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Lilmike's Cinema F-20 - Page 51

post #1501 of 1589
1/10/13 at 9:47am
Thread Starter 
Quote:
Originally Posted by chrapladm View Post

After building a few subs in my time I would have to agree that ply is 10x's better. Working with, smelling, cleaning up and rigidity. But to each there own. I love MDF for mockups but would never buy anything built with it commercially. Secondly I hate working with it any more. Just a pain really.

Mike is this a TH?

Yes, it is a tapped horn.

This one is 20 cubic feet, it is just under 48" tall, 24" wide, and just over 30" deep. Initial measurements suggest that it is -3 dB at 21 Hz, and it averaged over 96 dB 1W /1m from 20 to 80 Hz.

The cabinet is loaded with a 15, it is too small for an 18. I used a Kicker CVX, because I have some. According to the models and the specs I have, there are other driver choices available.

As usual, more info, including plans, measurements, and discussion will be forthcoming. I have a few things to change in the plans to make it an easier build, and since the Internet never forgets, I want to get some better measurements before I post them. I managed to clip my EMM6 with the 50 watt sweep, and clipped it quite badly at 100 watts.

Looks like I have a couple threads to start now.
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post #1502 of 1589
1/10/13 at 4:43pm
As far as MDF vs plywood, i would prefer to use plywood any day over MDF if it were all about comfort.

If im making pro subs for gigging that are gonna get drug around and beat up, plywood all the way.

Panel resonance is a function of panel mass and unbraced panel size. It makes no link to rigidity that im aware. See BBCs paper on resonating panel absorbers and its formula to calculate a panel resonance. AFAIK the panel resonance has more to do with mass.

Im not at all being comtrarian but i think its an important discussion. If MDF does not have a resonant advantage ill never use it again! smile.gif
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post #1503 of 1589
1/10/13 at 4:52pm
Quote:
Originally Posted by lilmike View Post

Yes, it is a tapped horn.

This one is 20 cubic feet, it is just under 48" tall, 24" wide, and just over 30" deep. Initial measurements suggest that it is -3 dB at 21 Hz, and it averaged over 96 dB 1W /1m from 20 to 80 Hz.

The cabinet is loaded with a 15, it is too small for an 18. I used a Kicker CVX, because I have some. According to the models and the specs I have, there are other driver choices available.

As usual, more info, including plans, measurements, and discussion will be forthcoming. I have a few things to change in the plans to make it an easier build, and since the Internet never forgets, I want to get some better measurements before I post them. I managed to clip my EMM6 with the 50 watt sweep, and clipped it quite badly at 100 watts.

Looks like I have a couple threads to start now.
Awesome I have been looking forward to seeing a new horn build with the CVX.
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post #1504 of 1589
1/10/13 at 5:10pm
Thread Starter 
Quote:
Originally Posted by NicksHitachi View Post

As far as MDF vs plywood, i would prefer to use plywood any day over MDF if it were all about comfort.

If im making pro subs for gigging that are gonna get drug around and beat up, plywood all the way.

Panel resonance is a function of panel mass and unbraced panel size. It makes no link to rigidity that im aware. See BBCs paper on resonating panel absorbers and its formula to calculate a panel resonance. AFAIK the panel resonance has more to do with mass.

Im not at all being comtrarian but i think its an important discussion. If MDF does not have a resonant advantage ill never use it again! smile.gif

Panel absorbers aren't quite the same. Near as I can tell, there are a lot of assumptions left out of the math, because with a thin panel (low modulus of elasticity) the actual numbers are not that different. They are designed to be non-structural and vibrate freely. Essentially - it is a weighted membrane, not at all the same as a structural panel where the stiffness of the material is an important consideration in design.

Think of it as a spring and a weight. This is the easiest way I know of to describe a resonant system. Certainly, there is a bit more to it in the real world.
The spring is described by the modulus of elasticity, the weight is the mass of the panel.

Increase mass, the resonant frequency drops. Decrease the spring constant, it drops further.

The data I linked to on the previous page suggest that MDF is weaker (has a lower spring constant) and heavier (has a higher mass) than plywood, making the resonances of an unbraced panel of equivalent size lower in frequency for MDF vs plywood.

To put this another way, the same size cabinet made of MDF will require more bracing (smaller unbraced areas) to achieve the same resonant behavior of a cabinet made of of plywood.
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post #1505 of 1589
1/10/13 at 5:52pm
I
Quote:
Originally Posted by lilmike View Post

Quote:
Originally Posted by NicksHitachi View Post

As far as MDF vs plywood, i would prefer to use plywood any day over MDF if it were all about comfort.

If im making pro subs for gigging that are gonna get drug around and beat up, plywood all the way.

Panel resonance is a function of panel mass and unbraced panel size. It makes no link to rigidity that im aware. See BBCs paper on resonating panel absorbers and its formula to calculate a panel resonance. AFAIK the panel resonance has more to do with mass.

