Turntable feedback from nearby speaker

I've just gotten finished, (or so I thought) upgrading and servicing all the equipment in my entertainment center. I just replaced my mediocre speakers with a pair of nice 12 inch JBL's that were abandoned in the building we just bought. My turntable is an old Thorens belt drive, supported with a spring arrangement that I thought would absorb any vibration. The turntable is in a cabinet about a foot off the floor and right next to the left channel speaker. If I crank up the volume when listening to a record there is distortion, the severity directly proportional to the increase in volume. At first I wasn't certain about this but you can actually "feel" the vibrations on the turntable base. There are these springs supporting the platter and arm and these springs are "stuffed" with a foam material but this vibration is coming through anyway. I know that one solution is to relocate the speaker however the room is not large enough to do this. I was thinking of putting foam under the speaker which would be easy and perhaps even a soft foam block under the turntable as well but I'm afraid that trying to support and level a turntable supported like this could be a nightmare. Does anyone have any ideas? Thanks, Lenny

 

On Wednesday, December 18, 2013 8:10:39 PM UTC-5, captainvi...@gmail.com wrote:
> I've just gotten finished, (or so I thought) upgrading and servicing all the equipment in my entertainment center. I just replaced my mediocre speakers with a pair of nice 12 inch JBL's that were abandoned in the building we just bought. My turntable is an old Thorens belt drive, supported with a spring arrangement that I thought would absorb any vibration. The turntable is in a cabinet about a foot off the floor and right next to the left channel speaker. If I crank up the volume when listening to a record there is distortion, the severity directly proportional to the increase in volume. At first I wasn't certain about this but you can actually "feel" the vibrations on the turntable base. There are these springs supporting the platter and arm and these springs are "stuffed" with a foam material but this vibration is coming through anyway. I know that one solution is to relocate the speaker however the room is not large enough to do this. I was thinking of putting foam under the speaker which would be easy and perhaps even a soft foam block under the turntable as well but I'm afraid that trying to support and level a turntable supported like this could be a nightmare. Does anyone have any ideas? Thanks, Lenny

I'll try removing the spring foam and see what happens. Thanks, Lenny

 

HEY ! Try reversing the phase of the speakers. I shit you not. that howl is the same as what you would get out of a microphone.

One phase of the speakers (ALL OF THEM) will result in less acoustic feedback than the othsr.

Also, get the thing off the op of it. Thsat cover. It is a reflector and amp;lifier of feedback. (sound)

 

[gregz]

<captainvideo462009@gmail.com> wrote:

I've just gotten finished, (or so I thought) upgrading and servicing all
the equipment in my entertainment center. I just replaced my mediocre
speakers with a pair of nice 12 inch JBL's that were abandoned in the
building we just bought. My turntable is an old Thorens belt drive,
supported with a spring arrangement that I thought would absorb any
vibration. The turntable is in a cabinet about a foot off the floor and
right next to the left channel speaker. If I crank up the volume when
listening to a record there is distortion, the severity directly
proportional to the increase in volume. At first I wasn't certain about
this but you can actually "feel" the vibrations on the turntable base.
There are these springs supporting the platter and arm and these springs
are "stuffed" with a foam material but this vibration is coming through
anyway. I know that one solution is to relocate the speaker however the
room is not large enough to do this. I was thinking of putting foam under
the speaker which would be easy and perhaps even a soft foam block under
the turntable as well but I'm afraid that trying to support and level a
turntable supported like this could be a nightmare. Does anyone have any
ideas? Thanks, Lenny

Is the cabinet vibrating ? Putting the turntable further away ?

Greg

 

[Phil Allison]

<captainvideo462009@gmail.com>

There are these springs supporting the platter and arm and these springs
are "stuffed" with a foam material

** Remove the foam.

> I was thinking of putting foam under the speaker

** Waste of effort.

The low frequency vibrations are transmitted through the air, shaking the
floor, walls and ceiling.

..... Phil

 

[David Platt]

I was thinking of putting foam
under the speaker which would be easy and perhaps even a soft foam block
under the turntable as well but I'm afraid that trying to support and
level a turntable supported like this could be a nightmare. Does anyone
have any ideas? Thanks, Lenny

One approach I've seen used is to add both mass, and decoupling, to
the turntable.

