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Multiple subwoofers using high level input?

Koeitje

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At the moment I have an integrated amplifier without pre-outs to connect a subwoofer to. So I have to use the high level connection. But how do I do this if I want to use multiple subwoofers?

I have a and b outputs on my amplifier, so I got plenty of room for the wires. Do I connect both R+L speaker channels to each subwoofer? Do I actually set them up in stereo if I place them in such a configuration? Will that even work properly if I feed them only one channel (should I boost the output?)?

Eventually I want to go to something with a power amplifier + multichannel dac and a cross over in the digital domain, but for now I will be running the fronts full range.
 
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Koeitje

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What model subwoofer are they?
I haven't bought them yet, because I first want to know how its going to work out. Its also going to a choice between 1 more expensive subwoofer or 2 cheaper ones.

Couple of years ago I had a BK 10" subwoofer, but I sold it. I also used the high level inputs on that, but I don't know if multiple subs are possible using high level.
 

andreasmaaan

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I haven't bought them yet, because I first want to know how its going to work out. Its also going to a choice between 1 more expensive subwoofer or 2 cheaper ones.

Couple of years ago I had a BK 10" subwoofer, but I sold it. I also used the high level inputs on that, but I don't know if multiple subs are possible using high level.

Ok no worries. Was just checking because your connection options will obviously partly be determined by the subwoofer(s) too.

But to try to answer your question generally, the benefits of having two subs are likely to outweigh the costs, all else equal. Not only do you take 6dB of stress off each sub when you have two subwoofers (likely making up for their lesser performance relative to a single more expensive model), but you can also use the two subs to cancel out room modes and provide a smoother low-frequency response across a wider sweet spot - so long as your room is more or less rectangular and symmetrical.

Assuming that's the case, the optimum setup would be: high-level output from the amp to one sub (both channels), then high-level output from that sub to the other sub (both channels), then high-level output from the second sub to each of the speakers.

You would then place your subs halfway along opposing walls. By having the subs play in mono in these locations, you'd ensure the smoothest possible response and the widest possible sweetspot (relative to other possible locations, or to a single subwoofer).

I should add, this is basically the orthodox view I've given here. There's an alternative approach developed by Griesinger, which involves placing the two subs in highly asymmetrical locations and feeding them a stereo signal. So essentially, the opposite of the orthodox approach. Griesinger's approach (as he admits) is worse from the perspective of smoothness of frequency response, but he believes it creates the greatest sense of "envelopment". I'm not aware of scientific studies to substantiate this, although the idea has an interesting theoretical basis.

Here and here are some good resources examining the optimisation of sub placement.
 

QMuse

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..but he believes it creates the greatest sense of "envelopment". I'm not aware of scientific studies to substantiate this, although the idea has an interesting theoretical basis.

Wouldn't you expect that the sense of "envelopment" doesn't depend on subs position as directivity of their waves is pretty much equal to zero? :D
 

andreasmaaan

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Wouldn't you expect that the sense of "envelopment" doesn't depend on subs position as directivity of their waves is pretty much equal to zero? :D

I'm not advocating for Griesinger's view myself, but FWIW it's largely to do with phase as opposed to amplitude.

The idea is laid out in this powerpoint presentation, and some more detail can be found in the papers on his website. I think his ideas need to at least be taken seriously until they are experimentally tested (it's been a few years since I looked into this though, so the memory is a little hazy now).

EDIT: just found another interesting link, this time a video.
 
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Koeitje

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Ok no worries. Was just checking because your connection options will obviously partly be determined by the subwoofer(s) too.

But to try to answer your question generally, the benefits of having two subs are likely to outweigh the costs, all else equal. Not only do you take 6dB of stress off each sub when you have two subwoofers (likely making up for their lesser performance relative to a single more expensive model), but you can also use the two subs to cancel out room modes and provide a smoother low-frequency response across a wider sweet spot - so long as your room is more or less rectangular and symmetrical.

Assuming that's the case, the optimum setup would be: high-level output from the amp to one sub (both channels), then high-level output from that sub to the other sub (both channels), then high-level output from the second sub to each of the speakers.

