Woofer Pumping Take 2

[davidsss]

Hi

I have had some pumping woofer problems and have looked at isolating my turntable to try and stop this. However, something made me think yesterday, I'll explain. A guy from one of the other forums I am on brought his turntable around so I could help him set it up. Now, while his TT did not sound great (it sounded like the music was being played in a small box and lacked dynamism and clarity (also had tracking problems on one record mine tracked fine) - any suggestions what this might be, I think it might be his cart) but there was one interesting factor. No woofer pumping, even at high volumes where I get plenty.

Now, the turntables are quite different. His is a Yamaha PF800 and is a suspended deck while my Micro Seiki MR611 is not suspended. His deck also weighs more. However, the fact there was no woofer pumping got me thinking.

My problem is that I cannot find out anywhere what the effective mass of my tonearm is. The arm is a Micro Seiki MA101II. There is quite a bit of information on the 'net but no effective mass figures. I have always assumed that it is medium mass. My current cart has a dynamic compliance of 15 and I figured that would be a match. But what if I'm wrong?

Now there is one way to try and work out what the mass of the arm might be. In the manual for the turntable there is mention of the standard cart which comes with the turntable - it is a Micro Seiki VF3200. Now there are a few versions of MS VF3200s but I remember seeing somewhere that my TT was made in 1973, the only VF3200 made before 1973 is the VF3200/E. This cart has a compliance of 30 and weighs 4.5 grams. According to the Cartridge database it is well matched with an arm of an effective mass of 4 to 7 grams. This would seem to indicate that my arm has an effective mass of somewhere between 4 and 7 grams, after all, surely Micro Seiki would make their standard cart a good match with the arm which comes with the TT.

So, my first question is: is this a reasonable supposition?

To the next quandary. My current cart, an Ortofon MC15SuperII, has a dynamic compliance of 15 and weighs 7 grams. It is most suited, according to the cartridge database, to an arm with an effective mass of 6 to 22 grams. This would seem to not be a good match for the arm and may be the cause of the pumping woofers - seem reasonable? Anyway, the chart in the cartridge database indicates that, if the Ortofon was heavier, say about 3 grammes heavier, it would be a better match for a low mass arm. At 10 grammes it would suit an arm of 4 to 19 grammes effective mass.

Which leads to question 2 - if I add weight to the cart, by say (temporarily) blu-tacking a 5cent coin to the headshell, would this be likely to solve the pumping woofers problem? I don't quite understand how this can work given I would also adjust the VTF back to about 1.8 grammes. Maybe I just need an explanation (please avoid maths if possible, if not I'll cope ).

A third question is - is there a way of working out the effective mass of my tonearm without removing the tonearm?

Lastly, an extra question - what could be causing the problems I described above with my friend's turntable? Any ideas.

Thanks
DS

[davidsss]

Thanks for the reply - it makes sense that the mass of the cart adds to the total mass of the arm.

I, too, would be surprised if the arm mass is really as low as would be indicated by the compliance of the original cart, ie: 4 to 7 grammes. This is a 70s Japanese S shaped arm so I really doubt that.

Anyway, I'll try the coin in the morning and see what happens.

DS

[Beltway]

David:
I think you have picked up some incorrect information/assumptions in your search. As you know I was using the identical table/tonearm.
I can tell you that the weight of the tonearm at the headshell with no counterweight, no cartridge and the with headshell attached is 11 grams.
I don't know if that is an accurate measure of "effective mass" but as you suggested it is unlikely to be low mass--maybe on the low side of average mass?
Using the same method the weight of a Mission 774 (which is a low mass arm) is 7 grams.
If others who know more about this can advise I can measure the arms again as I still have them both.

[idiotec]

Sorry, no help, but I am interested since I have had the same problems. I have had woofer pumping with two different tables, one suspended, one not. When they were on a wall shelf, when they were not, etc.

I cannot isolate it other than the fact it has to be sonic feedback. However, in a small room I do not have much in the way of options. I also seem to see plenty of other systems with similar placement.

My current setup is a VPI Scout with DV 10x5. This is supposed to be a very good match, so IDK. Mine is completely dependent on volume level.

Not to hijack, but I thought further information with someone having the same problem could help.

[ben556473]

Do either of you play music with the turntable lids/covers in place?

[idiotec]

Do either of you play music with the turntable lids/covers in place?

I do not.

[bastlnut]

hallo,

David,
it seems that this is a more recent phenomenon for you.
you have been using this cartridge for a while, have you not?
it may simply be that the cartridge suspension is failing.

time for a new cartridge maybe.....?

regards,
bastlnut

[Beltway]

Do either of you play music with the turntable lids/covers in place?

If you mean that question for the MR611 owners there is clearance to close the cover on mine but I generally don't do that.

[ben556473]

I just thought as Idiotec has already tried to address ground born feedback that it might be airborne? Is that a possible cause of woofer pumping? I don't know.

[Beltway]

I see what you are getting at now.

[Paladin]

Knowing audio engineering could be helpful here. We’ll see.