Mass: go buy a sheet of rock. Stone. Cement. Something like that.
If you want to be elegant, go to a stonecutter, pick out a piece of
marble or limestone or granite whose color appeals to you, and have a
slice cut and polished which is just the size of your turntable base.
If you're on a budget and don't care terribly about looks, get thee
hence to a home-improvement/garden store and buy a concrete or brick
"paver" roughly the size of your turntable base (18"x18" is a good
size to look for). All else being equal, thicker is better than
thinner.

Decoupling: go to a bicycle store, and buy a small-diameter heavy-duty
bicycle inner tube. If you bought an 18"x18" paver or marble slab, a
16" inner tube would be a good size to try. You want it to be just a
bit smaller in diameter than the smaller side of the stone slab, so
that the slab will sit on it in a stable position without the tube
"bulging out" in any direction.

Partially inflate the inner tube. Lift your turntable out of position
(unplug first, of course). Put the partially-inflated inner tube in
its place. Put the stone slab on top of the inner tube, and put the
turntable on the stone. If it doesn't sit entirely level, lift the
turntable and slab and try moving an inch or so in each direction to
get it to level out.

If the weight of the slab makes the cabinet collapse and dump your
turntable onto the floor... oops :-( Sorry about that.

This approach will greatly reduce the amount of structure-borne
vibration which gets up to your turntable through the cabinet or
shelf.

It won't do anything much to reduce airborne vibrations (acoustic
pickup). Removing the dust cover entirely when you're playing music
can help to some extent.

A somewhat similar approach involves building a heavy platform for the
turntable to sit on, and suspending it from above using rather long
springs.

In either case, you want the resonant frequency of the mass/spring
system (whether it's a metal spring, or the "air spring" of an inner
tube) to fall below the lowest bass frequency from the speakers. This
creates a "low pass" filter which will tend to attenuate the bass
before it feeds back into the turntable system. It's also good if it
falls below the resonant frequency of the arm/cartridge system, so
that the two resonances don't reinforce one another and cause
excessive stylus "wobble". If you can get it to the point where it
"bounces" 2-3 times per second and no faster, it should help stabilize
the turntable's playback quite a bit.

 

[isw]

In article <527518ff-54ad-43e6-9915-dfcbec6b014b@googlegroups.com>,
captainvideo462009@gmail.com wrote:

I've just gotten finished, (or so I thought) upgrading and servicing all the
equipment in my entertainment center. I just replaced my mediocre speakers
with a pair of nice 12 inch JBL's that were abandoned in the building we just
bought. My turntable is an old Thorens belt drive, supported with a spring
arrangement that I thought would absorb any vibration. The turntable is in a
cabinet about a foot off the floor and right next to the left channel
speaker. If I crank up the volume when listening to a record there is
distortion, the severity directly proportional to the increase in volume. At
first I wasn't certain about this but you can actually "feel" the vibrations
on the turntable base. There are these springs supporting the platter and arm
and these springs are "stuffed" with a foam material but this vibration is
coming through anyway. I know that one solution is to relocate the speaker
however the room is not large enough to do this. I was thinking of putting
foam under the speaker which would be easy and perhaps even a soft foam block
under the turntable as well but I'm afraid that trying to support and level a
turntable supported like this could be a nightmare. Does anyone have any
ideas?

You're probably not going to like this, but the easiest -- and maybe the
best -- solution is to digitize the records and play the resulting
files. No acoustical feedback. No (more) degradation from the stylus
damaging the groove, either.

Years ago,when I still used vinyl records, I became concerned about the
exact same phenomenon, but when it was at a level where it couldn't be
*overtly* heard, but still was causing a modification of the desired
output signal. I figured that it just had to be there and I wanted to
measure it.

I came up with a scheme for placing a second cartridge on the record
that rotated with it, and taking the output of that as the signal to be
measured. Not only would it detect the acoustical feedback from the
speakers, but also the direct vibrations of the active stylus in the
groove, which has to be creating stuff that bounces off the edges of the
disc and back to the stylus as distortion.

Then CDs came along, and I totally lost interest in the whole project.

