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Old 25th February 2005, 07:03 AM   #1
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Default Cabinet construction tips needed

Hello,

I plan on building the Fostex 208ES enclosure as described on the Fostex website. I'm unfortunately unable to get my hands on birch plywood (I live in Thailand), so I'll stick to MDF.

- Is there a need to apply sealer to the MDF inside the cabinet to ensure long term stability against humidity, bugs, etc?

- If I seal+paint the inside of the horn mouth, will there be any impact on the sound?

- Should I directly solder the internal cables to the drivers' posts, or use clips instead?

Thanks a lot,
Guillaume
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Old 25th February 2005, 05:52 PM   #2
Sherman is offline Sherman  United States
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Default Re: Cabinet construction tips needed

Quote:
Originally posted by guillaume
Hello,

I plan on building the Fostex 208ES enclosure as described on the Fostex website. I'm unfortunately unable to get my hands on birch plywood (I live in Thailand), so I'll stick to MDF.

- Is there a need to apply sealer to the MDF inside the cabinet to ensure long term stability against humidity, bugs, etc?

- If I seal+paint the inside of the horn mouth, will there be any impact on the sound?

- Should I directly solder the internal cables to the drivers' posts, or use clips instead?

Thanks a lot,
Guillaume
Guillaume,
MDF is relatively unaffected by humidity compared to a lot of wood products, but since Thailand is *very* humid it wouldn't hurt to seal the MDF. Don't forget the cut edges as well. I think I would also use a waterproof or water resistant glue. I don't know about bugs attacking it but since it is a wood/paper product I would think it is possible.

It shouldn't affect the sound, the surface of MDF is pretty hard and reflective anyway. If it does cause a problem you could then overpaint with something softer or use damping material.

I would recommend soldering the wires. Clips are nice when experimenting and testing but once you have it ready to go use solder. The clips will oxidize over time (especially with the humidity) and that will affect their ability to conduct the signal.
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Old 26th February 2005, 04:09 AM   #3
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I've heard a number of horn guys recommend not to use MDF for horns. The feedback was that they were too dead sounding.
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Old 26th February 2005, 04:30 AM   #4
GM is offline GM  United States
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Greets!

Yeah, it can suck the life out of the music, but if no-void ply isn't available, then I recommend gluing one or more layers as required to the outside to increase rigidity. A ~1.125" ( ~29mm) thickness of MDF has ~the same MOE of 19mm BB ply. The internal baffles should be OK since they aren't very wide. Due to the thickness, chamfering the backside of the driver mounting hole at >45deg. is required.

GM
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Old 26th February 2005, 05:11 AM   #5
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Quote:
Originally posted by johninCR
I've heard a number of horn guys recommend not to use MDF for horns. The feedback was that they were too dead sounding.
Is this to suggest that the ringing of the horn is an asset? Isn't that sort of like saying that the best speaker enclosure is an acoustic guitar body because it has a nice tone? And, wait, the tone would be better if you left the strings on and the mid driver blew right across them.
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Old 26th February 2005, 08:18 AM   #6
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Quote:
Originally posted by Bill Fitzpatrick


Is this to suggest that the ringing of the horn is an asset? Isn't that sort of like saying that the best speaker enclosure is an acoustic guitar body because it has a nice tone? And, wait, the tone would be better if you left the strings on and the mid driver blew right across them.

That's not what I was suggesting at all, however I would suggest that for horns other than maybe bass horns, the construction material will color the sound and if I was going through the trouble of building a nice horn I definitely would not want it's sound to be the color of MDF.
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Old 26th February 2005, 08:38 AM   #7
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Well, MDF may not be the material of choice but certainly you will admit that dead is the name of the game?
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Old 26th February 2005, 06:28 PM   #8
GM is offline GM  United States
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Quote:
but certainly you will admit that dead is the name of the game?
As stated, only for very high Q systems. For the rest, it's rigidity, ergo 'dead' would only be applicable during the rigor mortis stage. Indeed, a body in rigor is the ideal 'construction', i.e. max mechanical efficiency with a high DF.

GM
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Old 26th February 2005, 06:34 PM   #9
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Semantics. You know what I mean.
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Old 2nd March 2005, 01:40 PM   #10
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I could not get birch ply here too, so I used a commercially available ply which is just a bit more than 3/4" in thickness. Worked well, I think. Finished the cab with several coats of polyutherane. Sanded down and coated again. The cabs have stood up to some very high humidity without any warping or peeling.

Better than any previous cabs we made with MDF.
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