Lilmike's Cinema F-20 - Page 2

Thanks. I was definitely after easy, and this is the easiest horn I've come up with yet, at least when it comes to something that will do reference levels at 20 Hz in room with a little left in the tank. Though the fold looks simple enough - it isn't a single flare rate, there are actually three separate flare rates there. Sometimes simple isn't.

As far as the name - F= Front Loaded, the 20 is the cabinet volume in cubic feet.

22.5" wide internally looks nice in the model, but is not nearly as material friendly as 18.5" internally. At 18.5" internal width, you can get a side and an internal strip out of each sheet, with next to nothing but sawdust left, then cut the scrap into two of the three remaining pieces required. I cut the last piece out of a 2'X4' handy panel, cause I did not want to carve into another full sheet of ply and I was not driving the truck that day (can't fit a 4X8 in the Jeep). I only have two sheets of 3/4" ply left, and I have plans for those, namely the T-12 .

Got specs for them? I don't think I do.

Model will be posted up in a few.

Edit:

Just looked - nope. The current Tempest X2 works well though. Models and design attached to post 1.

3.04 according to specs, mine was a couple hundredths higher.

Model, sketchup and cutlists, as well as lot more data are attached to post one.

Working on some instructions and plotting up the impedance.

Mild? Maybe.

Inexpensive? Yes. ~1/4 the cost of a Tempest X2, or ~1/2 the cost of your Tempest or the Dayton DVC.

As far as bang for the buck? Remember, it did manage 114 dB at 20 Hz in a groundplane setting, and I ran out of amp.

Thanks to the Google, I've found some specs for your Tempest. It might work in this cabinet, I'll check tonight.

Thanks CZ Eddie. Far better than what I found.

That driver will work fine in this horn. 500 watts should be safe, but it would not be a bad idea to run a 20 Hz highpass.

Amp requirements are pretty modest. 300 watts into 4 ohms is all you need (for each cabinet). Wired in series, you'd want an amp that could deliver 600 watts into an 8-ohm load. Parallel wiring would be a 2 ohm nominal load, and looking at the impedance chart I posted, there are a few ranges where impedance will be below 2 ohms, which may cause issues with some amps.

I'd wire a pair in stereo for 2 4 ohm loads. Much more flexibility this way. As far as an amp, the Behringer A500 would do fine, and has no fan. According to the propaganda, it delivers 300 watts into a 4 ohm load, but a closer look suggests that the real RMS rating for 4 ohm stereo operation is 185 watts. At over 400 watts per channel, the Peavey IPR-1600 would be overkill, but I like overkill. The Crown XLS-1000 delivers 350 watts per channel, and has a built-in limiter, but the rest of the DSP fuctions are of limited value. Any of these amps will need a separate highpass, something like a MiniDSP can do that as well as loads of EQ to correct the room response issues.

Plate amps? There are a few options. I ran the test mule with a BASH 300 and had no problems at all. The Dayton 240 might also be a good option, but I don't have any experience with those. You would probably want one amp per cabinet. Most plate amps will need a filter modification for the highpass. This is usually as simple as swapping a pair of resistors.

Ohhhh, if I had the room.....

Reference levels plus at least 10 dB at a meter, in a 2pi setting, easily 10 dB more than that inside....

All four in one room? You'll break stuff.

The test mule was flexing all the windows on the side of my house visibly while we were doing the distortion measurements. There was 10 dB left in it at that point, and the sub was 4 M away from the house, facing the opposite direction....

You're welcome.

As it looks currently, I'll have 4 designs in my Cinema series, each with a variation or two. I have models and ideas for folds for a large tapped horn with a single 15" driver, and an F3 below 20 Hz, but I don't have a dimensioned fold yet, nor do I have a driver to work with.

Here's the remainder of the Cinema Series (as I see things now):

Cinema F-20 (this thread) with a stretched variant that's in the works. The stretched one (F-24) will play a little lower, but might need a more capable driver.

Cinema T-6 (coming very soon - fold is done, plans are done, multiple suitable drivers in hand, my initial beta was a fail, but the current refold's beta results are great) Tapped horn with an 8" or 10" driver, cabinet is 6 cubic feet, F3 of ~28 Hz, single 4X8 sheet of 1/2" plywood. Widths will vary based on the driver used, 11.75" internally is about the limit for an unbraced cabinet, no point in going wider, the aspect ratio of the throat (width/depth) gets too large IMO.

Cinema T-12 (coming soon, model is done, fold is sketched, scaled plans are started, drivers are in hand and need a proper home) Tapped horn, 12 cubic feet, F3 of 20 Hz, 10" or 12" drivers, two sheets of ply. Widths will also be varied on this one, and it might get a stretch, all of this depends on the results of the beta build.

Cinema T-16 (a little further out, model is done, fold is sketched, but I currently have no suitable drivers to test with, though I am working on that too...)
Tapped Horn, 16 cubic feet, F3 ~17 Hz, 15" drivers, less than 3 4X8 sheets of ply. As with the T-12, widths will be varied on this one, and it might also get a stretch, this all depends on the results.

My design goals for these?
Capable of at least 115 dB in a groundplane setting within 1/2 octave of F3.
No more than a 6 dB drop from 2 octaves above F3 to F3.

Not significantly.

Horn length sets the corner.

Placement and boundary loading might give you a Hz or two, but that is it. Horn length is the variable that drives the bus here.

Lower requires a longer horn. To go from 20 Hz to 10 Hz means doubling the length of the horn. That's the easy part. The hard part is finding a driver that can handle the added demands. There are not any single-driver solutions that I'm aware of.

That being said - I am working on a 1-foot stretch to this cabinet that should get the F3 down a few Hz lower by adding approximately 3 feet to the horn path, but since nothing is free, it will cost a dB or two. The MFW might be able to handle the demands. If not, I know of several more capable drivers that will do just fine.