Subwoofer "feedback" from turn table source?

[ericsdeadletteroffice]

Hey guys, some of you may remember me. I just bought the Marantz 6011. I have been running my Pro-Ject Carbon Debut through it's Phono input since I brought it home. At first the level was low compared to the CD player but I learned that I could increase the input of just the particular input so I did that and it's been great. I've only had everything hooked up for maybe 10 days.

Tonight I got home from work and threw on a vinyl and when I put the needle down I got a low rumble that behaves almost like a sort of feedback, but it's just threw the subwoofer. A very low rumble. It's not a trace thing. It's pretty strong. I tried a different vinyl, same thing. I switched over to CD and it's gone and the CD sub performs normal.

Nothing else has changed.

Any ideas what might be going on?

 

[Swerd]

That low rumble you heard is acoustic feedback. Sound waves from the sub woofer, or any woofer, carries through the air and sets up sympathetic vibrations in the furniture and turntable. It was a common problem back in the LP days. CDs eliminated that as well as other problems.

There is no one single way to prevent your turntable from picking up those bass sound waves. Try these various things:

• Acoustic feedback varies in different places throughout the listening room. Try moving the turntable or sub woofer to various different locations until the feedback problem goes away. Keep the turntable as far as possible from the sub woofer.
  
  
• If the turntable is on furniture where the bass speaker is also located, move it to a different location.
  
  
• A sub woofer on the floor can transmit sound waves to the turntable via the floor. If so, shelves mounted to wall studs, but not in contact with the floor, can isolate a turntable from the floor.
  
  
• Put something under the turntable to absorb vibrations. Something cheap and simple, like 2 or 3 magazines can quickly tell you if this works. If so, get something soft but stable, like thick wool felt. I found Soft Touch heavy duty felt pads in a hardware store. They come in a variety of sizes, and are sold under a variety of names such as SoftTouch, SuperSlider, Slipstick, etc. I got ½" × 2+5/8" strips and stuck them under my turntable. There are a variety of expensive 'audiophile' items sold for this purpose, but they don't work any better.

Good luck. Now you are beginning to learn why digital sound sources were so welcomed when they first arrived.

 

[Verdinut]

What is very efficient to prevent a woofer feedback to a turntable is to put the turntable on a wall shelf. That way, no floor vibration will get to the turntable.

 

[lovinthehd]

Older 2ch gear often had a rumble/subsonic filter for use with tt's, doubt your avr has one, though; you could get a separate phono pre-amp with such a feature or apparently even a stand-alone unit. Best you can do otherwise is isolate the tt as mentioned; sorbothane pads might help.

 

[TLS Guy]

As I understand it, you used this turntable without this issue for 10 days. Is that correct? Did you move the turntable at the time this issue started?

If not then you are probably one of many that have Project turntables that quickly develop serious rumble. This is well known, and Project refuse to take responsibility.

There are numerous fixes like this on the Net.

If you don't want to DIY the fix, then send the turntable back and get something else.

Project are now off my recommended list.

I actually think modern turntables are way inferior to good older vintage ones.

If you want good results, then get a good vintage turntable.

 

[ericsdeadletteroffice]

I moved my speakers, but literally like 12 inches outward. At first I didn;t even think that was worth mentioning. If that was enough to cause the problem, that's mental. But I'm going to move them back and see.

 

[lovinthehd]

I moved my speakers, but literally like 12 inches outward. At first I didn;t even think that was worth mentioning. If that was enough to cause the problem, that's mental. But I'm going to move them back and see.

Where is the tt located in relation to the speakers and sub? What furniture is underneath it?

 

[ericsdeadletteroffice]

Where is the tt located in relation to the speakers and sub? What furniture is underneath it?

 

[-Jim-]

In the olden days, I've seen guys hanging their turntables from the ceiling so they could try to minimize Rumble at high volume.

 

[MR.MAGOO]

Glad I found this thread, need to rearrange things!

 

[KEW]

In the olden days, I've seen guys hanging their turntables from the ceiling so they could try to minimize Rumble at high volume.

I was one of them! This was before subwoofers. My open basement below made for a "soft" floor above where my tt was and while I would not hear my footsteps while walking, I would definitely hear them while playing back recordings! I did have a subsonic 16Hz filter on my amp which I kept on, it probably helped, but the noise from the vibrations making it to the platter was well above that.
Generally, I did not hear a difference when I switched on the 16Hz filter, but it was gratifying to see my woofer cones stop jumping around while playing music.

 

[Johnny2Bad]

I moved my speakers, but literally like 12 inches outward. At first I didn;t even think that was worth mentioning. If that was enough to cause the problem, that's mental. But I'm going to move them back and see.

That's enough to change the standing waves in your room, or may have moved the speaker to a less supported /more coupled floor element (between joists or on a joist; each can be a contributor) which in turn can be the source of acoustic feedback.

I too recommend the wall shelf for your turntable; most LF is coupled through the floor rather than the air.

Now you know why people buy double-isolated Technics tables, classic Thorens tables, and Linn Sondeks and their similar examples (eg Systemdek, AR, etc).

Another option would be to create a de-coupling platform to place your turntable on. Basically you make a wooden box a bit bigger than the TT L and W and maybe 4" high, cut a top platform a bit smaller than the inside dimensions of your box, so that it's sides don't touch the inside of the box walls, and between the box and your top platform, buy 3~4 small tire tubes and fill them with the correct air PSI (it will be low) so that they absorb any structure-borne resonance. Tie the valves of the tubes to each other so that the pressure is automatically equal in all of them.

Such a platform has the ability to eliminate any structure-born resonance 100%.

 

[KenM10759]

Funny, but I went through this just yesterday.

I have a ProJect RPM-1 Carbon and recently replaced the US-spec Sumiko Pearl with an Ortofon 2M Red cartridge. I use a ProJect Phonobox MM amp. After a couple months (very intermittent use) I started getting a serious rumble at higher volume. I mean "talking loud", not blasting at "11." This never happened with the Sumiko, and I had a couple of months of no problems with the new cartridge.

Yesterday I got out all the tools and re-checked tracking force, verified the 3-point "legs" of the TT are on their pads, reset anti-skating, cleaned the stylus, everything possible. I was still getting it. I then switched the receiver from "Stereo" to "Analog Bypass" to take the subwoofer out of the picture. Problem gone. I can go as high as I want now, but my speakers aren't giving me what a subwoofer does.

I'm going to try isolator feet on the sub. I cannot move the TT, there's just no place to put it. In fact, the whole reason I have this TT is because the space I have won't fit a proper TT and this one is tiny. We'll see if isolators on the sub do anything, and I'll try a damping method of some sort under the TT too. I just wonder what's going on with this in that I didn't have a problem for a year & a half, until now.