Turntable Isolation - A Different Approach to a Sandbox

AvFan

Super Member
I have been concerned that after nearly 40 years the Technics SH-15B3 base and its feet are not isolating my SP-25/Jelco tonearm from external vibrations as well as it did when new. @marcmorin and I were discussing TT isolation and he reminded me that sandbags are the best way of minimizing recoil at the rifle range and they should be very effective at isolating turntables. He also noted that each sandbag could dissipate vibration independently of the sand in the other bags. So I set out to build a sandbox using sandbags versus filling the entire box with sand.

I carefully measured my TT base and its feet to determine the inside dimensions of the sandbox and laid it out on my kitchen counter. Mrs. AvFan pitched in and made four sandbags that use closures from hospital ice bags (Amazon). These closures are important to keep the sandbags relatively flat. I added 3 pounds of dry play sand to each bag.

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Next to build the box itself. The bottom and floating plate the TT sits on are made from 3/4" birch plywood. The sides are 1/2" alder dadoed and rabbeted around the bottom plate. I primed and painted the box

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The bottom has short feet with thin felt on them to protect the surface it sits on. I added a center foot to minimize any deflection of the bottom panel.

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Added the four sandbags and the top plate.

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The top plate has about 1/8" clearance around the inside edge. And here are some photos of the installed sandbox.

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The TT feet have about 1/16" of clearance from the sides and I can reach in and turn each foot to fine level the TT. Total weight is about 17 or 18 pounds, 12 of which is the sand. The box is 3 3/4" tall and the same width and depth as the Technics base. I need to evaluate the sandbox's performance over time but I hope it will isolate my TT from vibrations induced in the cabinet it sets on plus any vibration that could be coming up through my concrete floor (e.g. spiked speakers).
 
Doesn't the top plate need to rest on the sand bags, not the lower portion of the box? Seems to me that that isn't going to do much. A sand box isolated the top from the bottom. In other words. the top plate rests on the sand, not the wood of the box bottom.
 
Doesn't the top plate need to rest on the sand bags, not the lower portion of the box? Seems to me that that isn't going to do much. A sand box isolated the top from the bottom. In other words. the top plate rests on the sand, not the wood of the box bottom.
From what i see it does. There is an 1/8" gap around all edges of the top plate. The sand bags sit inside the frame and the top plate rides on them.

Cheers
Mister Pig
 
From what i see it does. There is an 1/8" gap around all edges of the top plate. The sand bags sit inside the frame and the top plate rides on them.

Cheers
Mister Pig

That is correct. The top plate rests on the sandbags and there is no contact between the TT and the lower portion of the box except via the top plate and then the sandbags. Sorry if my explanation and photos weren't clear enough. The third photo is just the underside of the box showing the feet.
 
I have been concerned that after nearly 40 years the Technics SH-15B3 base and its feet are not isolating my SP-25/Jelco tonearm from external vibrations as well as it did when new.

I need to evaluate the sandbox's performance over time but I hope it will isolate my TT from vibrations induced in the cabinet it sets on plus any vibration that could be coming up through my concrete floor (e.g. spiked speakers).

Why the concerns?
What's it doing?
What external vibrations?, as I read on you have slab concrete floors
You have had the Jelco on this table 40 years?

I'm having a hard time thinking of any vibration from speakers to the table on concrete floors. Walking, dancing, jumping around should not effect anything with the table unless you bump the cabinet.
 
Why the concerns?
What's it doing?
What external vibrations?, as I read on you have slab concrete floors
You have had the Jelco on this table 40 years?

I'm having a hard time thinking of any vibration from speakers to the table on concrete floors. Walking, dancing, jumping around should not effect anything with the table unless you bump the cabinet.


although the concrete floor won't heave like wooden floors, concrete certainly will pass energy from one source to another.
 
although the concrete floor won't heave like wooden floors, concrete certainly will pass energy from one source to another.

