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crazy speaker pulsating with turntable

And you can't tell if the vibration is coming up through the platter & record or up through the tonearm.
 
spark1 said:
Uhhhh, yeah...I understand the notion of subsonic vibration. And I understand the notion of a self-perpetuating feedback loop. The OP made no mention of other vibration sources....audible or not.

I would still like to know if the table is powered on when this happens.

If not, then I agree there is some external source initiating the feedback cycle.

I see that there are smartphone apps for identifying infrasound sources, but I have no idea of their effectiveness.
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So @spark1 you have kind of nailed what I'm still struggling with. First off, to answer you question, yes the TT is powered on.

Here's my confusion. There is no audio playing or overt vibration during the video clip. This is a quiet room. I know that's damn near impossible, but I can say pretty certainly there's nothing I can determine that's causing a vibration. I'm not saying vibrations not a cause when there's music pumping through the speakers; it is. But when it's not outputting audio? ¯\_(ツ)_/¯ It's also never any better or worse, meaning I can reproduce this behavior myriad times over. It doesn't seem to have an intermittent variable that could be starting the vibration (e.g. washing machine, traffic, footsteps etc.)

This leads me to question the cartridge. Is THAT so sensitive or prone to picking up frequencies that simply placing it on a record (which means non-spinning, non audio portion of record and jacking up the volume on the receiver enough to make it feedback?

The only analogy I have that I'm familiar is a microphone and a PA speaker. There can be no audio coming out of the speaker, but aim the microphone directly at the center and it'll start to howl. Can the cartridge do something like this?

Moreover, thank you AK people for all the thoughtful responses! I'm definitely going to look into some isolation pods or a board for the TT, but I'm also really curious what the root cause could be.
 
I still say, a good rumble filter will make it go away. I use one, with a pretty high end table and phono stage, I don't feel it has any negatives to it.
A cart is a pretty sensitive thing, it's designed to pick up very minute signals.
Like your microphone analogy, I was thinking of my guitar on the high gain channel, if the volume knob is turned up, and the guitar in close-ish proximity, it will start to wail on it's own.
 
I suspect, a different cart that has a different compliance could make a difference, I'm no expert though..Rothwell is definitely the expert!
 
rothwellaudio said:
Yes, that's what's happening. A subsonic filter like the one mentioned by vonclod would probably cure it. Some phonostages have subsonic filters built in, some permanently on, some switchable. They used to be quite common on phonostages but seem to be less common now.
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I used to have a pair of KEF transmission line speakers with a Pioneer integrated amp and those B139 woofers would pump in and out on phono, I would engage the 20hz filter on the amp and they would stop.
 
brightpav said:
So @spark1 you have kind of nailed what I'm still struggling with. First off, to answer you question, yes the TT is powered on.

Here's my confusion. There is no audio playing or overt vibration during the video clip. This is a quiet room. I know that's damn near impossible, but I can say pretty certainly there's nothing I can determine that's causing a vibration. I'm not saying vibrations not a cause when there's music pumping through the speakers; it is. But when it's not outputting audio? ¯\_(ツ)_/¯ It's also never any better or worse, meaning I can reproduce this behavior myriad times over. It doesn't seem to have an intermittent variable that could be starting the vibration (e.g. washing machine, traffic, footsteps etc.)

This leads me to question the cartridge. Is THAT so sensitive or prone to picking up frequencies that simply placing it on a record (which means non-spinning, non audio portion of record and jacking up the volume on the receiver enough to make it feedback?

The only analogy I have that I'm familiar is a microphone and a PA speaker. There can be no audio coming out of the speaker, but aim the microphone directly at the center and it'll start to howl. Can the cartridge do something like this?

Moreover, thank you AK people for all the thoughtful responses! I'm definitely going to look into some isolation pods or a board for the TT, but I'm also really curious what the root cause could be.
Click to expand...

Yes. any cart given the right conditions will do it. Some may be more prone than others, or encouraged to by resonances and amplification within the arm/plinth/platter.
 
brightpav said:
The only analogy I have that I'm familiar is a microphone and a PA speaker. There can be no audio coming out of the speaker, but aim the microphone directly at the center and it'll start to howl. Can the cartridge do something like this?
Click to expand...
Yes.
vonclod said:
I still say, a good rumble filter will make it go away. I use one, with a pretty high end table and phono stage, I don't feel it has any negatives to it.
A cart is a pretty sensitive thing, it's designed to pick up very minute signals.
Click to expand...
Exactly.
 
timmy.timmy said:
My lead also indicates some platter (alloy) vibration/resonance transmission to the cartridge. This requires some isolation/dampening under the turntable feet and/or plinth. This turntable effective mass is not the highest I believe (higher = better) and so a "spring" solution is not so good IMHO.

The turntable requires a maximum of inertia for the cartridge to perform as it should. So I'd rather have a heavy and sturdy support even if one uses some sorbothane discs under the turntable's feet to couple and dampen the support and the turntable . Caution with the calculation in calibration there.

And why not dampen the platter from the cartridge pick-up with extra and/or thicker mats ? As for under the speakers, it's true that a little damping is always welcome. Especially if the support is not of the sturdiest kind. Here I have taken some spare dense thick "industrial" carpet I had and cut it to size.
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Not seeing how getting things wet will help the OP lol.

Good advice on the isolation pads, I have several sets, they work great.

