Effect of Compression on Peaks - Page 2 - AVS Forum
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post #31 of 48 Old 02-09-2012, 06:34 PM
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Quote:
Originally Posted by FOH View Post

All sounded well, but I noticed some imaging/interaction problems,..kinda a blurring of the MF/HF. So to find the issue, I disconnected the inward fill mains, and only had the one regular two way per side. BAM! Perfect. The entire system became perfectly focused,..no destructive interference from adjacent boxes not meshing, no interference (this is huge) from acoustics being outdoors, just wonderful. Control room type studio monitor clarity. No sidewall issues, no modal issues,.. just a wonderful window into the recording.

The take-aways here include; headroom is our friend,...this comes up so, so often. Also, (OT but whatever) there is so much negative interaction between a multi cabinet approach to MF/HF. Even the engineered "J" line arrays have issues, that's why the work Tom Danley's doing in the mega/single cabinet pro live sound stuff makes so much sense,...plus the dude an audio genius anyway.



Thanks

The first time I really ran into the interaction issue was at a local 2500 seat room that i did all the time for all types of acts. I usually took our 4 stacks per side (subs and full range cabinet in each stack). It got plenty loud and did a good job.

I got a call to do a wedding in the same room, and they didn't have a lot of money and didn't want it that loud-so i only took out 1 stack per side.

We all noticed that the sound was a lot cleaner and clearer. Then I realized that the issue was using the other cabinets.

But that is the problem. Everybody agrees that a single box is going to sound better than multiple boxes-no matter how good the boxes are.

But the problem is that often a single box will not get loud enough to do the job-so we have to use multiple boxes to get loud enough.

That is the reason for the whole Jericho series from Danley. Really loud-good sounding single boxes-without the interference.

The big problem is getting the high freq to work together and sum without interference. The lows and mids are not that big of an issue. That is where Tom Danley has been working so hard on lately.

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post #32 of 48 Old 02-10-2012, 07:36 AM - Thread Starter
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Ivan, The SH-60F is spec'd for 800w continuous, 1600w program.

While it's not given, do you think that the speaker would handle peaks of 3200w without destruction? Or without compression? Is this something Danley Sound Labs would be willing to measure?

Thanks!
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post #33 of 48 Old 02-10-2012, 08:06 AM - Thread Starter
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MKTheater, I did use REW last night to measure peaks...maybe as you were referring to having done previously? I used the [logging] button of the REW SPL Meter, which continuously tracks SPL, the max, etc.

This gave me more surety on how high the levels were reaching with a soundtrack peak (Die Hard 4 apartment explosion), with a given volume level than trying to watch a hand-held SPL meter.

Next I want to try the Linkwitz Shaped Burst tone (at bottom of page) (explained here).
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post #34 of 48 Old 02-10-2012, 08:11 AM
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To measure just the speakers make sure it is A weighting only.
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post #35 of 48 Old 02-10-2012, 08:16 AM - Thread Starter
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Quote:
Originally Posted by MKtheater View Post

To measure just the speakers make sure it is A weighting only.

I was actually wondering about that when I was doing complete frequency response sweeps the other week.

I have the Galaxy CM-140 meter that's been tested by Cross Spectrum and gave me a calibration file for C and A-weighted, on-axis and off-axis. I was wondering whether using C-weighted, and the c-weighted calibration file, negated the need to switch to A-weighting?
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post #36 of 48 Old 02-10-2012, 02:20 PM
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Quote:
Originally Posted by Ivan Beaver View Post

The first time I really ran into the interaction issue was at a local 2500 seat room that i did all the time for all types of acts. I usually took our 4 stacks per side (subs and full range cabinet in each stack). It got plenty loud and did a good job.

I got a call to do a wedding in the same room, and they didn't have a lot of money and didn't want it that loud-so i only took out 1 stack per side.

We all noticed that the sound was a lot cleaner and clearer. Then I realized that the issue was using the other cabinets.

But that is the problem. Everybody agrees that a single box is going to sound better than multiple boxes-no matter how good the boxes are.

But the problem is that often a single box will not get loud enough to do the job-so we have to use multiple boxes to get loud enough.

That is the reason for the whole Jericho series from Danley. Really loud-good sounding single boxes-without the interference.

The big problem is getting the high freq to work together and sum without interference. The lows and mids are not that big of an issue. That is where Tom Danley has been working so hard on lately.

I'd really enjoy hearing a big, Jericho based rig.

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post #37 of 48 Old 02-13-2012, 07:57 AM - Thread Starter
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So, does anyone know how a speaker behaves when you send it peaks that are near the stated max peak power handling?

