[undertow]

It was not clear should I post this here or in the lab circle.

In any case its not really a question or issue just curious who has had certain experience with -

Subsonic noise generated by pressings which even can happen during silent passages or more so due to surface noise under 20hz.

Its easy to see subsonic movement in systems with records pumping silent air thru woofers due to surface noise under 20 hz.

I am sure many here have experienced it.

- My weird experience recently was I have a phono stage I have been using for years and with 3 way speakers probably 3 different pairs.

- Never notable subsonic movement.

- No change in turntable or isolation and it is pretty well isolated.

With 2 way speakers using smaller woofers it definitely exhibits pretty noticeable subsonic woofer response... Basically the amp is pumping air into the speakers.

I know what it is why it happens, and how to solve it.

But my question is how would a speaker change exhibit this?

Originally the 3 ways had passive crossovers with cut off on the bottom end at about 250 hz.

The 2 ways have a much higher cut at 1750 hz.

I don't see how this would have anything to do with it, but maybe 2 ways due to crossovers do not absorb this well. I mean all this noise is under 20 hz anyway, neither speaker or crossover would do anything different below 200hz so why it would make a difference is a mystery to me!

Hence the thought experiment here and peoples thoughts on this.
Very weird another one of those audio anomaly you just got to deal with even if explanation is a bit strange and no good technical reason to do it.

- Yes I am adding a subsonic filter to the phono rca outputs to prevent and block "Rumble filter". By the way some records after a couple tracks stop completely letting it thru, but obviously this comes down to the cut on the record being amplified by the cartridge or not.

[BobM]

When this happened to me it was because of a recent cartridge change. The new cartridge wasn't compatible with my arm. The resonant frequency was the culprit and changing the cartridge to one that was compatible solved the issue.

There are several calculators that can help you figure this out plus explanations on why it matters. Here's one.

http://www.mh-audio.nl/Calculators/RF.html

[undertow]

BobM,

Appreciate your insight, yes this is a good angle I forgot about. But I can be pretty sure my cartridge compliance has little to zero to do with it.

As a matter of fact I did play with your calculator and I can do a very high range of tonearm effect mass calculations from 10 grams up to 20 grams and variations in cartridge weight and compliance which I know the accurate measurements anyway and it always falls in the green. I basically have between 7 and 9 hz resonant frequency. Hence really low and should never be an issue.

I know mostly this is from sensitivity of surface noise just causing the huffing and puffing for the most part.

And in the end a subsonic filter is the only guaranteed solution I believe otherwise people can play with tables, arms, cartridges till the cows come home and get little to sub optimal results trying to chase this issue based on compliance or isolation of the equipment.

I think a rumble filter is the cheapest and fastest unfortunately.

[stonedeaf]

Q: by any chance are your smaller two way speakers ported and your 3 ways weren't ported ?
I had a interesting experience yesterday with a new to me piece of equipment - a Parks Audio Puffin phono preamp. Took it over to buddy's house -hooked -hooked it into his system. He has the last generation Linkweitz four way system including  the really interesting subwoofer -arm is a SME III and ADC XLM with OEM stylus. He has previously had issues with subwoofers pumping when playing LP's. The changes we made were : a.) Puffin SPDIF out and 25 hz fourth order Butterworth  low filter engaged (this is the setting that the Puffin ships with-easily changed -but I haven't bothered) -this into a Benchmark DAC-1 and then onto his electronic (analog) four way filter. At simply shattering volume levels (briefly) - there was some woofer wobble -but no voice coils bottoming. Please note _This is not the rumble filter -I haven't tried that yet. 

[undertow]

Yep both speakers ported which is strange ... i am aware bass reflex has this issue more so it was noted when I first saw it I was surprised I never noticed with the 3 way.

It may have been there very rarely because generally didn't pay to much attention but its for sure there with the smaller monitors on stands. It just so happens these 2 ways can dig to about 32hz, the 3 way towers only hit about 37 hz,  but seems that should have nothing to do with it. Again an audio mystery.