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Old 7th April 2008, 06:42 PM   #1
Bluto is offline Bluto  United States
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Default OB Reflection - cheap & thin

I'm sure it's been covered but couldn't find it with words I used.

I'll definitely be going at least partial OB with Hawthorne SI's.

I have a bad wall to work with that requires everything be as close as possible to it so I need to minimize everywhere I can.

I'm not interested in the standard ' made for the job' stuff that comes from the acoustic manufacturers and therefore sells for the price of crushed Diamonds.

I'm wanting a very thin sheeted material that I can cover with speaker grill cloth that can be affixed to something of substance such as hardboard (masonite) that has some reflective qualities for the back wave for the OB. . Why speaker grill clothe? Because above the OB's will be other 'in wall' mounted drivers I need a cut out for and this entire 'panel' will run from the baseboard likely to a height of 56" where it will meet a decorative piece of Oak molding so it serves aesthetic purposes as well. This entire 'panel' will mount to the drywall and can't exceed the depth of the baseboard ... approx. 1/2 ".

It needn't be Rocket Science in approach, perhaps hardboard in and of itself would be reflective enough?

Thanks -

Bluto
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Old 7th April 2008, 11:30 PM   #2
badman is offline badman  United States
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I think you're going to need a diagram for us. If I understood correctly... it STILL didn't make any sense to me!

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Old 8th April 2008, 01:30 AM   #3
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Hi Bluto - If I am following your idea I get the impression that you are using the Hawthorne 15 inch (a speaker I have been looking at for OB use as well and thus my interest) in an OB configuration with one (perhaps both?) of the speakers placed very close to the wall - perhaps just a matter of inches - and making an attempt to use some type of material to provide sound absorption to some controllable degree. I'm playing around with trying to get my stuff to work right when it's closer than 2 ft. (61 cm's) to a reflective surface that is fairly "hard" such as drywall or brick and it's a problem. Have you considered going "in-wall" and going IB?
Another thing I have considered is going over to the "dark side" and actually using the wall as a reflector ala Dr. "B" - except that I want to shape the reflector to have a specific pattern that I can "aim" (or direct) to my desired listening area. Before that starts to sound just a little crazy bear in mind that I have been around parabolic radar reflectors my entire professional life and know a thing or two (ok ..... maybe three) about waveguide and antenna theory - so there might be something there. I'm unclear as to your intended needs tho - perhaps a photo or drawing of your intentions will help to make things a bit more clear.
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Old 8th April 2008, 12:29 PM   #4
Bluto is offline Bluto  United States
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C2 & Badman -

Can't help out with diagram . I've tried. Computer is old, runs Millenium and in attempting to rid a virus at one point I destroyed some shared files so I can't even save half of what I want let alone download and post to a site.

C2 - you are close. Just imagine a sheet of something hard surfaced running the distance of the wall up to a height of near to 56" where it meets some decorative moulding. It has to go that high because CSS FR125's are mounted 'in wall' above the height of the Hawthorne SI's which are OB. The moulding does act to a slight extent as a waveguide in that it's likely 2" curved stock. I didn't want to confuse the issue further but there will also be mouldings running vertically approx. every 24" for both decorative purposes and to further act as somewhat of a waveguide as well. I won't be getting much here but with OB every little bit will help. All - because as you state, the OB's will unfortunately be fairly close to the wall. OB's can work close to a wall but not optimally. I can't adhere the speaker clothe directly to the drywall for 2 reasons. 1) Drywall does not reflect well, it's porous and absorbs and for OB I need that reflective quality directly behind drivers and 2) I will need to replace section of drywall that CSS drivers mount in with plywood for baffle and I'll need to put some type of mesh screen over driver itself. As thin as speaker clothe is even drywall tape would show through. For this reason I brought up hardboard as it can be purchased in stock as thin as 1/8" , grille cloth could be spray glued to it and it could be drywall screwed to both actual drywall as well as plywood baffle and screws would be hidden under moulding. The top of the OB's will be at about 32"s but the CSS are actually in a horn of my design so we need the 56" height for moulding, driver and terminus before you run into the 32" top of SI. . Further increasing the need for a harder surface although reflection not necessary here is that Subs will be AE's and IB mounted on either end of the room. I also need to protect those drivers and conceal them as well.

What you are saying doesn't sound crazy at all and if you get a chance and spend more time at the Hawthorne site you'll see others have applied similiar principles. I've been reading on these near to a year and have played with over a dozen drivers to date. What I'm getting out of some 8" Oakton's I'd never heard of and haven't been made since the late 80's it appears is blowing me away. Paid $26 a pair for NOS. Like all else, lot of arguing I see as unnecessary cause it's easy for me to see near to all OB drivers respond differently under different circumstances. Hawthorne SI's actually are giving better performance with narrower baffles. Thats blasphemy with most OB drivers. I was gona mount center of driver at 34" , guys are stating best response at between 18-24" ????

