A few years ago, one of Danley's guys said they only used air driven ring-shank nails and TiteBond. Of course, that requires careful cutting or CAD-CAM so there are no gaps. Many of the guys who built LabHorns used West System Epoxy, which is hard stuff to work with. All this was with 13 layer ply, so it might not apply to MDF and OSB.
If the joints are close and clean, TiteBond II is stronger than Ply, OSB, or MDF. When manufacturing these materials, the factory uses a small amount of mould release, to keep the sheets from sticking in the press. This is a wax, which can compromise the bond, no matter what glue you use. A little sandpaper can clean any wax or oil from the glue-line.
The acoustic loads can't be more than a pound per square foot, so if you break your cabinet, it'll be when it falls off the truck.
If the joints are close and clean, TiteBond II is stronger than Ply, OSB, or MDF. When manufacturing these materials, the factory uses a small amount of mould release, to keep the sheets from sticking in the press. This is a wax, which can compromise the bond, no matter what glue you use. A little sandpaper can clean any wax or oil from the glue-line.
The acoustic loads can't be more than a pound per square foot, so if you break your cabinet, it'll be when it falls off the truck.
Thanks for the glue suggestion guys. I've used titebond wood glue with MDF before with excellent results and I'll use it for everything but the "lid". I'd feel better with something that will fill any gaps just in case.
The other idea I had was to line the top of the box and baffles with speaker gasket and screw the lid on.. screws every 8 inches or so. That way I can gain access to the horn if I need to add any additional bracing or hunt down a rattling bit of wire etc? Any reason why this wouldn't work?
Something about sealing up $260 worth of ply without testing it first is a little scary.
The other idea I had was to line the top of the box and baffles with speaker gasket and screw the lid on.. screws every 8 inches or so. That way I can gain access to the horn if I need to add any additional bracing or hunt down a rattling bit of wire etc? Any reason why this wouldn't work?
Something about sealing up $260 worth of ply without testing it first is a little scary.
Foam gaskets work, but are not cheap when you need that much, maybe $20 worth or more to seal a big box.
For testing, you can even lay it open end down on the carpet without sealing it at all. It will sound considerably different than it would with a sealed panel, but it's a quick and easy way to test for rattles.
On one project, I "glued" the "lid" with silicone so I could remove it later. I was able to later remove the "lid" but not without considerable damage to the wood (cheap mdf) from prying and such. I wouldn't recommend trying silicone for this purpose. I am fairly confident though, that silicone could be used instead of glue in a pinch, although I can't imagine in being in THAT much of a rush.
For testing, you can even lay it open end down on the carpet without sealing it at all. It will sound considerably different than it would with a sealed panel, but it's a quick and easy way to test for rattles.
On one project, I "glued" the "lid" with silicone so I could remove it later. I was able to later remove the "lid" but not without considerable damage to the wood (cheap mdf) from prying and such. I wouldn't recommend trying silicone for this purpose. I am fairly confident though, that silicone could be used instead of glue in a pinch, although I can't imagine in being in THAT much of a rush.
Wow - $260???
These must be HUGE huge cabinets!
What sort of ply are you using?
$260 would buy me 8 sheets of the cheap ply I have been using for the prototyping and testing, or 15 sheets of the heavy duty OSB I plan to use for the next round of subs.
I've had generally good results using the thin closed-cell foam weatherstripping tape on access flanges. From experience, I can say that this approach works best when the flange sealing surface is wide and flat, which often compromises the appearance of the final product. Experience (mostly bad) has taught me to include removable access panels to allow for driver replacement in enclosures where the drivers are hidden, I have had to use them (or wished that they were there) after letting the magic smoke out.
just a guy said:
Thanks for the open end down on the carpet tip. Unfortunately my home was built is 1890 and has "undulating" wood floors! If I'm determined enough I might be able to find a flat area large enough and lay down a rug
.I'd need about 737cm (24ft) of gasket which I have left over from a 50ft roll. This stuff should do the job at a reasonable cost, no?
