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
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 said:
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.
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
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
johninCR said:
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.
Bill Fitzpatrick said:
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.
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.
Better than any previous cabs we made with MDF.
guillaume said:
I would recommend it... MDF will change shape & will suck up moisture quite readily... a couple coats of polyurethane (don't use the water soluable versions) will also stiffen up the panels a little bit -- fiberglass or expoxy resin would do an even better job, but is much more of a pain to use.
dave
Thanks for all the replies.
Additional questions:
1/ What internal cable would you recommend?
2/ The fostex diagram shows some sound absorbent used behind the driver and at the bottom of the enclosure... Do you know what kind would be ok: wool type, lead / blackson, computer packing foam (a friend of mine in Singapore is using that...), etc?
Guillaume
Additional questions:
1/ What internal cable would you recommend?
2/ The fostex diagram shows some sound absorbent used behind the driver and at the bottom of the enclosure... Do you know what kind would be ok: wool type, lead / blackson, computer packing foam (a friend of mine in Singapore is using that...), etc?
Guillaume
Don't worry about wire types. It's a short run for a start. A double run of CAT5 is fine; I've had decent results with it in the past. I usually use a heavy copper zip-cord or mains cable in my projects now for convinience sake. Any and all beat most alleged 'high-end' cables on the test bench that cost an abosolute fortune. Just avoid very thin wire (resistance is too high) or odd construction techniques that push capacitance or inductance through the roof for no discernable reason to those living on planet Earth. Oh; try to avoid silver insulated by teflon as well -the worst triboelectric cobination you're likely to get. Not a major issue in hifi; it's more for microphones, but worth remembering in engineering terms. Solder them to the driver's posts -forget the push on clips; as suggested above, far too much chance for the contacts to corrode over time.
Persoanlly, I wouldn't worry about using 18mm MDF providing it's well sealed -I use it all the time. As a rule, it's more resistant to vibration than any form of ply, which is the whole point after all -you want the cab. to be as dead as possible.
Persoanlly, I wouldn't worry about using 18mm MDF providing it's well sealed -I use it all the time. As a rule, it's more resistant to vibration than any form of ply, which is the whole point after all -you want the cab. to be as dead as possible.
Scottmoose said:
Compared to the wire in the voice coil the resistance of this piece of wire is insignificant... thin wire can sound better. I use a single pr of Cat 5 because it is high purity copper, solid (don't use the stranded stuff), relatively thin, but still fairly easy to work with, and above all, usually free (lots of scraps from network installs)
The Fostex enclousures don't work well in MDF. Use plywood. I've mostly given up on MDF as a speaker building material (even thou it is free -- i know where thre are lots of scraps)
dave
planet10 said:
Agreed 100% that it's pretty insignificant. In fact, most cabling is as far as I'm concerned. (yes, I'm a heretic...
I'll take your word for it that thin wire sounds better -it doesn't measure as well in any test I've run. Bigger is better for me any day with speaker cabling (within reason)! That's just my taste & opinion though; I realise I'm in the minority! I've often used CAT5 myself, for various purposes, and in various configurations, and liked it, though I generally use[d] more than 1 run. I've currently got a 300 foot reel of 12g zip-cord in the garage, which is what I propose to use until I run out. After that, I might go back to good old CAT5 as that's something I can generally pick up for free too! (unlike MDF unfortunately). I've never heard or measured a difference between equally sized and constructed stranded and solid conductors though. I haven't tried out a Fostex Factory horn enclosure in MDF; other than the large BIB box Terry Cain brought to light, which apparantly is a Fostex design from the currently unavailable craft-handbooks. Any reason the horns don't? -I defer to your experience, as I believe you've built quite a few of these things! Knowing Fostex, I could well believe they factored the resonant quality of the box material into their estimation as well as room gain. I really should have thought of that before.
All the best
Scott
Oh, by the way; I finished the 2nd pair of Zigmahornets last week: the drivers are broaken in now, and are producing much music in the study. They're very good for New Age stuff, which I wasn't expecting, as well as Jazz. Brilliant little things, and many thanks once again for posting a decent diagram! The first pair are still a big hit with my friend too. Two very happy users!
S.
My view - not MDF IF YOU CAN HELP IT
If you can't get birch ply try laminating thin sheets of ordinary ply to achieve your desired thickness.
Any OFC wire that is reasonably thick and therefore of low resistance is fine and yes solder them once you think you are done.
I use some super glue over the termination when done to prevent oxidation essentially making it airtight.
If you can't get birch ply try laminating thin sheets of ordinary ply to achieve your desired thickness.
Any OFC wire that is reasonably thick and therefore of low resistance is fine and yes solder them once you think you are done.
I use some super glue over the termination when done to prevent oxidation essentially making it airtight.
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