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A friend of mine placed some acoustic foam about 1.5 inches thick on the back of his speakers.Then placed a sheet of MDF 1\2 inch thick on top of that.He then screwed the MDF to the box lightly with the foam wedged between the MDF and rear of box.The foam he used was rather stiff not very soft.The idea is to stop unwanted vibrations/sound coming off box and reflecting into room.If you feel the back of a box when playing some vibrate more than others depending on area and internal bracing and power of drivers.After hearing the difference I am doing all mine especally the subs.I think it is an excellent tweak and not expensive.
dennis
I very best material I have ever used is Blackhole5.It takes care of the standing wave problem and the enclosure resonance problems.
It is better than simply adding addition MDF. Adding more MDF straight to the inside of the enclosure will shift the resonance to a different frequency and in some cases only reduce the resonances slightly. It also begins to reduce the air space in the enclosure.
A cheep fix it is not. We sell it for 48.00 a sheet. It's 27" by 24".
we try to keep 30 to 40 sheets of the stuff on hand. It is also very easy to install ( self adhesive backing )Want a CHEEP solution to enclosure resonances? When you build your boxes build an inner and an outer layer of MDF. Then fill the space between them with sand. This works great for sub-woofers. However it does not address standing wave problems. For that go for some open cell foam.
Danny Richie
GR Research
is a very effective way of controlling vibration. I found out about it through talking to an engineer who specialized in acoustics. He used the same basic technic as yours. A sandwich of materials in which the speed of propogation of sound is different for the middle material. Same principle as Dynamat etc. Much more effective than a thicker wall or adding more internal sound absorbing material.
in this case the cabinet requires thick MDF to STOP unwanted vibration
(take the bull by the horn).
Next time do it inside the box with a smaller stiffer piece of MDF or hardwood. Screwed diagonally across a layer of rebond carpet padding.
Æ
If you want to eliminate resonances from the enclosure it is better to use acoustic foam on the inside panels of your speakers. The shape of the foam is important as well, a 2" thick blade or pyramid pattern is best for breaking up the standing wave reflections. Placing a piece of MDF or hardboard on top does nothing to prevent the standing waves from bouncing off parallel surfaces. Instead of placing the foam/board on the back of the speaker, use a Teckna Sonic Vibration Absorber on the rear of each speaker. At about $100 a pair, they're not a major investment and they dissipate vibrational energy from 50Hz-2kHz. The magnets on your drivers should be considered also. Spectra Dynamics makes Magnapads- a tacky polymer pad which sticks to the back of your magnets absorbing and dispersing sound waves reflected from the back panel. Another cheap tweek is tennis racket lead weights- sold in packs of four by Gamma, about $4 at a sporting goods store. They have an adhesive back which allows you to apply them to the speaker baskets damping the internal vibrations from feeding back into the drivers. You combine all these things together and you will be surprised at the detail and soundstaging that was being covered up by resonances in the speaker panels and drivers.
I was told by vibration gury, that the right way to dump any vibration - connect (glue) two layers of same material with non-hardening adgesive. This approach is widely used by rocket designs.Another idea - cover all walls inside of the speaker cabinet with mateial, widely used in car audio to dump vibrations. These are V-Block, Dynamat, etc. These materials do convert vibration into heat and they will definetly reduce resonance reproduction of sound through the walls.
Why not to use extra mdf at the back of the speaker,most speakers use 18mm mdf which is quite thin for most woofer as such you get vibration
There should be no vib.in the first place,in this case what i suggest is to use very thick mdf all around.
Hi everyone,
I guess a sandwich will be more effective, as losses are said to be the greatest between materials with distinct different inner "speeds of sound"
bad English
Philipp
Why is it that no speaker that i know of uses sandwich,regardless of price.
Please forgive my english.Thanks
I wonder if the same effect might be achieved by placing acoustic foam on the wall directly behind the speaker. Saves drilling into the cabinet. Just a thought.
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