rumble issues - see old thread update

diagnosis round II

Richard came over with his 'higher tech' scope

we found a little isolation issue caused by the light hollower SRA platform under the turntable - we replaced that with a 3 cm granite slab which isolated the table much more efficiently

the scope showed resonance problems in both channels around the 4-7 htz range - which Richard said were caused by a low mass arm being mated with an overly compliant cartridge. I told him that the ZYX and Triplaner often matched with great results - as many of you can attest to

we tried additional shims, counterweight options and also more and less weight to no avail
I typically run 1.75 g

he felt the high compliance of the cartridge and tonearm
combined with the highly resolving low end of the Dodd pre and Moscode amp were allowing the tonearm/cartridge resonance issues to be reproduced by the speakers

we checked the speaker baffle output and it wasn't sufficient to cause an issue

next step - Richard will bring a lower compliance cartridge to test out and see how it mates with the arm resonance wise

I'll call the various manufactures to get their input

any suggestions from others here on the arm / cartridge synergy would be very helpful

thanks

Tom

hit up an excellent website calculating resonance

http://www.gcaudio.com/resources/howtos/tonearmcartridge.html

I did a little research and calculations using the formula stated


check out the ZYX Universe site


http://www.sorasound.com/products/zyx/zyx-universe/

that's a pic with a triplaner from their beloved US dealer Mehran

ZYX universe specs

http://www.hifi.com.sg/products/cartridge/zyx/universe.htm

Universe specs

compliance
horizontal 15 x 10 -6 cm/dyne
vertical 12 x 10 -6 cm/dyne

I have the SB (0.24mv) version


Triplaner specs

http://www.triplanar.com/tonearm.html

11 grams

resonance freq = 1000/6.28 *suare root (M*C))

for vertical 12 compliance = 13.86 hz

for horizontal 15 compliance = 12.40 hz

these are both in the ideal range stated in the gc audio article

high enough to be out of the record warp subsonic stage but low enough to be out of the musical relm (well, most music these days)

so what gives?

perhaps dampening trough needed?

Hi Tom,

I spend Sunday at Doug's and we were thinking about your issue. There were a couple of noticeable woofer excursions but I believe each could be attributed to vinyl anomalies. I think from your description your woofer pumping is much more frequent.

There are obvious differences between speakers. Driver suspension, crossovers, internal box pressures, etc. The Salks may simply be use drivers with different mechanical properties and parameters. The fact that your friend also has Salk's and they pump as well is telling us something. I do remember my 10t being susceptible to woofer pumping with vinyl. A local brick and mortar guy once told me "Perhaps it is time to put the covers back on and quit watching them." This was after he was satisfied no damage was being done. He's an experienced Linn-ey. Don't rule this out as possibly the final solution. If you don't hear problems, don't go looking for them. :-)

If this is increasing with volume, Doug could be on to right track. It should be easy to get an idea if this is the problem. If you haven't already tried this, here is an experiment that may help show you something. Try moving your speakers farther into the room at least 4-5' from any wall, back and sides, and see if the pumping decreases.

BTW, what are the room dimensions? Sorry if you previously posted that information. It is possible to calculate room nodes and your speakers may indeed be close to one.

What is the weight of your Universe? I'm assuming you have the extra weight from the little plate.

I seriously doubt that anything you do to the tonearm will fix this without choking off the music.

I agree that the first thing you should try to ascertain is the pumping caused by airborne or mechanical anomalies. So ...

- move the speakers
- put up some kind of baffle between the TT and the speakers
- move the TT off the rack onto the floor or in another room
- check and double check your cartridge alignment
- try a different counterweight and play with location (heavier weight closer to the pivot point, or lighter counterweight placed farther from the pivot point)
- try a record clamp or periphery ring (if you can) to see if you can get a better interface between the vinyl and your platter surface

If that doesn't work then check your cartridge compliance and theoretical resonant frequency. Add something to the headshell to increase the mass of your tonearm (rebalance and reset it all, of course) and see if that alleviates anything.

In my case it was definitely caused by the arm-cartridge compliance. Switching cartridges removed the problem entirely.

Good luck,
Bob

I usually run the ZYX a little more than 1.75 grams FWIW, more like 1.85-2.0.