Isaac

 

[Phil Allison]

<jurb6006@gmail.com>

= Raving Nut Case

> HEY ! Try reversing the phase of the speakers.

** ROTFLOMAO !!!!!!!!!


> I shit you not.

** You shit folk - big time.

that howl is the same as what you would get out of a microphone.

** Not it isn't.

One phase of the speakers (ALL OF THEM) will result in less acoustic
feedback than the othsr.

** Sure - put the stereo pair out of phase.

Brilliant solution.

Wot an IDIOT !!!!



..... Phil

 

>"** Sure - put the stereo pair out of phase. "

That is NOT what I said !

Reverse the phase of ALL the speakers, then they wind in phase with each other but in the oposite phase regarding the phono cartridge.

I've done this a whole bunch of times and sometimes it does have a quite significant effect. The problem is that it's a 50/50 chance that it could get worse. In that case reverse them all back.

Concievably you could accomplish the same thing buy reversing both channels of the cartridge itself, but it is not designed for that. Some of them automatically ground the shell to one of the - terinals. Even if not it still kinda beelongs one way.

Ergo, you reverse the phase of the speakers. All of them. Unnastan now kid ?

 

[William Sommerwerck]

wrote in message news:527518ff-54ad-43e6-9915-dfcbec6b014b@googlegroups.com...

The turntable is in a cabinet about a foot off the floor
and right next to the left channel speaker.

I'm reminded of the old joke where a patient tells his doctor that his arm
hurts when he holds it vertically. "Then don't do that!"

I remember when H H Scott made console phonographs. They went through quite
some trouble preventing feedback when the turntable was in the same cabinet as
the speakers. And I doubt their speakers went as low as the JBLs.

Some of the suggestions are good (such putting a huge chunk o' granite under
the 'table), but you really need to move the turntable away from the
speakers -- and the walls.

 

[jimmy mac]

In article <t02aoa-m01.ln1@coop.radagast.org>,
dplatt@coop.radagast.org (David Platt) wrote:

I was thinking of putting foam
under the speaker which would be easy and perhaps even a soft foam block
under the turntable as well but I'm afraid that trying to support and
level a turntable supported like this could be a nightmare. Does anyone
have any ideas? Thanks, Lenny

One approach I've seen used is to add both mass, and decoupling, to
the turntable.

Mass: go buy a sheet of rock. Stone. Cement. Something like that.
If you want to be elegant, go to a stonecutter, pick out a piece of
marble or limestone or granite whose color appeals to you, and have a
slice cut and polished which is just the size of your turntable base.
If you're on a budget and don't care terribly about looks, get thee
hence to a home-improvement/garden store and buy a concrete or brick
"paver" roughly the size of your turntable base (18"x18" is a good
size to look for). All else being equal, thicker is better than
thinner.

Decoupling: go to a bicycle store, and buy a small-diameter heavy-duty
bicycle inner tube. If you bought an 18"x18" paver or marble slab, a
16" inner tube would be a good size to try. You want it to be just a
bit smaller in diameter than the smaller side of the stone slab, so
that the slab will sit on it in a stable position without the tube
"bulging out" in any direction.

Partially inflate the inner tube. Lift your turntable out of position
(unplug first, of course). Put the partially-inflated inner tube in
its place. Put the stone slab on top of the inner tube, and put the
turntable on the stone. If it doesn't sit entirely level, lift the
turntable and slab and try moving an inch or so in each direction to
get it to level out.

If the weight of the slab makes the cabinet collapse and dump your
turntable onto the floor... oops :-( Sorry about that.

This approach will greatly reduce the amount of structure-borne
vibration which gets up to your turntable through the cabinet or
shelf.

It won't do anything much to reduce airborne vibrations (acoustic
pickup). Removing the dust cover entirely when you're playing music
can help to some extent.

A somewhat similar approach involves building a heavy platform for the
turntable to sit on, and suspending it from above using rather long
springs.

In either case, you want the resonant frequency of the mass/spring
system (whether it's a metal spring, or the "air spring" of an inner
tube) to fall below the lowest bass frequency from the speakers. This
creates a "low pass" filter which will tend to attenuate the bass
before it feeds back into the turntable system. It's also good if it
falls below the resonant frequency of the arm/cartridge system, so
that the two resonances don't reinforce one another and cause
excessive stylus "wobble". If you can get it to the point where it
"bounces" 2-3 times per second and no faster, it should help stabilize
the turntable's playback quite a bit.

