Dual 18 Tapped Horn Design Concept

[SUBduction]

Hello all,

I've recently taken an interest in tapped horn subs and I wanted to pick the more experienced minds regarding this topic. Last fall I built two cabinets based on the Danley TH118 and now I would like to attempt a dual 18" tapped horn design where both drivers fire into a shared chamber.

I scratched out a doodle of the concept at work one day (please excuse the sloppiness). I am going to be making a more refined version in FreeCAD shortly. The flare rate with be optimized as well. So far my goal with this post is to explore the design concept and get your input on the design, primarily flaws and other important considerations.

I plan to use two 18 Sound 18LW1400 drivers (parallel)

Any comments/advice is always appreciated.

Thanks guys!

 

[SUBduction]

Not sure if the attached file uploaded. Here it is again.

An externally hosted image should be here but it was not working when we last tested it.

http://imgur.com/u4sE0Wa

 

[GM]

Well, due to its high Vas it wants to be up around 1300 L net for an Fs tuning, though with a bit of EQ it can get by with ~519 L net with a 3:1 CR. Still good for 130 dB/1 kW/m/2pi, so not too shabby.

GM

 

[SUBduction]

Thanks GM,

My mind is still back in bass reflex land. How do you effectilytively calculate volume for a tapped horn? Throat to mouth volume?

The total box volume will be about 16' (4x2x2) or 453 liters. Hmmmm so the box should be bigger from what I'm gathering. I'd like to keep those outer dimensions so I can fit the box in my vehicle for transport.

Perhaps another driver with lower vas?

Thanks.

 

[SUBduction]

Thanks GM,

My mind is still back in bass reflex land. How do you effectilytively calculate volume for a tapped horn? Throat to mouth volume?

The total box volume will be about 16' (4x2x2) or 453 liters. Hmmmm so the box should be bigger from what I'm gathering. I'd like to keep those outer dimensions so I can fit the box in my vehicle for transport.

Perhaps another driver with lower vas?

Thanks.

 

[chrapladm]

Why not use the 2400 model 18?

It works well in smaller cabinets.

 

[GM]

Thanks GM,

My mind is still back in bass reflex land. How do you effectilytively calculate volume for a tapped horn? Throat to mouth volume?

The total box volume will be about 16' (4x2x2) or 453 liters. Hmmmm so the box should be bigger from what I'm gathering. I'd like to keep those outer dimensions so I can fit the box in my vehicle for transport.

Perhaps another driver with lower vas?

Thanks.

You're welcome!

Correct for net Vb and + any losses through the bend, divider, bracing.

Correct.

Yes, a lot lower, like at least in half, i.e. the same driver specs except 1/2 Vas = ~346 L net, though of course efficiency/peak SPL drops too, HR predicts ~3.5 dB.

GM

 

[SUBduction]

This is great! I really want to pick the best driver for the box. I'd love to find a balance of SPL and response.

So GM, I'm curious where a net vas of 1300 L is determined. I know I'm missing something here: 18LW1400 vas = 297 L x 2 drivers = 594 L + (?) = 1300 L. I did see the 18LW2400 has a vas that is 1/2 my cabinet size. Would this be more optimal? If not, why?

http://www.eighteensound.it/Portals/0/PDFs/18LW1400.PDF

http://www.eighteensound.it/Portals/0/PDFs/18LW2400.PDF

 

[chrapladm]

What extension are you after?

Your not going to be able to do dual 18 TH get it into a tiny cabinet and have any real spl near 40hz.

The TH18 is a single 18" cabinet and about 320 liters net design. Thats before you build it. So for dual 18's I would look at something like a pair of those cabinets in a singe cabinet. 650l design.

Or look for higher tuned TH's like the SS15 but in18 design.

Your other bet is to build a hybrid cabinet using the 18 LW1400 that you have. Did we establish you have these already?

If you do own these already then build a dual Cubo 18 in a single cabinet. Will be about 48" x 24" x 24" roughly.
https://freespeakerplans.com/plans/14-plans/basscab/11-cubo-18

 

[SUBduction]

Thanks chrapladm,

I like the cubo 15 ext so much I built 4 using the Dayton PA380. Great results for a $75 driver. The Cubo 15 ext has pretty good punch so I'm looking to add extension below 40 Hz, say about 30-40Hz. I'm not opposed to a single driver design If I can get solid performance from it. Cubo sub looks like it will extend into the 30-40 Hz range fairly well. I also know the 18LW1400 was used in the Cubo 18 by the designer... Hmmm, it may not be as original of a design but results are results.

I wonder what kind or extension and SPL I can get hypothetically from 350 L dual tapped horn. I would imagine much more SPL than extension.

Again, Thanks everyone.

 

[djk]

"Any comments/advice is always appreciated."

Buy a forklift.

