In pro audio, a distribution amplifier is the answer.
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.
Appreciate any input.
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- 33 posts total
@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. |
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 :) |
@kalali, The impedance ("capacitive reactance") of a 2.2 uF cap at 20 Hz is 3619 ohms! The impedance of a 3.3 uF cap at 20 Hz is 2413 ohms. The specified 600 ohm output impedance is presumably at 1000 Hz or thereabouts, and mainly represents the output impedance of what is "ahead" of the cap (since the impedance of the cap is low at those frequencies). The output impedance of that circuitry is probably fairly constant within the audible frequency range (i.e., it is mostly resistive in nature). The overall output impedance at 20 Hz is probably just a little bit higher than the impedance of the cap, as series combinations of resistive and capacitive impedances combine as the square root of the sum of the squares, rather than adding directly. Best regards, -- Al |
Thank you. Those impedance values pretty much rule out the use of the second (parallel) output from the Unlimited to drive all the powered subwoofers. I also remember reading somewhere that selecting too large uF output coupling capacitors can have some undesirable sonic side effects and the designers generally strike a balance between the size (uF) and coloration. Anyway, researching some older discussions on the distributed bass array topic, it looks like a more practical approach is what AudioKinesis uses in his acclaimed Swarm where I believe he utilizes a single kilowatt class AB amplifier to drive four passive subwoofers. https://www.parts-express.com/dayton-audio-sa1000-subwoofer-amplifier-rack-mountable--300-811 But even with this amplifier with a published 12K Ohms input impedance, I'd get a combined ~11K Ohms which probably works well with most if not all SS preamps but borderline for most tube preamps. I'd like to hear if anyone is driving a distributed bass array system similar to the Swarm using a tube preamp as the signal source. Thanks again. |
- 33 posts total