There's resonance & there's resonance. You cannot remove panel resonance in any practical cabinet, only shunt it to a region where it's not going to cause problems. The principle behind Dave's cabinets is to raise it significantly above the functional BW of the box, where there is little energy left to excite it. Adding damping beyond what is specified in the design isn't likely to bring any benefits & if done excessively may ultimately start to reverse this trend.
unless the damping scheme / materials can magically transport those vibrations to another fixed point in the time space continuum (you're welcome Jack Harkness fans), all it's likely to do is slow down the rate at which the "absorbed" energy is dissipated - often to the detriment of the music's transient response
that piece of baffle-gab fluff brought to you by the folks at Barrowman Labs
I've often finished exposed surfaces of ports, horn mouths, etc, but I wouldn't worry about sealing inside of plywood cabinets
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Major Respect for the Dr.Who/Torchwood reference, you warmed my heart!
Blast it. I thought black tar was a must in basically every speaker build. Are you telling me it's not that common and that it can even be harmful? How many speakers out of 10 do you see it used in?
The more i read about speaker building, the less i know. Oh well.
excellent point - even if you can't smell it doesn't mean it's not still off-gassing
solvent based lacquer products that are air dried and "cured" in a ventilated spray booth can still take several weeks to completely off-gas
In order, correct, correct (but that doesn't automatically mean that it is), and never thought about it in those terms, but very few in the wideband world at any rate. Don't panic re your own though; I doubt you'll have any issues with using it on those boxes.
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This whole discussion sounds like some of the elaborately contrived scenarios dreamed up by USAF Standardization/Evaluation shops. I spent 25 years riding around in C-130's and reacting to the craziness propagated by HQ. They were trying to outguess Murphy. They would spend hours dreaming up wildly unlikely sequences of failures that might possibly result in an accident. Then they would publish directives that required aircrews to perform some really unreasonable actions.
OT: I have build more than a few speaker cabinets out of MDF and birch plywood without sealing the interior. I have never had a failure, either personal or by a customer.
Why are you applying tar to the interior of your cabinets? Exactly what are you trying to achieve? Insulate the interior from the exterior? Add mass? Seal leaks? What?
If you slap the drivers into the cabinet while the tar is still wet, you might get enough solvent outgassing to cause a problem. Wait a few days and there won't be a problem. Same with lacquer. Freshly lacquered cabinets will stink for about a week. If you are worried about solvents, use shellac. The alcohol with be pretty much outgassed in 24 hours.
Bob
So the big question comes next:
What is the "default" internal treating for full rangers?
At the moment i use Cork + Black tar + Sonofil on the back panel + felt on the back of the magnet.
As with numerous philosophies regarding materials & construction techniques, types of glue etc ad naseum , there really is no absolute correct default for treatment
Personally I use Baltic Birch plywood (generally 15 & 18mm), inter-panel & driver bracing, and line cabinet walls with 1/2" Ultratouch (felted recycled denim) insulation. Additional fill ( Sonofil or generic dacron fiber) varies with individual enclosure design and driver / system tuning.
(it's bigger inside)
Hi Bob, sorry for the delayed reply but i posted my prior message before reading yours.
To seal the cabinet i use a mix of vynil glue and wood powder (what comes off the collector bag of my orbital sander) applied in the corners and junctions.
Black tar was suggested on several italian DIY forums 3 years ago when i made my very first built, at the time i was a complete neophyte (i'm not far from there now either) and i just assumed the info i gathered prior to starting the build was accurate.
The rationale behind adding black tar car damper was to damp vibrations.
Is this without basis? Is it useless?
As far as i know, it's considered pretty standard in all the italian DIY forums but only now i'm starting to realize it's not so standard on diyaudio.com. Between the two, i'm much more inclined to believe the tips posted here rather than there but up to now i saw no harm in adding it.
To sum it up, my "recipe" so far used:
- Birch Plywood - 20/30mm thickness (FE167 BR enclosure used 30, FF85-WK BR enclosure used 20)
- Cork Pads glued to sides and back, to damp vibrations.
- Black Tar Car Damper ("Antirombo" is the commercial italian name), applied with a brush and usually diluted with nitro thinners or laid as-is, to damp vibrations.
- Sonofil or similar material on back panel.
- Felt on the back of the magnet. IIRC, this was suggested here on diyaudio.com to avoid resonance, i think?
