Very low frequency hum when playing records at high volume

[Thunderbox]

I noticed today that if I crank up the volume during playback on my TT I get a very low frequency hum through the speakers, almost inaudible but I can see the woofer moving like crazy. It only happens while the needle is touching the record.

Is it some kind of feedback? Or some other kind of motor hum? There is a slight hum in the system already, I believe from the ground, but this is different as it is only while playing and only at higher volumes (80-90db) If I turn the volume down it goes away. Most noticeable during the gaps in songs or quiet sections.

I do have it pretty close to my left speaker which is why I'm thinking feedback but curious to hear any other opinions.

You are looking at Rumble and hearing feedback. Every table has rumble. Some have more some have less. It would be interesting to know what turntable you are referring to. If you can see the woofers moving it's rumble if you can hear it as a hum it is probably feedback. I think you may have both issues.

 

[welcomdmat]

I have read through most of these comments, but I admit that I read quickly.

Do you have a dust cover on your turntable? Does it make a difference if you take it off?

Turn your volume to zero and place your stylus on an album that is not moving. Slowly increase your volume. There will be a harmonic that feeds back onto itself. How quickly to get that?

Be careful -- I could increase exponentially. Don't walk away from it.

 

[savatage1973]

Come on guys--lets not make it more complicated than it is. You have speakers, a TT and a subwoofer all on the same substrate within feet of one another--duh?

 

[pyoung272]

Agree with savatage. Unless the shelf is made of concrete and weights several hundred pounds, your tt should not be on the same shelf as your speakers and sub. Other suggestions has merits but what savatage is saying is basic setup recommendations when setting up a turntable. As a test to see how much feedback your turntable is receiving with the speakers/sub is on the same shelf/unit as the tt, place a glass of water on the shelf next to the turntable. Crank up the music and I think you will see ripples in the water.

 

[restorer-john]

Yes, that looks just wrong - it takes off a huge amount in the audio band and yet is only taking off 8dB at 10Hz. Subsonic filters need a much steeper slope and they need to come in at a much lower frequency. The others look much better.

Sadly, it's not wrong. (all the little Sansuis (555 etc) look like that) That's part of the 'magic' of the cheap Sansui cap coupled amps- have a look at the 'flat' response (the white trace)- that's why people think they are 'warm sounding'.

With respect to the 'flat' trace, the low filter is 14dB down (remember we are dealing in voltages here) at 50Hz (it's spec was -10db@50Hz @6dB/oct). To be fair, it is designated a 'low' filter, not a infra/sub sonic filter. All the same, it is pretty useless. Note the high and low filter slopes are the same matching slopes (and only 6dB/Oct).

The Marantz (18dB/oct at 15Hz/9KHz) and Yamaha (12dB/oct at 15Hz/10KHz) are much better filters and align closer to their rated specs.

Anyway, it was simply to show that some low filters are excellent, others are complete crap. A good subsonic/infrasonic filter is essential for LP playback, unless you like wasting power and causing all sorts of intermodulation distortions along with excess woofer excursion and low frequency feedback.

 

[birkbott]

Thanks for the replies, all.

I tried putting the stock cartridge back on and still had the issue.

I turned the sub off and still had the issue.

I moved the speakers off of the surface but still had the issue (this maybe helped a small amount but hard to tell).

The vinyl I’m using is all new and clean so it’s not warpage.

I’m thinking it may just be rumble that needs to be filtered out. Will take a look at some of the highpass filters recommended here.

Thanks again for all the thoughtful input.

 

[edwyun]

The static compliance of the M97xE is 25cu and weighs 6.6 grams. Shure, amazingly, frees themselves from the curtsy of measuring dynamic compliance for their carts. Can you believe that??? It's the dynamic compliance that we need, not the static compliance... Dang! There's a loose way to extract the dynamic compliance from the static compliance figure, but it's highly inaccurate. You just multiply by a constant that's anything from 1.5 to 2.0, so let's just assume the dynamic compliance of the M97xE is more than 30cu, which is bordering the rather high range, and makes the M97xE rather 'springy' if you will. I guess the Technics universal tonearm has about the standard 12.5 - 14 grams of effective mass. Either way, 12.5 grams or 14 grams, it's a mismatch. The Shure is just too springy!