Im not at all being comtrarian but i think its an important discussion. If MDF does not have a resonant advantage ill never use it again! smile.gif

Panel absorbers aren't quite the same. Near as I can tell, there are a lot of assumptions left out of the math, because with a thin panel (low modulus of elasticity) the actual numbers are not that different. They are designed to be non-structural and vibrate freely. Essentially - it is a weighted membrane, not at all the same as a structural panel where the stiffness of the material is an important consideration in design.

Think of it as a spring and a weight. This is the easiest way I know of to describe a resonant system. Certainly, there is a bit more to it in the real world.
The spring is described by the modulus of elasticity, the weight is the mass of the panel.

Increase mass, the resonant frequency drops. Decrease the spring constant, it drops further.

The data I linked to on the previous page suggest that MDF is weaker (has a lower spring constant) and heavier (has a higher mass) than plywood, making the resonances of an unbraced panel of equivalent size lower in frequency for MDF vs plywood.

To put this another way, the same size cabinet made of MDF will require more bracing (smaller unbraced areas) to achieve the same resonant behavior of a cabinet made of of plywood.

i see what your saying.

My questioning is getting at the fact that the resonant frequency of the panel is proportional to the relationship of the stiffness/mass ratio or (k/m). IOW just higher mass or higher stiffness is not the determining factor, its the relationship of its stiffness/mass. Right? Is there a complete equation for panel resonance that you know of? That should answer all questions, right?

All these questions are just that, questions. Its actually a little OT here so i apologize. Maybe tomorrow ill open this discussion in its own thread......

Back to the F20.
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post #1506 of 1589
1/10/13 at 6:11pm
Quote:
Originally Posted by lilmike View Post

Yes, it is a tapped horn.

This one is 20 cubic feet, it is just under 48" tall, 24" wide, and just over 30" deep. Initial measurements suggest that it is -3 dB at 21 Hz, and it averaged over 96 dB 1W /1m from 20 to 80 Hz.

The cabinet is loaded with a 15, it is too small for an 18. I used a Kicker CVX, because I have some. According to the models and the specs I have, there are other driver choices available.

As usual, more info, including plans, measurements, and discussion will be forthcoming. I have a few things to change in the plans to make it an easier build, and since the Internet never forgets, I want to get some better measurements before I post them. I managed to clip my EMM6 with the 50 watt sweep, and clipped it quite badly at 100 watts.

Looks like I have a couple threads to start now.

I don't suppose it would work with the Dayton DVC 15" that PE just sold 10,000 of would it?

I'm just waiting for things to settle to buy some wood. A project is just around the corner for me. smile.gif
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post #1507 of 1589
1/14/13 at 6:09pm
After reading through this thread, getting some guidance from lilmike, and reading through countless other DIY designs I am convinced that the F-20 will be my "intro to speaker DIY" project. Thanks to the designer for giving me the opportunity to learn about the design/build/measurement process firsthand. Now the hard part, approval from the BOSS. I'm thinking dinner/flowers may do the trick, even doing the dishes as a last resort. rolleyes.gif Hope to make some sawdust by the end of next week!
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post #1508 of 1589
1/14/13 at 8:35pm
My Wife loves the F20 becuase even though it is capable of HUGE output the bass is so much cleaner and crisper as opposed to my previous subs boominess which is what she didn't like. So add that to the "sell" points!
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post #1509 of 1589
1/15/13 at 9:08am
Thread Starter 
Quote:
Originally Posted by ovrrdrive View Post

I don't suppose it would work with the Dayton DVC 15" that PE just sold 10,000 of would it?

I'm just waiting for things to settle to buy some wood. A project is just around the corner for me. smile.gif

Not a perfect fit, but it isn't "that" bad.
To be honest, the DVC works better in the F-20 than my new tapped horn, and the F-20 (even fully braced) is an easier build.
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post #1510 of 1589
1/15/13 at 7:38pm
I need to build a grill of some sort to keep critters out of my F-20. There are many ways to do this but I was considering cutting 6 or 7 sections from the scrap 3/4" ply, roundover bit and screw them from the ends (sides) so they are stretching accross the mouth. Could bridge together if needed. Is there concern for blocking too much of the area of the mouth? Should I pick something slimmer such as metal rods? Or if someone made a grill that worked out well feel free to share.
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post #1511 of 1589
1/15/13 at 8:27pm
my cat was curious when the sub first arrived at the house. i cranked it up loud the first time I caught him in the mouth and as far as I know he's never ventured back in there. cool.gif
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post #1512 of 1589
1/16/13 at 7:53am
Quote:
Originally Posted by lilmike View Post

Not a perfect fit, but it isn't "that" bad.
To be honest, the DVC works better in the F-20 than my new tapped horn, and the F-20 (even fully braced) is an easier build.

Having a CVX now, I am excited to read more Mike.
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post #1513 of 1589
1/16/13 at 9:49am
Thread Starter 
I'd suggest something other than full strips of 3/4 ply, that would block a fair bit of the mouth. I'm considering using some welded wire mesh fencing as a cover on my latest to keep the cats out.

Cat tails get really big when the bass hits as they're crawling into the sub. Still - they keep exploring them, something about curiosity comes to mind....
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post #1514 of 1589
1/16/13 at 9:57am
Thread Starter 
Quote:
Originally Posted by chrapladm View Post

Having a CVX now, I am excited to read more Mike.

