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AR14 Foam Grill


djcheung

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Hi all,

I have recently purchased a pair of AR14.

The original foam grills are long gone.

The question is, what type of foam can I get to closely match the original, or should I just make a grill frame with grill cloth?

Best regards,

David.

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Not sure what's available on your side of the pond. I like the grille frame and cloth idea. Instructions here for making the frames and covering them: http://www.humanspeakers.com/diy/index.htm

Here are some examples of foam that would work:

http://www.tchweb.com/tchstore/category/acoustic-foam/s0/Acoustic-Foam.html

http://www.amazon.com/0-39-Foam-Speaker-Grill-Material/dp/B00AZU22QA/ref=sr_1_2?ie=UTF8&qid=1403883015&sr=8-2&keywords=foam+speaker

http://www.speakerworks.com/Custom_Foam_Speaker_Grill_p/cgf1.htm

http://www.parts-express.com/speaker-cabinet-grill-foam-19-wide-x-31-long-x-3-8-thick-black--260-519

There are many more. If you google "speaker foam" that will probably be the most expensive. "Filter foam" or "acoustic foam" can yield good results.

I actually purchased some grilles from http://www.foamspeakergrilles.com/ because they would make dark brown foam grilles and recess the backs but they were pricey and I think you can spray paint the charcoal foam as long as you just do a very light coat. I painted some gray filter foam to make a replacement grille for a KLH radio and it worked out fine.

Good luck!
-Kent

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AR specified a very porous, "reticulated" foam material for the grills of the Advanced Development Division speakers, which included the AR-10Pi, AR-11, AR-12, AR-14 and a few others. These foam grills were polyurethane-foam machined units (there were portions that were milled-out to be thinner where the mid and tweeter units were located, and the grills were very porous and acoustically transparent. Ordinary, garden-variety foam will work, of course, but it will definitely reduce the high-frequency output and therefore should not be used if reticulated foam can be found.

—Tom Tyson

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AR specified a very porous, "reticulated" foam material for the grills

Important point, Tom. You also have to consider the PPI (pores per inch). The filter foam I mentioned is reticulated (I did not realize that was what it is called) but the PPI varies from 10 to 100. I'm assuming 10 or 20PPI is best. Lots of outfits sell filter foam and I'm sure David can find it in England. Here's a page that explains various types of reticulated foam: http://www.newenglandfoam.com/filter.html

-Kent

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It is confusing that the website linked to in Kent's post #4 shows one of the properties of reticulated foam as sound absorption. I would have thought it would have been better for it to be acoustically transparent (or as near as possible) for use as a grille, as Tom Tyson has said in his post #3. The sculpting of the foam around where the drive units were postioned did make the foam very thin in the crucial areas.

Or did the engineers at AR test how much sound (particularly HF) the grille absorbed over the frequency range and take this into account when designing their foam grille speakers in the ADD era?

My personal experience is that the foam grilles were extremely transparent, and I (with younger ears then) could not tell any difference whether the grilles were on or off. I will be interested to see if the OP David finds suitable foam to replace on his AR-14. I made some cloth covered grille frames for my AR-16 after the original foam crumbled to dust, but I only use them as protection. All listening is now done with the grilles off. Even my ageing ears perceive some HF cut with the cloth grilles on.

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Good point Jeff. This page explains a bit more http://www.newenglandfoam.com/polyurethane.html

They list Polyether, Polyester, Filter (Reticulated), Furniture and Rebonded. Not all poyurethane foam is reticulated. For example the "rebonded" type is typically used for carpet padding. The "eggcrate" style shown in the link works well as sound damping in bass reflex speakers. I think you want a very open reticulated foam and as thin as practical.

I cut up a reticulated filter for a Shop-Vac to use as a radio grille. It is quite open but I don't know the exact PPI.

-Kent

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Thanks very much for all your information.

I have looked at the 'filter' reticulated foam material product in the pet shop but can't seem to be able to find them in large/cheap enough sheet of the material.

I will keep looking.

I have a similar material on the port hole covering on the M4.

I will try to match something with that.

Will post a picture later.

Best regards,

David.

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Hello David,

Attached is a pdf of the AR foam grill mentioned by Tom Tyson.

The grill was multi-purpose and used on all 4 models, as Tom said

You can see " there were portions that were milled-out to be thinner where the mid and tweeter units were located".

Making a duplicate may be difficult in foam.

I prepared the pdf a while ago, I think it is ok.

(note the picture of the foam is the same picture rotated - interesting)

R

<<<<<<Amendment.>>>>>>

I rechecked the length of foam - it measures 51.5 cm.

I will need to recheck the centres of the tweeters.(may vary by 0.5-1.0cm).

AR10pi,11,14 Foam Grille.pdf

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Hi all,

Thanks very much for the information.

The technical details on the foam grill are fascinating but I don't think I will be able to replicate it.

As promised, here are some pictures of the foam material and the refoamed AR14.

Best regards,

David.

post-125249-0-25363100-1404064499_thumb.

post-125249-0-99570000-1404064520_thumb.

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Hi all,

After some thoughts I think the best option for me is to get a frame made as you can see the plaster 'sticker' pads on one of the speakers are all gone.

I can use the document provided by RLowe to get the correct dimension.

Will post more updates when done.

Best regards,

David.

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