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Old 31st January 2013, 04:51 PM   #1161
ravener is offline ravener  Singapore
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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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Old 31st January 2013, 05:59 PM   #1162
ravener is offline ravener  Singapore
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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.
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Old 31st January 2013, 06:25 PM   #1163
xrk971 is offline xrk971  United States
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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.
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Old 31st January 2013, 07:16 PM   #1164
ravener is offline ravener  Singapore
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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...
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Old 1st February 2013, 01:18 AM   #1165
IG81 is offline IG81  Canada
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More foam-core wackiness:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

IG
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Old 1st February 2013, 02:32 AM   #1166
xrk971 is offline xrk971  United States
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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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Old 1st February 2013, 02:59 AM   #1167
IG81 is offline IG81  Canada
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Quote:
Originally Posted by xrk971 View Post
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
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Old 1st February 2013, 09:14 AM   #1168
xrk971 is offline xrk971  United States
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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?
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Old 1st February 2013, 09:35 AM   #1169
ravener is offline ravener  Singapore
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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.
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Old 1st February 2013, 10:49 AM   #1170
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Default 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?

Click the image to open in full size.
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