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Tuning the resonant freq of cart/arm can damp some vibrations or at least reduce the excitability. It is part of the feedback loop. If the floor vibrates at higher frequency than the reson freq of the cart/arm, it will provide damping. If the floor freq is the same as the arm/cart reson frequency, the effect is amplified. If the floor freq is lower, the carm/cart tuning will not provide adequate damping. See Minus K article on transmissibility of vibration.
Some speakers have output below 20Hz. More so, while the floor will damp a lot of the higher audible frequencies, it may end up moving at a lower frequencies after being excited. Many of us feels the floor vibrates at heavy bass passages but we don't hear the floor playing bass. |
Saw a number of typos in my reply but can't seem to find the edit control. |
Hi Ct0517,
Thank you for your reply.
I did see that but I still feel the arm/cartride relationship needs to be examined again. Moving the TT probably only reduced the problem exhibited by that relationship.
The low freuency pumping of the woofers is probably not sourced from the speakers because it is much lower than their cutoff frequency. If it is sourced from some other source (like a large ac/heating system or a nearby industrial plant or highway) it can be verified by removing the belt from the platter and lowering the needle into the groove of a stationary record. If those are the source the pumping will be evident. The owner can also start the TT motor to see if that is the source coming up through the platter. If none of those are the source it is most likely an arm/cartridge mismatch or misalingnment.
Best,
Barry |
Bright-star-audio
Absolutely the arm/cartridge relationship needs to be correct. But if you read the post from the OP.
"I have moved my TT to another spot at the back with some success. The movement is not as big as before."
With no other changes to cartridge/arm. This indicates an isolation/vibration issue. |
It is probably not a vibration control / isolation issue.
Barry |
Hi Luna,
As Ralph (Atmasphere) said, you should make sure that the arm/cartridge relationship is correct. If there is a mis-match between the resonant frequency of the arm and cartridge it will cause very low frquency problems which will translate into pumping woofers.
If your analog set up is new you may want to contact the dealer that put it together for you for assistance. Brooks Berdan is widely considered to be an analog expert.
Best,
Barry |
Just because you experience this phenomenon doesn't mean there's a problem to address. Period, end of story. |
Vinyladdict, All filters affect phase. Period, end of story. As was said earlier, a filter is a band-aid. The OP needs to find the source of the problem and address it. |
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. |
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. |
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. |
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. |
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. |
Someone might want to ask Luna if his speakers are ported.
Oh, Luna: Are your speakers ported?
If so, do yourself a favour and buy the KAB. Your speakers, your amplifier and your ears will all thank you for it. |
BTW: I think someone mentioned this, but- a record weight(just in the middle), will cause the circumference of some thinner vinyl records to lift off the mat. If there is an acoustic feedback issue, this will exasperate it. The one mentioned by Ct(with the black felt washer under the label), addresses that nicely, as long as it can clamp to your spindle. Mine is tapered, and I have a thicker than stock mat. I can't use a center clamp, as a result. |
They do work, but- the good ones are not cheap, timed cooling and all that: (http://drhifihousecalls.com.au/New%20Equipment/Furutech/Furutech%20Record%20Flattener%20DFV-1/Furutech%20Record%20Flattener.htm) It can also be done, in the oven, between two thick pieces of glass(with extreme care). (http://www.radiodismuke.com/forum/index.php?showtopic=670) Happy experimenting! |
Rodman, Thanks for the info. Very useful! Ah.. Has anyone used those heated device to flatten a wrapped disc? |
Cool responds. I am only using Thorens weight at the middle. Most of my LPs are used so the arm is moving up and down some times! I will have a look at rings and weights than. Thanks. |
Its an isolation problem as other have mentioned - keep experimenting to find the location that causes the least disturbance. Understanding how the sound waves radiate from your speakers based on how you set them up will help alot here. Keep it away from the sound waves as best as possible.
What type of clamp or weight are you using. Before spending big dollars on rings get one of these. Used with the rubber washer under the lp it will flatten the record edge to ensure it touches the platter all around.
http://www.needledoctor.com/JA-Michell-Record-Clamp?sc=2&category=421
If you are using a weight alone in the middle it will make the lp ends go up as well.
A filter is a band-aid as other have mentioned and not a fix.
Good Luck |
Luna- If the degree of woofer movement varies with the record; look at the circumference of the discs, as you play them. If the excursions increase with the warp of the outer edge; you've found your problem. Barring the use of a subsonic filter; a damping ring would be the cure for that particular problem. ie: (http://www.soundfountain.com/amb/ttring.html) (http://www.ttweights.com/480_gram_alloy_outer_ring.html) |
I can not recommend the KAB unit highly enough. I would not have a vinly based system (the only way I really listen to music...) without one. It's sonically transparent and, in fact, will tighten the bass up a good bit since your amp is having to expend energy modulating your woofers like you're seeing. |
Filters are a last resort. All filters will effect the phasing of the signal... Find and fix the real problem. |
KAB sells a subsonic filter that seems to be highly regarded. I agree with Artis4n; that's probably the only way to really solve the problem, if that's what you want to do.
-Bob |
True, the degree varies with different records. As long as it is not causing damage to the speakers, I will be able to live with it! |
This WILL happen depending on the LP's played. A subsonic filter is your only chance of getting rid of this. Personally, it doesnt bother me. |
I have moved my TT to another spot at the back with some success. The movement is not as big as before. I call the manufacture and he said some movement is OK as long as it does not bottom out the woofers. I also find the movement heavier at the outer rim and less when the arm reaches the middle of the LP. Does that means it is related to the arm's set up? |
I can rule out DC leak as there is no problem with CD playing. Thanks. |
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Intermintant DC leaking from power amp could cause woofers to move??? |
There is absolutely nothing wrong with equipment being in between the speakers. 99.9% of systems are setup this way. Of course, ideally, the speakers should be farther out in the room than the rack the equipment is on.
I suspect, as others have said, you have an isolation problem, or a mismatch betweem arm and cart. |
My turntable, a Dual 1219, was into woofer pumping too. Search A-gon's database for that and you may find more discussion. You're far from alone. |
Your idea is good, just happened that it brought about another problem. I've had things like that happen ever since I set up my first system.
If you don't make some mistakes you're not trying :^). |
It made sense as I have only moved the set up to the location next to one speaker on the side wall lately. It was between the speakers before. I thought equipment on the side is better than in the middle. I will try to move them back. I was thinking the tubes has gone bad or something? Thanks for the help and I will get back when I have some progress. |
From your description I'm guessing turntable isolation is the problem.
Is the turntable near the speakers? Is it in a room with a suspended (pier and beam) floor?
Lots of ways to help this situation, the best are all mechanical in that you resolve the problem by removing the interaction. Those options include a wall bracket, isolation stand, isolation feet or maybe even several of these together.
The fast and easy way is a rumble filter but it cuts low bass and puts another layer between the music and your ears. |
You are getting rumble in your turntable setup. It could be an isolation problem or poor setup. It also could be microphonics in the phono stage. Try tube dampers on your phono stage |
