Acoustic transparency - grill material

[casey73]

I have a question about acoustic transparency of grill material. I was thinking about using an old burlap sack with a logo printed on it as a grill cover for a small amp, just to make it funky, unique, (insert your favorite adjective here).

Anyway, it got me to thinking about acoustic transparancy. I have used, and have on hand several types of "acoustically transparent" grill cloth material laying around. But I've often wondered exactly what makes a material acoustically transparent. Logic tells me that anything in front of the speaker is going diffuse the sound waves passing through it to some extent, even if it is almost undetectable to the human ear. I remember seeing a photo of Santana on stage during his pre-Boogie days and his amp speaker cabinets were covered with what appeared to be paisley print cotton cloth. Since then I've wondered what kind of material should or shouldn't be put in front of a speaker. I may just go ahead and use my burlap sack, but I was just wondering if there is alot of science behind grill cloth. I think there's a reason that some reference speakers in studios don't have speaker covers at all, but I wonder how critical it is in guitar amps.

[Ray Ivers]

casey,

To check grill cloth for acoustic transparency, here's what I've done:

a) put my guitar on a stand, or in its case

b) pulled the grill off one of my hi-fi speakers, if possible

c) put on a recording I knew by heart - I've had good results with Dire Straits' Brothers in Arms CD, YMMV - and

d) held the cloth up in front of & close to the speaker, and listened to the effect it had on the sound.

Using this method, I always hear at least some effect on the treble response from pretty much any material, and often a whole lot more - including full-range volume drops. Of course, I've tried hanging a piece of cloth in front of my guitar speakers, playing for a little while, pulling it off, and then playing some more, and always hear little or no difference from the very same material(s).

For those who feel that grill cloth material doesn't make much difference sonically, I have four words: "Marshall basket-weave cabs".

Ray

[Jim Jones]

Ray's method sounds like a good one...just keep in mind your personal tastes when it comes to tone. I'm not a fan of a lot of highs so if the cloth "softens" a bit of the top end - for me personally - that's a good thing.

Go ahead and try the burlap, that sounds like a cool idea! I used some upholstery fabric I liked the looks of for my 4 x 12 and I think it sounds great.



Post some pics when you get it done!

Jim

[John_H]

That's sharp Jim! welcome to the forums

[Steve Dallman]

I take cloth I'm considering for grill cloth, and hold it over my mouth and speak, using lots of sibilance. If the cloth muffles my voice at all, I pass. The other test is to hold it up to your eyes and see if you can see through it. The more opaque it is, the more it will muffle the tone.

[markbul]

I bought burlap at my local fabric shop and used it for two cabs. If it makes any difference, I certainly don't hear any harm.

[Jon Anderson]

I was just looking at some burlap at my local Walmart. They had some special 'metallic' burlap for Halloween already. It was tan with a gold fleck. They also had some bright red stuff with a gold fleck in it.

I would have bought some, but I found this as well, for $2.99 a yard. (The picture is with it just draped. I hadn't straightened and stapled it yet...)

Jon

[Bill Durham]

Jon,

Is that for your October?

BD

[Jon Anderson]

Actually, it's for a Hi Octane, that had previously been a modern 'interpretation' of tweed. Unfortnately, the laquer I used was a solvent for the glue I used. So a recovering was in order. This time I just stuck with standard tolex.

My October is going to have a checkered twill covering. Looks very retro.

Jon

[Bill Durham]

Cool, I was just curious. Is there a pretty big learning curve on the tolex? I hope to attack that project this weekend.

BD

[dsouder]

Bill,

You may find Casey4s tolex tutorial helpfull. http://us.f13.yahoofs.com/bc/43c71b6....oj0EBAQ.2S39W

I've done a couple of tolex jobs, and patience is key. Also get a heat source, like a hairdryer to help stretch the tolex and soften glue for adjusting seams and corners. I use WBCC(water based contact cement) with good results.

Dan

[Jon Anderson]

Another thing I've found invaluable is using masking tape to hold things in place as it dries. This is especially necessary if you need to 'heat and stretch'.

And let the glue dry for a few days before you take the tape off! I got anxious a few times to check it out, and took the tape off to check it out after 12 hours. It looked great! But then the next morning, my invisible seam wasn't exactly invisible.

Also, it's worth it to buy some cheap marine vinyl (not the fuzz backed stuff) from a local fabric store to practice. You should be able to pick up a yard or so for just a couple of bucks. Then, just cut up some odd shapes of wood, and try to cover each one, without any seams showing.

Jon

[Bill Durham]

Guys,

Thanks very much for the hints. The piece I bought should give me enough extra to practice some with the real thing. I had no idea about the hair dryer idea... I have a heat gun as well my wife has a hair dryer.

thanks again
BD

[Jim Jones]

If you can wrestle the hair dryer away fom your wife - use that when tolexing. I imagine you'll fry the livin' crap out it with a heat gun.

Jim

[Bill Durham]

Originally Posted by Jon Anderson

Another thing I've found invaluable is using masking tape to hold things in place as it dries. This is especially necessary if you need to 'heat and stretch'.

And let the glue dry for a few days before you take the tape off! I got anxious a few times to check it out, and took the tape off to check it out after 12 hours. It looked great! But then the next morning, my invisible seam wasn't exactly invisible.

Also, it's worth it to buy some cheap marine vinyl (not the fuzz backed stuff) from a local fabric store to practice. You should be able to pick up a yard or so for just a couple of bucks. Then, just cut up some odd shapes of wood, and try to cover each one, without any seams showing.

Jon

Jon,

At any time, do you staple the tolex?

BD

[Jon Anderson]

Nope. You don't really need much to hold it in place. It's just that I've found that contact cement shrinks just a little bit as it sets. This is made worse if you used heat to stretch the tolex around a corner, or to match up a seam. Masking tape seems to hold it in place 'just enough' to keep it from shrinking back. Plus it's easy to remove.

This is especially nice around corners, where you can sometimes get little parts of tolex puckered up, right in the point of the 'V' that you cut. A little bit of heat, and you can mash it right down, and hold it in place with tape, until it is thoroughly set.

Also, it helps to spray paint first where you might have a seam. Especially with black tolex. Just the smallest of a pinhole gap, and the bright wood underneath will draw the eye. Painting it black first will make it invisible.

(Sorry for the blurry photo)

[Bill Durham]

Jon,

thanks very much for the info, I would have learned the hard way!

BD