Are you using bass reflex speakers and is the record warped? A subsonic problem would rear its ugly head if we added a compliant cartridge plus a mismatched tonearm into the equation. That sounds like math. Yeah, it is coming but we will start simple and work into geometry.

Time the movement of the woofer with the record to see if they are moving in sync, about one pump per revolution of the record. If it is then you should be very worried and read on. If it isn’t, stop here.

Here comes the math and the scary stuff. The stylus is transferring the mechanical warp into an electrical signal then it does it at 33.3 Hz per minute or 0.55 Hz per second plus the duration of the warp. On 45 RPM records it is 0.75 Hz plus duration. This is virtually pure power being dumped from the amp into the woofers. You can see the result- the woofers bulge and recede so slowly that you can see them move. We all know that DC kills amps and speakers but it truly tests the limits of bass reflex designs.

Before I forget- we live in the 3rd dimension. Another problem could be if the record was running with an off-center hole causing tonearm wobble. And we can also vector the tonearm in the diagonal and is a truly complex problem for the stylus to track. That poor stylus could be literally running in circles on a big circle of vinyl, a dance of death.

The bass reflex port is designed to dampen the woofer resonant frequency but any frequency below resonance easily passes through the open hole, like subsonic sounds. A slight warp makes the woofers wheeze but a big spike- bam, bam, bam! Subsonic distortion pushes the woofers close to the excursion limits and banging sounds are woofers way of alarming you that they are beyond the limits. And the amp doesn’t like pouring out pure DC either. They get too hot, go into distortion, and that is another story.

A heavier arm would exaggerate the problem like a big car bouncing on lightweight shocks.

For a subsonic problem, a less compliant cartridge would be an advantage. It would have less movement and less electrical signal but the danger would still remain. Partially or fully plugging the port should also minimize the problem.

I’ll bet you didn’t know a bad record could ruin an audio system! The simple answer: if the record is warped, toss it! An old and wobbly arm with loose bearings could also be a cause. Of course, this post could be completely off too!

Well, I gave it a shot. Did you survive the math?

[idiotec]

OK, so let me ask a stupid question. And sorry David if I am derailing your thread, but I figure addressing these questions in one thread may help us both.

How is woofer pumping defined? Mine is not a slow in and out (minds out of gutter now!), it is quick pumping that is more of an exaggeration of the bass. They barely move at all while listening to CD's, but they are thumping like crazy if I turn the volume up while listening to vinyl. It IS also completely dependent on volume level.

Also, I have been experimenting with the subsonic filter on my preamp (640P), and it really only reduces it, doesn't eliminate it all together.

I just want to make sure we are talking about the same thing before I confuse things even more.

BTW, this happens on flat LP's...

[davidsss]

Idiotec you are certainly not hijacking as my woofer pumping is very similar to yours. It is different on different records (more or less severe) and there is some woofer pumping on the silent grooves on the test record I just bought, but not as much as some music I have (I usually use The Joshua Tree for testing as it is a quiet record). The pumping does not time with the revolution of the record as I got my daughter to tell me when it pumps while I watched the record. There was no particular spot or spots in the revolution which coincided with the pumping. Basically it is just a greater excursion of the woofers when this happens. They are not reaching the end of their excursion but are pumping harder than I see on CDs. Occasionally they don't pump much at all. It doesn't affect the sound much just makes me worry about the speakers and amp.

Anyway I tried adding weight to the arm by attaching a 5cent piece (2.83g) and a 10cent piece (5.65g). This made no difference so I figure it's not a cart mismatch. In any case I really did doubt that the arm was so light and the Ortofon cart I use has a pretty wide range of arms it can hang off: 6 to 22 grammes was recommended on the Cartridge database. Also the turntable recommends a cart of 4 to 15 grammes.

I'm not sure whether to try more isolation or not. I just put some reinforcement under the floor and this has not helped. The floor is still not greatly stable but under the stereo rack it is much more stable than it was. I'm now thinking of a sandbox under the turntable to see if that works.

Maybe it is the arm.

Also, I should add that I'm not sure if this is a recent phenomenon, I only noticed it after buying new speakers which have a lot better bass than the old ones. They are bass reflex speakers and they do go low.

Would more isolation be reasonable? I suppose it can't hurt.

DS

[idiotec]

I added weight to the tonearm, approximately 2.5g, with no success, same thing.
Let me run through the facts:
Table: VPI Scout
Arm: JMW 9
Cartridge: Dynavector 10X5
Speakers: Paradigm Mini Monitors (ported)

The house has suspended wood floors. I previously did have a wall shelf, and the problem was still there.
The problem is identical with my other table, a Pioneer PL-12D with a Grado Black.
The pioneer is suspended, while the VPI is not.

To further troubleshoot, I wired both decks up with a long cable to another room; the problem was pretty much the same. I guess that kills my theory of acoustical feedback.

On paper, and from others experiences, the JMW 9 and DV10X5 should be a good match, with a resonant frequency around 11-12.

I recently added a CA 640P which has a subsonic filter. This reduces the pumping, but does not completely eliminate it.