Dual 18 Tapped Horn Design Concept

[Brian Steele]

I just wanted to illustrate as clearly as I could, how Hornresp takes the throat chamber length into account in offset driver simulations, and how the chamber can contribute to the effective overall horn path length.

Thanks David.

If we go back a few posts, (e.g. posts #85 and #92) I think what JAG was trying to suggests that yes, it would increase effective path length, but not as much as if that section of the TH118 we are looking at was actually treated as part of the horn and the path length increased accordingly. In other words we have to "redraw" the path line to go into that additional volume that's trapped between the driver's cone and the internal section to get the correct results in the sim.

I think that topologically it's one and the same thing, which means that if it was sim'd either way the results should be the same, once the wavelengths in question are long compared to the physical layout of that section of the horn.

 

[weltersys]

Did he take a look into them to see if they differed substantially in build to the TH115?

Langston never mentioned internals, but there can't be much difference since the external dimensions are the same, and frequency and phase response would indicate the same path.

The heavier cone, increased Xmax and BL of the 18SW115-4 (or the 18Sound driver) compared to the 15" simply allow more output from the same size package.

 

[CRESCENDO]

Hi Zwiller,

Would this be a 30Hz TH (or are you looking for -6dB@30Hz)?

Regards,

Hi all,

tb46, your sim looks nice and raises a concern I've been meaning to put out there. I noticed, in your above design simulation, that your ~(-3dB) point is approx 5Hz below the driver's Fs.

All, I was under the impression that a system's excursion minima, in a tapped horn at least, should be at or just above the driver's Fs (for balance reasons). I also seem to remember another member stating that they liked to do the opposite in a tapped horn - placing the first excursion dip below driver Fs.

How many of you have experience using tapped horns where the excursion mimima is lower (~5Hz or more) than the driver's Fs? Have you compared it/them to a TH system with the excursion minima at or just above the driver's Fs? Which sounds more balanced? Which had more distortion? Which sounded better to you? Any other comments regarding the above?

 

[sine143]

Tapped horns benefit from a low corner below the drivers fs. It helps reign in the in passband excursion peak

 

[CRESCENDO]

Thanks for your input! Might you have a good example or sources I could read into?

Below is a 30Hz TH model. Excursion minima is 31.40Hz. Black trace is 18SW115-8 (Fs: 32Hz, quite close); Grey trace is 18TBW100-8 (Fs: 35Hz, ~3.6dB higher) - maybe you have a better example, but I'm having trouble relating your statement to this one:

 

[epa]

Hi all,

tb46, your sim looks nice and raises a concern I've been meaning to put out there. I noticed, in your above design simulation, that your ~(-3dB) point is approx 5Hz below the driver's Fs.

All, I was under the impression that a system's excursion minima, in a tapped horn at least, should be at or just above the driver's Fs (for balance reasons). I also seem to remember another member stating that they liked to do the opposite in a tapped horn - placing the first excursion dip below driver Fs.

How many of you have experience using tapped horns where the excursion mimima is lower (~5Hz or more) than the driver's Fs? Have you compared it/them to a TH system with the excursion minima at or just above the driver's Fs? Which sounds more balanced? Which had more distortion? Which sounded better to you? Any other comments regarding the above?

imho ,when a driver is in the horn system,it becomes one system.
when you measure the parametrs in a system you wil see difference.
i recently made some th for a bar with 18sound 15 lw1500(fs35)flat to 30
they sound teriffic with no problems.
excursion minimum was 28hz

 

[djk]

"excursion minimum was 28hz "

Now that sounds like the TH118.

 

[tb46]

Hi CRESCENDO,

Post #143: "...your sim looks nice and raises a concern I've been meaning to put out there. I noticed, in your above design simulation, that your ~(-3dB) point is approx 5Hz below the driver's Fs..."

In the previous simulations in this thread I used the B&C 18TBW100 w/ fs=35Hz. I have gone back to look, I don't think I got the low point in the displacement graphs below 33Hz, and the -3dB points were in the high 30's, nothing close to 30Hz.

