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Discussion Starter #1

Here is the first of my Cinema Horn series. This model is pretty good sized, at just over 20 cubic feet, but has a manageable footprint of 4 square feet. Dimensions are 29.375" wide, 20" deep, and 60" tall. It cuts out of 2-1/4 4'X8' sheets of 3/4" ply, bracing is strongly recommended based on what I've learned since I designed and built this cabinet. I designed the enclosure to stand as a tower or lay on its side. The driver orientation keeps the cone in a generally vertical plane in these two orientations.




I designed this enclosure for the MFW 15, which is an American-made (Eminence) driver that was used in a ported sub a while back. This is a healthy driver, and in fact, has a larger voice coil than the venerable Dayton DVC.


This is an offset-driver front-loaded horn. This is not a complicated cabinet. Though it is big, it is a simpler build than the Insubnia, there are less pieces. There are 5 internal panels and four external ones, all the same width. Two sides complete the package. That is only 11 boards total.

 

Did I mention no bracing? Well, forget that I said that. A bit more experience building and measuring horns suggests that this one needs some bracing too. That being said - the test mule (pictured here) was not braced, and seemed to do OK. I would suggest bracing as discussed, it actually helps with the cabinet construction.

 

Working alone, I was able to cut all the wood and make the baffle in one evening, then assemble the cabinet the following evening. Final assembly and some sanding and cleanup took me a few more hours before testing today.




Here are the results of today's testing. Thanks to maxmercy and his buddy for dropping by and helping out. It was a lot of fun, we had beautiful weather, enjoyed some excellent beer, and measured a great sub.




Measured with REW 5.0, with a UCA-202 and a Lilmike mic. First sweep was set at a drive level of 2.00 volts into a 4.00 ohm load resistor, each sweep higher is +5 dB from the previous, so the final sweep is 25 dB higher than where we started, or essentially at the limit of my 300 watt amp, and past the thermal limit of the driver. I'm not sure if the compression is the limit of the amp, driver, or both. We limited the start to 20 Hz for the highest level sweep. I was well within the limits of my soundcard and mic at these levels. No mic calibration was used, the soundcard was calibrated via a loopback.


Yeah, it is flat. I measured +/- 3 dB from ~20 Hz to ~100 Hz. This is a front-loaded offset-driver horn, in a groundplane setting.


Though the noise floor was high due to the highways and industrial activities near me, we also did a little THD experiment. I just raised the drive level to compensate.....


Here is 15 Hz. As expected, distortion is pretty high, and SPL is low.




Looks a lot better at 20 Hz. Well below 10 %, and the SPL is 105.9 dB.




Look what happens at 21 Hz, same drive level...3% THD, and 107.6 dB




25 Hz = 4% at 106.7 dB




Back down to 21 Hz, but more power...113 dB, 21 Hz, 5% THD.



Erich can help with drivers, I have a complete set of dimensioned plans and cutlists done already (currently only in 2D - not spiffy like radman12 did with the Anarchy). I also have impedance measurements as well as the model to post. More to come.


Edit:


Here is the impedance and phase plot - nevermind it says SPL - that is a REW thing... As usual, I measured this with my Woofer Tester II, I'm still working on proper test leads for the REW approach.




Here is a comparison. Modeled is red, measured is blue.




Hmmm, I might have a leak yet - that low peak could be a bit higher. I have a couple ideas about where it might be. I'll report back if/when I find anything.


Here is the requested group delay plot:




And the SPL and unwrapped phase:




Edit:


I've attached the model, as well as the sketchup diagrams I used and an optimized cutlist. I am currently working on some assembly instructions


Edit 4-25 - I updated the cutlist to match the instructions I am working on


Edit 4-28 Based on review comments like this:


"The instructions on the F20 are rather concise and easy to understand. If you can't build one from these instructions you might want to get on down to Best Buy and get your HTIB on."


and


"Okay, you suck! Not really, I actually suck. Your directions even have 3d renderings."


I figured it was OK to attach some step by step assembly directions to the post..... Somehow or another - the instructions are a 12-step program....



5-12-2011 Updated Zip with an additional Sketchup showing the flange details, fixed a few typos in the instructions


Edit 11-1-2012:

Since the direct links broke, here is the 5X5 Cutsheet post:

 

http://www.avsforum.com/t/1329971/lilmikes-cinema-f-20/420#post_20501440

 

Edit 11-1-2012:

Bracing discussion starts here if you wish to use it. Again, it appears that direct linking to attachments in different posts seems to be broken, so the post is linked.:

 

http://www.avsforum.com/t/1329971/lilmikes-cinema-f-20/960#post_21160972

 

If you wish to retro-fit bracing into one that is already built, these suggestions should work too, as you can access both ends of each brace by opening the panel, removing the driver, and working through the chamber. All braces are a cut-to-fit item.

 

Edit 6-24-2013

Made clearer recommendations for bracing per LTD02.

 

 

 

 

 

cinef20.txt 0.443359375k . file

 

 

 

 

 

 

 

 

 

 

 

 

 

Cinema F-20 Cutlist by Mike Piechowski.pdf 6.3662109375k . file

 

 

 

 

 

 

 

 

 

 

 

 

 

Cinema F-20.zip 48.2529296875k . file

 

 

 

 

 

 

 

 

 

 

 

 

 

5-12 Cinema F-20 Instructions.zip 397.798828125k . file

 

 

 

 

 

 

 

 

 

 

 

 

 

MFW Specs.pdf 126.7783203125k . file
 

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Pretty cool,


Personally Id like to see a bit of EQ around the 80 range.
 

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good job mike, nice to see all your hard work paying off.
 

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Discussion Starter #13

Quote:
Originally Posted by jleonard711 /forum/post/20329852


Do I see a flatpack in the future for this bad boy?

At over two sheets of 3/4" ply, I doubt it. Shipping costs and logistics will be prohibitive. The finished cabinet is a 2-man lift.


This one is not that hard to cut out and build. The layout really only keys off of four points, and it assembles easily if you do things in the right order.
 

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Discussion Starter #14

Quote:
Originally Posted by notnyt /forum/post/20329830


Looks good, are you going to post measurements so we can recreate? =]


Those should be pretty loud corner loaded =]

Full plans, cutsheets and all details to make your own are coming. I want to make sure I have things clear enough for people to follow along, and I want to get a basic set of assembly instructions done, because if you do things out of order, you get to undo things.....go ahead...ask.....



I will try to get the plans posted tonight.


I ran out of amp before I hit the driver's limits, so a 300 watt amp is a great match. Highpass at 20.
 

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Discussion Starter #17

Quote:
Originally Posted by notnyt /forum/post/20330640


Can you show the group delay and phase from one of those measurements?

I have both, but they're on the laptop. I'll try to get that plotted up tonight, as well as the impedance data.
 

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LM,


I have a quick question on this part of your setup "First sweep was set at a drive level of 2.00 volts into a 4.00 ohm load resistor". Did you set your master volume of your pre-pro at value X and then adjust the "RMS Level db FS" in REW until you reached the 2 volts? Thanks.


James
 
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