I'm hoping someone can give me a simple, ballpark answer. I'm considering an unusual subs project, making a TH design that is NOT folded into multiple internal channels. Rather, I'm considering building a long, thin box, with only one internal baffle. (My reasons to follow later, if the specs work out.)
I don't yet know how to use Horn response, etc, but just need the length. Let's say to get reasonably flat to 40 Hz, maybe with a touch of EQ but not too much.
Full dimensions would be even more helpful, if possible, but the total length (including the space the driver would be in) is my main need right now.
I need this for both an 18" (most likely the B&C 18SW115) and whatever neo 15" is currently considering best for TH subs.
I've seen some "unfolded" diagrams that look like around 9' for the 18" driver, but I need to be sure, and reasonably accurate.
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Thanks a ton if you can get me this.
I don't yet know how to use Horn response, etc, but just need the length. Let's say to get reasonably flat to 40 Hz, maybe with a touch of EQ but not too much.
Full dimensions would be even more helpful, if possible, but the total length (including the space the driver would be in) is my main need right now.
I need this for both an 18" (most likely the B&C 18SW115) and whatever neo 15" is currently considering best for TH subs.
I've seen some "unfolded" diagrams that look like around 9' for the 18" driver, but I need to be sure, and reasonably accurate.
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Thanks a ton if you can get me this.
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The length of the red line should be approximately 1/4 wavelength of the desired Fb (lowest frequency impedance and excursion minima).
Taking speed of sound at 1130 feet per second, 1130/40(Hz)=28.5'/4=7.06 foot path length.
To be "reasonably flat to 40 Hz", may want to shoot for around 36Hz Fb, closer to 8 foot path length.
As in a bass reflex, the driver size does not affect the TH Fb, but driver TS parameters and cabinet volume will affect the output level at Fb.
Taking speed of sound at 1130 feet per second, 1130/40(Hz)=28.5'/4=7.06 foot path length.
To be "reasonably flat to 40 Hz", may want to shoot for around 36Hz Fb, closer to 8 foot path length.
As in a bass reflex, the driver size does not affect the TH Fb, but driver TS parameters and cabinet volume will affect the output level at Fb.
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Brian, your explanation of taper and Fb has answered a question that had been bugging me- why the DSL TH-115 has a higher Fb than the TH-118, which has nearly an identical (within 3 inch) path length.
The larger driver in the TH-118 constricts the area of the final two horn sections, decreasing the S3/S4 taper slightly compared to the TH-115, evidently enough to lower the Fb several Hz.
Art
The larger driver in the TH-118 constricts the area of the final two horn sections, decreasing the S3/S4 taper slightly compared to the TH-115, evidently enough to lower the Fb several Hz.
Art
I remember having a long argument with JAG about the much lower Fb of the TH118, me telling him that the measurement must be wrong because there's no way that the Fb would be reduced so much by just changing the driver, and he arguing that all sorts of stuff contributed to the lower Fb.
Turned out that the measurement was wrong, LOL. It was suggesting that the Fb for the TH118 was as low as 28 Hz. This impedance measurement of the TH118 looks at lot more like what I'd expect. Fb has gone down a little (I suspect due to the increase at S2 and decrease at S4), but not by much.
Turned out that the measurement was wrong, LOL. It was suggesting that the Fb for the TH118 was as low as 28 Hz. This impedance measurement of the TH118 looks at lot more like what I'd expect. Fb has gone down a little (I suspect due to the increase at S2 and decrease at S4), but not by much.
The DSL TH-118XL looks around 30Hz Fb, but it is 5" taller than the TH-118, adding about 20" to the path length, assuming it has the same fold pattern as the TH-115 and TH-118, with four vertical sections and a horizontal mouth section.
The TH-118XL has another downward "stair step" on the low end response, 101dB at 40Hz compared to the TH-118 at 105dB at 40Hz.
The XL (extra low) extension reduces sensitivity 4-5 dB overall.
The TH-118XL has another downward "stair step" on the low end response, 101dB at 40Hz compared to the TH-118 at 105dB at 40Hz.
The XL (extra low) extension reduces sensitivity 4-5 dB overall.
Thanks, Art ! Yeah I'd definitely like a little buffer room there, to be safe. 8' will be more than fine, if this idea pans out.
I figured the horn length would be the same for either driver, as I remember you saying that a 15" Keystone wouldn't be any shorter than the 18". (IIRC) But of course the 15" driver, in either case, allows for a bit less depth (correct?) which I might want.
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Where I'm going with this:
I'm still trying to find a way to have some reasonably-deep TH horn subs that I can carry around by myself. I've done tons of research on composite materials and honeycomb sheets, but the tech details just don't exist to the point that I'd spend $6-8 grand on an experiment. (and that's for one sub!)
Stiffness is easy, but the big question is STC - can those materials keep the sound energy inside the cabinet. CF with a Nomex core is a top contender, but I still can't find anyone who really knows.
## AND SO, I'm back to an idea a raised here many years ago: Why not build a sub in two pieces, and assemble it at the gig?
The overwhelming consensus was that this would be extremely hard to pull off with a typical TH design, and I agree, so I left it there.
- But then I saw the above diagram. A simple design like that should be fairly easy to "cut in half." But more than that, IMO a long, low sub is exactly what most bar & wedding bands need: There's no question that, for mobile applications where you don't have the option of lengthy experimentation, centered floor subs are by far the best placement. But bands always complain because centered subs block the audience's view.
OK then, make a sub that's 8' across but only 18" or so tall, and also not overly deep. Lovely.
And hopefully it will also be easy to transport in 2 pieces.
You see how a couple of 8' long simple TH with 15' drivers might be perfect for this.
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And suggestions for the absolute best bet in a 15" driver? (It must have a neo magnet, and cost doesn't matter.)
Hmm, I should probably add another 2 questions:
1: Are there any possible downsides to this "one divider" design, vs a more convoluted internal structure? (I would think that if anything, it would be more predictable.)
2: Reading Brian's post, would I be crazy to consider a full TL design, at maybe 10' or 11'? That's getting borderline heavy again, but each half would still be less than an 18" Keystone (I'm pretty sure) and it would still fit on stage.
The downside of a two piece "one divider" TH design would be coupling the two together with a solid air tight connection- if you can figure out how to do that with less weight than a single cabinet, and no path restrictions, go for it. Reducing driver displacement (a 15" rather than 18" is a backwards step.
For individual cabinet weight savings, I think you would be better off with two bass reflex cabinets equaling the TH net volume than this concept.
For individual cabinet weight savings, I think you would be better off with two bass reflex cabinets equaling the TH net volume than this concept.
I hear you, Art, but what I'm after with this design is not more volume than I have now with my current BR cabinets, but rather a different sound.
I just prefer that sort of "less constricted" sound most horns have.
Hopefully in the future there will be lower-cost lightweight materials with good acoustic properties for subs cabinets, but for now I think this idea is worth pursuing.
I just prefer that sort of "less constricted" sound most horns have.
Hopefully in the future there will be lower-cost lightweight materials with good acoustic properties for subs cabinets, but for now I think this idea is worth pursuing.