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Can an unused amplifier pair of Denon AVR-X3700H AVR be used to feed passive subwoofers? (Yes)

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sarumbear

sarumbear

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Could the X3700H technically drive passive subs, yes. If you hooked them up to the Height 2 binding posts, then looped the subwoofer RCA output into one of the analogue inputs such as CD, and selected that as your Zone 2 playback source.
Thank you for this suggestion. That will work fine for my friend.

However, that is a bit of a hack and not recommended. The power availability drops as more channels get loaded, and the X3700H only has typical class A/B output efficiency.
Other than the power load increase is there anything else that is not recommended.
 

alex-z

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Right thanks.

And during the measuments? The Zone 2 outputs need to be engaged then too, correct?

Yes. In the setup menu, you will need to reassign the Height 2 channels to Zone 2. Then you will need Zone 2 turned on any time you wish the subwoofers to work, including during the remainder of the setup process.

Other than the power load increase is there anything else that is not recommended.

In theory the X3700H should handle the additional load, as long as the unit is properly cooled. I cannot vouch for long term reliability or sound quality, never heard of anybody else trying this.
 
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sarumbear

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In theory the X3700H should handle the additional load, as long as the unit is properly cooled. I cannot vouch for long term reliability or sound quality, never heard of anybody else trying this.
The same amplifiers are driving the LCR and the surround speakers, why would the unused pair will have a sound or reliability issues? The LCR amplifiers are driven much harder then the LFE channel.
 

Chrispy

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Why bother connecting subs to channels (let alone whether the amp's sufficient for the particular sub) you can't use bass management with?
 

pedrob

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I've not seen inputs to the individual amps, so it seems you can't bypass the inbuilt processor.

Powered subs are the way to go.
 

Head_Unit

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2*70W for a sub sounds underpowered.
https://en.wikipedia.org/wiki/Clipping_(audio)
;)
Yeah even in a car that is not enough for more than modest sound pressure. I designed a number of powered subs, and I remember one 150W model which visibly clipped on an oscilloscope. And per
https://www.aes.org/e-lib/online/browse.cfm?elib=5147
if you can't generate fairly loud sound pressure at the low frequencies, it is useless. Due to the nature of hearing (Fletcher-Munson) you just won't hear it.

Sensitivity is a frequency independent value.
Um, NO. Or what do you mean by that? I misunderstand? Sensitivity varies tremendously with frequency. Richard Small's calculated value is frequency independent but has nothing to do with bass, and is only a theoretical value anyway.

As for the AVR, I would not want to load further with bass. Power supplies are all weak, that's why they all droop power as more and more channels are driven. Now for the friend's 100 dB, and @voodooless 115 or whatever, is that simulated at one meter? Or actually in a room at the listening distance? How about actually measured? I find it hard to believe big subs put in huge amps just for overkill.

Makes me ask this question: is there a good storage oscilloscope app which will let you look at actual clipping? It would be nice to gather actual DATA without which all is hot air (including my opinions, eh)

Back to the original question, I have not seen an AVR with main-ins, or channels assignable to the sub, so all this discussion is academic, you can't do it.
 
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sarumbear

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https://en.wikipedia.org/wiki/Clipping_(audio)
;)
Yeah even in a car that is not enough for more than modest sound pressure. I designed a number of powered subs, and I remember one 150W model which visibly clipped on an oscilloscope. And per
https://www.aes.org/e-lib/online/browse.cfm?elib=5147
if you can't generate fairly loud sound pressure at the low frequencies, it is useless. Due to the nature of hearing (Fletcher-Munson) you just won't hear it.
Please read this post earlier in this thread.


Back to the original question, I have not seen an AVR with main-ins, or channels assignable to the sub, so all this discussion is academic, you can't do it.
Please read this post as well, which gave clear instruction on how to do it, and furthermore, I set it up as described and it is working!


Not reading a thread or not understanding posts but giving concrete answers like "you can't do it" is not helpful.
 
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sarumbear

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Well we have at least one proposed solution that is still to be refuted.

What did I miss?
You missed nothing. I used that solution and it’s working. I wish people don’t assume what is in only their heads as reality. It doesn’t look good on them.
 

Chromatischism

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Can you do some compression tests? Would be interesting to see what you can get out of them with only AVR power and whether you run into any issues.
 
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sarumbear

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Can you do some compression tests? Would be interesting to see what you can get out of them with only AVR power and whether you run into any issues.
I checked the subwoofer outputs using a portable scope when the full system (5.1) blaring at full blast, measured around 95-96dBSPL C-weighted and saw no clipping. I expect the subwoofers to be producing more than 100dB at the time. That is enough for me as I expect for most people who care about their hearing.

You must realise that the subwoofer drivers are very efficient. Not much power required to reach silly volumes. Denon replaced a 2x70W amplifier.
 

Head_Unit

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Not reading a thread or not understanding posts but giving concrete answers like "you can't do it" is not helpful.
sigh, I guess I missed a few pages in the middle. I did not realize you could put an output to an input without feedack so that's pretty ingenious. But by now an admin should change the thread title to HOW to use unused channels to run a subwoofer.

I'm still puzzled by the power demands i.e. why most subs have much larger amps-I suppose their working band sensitivity is much less due to smaller enclosures etc. I want to get back to investigating some stuff about driver sensitivity; want to find a simulator that would let me input cone mass and so on directly (yeah I could keep iterating Thiele-Small parameters offline to input but that's slower).
 

Head_Unit

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According to this calculator the amplifier power required to produce 100dB is just 2W if the units are at a corner, which they are.
Wait, what? If I put in 91.5 dB sensitivity, 2W, 3m, in corner, I get 91 dB. Not 100 dB. Did I do something wrong?

Then @voodooless posted a Hornresp showing like 105 dB for 1W-that is a hell of a lot more (closed perfect shoebox room?). I gotta wonder if there is really that much gain in a real room. And given that much room gain, do two subs really give another 6 dB? From some theoretical idea yes but I've never seen it tested that I recall.

Any possibility to measure the actual response of these subwoofers? My interest is very piqued. Ideally each separately and then together. I'd also be curious your comments why you chose that driver over a more "pro" driver (not disagreeing, mind you, just wondering what factors were considered)
 

SKBubba

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I don’t think there's any way to get the avr to do proper bass eq/management/crossover etc. without using the sub outs.
 
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