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Running 6 subs per amp channel |
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tv00 
Old Croc 
Joined: 10 August 2009 Location: Denmark Status: Offline Points: 1886 |
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 Topic: Running 6 subs per amp channelPosted: 04 October 2016 at 10:44am |
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Ok please think twice before calling me an idiot again, -thank you :-)
Usually I run no more than 3 subs per channel on my labs. Nevertheless I decided to do an impedance measurement of 6 BPH stacked into one big horn, MACH ms-118s in this case, the result is great, above 2 ohms from 36 to 140 hz, except for a naroow dip at 70 hz where it comes to 1,5 ohms as I recall, but at 50 & 100 hz it's closer to 8 ohms! This must be due to impedance from hornloading & resonance of driver in chamber, like seen in sims. Of course damping factor might be affected & thick AWG is required, but in one occasion I just had to do this as one amp went down, afterwards I measured how bad it reall was, -not too bad:-) I used 2x4mm2 per 3 cabs, which means 2x 8mm2 ! :-) Did any of u guys run 6 per channel? I know a guy here who ran 8 per channel of his crown hd12000! At least I try using my brain here, so even though this forum is about putting each other down I'm going to pretend it's actually for discussing sound:-) Edited by tv00 - 04 October 2016 at 10:44am |
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Elliot Thompson
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Joined: 02 April 2004 Location: United States Status: Offline Points: 5175 |
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Posted: 11 October 2016 at 5:44am |
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It's good that you took the time to measure the impedance curve of all the boxes connected to the amplifier per channel. By doing so, it will allow you to know how much pressure you are actually placing on the amplifier. Bear in mind, your bins and, loudspeakers will not reflect someone else's impedance curve using the same arrangement. This is due to you using proprietary designed bins and, not bins you purchased from a company such as Void, Funktion One, etc. So inconsistency will vary unless someone is using the exact bins and loudspeakers as you. How the loudspeaker reacts in the enclosure will determine the impedance curve from the starting point to the ending point of the measured frequency. Twenty-One years ago, I powered 12 Scoops on one Crown MA 5000vz. Unfortunately, I did not have the tools more so the knowledge of measuring impedance curves 21 years ago. Today, my amplifiers only see one cabinet per channel (Whether 8 ohm nominal load or 4 ohm nominal load) due to having more than enough amplifiers at my disposal. Edited by Elliot Thompson - 11 October 2016 at 5:45am |
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Elliot Thompson
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tv00
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Joined: 10 August 2009 Location: Denmark Status: Offline Points: 1886 |
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Posted: 11 October 2016 at 8:33am |
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Nice knowing, several of my bins are from a company (well all)
16 are from mach, some from turbosound. But most are danish hornloaded oddities: SRT-Nucles 3x15" hornloaded cabs like a tse-"315", runs l15s800 as they were at hand and sound better than jbl 2225 that was in there before, I will measure these in pairs, I have 8 cabs = 24 drivers :-) I'd like to get away with 2 digam 7ks for them all, but first I'll A/B test it. TT1000: BPH not too far from tsw-218 etc, fane 18-1500 loaded, they have a nice high impedance in stacks of 6, I', curious if the lab13 / 14000 will sound louder with 6 per channel than they do with a digam 7k per 6 pcs, I think so. Also 24 drivers:-) Mach MS-118: PD.1850 loaded, the impedance curve here is a bit weaker, I assume it could be due to smaller cabnet size & thereby less air impedance? 24 drivers soon:-) I like stacks of 6 Edited by tv00 - 11 October 2016 at 8:34am |
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Sinai Sound
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Joined: 09 November 2009 Location: Sheffield Status: Offline Points: 631 |
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Posted: 11 October 2016 at 11:11am |
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My friends run 6 x PD1850 Super Bass Horn per side of a K20 on occasion
We've also ran 8 x PD1852 hogs on one side of a K20 for day once (when a fuse on the other side of the amp went)
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odc04r
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Joined: 12 July 2006 Location: Sarfampton Status: Offline Points: 5482 |
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Posted: 11 October 2016 at 12:09pm |
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There is absolutely nothing wrong with running 3 cabinets per channel if the equipment can handle it. And measuring the real impedance as you have done is a great start to figuring that out.
