Mitchell donut - foam?

moz91

Morning chaps
Just wondering if anyone has experimented with this idea?
Quite fancy trying it in a 112 cab i use. 

Anyone who's had success with it; what foam did you use? I guess its not just a case of nipping down to dunelm and buying a sheet of 1/2"? I'd presume it needs certain properties in relation to density etc??

Thanks!

Chris

timmysoft

I don't know anything about the donuts but I do foam out my closed back cabs/combos with egg box style foam.

the principle is used in car audio so I tried it and liked the results. By slowing the reflections down you can give the impression of a bigger cab. It's night and day on my little tubemeister combo, really noticeable.

moz91

I'm intrigued, might have a go at that. It's an oversized 112 in question. 1/3 open back. Front loaded speaker
Would you foam out the whole thing, or just parts?

timmysoft

moz91 said:

I'm intrigued, might have a go at that. It's an oversized 112 in question. 1/3 open back. Front loaded speaker
Would you foam out the whole thing, or just parts?

To be honest, it doesn't really do anything in an open back, it needs to be a sealed or ported enclosure to get any benefit. I usually foam the inside bottom and and some of the inside back panel 

moz91

Fair enough, i did wonder!
Think i'll give the donut idea a try, though

ICBM

moz91 said:

I guess its not just a case of nipping down to dunelm and buying a sheet of 1/2"? I'd presume it needs certain properties in relation to density etc??

According to Mitchell, most standard foam should work. It doesn't really need any special acoustic properties other than breaking up the direct transmission of high frequencies slightly.

I haven't tried it myself, but I understand the physics behind it and I have no doubt that it works.

hywelg

When I get to my PC I'll dig out the place where I got mine. I got 10mm, 12mm and 15mm. Which you use will depend on how bright and beams the speaker is. Also the hole size will limit the 'beam' as well. (yes I know it's not a 'beam' as such).

You'll also need some spray contact adhesive.  Be careful using it, let it dry thoroughly before sticking the foam to the grille cloth otherwise the glue will mark the cloth.

MartinB

For anyone who has tried the Mitchell doughnut idea, does it affect how you mic the speaker at gigs?  I like the idea of making the on and off-axis sound of my combo more consistent,  but I wouldn't fancy having to explain how to mic it it to every sound guy I encounter. 

steamabacus

eFoamUK will do acoustic foam cut to size in small pieces.

andy1839

I did it on mine using:

 https://www.efoam.co.uk/quote-foam-cut-to-size.php?FoamCutToShape=ACrectangle&shape=SACrectangle&size=48&len=13&thickness=1.57&width=13&specialf=11&inito=11c1c0&meas=in

using the acoustic foam, 1" thick and 13" x 13". Can't say I noticed a huge difference 

I may still have a tile spare. Pm me your details and I'll send you one to have a play with. 

ICBM

MartinB said:

For anyone who has tried the Mitchell doughnut idea, does it affect how you mic the speaker at gigs?  I like the idea of making the on and off-axis sound of my combo more consistent,  but I wouldn't fancy having to explain how to mic it it to every sound guy I encounter. 

Has the out-front sound ever borne any relation to what you hear on stage any time in the past?




Actually it should make the mic position less critical, I think.

TimmyO

I've done it before and it really does work (including on an open-back for those that think it doesn't have an effect there) 

Used the foam from efoam iirc I went toward the thicker end of what's recommended in the original instructions 

And yes it makes mic positioning simpler - there just seemed to be no issues with frequencies that couldn't be dialled out or in - just get it up there capturing enough level and off you go. 

we all know that sound guys can mistakenly eq the mic'd sound influenced by what they are hearing direct, so if anything removing those piercing/beaming frequencies just makes the whole thing seem simpler.

I'd do it to any amp/cab I was going to gig

hywelg

Yes I got mine from efoam.

https://www.efoam.co.uk/index2.php?shape=ACrectangle

Way back in 2009, so I must have been one of the first in the UK!

And yes it does work. I was shocked when in a band setup I took a very long lead out front to hear the band play so we could set levels, and my amp sounded awful, so harsh and brittle but on stage it was great. Ended up having it facing the back of the stage a,d then didn't use that amp again (Ceriatone DZ-30, quite a bright amp anyway)

In order to cut the outer diameter, slip an oversize piece of foam between the baffle and the grille cloth. Make sure its not under tension then mark it with a felt pen. Scissors will then cut it accurately enough. It needs to be a snug fit.

IIRC I used 12mm foam on nearly all my cabs with a hole size from bean tin up to golden syrup     Yes you need someting very robust to cut the round hole. You'll need a very sharp stanley knife blade or better still a modelling knife. Press very hard with the tin on a cutting board (not the kitchen worktop!)  so that the foam is completely compressed, then cut. This will render a very neat hole. IT works as well if you need to enlarge it slightly using a bigger tin but you need to press even harder to stop the foam slipping out from under.

You will re-EQ your amp slightly afterwards as you will lose a little high end, but you will also sound the same from wherever you listen.

Oldbramwell

Bumping an old thread....

I cannot believe how long it's taken me to get to grips with the on-axis ice-pick tone of a guitar amp & to stumble on the Mitchell donut as an effective solution. The Michell donut is just amazing!

My foam arrived today & I've applied the donuts to five speaker apertures (Three 1x12" & one 2x12"). The difference is really significant. The tone on and off axis is now much more consistent.

A real bonus was discovering that efoam will supply the foam already cut to a circle - just specify the diameter you want. All I had to do was cut out the middle 75mm hole using a baked bean tin as a template (following Hywelg's advice above).

Such a good result...!

mart

Oldbramwell said:

....

A real bonus was discovering that efoam will supply the foam already cut to a circle - just specify the diameter you want. All I had to do was cut out the middle 75mm hole using a baked bean tin as a template (following Hywelg's advice above).

Such a good result...!

Presumably if you open the baked-bean tin in the right way, cutting through the sides rather than the top, you could leave it with sharp edges that could be used to cut the foam directly, rather than just serving as a template?

Probably a good idea to clean the baked beans out first, though.

p90fool

Just bumping this to say I fitted these to my three gigging amps last night and as far as I can tell at home volume it seems to work very well. 

Years of chopper building including their seats has taught me the best tool for cutting foam that you're likely to find around the house is an electric carving knife. 

p90fool

Hoo-bloody-ray, finally managed to get the images to attach....

ICBM

p90fool said:

Is that the large-magnet (with a small vent in the middle) version of the Fender/Eminence 'blue label' speaker? If that's the cabinet from a Stage it would have been stock.

If so those are truly great speakers, if a little heavy!

p90fool

*runs upstairs to check*

No, it's the Celestion A-type I pulled out of my HRD - it works well as an extension cab for my Jet City. 

Good spot on the Stage cabinet thought!