AR9 form/blanket material

[Guest David in MA]

Hi all,

Still working on the AR9s...got the surround reformed without any problems thanks to all the knowledge base in this forum. I will definitely be work on the replacing the caps in the crossover sometime in the near future. For now, I am enjoying them. It has reinvigorated my interest in music. I even pull my old Thorens turntable and 400+ vinyls from my basement, which my wife didn't appreiciate (lol). Went thru them and I couldn't believe some of the stuff I had...Thompson Twins, Joan Jett, Softcell...etc...stuff from 70's and 80's...

Just wanted to ask one question here - what sort of acoustic material is used for the high-midrange (shown below where it is exposed)?

http://www.classicspeakerpages.net/dc/user_files/898.jpg

Is it absorptive in nature or reflective? Is this available at partsexpress?

Thanks to all for reading...

[soundminded]

The material is absorptive. If I were to have to replace mine, I'd probably try the felt (not rubber) underlayment used by carpet installers. On almost any carpet installation job where it is used, there should be enough scrap for a pair of AR9s and if you ask nicely, they will probably let you have it for free. Or just pick it up off the sidewalk, they usually bag it and leave it out for the trash collectors.

[Guest David in MA]

>The material is absorptive. If I were to have to replace

>mine, I'd probably try the felt (not rubber) underlayment used

>by carpet installers. On almost any carpet installation job

>where it is used, there should be enough scrap for a pair of

>AR9s and if you ask nicely, they will probably let you have it

>for free. Or just pick it up off the sidewalk, they usually

>bag it and leave it out for the trash collectors.

Soundminded,

Thanks for that information. My friend works at a felt manufaturing company (I don't know if he still does). I'll check with him and see if I can get some in black.

Thanks again.

[Robert_S]

RE: Just wanted to ask one question here - what sort of acoustic material is used for the high-midrange (shown below where it is exposed)?

Hello,

My understanding is that the material (for the specific area you refer to) is acoustically 'transparent'. It is the same material that is used in the (felt cut-out) area surrounding the tweeter (assuming you have the original material to refer to -- the photograph does not show sufficient detail to determine this).

Hope that helps,

Robert

[soundminded]

The material was referred to by AR I think as an "acoustic blanket." It's all one piece. Its purpose was to prevent diffracted sound from the front firing drivers from being reflected by the cabinet towards the listener. There was some debate here a long time ago and frankly skepticism about how useful or significant this was but as I understood it, that is its purpose, to prevent sound from being reflected off the front face of the cabinet. It appears to be a dense felt like material about a 1/2 to 3/4 inchs thick with circular cutouts for the tweeter and lower midrange and a rectangular cutout for the upper midrange. The metal flanged face plates of the upper midrange and tweeter are exposed so they can reflect some sound. The felt seems well glued onto the wood, I find it hard to understand why anyone would ever have reason to remove it unless it was damaged.

[Guest David in MA]

>The felt seems well glued onto the wood, I find

>it hard to understand why anyone would ever have reason to

>remove it unless it was damaged.

I got these AR9's from my friend. The original form was still intact but it was falling apart. Half the stuff fell off during transit from his house to mine. It just looked really bad so I took it all off, thinking that I should be able to cover it up with replacement part.

[Guest David in MA]

Robert,

>My understanding is that the material (for the specific area

>you refer to) is acoustically 'transparent'. It is the same

>material that is used in the (felt cut-out) area surrounding

>the tweeter (assuming you have the original material to refer

>to -- the photograph does not show sufficient detail to

>determine this).

The surrounding for the tweeter is original. It is very fragile and so I'm not going to touch it. The midrange surrounding, however, was in really bad shape. It was falling apart so I remove them. I guess the speaker still sounds great but I'd like to cover those areas to see if there is any difference. Of course, I think it would look better that way as well.

[Guest Bret]

It's the same foam material that's around the tweeter. With age it just falls apart and makes a mess. I have no idea where any more can be had.

Early models didn't have this foam close to the either the upper midrange or tweeter. Thusfar nobody has said they can hear any effect.

BTW - the early models had black paint in that rectangular area around the upper midrange, I'm guessing to make the exposed cabinet "blend in" with the rest of the acoustic blanket since there was no foam.

Bret

[Robert_S]

Hi David,

> The surrounding for the tweeter is original.

Use that as your reference when sourcing a replacement for the missing area.

> It is very fragile and so I'm not going to touch it

A wise decision. I have one pair of AR-915s with the original cut-out 'insets' still in pristine condition -- the exact cause of deterioration remains enigmatic.

> I guess the speaker still sounds great but I'd like to cover those areas to see if there is any difference. Of course, I think it would look better that way as well.

I agree, the aesthetic is improved. The key is to use an acoustically transparent material, not reflective or absorptive.

As soundminded has stated: "The metal flanged face plates of the upper midrange and tweeter are exposed so they can reflect some sound."

Acoustically transparent material will not interfere with the designers intention.

Incidentally, the same (open cell foam) material was used as a one piece grille panel on the U.K. version of the AR-7x (circa 1975), and perhaps others, thereby standing in testament to its sonic transparency.

Robert

[ar_pro]

You're 100% correct, Bret - the early production of the 9 did not have the dissolving foam blanket inserts - one wonders why they were ever added, since it would seem to be simpler to just enlarge the blanket.

The last two AR-9 restorations that we've completed have not included Acoustic Blankets. The system's performance in a large room actually seems to be enhanced by their absence, as Minh Luong mentioned in an earlier thread. Here's a pic from that thread:

[Guest David in MA]

>

>You're 100% correct, Bret - the early production of the 9 did

>not have the dissolving foam blanket inserts - one wonders why

>they were ever added, since it would seem to be simpler to

>just enlarge the blanket.