Like:

"Speaker A distorts like crazy when I sent burst tones and music beats to the mains that peaked from a voltage near its stated peak limits. And it didn't reach its theoretical SPL due to compression beyond 75% rated peak power. So I think its spec'd limit was 'Level the speaker explodes.'

Speaker B sounded strained at 25% above its peak limits, and I measured high THD, but within its limits its distortion was no higher than at lower levels. So I think this speaker is spec'd as, 'level at which distortion starts to rise quickly past 5%.' "

Apparently there's the rule of thumb for RMS levels, so I'm wondering if there's one similarly for peak levels.
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post #38 of 48 Old 02-13-2012, 08:19 AM
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Some companies' speakers are lower efficiency because they have a low distortion motor. Speakers designed without these features could be said to have a poor design. But there are those for whom 115db levels are more important than anything else, for them sensitivity is most important. My amps never clip, I have an XPA-3 driving the "low sensitivity" ScanSpeak Revelator midwoofers, so I don't need higher efficiency speakers and the amp power I have is sufficient and the output is as low distortion as practical. I will continue to recommend low distortion speakers especially for music.
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post #39 of 48 Old 02-13-2012, 09:03 AM - Thread Starter
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Quote:
Originally Posted by Theresa View Post

Some companies' speakers are lower efficiency because they have a low distortion motor. Speakers designed without these features could be said to have a poor design. But there are those for whom 115db levels are more important than anything else, for them sensitivity is most important. My amps never clip, I have an XPA-3 driving the "low sensitivity" ScanSpeak Revelator midwoofers, so I don't need higher efficiency speakers and the amp power I have is sufficient and the output is as low distortion as practical. I will continue to recommend low distortion speakers especially for music.

But this discussion isn't about advocating high efficiency designs. Or even reaching high SPL.

It's completely applicable to an 82dB sensitivity speaker, that's being asked to handle 20w continuous or 80w peaks. And specifically for you, it's applicable to low sensitivity, low distortion, high-power-handling drivers as well.

It's about differentiating between the type of compression that occurs on average levels and peak levels. The rule of thumb is compression occurs at around 1/8 continuous or program levels, and I've never heard the caveat "for high sensitivity speakers."

So, we were talking about if that's applicable to peak levels.
People said that continuous/average/program levels will generate thermal compression.
Peak levels won't exhibit thermal compression. There will be physical limits and magnetic effects.

It doesn't matter what your amp / driver is: your driver is still designed to handle some level of power continuously, and some higher level of power in brief bursts. Unless you listen to sine waves, your program material has brief bursts of power, even if you listen at extremely low volumes.
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post #40 of 48 Old 02-13-2012, 09:20 AM
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Sorry to get away from compression. The midwoofers I have are rated at 80 watts for 8 hours (I believe this is a 100% duty cycle), but given their generous xmax can handle much larger signals for short periods. I think the 80 watt rating would be considered the thermal limit. My previous Eton midwoofers would get muddy at loud levels, the ScanSpeak drivers sound perfectly clean at the reasonable volumes I use (and much louder at times) and when the peaks come they still sound clean and don't muddy large scale pieces.
The point is someone said that low sensitivity speakers are poorly designed, poorly designed for 115db levels yes, but not for how I listen. I've found high sensitivity speakers to be harsh sounding, especially horns.
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post #41 of 48 Old 02-13-2012, 09:35 AM - Thread Starter
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Quote:
Originally Posted by Theresa View Post

...the ScanSpeak drivers sound perfectly clean at the reasonable volumes I use (and much louder at times) and when the peaks come they still sound clean and don't muddy large scale pieces.

I read that you did a DIY with that Revelator? Is this a good candidate for a cheaper DIY like Econowave? Where can you cross-over with that woofer?

Quote:
Originally Posted by Theresa View Post

The point is someone said that low sensitivity speakers are poorly designed, poorly designed for 115db levels yes, but not for how I listen.

Yes, someone said that and I (thinking of you!) pointed out that all speaker designs fit a purpose and make compromises.

I've also tried to point out other high-output speaker designs, like those that have higher power-handling but with lower sensitivity, like Dynaudio's.

Actually, this here thread is more tailored for that design. Super high-sensitivity designs mean that the speaker is loafing even on peaks, so no one's concerned with level-induced ill effects.
Whereas with a low-sensitivity high-power-handling design, one is more likely to use external amps, as you have done, to get the most out of the speaker. How it behaves at what level of peak power is more important.

Quote:
Originally Posted by Theresa View Post

I've found high sensitivity speakers to be harsh sounding, especially horns.