Something else worth looking at is the phase angle of the impedance spectra, I expect you are looking at the real magnitude of it mostly. Whenever the phase angle deviates from 0 degrees the amplifier is working harder. Heat dissipated in the amplifier is a combination of how much current you ask it to source, and frequencies at which it is working, and the phase angles at those frequencies. Whenever the phase angle is non zero the amplifier is dissipating some of the power it is supplying to the drivers so it gets hotter. Whenever you see a peak in the impedance magnitude spectrum, this is a resistive load and the amplifier is performing least work for most SPL. When the impedance is rising the load is behaving as an inductor, when it is decreasing as a capacitor. The steeper the rise, the higher the phase angle (but for a smaller frequency bandwidth). There is a lot of interesting things impedance plots can tell you! But bear in mind that small signal impedance plots could be quite different from large signal impedance plots once your drivers have heated up and started to perhaps to behave non linearly etc. Would you mind posting up the spectra out of interest? |
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Elliot Thompson
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Posted: 11 October 2016 at 12:29pm |
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Once you know the impedance curve of the loudspeaker in the enclosure at the given frequencies, you can calculate how much wattage the loudspeaker is getting at the given frequencies. What is written below is based on a hypothetical standpoint Four 8 ohm Nominal bins wired in parallel (2 ohms Nominal) One Channel of a Powersoft K 10 (4000 watts burst @ 4 ohms, 6000 watts burst @ 2 ohms) Measured Impedance Curve of four bins at the given frequencies; 40 Hz: 32 ohms 50 Hz: 24 ohms 60 Hz: 20 ohms 70 Hz: 16 ohms 80 Hz: 12 ohms 90 Hz: 10 ohms 100 Hz: 7.4 ohms 110 Hz: 6.2 ohms 120 Hz: 4.0 ohms 130 Hz: 2.4 ohms 140 Hz: 2.0 ohms Wattage fed to four bins based on the measured impedance curve 40 Hz: 500 watts 50 Hz: 667.50 watts 60 Hz: 799.68 watts 70 Hz: 997.96 watts 80 Hz: 1331.36 watts 90 Hz: 1196.83 watts 100 Hz: 2174.53 watts 110 Hz: 2599.98 watts 120 Hz: 4000.00 watts 130 Hz: 5091.22 watts 140 Hz: 6000.00 watts Best Regards,
Edited by Elliot Thompson - 11 October 2016 at 12:30pm |
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Elliot Thompson
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odc04r
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Posted: 11 October 2016 at 1:20pm |
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Sure you can. But is that power really going to the speaker, or is some of it reaching the driver and some of it being dissipated in the amplifier output stage? In real life it is the latter. The amp gets hoto due to its native efficiency and also the phase angle of the load it drives. What you have written is only true for a pure resistive load - which speakers only are at a few points.
It's nitpicking really, but it is good to know. it also gives an insight into why a particular enclosure may be harder to drive than another based on musical content. For example if you are driving 500W into a resistive frequency at perfect phase, then the phase angle moves to 20 degrees which is quite possible for a typical enclosure then now you have 470W into the speaker and 30W for the amplifier to dissipate. It's worth considering on top of an impedance magnitude plot I think. And especially if you are optimising an enclosure. Basic impedance modelling is a very good first step. |
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toastyghost
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Posted: 11 October 2016 at 1:53pm |
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You can see both phase angle and impedance on the same plot using a Powersoft K or X series, by the way. Quite a quick and easy way to do it, mid show if necessary when you want to see the impact of real world use vs low level.
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Teunos
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Posted: 11 October 2016 at 1:59pm |
This could not be more true. Especially when considering heavyweight amplfiers vs lightweight full bridge topology class D amplifiers driving complex impedances. The Class D in full bridge is inherently better at driving such loads due to the energy that is normally dissipated by the amplifier in a class AB or H/G config is now stored in the ouput filter, returned to power supply secondary caps and fed back to the ouput stage during the second phase cycle. Its what gives amplifiers such as the K20 and X series the ability to drive enormous loads and sustain music power for longer times on realistic impedances, even though tests on resistive loads show it will never do so.
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Best regards,
Teun. |
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nickyburnell
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Posted: 11 October 2016 at 4:48pm |
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Quote :This could not be more true. Especially when considering heavyweight amplfiers vs lightweight full bridge topology class D amplifiers driving complex impedances. The Class D in full bridge is inherently better at driving such loads due to the energy that is normally dissipated by the amplifier in a class AB or H/G config is now stored in the ouput filter, returned to power supply secondary caps and fed back to the ouput stage during the second phase cycle. Its what gives amplifiers such as the K20 and X series the ability to drive enormous loads and sustain music power for longer times on realistic impedances, even though tests on resistive loads show it will never do so. [/QUOTE] Right, now I get it. You should have said this earlier in a few other posts so us without in depth electrical knowledge could understand Joking aside, that is a nice easy to understand explanation, thank you...So what we now need is a new set of standards (marketing/measurements) for this type of creature?? Edited by nickyburnell - 11 October 2016 at 4:48pm |
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It's everything, not everythink!
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Elliot Thompson
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Posted: 11 October 2016 at 6:23pm |
It is not even that complex. The main difference is amplifiers designed today have higher voltage rails than those that fall in the heavy weight class decades ago. Professional Amplifiers have been designed to be stable under mismatched and reactive loads for nearly 40 years. Many on Speakerplans are using speakers which, generally offer TS Parameters that are aimed for horn-loaded enclosures. Such loudspeakers are notorious of offering very high impedance curves. So it is easy to see why an amplifier with higher voltage is going to drive a loudspeaker with a high impedance curve better than an amplifier with lower voltage rails. It does not matter if it is Class D, A/B, B, G or H. For if you put a Class D amplifier against a class AB amplifier offering the same voltage rails, the Class D will not supersede over the Class AB when driving a loudspeaker that offers a high impedance load. The biggest problem many face is buying loudspeakers that require excessive amount watts in order to attain the proper SPL they are seeking. Under those conditions the user has no other choice but to reach for the K 20, or K 10 in order to achieve the proper SPL. Interesting enough, if you go back to the 1980's a 250 watt - 400 watt 8 ohm nominal driver were paired with amplifiers that offered 500 - 800 watts @ 8 ohms per channel. Today, many are running down loudspeakers that boast 2000 watts (8 ohm nominal) and are settling for amplifiers that deliver at best 1000 - 1300 watts @ 8 ohms per channel. Best Regards, Edited by Elliot Thompson - 11 October 2016 at 6:30pm |
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Elliot Thompson
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nickyburnell
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Posted: 11 October 2016 at 6:38pm |
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D&B seem to keep to the high efficiency low watts stuff in some systems
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It's everything, not everythink!
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odc04r wrote: