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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.
kalali
Post removed 
rooze's avatar
rooze
685 posts
 
Just pick up a cheap miniDSP 2x4 or 2x4 HD.

If you’ve only one pre-out, just use a simple solid rca splitter. Run to one of the inputs on the miniDSP, then run 4 outputs, one to each sub. Bypass the XO on all 4 subs, if you don’t have a bypass then just wind the frequency pot to the highest setting. Set your phase toggles to zero.

Then set up your crossover points in the miniDSP. You can now do some basic time alignment and EQ, though it’ll be trial and error without a mic. If you like what’s happening and you want to go a stage further, spend another 50 buckazoids on a USB Mic.
The miniDSP non HD can be had for about $100, so without a mic that’s your total outlay.

Incidentally, I did NOT have the same experience as MillerCarbon, adding 4 subs without a measurement device and EQ unit to create  filters and add a room curve. It may be down to the shape/size of my room.

Four subs no room measurement blah..
Four subs plus miniDSP whoopee
Four passive subs, two high powered digital power amps and miniDSP WOWZEE.


kearkg312
13 posts
 
In the scenario described by mkgus, im in a similar situation and i have a couple of questions

is there a way to do that and also limit full range signal going to the front mains ? So anything below 80hz is going to the sub.

are there some examples of appropriate pre amps to use in this scenario to run two subwoofers?
tonywinga's avatar
tonywinga
844 posts
 

I found the Artcessories Clean Box Pro to be a good line level buffer to run a pair of subwoofers in parallel with the main amps.  My preamp has two sets of outputs in SE and XLR configurations.  But that doesn't mean the preamp can drive both lines in parallel.  I confirmed this talking to ARC.  My preamp spec states a minimum impedance of 20 kOhms load.  My main amps have 22 kOhms impedance on their inputs and my Subs also have 22 kOhms impedance.  That means my preamp was seeing less than 11 kOhms total impedance.  That is too low and will affect the sound quality of the preamp as well as, I believe, affects the life of the tubes.  I found the Clean Box Pro which converts unbalanced to balanced or vice versa.  The SE (RCA) input side has 100 kOhm impedance and the output is balanced to my subs.  This was a perfect solution.  Now my preamp load totals 18 kOhms impedance.  Sound is much improved and the subs sound the same through the Clean Box Pro as when connected directly to my preamp.  It is possible to route the cables to the subs and then to the main amps but my current, already expensive cables are not long enough to reach the subs.  I would have had to replace all of my XLR cables to the main amps and subs.

figuy's avatar
figuy
45 posts
 

@tonywinga I just wanted to say thank you! Your previous post was a game changer for me. I own a few different preamplifiers and power amplifiers, and noticed that the sound from my dual powered subwoofers seem to change and sounded inferior when I had one particular power amp in the system even though I have my dual powered subwoofers connected via low level connection to the preamp. I had been doing some research lately and started realizing that it might be some sort of an impedance issue, and perhaps my preamplifiers were struggling to drive the power amplifier. I checked the specs and found that this particular power amplifier has a 22k ohm input. It then occurred to me that perhaps the low level input on the subwoofers plate amplifiers might possibly be on the lower side as well. Did more research and landed on this thread here which seemed to confirm my suspicions. And then saw your recommendation for the Art Cleanbox Pro and so I ordered one from Amazon yesterday and received it today. Wow, I cannot believe the difference this thing has made. I have it connected to the set of pre-outs on my preamplifier and then from it to each of my subwoofers and the bass is absolutely fantastic. But in addition to this, I noticed as others have pointed out in this thread, that a struggling preamplifier can affect more than just the bass and so I am now hearing an improvement through the entire audio band, including hearing more detail, bigger sound stage, better imaging, and better separation and layering. I can’t get over how much of a difference this has made. Thanks again! 

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