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

[sarumbear]

I am considering upgrading a friend's AVR. As an entry level AVR Denon AVR-X3700H seems to be a good choice. The unit has nine amplifiers but my friend's setup is 5.2, hence there will be two redundant channels of amplification. My friend's subwoofers are passive. They are currently run through a power hungry (and large) power amplifier. So I am wondering if that redundant amplifier pair can be assigned to the subwoofers?

I read the manual but there as far as I can see there is no mention on how to do what I want other than a bi-amp option for the front speaker pair.

Guidance on setup is appreciated.

 

[Vincentponcet]

The result would probably be not be great.
Subs eat a ton of energy.
The power supply and the amps of an AVRs are sized to offload the low end to an external amplified subwoofer.
One sub generally have a 500-1000W amp, so as much as the 9 channels of the x3700h.

 

[AudioJester]

No wont work. Connect the subouts from denon to subwoofer amp. Can then use Audyssey as well which may make the biggest difference.

 

[sarumbear]

The result would probably be not be great.
Subs eat a ton of energy.
The power supply and the amps of an AVRs are sized to offload the low end to an external amplified subwoofer.
One sub generally have a 500-1000W amp, so as much as the 9 channels of the x3700h.

Thank you but he is currently using a 2x70W amplifier. Replacing it with more powerful amplifiers in the AVR will not make things worse.

 

[BDWoody]

I read the manual but there as far as I can see there is no mention on how to do what I want other than a bi-amp option for the front speaker pair.

I don't believe so, as I'd like to do the same myself. I just picked one up, and was hoping to be able to use my 2 passive subs with it's internal amplification, but looks like that's a no go.

 

[sarumbear]

No wont work. Connect the subouts from denon to subwoofer amp. Can then use Audyssey as well which may make the biggest difference.

Are the sub outputs mono in parallel or stereo? Does Audyssey process them as mono or stereo, do you know?

 

[Vincentponcet]

Thank you but he is currently using a 2x70W amplifier. Replacing it with more powerful amplifiers in the AVR will not make things worse.

There are not more powerful.
x3700h is rated for 9*150W 4 ohms, but with a transformer of less than 1000W, do the maths.
The power supply cannot sustain the max power of all amps at the same time.
Sub amps are more in the range of 500-1000W generally, so 2*70W for a sub sounds underpowered.

 

[BDWoody]

Are the sub outputs mono split to two or stereo? Does Audyssey process them as mono or stereo, do you know?

Mono, with each sub processed separately.

 

[sarumbear]

Sub amps are more in the range of 500-1000W generally, so 2*70W for a sub sounds underpowered.

Thank you for the education but I am asking for a specific advise on a specific amplifier's setup. I rather you don't preach if you don't have an answer to my question.

 

[Vincentponcet]

Thank you for the education but I am asking for a specific advise on a specific amplifier's setup. I rather you don't preach if you don't have an answer to my question.

It was my first response then.
It will work, but the sound will be most be most probably not great or even worse than your actual setup, because your current setup has an independent power supply for the subs. When connected to the Denon amps, the subs will eat the current of the other channels.

You need to setup the Denon with subwoofer to None and Fronts to Large. For Denon, "subwoofer" is the sub preamp output only, as you are not using it, you have to disable it, to get the bass back to the front.

Speaker Config. AVR-X3700H

manuals.denon.com

And set amp config front bi-amps mode, one pair of amps goes to the front, and the other pair goes to the subs.

Amp Assign AVR-X3700H

manuals.denon.com

The limitation is Audyssey does not see this as subwoofers, you have fronts with all band pass.
I assume it will redirect LFE channel to Fronts, but I never see an explicit statement about this.

 

[sarumbear]

Sub amps are more in the range of 500-1000W generally, so 2*70W for a sub sounds underpowered.

... the sound will be most be most probably not great or even worse than your actual setup, because your current setup has an independent power supply for the subs. When connected to the Denon amps, the subs will eat the current of the other channels.

My friend's subs have 15" JBL drivers with stated sensitivity of 91dBSPL/W and Xmax of 5mm

According to this calculator the driver can produce 100dB at 30Hz and 5mm Xmax. The subwoofer's enclosure is vented with a port tuned to around 30Hz. This allows it to produce more than 100dB as the port will be adding to the output and there are two subwoofers, adding another 6dB.

According to this calculator the amplifier power required to produce 100dB is just 2W if the units are at a corner, which they are. That is a power crest ratio of 35. Now tell me again why a 70W amplifier is underpowered at my friend's setup?

 

[voodooless]

My friend's subs have 15" JBL drivers with stated sensitivity of 91dBSPL/W and Xmax of 5mm

At what frequency? No way they are 91 dB in the usable bandwidth.

Having said that, I doubt 70W will be a real issue with these things. They will still get plenty loud.

A simple cheap class D amp will do just fine and keep cool.