I'm hoping I made that easier to understand. Very simply is there any inexpensive, relatively thin, hard surfaced sheeted building material out there besides masonite that has known reflective qualities that I'm not thinking of ? Plexiglas? Not exactly cheap. 5 coats of Poly on masonite? No air gettin in there.

Bluto
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Old 8th April 2008, 04:38 PM   #5
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I misunderstood you Bluto - I thought that you wanted to absorb a bit of the reflective back wave and now I get the impression that you want to have a high amount of reflective quality (for sound that is) and still be able to cover it with a grill cloth material. Yet the grill cloth material that you want to cover the surface with could be used to control the amount of sound being reflected from the wall. I have to assume that because you are using "speaker grill" cloth that you want to have the wall material reflect as much sound as possible and that the "grill cloth" is there for "looks" and WAF.

How about sprayed on Granite? http://www.culturedmarbleproducts.com/sprayon.htm

I like the hardboard idea - bendable and formable to some degree. The best things to reflect sound are stone and metal. Hmmm perhaps if you formed your hardboard and glued on some aluminum foil and covered that with the grill cloth? You can also glue on some different types of cloth or wallpaper to "dampen" the reflections if needed - and use grill cloth on top of that if you desired.
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Old 8th April 2008, 07:06 PM   #6
Bluto is offline Bluto  United States
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C2 -

You have it.

Waf, the fact that I must cover alterations I made to do in -wall installation , the hard surface for OB reflective qualities and that the grille cloth serves double duty both as decoration and allowing sonic exit for in wall speaks.

I had thought of light gauge galvanized steel as well. I'll have to see what they get for that these days. It really only has to be behind OB , masonite would work for the rest of distance of wall.

I like your other ideas as well. 'Forming' these panels would give a uniformity to it and increase wave guide effect. 'Brilliant' ... like the Guiness commercial. It needn't necessarily be grille cloth either as you state and truthfully I used that so it was understood that those qualities were necessary where CSS drivers exit. In the past I've used burlap and corduroy in lieu of grille cloth and noticed no loss in sound reproduction. Despite needing reflective values for OB I tend to think as you that some 'dampening' a good idea to take sharpness off of sound. I had a friend that used wallpaper as you state, and despite it being some type of vinyl , I was amazed clarity seemed fine. This material is actually only needed in the 5" section driver exits and at terminus - leaves many possibilities open.

Bluto
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Old 8th April 2008, 08:17 PM   #7
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Bluto - a couple of things to consider with your "thin reflector" ..... Drum heads are thin and hard and taunt - and you are creating a form of drum head because your reflector is "thin". Not only will your reflector bounce some sound around - if it is not damped it will add its own sound to things. Assuming that you don't want to add the sound of a tin wash basin emitting Caribbean calypso music (well ..... I donno ...... maybe you like like steel bands) from the galvanized metal baffle then this little toy will need some degree of rigidity to it, and have the rear side and edges "damped" so that they don't create their own sound. To illustrate what I am talking about go grab a large metal pan and drag your finger nail across the bottom surface. You should be able to hear the pan emit a metallic sound. Plus - if you have "curved" or "formed" your baffle to make a waveguide then things can get complex in a hurry - and that may result in a " this sucks" effort. If you are going to go forming some reflectors or waveguides you are for sure going to want to do some prototypes (cardboard) to get a feel for things. Neoprene rubber on the backside of the reflector will help to quite down it's "drum head" effects - just get some old inner tube rubber or an old wet suit and glue on a couple of layers with contact cement. Oh-yeah I remember using some old carpet that had rubber backing on it and it would get things damped pretty good too.
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Old 8th April 2008, 08:28 PM   #8
cuibono is offline cuibono  United States
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Um, drywall (especially painted) is highly reflective, particularly at low frequencies...

1/8" hard board would be very similar.

If you place your low frequency OB driver near the back wall, you will have large reflections from the back of the baffle which will cancel out with the front baffle sound waves, resulting in very quiet/ notched bass response....
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Old 8th April 2008, 09:08 PM   #9
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Bluto - please clear one thing up for me - are the Hawthorne SI's going to be on an OB that is close to the wall and the CSS FR125's in the wall - or are all of the speakers going to be "in wall"? The SI's look pretty deep for such a set-up but I see that you are going IB with the subs so maybe the wall depth isn't a problem for you. If the Hawthorne's are sitting out 3 or 4 feet from the wall then things are different. But that doesn't make any sense if the 125's are "in-wall". Hmmmmm..... are the SI's being used as an "in wall" OB?
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Old 8th April 2008, 11:55 PM   #10
preiter is offline preiter  United States
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I would not use an open baffle configuration if it has to be placed close to a wall.
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