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Subsonic filter wish and a solution

I started a thread a while back called anyone wish they had a subsonic filter. Thanks to everyone for their input to that question, btw. I have a very mild case of woofer pumping as it is sometimes called. I can't hear it, as far as I can tell, but it bugs me because, as some of you have commented, it results in the amplifier using energy in it's effort to produce the very low frequency junk signals. I figured out quickly that I could not simply add a high pass section to the actual speaker crossover because of the huge size of the caps and inductors needed to do this. And since I like the match of my phono pre/cartridge/arm, I have been looking at either an internal modification of the phono preamp or a high quality outboard filter. It looks to me that Marchand's XM-46SB is my solution. It can be customized as to frequency rolloff. I ordered one that rolls off at 24dB starting at 18Hz. It does what I want it to do, and no more. I'm hoping that the benefits will outweigh the downside of adding two interconnects and the circuit to my system. My main objective is to solve the problem with little or no affect on the frequencies above the 18Hz, and also to avoid buying a new phono preamp. I'll post again once I get the filter, in case anyone is interested in the results.
240zracer

Showing 3 responses by eldartford

eldartford
4,262 posts
 
The ferrite inductors used in the line level passive crossover will cause more sonic degradation than any interconnect. This is particularly true for the low frequency you are talking about, and the large amount of signal at that frequency. And, how will you hook up the XM-46SB without using interconnects?

Marchand makes good crossovers, reasonably priced. You would be better off with one of their active models. Actually, you would be best served by one of the purpose-designed rumble filters that were suggested in the other thread.

Lots of luck!
eldartford
4,262 posts
 
Marchand active crossovers (all the ones I have used) use no inductors.

Summing to mono at low frequency is perfectly appropriate for stereo speakers. In fact, in producing LPs, it is commonplace to do this. You should not be so upset by the 180 Hz number. The reduction of separation is a gradual thing, not an abrupt change at 180 Hz. At 20 Hz there is no musical signal separation on the LP to be lost. Just rumble, which you want to loose.

But you seem to have your mind made up. As I said, lots of luck.
eldartford
4,262 posts
 
Most of us have power amps that won't be bothered by the need to pump the woofer cones in and out, and we sure won't hear 8 Hz or whatever it is. It's the audible frequencies produced by the woofers when they are pumping that should be of concern. The pumping will mean that the driver is sometimes functioning towards the ends of its excursion where its performance is compromised. For instance, a 200 Hz signal reproduced while the cone is pushed out by 12 mm will sound different from a 200 Hz signal reproduced when the cone is near zero excursion. The change of the 200 Hz signal will vary at 8 Hz (or whatever the pump frequency is). Not good. Also, there is Dopler effect to consider. The 200 Hz tone will increase in frequency as the cone is moving out, and decrease as it pulls in. Also, not good.

Bottom line is get a rumble filter (or stick to CDs).
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