I have since started to redraw the speakerplans drawing JAG posted in Post #44 using the B&C 18SW115. I tried to incorporate JAG's sketches of the TH-118. Thanks to Neo Dan's fine work on the Keystone sub I now have a more accurate side view of this driver, including cone position. My first impression is, that the path around the driver (from entry to exit of the "throat chamber") pretty much stays at a relatively even cross-sectional area. I have not found the concentrated time that I need to refine this, and transfer it into AkAbak. Right now I'm at 56 cross-sectional areas, and I think I need to par that down a little.

Regards,

 

[CRESCENDO]

Hi tb46,

Are we speaking about the same simulation? If I'm not mistaken, the post of yours I'm referring to is a 30Hz TH attempt (which interests me), but it doesn't appear to have a -3dB point "in the high 30's" and appears to be very close to 30Hz.

 

[CRESCENDO]

Follow-up

Hi tb46,

This is the input screen of yours I'm referring to (below)

Cheers!

 

[CRESCENDO]

i recently made some th for a bar with 18sound 15 lw1500(fs35)flat to 30
they sound teriffic with no problems.
excursion minimum was 28hz

Hi epa,

Was thinking of emailing you next (my PM box is still full ) Wanted to bounce some ideas off of you. I'll see if I still have your email addy.

Was that TH a symmetrical design or a more conventional style?

Cheers!

 

[tb46]

Post #149/#150

Hi CRESCENDO,

I see, you were looking @ Posts #36/#40. That was an unfinished first stab @ a true 30Hz TH, but at least there was a drawing to go with it, and not just a complete blue sky attempt. It was more to show how big a true 30Hz TH will actually be.

Regards,

 

[CRESCENDO]

Hi tb46,

Yes, those are the ones. Post #36 is the one I initially quoted. Just wanted to briefly touch on the whole Fs vs Fb in a tapped horn situation.

I'd really like to see fruition come of this thread title.
Now, where were we...? Something about a dual 18 tapped something or other

 

[epa]

Hi epa,

Was thinking of emailing you next (my PM box is still full ) Wanted to bounce some ideas off of you. I'll see if I still have your email addy.

Was that TH a symmetrical design or a more conventional style?

Cheers!

they where a special design to fit under stairs and in a closet,with some dimension limmits.
one was simple single fold the other a 4 fold.

 

[tb46]

Hi CRESCENDO,

I think the OP gave up on the dual TH in Post #13.

I don't have a good answer to the fb v. fs question either. Maybe epa or djim?

Normally I would say that you use the simulator to optimize efficiency in the passband, but after the discussion in this thread I'm not so sure anymore.

Have you looked through this thread: http://www.diyaudio.com/forums/subwoofers/262305-faitalpro-15hp1060-vs-3015lf-tapped-horn.html
it ended up with a nice result, and has some interesting cabinet drawings along the way.

Regards,

 

[CRESCENDO]

Hi tb46,

I have not yet. Thanks for linking me!

Wow, 52 pages already. I've got some reading to do tomorrow!

I've also got some measurements to post tomorrow as well. Off to bed early (for me) tonight.

Cheers!


Hi epa,

Great work as always! I will still plan on contacting you soon. Or maybe I'll start a thread and invite you all to come bombard another idea I haven't seen built here yet (I've seen some drawing ideas is all).

Cheers!

 

[SUBduction]

Well, that was a wealth of knowledge!

Here's a pic of my subs so far. I'm doing some work on them before a big gig in June. Enjoy.

http://i.imgur.com/PI44nX4.jpg

 

[stewin]

cool work . how does it sound ??

 

[SUBduction]

Thanks stewin

They sound good. The 4 Cubos are awesome considering the drivers are only $75. Good extension to about 40 Hz. The tapped horns are much better with 18Sound in them versus the Dayton drivers that were previously in them. I'm planning on taking them down to 30Hz, LR48 filter. I still need to do a full scale test. Soon!

I'm 26 so needless to say there is SO much to learn in terms of design and measurement but the passion is there!

 

[chris661]

Butterworth highpass filters are the ones to go for - they have a sharper cutoff corner. You can also get away with 24dB/octave filters - going higher just takes more processing and results in extra group delay/ringing.

Chris