You would then place your subs halfway along opposing walls. By having the subs play in mono in these locations, you'd ensure the smoothest possible response and the widest possible sweetspot (relative to other possible locations, or to a single subwoofer).

I should add, this is basically the orthodox view I've given here. There's an alternative approach developed by Griesinger, which involves placing the two subs in highly asymmetrical locations and feeding them a stereo signal. So essentially, the opposite of the orthodox approach. Griesinger's approach (as he admits) is worse from the perspective of smoothness of frequency response, but he believes it creates the greatest sense of "envelopment". I'm not aware of scientific studies to substantiate this, although the idea has an interesting theoretical basis.

Here and here are some good resources examining the optimisation of sub placement.
You make a good point about reducing the load by using two subwoofers, because that is what its going to be: 1 expensive sub or 2 cheaper ones.

But I highlighted what confuses me. Why would I route my mains also through the subwoofers? Can't I just connect them in parallel on my amplifier?
 

QMuse

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Can't I just connect them in parallel on my amplifier?

Of course you can, but only for a short time. After that you'll have to buy a new amp as your current one will probably be burned because of low impedance.
 
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Koeitje

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Of course you can, but only for a short time. After that you'll have to buy a new amp as your current one will probably be burned because of low impedance.
Why does connecting 2 subwoofers in parallel burn my amplifier, but 1 in parallel doesn't?
 
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Koeitje

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1/R total = 1/R1 + 1/R2
8 ohm speakers, 150k ohm subwoofers (REL T5 for this example), all in parallel is 7.99 ohm. What am I doing wrong?

I'm not hooking up passive subwoofers, I'm looking for active subwoofers with high level inputs.
 

HammerSandwich

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If the subs have their own amps, then the high-level inputs will be high impedance. Parallel connections will be fine.

If the subs' high-level outputs are a direct connection - no crossover - then connecting directly to the amp will be the same (minus tiny differences to cable lengths).
 

Soniclife

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Of course you can, but only for a short time. After that you'll have to buy a new amp as your current one will probably be burned because of low impedance.
The high level input on a sub is high impedance, so it takes no power.
 

QMuse

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8 ohm speakers, 150k ohm subwoofers (REL T5 for this example), all in parallel is 7.99 ohm. What am I doing wrong?

I'm not hooking up passive subwoofers, I'm looking for active subwoofers with high level inputs.

Well, if they have input impedance of 150Kohm at high level inputs then nothing. As @andreasmaaan suggested both your subs and corresponding main will receive the same signal. Do you have high-level output on your sub so you can route signal further?
 
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Koeitje

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Well, if they have input impedance of 150Kohm at high level inputs then nothing. As @andreasmaaan suggested both your subs and corresponding main will receive the same signal. Do you have high-level output on your sub so you can route signal further?
I haven't bought any subwoofer yet, so I'm not sure they will. That will just split the signal and save me some cables I guess?
 

Kal Rubinson

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At the moment I have an integrated amplifier without pre-outs to connect a subwoofer to. So I have to use the high level connection. But how do I do this if I want to use multiple subwoofers?
You can derive a line level signal from the speaker taps with a pair of resistors per channel. Those will isolate the line level outputs so that they can be connected to the subs and/or combined without shorting the amp's output to the speakers.
 

andreasmaaan

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But I highlighted what confuses me. Why would I route my mains also through the subwoofers? Can't I just connect them in parallel on my amplifier?

Yes sorry, you could also do that. I was focused on how to hook up the subs, had overlooked that you could directly connect the speakers (as long as you're happy to run them full-range).
 
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Koeitje

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Yes sorry, you could also do that. I was focused on how to hook up the subs, had overlooked that you could directly connect the speakers (as long as you're happy to run them full-range).
I plan on not running them full-range eventually, but it looks like there are not many subwoofers that have a high pass high level output. So I'll have to use something from Minidsp or whatever to create a crossover. So until I have all the part they will run full range :p.
 
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Koeitje

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