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 31st January 2013, 04:51 PM #1161 diyAudio Member   Join Date: Oct 2008 Location: Singapore Ah realised I've been doing the calculations wrong. The throat is the opening where the compression chamber connects to the horn right? If that's the case, the formula would be: fh = (c * S_throat) / (2 * pi * Vol_CC) fh = (342m/s * 0.0035m^2) / (2 * 3.142 * 0.00154m^3) fh = 123Hz
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Join Date: Oct 2008
Location: Singapore
I guess it's time for me to sleep, made a mistake in the previous calculation, resultant fh should be 1233Hz.

How bout this for a change?

Tapering the end to close, and making the horn port(mouth?) wider.

Based on the dimensions of 21" x 13" x 3"(deep)

fh = (342m/s * 0.00464m^2) / (2 * 3.142 * 0.00034^3) = 743Hz

hmmm, doesn't seem to work, any suggestions?

Argh... hate the calculations. Guess I will just make a prototype and listen from there.
Attached Images
 FibonacciHorn3.png (27.5 KB, 338 views)

 31st January 2013, 06:25 PM #1163 diyAudio Member     Join Date: Oct 2012 Location: Metro DC area Ravener, According to your drawing in post 1162, the compression chamber would be approximated by a circular chamber of 3.6 in in diam by 3 in deep = 0.50 liters. The throat area I am guessing is about 1.75 in across x 3 in deep = 34 cm^2. (You have a throat that goes to nowhere, which I mistakenly thought led to an output). So fh = (342 m/s * 0.0034 m^2)/(6.284 * 0.0005 m^3) = 370 Hz. 370 Hz is a little on the high side and it means that lots of mid-range will come out of horns and cause phase delay problems with your ears and ruin spatial imaging. You can fix this by expanding the driver chamber volume by adding a sub chamber beneath the main horn connected with a hole, or add raised (hollow) suprabaffle above where you mount driver to boost volume. Alternatively, the easiest fix is to simply clamp down on the throat area by a factor of 0.75x - put a constrictor plate there (1.3 in wide gap). The horn expansion you have is good - it will result in quite a bit of gain in the bass notes. The mouth area/throat area looks approximately 10:1 - so not bad. Last edited by xrk971; 31st January 2013 at 06:50 PM.
 31st January 2013, 07:16 PM #1164 diyAudio Member   Join Date: Oct 2008 Location: Singapore Good to hear, I will adjust accordingly and build using this then... Time for me to get some sleep, hopefully I can wake up early enough to go source for materials, and hopefully they are as cheap here as in the states...
 1st February 2013, 01:18 AM #1165 diyAudio Member     Join Date: Feb 2008 More foam-core wackiness: IG
 1st February 2013, 02:32 AM #1166 diyAudio Member     Join Date: Oct 2012 Location: Metro DC area IG, You beat me to it. Nice work I have been thinking about doing a front horn but in 8 segments and curving it. I have been looking at Tractrix profiles and such but haven't gotten to the point of cutting foam yet. I made a mock up in plain paper just to see if the segments bend and curve the way I intended. How does it sound?
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Join Date: Feb 2008
Quote:
 Originally Posted by xrk971 IG, You beat me to it. Nice work I have been thinking about doing a front horn but in 8 segments and curving it. I have been looking at Tractrix profiles and such but haven't gotten to the point of cutting foam yet. I made a mock up in plain paper just to see if the segments bend and curve the way I intended. How does it sound?
Not too bad. The small BLH counters baffle-step pretty well and upper-bass is even hot enough on certain material that I wanted to try a small front horn to lift midrange a bit. I just threw it together with no calculations, came out ~40°, a bit too aggressive, did not have enough foamcore left to make a larger mouth. Gives ~6dB of gain from 400Hz to 4kHz, with some peaking on both ends of the BW. Also had to add a super-tweeter because it killed upper treble output.

IG

 1st February 2013, 09:14 AM #1168 diyAudio Member     Join Date: Oct 2012 Location: Metro DC area IG, 6 dB is not too bad. Too bad it impacts the high bandwidth. With properly designed curved horn, can that impact be reduced? Something like tractrix shape is used on HF correct?
 1st February 2013, 09:35 AM #1169 diyAudio Member   Join Date: Oct 2008 Location: Singapore Hot day outside, just got home from shopping. Got myself some 5mm thick foam board, a glue gun, and gorilla glue to seal the top. Shall rest a bit first and start after I had my dinner.
 1st February 2013, 10:49 AM #1170 diyAudio Member   Join Date: Nov 2008 Foam core Open Baffle computer speaker. Below is a rough sketch. Is there an OB 3" driver that would work well in this? Maybe bass down to 100-200hz?

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