Thanks for some good advice!

--
jimmymac

spell usenet backward for email

 

[dave]

On 12/18/2013 06:25 PM, David Platt wrote:

I was thinking of putting foam
under the speaker which would be easy and perhaps even a soft foam block
under the turntable as well but I'm afraid that trying to support and
level a turntable supported like this could be a nightmare. Does anyone
have any ideas? Thanks, Lenny

One approach I've seen used is to add both mass, and decoupling, to
the turntable.

Mass: go buy a sheet of rock. Stone. Cement. Something like that.
If you want to be elegant, go to a stonecutter, pick out a piece of
marble or limestone or granite whose color appeals to you, and have a
slice cut and polished which is just the size of your turntable base.
If you're on a budget and don't care terribly about looks, get thee
hence to a home-improvement/garden store and buy a concrete or brick
"paver" roughly the size of your turntable base (18"x18" is a good
size to look for). All else being equal, thicker is better than
thinner.

Decoupling: go to a bicycle store, and buy a small-diameter heavy-duty
bicycle inner tube. If you bought an 18"x18" paver or marble slab, a
16" inner tube would be a good size to try. You want it to be just a
bit smaller in diameter than the smaller side of the stone slab, so
that the slab will sit on it in a stable position without the tube
"bulging out" in any direction.

Partially inflate the inner tube. Lift your turntable out of position
(unplug first, of course). Put the partially-inflated inner tube in
its place. Put the stone slab on top of the inner tube, and put the
turntable on the stone. If it doesn't sit entirely level, lift the
turntable and slab and try moving an inch or so in each direction to
get it to level out.

If the weight of the slab makes the cabinet collapse and dump your
turntable onto the floor... oops :-( Sorry about that.

This approach will greatly reduce the amount of structure-borne
vibration which gets up to your turntable through the cabinet or
shelf.

It won't do anything much to reduce airborne vibrations (acoustic
pickup). Removing the dust cover entirely when you're playing music
can help to some extent.

A somewhat similar approach involves building a heavy platform for the
turntable to sit on, and suspending it from above using rather long
springs.

In either case, you want the resonant frequency of the mass/spring
system (whether it's a metal spring, or the "air spring" of an inner
tube) to fall below the lowest bass frequency from the speakers. This
creates a "low pass" filter which will tend to attenuate the bass
before it feeds back into the turntable system. It's also good if it
falls below the resonant frequency of the arm/cartridge system, so
that the two resonances don't reinforce one another and cause
excessive stylus "wobble". If you can get it to the point where it
"bounces" 2-3 times per second and no faster, it should help stabilize
the turntable's playback quite a bit.

Why not just fly the speakers?

 

[Gareth Magennis]

wrote in message
news:527518ff-54ad-43e6-9915-dfcbec6b014b@googlegroups.com...

I've just gotten finished, (or so I thought) upgrading and servicing all the
equipment in my entertainment center. I just replaced my mediocre speakers
with a pair of nice 12 inch JBL's that were abandoned in the building we
just bought. My turntable is an old Thorens belt drive, supported with a
spring arrangement that I thought would absorb any vibration. The turntable
is in a cabinet about a foot off the floor and right next to the left
channel speaker. If I crank up the volume when listening to a record there
is distortion, the severity directly proportional to the increase in volume.
At first I wasn't certain about this but you can actually "feel" the
vibrations on the turntable base. There are these springs supporting the
platter and arm and these springs are "stuffed" with a foam material but
this vibration is coming through anyway. I know that one solution is to
relocate the speaker however the room is not large enough to do this. I was
thinking of putting foam under the speaker which would be easy and perhaps
even a soft foam block under the turntable as well but I'm afraid that
trying to support and level a turntable supported like this could be a
nightmare. Does anyone have any ideas? Thanks, Lenny




It's been common practice for decades now in nightclubs, to sit the Technics
1210 turntables on a heavy slab of whatever material is available, to reduce
such feedback from large PA systems in close proximity.

