Model 19 acoustical foam.....

[Russnohio]

Am I correct in thinking that the horns foam insert was originally designed and installed ONLY because of the grill frame interferring with HF dispersion and to prevent HF reflection? In other words, if you do not use grills on your speakers then the foam is totally useless and serves no purpose? My thinking is that with the horn section grill attached.....you then have at least 4" of wood surrounding the horn completely and this would have an adverse effect on HF sound quality (Maybe!to some degree). FWIW my speakers do not have this foam and I could care less because the speakers mid/HF sound is as great as can be expected, and also, I do not use the grills. In fact I removed all the grill "clip ons". My brother is also a model 19 owner and we discussed this on the phone just the other day. I can recall NO other Altec sectoral horn application using acoustical foam other than the nineteen with its bulky grill frames. Maybe you Altec experts out there can shed some light.

Thanks, Russ

[Altec19]

I obtained reproduction foam inserts for my 19's not because I thought it would make a sonic difference but because I wanted the speakers to be original and complete. After I installed the inserts it was rather obvious that something had changed. It was as if a layer of grunge had been wiped off an outside window and you could now see clearly through it. Upon further reading, I think the foam was actually intended to eliminate early reflections from the baffleboard and the side protrusions. Of course, the only way you'll know for sure is to try it.

[bfish]

It's not an M19 exclusive, later Vals used closed cell foam too;



Models with 511s and deco grills used fiberglass on both sides.

Any model with the same HF horn baffle step could benefit as well, with or without grills.

<font color="#FFFFFF" size="1">[ November 09, 2007 02:34 PM: Message edited by: bfish ]</font>

[Russnohio]

Originally posted by Russnohio:
I can recall NO other Altec sectoral horn application using acoustical foam other than the nineteen with its bulky grill frames.

<font size="2" face="Verdana, Helvetica, sans-serif">I stand corrected then.



Russ

[highfidelity]

Personally, I felt my 19's sounded better after I purchased the foam inserts. Everything was a little clearer and imaging was a bit better too.

[Russnohio]

Ok then. I'm gonna locate some sheet foam and experiment! No, I'm NOT going to buy the dedicated inserts occasionally sold on ebay.....I'm gonna rig my own purely to experiment. Just got to find a store that sells the stuff. I'm thinking sheet acoustical foam NOT weather insulation. 1/2" to 1" thick...dark gray. It'll be fun!

[Jim Butler]

Having seen the early acoustic fiberglass on the 846's (I've seen pics that show it was clearly spray painted black) I tried filling the cavity around the 811 horns in my 411 Santiagos with black felt. It does, to me, make an audible difference of the clarity of the horn. I used a fair amount of heavy felt I bought at the fabric store and bunched it up all round the horn flare. The black color also has the advantage of not being seen through the grills. I now use it in my Model 19's too.

[GM]

Greets!

30 ppi filter material is a good place to start, though I prefer the more broadband damping of 1" acoustic fiberglass as used in the 846B, etc., before the more cosmetic M19 inserts became available.

GM