You will.

I still don't have measurements that I trust as accurate. I've tried 3X now, but conditions have just not been cooperative. It has either rained or been too cold, tis the season, I guess.

Might have to break from the norm and just move forward on this one without doing a full set of proper outdoor groundplane sweeps.

I've been listening to it for a couple days now. It still needs proper crossover and EQ, as well as a lot more power, but as it sits, it is certainly an improvement.

I've purchased more ply for the second build. The current plan is to start that this weekend, I will do a better job documenting this one.
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post #1515 of 1589
1/16/13 at 5:28pm
Yah with the tapered sections of a horn you would hate to have a cat get wedged in there. Welded wie and staples would be super simple, could fold or roll the edges.
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post #1516 of 1589
1/16/13 at 7:54pm
How about some fishing line? high test monofilament, should keep the cat out and be just about acoustically invisible. Positioned a little inside and you might not even see it.
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post #1517 of 1589
1/16/13 at 8:15pm
My cat crawled into it before I got it off of the saw horses. First thing I did was put it in the corner and hit it with heavy bass music... and he just slowly walked towards it in awe, kind of like I did. It doesn't bother him, I'm guessing lower frequencies don't really bug them, or maybe he's just a fellow bass head.
Edited by doodoobutter - 1/16/13 at 8:38pm
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post #1518 of 1589
1/16/13 at 8:18pm
Quote:
Originally Posted by Mr.Tim View Post

IMG_1474.JPG

I recommend installing the extra bracing.




*note: no children were harmed in the making of this F-20

I actually had a problem with the bracing, I measured a cut wrong for the first brace and said **** it. It doesn't vibrate much but... I have to shove it back into the corner about once a week, so I would recommend bracing it.
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post #1519 of 1589
1/18/13 at 3:17am
Quote:
Originally Posted by lilmike View Post

You will.

I still don't have measurements that I trust as accurate. I've tried 3X now, but conditions have just not been cooperative. It has either rained or been too cold, tis the season, I guess.

Might have to break from the norm and just move forward on this one without doing a full set of proper outdoor groundplane sweeps.

I've been listening to it for a couple days now. It still needs proper crossover and EQ, as well as a lot more power, but as it sits, it is certainly an improvement.

I've purchased more ply for the second build. The current plan is to start that this weekend, I will do a better job documenting this one.
New thread or will you keep us posted here?
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post #1520 of 1589
1/18/13 at 9:33am
Thread Starter 
Will start a new thread.
Don't want to cross the streams.....
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post #1521 of 1589
1/21/13 at 2:33pm
What do you guys think of this bracing?



Just using scraps of the 3/4 ply. Overkill?
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post #1522 of 1589
1/21/13 at 2:36pm
Quote:
Originally Posted by cogeng182 View Post

What do you guys think of this bracing?

I like it smile.gif

IMG_1317.JPG
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post #1523 of 1589
1/21/13 at 3:11pm
Thread Starter 
Certainly not overkill.

Looks like a great start.
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post #1524 of 1589
1/21/13 at 5:30pm
Quote:
Originally Posted by lilmike View Post

I'd suggest something other than full strips of 3/4 ply, that would block a fair bit of the mouth. I'm considering using some welded wire mesh fencing as a cover on my latest to keep the cats out.

Cat tails get really big when the bass hits as they're crawling into the sub. Still - they keep exploring them, something about curiosity comes to mind....


I used spandex over mine, not f20's but horns none the less.
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post #1525 of 1589
1/31/13 at 11:25am
Thread Starter 
Looks like Dayton's new Ultimax 15 is a decent option for the F-20.

Still definitely want to highpass things at 20, but the Ultimax will take its full RMS rated power in band within xmax.
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post #1526 of 1589
1/31/13 at 11:32am
Good! We can always use more options/alternatives in the DIY world.
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post #1527 of 1589
1/31/13 at 1:44pm
Quote:
Originally Posted by lilmike View Post

Looks like Dayton's new Ultimax 15 is a decent option for the F-20.

Still definitely want to highpass things at 20, but the Ultimax will take its full RMS rated power in band within xmax.

Would there be a noticeable increase in output?
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post #1528 of 1589
1/31/13 at 3:05pm
Thread Starter 
Only a bit, and it is all due to the increase in power handling, as the Ultimax is not quite as efficient as the MFW.

How much one would actually get remains to be seen, because compression losses will eat up some of the output.

Still - the model says 1M groundplane SPL is north of 120 dB at full power....

All calculations are based on Dayton and PE's published specs - I don't own an Ultimax and have not tested one, so let's hope that things are accurate.
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post #1529 of 1589
2/1/13 at 5:35am
Hi Mike,

That Ultimax looks like a nice driver option. Have you plugged in the SI HT 15? IDK squat about horns but Vas is pretty similar with more excursion cap.

Nicholas
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post #1530 of 1589
2/1/13 at 6:17am
if I remember right the SI was not a good fit.
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