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Multi-Way Conventional loudspeakers with crossovers

Line Array Corner Horn for any 4" driver
Line Array Corner Horn for any 4" driver
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Old 21st November 2004, 01:03 AM   #1
johninCR is offline johninCR  United States
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Default Line Array Corner Horn for any 4" driver

Chipco issued the challenge so here it is:

A 2 meter tall array of 16 NSB drivers as a front loaded horn. Bill said it couldn't be done but I believe the combined Sd of 800cm is what does the trick. HornResp is showing me 102-105db/w/m from 40hz to 200hz with 8 ohm wiring. That should match well with the array since I don't think the horn will get array projection. If the room makes it too bass heavy just add the optional final flare and move it out of the corner.

Using a corner to form the final horn segment, it's only 16.5cm (6.5") wide at the front, 23cm (9") in the back and only 50cm (20") deep....... but 2 meters (6.5ft) tall. It does need to go in a corner, but using side wall placement will only cost you about 3db between 40 & 80hz. I stayed middle of the road with the rules of thumb for horns and trying different driver and construction variances got the same result. It should work with just about any 4" driver and be forgiving to minor construction variances. Changing the angle of the cab to the side wall has little effect so placement can be used to fine tune the horn's upper cutoff and to suit your listening position.

3 sheets of 3/4" or 18mm ply plus $16 worth of NSB's and whatever you are going to do about the tweets will get you from 40hz on up. It still has over 92db/w/m at 30hz, so with room gain it should have nice extension.

Construction will be pretty simple. Just 7 rectangular pieces each 2 meters long, plus top and bottom caps gives you the basic construction. 27 narrow rib divider/braces would be ideal and might be tedious. I believe rounded corners are unnecessary due to the low 200hz upper cutoff, but if you wanted to, simple 3/4" corner moulding would be sufficient for most of the corners due to the narrow widths of the passages.

I'll attach the Hornresp parameters and response graph if someone tells me how.

If I've lost my mind and completely missed the boat somehow, will someone please throw me a rope.

Below is a drawing done in paint. Sorry I don't have any kind of construction drawing program, so it's not to scale.
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File Type: jpg jarray nsb corner horn array.jpg (84.3 KB, 1010 views)
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Old 21st November 2004, 03:28 AM   #2
bzdang is offline bzdang  Canada
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Hi, I don't know much about horn design but I can advise on ribs. It looks as though each rib could be made up of two or more parts so make a set of templates out of thin hard stuff like masonite and cut out copies on the router table with a template bit.
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Old 21st November 2004, 07:30 AM   #3
johninCR is offline johninCR  United States
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Actually I have the dimensions all calculated for the ribs to be cut from the same plywood. Their all just long skinny triangles easy to rip with the table saw. Those for the 1st and 2nd segments would probably be best cut as one piece, so I don't have open space at the turn. Again easy with the table saw. I need so many because the throat starts as only 324sq cm which with 11 dividers is 12 channels with an 18mm width (easy spacing with scraps) by 150mm high. That's an 8/1 ratio and I think much larger than that is problematic. The termination of segment 2 is a total cross sectional area of 980 cm sq comprised of 12 150mm high channels a hair over 54mm wide, a good ratio. Pairs of channels coming out of segment 2 will flow into single channels using the 5 ribs in section 3. They'll start at 318mm by 55mm, ratio of less than 6/1 and terminate at less than 4/1. The final segment should probably be channeled too, but we'll see how it sounds without it.

With all those effective braces, it should be as solid as a rock. There's no dead spaces to waste volume and with the back not closed, some fudging at the end will be easy. The 2 side panels will go on last, so if something is off a little at the end it will make zero difference unlike a typical box.

I really got lucky how everything just flowed together perfectly from what I had pictured in my head. Once I got the horn length range down to a single wavelength at 200hz, the response gelled in the models almost instantly. At first I was thinking that I needed a much longer horn, but it was unnecessary due to the height of the cab.

Just have to set aside a day to build them. I already have a pair of 12 driver 7" wide hardwood baffles I can use, so no holes to cut, which makes 1 long day realistic. 12 of the B/K 4"ers I have have a +/- 2db from 42-200hz with the same dimension cab, so it's worth a shot.
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Old 21st November 2004, 01:33 PM   #4
chipco3434 is offline chipco3434  United States
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Quote:
Chipco issued the challenge
I'm not smart enough at this stuff to challenge anything! Looks like a GREAT project!
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Old 21st November 2004, 01:37 PM   #5
chipco3434 is offline chipco3434  United States
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...and this could be the final project before she throws me out. At least I can live in these cabinets.
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Old 21st November 2004, 02:50 PM   #6
johninCR is offline johninCR  United States
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Chipco,

Can't live in these. It's only about 14" wide and 20" deep with the optional final segment built on, so it takes up less real estate than a typical floor plant. Using the corner and wall as the final segment, the cab is only 6.5" wide (9" at the back) by 20" deep.
You can sell the wife on the fact that it's smaller than you have now.

I've been thinking that with all that bracing, 1/2" ply will be fine which will cut an inch off of those dimensions. You'll barely be able to fit the drivers.

Probably a strip of thick vinyl or something similar would be a good way to attach it to the wall for stability and to seal the final bend, while leaving the angle somewhat adjustable.
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Old 21st November 2004, 03:28 PM   #7
chipco3434 is offline chipco3434  United States
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John, what would the dimensions be with a double row of 4" drivers? I'm hankering to build upon the McIntosh XRT series.

What is your solution for the HF on these?

As for the wife, she's really quite amenable to all this wackiness.
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Old 21st November 2004, 04:12 PM   #8
johninCR is offline johninCR  United States
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To get down to 40hz, you need the 16 drivers. Whatever the layout, you have to retain the horn length and cross sectional areas through that length. Essentially the volume has to remain the same and if you cut it in half, the cab width would need to double and the distance from the wall would need to double. It would be 40" tall and require approximately 2ft by 2ft of floor space in the corner, since the mouth would need to be 13-15" wide. Still not bad considering $16 of drivers and sensitivity of about 100 from 40hz on up. Each would take less than a sheet of 3/4" ply. You'd give up line array dispersion except in the higher frequencies, so that might affect tonal balance. Without the array affect the 16 drivers won't keep up with the horn, so you'd have to also have to EQ the bass down some.

A lot less divider/braces would be required. Just 3 in the 1st horn segment and 1 in the 2nd and 3rd segments should be sufficient for keeping the channel width/hieght ratio low enough, but I'd go with 5 and 2 to minimize panel resonances.
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Old 21st November 2004, 07:19 PM   #9
pblossom is offline pblossom  United States
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Default Hornresp input parameters and spl chart

Here are the Hornresp input parameters and SPL chart from the data john supplied.
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File Type: jpg 4 in hornresp spl chart.jpg (48.2 KB, 642 views)
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Old 21st November 2004, 07:35 PM   #10
pblossom is offline pblossom  United States
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Default Once more...

Here's the input parameters
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