 

[GM]

So GM, I'm curious where a net vas of 1300 L is determined.

I did see the 18LW2400 has a vas that is 1/2 my cabinet size. Would this be more optimal? If not, why?

As I noted, ~1300 L is required to get a ~flat response with this driver's specs plus the driver wants to 'feel' a low compression ratio [CR] due to its high Vas, so I used 2:1 and frankly, it should ideally be 1:1, but then it would need to be a built in place sub.

Note too that just like with a reflex alignment, a driver's Qt dominates until Vas gets very high like this driver, so to get an even lower net Vb with a lower Vas requires reducing Qt also. Drop the low Vas driver to a 0.24 Qt and the TH is reduced to a ~270 L net simple tapped pipe [TP], so any smaller and you're down into reflex alignment 'country'.

The 18LW2400's Vas is way too high to get down to where you want to be space wise.

GM

 

[SUBduction]

All valid points gents.

So I have relented to a single driver design. The dual tapped horn would not be feasible for my circumstances. I'm highly considering the Cubo Sub or anything in the 350-400L area for transportation and my back's sake.

Desired extension around 30-40 Hz.

Driver size 18" - 21"

What driver would you guys use for this build?

https://www.freespeakerplans.com/plans/14-plans/basscab/6-cubo-sub

Edit: I'm sure there is a thread already out there, but you guys have already taught me a thing or two! I'll search through the forum but I'd love to get your input as well.

Thank you.

 

[Brian Steele]

The TH18 is a single 18" cabinet and about 320 liters net design.

That seems actually quite small for a TH based on an 18" driver. How low does it go? I've been looking at a few designs, and they seem to be 450+ liters for ~30-35 Hz cutoff.

 

[GM]

The TH18 is a single 18" cabinet and about 320 liters net design.

Do you mean DSL's TH118? It appears to be ~320 L net: http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH-118-spec-sheet.jpg

GM

 

[chrapladm]

That seems actually quite small for a TH based on an 18" driver. How low does it go? I've been looking at a few designs, and they seem to be 450+ liters for ~30-35 Hz cutoff.

The Xoc1's TH18 needs a Hpass at 34hz I believe. BUT that could be an option. If wanting a bit more extension build the Keystone sub with your 18. Easier build also.

Maybe your a bit tired Brian but I know you have commented on the TH18 thread.

Do you mean DSL's TH118? It appears to be ~320 L net: http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH-118-spec-sheet.jpg

GM

Well I meant Xoc1's TH18 design which is 318.926 liters in schematic. SO before wood and bracing it is a 319 liter design. Othorn is only 420 also with a 21". But yes the Danley design is the same size as the TH18.

 

[sine143]

Um, the th18 does not need a 34hz hipass. It has a displacement mimima at 34hz. 28hz, 18db/Oct buttersworth has worked great for me, with a bridged macrotech 3600 per 8 ohm 18 nlw 960

 

[Brian Steele]

Do you mean DSL's TH118? It appears to be ~320 L net: http://www.danleysoundlabs.com/danley/wp-content/uploads/2012/04/TH-118-spec-sheet.jpg

GM

The FR and impedance curves for TH118 are very interesting. Notice that the lower dip occurs below 30 Hz? Looks like it may be around 28 Hz or so. and the upper dip occurs around 68 Hz? The response in the passband also slopes down about 5dB before it starts to drop off precipitously. I'll bet that smooths out nicely when that cab is used in multiples. All in a cab that's 100L less than some of the DIY 18" THs, including the one I'm considering to build. This is likely going to push me to redo my design. Building should start in a week or two - it's got to be ready for my birthday .

 

[GM]

IIRC it was either this one or the TH-mini that Tom used to show us how to get a near billiard table flat response with a TH [four stacked IIRC].

GM

 

[Brian Steele]

The FR and impedance curves for TH118 are very interesting. Notice that the lower dip occurs below 30 Hz? Looks like it may be around 28 Hz or so. and the upper dip occurs around 68 Hz? The response in the passband also slopes down about 5dB before it starts to drop off precipitously. I'll bet that smooths out nicely when that cab is used in multiples. All in a cab that's 100L less than some of the DIY 18" THs, including the one I'm considering to build.

Here's a 18" TH in a cab with the same external dimensions as the TH118 (28.5x22x40 inches), using the "SS15" type fold. Problem? The impedance curve of the resulting cab suggests that Fb is too high - the path has to be just over 100cm longer for the minimum points to be a close match. I think I'm going to try to redo the spreadsheet and break the first internal panel (the one in front of the speaker) into two and see if I can insert an "adjustment" for "cone correction", or more correctly "volume" correction right in front of the driver. Once this is done, and the center panel right behind it is lengthened, this should increase the path length, but still it's not going to be an extra 100cm.