51mcC+9uRNL.jpg
vibrapod-vibrapods-4-pieces.jpg

Here's a picture of them under my Kenwood KD500.
20170904_152614.jpg
 
brightpav said:
So @spark1This leads me to question the cartridge. Is THAT so sensitive or prone to picking up frequencies that simply placing it on a record (which means non-spinning, non audio portion of record and jacking up the volume on the receiver enough to make it feedback?
Click to expand...

Simple way of seeing if it's feedback causing the problem (based on over 40 years of engineering experience, I think it is):

1. Get a cushion or pillow, and place it underneath the turntable (use some plastic etc to prevent getting them dirty, if necessary).
2. Turn your receiver on, and place the stylus on the stationary record, as before, then turn up the volume.
3. Problem gone? Feedback was the problem, possibly exacerbated by the resonant frequency of your cartridge and tonearm combination, which seems exceptionally sensitive to the infrasonic (sub-20Hz) output of your vented speakers. Note that vented speakers ( I can see from your video that yours are vented) are more prone to this type of thing, since the woofer cone doesn't have as much rear air pressure to control it as a sealed (acoustic suspension) speaker has, so the problem is now much more prevalent than it was in the 1970's, before Thiele (RIP) and Small made it easy to design vented speakers.

It may be that using a different cartridge will change things, by moving the resonant frequency of the tonearm and cartridge up or down from the frequency it’s now at, where it’s so sensitive and is obviously being excited by something (maybe even the click as the stylus hits the record), but it should be possible to do it much more cheaply with some isolation under the turntable (springs, foam, flexible feet or anything absorbent like that). That will most likely completely eliminate, the problem, or make it much better.

A rumble filter will also remove the infrasonic frequencies (below 20Hz) which are causing the problem, and is another way of going about it, but will cost a bit more, since you’ll need to buy either a phono preamp or amplifier with a rumble filter. Note that while you may not be able to hear the frequencies which are causing the problem, that’s because they are probably mostly infrasonic (below the lowest frequency which humans can hear). Because the arm/cartridge resonant frequency is also infrasonic, that’s exacerbating the problem by increasing the level (perhaps by 10dB, a very typical arm/cartridge resonant peak), as is the RIAA equalization, which is amplifying them further (20dB – see https://en.wikipedia.org/wiki/File:RIAA-EQ-Curve_rec_play.svg). So you’ve got maybe 30dB of extra gain at those frequencies (compared to midrange frequencies, around 1kHz), before even hitting the power amplifier stages of your receiver, which provide more gain.

Note that you can experiment with a very crude rumble filter, by turning the bass control on your HK receiver right down, which will reduce the level by at least 10dB (probably more), or even more if you’ve currently got it set at ‘boost’ (above 12 o’clock), and that should reduce your system's sensitivity to feedback. However, that also affects a lot of audio frequencies, so isn’t a good way of doing it.



.
 
I'm not sure I saw this information but no music playing: does it mean that the stylus runs in a silent groove, or is the arm/cartridge in resting position without any record on?
 
rothwellaudio said:
Yes, like a Thorens suspended sub-chassis. In that type of design the suspension will isolate the platter from both external vibrations and from motor noise. A similar thing can be done to suspend an entire turntable like the one the OP has, but it would only isolate the platter from external vibrations, not motor noise.
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Yes; the suspension will spare the platter from the chassis and plinth external vibration transmission and evidently from the motor. Now add effective mass to the plinth of such a suspended turntable and you will enhance the plinth real/absolute inertia and allow the cartridge to work with better precision. And that I heard (clear, neutral big sound stage home) doing that on my DIYed thick and heavy plinth.

I got a better "focus" and a "cleaner" image. I will add some more effective mass in my plinth since I still have a chunk of marble and enough room to fit it in there the day I'll finish the last lacker layer on the plinth. The "trampoline" trick addresses the "foot fall" issue and is likely a drawback that one can hear during playback since the real/absolute inertia of the turntable must be in constantly challenged...
 
rothwellaudio said:
The issue is subsonic resonance. Any movement in the structure of the building due to traffic outside, or a door slamming, or footsteps in the room, would cause enough subsonic vibration to set the system off. There doesn't need to be any audible sound to cause the problem.
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That would be my assessment as well. Dealt with this a while back, put the turntable on a wall shelf and found that the problem was gone until the climate control system comes on, which employs a large fan (evaporative cooler),that still imparts a very small amount of subsonic vibration. Bottom line, get the subsonic filter and be done with the problem as has been stated several times earlier. Beats me why most phonostages don't have one of these any more. Every one of my vintage receivers has one and they work very well indeed. End of problem. I built the wall shelf because I wanted my TT on one to cure the footfall problem, which it did extremely well. In a month or so when I fire up the A/C again, if it still causes the vibration I'll either try to isolate the fan better or just get one of the KAB filters which has been linked to I believe very early on in this thread. Good luck. I like your Heresy 1's......got a minty set myself a while back and am going to find a worthy recipient as I don't have room for them anywhere!
 
timmy.timmy said:
:trebon:



What material are these 'Vibrapod' made from ? In the seller's advert it says 'vinyl Vibrapods'... Odd as they recommend 5 different model for different weight carriage like for sorbothane material in order to perform as it should...
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They come in various weight support sets, it's not the material it's the construction that's different.
 
Grenadeslio said:
They come in various weight support sets, it's not the material it's the construction that's different.
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OK, but they do come in set of 4 pads and they offer 5 models for different weight support capacities. Are they "soft" like sorbothane or hard like vinyl ?
 
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