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Peak limiting for driver protection

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Elliot Thompson View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 27 December 2022 at 5:27pm
Originally posted by toastyghost toastyghost wrote:

 
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.

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,




 
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 27 December 2022 at 5:35pm
Thank you, that is very encouraging
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 12:32am
Originally posted by Elliot Thompson Elliot Thompson wrote:

Originally posted by toastyghost toastyghost wrote:

 
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.


<p ="western" style="margin-bottom: 0in">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.


<p ="western" style="margin-bottom: 0in">


<p ="western" style="margin-bottom: 0in">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.


<p ="western" style="margin-bottom: 0in">


<p ="western" style="margin-bottom: 0in">Best Regards,


<p ="western" style="margin-bottom: 0in">



 


“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

Edited by toastyghost - 28 December 2022 at 12:47am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post 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?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 10:11am
Originally posted by toastyghost toastyghost wrote:

 

“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.

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...


Originally posted by Elliot
Thompson Elliot Thompson wrote:



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.


Originally posted by Augusts Augusts wrote:

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.



Best Regards,       




Edited by Elliot Thompson - 28 December 2022 at 10:15am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 10:25am
Originally posted by Augusts Augusts wrote:

I have just one simple question - does the value that reaches Xmax would be considered Program power or AES?

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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote bob4 Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 10:37am
Originally posted by Elliot Thompson Elliot Thompson wrote:

Originally posted by Augusts Augusts wrote:

I have just one simple question - does the value that reaches Xmax would be considered Program power or AES?

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, 

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?

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Post Options Post Options   Thanks (0) Thanks(0)   Quote Elliot Thompson Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 10:47am
Originally posted by bob4 bob4 wrote:

Originally posted by Elliot Thompson Elliot Thompson wrote:

Originally posted by Augusts Augusts wrote:

I have just one simple question - does the value that reaches Xmax would be considered Program power or AES?

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, 

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?


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
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 10:54am
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?


Edited by Augusts - 28 December 2022 at 10:56am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Earplug Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 10:58am
"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.


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Post Options Post Options   Thanks (0) Thanks(0)   Quote Augusts Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 11:08am
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.


Edited by Augusts - 28 December 2022 at 11:12am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote toastyghost Quote  Post ReplyReply Direct Link To This Post Posted: 28 December 2022 at 11:44am
Originally posted by Elliot Thompson Elliot Thompson wrote:

Originally posted by toastyghost toastyghost wrote:

 

“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.

<p ="western"="" style="margin-bottom: 0in"><font face="Arial, sans-serif">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. 




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.
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