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A 12 inch horn loaded MTM top: 12NDL76 and N314T-8
A 12 inch horn loaded MTM top: 12NDL76 and N314T-8
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Old 6th March 2017, 01:59 AM   #1
msibilia is offline msibilia  United States
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Default A 12 inch horn loaded MTM top: 12NDL76 and N314T-8

I am starting to work on a new PA system. I am replacing my four 18 inch Dayton PA460 subs with eight 15 inch PA385 subs. They are easier to carry since they are smaller, lighter (63 lb individually), and will go about 12 dB louder combined and about 8 Hz deeper (albeit with a lot more amplifier). I will start a separate thread soon when I get outside to make some measurements. Eight of them should still fit in the back of my SUV with the tops and amps.

This thread will be about my new (not built yet) PA tops (mid/high). I was inspired by Peter Morris' DIY Mid High 90's. Peter used the amazing BMS 4594HE two way compression driver and two RCF MB12N351 twelve inch woofers to make a 136 dB capable pole mount speaker. They are a little rich for my blood, with $650 compression drivers and two $290 woofers. Mine are not a poor man's version but more like a middle class version.

I am going to use the same RCF HF950 horn, but with a FaitalPro HF146 and a single B&C 12NDL76 twelve inch in a folded horn. It is considerably less expensive, and considerably lighter (under 30 lb). Before I build this, I wanted to run the concept by some of people with more experience than me. The mid/bass will go from about 120 Hz up to 1100 or 1200 Hz. In my modelling with Hornresp, it is hard to get the horn to go that high.

My concept is to use the port and back chamber resonances to extend the upper end of the mid response. It is sort of a combination of a front loaded folded horn and a rear loaded transmission line cabinet with combined output. I split the horn and ports vertically the way Peter did to get the horizontal and vertical directivity of the mids to match more closely the 90H x 50V degree directivity of the compression horn. It is going to need a little boost between 700 and 1100 Hz, but is is still at least the same output as a direct radiator cabinet. The ports should give good cooling to the mid/bass driver and the handle cutouts should allow adequate airflow to cool the compression driver.

It is a bit of a goofy looking cabinet with the high horn and ports projecting forward. I kept the offset between the ports and the high horn small since they interact in the crossover region. The folded horn mid is 6 or 7 inches behind the horn, but I don't believe the horizontal directivity will be too bad since the folded horn output starts to fall off around 700 Hz. Each cabinet should be capable of about 130 dB/1m continuous which seems like it should match up pretty well with the 140 dB/1m capable subs.

The high horn chamber will mount to the cabinet with screws and gaskets to be removable so that the 12 inch is accessible from the front of the cabinet and is replaceable.

So, does this have a chance of working?

Marc
Attached Images
File Type: png PA top.PNG (10.0 KB, 793 views)
File Type: png Hornresp PA top input.png (11.7 KB, 774 views)
File Type: png Hornresp PA top schematic.png (11.2 KB, 767 views)
File Type: png Hornresp PA top output.png (19.5 KB, 768 views)
File Type: png Hornresp PA top out horn.png (10.4 KB, 758 views)
File Type: png Hornresp PA top out port.png (10.6 KB, 102 views)
File Type: png Hornresp PA top offset.png (4.5 KB, 113 views)

Last edited by msibilia; 6th March 2017 at 02:01 AM.
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Old 14th March 2017, 10:13 PM   #2
msibilia is offline msibilia  United States
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A bit of progress, a HF horn change and a couple of corrections.

I switched to an RCF HF94 horn since it is shorter and should still work well because the mid-bass goes up to 1000 Hz. It makes the cabinet smaller and pack better.

I changed the sim to 4 pi (full space) instead of 2 pi (half space), so the output should be more realistic.

I started putting together a test box out of a piece of scrap 1/2" plywood sitting in the back yard (next time I will buy a sheet-- warped plywood is a pain). I made a makeshift lathe from a treadmill motor and used a wire brush on a drill as the cutting tool to carve a phase plug from blue polystyrene insulation.

And I made a mistake on the weight. I tried calculating based on the volume from the CAD model, but made a mistake somewhere.

The weight of the test box plus the components comes in at 42 lbs. Not bad, but a lot more than the 26 lbs I was thinking before.
Attached Images
File Type: png Hornresp HF94 top input.png (12.0 KB, 98 views)
File Type: png Hornresp HF94 top output.png (19.6 KB, 103 views)
File Type: jpg PA top test box.jpg (430.1 KB, 210 views)
File Type: jpg PA top test inside.jpg (505.2 KB, 253 views)
File Type: jpg Phase plug lathe.jpg (536.0 KB, 264 views)
File Type: jpg Phase plug.jpg (483.9 KB, 216 views)
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Old 15th March 2017, 12:50 AM   #3
Old Ears is offline Old Ears  United States
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Default I'm following this one

I'm following your progress as I need to build some new tops and your design is intriguing.

