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Speakers close to turntable, woofers go nuts from feedback

ChopperCharles

Standard Member
I have a stereo setup in my bedroom on the dresser. Sony amplifier with a Technics turntable on top, and bookshelf speakers on either side. I don't have room to move the speakers off of the dresser unfortunately.

When I get up to about 1/4 volume, the woofers in the speakers start going nuts. It's slightly better with the lid to the turntable raised. I've installed subsonic filters (20Hz high-pass), and put some cheap rubber feet on the bottom of the speakers, and both of these helped a *little*. But the problem is still there. Of course, CDs and mp3s play fine with no woofer craziness, but the turntable is picking up vibrations from the speakers and is feeding it back into the system.

So, does anyone have a recommendation for an inexpensive way to isolate the turntable and fix the problem? Or am I pretty much SOL?

Charles.
 

Gaspode_TWD

Active Member
As you've identified you need to break the loop. Could the turntable go on a shelf fixed to the wall? If not them minimising the fedback might be helped by putting the turntable on some sort of isolation shelf may help.

The cheap way to do this some time ago was to het a cheap slab of concrete (e.g. slap for a patio) and a bike tyre inner tube. Put the slab on the partially inflated tube (its there to absorb, not to bounce) and the turntable on the slab.

Or put the 'speakers on wall shelves?
 

BlueWizard

Distinguished Member
There are many ways that feedback like this can manifest itself.

It sounds like you are getting low frequency rumble, which is the most common type. But I've also had mechanical resonance occur.

I had two pair of floorstanders, each with twin 8" woofers. I have one pair in the front of the room and the other at the back or the room, and wired them so they were mechanically in-phase. Usually about 2/3rds of the way through an album the tone arm would start jumping around, literally jumping around. I have hit some mechanical resonance of the turntable cabinet and suspension.

You might want to watch your tone arm closely when the 'rumble' is occurring to see if there is any unusual movement.

As you already seem to know, you need some kind of isolation between the speakers and the turntable. I'm suspecting in your case, the problem is the speaker vibrating the stand and the tone arm is picking up that vibration. That is, I think it is mechanical transfer rather than the air in the room vibrating. Especially since the volume seems pretty low.

You can get Deflex polipods pretty cheap, not free but reasonably cheap.

Deflex Polyurethane

The come in small, medium, and large. The Foculpods are the medium size and can handle 5kg each; 4 for £9.95. These would be good for your speakers. The smaller Polipods are 8 for £9.95 and can handle 1.25kg each. These would be good for your turntable. You can also use 5 or 6 of these under your speakers, if they are light enough.

Deflex Polyurethane

Deflex Polyurethane

There are several brands of the 'polypods' on the market, but the Deflex seem popular and they are reasonably cheap.

Alternatives, build a small shelf to lift the turntable up off the amp. If nothing else, this is better cooling for the amp. Then set a foam rubber square, .75" to 1" (available at fabric stores), between the shelf and the turntable, that should help isolate the turntable from mechanical vibration. If you don't like the look of the foam, put a pillow case on it, or wrap it in some cloth.

All the response you are getting, are telling you the same thing. You have to isolate the vibration. You have to stop the speaker from sending vibration down into the equipment stand where it can be picked up by the turntable. You will likely have your best results if you isolate both the speakers and the turntable from each other.

This stops mechanical transfer of vibrations. But there can still be feedback from the vibrations in the air. That, though, usually takes some pretty high volume levels.

Depending on how much your speaker weigh, as I said before, you might be able to use 5 or 6 of the smaller polipod under the speaker. Five of them will hold 13.75 pounds, six will support 16.5 pounds. Two sets of the polipods (16x total) would give you four for the turntable, and leave you 12 for the speakers. Total cost about £20. Otherwise, you need two set of four Foculpods at £10 per set, and the smaller Polipods are available individually at about £1.25 each. For a total of about £25.

No solution is going to be free. So, it is down to how much money you want to dedicate to the solution.

Steve/bluewizard
 

bxd

Active Member
Steve,

Thanks for posting the link to Deflex _ that's much cheaper then buying Foculpods from a Hi-Fi shop.

Brian
 

BlueWizard

Distinguished Member
These 'pods' are sold all over the world, but under different brand names. I'm not sure of brands in the USA, but I know the Needle Doctor has a small selection. You might be able to get local brand names from them.

Isolation Feet

As you can see they carter to high end clients, but the Bright Star and the Vibrapod might do the job, depending on what job you need done.

The Bright Star are the most similar. The Large Bright Star can support 42 pound, and the Small Bright Star can support 30 pounds. Though it is unclear if that spec is per pod or per set.

I think the Vibrapod are more intended for light duty under amps, CD, and turntable. Also, Vibrapod is the trade name for a full range of isolation feet.

However, now that you have a brand name, you can look it up and maybe even find their website.

I have no experience with the products, but I have done business with the Needle Doctor, the ship internationally, and advertise in all the top HiFi and Home Cinema magazines.


As a side note, and just a point of curiosity, take a look at these-

http://www.audioadvisor.com/prodinfo.asp?number=GIMC

People sometimes suggest cutting Squash balls in half and using them under sensitive equipment. This company seems to have take that to heart.

They use bases that have had small circular arcs cut into the to hold the rubber ball in place. Into that they set a somewhat expensive rubber ball -

http://www.audioadvisor.com/prodinfo.asp?number=GISRB

OK, it is only US$7.00, but it is a rubber ball.