I'm going to insert some felt material and hear if it makes any difference. Probably not much. At least it will look better.

>The last two AR-9 restorations that we've completed have not

>included Acoustic Blankets. The system's performance in a

>large room actually seems to be enhanced by their absence, as

>Minh Luong mentioned in an earlier thread. Here's a pic from

>that thread:

Very nice job. The cabinet of the AR9's I got from a friend was in very good condition. I was told by my furniture maker friend that I should just apply some butcher's wax to bring out the natural grain. Here is a picture of it if anyone is interested.

Thanks.

[Guest Bret]

>one wonders why they were ever added, since it would seem to be simpler to just enlarge the blanket.<

I hate to be cynical, but I'm guessing four things might have contributed:

1) AR was still producing some parts of the "Truth" line when the 9 was introduced. (or at least many were still in the channel) They (the Truth in Listening bunch) used felt stick-on stuff around the tweeters in their final days. "If it was good enough and important for an AR-11, why was it not-included on an AR-9?" asked the buying public about to shell-out 1,500 1978 dollars at their authorized AR catalog showroom retailer where the teenage part-time help said, "Huh? I dunno."

2) In the end it was probably cheaper to stick the foam in the hole than it was to paint the cabinet black in just that one area.

3) The "blankets" couldn't be made to cover-up the screw heads of the drivers without goofing-up the assembly and servicability mightily.

4)There were thousands and thousands already made sitting around waiting for cabinets.

[Guest cober]

The original material is an acoustically transparent open cell polyurethane foam about 1/2" thick, much like the speaker grill material I remember on my AR-11s. The best replacement material I have so far is found at Walmart, believe it not. They sell an A/C filter element replacement. It is, however, thinner than the original material and almost black enough. I toyed with the idea of doubling up on the material for a thicker look but bonding foam to foam is problematic and I settled for one layer - it's close enough to the original look of my beloved AR-9.

[Guest David in MA]

>The original material is an acoustically transparent open

>cell polyurethane foam about 1/2" thick, much like the speaker

>grill material I remember on my AR-11s. The best replacement

>material I have so far is found at Walmart, believe it not.

>They sell an A/C filter element replacement. It is, however,

>thinner than the original material and almost black enough. I

>toyed with the idea of doubling up on the material for a

>thicker look but bonding foam to foam is problematic and I

>settled for one layer - it's close enough to the original

>look of my beloved AR-9.

That actually looks fantastic! A/C filter, heh? Guess where I'm going by tommorow? lol...

Thanks.

ps, nice speakers...

[soundminded]

"I toyed with the idea of doubling up on the material for a

thicker look but bonding foam to foam is problematic and I

settled for one layer - it's close enough to the original

look of my beloved AR-9."

An attachment method which will work and is inexpensive are called "stick clips." These inexpensive devices are used to attach things like fiberglass panels to boiler room ceilings. (They are probably not available at Home Depot so you will have to hunt for them. The sticks look like thin nylon nails with a large flat head you glue to the attachment surface. After they set, just push the blanket over it until it is firm against the enclosure. Then push the clip over the stick and push until it is secure against the blanket. You could do one blanket at a time or two together to get a double layer. Then just cut off the end of the stick. You might want to paint the exposed clip and stick with a drop or two of black paint to make them invisible against the blanket.

[ar_pro]

Yes, of course - it would have been impossible to access the tweeter if it was covered by the blanket.

The cabinet is actually painted black beneath the entire blanket - a big rectangular area that was partially exposed in the earliest iteration of the 9.

Butcher's wax will give a good sense of depth to the grain, and will provide a very smooth appearance to the finish. It can spot with moisture, and could be affected by strong sunlight. This is also true of lemon oil, which seems to act as a mild bleaching agent when exposed to direct sunlight.

My recollection of the introduction of the 9 as AR's flagship loudspeaker was that it was quite revolutionary. Prior to that point, each top-of-the-line AR system had been either a 2 or 3-way bookshelf model (exception noted for the LST, which was not truly presented as a consumer product). This was a real sea-change, in that the lineup offered *two* floor-standing, dual-woofered, 4-way systems, before the traditional 3-way loudspeaker was even reached (and it too, was a floor-standing design). The only thing that would have been more dramatic would have been the inclusion of a ported woofer! ;-)

[Guest Bret]

>Yes, of course - it would have been impossible to access the tweeter if it was covered by the blanket.<

Whether that was on-purpose or not, I loved it. See, I was thinking the screws might have been under the blanket, but the whole tweeter under the blanket just hadn't crossed my mind.

What a visual!

I can hear the regional guys now, "And here is our newest feature, the Acoustic Blanket. Used to completely cover the tweeter and midrange drivers, it prevents cabinet reflections by totally absorbing all sound which might reflect!"

Well, it would have been very effective.

>The cabinet is actually painted black beneath the entire blanket - a big rectangular area that was partially exposed in the earliest iteration of the 9<

Thanks for that. This I did not know. So, sticking the foam in there was cheaper than painting any of the cabinet black!

I always wondered about that and the AR-90. Behind the woofer covers and the whole front was black. I don't know about the baffle, but the sides of the speakers were "American Walnut" veneer and it looked like painting walnut veneer black was a lot of trouble to go to.

Bret

[Guest cober]

I just noticed your AR-9 has wood grain finish under the now missing foam insert of the upper mid. You might see this through the thin Walmart foam material. My AR-9 happens to be black in this same area. Attached jpeg shows mine without the foam inserts.