Just noticed a downside to dual subwoofers - AVS Forum
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post #1 of 16 Unread 11-22-2014, 08:24 PM - Thread Starter
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Just noticed a downside to dual subwoofers

The receiver/processor can run out of power supplying 2 subs instead of 1 with voltage, leading to dynamic compression. Took me 2 week to figure this one out...

Thankfully the solution is easy, turn the volume on the sub up, then rerun calibration.

Assuming noise is not a problem and the receiver/processor has enough range to compensate...
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post #2 of 16 Unread 11-22-2014, 09:13 PM
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Couldn't that happen just as well with just one sub?
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post #3 of 16 Unread 11-22-2014, 09:21 PM
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Could happen with one I believe. If that subs gain is turned so low that the AVR and calibration system is trying to make up a lot.

coli did the right fix though. Find a sweet spot where the gain on the amp isn't too high and the processor/AVR doesn't have to bump up the output levels as much. On a bigger scale, this problems can also happen when a sub too small for the space. The gain on the amp and the calibration gain can't make up for the lack of driver displacement.
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post #4 of 16 Unread 11-23-2014, 08:01 AM - Thread Starter
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Quote:
Originally Posted by IndianaGeorge View Post
Couldn't that happen just as well with just one sub?
Hey you are right, it's just happens when I had only 1 sub it sounded sweet enough
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post #5 of 16 Unread 11-24-2014, 01:09 AM
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If you had a given subwoofer with the gain set at a certain level and all was fine, but then added another identical subwoofer with the gain set at the same level it would increase low level bass output by theoretically 6 dB, so the AVR would be able to drive it at a lower level. Something seems odd
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post #6 of 16 Unread 11-24-2014, 01:54 AM
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To get 6 db, you added added another power supply and double the displacement. What is odd? LoL.

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post #7 of 16 Unread 11-24-2014, 03:04 AM
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This sounds like 420 logic.

"I realize that somebody playing free music isn't as commercial as a hamburger stand. But is it because you can eat a hamburger and hold it in your hand and you can't do that with music? Is it too free to control?" - Don Van Vliet (aka Captain Beefheart) discussing commercial success in the music biz


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post #8 of 16 Unread 11-24-2014, 05:00 AM
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Quote:
Originally Posted by lovinthehd View Post
This sounds like 420 logic.
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post #9 of 16 Unread 11-24-2014, 06:25 AM
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Quote:
Originally Posted by lovinthehd View Post
This sounds like 420 logic.
Ok, You have to explain this one to me.

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post #10 of 16 Unread 11-24-2014, 06:44 AM
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Quote:
Originally Posted by flyng_fool View Post
Ok, You have to explain this one to me.
Just seems like a bit of stoner logic, 420 http://en.wikipedia.org/wiki/420_%28cannabis_culture%29

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post #11 of 16 Unread 11-24-2014, 07:11 AM
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Quote:
Originally Posted by coli View Post
The receiver/processor can run out of power supplying 2 subs instead of 1 with voltage.
With parallel connections the same voltage will be input to every driven device, no matter what the number. What will happen with a sufficient number of driven devices/amps is that the total load impedance will go too low compared to the output impedance of the line driver, but the average AVR can drive at least six sub amps without impedance loading issues. So whatever is happening isn't what you think is happening. I'd be looking at phase/polarity issues.

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post #12 of 16 Unread 11-25-2014, 07:32 PM
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Quote:
Originally Posted by derrickdj1 View Post
To get 6 db, you added added another power supply and double the displacement. What is odd? LoL.
The output to the subs should be 6 dB lower after adding the second sub and recalibrating the AVR, yet he says he had to increase the gain on the subs because the AVR went into dynamic compression. Theoretically he would have gained 6 dB of headroom, so something is odd in the assessment of the situation.
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post #13 of 16 Unread 11-26-2014, 03:17 PM
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How does one find out that the AVR is going into dynamic compression ?
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post #14 of 16 Unread 11-26-2014, 03:20 PM - Thread Starter
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Quote:
Originally Posted by qguy View Post
How does one find out that the AVR is going into dynamic compression ?
Your ear + a song you really like. In my case, there's this song with a lot of 30hz+60hz ramp in the 2nd half of the song, it's this part that clued me in the problem.

Last edited by coli; 11-26-2014 at 03:25 PM.
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post #15 of 16 Unread 11-26-2014, 03:57 PM
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In this case the compression is part and parcel of THD. If it is not audibly distorted it is unlikely to be dynamically restricted by the preamp. Its one of the great things about really pushing an old style single channel guitar amp. Distortion sounds cool and the dynamics are more naturally constricted than any compressor could accomplish. Compare Hendrix to Messina (and I like them both).
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post #16 of 16 Unread 11-26-2014, 04:45 PM
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Quote:
Originally Posted by coli View Post
The receiver/processor can run out of power supplying 2 subs instead of 1 with voltage, leading to dynamic compression. Took me 2 week to figure this one out...

Thankfully the solution is easy, turn the volume on the sub up, then rerun calibration.

Assuming noise is not a problem and the receiver/processor has enough range to compensate...
Although you fixed the problem by doing the "right" thing, your diagnosis of the problem is all wrong...

If your subs volume controls are set too low, the receiver has to send them too strong a signal. The excessive signal overdrives the inputs of the sub amps, and THIS is what's causing the distortion you're hearing. It is NOT the receiver running out of power to drive the subs.

Fortunately, the way to correct this is to turn UP the subs' volume control and recalibrate the system, which is exactly what you did.

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