Jim Bell, others - will this new horn design work? - diyAudio
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Old 15th August 2008, 01:23 AM   #1
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Location: Sydney
Default Jim Bell, others - will this new horn design work?

I am working on a design to incorporate a full range 8 inch driver plus a bass horn, all in the one cabinet. I'm using CNC routing to come up with the internal structure, so there's quite some flexibility in changing the shape.

Folks on the Sydney Stereo Net forum suggest I look at Jim Bell's tapped horn design. So I've drawn this up in the attached PDF doc.

I welcome feedback on this idea, noting I'm not very clued up on all the math and specs....but am a keen explorer!

Also, the Sydney thread is here -

http://www.stereo.net.au/forums/showthread.php?t=8850

Kind regards.
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File Type: pdf horn dual driver v3.pdf (7.8 KB, 115 views)
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Old 15th August 2008, 03:48 AM   #2
jbell is offline jbell  United States
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just plug your numbers into hornresp. Don't know from your drawing what your throat/mouth/horn path length is. hornresp is SCARY accurate..

Your fold style is exactly the same as mine, it's valid.

One thing to keep in mind, in a horn with no sealed rear chamber, there is nothing to limit cone excursion below the horn loading Fc. In my PA sub, I use a 48db/oct High Pass filter at 38hz. A typical plate amp may not have a high pass filter sufficient for your needs.

The only other comment I would have is:
How in the world is a 8" full range driver going to keep up with a 15" TH sub? Most who go FR, use the back side of the FR driver to load into a horn to extend bass response (or use TL) because they are looking for a sound without crossover distortion, etc...


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Old 15th August 2008, 06:00 PM   #3
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CNC routing the tapped horn may be a waste, there is no need to get that fancy with a tapped bass horn. Simple construction techniques will get you by. I did not even use corner reflectors in mine, and I only experienced minimal differences between what was simulated and what was built. Jim's cabinets are much the same, very simple butt-joined construction, and his measurements were also very close to the predictions.

Of course - if you wish to, the curves and resulting cabinet will sure look neat when completed and should not detract from the performance. Do not forget to brace the enclosure, especially the narrower sections of the horn path.

Hornresp simulations are much quicker and easier with the latest version. (THANK YOU DAVID!!!) Find the parameters for your driver, enter them into the software, create your TH (there are MANY examples out there, all discussed at length on this and several other forums).

Be ready, as a typical pro-sound 15 in a decently designed TH will produce 105 dB or more at 1W into 1 pi space (wall loaded) which is about 10dB more than a typical full-range driver, and will reach well into the 30's at these levels. Placing the TH in a corner may add a few more dB, it all depends on the room. Typical bandwidth will be limited to 100 Hz, though some combinations of driver and horn can reach past 200 Hz.
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Old 18th August 2008, 01:08 AM   #4
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OK, thanks guys.

When you say how will the 8-inch FR 'keep up' with the 15-inch, do you mean volume? The application is home only, not a sports statium! Besides, the bass will be running off a separate amp with volume control. I guuess what I'm aiming to do is to be creative by combining the best of two worlds - a nice full ranger, plus a very capable bass....hence me fussing around with CNC routing to get the two applications into one cabinet.

One of the Sydney guys suggest I use as little bass as possible on the full ranger - eg 150Hz/200 and above. To do this, I'd create a sealed section of approx 3 Litres. This then means I can play around with the bass horn/driver/amp to get a solid range of 40Hz to 150/200. I might consider reducing the tapped horn size a little, given the home application. Perhaps a 12-inch driver is better.

Does this general concept work, or am I kidding myself? (Note, I'm not one to give up easily, and I'm prepared to cut some MDF to trial this....)
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Old 18th August 2008, 07:40 AM   #5
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Further to my last post, here's the scaled down drawing. Overall measurements are much more home friendly (1400h x 400w x 700d).

The top cabinet will be sized to 3 litres for the Fostex 206E.

The bass driver is this:

http://www.cannonsound.com/info_pgs/.../C12-300MB.pdf

The amp is this:

http://www.jaycar.com.au/productView...=&SUBCATID=443

My target is 150Hz up for the Fostex, and 50-150Hz for the bass horn.

MDF is out.

I've included the specs, but can somone kindly check what the rolloff and cross over points will be?
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File Type: pdf horn dual driver v4.pdf (31.5 KB, 40 views)
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Old 18th August 2008, 06:13 PM   #6
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Default Give it a shot

Interesting idea, looks like it might work really well. Only issue I see would be delay/phasing issues between the bass TH and the full-range, but with active crossovers and biamplification, you should be able to smooth things out.

With the specs provided, hornresp predicts 105 dB +/- 5 dB @ 2.83V 1 pi from 45 Hz to 300 Hz in the simple conic tapped horn you've drawn, though the predicted response curve gets a little choppy above 150 Hz. I would not cross over any higher than 150 Hz, and you might think about a subsonic filter to save your driver below 30 Hz.

If you want more low-frequency response, that driver also models well (100 dB +5/-0 from 30 Hz-150 Hz) with a longer horn (~3m). Placement of the woofer will be different than you have drawn (a longer throat stub is required to increase the bandwidth). Though the horn is longer, you can decrease the throat and mouth size (throat = 300 cm2, mouth = 1000 cm2), which makes for a smaller enclosure overall. Cone excursion increases, but this should not be an issue at normal listening levels.

That amplifier should be fine. Assuming that it is rated into a 4 ohm load, a single amp will be happy driving both horns in parallel, and 150 watts will certainly shake the walls.

Oh - wait a minute - just saw that you're Australian......

Based on what I've read, it might not be enough bass for you....

You'd better build about 14 more cabinets and and run them with a kilowatt - each....
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