My understanding is that it's due to the design of those horns. Cheaper Klipsch, to some extent the Klipsch Reference, through which most people have been exposed to horns, and I'm sure many pro speakers, exhibit the "horn honk" sound.

But I understand that not to be the case with designs from Seaton, Danley, Geddes, Genelec, Pi Speakers, and even Econowave designs.
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post #42 of 48 Old 02-27-2012, 03:55 PM - Thread Starter
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Quote:
Originally Posted by Bill Fitzmaurice View Post

Power compression has little effect on peaks. Power compression results from long term heating of the voice coil.
...
This points out the fallacy of manufacturer 'maximum SPL' figures, because those are calculated as linear with respect to 1m/1w sensitivity, and assume that power compression does not exist. In reality you can expect the real maximum SPL to be 3 to 6dB lower than claimed.

I was just re-reading this, and I had a question. Aren't the "maximum SPL" figures typically for peak power? And thus we don't have to be concerned with power [thermal] compression effects?
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post #43 of 48 Old 02-27-2012, 04:46 PM
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Quote:
Originally Posted by Eyleron View Post

I was just re-reading this, and I had a question. Aren't the "maximum SPL" figures typically for peak power? And thus we don't have to be concerned with power [thermal] compression effects?

They're quoted both SPL and peak. Thermal compression is real and almost unavoidable at levels even as low as 100w. Compression of 6dB and higher at maximum power is not unusual with high power woofers.

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post #44 of 48 Old 02-27-2012, 05:24 PM - Thread Starter
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To be clear (because I didn't write it well), I meant we don't have to worry about thermal compression when looking at a speaker's max output (if the max output is given as "peaks using peak max amplification,") which would suggest a theoretical burst signal, and not a continuous one, because you and others that thermal compression doesn't occur on peak signals due to their brief nature.

Quote:
Originally Posted by Bill Fitzmaurice View Post

Compression of 6dB and higher at maximum power is not unusual with high power woofers.

So, you're referring to non-thermal compression here, and thus the magnetic flux effects and mechanical limits such as the spider's non-linear "springiness"?
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post #45 of 48 Old 02-27-2012, 06:32 PM
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Not sure whether this is a tangent or will inform on the debate, but I have tried keeping an eye on power draw from the mains socket. Perhaps this is what MKtheater was addressing, too.

Quote:
Originally Posted by MKtheater View Post

Yes, I think I use about 20 watts for the loudest peaks in movies.

The setup in question uses a TX-NR1007, an XPA-5, 2 x B&W683, 4 x B&W685, 2 x B2031P, 1 x Emotiva Ultra 12 (with builtin amp), and 1 x MFW-15 + 1 x RSS390HF-4 off of each their channel on the XPA-5. The speakers are between 1m and 3m from the MLP, and the whole thing is connected to a big APS power-supply unit with LCD and is flat down to 12Hz with an LR-8 HPF thereabouts.

Running at -20dBFS and with Audyssey DynEQ (with 0dB offset), the biggest power draw I have observed is ~320W above rest consumption. This is for the scene in the shop after the monster first attacks in Cloverfield, just as the light goes out. A close second is the scene where the big dragon breaks out from the mountain in How To Train Your Dragon, at ~300W. In particular, this scene draws more power than when the dragon crashes, ~275W. I can't remember the numbers for War of the Worlds, and similar bass movies, but their draw does not go above these numbers, at least not by much.

My main point is that power draw does not line-up perfectly with subjectively impressive bass scenes, in a way I still haven't quite pinned down. The best I can say is that the mentioned scenes have more of a rumble thing going than an outright transient shock.
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post #46 of 48 Old 02-27-2012, 06:55 PM - Thread Starter
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Since amplifiers are not perfectly efficient, the power they draw from the wall is greater than what they send to speakers. The waste comes out as heat.

I suspect the 20 watts MKTheater refers to is how much he thinks or measures he's using, with super sensitive speakers.
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post #47 of 48 Old 02-27-2012, 08:07 PM
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Yeah, I was just talking what each speaker needs to reach reference at my LP and not total watts of the system. I am not sure what the subs would require but I can guess about 200 watts to reach reference at 20hz and 800 watts for 10hz and 3200 watts for 5hz. I have 2100 watts per sub RMS and plenty for that 5 hz peak. Now this is just using specs and my loss of spl from the speakers to my LP which is 12 dBs!
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post #48 of 48 Old 11-28-2012, 12:43 PM
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Quote:
Originally Posted by MKtheater View Post

...my loss of spl from the speakers to my LP which is 12 dBs!
guys at the other thread are wondering if the 12dB loss was measured or estimated
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