I think Jurb's advice is well worth trying. You might find the turntable
is currently in one of the room's many resonant bass peaks, and reversing
overall phase might put it in a trough.
Or you could move the turntable and speakers as much as is possible to try
and get them out of this peak, perhaps reversing phase as well to see what
works best.

As Jurb implies, it is always possible you are in a trough already, and
anything you try could make things worse, but that would be the absolute
worst case scenario.



Gareth.

 

[Phil Allison]

"dave"

Why not just fly the speakers?

** ROTFL

High time for you to FLY - fuckwit.




..... Phil

 

[Phil Allison]

<jurb6006@gmail.com>

"** Sure - put the stereo pair out of phase. "

That is NOT what I said !

** You should have - cos that at least has a chance of working.

Reverse the phase of ALL the speakers,

** Makes no difference at all.


I've done this a whole bunch of times and sometimes it does have a quite
significant effect.

** Makes no difference at all.

The problem is that it's a 50/50 chance that it could get worse.


** Makes no difference at all.


> Ergo, you reverse the phase of the speakers. All of them.

** Makes no difference at all.

Dickhead.


..... Phil


Unnastan now kid ?

 

>"* Makes no difference at all."

How could you claim to be any kind of engineer and say that ?

OK supposedly smart fuck, design an oscillator with negative feedback instead of postitive and see how far you get.

Anyway, whoever mentioned the turntable havinmg isolation, I had this Dual 1229 for a while that you could pretty much just sit right on top of the speaker. And I did. And my speakers always have bass. If it ain't got bass out the fucking door it goes.

 

[Boris Mohar]

On Thu, 19 Dec 2013 11:12:20 -0700, jimmy mac <usenet@fastmail.fm> wrote:

the turntable's playback quite a bit.

Thanks for some good advice!

For a real torture test play Dark Site of the Moon.

--
Boris

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

 

[Leif Neland]

Efter mange tanker skrev jurb6006@gmail.com:

"* Makes no difference at all."

How could you claim to be any kind of engineer and say that ?

OK supposedly smart fuck, design an oscillator with negative feedback instead
of postitive and see how far you get.

You have to take into account the speed of sound and the distance
between speaker and pickup.

It does not matter if the speaker is in phase or not, it matters what
the phase of the soundwave when it hits the record a little later.

Leif

--
Husk křrelys bagpĺ, hvis din bilfabrikant har taget den idiotiske
beslutning at undlade det.

 

[Michael A. Terrell]

Boris Mohar wrote:

On Thu, 19 Dec 2013 11:12:20 -0700, jimmy mac <usenet@fastmail.fm> wrote:

the turntable's playback quite a bit.

Thanks for some good advice!

For a real torture test play Dark Site of the Moon.

Take plenty of oxygen with you. ;-)


--
Anyone wanting to run for any political office in the US should have to
have a DD214, and a honorable discharge.

 

[Phil Allison]

"Leif Neland"

"* Makes no difference at all."

How could you claim to be any kind of engineer and say that ?
OK supposedly smart fuck, design an oscillator with negative feedback
instead of postitive and see how far you get.
You have to take into account the speed of sound and the distance between
speaker and pickup.

It does not matter if the speaker is in phase or not, it matters what the
phase of the soundwave when it hits the record a little later.

** If low frequency sound waves were vibrating the LP direct - there would
be no fix other than removing the TT from the room. So this is not the usual
case.

Turntable feedback IS a result of the room's *structure* vibrating in
sympathy with standing waves at particular
wavelengths - mainly the floor if the TT is supported by that OR the walls
if a shelf is being used. The frequencies of such standing waves depend on
the room's dimensions and the speed of sound.

Any TT must be isolated from these vibrations and the oldest and by far most
effective way is by use of coil spring.

IME, the ideal set up is 3 conical springs and enough weight above them to
result in vertical oscillation at about 2 Hz. When displaced, the TT system
should move freely and oscillate up and down for a couple of seconds - so
any connecting cables must be looped and able to follow the movement easily.
No damping material should be used.

If done correctly, room surface vibrations no longer affect the TT - even
jumping on the floor - so the chance of actual feedback is eliminated.


.... Phil