Woofer sucking in and out

When i had my old setup, the woofer pumping was mostly due to acoustic feedback via the floor. The speakers shook my suspended wook floor which shook the table and generated very low frequency output at the cartridge. Playing these inaubdilbe low frequencies suckup lots of power from the amps and displace the woofer cones outside of the linear operation zone. Distortion is generated at the amp level and at the speaker level. Bass is indistinct and spatial clues became weird probably from from increased THD + phase distortion. In addition, the wild woofers may generate a reactive load for the amps.

I got a minus K isolation and put this problem to rest.

The contribution from record warp is solved with a record weight along with a ring. However, acousic feedback is the key issue which magnifies warp problems.

Without properly addressing acoustic feedback, the record warp generate low freq signal from the cart - > speakers ->floor -> table -> cart -> speakers -> etc. The dance of the woofers is a result of positive feedback loop.

Subsonic filters will break this loop too. Betw the woofer dancing and phase shift with the filter, I take the filter anyday; but not all filters are the same though.

I got rid of woofer excursion by paying attention to the effective mass of the arm/cartridge system. Once that was set up right, I had the added benefit of flawless tracking, in fact a lot of LPs that I thought had some wear turned out to have none at all.

The KAB unit does NOT effect phase. Period. Call Kevin at KAB he will be happy to verify and explain this, but here's technical info from his site:

"1. When records are made, frequencies below about 150Hz are combined to mono. This is done to avoid large out of phase groove excursions.
2. When the stereo stylus moves vertically, the two signals produced are equal and 180 degrees out of phase. Therefore, below 140Hz, the music is in phase in the lateral stylus motion, and only out of phase noise is found in the vertical stylus motion. The KAB RF-1 takes advantage of this by electronically combining the left and right channels together below 140Hz. In so doing the filter effectively cancels vertically modulated noise. Vertical rumble comes generally from bearing noise of the disc cutting system. But since the music below 140hz is already mono on the disc, the musical information is unaffected. Below 20Hz, all signals are quickly attenuated at 18dB/Octave."

I have many records that cause this phenomenon with my ported Usher X-718s and it is not an isolation problem (record a bit of the LP to CDR with the speakers off, play back the CDR and see if it still does it, if it does it's not an isolation issue), my cart is perfectly matched (resonance of 9hz). The KAB solves it.

Vinyladdict, just for the record (if you will pardon the pun) I have a Westerx LP mastering system, and it does not do any mixing whatsoever of the channels at any frequency, and every attempt is made in the design of the cutter itself to enhance stereo separation- at all frequencies.

Now I can't say how other LP mastering systems work- I only have exposure to my own- but the Westerex 3D cutting system did a lot of the stereo LPs made in the US. So I am regarding this comment

"1. When records are made, frequencies below about 150Hz are combined to mono. This is done to avoid large out of phase groove excursions.

with suspicion.

Of course it doesn't have to be done but very often and more often than not it is. It's a common practice that has been around since the dawn of stereo - do a search for "LP mastering 150hz mono" and you'll have enough to read for quite some time on the matter.