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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
dan_ed
2,451 posts
 
Dave, I posted in haste. I didn't mean to imply that your amps were crap. I probably should have said "if one's amps are worth a crap".

Anyway. Yes, I can hear LF signals and that's my point. I don't use subs in my 2 channel system but both speakers I use (Aerial 10t, 16Hz and LaCampanella, 20Hz) are quite capable of getting down low with a great deal of authority. But the kind of LF signals that cause the woofer dance are the result of system problems or warped records.
dopogue
1,773 posts
 
Dan, let me tell you a story. I bought a pair of non-powered Hsu subwoofers a while back and was faced with a choice of crossovers -- their passive one for $50 or an active one that included a subsonic filter, at $349. The Hsu advertising material said that if you played LPs, the active crossover was essential but I figured, what do they know, so I popped for the cheaper one.

Well. I was flat astonished to hear what was down there below 15-18 hz. Not music, God knows, and nothing anyone would want to hear. And only on LPs. Buying the active crossover eliminated the problem and, I swear, really cleaned up the low end response to boot. A friend without subwoofers but with very strong main speakers suffered from woofer-pumping -- with LPs -- and a subsonic filter fixed his problems too. I'm glad you haven't experienced this sort of thing; count your blessings. Dave
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).
240zracer OP
121 posts
 
I swear, you guys, I did not mean to ressurect the same discussion. On the other hand, it is good discussion. I was watching my tonearm track a record last night. Record is tightly clamped down, cartridge is moving side to side and up and down as it tracks. What is really annoying is that I have a new mfsl with the spindle hole slightly off center. It's no wonder crap gets sent down the line. Anyway, I'm pretty new to analog and I'm paying attention. I don't think there is any one set in stone solution and I'm second-guessing my solution. I've had one person, with apparently lots of expertise, tell me to reduce the values of the caps in my tube amp. I'm not doing that but it probably is a legitimate thought and it probably is another solution. I am stepping back and considering everything all over again starting with the tonearm. Thanks for the responses, and Accoustat, for the poke in the ribs. Like I don't know how to spend money....this is the money pit!
acoustat6
357 posts
 
Hi 240Z, Sorry, I know you were not looking for advice in this thread, so perhaps I should have kept my mouth shut. Around here everyone, my self included, wants to spend everyone elses money, its too easy to do.
Bob
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