Steve
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Old 16th March 2017, 03:52 PM   #4
msibilia is offline msibilia  United States
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I have done a preliminary assembly and first test. I glued the horn and chamber panels to one side panel. I put weatherstripping on the edges of all the panels, put the other side panel on and put 100 lbs of weights on. I don't want to glue on the other side panel until I am satisfied that everythingis working well enough.

Unfortunately, there is snow on the ground outside, so I can't get outside for a reflection free test yet. I did the next best thing I know, which is a moving microphone measuurement at about 1 to 1.5 meters with band limited pink noise, roughly covering the 45 degree lateral and +-20 degree vertical beamwidth of the HF horn. I had a big suckout at 300 to 400 Hz until I put a panel and some insulation in the cavity for the HF driver and horn. The response compares reasonably to the Hornresp model. The levels are pretty low because I was testing at 4:30 AM while my wife was sleeping. The average level was 91 dB at 1/2 m in 1/2 space with 0.141V rms.

Lastly, I need the moderators to change the title of the thread from "A lightweight, high output 12NDL76 and HF146 top" to "A 12 inch horn loaded MTM top: 12NDL76 and N314T-8", since I changed my mind about which HF driver I'll be using and its not as light as I initially thought.

Marc
Attached Images
File Type: png PA top first trials.png (54.5 KB, 229 views)
File Type: jpg 20170316_081452.jpg (879.3 KB, 305 views)

Last edited by msibilia; 16th March 2017 at 04:11 PM. Reason: Request for thread title change
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Old 17th March 2017, 04:34 AM   #5
johnnyjo is offline johnnyjo
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Very interesting. I'm a fan of Peters work. Do you have a photo of the 12-inch mounted inside?
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Old 17th March 2017, 09:19 AM   #6
chris661 is offline chris661  United Kingdom
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Cool!

I keep thinking about going for horn-loaded mids on my PA system, so it'd be 2x10".
How did you find the construction?
Any measurements or impressions of the sound?

Chris
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Old 17th March 2017, 11:00 AM   #7
msibilia is offline msibilia  United States
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Here is a photo with the midbass mounted.

I just ordered the Eminence N314T-8 and the RCF HF94, so I may have some listening impressions by the middle of next week. Initial impression from listening to just the mid and a sub is that it has pretty uniform coverage when crossed at 1000 Hz. Not a lot of change in the sound of pink noise when I move around. It gets pretty flat with a -5 db Q=5 at 480 Hz and +2 dB Q=3.6 at 370 Hz. I am sure I'll be doing more tuning, but that got me in the ballpark

Construction was really easy. For the test box, I didn't even do any angled cuts except jigsawing the side covers. I just used lots of Loctite Premium PL to fill gaps. For the real boxes, there are two cuts at 11 degrees and four cuts at 9.5 degrees. I'll probably just cut everything at 10 degrees. Otherwise everything is square cuts at 12.5" wide. Eventually I'll clean up a drawing, but for now, if you are interested in dimensions, here is the sketch from the CAD model.

I need to make a 1/4" spacer to stand the driver off the back wall a bit. Diaphragm displacement is 3.7 mm max in Hornresp, but I want some margin.

Marc
Attached Images
File Type: jpg PA top w 12.jpg (154.6 KB, 328 views)
File Type: png PA top EQ.png (58.8 KB, 296 views)
File Type: png PA Top HF94 sketch.png (204.1 KB, 240 views)
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Old 22nd March 2017, 01:49 AM   #8
msibilia is offline msibilia  United States
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I was waiting anxiously to get home from work today to pick up my UPS package with my driver and horn. Unfortunately, my supplier packed only the adapter part of the HF94 and not the horn. I'll have to wait until Thursday or Friday now. It's hard to wait!

Marc
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Old 24th March 2017, 06:18 PM   #9
msibilia is offline msibilia  United States
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I got the 90 x 40 RCF horn yesterday. I did a rough cut at tuning last night, and I can say I liked it enough to immediately order the second HF horn before it was snapped up by someone else and out of stock until May. The horn is really nice. After EQ, it works well with the N314T to about 17kHz, and holds essentially constant directivity down to 1000 Hz out to 45 degrees to the side. The speaker sounds really good independent of where I stand. Even the midrange seems to have good pattern control to match up. I'll know more when I get out of the basement. The midrange efficiency once EQ'd flat is about 104dB at 1m at 2.83Vrms averaged pink noise crossed LR24 at 130 Hz and 1000 Hz.

I won't say more until I get some proper outdoor measurements, but I am very encouraged. I will get it outside this weekend, weather permitting, to do some tuning and testing. Dimensions are 13.5" W x 29.5" H x 18.5" D.
Attached Images
File Type: jpg HF94 side.jpg (187.9 KB, 297 views)
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Old 24th March 2017, 07:06 PM   #10
chris661 is offline chris661  United Kingdom
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I have the same horns. Rather nice, not much EQ needed to get something good.
I'd recommend being able to tilt them down if possible, though - 40 degrees vertical is fairly narrow.

Chris
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