AudiogoN Forums: Possible impedance matching issue with subwoofer?

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.

Grannyring (Reviews | Threads | Answers | This Thread)

02-05-12

Responses (1-33 of 33)

Click title to read one, or click date to read all below it.

02-05-12 Hi granny, yep, this is another example of poorly executed b ... Sgr

02-06-12 Sgr, as for balanced tube designs, bat and audio research ha ... Spinaker01

02-06-12 Thanks for the responses, but looking for an answer to my qu ... Grannyring

02-06-12 Grannyring, all of the understandings you expressed your op ... Almarg

02-06-12 you can add a ss buffer ... 1 to 1 gain amp ... to 2nd out ... Davehrab

02-06-12 Al, understand all your comments and thanks. very interestin ... Grannyring

02-06-12 This burson buffer may be just the ticket. thanks for the id ... Grannyring

02-06-12 yes, again you are completely correct. the amp would see a ... Almarg

02-06-12 Al, you are the man! thanks so much for your help. Grannyring

02-06-12 Btw, my pre to amp ic is only 3 feet long. yes, i use the lc ... Grannyring

02-07-12 Not sure what kind of sub you have, but with the ones that h ... Nsgarch

02-07-12 hi neil, not sure what you mean by the word "samples&q ... Almarg

02-07-12 No al, that's not the way it works (anymore ;--) yes, in th ... Nsgarch

02-07-12 Hi neil, i recognize and agree with everything in your last ... Almarg

02-07-12 Al, your erudite response notwithstanding, it's unlikely any ... Nsgarch

02-07-12 Thanks nsgarch and almarg for your comments and help. Grannyring

02-07-12 Input impedance is stated to be 20k so the preamp sees 20k t ... Koestner

02-07-12 Koestner, thanks. grannyring, koestner makes a very impor ... Almarg

02-07-12 Al, the builder told me if the plate amp has the negative hi ... Grannyring

02-07-12 Yes, but in addition to connecting the + output of the atlas ... Almarg

02-07-12 Ha, ya a big hum is the last thing i need1 Grannyring

02-07-12: Grannyring
Ok, one last question so I can make my final decision. I am not sure I want to go the high level hook up route as I simply don't know how the plate amps are wired. Can't see anything as all the sub binding posts are hooked together on a circuit board with the traces hidden from view. I would have to take boards off etc and I don't want to do all that. My amp is fully balanced and I fear causing an issue due to the way the sub high level inputs may well be wired -Keiga KG 5150.

Bottom line. Is the line level hook up going to cause an issue in terms of impedance mismatch or not? Al comments as well as Nsgarch suggest I will not have an issue in terms of sound degregation. Here are the facts on my gear.

Preamps output impedance is 5k ohms
Plate amps input impedance is 22k ohms
My stereo Atlas amp has an input impedance of 470k ohms
My sub cable is very, very low capacitance -Al referred to it above and they 10 feet long. I run two subs.
My ic's between the pre and amp are 3 feet long

While the music sounds good I do wonder if I am rolling off in the bass area and possibly compromising the sound of my main speakers. Again, both Al and Nsgarch seem to suggest no issue. But some other comments suggest otherwise? I would buy a Buson buffer to place between my pre and subs if that is deemed as best. I understand that such a buffer would reduce what the subs see as output impedance down to under 600 ohms and perhaps as low as 100 ohms.

I would rather not spend the money if there is nothing here to be concerned with. I set my subs to play 40 hertz and below only. Since I have 2 I set the volume very low - near the minimum really.

What do you expert say.
Grannyring (Reviews | Threads | Answers | This Thread)

02-07-12 I would add to the key facts that you listed for your gear t ... Almarg

02-07-12 That is what i thought and thanks al. Grannyring

02-08-12 If you hook the sub up in parallel to the preamp you will go ... Koestner

02-08-12 Koestner, i'm curious as to what preamp you were using. per ... Almarg

02-08-12 Koestner, i have only seen these placed between the preamp a ... Grannyring

02-08-12 Grannyring, the answers to the four questions in your last p ... Almarg

02-08-12 First off, i must say that al definately knows more about el ... Koestner

02-08-12 Hi koestner, agreed 100%, assuming that only a nominal pream ... Almarg

02-09-12 Thanks al for taking the time to write such an informing res ... Koestner

02-10-12 Hi all, while it is true that many manufacturers including a ... Sgr

02-10-12 Wanted to update folks on my progress. well i have two subs ... Grannyring