YAPCA (Yet Another Power Configuration Analysis)

SeanBrothers

Active Member
If you want, I can estimate this for you if you give me the following:

  • Distance to LCR speakers from MLP
  • Room volume (ft3)
  • Maximum listening level with a reference source (e.g. DVD, Blu-ray) - this assumes your system is calibrated to 0dB volume being reference level, not all are.
  • Model of AVR/amp

I assume your quoted speaker specs are for the LCR speakers. If not, I’ll need those too.

Thanks for looking into this @Mr Wolf!

AVR: Denon AVR-X3700H
Power Amplifier: Adcom GFA-545 II (100 WPC into 8 Ω applied to front LR)
Front LR: Elac Uni-Fi UF51 (Nominal impedance: 4 Ω; minimum 3.4 Ω; Sensitivity: 85 dB at 2.83 V/1m; Distance: 2.34m)
Center: Elac Uni-Fi UC51 (Nominal impedance: 4 Ω; minimum 3.4 Ω; Sensitivity: 85 dB at 2.83 V/1m; Distance: 2.31m)
Surround L: Elac Uni-Fi UB51 (Nominal impedance: 4 Ω; minimum 3.4 Ω; Sensitivity: 85 dB at 2.83 V/1m; Distance: 1.50m)
Surround R: Elac Uni-Fi UB51 (Nominal impedance: 4 Ω; minimum 3.4 Ω; Sensitivity: 85 dB at 2.83 V/1m; Distance: 1.59m)
Rear Surround L: Pioneer SP-BS22-LR (Nominal impedance: 6 Ω; Sensitivity: 85dB/2.83 V/m; Distance: 2.79m)
Rear Surround R: Pioneer SP-BS22-LR (Nominal impedance: 6 Ω; Sensitivity: 85dB/2.83 V/m; Distance: 2.88m)
Top Front L: Polk OWM3 (Nominal Impedance: 8 Ω; Sensitivity: 89dB/1 W/m; Distance: 1.74m)
Top Front R: Polk OWM3 (Nominal Impedance: 8 Ω; Sensitivity: 89dB/1 W/m; Distance: 1.71m)
Top Rear LR: Polk OWM3 (Nominal Impedance: 8 Ω; Sensitivity: 89dB/1 W/m; Distance: 1.89m)
Subwoofer: Velodyne DD12 (Amplifier output: 1250W RMS, 3000W peak; Distance: 2.67m)

Room: 1600 ft3
Volume: Sometimes as high as -18db
 
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Mr Wolf

Well-known Member
OK, the analysis is below. Input assumptions are the yellow boxes, the rest is formulae so this was actually very quick to do.

When in doubt I've been conservative with the input assumptions that affect in-room speaker sensitivity but the result still shows between 10dB ands 20dB of dynamic headroom in all channels. As soon as I saw -18dB volume I knew there wasn't going to be a problem. In practice, based on actual measurements I've taken of my own system I expect the headroom might be even higher than this due to greater in-room speaker sensitivity than I've assumed.

Anyway, it shows the centre channel has the least amount of headroom (10dB) and is therefore the limiting factor on overall output capability. As >3dB minimum headroom is recommended the system should be OK to drive 7dB higher so up to -11dB volume.

You may be pleased to see that, despite only powering two of the system's 11 channels, the use of a power amp on the front L/R mains reduces the peak power burden on AVR by about 48%. This doesn't surprise me as the mains contain up to 50% of a soundtrack's peak SPL output, the remaining being centre 25% and surrounds (collectively) 25%. That said, the system's overall maximum peak power requirement (31.5W) is still very low so if you had an 11 channel AVR (e.g. X6700) it shouldn't break into a sweat running all the speakers at your volume level.

1643886146219.png
 
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D

Deleted member 901590

Guest
So @Mr Wolf would you say that if (and I say if because I don't think he is) considering an upgrade, it may be wiser to consider a more efficient centre speaker than change the AVR or add a power amp?
 