- While finishing, i also plaster every junction either using commercial wood paste or with the above mentioned mix of vynil glue and wood powder. This + the powder in the corners from the inside are meant to seal everything air-tight.
- While building the structure, i use wood plugs (glued in place) to bond the wood panels. I'm not skilled enough to create a box without them.
Hope i've been clear enough on my process. Any further tips to improve it are very MUCH welcome. Feel free to debunk every step of the way
karmik:
Unless (poorly) built with materials as thin and resonant as the sheet metal used in cars, the type and degree of vibrations encountered therein are less likely be as significant in a home audio speaker
That's not to say that those materials / treatments aren't highly appropriate to the inhospitable audio environment of a car / truck
Where I'll likely encounter some disagreement from others is in my opinion that the type of speaker cabinets you're describing needn't be fabricated from materials any thicker/massive than, say 15mm - 18mm HDP (high density plywood - eg Baltic Birch or any number of generic / trade names for similar material), and that attempts to control resonances with mass rather than strategic bracing can become an exercise in chasing your tail, with diminishing returns.
A lot of the other practices you describe are just fine
Unless (poorly) built with materials as thin and resonant as the sheet metal used in cars, the type and degree of vibrations encountered therein are less likely be as significant in a home audio speaker
That's not to say that those materials / treatments aren't highly appropriate to the inhospitable audio environment of a car / truck
Where I'll likely encounter some disagreement from others is in my opinion that the type of speaker cabinets you're describing needn't be fabricated from materials any thicker/massive than, say 15mm - 18mm HDP (high density plywood - eg Baltic Birch or any number of generic / trade names for similar material), and that attempts to control resonances with mass rather than strategic bracing can become an exercise in chasing your tail, with diminishing returns.
A lot of the other practices you describe are just fine
30mm plywood for a 167 BR????? And braced at that? I think that this would qualify as overkill.
OK, you use the tar to damp vibrations. On top of the cork. Do this: Tap the sides of you cabinet -- the largest panel between braces. That is the fundamental resonance of the panel. Run up a signal generator or test CD and find out what frequency that is. (If you have the equipment, place a surface mic at that spot and look at the spectrum.) Now ask yourself if that frequency and any higher harmonic are in the operating bandwidth of the cabinet. If not, there is no need to do any further damping. Any movement on the cabinet walls at lower frequencies will be due to the pressure variations in the cabinet and with 30mm(?) walls and at levels that the 167E can produce, thats not going to happen.
As Dave P10 has said many times, adding mass to the walls of a cabinet is usually counterproductive. If one is not careful, the panel resonance can be lowered into the operating bandwidth. Better than cork and tar, 25mm of acoustic fiberglass will damp high frequencies from reaching the cabinet walls and have the added advantage of reducing standing waves and probably reduce tha amount of stuffing needed.
Bob
OK, you use the tar to damp vibrations. On top of the cork. Do this: Tap the sides of you cabinet -- the largest panel between braces. That is the fundamental resonance of the panel. Run up a signal generator or test CD and find out what frequency that is. (If you have the equipment, place a surface mic at that spot and look at the spectrum.) Now ask yourself if that frequency and any higher harmonic are in the operating bandwidth of the cabinet. If not, there is no need to do any further damping. Any movement on the cabinet walls at lower frequencies will be due to the pressure variations in the cabinet and with 30mm(?) walls and at levels that the 167E can produce, thats not going to happen.
As Dave P10 has said many times, adding mass to the walls of a cabinet is usually counterproductive. If one is not careful, the panel resonance can be lowered into the operating bandwidth. Better than cork and tar, 25mm of acoustic fiberglass will damp high frequencies from reaching the cabinet walls and have the added advantage of reducing standing waves and probably reduce tha amount of stuffing needed.
Bob
I'll keep all this in mind. I never used braces tho. And the plywood thickness was chosen mostly due to ease of construction. It's harder to mess up routing if you have to "dive" deeper to do so
Thanks for all the feedback. I don't know when i will have time to build something again but when that will happen, i'll make treasure of this info
Thread bookmarked
EDIT: I realize now the definition "wood plug" is not correct. I still have no idea what's the english word. But here they are:
You make corresponding holes in two wood panels, put the little wood cylinder in between and this way the panels are stuck in places while the glue dries.
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