Nice work but the question still remains the same. Will you really get better sound quality with it or not? In my world you might, but I probably wouldn't notice.

If I thought it would i'd be firing up my table saw tomorrow.
 
Nice work AvFan. Seems like the trick is to make the sandbags as uniform as possible so when the top plate is added it sets level (or very, very close). Also maintaining the gap separating the top plate from the sides is a must, and your TT would need adjustable feet or shims to get it exactly level.

Do you hear any improvement?
 
Why the concerns?
What's it doing?
What external vibrations?, as I read on you have slab concrete floors
You have had the Jelco on this table 40 years?

I'm having a hard time thinking of any vibration from speakers to the table on concrete floors. Walking, dancing, jumping around should not effect anything with the table unless you bump the cabinet.

Good questions! I can feel my cheap IKEA cabinet vibrating from my speakers (the right speaker is 2 feet away from the turntable) and I want to make sure those vibrations aren't negatively impacting the sound from the turntable. No, I've not had this turntable or the Jelco tonearm for 40 years but this model was introduced in 1979 and I have no idea whether the composite material in the base or any portion of the feet have degraded and letting vibrations through. As I said, I need to evaluate whether this isolation results in anything positive so what I intend to do is listen to my system for a while with it in place and then remove it. Will I hear anything different? I'll find out.

I have no idea whether I'm getting vibrations through my concrete floor from my spiked speakers or any other vibration sources in my house. But vibrations move through concrete at about the same speed as brass or copper, 3000m/s. Maybe some of that IKEA cabinet vibration is via the floor? Or maybe I need to make some sandbag speaker stands?

I'm sure some folks will advise that I just move the turntable away from the speaker. I'd really like to do that but my system is in my living room and compromises are a fact. The sandbag sandbox is an attempt to deal with what might be a problem.

Nice work AvFan. Seems like the trick is to make the sandbags as uniform as possible so when the top plate is added it sets level (or very, very close). Also maintaining the gap separating the top plate from the sides is a must, and your TT would need adjustable feet or shims to get it exactly level.

Do you hear any improvement?

Hats off to Mrs. AvFan for her excellent sewing skills and willingness to indulge my audio lunacy. The bags are very uniform and the ice bag closures worked very well. It was very easy to level the TT and I intend to check it in a couple of days. Funny, Mrs. AvFan cringed when I brought in 12 pounds of sand and put them in her jelly roll pans to dry in the oven! I did get the look that means "You make the mess, you clean up the mess" but we are all good.

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It is very early, but the first album, Eagles ST, seemed to have cleaner bass. However, it is too soon to say for certain. It could have been my mind just hoping.
 
Nice work but the question still remains the same. Will you really get better sound quality with it or not? In my world you might, but I probably wouldn't notice.

If I thought it would i'd be firing up my table saw tomorrow.


My sandbox is not nearly as elegant - I did not use separate bags, nor does it have adjustable feet. But after several other approaches for dealing with a vibrating stereo cabinet in our great room (beautiful piece of furniture, but not built for the purpose), I found that the sandbox made a very significant difference.

Now in my case, I was actually getting audible feedback thru the cabinet, into the TT and then from its stylus back into the amp. At higher volumes, the feedback loop could actually bounce the tonearm!! For all I know, there was still some feedback with the sandbox, but it was no longer distinctly audible, even at higher volumes.

Most folks don't have that serious of a problem, but I believe that if you can feel any vibration in the shelf upon which the TT sits, sound quality will be improved by isolating the turntable from it. Interestingly, before I started using the sandbox (with a Rega Planar 3 at the time), I tried a Technics 1301 suspended table in the same spot, and found that it did indeed reduce - but not eliminate - the problem.
 
