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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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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:
View attachment 218798
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: "([email protected]) averaged from 60 to 200 Hz".

So how loud will 70W go (I assume 70W each)? Way north of 125 dB @ 1 meter :cool: 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.
I think I’ve done OK :)

Can you simulate the port output separately? Your chart makes it look like it its frequency is lower than what I thought I designed. It has been a while.

My memory must be hazy on sensitivity as well but what does 2dB among friends, especially if it’s conservative? :)

As I said earlier each subwoofer is driven separately by a stereo power amplifier, which can output large current (a NAIM NAP250).
 
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voodooless

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I think I’ve done OK in the design :)

Can you simulate the port output separately? Your chart makes it look like it its frequency is lower than what I thought I designed. It has been a while. My memory must be hazy on sensitivity as well but what does 2dB among friends, especially if it’s conservative? :)
Well, I don't know the tuning you choose, so I guesstimated something that looked halfway good given the volume. No point in doing so unless I have the real numbers ;)
 
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sarumbear

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Well, I don't know the tuning you choose, so I guesstimated something that looked halfway good given the volume. No point in doing so unless I have the real numbers ;)
I think I tuned to 30Hz but can’t be sure as it has been a while. I used a large but relatively shallow vent to avoid turbulence. As the amplifier was fed via a LP filter I wasn’t worried about high frequency resonances.
 
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sarumbear

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I think I tuned to 30Hz but can’t be sure as it has been a while. I used a large but relatively shallow vent to avoid turbulence. As the amplifier was fed via a LP filter I wasn’t worried about high frequency resonances.
Originally the enclosure was a closed box. I used a biquad filter, the clever Linkwitz Transform. However, the circuit was a PCB with wires dangling. We couldn’t find a ready made unit and at the end I thought instead of using miniDSP why not add a port? As you see it worked all right.

When you start with a quality driver suited for the job you are half way there. The remaining are, quarter way for size and quarter way for knowhow.
 
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sarumbear

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Well, I don't know the tuning you choose, so I guesstimated something that looked halfway good given the volume. No point in doing so unless I have the real numbers ;)
I checked my notes. The enclosure has an approximate 200 litre internal volume and the port was tuned to 25Hz in order to hit -10dB at 20Hz. The port opening is 15x5cm rectangle and it is 9cm deep. I had measured the resonance at the time and I recall it to be near 25Hz but not exactly, though my notes doesn't say what the measured value was.
 

voodooless

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I checked my notes. The enclosure has an approximate 200 litre internal volume and the port was tuned to 25Hz in order to hit -10dB at 20Hz. The port opening is 15x5cm rectangle and it is 9cm deep. I had measured the resonance at the time and I recall it to be near 25Hz but not exactly, though my notes doesn't say what the measured value was.
That's basically what I came at as well.
 
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sarumbear

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That's basically what I came at as well.
I always said there is often one decent solution for every driver in the hands of someone who know what they are doing :)
 

peng

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

If I were to guess, I would agree the AVR would not make things worse, may even be better depending on the material as the avr may be able to output more than the 2X70W power amp for short duration peaks. Obviously it also depends on the 70 W power amp's specs.
 

Rednaxela

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Or modify the sub further by adding a plate amp?

I like the original question though. Would be interesting to know if it could be done.
 
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sarumbear

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If I were to guess, I would agree the AVR would not make things worse, may even be better depending on the material as the avr may be able to output more than the 2X70W power amp for short duration peaks. Obviously it also depends on the 70 W power amp's specs.
Have you read and/or understood what @woodooless said on post #20?
 
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sarumbear

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unpopular opinion: sell the subwoofer amp and the subs. buy active subs. simple, proven solution :)
Show me a few subwoofers that has similar sub bass extension and capacity shown on post #20?
 
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sarumbear

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Or modify the sub further by adding a plate amp?

I like the original question though. Would be interesting to know if it could be done.
What will be the benefit, you think?
 

peng

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Have you read and/or understood what @woodooless said on post #20?

He said "Way north of 125 dB @ 1 meter". Based on the specs (93 dB/w/1m) two such subs can play quite loud but I am not sure about "way north of" as such.

You can drive them with the AVR and it may work well enough given the right conditions (placement/distance, spl requirement etc...). Not something I would do though.
 
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sarumbear

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He said "Way north of 125 dB @ 1 meter" based on the specs for two such subs linked. I don't know about "way north" though as I don't see the evidence. The main point is, while I won't do it myself, but you can do it and it may work well enough given the right conditions (placement/distance, spl requirement etc...).
Forget the way north, has anyone needs more than 125dBPL sub bass? What is there to improve?
 

peng

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Forget the way north, has anyone needs more than 125dBPL sub bass? What is there to improve?
That's @1 m, spl, it will be 121 dB at 2 m and 115 dB at 4m, still enough for a lot of people.
 

alex-z

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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.


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.

A simple TPA3255 mono amplifier can deliver 120-140 watts into 4 Ohms for $80. I have one of these driving a sealed 12" sub for a bedroom setup, no reliability issues two years in at max power.

 

Rednaxela

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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.
Does this work with Audyssey?
 

alex-z

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Does this work with Audyssey?

It should, because you are just using the standard subwoofer pre-outs. I don't know if Audyssey tries to apply any additional correction filters to the Zone 2 outputs, but I don't see that in the documentation, so I would assume not.
 

Chrispy

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The major difference these days with subs is simply where the amp is located and how integrated (i.e. crossover) with the rest of the system. Passive subs still need an amp, active subs may have them built into the same box.....somewhat strange terminology to describe a particular situation/application.....

(but of course for proper sub integration the details/software/dsp available makes a difference vs just crude "blending".....
 
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