Tapped horn design for 18TBW100-4

What size enclosure are you prepared to live with?

Are you looking for a proven design?
 

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Brian, I am looking for a proven design. If the 22.5 in width can be flipped for the height for transport, it should be ok. I sent the measurements to my guitarist to see if they would fit into the gear van. He can build anything, but the TH enclosure that he is running the driver in was optimized for a 12 inch sub originally, and he didn't use the TS parameters to get the design, he just adjusted the baffle board to make the 18 fit. Would this THAM enclosure work with a dsp sub amp built into it? Thanks a bunch ! Glenn.
 
The Keystone TH subwoofer is a proven design, in that it's been built, tested and more than one builder has expressed that they like the results. It does have an unusual shape though, which might not meet your size/shape requirements for the gear van.

The TH18 has similar external dimensions to the DanleySound TH118 and it is also a proven design, based on the parameters I gave above.

I don't think that there's a proven design for a THAM fold using the B&C 18TBW100, but the design techniques have been known for some time now, and in fact more design techniques like cone compensation and semi-inductance are known now than were known back when the TH18 and Keystone were designed. Most of those who used my workbooks to design their own subwoofers to meet their particular requirements have reported successful results, apart from one case where it turned out that the issue was with the driver (the t/s parameters were way off from published).

I have an example of a TH with a THAM type fold for the 18TBW100, to show what the workbooks can do. But there are other folds too that might be a better match, like the SS type fold (which removes the big 180 bend in the last section of the enclosure) or even the Cyclops type of fold, which results in a higher-tuned and more sensitive result in the same-sized enclosure.

So, knowing what driver you've got to work with, the next question is, seeing that this is going into a "gear van", what sort of maximum dimensions (length, width, height) should the subwoofer be?

BTW, I'm surprised that your guitarist actually got an 18" driver to fit into a TH designed for a 12" driver. Usually the internal width of these enclosures is only slightly more than the width of the driver, to ensure that the mouth is as "square" as possible. That TH must have a fairly large mouth...
 
22.5w×28d×38h would be max size. I was wrong in relaying info on the sub. It wasn't for a 12..I confused separate conversations. He did a napkin design off of the baffle dims for the 18, and said that the path length of the horn was 4 feet. What do you think would be the best choice of enclosure? He can build anything if he has a cut list. His complaint with the current setup was that it started to get flabby at 200-220 hz. We're playing classic rock/soul/Motown with guitar/bass/ drums/sax, so deeper than 40 hz extension isn't much of a concern, but fidelity is. Glenn.
 
22.5w×28d×38h would be max size.

If that's for one subwoofer, then it should be very possible to build a good TH for an 18" driver that can fit in that space.

What do you think would be the best choice of enclosure? He can build anything if he has a cut list. His complaint with the current setup was that it started to get flabby at 200-220 hz. We're playing classic rock/soul/Motown with guitar/bass/ drums/sax, so deeper than 40 hz extension isn't much of a concern, but fidelity is. Glenn.

Sounds like you're trying to get the bass that a good "kick-bin" can create :).

Seriously, if you're trying to get an 18" TH to do up 200 Hz well, that's likely not going to be possible. THs are a bit like bandpass devices, in that their operating range will likely be between one to two octaves, not wider. You can get a bit wider with an MLTL design, which will give up a bit of efficiency compared to a TH, but even then 200 Hz might be pushing it. A good vented box (with small vents) might do it as well. However, IMO, if you want to get 200 Hz sounding right, you really should be having a closer look at how your tops are performing, rather than trying to get the subs to cover a frequency range that they're typically not very good at.
 
Ok, maybe the solution to your issue then is to look at at some FLH/kickbin designs then :) .

First of all though, I suggest getting some details on that TH that he modded, so see if he's getting the best results from that B&C driver. Makes no sense building a new one if it shows only minor improvements over the current one that you've got, unless its physical dimensions are not really the best for transportation purposes. If you can provide some details about it, we might be able to use that to create a sim, which can then be used to compare against other sims.
 
In the interim, here's a THAM-style fold for that 18" driver that should work from 40 Hz to 100 Hz, with an Fb around 35 Hz, using the physical dimensions that you provided. Note: I'm NOT suggesting that you build this, at least until other designs are considered. My "issues" with the THAM fold are the large 180 degree bends in the final section of the horn (which can produce response aberrations at higher frequencies, hopefully out of the horn's useful passband - I'll be updating the workbook after Christmas to have it give an estimate of at what frequencies these aberrations might start) and that a high-pressure area (right in front of the driver) is located on an external face of the horn). The SS-type fold does not suffer from these issues.
 

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THAM18 might be worth looking at too. The THAM15s that I built work very well and many others have built the 18" version.
This is the one William is referring to (thanks for mentioning it William).

THAM18

The traditional THAM folding was reworked a bit for the 18" version in order to obtain a bigger aperture and shorter L23 (or L34 depending on sim resolution), this to balance towards higher efficiency and staying with the ~40Hz tuning.
 
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Here's a simple SS-type TH fold for the B&C 18TBW100-4 that should cover the 40 Hz to 100 Hz range, using a box that meets your dimensional requirements. The corresponding sim includes all of the improvements used for current simulations, e.g. PAR instead of CON segments, Cone volume accounted for using Vtc and Atc, and of course semi-inductance taken into consideration. The rolloff at the low end is a bit over-damped, but I've found I preferred the sound of such an alignment to underdamped ones (e.g. peaking at the low end of the passband).
 

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Brian, William, Martinsson..thank you all very much. J should be able to post once he gets approved by the mods. He'll be better able to understand the technical aspects of the options than I could begin to. I greatly appreciate all of the time that you fine gentlemen are giving to help. Happy holidays! Glenn.
 
Note: I'm NOT suggesting that you build this, at least until other designs are considered. My "issues" with the THAM fold are the large 180 degree bends in the final section of the horn (which can produce response aberrations at higher frequencies, hopefully out of the horn's useful passband - I'll be updating the workbook after Christmas to have it give an estimate of at what frequencies these aberrations might start) and that a high-pressure area (right in front of the driver) is located on an external face of the horn). The SS-type fold does not suffer from these issues.

What about the MTH fold?

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