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=260-542
littlemike said:
The box is a double folded TH which is about 133(w)x 82(d) x 50(h). which will take two 4x8ft and one 5x5ft sheet of (void free) BB to build. I bought the ply today and the total cost was a little less than expected - $215.
I really should make a proto out of OSB, but I don't have the time to make two boxes. Most DIY'er here seem pretty satisfied their horns are close to what HR predicted, hopefully mine will be no different... otherwise it'll make a great coffee table, right?
littlemike said:
That or a lovely bonfire....
For $215 I'd expect fireworks.And one last question.
Does the driver need to be flush mounted with the front (inside face) of the baffle? Since it's a doubled folded horn, it's a lot easier to just mount the driver on the back of the baffle, but does this offset S2 by the thickness of the ply (18mm)?
Mount it the easy way.
I've mounted drivers both ways, does not seem to make much difference, though one direction is usually much easier.
I doubt that the 18 mm is that critical. S2 and S4 would not really change that much - the driver hole only adds a small amount of area to S2. If you're really worried - glue/nail the cutout piece opposite the driver - that should mitigate all but the saw or router kerf.
Just make absolutely sure that the mounting hole is clean, the surface is smooth, and the gasket seals well (some well-known high-quality drivers have gaskets with gaps in them that cause leaks).
Oh - and be sure that your t-nuts are installed pointing in the right direction. (not a fun thing to find out...)
I've mounted drivers both ways, does not seem to make much difference, though one direction is usually much easier.
I doubt that the 18 mm is that critical. S2 and S4 would not really change that much - the driver hole only adds a small amount of area to S2. If you're really worried - glue/nail the cutout piece opposite the driver - that should mitigate all but the saw or router kerf.
Just make absolutely sure that the mounting hole is clean, the surface is smooth, and the gasket seals well (some well-known high-quality drivers have gaskets with gaps in them that cause leaks).
Oh - and be sure that your t-nuts are installed pointing in the right direction. (not a fun thing to find out...)
Something that has been whirling about in my mind RE: the Tapped Horns;
Given: this is a Sub horn, used to reinforce the very bottom octaves of the sound spectrum.
Given: to achieve said goal above, horn length of several meters is required.
If it is also given that you were going to use a " plate amp " to drive the horn, and there's a millisecond of sound delay for each aprox. meter of horn.
Here's the Questions:
1. With a 20Hz horn, your going to have 4+ meters of horn folded into your sub, is this much delay going to be audible, and therefore cause integration issues?
2. If the above is audible, and results in integration issues, can a passive line level delay circuit be placed between the " plate amp ", and the mains to alleviate this integration issue? Does such a circuit exist?
3. Am I waaaay out in left field here? is this a nonissue?
John
Given: this is a Sub horn, used to reinforce the very bottom octaves of the sound spectrum.
Given: to achieve said goal above, horn length of several meters is required.
If it is also given that you were going to use a " plate amp " to drive the horn, and there's a millisecond of sound delay for each aprox. meter of horn.
Here's the Questions:
1. With a 20Hz horn, your going to have 4+ meters of horn folded into your sub, is this much delay going to be audible, and therefore cause integration issues?
2. If the above is audible, and results in integration issues, can a passive line level delay circuit be placed between the " plate amp ", and the mains to alleviate this integration issue? Does such a circuit exist?
3. Am I waaaay out in left field here? is this a nonissue?
John
Don Snyder said:
Sorry about the delay in getting back with some pics and impressions. My in-laws and parents were visiting from Australia and everyone was getting quite sick of my time hogging speaker building projects
.Anyway initial impressions are quite good (80hz to 20hz). This TH is replacing two VMPS Larger subwoofers driven by two bridged crown XLS 402D amps. The VMPS subs were supposedly capable of 115db @ 20Hz. Sounds a little optimistic
.As for the TH, the thing that stands out to me is the sound quality. I'm getting cleaner (less woolly) sounding bass than either the VMPS subs or my old B&W Matrix 801 sII speakers. It's almost as if you can count the pressure wave cycles below 30hz. Quite an obvious improvement, not something you have to listen for.