It is easier for sound waves to go through solids than through liquids because the molecules are closer together and more tightly bonded in solids. Similarly, it is harder for sound to pass through gases than through liquids, because gaseous molecules are farther apart. The speed of sound is faster in solid materials and slower in liquids or gases. The velocity of a sound wave is affected by two properties of matter: the elastic properties and density. The relationship is described by the following equation.

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Where: Cij is the elastic properties and p is the density.

https://www.nde-ed.org/EducationResources/HighSchool/Sound/speedinmaterials.htm
 
Good questions! I can feel my cheap IKEA cabinet vibrating from my speakers (the right speaker is 2 feet away from the turntable) and I want to make sure those vibrations aren't negatively impacting the sound from the turntable.
So you fix a problem that you could not detect or observer even happening or having in the fist place. Now your going to listen to see if all your hard work improved the performance and SQ.

Don't get me wrong as some people need better or more isolation with their setups and space. I just wasn't seeing where you do, and as stated you had no actual issues. As far as the speaker being close to the table, I'd worry about feedback into the cartridge from sound waves far more.

Looking at this photo

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You can break up sound wave from getting to your cartridge by putting things around your table. A plant on the floor in that space between the speaker and table, a small potted one on the cabinet left of the table, can be fake. I'm sure the blinds help the back wall bounce of waves.

I first started using dry plant decor behind the speakers to break up waves behind the system.

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As my system got bigger and having a lot more cables you could see against the white walls. I decided to start disguising them with black dry twigs in vases behind the electronics. While not ideally the best design look I got three things out of this. The twigs help routing turntable wires and kept them from crossing and eliminating hums. They break up sound waves from hitting the cartridge and giving feed back, and disguising all the cabling.

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I did a major system clean up and reinstall and pulled out the dry twigs behind the tables. I started to noticed feedback at times so the twigs went back in behind everything.

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As far as isolation I have SOTA tables and it's top notch, I actually need them as my floors are supper bouncy, tall racks and a literally a ton of equipment, surprised it hasn't fallen through the floor. But listen and watch these vids, This is 2000 watts driving the two pairs of JBLs. You can see the twigs, pictures on the walls, chrome parts all vibrating from the extreme SPLs I was pushing in the room that day. You will also hear no feedback in the system even though I'm playing a record. I stopped the first vid because stuff was falling off the counter tops across the room that you will see in vid two. The point is that's vibration but yet the tables can handle it as well as breaking up the sound waves around the tables.


 
Thanks for the input and I responded within your post to various points.

So you fix a problem that you could not detect or observer even happening or having in the fist place. Now your going to listen to see if all your hard work improved the performance and SQ.

Don't get me wrong as some people need better or more isolation with their setups and space. I just wasn't seeing where you do, and as stated you had no actual issues. As far as the speaker being close to the table, I'd worry about feedback into the cartridge from sound waves far more.

I don't want to get you wrong but please don't give the impression that I might automatically find an improvement in the sound of my vinyl playback since I built a different kind of sandbox. I've clearly said how I was going to test whether the sandbox helps or not and I'm happy to hear any suggestions you may have on how to make that process as objective as possible. Constant improvement is part of this hobby and when I felt vibrations in the cabinet my TT sat on it was obvious to be curious whether those vibrations were negatively impacting my vinyl playback. The sandbox with sandbags is my experiment to find out.

One thing I have not mentioned is that about a year ago I did a quick test by putting my TT on a piece of plywood resting on some air filled packing pillows. The results were not overwhelming but I did think there was an improvement in the clarity of bass. That was on a different piece of furniture and I didn't pursue the sandbox because the changes weren't huge. When I felt the vibrations on the IKEA cabinet I decided to give the sandbags a try to see if they'd make a difference. Knowing that is a way off.


Looking at this photo

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You can break up sound wave from getting to your cartridge by putting things around your table. A plant on the floor in that space between the speaker and table, a small potted one on the cabinet left of the table, can be fake. I'm sure the blinds help the back wall bounce of waves.

I first started using dry plant decor behind the speakers to break up waves behind the system.

