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Possible impedance matching issue with subwoofer?

Ok, many of us know about the importance of impedance matching with gear. I guess I have not thought enough about this with my sub. My sub is a powered sub like many are. It has it's own built in plate amp. The input impedance of these plate amps/powered subs is often quite low. Mine and many are 20k ohms or so. My preamp has an output impedance of 5k ohms, making for a possible poor match with the sub if I use the 2nd outputs on my pre into the sub's RCA inputs. This is the way I now use the sub.

I suppose I could hook the sub up by going from my amp to the high level inputs on my sub? I could simply run a second set of speaker cables out from my amp to my 2 subs this way right? This would avoid the impedance issue with my pre. Am I thinking correctly?

I think my subs may be rolling off the deep bass because of the impedance issue?

The system sounds very good as is, just wondering if perhaps I am onto something I have missed with possible bass performance improvement.
128x128grannyring
grannyring's avatar
grannyring OP
6,541 posts
 
That is what I thought and thanks Al.
koestner
680 posts
 
If you hook the sub up in parallel to the preamp you will go from an output to input impedance ratio of 94 to only 4. I feel that will certainly result in high frequency sparkle loss. You should look into a buffer between the preamp and sub for the line level inputs. The Musical Fidelity X10 v3 has a high input impedance around 400K that will mate well with your amp. I think the ratio would then be about 44:1 and certainly acceptable compared to 4. I am speaking from experience here, not just textbook. I noticed a definate drop in the highs when I hooked up my sub the same way without the buffer. These buffers don't cost that much. Just get one and try it both ways... you will hear a difference.
almarg's avatar
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almarg
9,670 posts
 
Koestner, I'm curious as to what preamp you were using. Perhaps it has an output impedance that rises in the upper treble region.

Also, what were the lengths of the cables to both the sub and the power amp, and what was their capacitance per unit length (or alternatively, what was their make and model)? As I mentioned earlier in the thread, the capacitance of the cable from preamp to sub, as well as the capacitance of the cable from preamp to power amp, can roll off the upper treble (as seen by the power amp) if it is high in relation to the preamp's output impedance.

Best regards,
-- Al
grannyring's avatar
grannyring OP
6,541 posts
 
Koestner, I have only seen these placed between the preamp and cd or dac. Can it be placed between my preamp and sub amps and work fine?

I assume the second set of preamp outs go into the x10 inputs and then I output to the sub's plate amps right? Is this better or the same as placing the x10 between the cd player and pre? Will my preamps output impedance be lowered by placing the x10 between cd player and preamp? Lowered in the same way as placing it between the pre and subs......
almarg's avatar
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almarg
9,670 posts
 
Grannyring, the answers to the four questions in your last post are:

1)Yes
2)Yes
3)Different
4)No

Also, I would be cautious in extrapolating from the results a buffer provides in one system to the results it would provide in another system, unless there is a good understanding of the reasons for the improvements it provided in the first system.

Best regards,
-- Al
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