In-the-Wall Back Loaded Horns - Page 2 - diyAudio
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Old 30th June 2013, 03:30 AM   #11
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I am not sure if this option has been considered but I found it very interesting...

Square Pegs

Its worth reading the whole thread...

Last edited by thunk303; 30th June 2013 at 03:39 AM. Reason: Clarity
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Old 30th June 2013, 05:30 AM   #12
howardg is offline howardg  United States
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Hi xrk971, thanks for using my parameters in your simulation. Any chance that my extra 30" of length would help load the driver and limit excursion (in place of a greater expansion ratio)? Is there any indication that this is operating as something other than a horn(a TL or other tuned pipe, like most compromised designs apparently do)? Like maybe the peaks and valleys in the amplitude.

I tested a previous prototype with a sweep tone from 20 hz, and it actually sounded pretty smooth, with only slightly up/down noticeable variations in volume through the swept range.

Your drawing is extremely similar in important detail, and overall layout to my in-progress speaker, except that I have built in the 30" of extra length.
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Old 30th June 2013, 10:19 AM   #13
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Simplifying like mad, in essence, the 1d wave equation assumes plane-waves unless otherwise adapted, i.e. that the wavefront is flat. It's (extremely!) useful & functional, but doesn't always cover all aspects of design, since the wavefront technically may be better thought of as an expanding bubble.
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Old 30th June 2013, 11:28 AM   #14
xrk971 is offline xrk971  United States
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Default Add extra 30 inches + restrict terminus

Howard,
Here is sim with 30 inches more - it helps smooth response and gets deeper extension. However, the peak excursion is just pulled to lower frequency. I tried restricting terminus to a 1.30 x 4 in hole and this smooths even more but peak excursion actually worsens. I then tried adding a horn extension to get the final expansion ratio to be similar to Austin with additional 12 inches of exponential exit horn - and this still does not reduce cone excursion. The solution may lie in the chamber and throat more.

First plot is freq response with +30 inches in main lengths, second is corresponding cone excursion.

Third plot is freq response with +30 inches and restricted terminus and corresponding excursion.

Fifth plot is freq response with +30 inches and 140 sq in mouth x 12 in long exponential external horn and corresponding excursion.

I think with stuffing to damp the resonances more like a TL, you may be able to get this to sound pretty good. The cone excursion is an issue still.
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Old 30th June 2013, 11:35 AM   #15
xrk971 is offline xrk971  United States
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Default Swap with Alpair 10.2 driver

If you use the MA Alpair 10.2 driver, the cone displacement is not an issue and you still get lots of bass but the mids and HF are not high enough to keep up with the extensive bass.
Attached Images
File Type: png Wall-BLH-Long-Freq-1m-Alpair10.png (36.2 KB, 15 views)
File Type: png Wall-BLH-Long-Displ-1m-Alpair10.png (25.4 KB, 14 views)
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Old 30th June 2013, 03:43 PM   #16
howardg is offline howardg  United States
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thanks Thunk,

I will need to get back home where you tube will play correctly. And take the time to read the tread check out the ideas about bass versions mentioned.
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Old 30th June 2013, 04:30 PM   #17
howardg is offline howardg  United States
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Thanks again xrk971 for simulating! It would be kinda amazing to end up with truly low bass from these speakers. If they also had good bass transients-wow! Won't have the punch of a large, top-quality, woofer I don't imagine, but small drivers/horns are a different experience.

I notice a dip around 160hz in the graph. I had a similar dip with a back horn I designed/made for the Fostex FE126e. Got rid of the dip by drilling a 1” hole from the comp chamber into the expansion about 50” down a 75” line (drilling the hole: just a hunch arising out of a pervading sense of frustration). Maybe the hole effectively changed the CC volume? Also ended up closing the horn mouth down to about 13 sq in, making the thing into a mass loaded pipe that still had a compression chamber. Won the single driver division in the 2008 PNWAS speaker contest with these speakers. Those “horns” are 32” high, taper from 12” at the top to 17” at the bottom and are 6” deep, with the mouth/port on the side, and driver on the face. The really rock for the size of the driver. I set them up in very large room (30x40', with 20' tall ceiling, powered by a mid 60's Sony 20 watt receiver ) and totally rocked the place----which of course will make me sound like I am exaggerating. I think that the balcony location with the sloping ceiling close above helped with a sort of amphitheater type of situation. Too bad the homeowner became another victim of the recession- he seemed about ready to hire me to make him a cool system for that space.

I also built a 3x deeper version that retained the horn mouth-now firing at the floor- using a FE206e and a SEAS passive radiator on the back side of the CC, facing backwards. Good bass from the PR and the horn! Maybe a PR used like this makes the CC effectively larger. Not sure how it would effect excursion.
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Old 30th June 2013, 04:43 PM   #18
xrk971 is offline xrk971  United States
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Howard,
You are welcome. I am surprised by how deep the bass is with the FE166EN, I think the powerful motor allows it to just womp out the low frequencies given a sufficient horn length to amplify. The cone excursion exceeds the limit, but run at softer levels. Your idea of drilling a hole is actually very good and can be modeled very accurately with Akabak - I had the same idea but to strategically place multiple holes to really flatten the response in a TL. Look at my 'Flute Pipe TL' thread. The Flute Pipe TL Basically, the holes serve as de-Q'ing devices to spoil a particular resonance frequency. I am interested in the speaker you describe that won the competition and rocked the house, do you have photos or drawings of the plan or layout? Sounds very cool.
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Old 30th June 2013, 07:10 PM   #19
howardg is offline howardg  United States
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I will look into my papers and see if I can find the drawings. I was not taking pictures at the time. Was thinking about opening up the cabs at some point soon-like by August, when I clean them up with a nice real-wood wrap. I thought there was a picture on the pnwas site, under Events, 2008 Speaker Contest, but the pdf file doesn't open for me now.
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Old 1st July 2013, 02:37 AM   #20
xrk971 is offline xrk971  United States
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Pdf is a bad link, I can't open it either.
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