Thanks for the suggestions. It is a little bare next to my gear and a plant or might look good and minimize any impact of the adjacent speaker. I will look into it.

View attachment 1394303

As my system got bigger and having a lot more cables you could see against the white walls. I decided to start disguising them with black dry twigs in vases behind the electronics. While not ideally the best design look I got three things out of this. The twigs help routing turntable wires and kept them from crossing and eliminating hums. They break up sound waves from hitting the cartridge and giving feed back, and disguising all the cabling.

View attachment 1394305

I did a major system clean up and reinstall and pulled out the dry twigs behind the tables. I started to noticed feedback at times so the twigs went back in behind everything.

I wonder how the twigs with such a small surface area alter the sound to eliminate feedback. Do they act as a diffuser?

View attachment 1394308

View attachment 1394310

As far as isolation I have SOTA tables and it's top notch, I actually need them as my floors are supper bouncy, tall racks and a literally a ton of equipment, surprised it hasn't fallen through the floor. But listen and watch these vids, This is 2000 watts driving the two pairs of JBLs. You can see the twigs, pictures on the walls, chrome parts all vibrating from the extreme SPLs I was pushing in the room that day. You will also hear no feedback in the system even though I'm playing a record. I stopped the first vid because stuff was falling off the counter tops across the room that you will see in vid two. The point is that's vibration but yet the tables can handle it as well as breaking up the sound waves around the tables.

I've seen the videos before and I have a suspended TT, a Marc Morin modified AR XB, that I have no doubt deals with any vibration in the IKEA cabinet. But I like my DD Technics SP-25 and I want to get the most out of it.


 
Nice work but the question still remains the same. Will you really get better sound quality with it or not? In my world you might, but I probably wouldn't notice.

If I thought it would i'd be firing up my table saw tomorrow.

you can try the experiment of just setting the stylus down on an un spinning piece of vinyl, carefully start turning the volume up and listen for outside energy entering into the vinyl. Or, putting a scope on the outputs to check for energy below the frequency your system can produce acoustically.
 
Doesn't the single top plate defeat the purpose of using separate bags? Since the sand is already nicely contained, I'd try resting the plinth either directly on the sand or on small pucks to take maximum advantage of the isolated bags.
 
you can try the experiment of just setting the stylus down on an un spinning piece of vinyl, carefully start turning the volume up and listen for outside energy entering into the vinyl. Or, putting a scope on the outputs to check for energy below the frequency your system can produce acoustically.
A somewhat collorary approach if you have digital recording capability is to do as Marc suggests and see if can turn the volume up to your max (normal) listening level (non spinning record) without obvious detrimental effects. Record the phono stage output during the volume adjustment and take a look at in Audacity or similar program and see if anything shows up even if it isn’t blatantly audible.

Leave the recording setup on the phonostage and pop in a cd or stream a heavy bass, loud dynamic track and see if anything shows up in analyzing the track recorded. You can start with the volume at minimum and ramp it up to your max during this test. No worries of a runaway feedback loop destroying your speakers since the output is going to the digital recorder and not through your system. It will reveal if any sensitivity to feedback is a concern and/or at what point it does impact your table/rack setup and allow testing any varied approaches to isolation or table location.

Should remove any guessing and listening bias.
 
AvFan nice sandbox build, the Technics SH15B3 plinth should be by itself pretty decent but as you say the Ikea cabinet isn't the stoutest. In days gone by radio stations filled their TT consoles with a 200-300 pounds of sandbags to tame any vibrations, you are doing the same thing but on a smaller scale. I have a sandbox not in use since both active tables are mounted on wall shelves with no noticeable vibration reaching them but I might give it a try someday using the sandbags as you did to see if I can hear a difference. The two tables are in different rooms, one room padded carpet over concrete the other room wood floor over basement. Neither table seems effected by high volume levels, system plays very clean with no distortion.
 
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