Dual MCM FLH

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Well, I'm far enough along in my test cabinets, that I thought I'd create a thread for this.

I reformed by dual 55-2421 cabinet to end firing, moved the first horn path to center, instead of offset, and made it out of fresh ply, so it's 'to length.' VERY respectable numbers down to 43hz. No it's not flat to 40. but it's within a half step, so I'm happy.

The numbers aren't bad.. I especially like the very flat 103db through the 50's and 60's, a little dip in the 80's, and then off to the races as you hit low hundred's.

For $50 in drivers and 1.5 sheets of ply.. it's pretty respectable.

Measured C-weighted, corrected to flat, rounded down to nearest .5 db 2.83v / 1M / Drivers in series

HZ DB
40 99.5
43 102
46 102
50 103
53 103
57 103
62 103
66 103.5
71 102
76 101
82 101
88 101
95 102
102 104.5
109 107
117 108.5
126 107
135 105
145 102.5
 

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JBell - What are the physical dimensions of the box?

As a "horn-rookie" it is going to be interesting to see how your sub compares to Patrick's dual 8" MCM sub that he is making over in the "smallest TH-sub thread".

That is, both of you are using the same drivers (dual 8" MCM's) and the rest of us get to learn/see the results. Thanks again for all the sweat and sawdust!

Steve
 
performance numbers are above. cabinet is 21x24x33. They are being installed this week, will let you know how they perform 'in room'

Yes, I refolded to 'end firing' for a couple reasons. First, in this auditorium that they are going in, end firing happens to work better, and second, I wanted to try them with as a base for my tops. (in my pa on the cheap application that I'm working on.)

They can easily convert from end to 'normal' firing.
One interesting thing to note. I goofed up one of them, and didn't transition on the first flare correctly, and got an extra db at 66hz, vs the 2nd one that is basically flat. If you look at the pic above, you'll see what I did wrong... Not sure, but the extra db at 66hz almost seems like a bonus.
 
Got everything in place in my auditorium install. Dual MCM is in an 'upper' tricorner of the room. It took awhile to get the room modes evened out on positioning/aiming into the corner, but I finally got a +-3db throughout the room. I had to aim the sub into the corner at about a 30degree to one wall angle, with enough room to corner, so that sound could come out both sides about evenly.

Basically the room is -10db vs 1meter levels, which means that about 10-12volts is about all I can stand, before metal conduit, etc. starts buzzing like crazy.

That's with one of them... don't think I need to install the 2nd.

A FLH that's flat to 40 (like a TH...) is pretty cool.
 
The numbers above are a single cabinet, drivers in series for 8ohm, outdoors over grass, so very close to 2pi.

Low 120's outdoors at 1M is as far as I've pushed. Indoors, once I get much above 100 at listening position, things start vibrating, so I can't really open it up, without things starting to sound nasty.

Unfortunately, it'd probably take a week to vibration-proof this building, just so I can turn it up a little.
 
jbell said:
Unfortunately, it'd probably take a week to vibration-proof this building, just so I can turn it up a little. [/B]

You'd be surprised how fast an airless spray gun can put one of the various coatings on a large area. Then you crank it up and bury the stubborn spots again. It makes everything(wires, pipes, ducts, structural...) look the same, but still servicable in the future
 
Flip: sorry, I thought I had...
Here's my original test cabinet, and fold. I since increased the length a little to get me flat to 40, as well as reoriented the drivers 90degree, and took the suggestions to put the first horn section centered, instead of offset to the side.. I'll try to dig up some dimensions and pics if you're interested.

BTW, the 8:1 compression, no problems with 8" cones. I've had these cabinets wound up, and no issues, I'm pretty sure the small chiwaneese voice coil will melt down before I have a cone issue.
 

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flipc:
arauco plywood, you can find it at most lowes. It's a 5 equal ply that I was introduced to at the BFM site. Hands down better than anything but baltic in my opinion. HomeDepot does NOT have this.. their cheap china made ply is crap.

I used the 3/4" 7 ply for my big stadium TH project... Now that's some serious ply.

The key to this cabinet is the compression chamber.. change your sims by even half a liter, and things change DRAMATICALLY. (4-5 liters is where things look best)

I think you see what I did by the construction pics, and can reverse engineer from there.

from memory, here's how I assembled.

cut back, attach compression board. (compression board has a 2x4 hole in it) attach first horn path, use PL and screws to connect compression board to horn flare, and cabinet back. Attach 4"x4" ply on top of first flare. Then attach driver baffle. Attach one side, then cover first horn flare, then top. Install board that divides the last 2 flares. (I used a single piece of ply that went the entire length, driver chamber, compression, horn path) Install bracing, and front and last side. If front firing, make front 12" short for opening, if end firing, make front full length. The 'bottom' panel is full size of cabinet, and also seals rear chamber, so it's removable.

I'm sure there are other folding schemes that are more efficient that this.. but I wanted the weight of the driver at the very bottom of the cabinet, and I wanted the driver chamber easily accessible.

let me know if you actually make 'dust on this.
 
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flipc:
arauco plywood, you can find it at most lowes. It's a 5 equal ply that I was introduced to at the BFM site. Hands down better than anything but baltic in my opinion. HomeDepot does NOT have this.. their cheap china made ply is crap.

For my TH-Mini clone and my MCM triple-8 tapped horn, I bought the most expensive plywood that Home Depot has, and it is GARBAGE. Looks awful, doesn't cut as well as what they used to have, and splinters in big chunks.

They had baltic birch a year ago, wish they'd bring it back. I'll check out Lowes next time.
 
Well unfortunately for me I live in Alabama.
No Lowes around this area carries anything other than Georgia Pacific pine based crap.
Except for $50 a sheet oak. I have seen others using the Arauco plywood and it always looks nice. I couldn't imagine buying that at $20 a sheet.
On this last build I used some 13 ply and 9 ply China Birch.
It definitely makes a difference in weight from MDF but it also isn't 100% Birch. There are a few things thrown into it. A few had a layer of something black-ish and hard. At $32 and $38 a sheet. It is allot better than anything I can get elsewhere. My only question now is sound and duration.

Thanks for the input jbell.
I am putting this on my build list. Though I am unsure when i will get to it. I have a dual 12" layout from tb46 and also another single 12 TH to build... my addiction .... :)
 
I imagine these folks can get what you want if they don't actually stock it, so contact them to find out which type/size of the void free plywoods they can get and which local retailer you can place an order from. Both the local Lowes and HD have done it for me through their local distributor for both marine and BB ply. FWIW, the last time I priced 19 mm/13 ply BB it was ~ $61 delivered for the standard 5 ft square panel.

GM
 
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