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cabinet material and back chambers
cabinet material and back chambers
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Old 26th November 2017, 05:54 PM   #1
mashaffer is offline mashaffer  United States
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Default cabinet material and back chambers

A couple of unrelated questions regarding FLHs.

1: 3/4" plywood seems to be the favorite material but I was wondering about using 1/2" MDF so as to take up less of the internal box volume.

2: Are the precise TS parameters of the driver of most concern in the design of the back chamber rather than the horn itself? If so would it be reasonable to make the chamber slightly smaller than you think you will need and tune with a resitive vent rather than making it larger and filling up excess space with wood to tune?
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Old 26th November 2017, 06:21 PM   #2
scottjoplin is offline scottjoplin  Wales
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Hi, I'm a bit confused, a front loaded horn subwoofer is going to be pretty damn large, I don't understand your desire to reduce the size of the chamber by what will amount to a very small percentage of the space it occupies
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Old 26th November 2017, 06:53 PM   #3
mashaffer is offline mashaffer  United States
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Just thinking it might be faster and easier to tune the resonant peak by popping off the vent cover and adjusting the stuffing rather than having to access the entire chamber to secure additional blocks of wood.
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Old 26th November 2017, 09:34 PM   #4
snappyturtle is offline snappyturtle  United States
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1/2" material can be used for smaller designs, so long as it's well braced. I'd lean towards plywood over mdf for weight and strength...mdf in my experience just doesn't hold up well. I have used 1/2" arauco ply for lower power designs using 15" drivers.
as for the chamber, I'd aim larger and fill it before going smaller and trying to correct it via a vent or otherwise. pretty much all flhs will have some sort of access hatch for the driver, so no real extra work.
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Old 30th November 2017, 12:16 AM   #5
GM is offline GM  United States
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Quote:
Originally Posted by mashaffer View Post
A couple of unrelated questions regarding FLHs.

1: 3/4" plywood seems to be the favorite material but I was wondering about using 1/2" MDF so as to take up less of the internal box volume.

2: Are the precise TS parameters of the driver of most concern in the design of the back chamber rather than the horn itself? If so would it be reasonable to make the chamber slightly smaller than you think you will need and tune with a resitive vent rather than making it larger and filling up excess space with wood to tune?
IME, a good rule-of-thumb [ROT] is limit MDF to horns > 500 Hz/0.75", i.e. make sure the panel resonance is at least an octave below the horn's passband since once cut will go up and bracing should be via mass loading to push it back down.

Well, in theory the chamber will be tuned to [Fl*Fh]^0.5, then when coupled to the horn it will mass load [shift] Fb down below the horn's passband, so the more accurate the as built horn is, the more accurate the T/S specs ideally need to be.

IME and what I've seen from some others DIY builds, better overall to go as predicted if the T/S are reasonably accurate since they still tend to be too big plus ~aperiodic will change tuning with loading unless always heated up, so recommend using solid objects to reduce net volume [Vb].

For instance, one well proven 30 - 500 Hz bass horn from the '30s had an impedance peak at ~30 Hz, but the chamber was tuned to ~130 Hz even though the simple math says ~122 Hz.

GM
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Old 3rd December 2017, 07:04 AM   #6
freddi is offline freddi  United States
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cabinet material and back chambers
make a good hornresp model, then keep adjusting back chamber volume until the passband response is good and excursion below the passband minimized. If the chamber is large then you can tune it by reducing volume with rigid foam blocks. 1/2" MDF is awfully weak. 15mm Baltic birch could suffice for a whole horn - if there's enough bracing. I think RCA-Fan uses 15mm BB in a lot of projects.

Last edited by freddi; 3rd December 2017 at 07:06 AM.
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