Actually, to convert from static compliance to dynamic compliance at the 10Hz standard, you divide by a number (typically at least 2; and my view is that the number has a bit of a correlation to the cart's VTF). Static compliance is greater than dynamic compliance (e.g., AT-OC9ML/II has a static compliance: 35 x 10-6cm/dyne and a dynamic compliance: 9 x 10-6cm/dyne).

 

[edwyun]

Thanks for the replies, all.
I tried putting the stock cartridge back on and still had the issue.
I turned the sub off and still had the issue.
I moved the speakers off of the surface but still had the issue (this maybe helped a small amount but hard to tell).
The vinyl I’m using is all new and clean so it’s not warpage.
I’m thinking it may just be rumble that needs to be filtered out. Will take a look at some of the highpass filters recommended here.
Thanks again for all the thoughtful input.

How is the Technics situated in your system - is it isolated in any way?

 

[tnsilver]

Thanks for that post. You're right. The formulas at the end of this doc supports your post too. Yet, for some reason, it doesn't gel up in the case of the M97xE. According to your comment it should be 12.5cu of dynamic compliance @ 10Hz (which is about like the Denon DL-110 compliance, only it's given @ 100Hz) which sounds, intuitively, too stiff for any Shure stereodynetic series cart. Isn't it? Is it possible Shure is stating their dynamic compliance after all?

 

[edwyun]

Thanks for that post. You're right. The formulas at the end of this doc supports your post too. Yet, for some reason, it doesn't gel up in the case of the M97xE. According to your comment it should be 12.5cu of dynamic compliance @ 10Hz (which is about like the Denon DL-110 compliance, only it's given @ 100Hz) which sounds, intuitively, too stiff for any Shure stereodynetic series cart. Isn't it? Is it possible Shure is stating their dynamic compliance after all?

The typical number used to divide is 2. But IMHO, it depends on a VTF of the cart. And then there are outliers out there.

Also, there is this (dunno how they arrived at it)...
https://www.musonic.co.uk/m97xe-cartridge-p-17620.html

 

[birkbott]

How is the Technics situated in your system - is it isolated in any way?

It’s on a DIY platform made with MDF and rubber feet. I also put furniture pads on the TT feet. It is close to the left speaker which is also on a similar platform + 3 mousepads. The right speaker is on an identical piece of furniture (they are both IKEA) pushed against the one that the TT and left spesker are on, also on its own platform + mousepads. The sub is sitting directly below the right speaker inside the cabinet, on the isolating rubber feet that I bought with it. The TV straddles both cabinets.

I’m sure more isolation would be good, however, moving the speakers and turning off the sub didn’t solve the issue.

 

[edwyun]

It could be a combination of issues:

@ isolation -
More or sometimes even different isolation can help with reducing large woofer excursions while playing an LP (especially feedback of the LF soundwaves from the SW affecting the cart).

@ cart resonance -
Manual indicates the SL-D202 tonearm has an effective mass of 11g.
M97xe has a mass of 6.6g
Mass of mounting screws/washers can be estimated at 1g
From my above link, M97xe appears to have a dynamic compliance of 20 (but unclear how they arrived at it)

So if you use total mass = 11+ 6.6 + 1 = 18.6g and assume dynamic compliance of 20, you get 8.252Hz as the resonance frequency
http://www.resfreq.com/resonancecalculator.html

It's borderline low (would want it between 9-11Hz optimally).

 

[birkbott]

It could be a combination of issues:

@ isolation -
More or sometimes even different isolation can help with reducing large woofer excursions while playing an LP (especially feedback of the LF soundwaves from the SW affecting the cart).

@ cart resonance -
Manual indicates the SL-D202 tonearm has an effective mass of 11g.
M97xe has a mass of 6.6g
Mass of mounting screws/washers can be estimated at 1g
From my above link, M97xe appears to have a dynamic compliance of 20 (but unclear how they arrived at it)

So if you use total mass = 11+ 6.6 + 1 = 18.6g and assume dynamic compliance of 20, you get 8.252Hz as the resonance frequency
http://www.resfreq.com/resonancecalculator.html

It's borderline low (would want it between 9-11Hz optimally).