BTW, I thought you had two spare AVR’s that you wanted to use to power subs .

 

[sarumbear]

At what frequency? No way they are 91 dB in the usable bandwidth.

Sensitivity is a frequency independent value.

Understanding Speaker Sensitivity - Geoff the Grey Geek

A simple explanation on how to understand and use Speaker Sensitivity specifications. Includes calculators to determine how loud your speakers will be.

geoffthegreygeek.com

BTW, I thought you had two spare AVR’s that you wanted to use to power subs .

My opening sentence of this thread: I am considering upgrading a friend's AVR.

 

[sarumbear]

It can work, but it is not great. There is a reason that most avr have preout sub. Subs are power hungry. Also, amped outputs do not have LFE which makes the signal unsuitable for subs. You want to pass something like 20-200Hz to subs but the only option you can use is Full range.

Better to buy dedicated sub amp

So you have not read any of my posts then?

 

[FrantzM]

My friend's subs have 15" JBL drivers with stated sensitivity of 91dBSPL/W and Xmax of 5mm

According to this calculator the driver can produce 100dB at 30Hz and 5mm Xmax. The subwoofer's enclosure is vented with a port tuned to around 30Hz. This allows it to produce more than 100dB as the port will be adding to the output and there are two subwoofers, adding another 6dB.

According to this calculator the amplifier power required to produce 100dB is just 2W if the units are at a corner, which they are. That is a power crest ratio of 35. Now tell me again why a 70W amplifier is underpowered at my friend's setup?

Seems your friend knows what he's doing... No doubt... Now , let's get to the OP.

He could, he must first find some subwoofers with great sensitivity and find a way to linearize these subwoofers.. say some DSP... He could start Rube Goldberg-ing, by using the available amplifers as Zone 2, find some ways to get the signal , loop through the DSP and back to the AVR , while trying to maintain proper timing and distance ... and integration, to the mains...
It might be do-able. There are plenty of things that are doable but ...
Contrast that, to finding an inexpensive stereo Class D-amplifier, say the Ayima or something... less than $100 that Amir measured and could produce upward of 100 watts per channel... plug the Subs output of the AVR-3700 to it, use Audyssey, massage it and be done and happy.. very.

My answer to the OP. You could make this work but don't go there.. It will be a waste of time.

Peace

 

[sarumbear]

Seems your friend knows what he's doing... No doubt... Now , let's get to the OP.

He could, he must first find some subwoofers with great sensitivity and find a way to linearize these subwoofers.. say some DSP... He could start Rube Goldberg-ing, by using the available amplifers as Zone 2, find some ways to get the signal , loop through the DSP and back to the AVR , while trying to maintain proper timing and distance ... and integration, to the mains...
It might be do-able. There are plenty of things that are doable but ...
Contrast that, to finding an inexpensive stereo Class D-amplifier, say the Ayima or something... less than $100 that Amir measured and could produce upward of 100 watts per channel... plug the Subs output of the AVR-3700 to it, use Audyssey, massage it and be done and happy.. very.

My answer to the OP. You could make this work but don't go there.. It will be a waste of time.

Peace

It seems you have not realised that the OP and the member you have replied above are the same

And it also seems that you failed to read that my friend has a subwoofer amplifier. I am not looking to find another amplifier. I am looking if I can get rid of it and use the spare pair on the Denon.

 

[FrantzM]

It seems you have not realised that the OP and the member you have replied above are the same

And it also seems that you failed to read that my friend has a subwoofer amplifier. I am not looking to find another amplifier. I am looking if I can get rid of it and use the spare pair on the Denon.

 

[voodooless]

Sensitivity is a frequency independent value.

Yeah, in the model. In reality it can turn out very different. What’s the driver, let’s see what it really does down low?

My opening sentence of this thread: I am considering upgrading a friend's AVR.

Yeah, I based it on the title. After reading the post it all became clear.

 

[sarumbear]

Yeah, in the model. In reality it can turn out very different. What’s the driver, let’s see what it really does down low?

https://jblpro.com/en-US/products/15sws800 in a roughly 200 litre vented enclosure.

 

[voodooless]

https://jblpro.com/en-US/products/15sws800 in a roughly 200 litre vented enclosure.

Well, I used Hornresp because WinISD is only half space. Was I in for a surprise This is what you get when putting these in a corner:

This is at 2.83V (which is about 2W when both are in parallel). That's no 91 dB either. Spec sheet says 93 dB BTW: "(2.83V@1m) averaged from 60 to 200 Hz".

So how loud will 70W go (I assume 70W each)? Way north of 125 dB @ 1 meter It's safe to say that this will be plenty.

Now I always found that Hornresp seems to be very positive in SPL graphs, but WinISD shows about 112 dB at the low end in half space, add 12 dB to that, and we're almost back at the Hornresp figure.