Steve/bluewizard
 
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cunny678

Distinguished Member
It may be worth buying a cheap graphic equaliser from the well know auction site. As long as it has some control below say 60 - 80hz you may be alble to reduce the low level imput going into the speakers! As they are bookshelves they probabaly wont be able to go down this low anyway and perhaps you could get rid of the signal up to a level that doesnt effect your listening pleasure but does reduce the unwanted low level signal.

Its only a suggestion and I bet you could pick one up for not much more than £10. But it will need to have controls under the 60- 80hz for it to work! Ideally 40, 60, 80, 100hz etc!!

Putting a GE in the signal path will affect sound quality but I would not have thought this would be an issue in your set up!
 

ChopperCharles

Standard Member
It may be worth buying a cheap graphic equaliser from the well know auction site. As long as it has some control below say 60 - 80hz you may be alble to reduce the low level imput going into the speakers! As they are bookshelves they probabaly wont be able to go down this low anyway and perhaps you could get rid of the signal up to a level that doesnt effect your listening pleasure but does reduce the unwanted low level signal.

Its only a suggestion and I bet you could pick one up for not much more than £10. But it will need to have controls under the 60- 80hz for it to work! Ideally 40, 60, 80, 100hz etc!!

Putting a GE in the signal path will affect sound quality but I would not have thought this would be an issue in your set up!


The receiver has bass controls, and turning down the bass does allow the volume to go up a little higher before the woofers start going crazy, but it sounds like crap with no bass.

Going to try some squash balls first and see if that makes a difference, and then will try and find something that doesn't look retarded.

Charles.
 

cunny678

Distinguished Member
The receiver has bass controls, and turning down the bass does allow the volume to go up a little higher before the woofers start going crazy, but it sounds like crap with no bass.

Going to try some squash balls first and see if that makes a difference, and then will try and find something that doesn't look retarded.

Charles.

I dont think the bass will control at a level below the frequency response of your speaker. The idea of a GE was to filter out those lower frequencies that your speaker cant make good use of, so theoretically it should make more of a difference than your bass control!

As I say just a thought - see how your squashed balls go first:D
 

ChopperCharles

Standard Member
Ok, so for testing purposes, I put a big bath towel under each speaker and cranked the volume. No more woofer issue. So it's definitely vibration through the dresser and not through the air. Now I just have to find something that both works, and doesn't look like a bath towel shoved under a speaker. :)

Also, does it matter that my 20Hz high-pass filters are between the turntable and the phono stage? (Phono stage is inside the amp). Might be able to do away with the filters completely, but if not, should I be using an external phono stage and putting the filters between the phono stage and the amp instead?

Thanks.

Charles.
 

BlueWizard

Distinguished Member
My old amp has a rumble filter on it, though it is simply called a "Low Filter", it cuts the frequency off at 15hz. So, I think your 20hz filter is definitely helping.

After you decide what you are going to do, try it with and without the filter.

If you amp has a internal PHONO equalization stage and you are satisfied with it, the just go with that, it doesn't matter where the filters are in the chain. The only important thing is they are either there or not.

How much do your speaker weigh?

You might be able to get an 8 pack of the light duty Polipods, and put five or six under each speaker, and the remaining four under the turntable. That would fix you up for a mere £10.

But, I think the small Polipods are 1.25kg per pod. So, your speakers would have to be in the range of five or six of these. (5 pods = 6.26kg or 13.8 pounds; 6 pods = 7.5kg or 16.5 pounds)

Sounds like you are on the right track now.

Steve/bluewizard
 

trailer

Well-known Member
If you've got the room why don't you get a wall mounted shelf for the turntable?

Two benefits:

1. You would completely isolate the turntable.
2. By taking it off the amp the amp would run cooler I suspect if it has top vents.
 

BlueWizard

Distinguished Member
If you've got the room why don't you get a wall mounted shelf for the turntable?

Two benefits:

1. You would completely isolate the turntable.
2. By taking it off the amp the amp would run cooler I suspect if it has top vents.

This actually works pretty well, if you can do it. A friend did this in an old farm house we lived in, and it certainly stopped the turntable from shaking as people walked across the floor.

But there was one drawback, when people would slam the front door, it should shake the walls and make the tonearm jump. So, a wall mounted shelf isn't a prefect solution, but it is a good solution - if you can do it.

If you are renting, or have solid walls, mounting a shelf might be difficult. But, it will certainly work.

Steve/bluewizard
 

JamesT888

Novice Member
I was having the same issue with my system when played at higher volumes. The sub and the bass speaker on my KEF 201/2 And JL Audio e-112 would start to oscillate uncontrollably. My bookshelf speaker is directly beside my Thorens TD550 which sits on a wooden side table with the sub directly below. I know that this is far from an ideal setup, but I am restricted in position due to the room configuration.

I set the turntable on a set of hockey pucks as one suggestion from above, but that had no effect. I also had a set of 4 SVS Soundpath Subwoofer Isolation System feet under my JL Audio e-112 sub. I removed these from under the sub and placed them directly under the 3 feet of my turntable. The SVS feet have threaded connection holes in the centre and the turntable feet fit in perfectly.

Once installed under the turntable, the problem was solved. I can play music at any level with no sonic feedback. I was amazed at the drastic improvement.

These feet are carried in Canada as well if you do an Internet search.
 

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