Mr Wolf

Well-known Member
So @Mr Wolf would you say that if (and I say if because I don't think he is) considering an upgrade, it may be wiser to consider a more efficient centre speaker than change the AVR or add a power amp?
Yes, because this system doesn’t need extra power anyway and I would expect larger, more sensitive LCR speakers would sound appreciably better. These Elacs all use 5.25” drivers and, personally, I‘ve never had an LCR speaker I liked that didn’t use at least 6.5” drivers. Unfortunately, affordable 6.5” driver centre speakers are getting rarer these days.
 

SeanBrothers

Active Member
Thank you so very much for the analysis @Mr Wolf! I'm glad it was quick to do!
Interesting results indeed! And I wouldn't have suspected my center speaker as a weak point. Go figure!

As for upgrades, I think I'm done for the foreseeable future. The Elacs are considerably better than the Home Theatre in a Box hand-me-downs I had before, and getting them at end of life prices helped me get better speakers within my budget!

I rarely ever go as high as -18db. It's bloody loud already!
 

SeanBrothers

Active Member
Another curiosity: shouldn't crossover settings matter since they redirect the more power demanding frequencies to the subwoofer(s)?

I'm guessing that there is an assumption that crossovers are at 80Hz?

And, if correct, couldn't a little a extra headroom be attained by moving the crossovers up say 10Hz? And conversely, the headroom be diminished by having the crossovers down lower?
 

gibbsy

Moderator
Another curiosity: shouldn't crossover settings matter since they redirect the more power demanding frequencies to the subwoofer(s)?

I'm guessing that there is an assumption that crossovers are at 80Hz?

And, if correct, couldn't a little a extra headroom be attained by moving the crossovers up say 10Hz? And conversely, the headroom be diminished by having the crossovers down lower?
You should always set the sub to it's maximum crossover when running in 5.1 or above.
 

Mr Wolf

Well-known Member
Another curiosity: shouldn't crossover settings matter since they redirect the more power demanding frequencies to the subwoofer(s)?

I'm guessing that there is an assumption that crossovers are at 80Hz?

And, if correct, couldn't a little a extra headroom be attained by moving the crossovers up say 10Hz? And conversely, the headroom be diminished by having the crossovers down lower?
As a maximum possible 20dB peak is presumed in the model the crossover setting is completely irrelevant but it does assume 30dB LFE peaks are sent to a sub. A 20dB peak could easily happen at say 180Hz which would not be redirected (or even attenuated) by the HPF of the bass management crossover and this is a frequency where many speakers have their lowest impedance dips. Think of this as the most demanding sound that could be required from the amplifier (especially if it's at a high phase angle).

In practice, a crossover is likely to significantly reduce the duty cycle of the AVR on dynamic peaks as, in general, the lower the frequency the longer the dynamic peaks last. Also, in general the lower the frequency the louder the peaks are so a soundtrack might only have say up to 17dB peaks >80Hz and up to 20dB peaks <80Hz in which case the crossover could reduce the AVR's peak power requirement by 50%. But then again it might not so I have presumed the worst in the model.

On Audioholics, one forum member (Peng) once did a peak voltage test with and without a 80Hz crossover with one movie scene (from The Dark Knight) and found peak power requirement on the centre channel (only speaker tested) was circa 40% higher when running it Large. Obviously the power saving will be wholly dependent on the source content. I've recently bought a True RMS meter that's capable of these measurements and will publish my own findings at some point.
 

gibbsy

Moderator
To be clear, I mean the AVR crossovers rather than the setting on the sub.
80hz is the recommended settings for those speakers that are capable of it. It the frequency that studio mix and was the THX setting. Many arguments for and against it and even though my front speakers (with Audyssey) roll off at 40hz I have them set to 80hz and that works for me.

Some speakers are not capable of sustaining 80hz and should always be set to the roll off that the calibration system has them. It's a recommendation that is certainly not written in stone.
 

SeanBrothers

Active Member
My LCR, SL, and SR speakers are all rated to -3db in the low 40s. I actually tried mine at 60Hz for a while and didn't notice a difference in the sound quality, so I returned them back up to 80Hz to take some load off the recievwr since my subwoofer is woefully overpowered.

Kudos to @dante01 for his Bass Management thread which I delved into.
 

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