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Preamp connection to multiple powered subwoofers

I'm trying to understand how those of you who have multiple, say four, powered subwoofers in your 2-channel audio systems feed the signal from your preamplifier to these amplifiers in addition to driving your main speakers. In addition to the physical connectivity, I'm also wondering how is the impedance matching between the preamp output impedance and the combined input impedances of these multiple amplifiers is addressed. Using my system as example, my preamp has two parallel outputs rated at 600 Ohms with one set driving a tube amplifier rated at 100K Ohms. Would the second output be shared across four powered subwoofers, most likely Class D with generally low input impedance around 10K-20K Ohms? Or folks mostly use the high level speaker connections through the main speakers and split through to the rest of the subwoofers?  I have the same question for those running passive subwoofers. Do you use the second preamp output to drive a dedicated 4-channel amplifier and out to the subwoofers, and if so, how do you handle the phase, gain, and frequency adjustments across the four subwoofers.
Appreciate any input.
128x128kalali
rocray's avatar
rocray
1,448 posts
 
I run 3 subs in my system. I run 2 off of my amp(speaker cable/hi pass) the 3rd I run off of my Unlimited preamps second set of out puts. Now,the 3rd HSU sub has a slight impedance mismatch. I run 2 rca's out of the pre to the 2 rca inputs on the sub. If I only run 1 out to 1 in,the volume on one channel is lower than the other. The outputs are run in parallel, therefore I run 2 to 2,to keep volume levels the same in both channels. I hope this helps. Any questions,feel free to pm me.
bdp24's avatar
bdp24
9,738 posts
 

If you buy Rythmik subs, the XLR versions of the company's plate amp allows piggy-backing of one sub to another. You can use the adjustment knobs (level, phase, x/o filters, etc.) on each sub separately, or control the piggy-backed sub as a slave from the sub feeding it the signal. The input impedance is 30K ohms.

But to get the XLR connections, you give up the high-level (power amp) inputs found on the PEQ model plate amps.

imhififan's avatar
imhififan
2,176 posts
 
In pro audio, a distribution amplifier is the answer.

cal3713's avatar
cal3713
1,421 posts
 
@mijostyn You think not using a high pass filter is a problem even if the subs are built to receive a full range signal? My coincident pre's have sub cabinets with their own binding posts and an inductor to cross them at around 200hz. I just started running them with subwoofer amplifiers and have been bypassing the amps' crossover circuitry.
kalali's avatar
kalali OP
1,977 posts
 
Thank you all, particularly Al for his detailed response, as always. Assuming a 10K input impedance for the sub plate amplifiers, the combined impedance will be about 2,500 ohms which is technically too low even for the (published) 600 ohm output impedance of the Unlimited. I suspect it'll get even worse at lower frequencies. As for the output coupling capacitors, I currently have 2.2 microfarad coupling capacitors in there now but they are relatively easy to change since I've already changed/upgraded them once before. The OEM values were 3.3 microfarad.  
rocray - I think using a combination of line level and speaker high level methods may be a reasonable option. Thanks.
I have a friend with a pretty decent woodworking shop and all kinds of tools and I'm thinking about building the subs with his help. Been itching for a good winter project having sold my bike a couple of months ago :)
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