Model 19 Foam Surrounds

[SOOTSHE]

Just finished doing some foam surrounds for the 811 flares to satisfy my curiousity as to whether it makes any difference to the sound. I've recently done the mod that disconnects the HF pot from the crossover & have found that to be a tad too bright in some instances, although I must say that it brings through a lot more detail. I changed my preamp to another type & that has smoothed things out a bit & now there is just a touch of bite to the top end.

After installing the foam surrounds I have found that it definitely has taken that slight edge off the sound, without any loss of information....so the best of both worlds really. I also notice a significant improvement in the imaging.....boy, these babies are really firing along now.

I know....It's a bit rough....but the best I could do with a Stanley knife. The material I used was only 25mm thick (acoustic foam) & so I had to glue 2 pieces together to get the required thickness. I'll try to see if I can get some 50mm thick & cut it on a table saw....should be much better.

Next step is to dampen the 811 with the paint & sand method.

[Altec Best]

Hi John, Good Job. If you get a chance you can try to taper the edges back farther along the sides of the 811.It is closer to what originals looked like.Here's a picture to help guide you.I can take measurements on thickness if you need them.:2thumbsup:

[SOOTSHE]

Thanks for that...now that I know that it makes a definite improvement I'll have another go with some 50mm foam & then it will be all in one piece. I get the idea of the taper & should be able to do that more accurately when cut on a table saw with a fine blade.

Thanks for the pics,
John

[GM]

Is that open cell as it should be? Looks closed on my monitor.

GM

[SOOTSHE]

Is that open cell as it should be? Looks closed on my monitor.

GM

I don't know....how would I tell the difference?
The company I bought it from said that it was "acoustic foam".
I can tell you that it is very dense & the "pores" of the foam are...how should I say?....very tightly packed together.

[GM]

You should be able to easily blow through it or use it as a sponge. Look at AB's to get an idea how densely packed the open pores should be. AFAIK, it's the kind used for filtration. If yours is acoustic foam (open cell), then I'm guessing it's the melamine type used for wall treatment, so designed to reduce room reverberation which handles a much lower BW than what's needed.

GM

[rontec]

Doesn't the foam also have some dampening factor on the outer horn (bell), thus improving sound quality?
Providing it's touching part of the outer rim of the horn?

[RonSSS]

Felt would be a better acoustic solution.

Ron

[SOOTSHE]

You should be able to easily blow through it or use it as a sponge. Look at AB's to get an idea how densely packed the open pores should be. AFAIK, it's the kind used for filtration. If yours is acoustic foam (open cell), then I'm guessing it's the melamine type used for wall treatment, so designed to reduce room reverberation which handles a much lower BW than what's needed.

GM

You can't really blow through it like you can with foam that you would use for filtration. Yes, I think it is the type used for wall treatment....similar to that in recording studios.....either way, seems to work OK.

[SOOTSHE]

You can't really blow through it like you can with foam that you would use for filtration. Yes, I think it is the type used for wall treatment....similar to that in recording studios.....either way, seems to work OK.

I'll have another take on that......you can blow through it fairly easily & here's a couple of better quality shots.