What about the Grado Black?

Or do you know of any carts that work well with my tonearm weight?

 

[birkbott]

I've been down the rabbit hole on cartridge/tonearm matching for the past few days and I feel like I'm going in circles. First off it's very difficult to get good dynamic compliance ratings on most carts. Some give you the # but have it at 100hz instead of 10hz and I don't know if this makes a difference.

I am also unsure about whether or not my tonearm spec includes the headshell or not. It says the tonearm weight is 11g and the headshell is 7.5 but it doesn't say if the 7.5 is included in the tonearm spec or not.

As I said I tried turning the sub off and moving the speakers off the shelf and still had the issue, which leads me to believe that it's a cart/tonearm mismatch as discussed above. It's pretty clear even based on rough #s that my current Shure is not a good match.

I've been looking at the following:
Grado Black or Blue
Nagaoka MP-110
AT cartridges like the 110E or 120Eb but the reviews I've seen have said they are a bit treble-heavy so I'm not that excited about those.

I ALSO read that simply using the stabilizer brush on my current Shure cart will solve any resonance issues but I have no idea if that is correct or not.

Any help on suggested cartridges or any other clarification on matching would be very welcome at this point. Turns out my stock cartridge is a AT5000 which I can't even find specs on anywhere so I'm not interested in going back to that one.

 

[Curtwheeler]

I had the same problem with my Realistic Lab 440. I did not want to, or could not move my turntable or speakers.
What worked for me was putting a small 12" bicycle inner tube under the plinth and inflated it just enough to float the turntable. It was hardly visible after it was installed and eliminated my feedback problem.
It's something to try and is inexpensive.

 

[SaSi]

Have you tried to put the stylus in the groove while the TT is powered off? Do you get feedback then? If not, then try to rotate the platter as constant as you can at around 33rpm and check if there is feedback on a silent groove (e.g. the run-out groove). In some cases the rumble comes from the TT itself. It's best to listen through headphones if the loudspeakers are on the same self or fire towards the TT.

It's hard to eliminate feedback but doable. Gets pretty impossible when the source is inside the TT. It could be a worn out bearing, one in need of a couple of drops of oil or even a buzzing transformer. It's best to try and eliminate these first. Having done that, in my experience, you can safely place the TT even on top of a loudspeaker provided you place a small piece of carpet between them.

With a high compliance cart however and a heavy mass tonearm, things get harder than necessary. I had similar issues with a Shure M95 mounted on a Dual 1009. Since it was "springed" on the plinth, the stylus almost didn't want to stay in the groove. Ended up removing the springs to make the whole thing solid and mounted it on a thick slab of marble which was mounted on the brick wall using three long self brackets. For that TT, the original M44-MG was a much better match compared to the M95 and the Stanton 681 I later tried.

 

[sqlsavior]

I think you have a combination of problems. Two very simple tests:

1. Move the speakers and sub out of the cabinet entirely. Fold up some towels and set them on the floor. Not as a final position, but as a test.
2. Put the brush on the Shure (if you have it).

I like the inner-tube suggestion. Some folks have to go to great lengths to solve these (plus footfall) problems. A wall-mount shelf for the turntable should help. I've had success with Sorbothane hemispheres for isolation. Not all rubber products work effectively.

 

[edwyun]

What about the Grado Black?

Not sure about the specs on the Grado Black, but IME (and others' experience), Grado's often have hum problems.

 

[Gibsonian]

Have had Grado Red, Gold, Platinum and Sonata carts, no hum ever. This covers 4 different TT's and 4 TT manufacturer's.

 

[birkbott]

Thanks for the replies, all.

I ordered a Sumiko Pearl to see what difference it makes. Even if it’s not the root cause of this issue it’s a much better matched cartridge for the tonearm so I’m going to give it a shot.

I have not tried putting the needle on the record with it powered off. Will it feedback if there is no power to it? I’ll try it.

Regarding isolation I have tried already moving the speakers off and still had the issue but I think I may try bricks? Like a big paver stone under the turntable and some smaller ones for the speakers. I like that inner tube idea but that seems like it would be bouncy.