Date Posted: 03 January 2023 at 6:21pm
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The track does not download Could you put it up on wetransfer??
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Posted By: Augusts
Date Posted: 03 January 2023 at 6:26pm
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I usually play around with these Ben Buitendijk - Side StEPping Ben Buitendijk - Near Mint [OBQ002] Aleksi Perälä - Ovuca Bonus - 05 Stochastic Process Aleksi Perälä - Ovuca Bonus - 07 Hydrophobic Effect Aleksi Perälä - Ovuca Bonus - 03 Kinetic Theory Oxia - Story mathew_jonson-pirates_in_the_9th |
Posted By: Augusts
Date Posted: 03 January 2023 at 6:29pm
| In forums, not always you get a straight answer, but I believe a group of people thinking about the subject make the collective subconscious shift. In this case a local sound engineer and also a PA speaker designer helped. Actually I knew this already but we refreshed our memories and hopefully now the subs are safe and also have a optimistic spl |
Posted By: Augusts
Date Posted: 03 January 2023 at 6:35pm
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@smitske Yes there was a lot of port noise :) I thought I had designed the boxes improperly, bet when I concluded that they are taking a hell of a beating than the port noise stopped, and there were no more over excursion problems And now recently, because I recenty concluded it was the attack time - at around 100hz the woofer made a really nasty cranking noise on the kick. with 10ms now its fine. God must have been watching over me, thanks old man!
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Posted By: Jo bg
Date Posted: 04 January 2023 at 3:06pm
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It is not haters. It is people sick of reading your wrong advice based upon surpassed knowledge, or your bashing of good information, just because you don't understand it. It may be viable for you to work as it still was the seventies, and dismiss all the knowledge that is available nowadays, but you are harming all the newbies coming by and reading your posts when you push your old man tecnique as the only one. It becomes ridicule when you try to reply Toasty while clearly not even understanding what you read.... Not a hater. Just someone sad for the disservice you are bringing to the comunity and you anti scintific approach... To science.
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Posted By: Augusts
Date Posted: 15 January 2023 at 12:45pm
| @jammin75 got it, sorry |
Posted By: jammin75
Date Posted: 15 January 2023 at 1:50pm
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good i knew it was on hardrive sum where maybe useful to others ------------- feel the vibes !!! "Who Feels it Knows it" Strong like Lion |
Posted By: Augusts
Date Posted: 20 January 2023 at 8:35pm
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for a speaker that reaches xmax at a 1000W ,I would set a limiter treshold @500W and +6db until it reaches peak brick wall limiter. Then the coil would stay in its magnetic field even if someone starts playing live synths, raw sinewaves. I would not overheat also, I think. Why bring more boxes if you can do the job with four, knowing exactly where the limit is. |