However, as a home theater sub I feel that a driver with more x-max would be nice. The new THX intro (the one with the mushroom) has my B&C 15PS100 coming awfully close to bottoming. I really should add a 16hz high pass filter since I'm running the sub wide open. Don't get me wrong though, it's an amazing HT sub that is more dynamic and solid sounding that the VMPS subs. Ridiculous performance from a single $200 15" driver with 8mm x-max! The down side is of course the huge size.
I'll post more impressions and the horns resp data when I've had more time with the sub, but for now here's a few pics. Aside from the midbass horns which my father inlaw did most of the woodworking on (I just watched and learned) , this is my first DIY project. Criticism and comment welcome.
Attachments
Good question John, something I was going to ask as well. I've got the luxury to be able to delay my sub/mains via my AVP. I ended up trying to get my mains and my TH out of phase to help cancel the 100hz peak that I notice in both the midbass horns and the TH.
At any rate the TH has a backwave that doesn't introduce much of a delay (L34), so if you delay the front wave (actually you'd need to delay the mains, no?) so that it's in phase with the mains, then the backwave would be out.
Sorry I can't be of more help, I'm sure someone who knows what they're talking about will chime in.
At any rate the TH has a backwave that doesn't introduce much of a delay (L34), so if you delay the front wave (actually you'd need to delay the mains, no?) so that it's in phase with the mains, then the backwave would be out.
Sorry I can't be of more help, I'm sure someone who knows what they're talking about will chime in.
mightym said:
Steve71,
Thanks for the kind words. I, for one, am interested in more information on your system. I like the looks of your project. Hornresp data would be enlightening too.
I likes horns! Just don' have the space now....
My own question arose from the desire to use an inexpensive pair of plate amps to drive stereo tapped horns to support small fullrange mains for HT, without resorting to an active multiamp setup.
I'm trying to keep the component count from getting out of hand due to space limitations. I would like to be able to add the delay circuit ( if such can be contrived ) to the mains after the sub amps to time align the signals, so it would probably need a range of adjustment too.
John
Thanks for the kind words. I, for one, am interested in more information on your system. I like the looks of your project. Hornresp data would be enlightening too.
I likes horns! Just don' have the space now....
My own question arose from the desire to use an inexpensive pair of plate amps to drive stereo tapped horns to support small fullrange mains for HT, without resorting to an active multiamp setup.
I'm trying to keep the component count from getting out of hand due to space limitations. I would like to be able to add the delay circuit ( if such can be contrived ) to the mains after the sub amps to time align the signals, so it would probably need a range of adjustment too.
John
Thanks Brett! I'll post up the HR data and FR screens in the next few days. I have a hand drawn drawing that I can take a pic of, but it's just the internal dimensions which doesn't take into account the thickness of the internal baffles. The final build plan is on the bottom of the sub .
You're welcome John! I hear you on the space issue, our HT is in a spare bedroom. No way would my long suffering wife allow these in the living room.
Assuming that you do need to time align a TH, then you could just use your receivers speaker distance configuration, no? You'll loose the stereo bass, but running your receiver without a sub configuration (using the sub out RCA) messes with the Dolby Decoding and you end up with -10db of bass for moives.
. Brett said:
You're welcome John! I hear you on the space issue, our HT is in a spare bedroom. No way would my long suffering wife allow these in the living room.
Assuming that you do need to time align a TH, then you could just use your receivers speaker distance configuration, no? You'll loose the stereo bass, but running your receiver without a sub configuration (using the sub out RCA) messes with the Dolby Decoding and you end up with -10db of bass for moives.
mightym said:
