Lilmike's Cinema F-20 - Page 9

ooooooooooo, after seeing how easy this one is I'm tempted... how does it compare against the THT for output?? and from what I'm seeing it looks like an easier build

Output should be very similar, however the F-20 goes slightly lower. And yes coming from someone who has built both. The F-20 is a much easier build and more user friendly being 3/4" plywood. :-)

I am really wanting to build these as well. The cuts look possible for a NOOB. ERICH H is in the same city as me so I have easy access to purchase some 15's from him. It is the amp and Highpass that get me and how it all works. I don't want to do any thing half and want to get it right, or as "right" as it can be for my first build. I have to do much more research before I ever start cutting wood.

Some basics:
For an amp, you need something with decent power but not crazy power. 150 watts or more when driving a 4 ohm load is probably okay.

Two general types of amps that differ in form factor.

A plate amp is single channel only, and designed to be bolted into a subwoofer enclosure. Here's a generic picture:


Normal chassis is just that - something that can be put into a conventional equipment rack or shelf that might look like this:


These aren't endorsements, just generic pictures! You can also use any regular mono, stereo or multichannel power amp that you might have lying around as long as it has enough power and is happy driving a 4 ohm load.

The high pass filter does just what the name implies. It blocks frequencies below a certian threshold, and passes higher frequencies. With this particular sub, the guru (lilmike) has recommended a 20 Hz high pass filter since there is a lot of distortion below 20Hz. So it's better to just block out those lowest frequencies instead of generating a bunch of distortion which may be audible. The filter is not like a brick wall. There is a gradual rolloff of the blocked frequencies (slope).

MiniDSP is a magic box that is a perfect high pass filter for this application.

DSP=Digital Signal Processor: a fancy name for a microprocessor that is optimized to deal with math needed for signal processing. It goes between the sub output from your receiver and the input to which ever power amp you choose. You can set the filter parameters by plugging in a laptop via USB. Note that the laptop is not required for operation, only programming. Once everything is set up the miniDSP does it's thing.

Since plate amps are designed to run subwoofers, they often have the high pass filter built in. Problem is, it might not be right for this particular sub design. Usually the filter parameters can be modified by changing out some components on the circuit board (resistors and capacitors) but that requires both information and electronics technical skills. But these will work:

Also available are passive filters that just plug into the cable between the receiver and amp.

These aren't generally recommended because they may not have the right filter characteristics and may not be too precise. They come from the car audio world.

Hope this helps.

ok box complete guys, sitting in my garage with NO ONE to help me move it to the theater room. Got the amp setup, however Im having some issues. First they sent me a XLS2000 instead of the 1500 I purchased, second, with my AVR's signal at +10 for the sub channel, im still having to run the gain at about half to get decent bass out of the one sealed MFW I ghetto rigged for the time being...

Does this sound right? or sound off? I guess I was expecting a lot more output with that much power running to a sealed 15, but the beast has yet to be unleashed, i will check back whenever someone shows up to help drag it down

That is a nasty situation right there.

I recommended staying within the limits of the driver and just building multiples.

Finally was able to get a friend over saturday night to help me and WOW, the effort put into the box was more than worth the return. I am truly amazed at the output vs. the sealed mfw cab I was using. This thing is incredible!!! I didnt run it hard, or for very long as I dont want to run tests and all until I get the HPF on it.

In regards to my previous post, I did keep the gains about where I saw the sealed box starting to see stress so I am at about the 2:00 position on the knob in those regards now. While I do have more than enough power now, 600 wpc at 4 ohm, this will match up quite well once the tempest goes in there I could even bridge to get 1500 watts at 8 ohm should I need/want to...

Next up is working on location location locations. Room response is decent in the front of the theater but I am still seeing the best response from way in the back, by the dart board and the corner of the steps going upstairs. While i dont have too many options of where this thing can go, the front row (money) seats are within 5 feet of the mouth of the cab so yea, need to find a new location, perhaps either beside the second row standing up, or in the bar area out of the way...

Once again, this cab is awesome! So glad I jumped in, new build thread coming in for it either tonight or tomorrow night

With the MFW drivers, does anyone know if real world I would get better bass (low end) going with 4 of the drivers in an infinite baffle setup (two sets of two drivers in manifolds facing each other) ? Would I really notice the 5-20hz band that much compared to the horn setup? Kind of on the fence as I could setup a room for IB if I was inclined to go that route and the cost isn't much different once you factor in horn box build costs for two.

Other option would be the F-20 up front and then a sealed 2.5 cu ft MFW in the back? Would the sealed sub be able to get really low end?

mixing those subs could be tricky, the horns will have at least 2x the output per driver above tuning, prob more. Sealed do go lower.

I will confirm this. perhaps the sealed in the back will help even respose somewhat...I plan on playing with this a little tonight if I get the time. Sealed MFW 15 vs this particular build, there is no comparison

Also, Mike, within the first 10 seconds of the first song I listened to, I became addicted to more. already ordered a tempest x-2 this morning, should hopefully arrive by next weekend. Depending on how this makes me feel, and if I can solve placement issues, I will be breaking ground on box #2, with the second tempest going in that, however, I may choose to do the MFW in there just long enough to measure differences in output, real world style.

I few side notes on the directions, I managed to still not do the access panel right, but ended up just making a flange to the exterior of the box instead of inside the access panel. I ended up with using about 1 1/4 tubes of PL so that was nice. I have pictures documenting the layout and panel installation steps should you want to link to them or use the pics in your directions. Might help other newbies like myself

It's hard not to like this sub. Really hits nice and stiff and does a good job with music and a great job with Movies. It definitely is a rock and roll sub as far as music goes. I think I am going to build something ported as soon as I finish the speaker build I just started.

now that my other mfw driver is on the mend I plan on building one of these baddies..

Plan on getting some birch or maple ply this weekend.

Matt

While I wont go into Mike's technical aspects of the box, I will speak for a well sealed MFW 15 in about 2.5 cuft, vs the f-20, across the entire band, the sub/cab displays less distortion, higher output, and all in all, better tonal quality than I can even explain... but only in an apples to apples comparison, one sealed vs one f-20 application comparison that is.

My advice, save the dough on 4,6,8 MFW sealed drivers, build one of these f-20's, find a nice place to put it, and GOPHER IT!!!!!

On another note, the tempest isnt showing getting here until either this weekend or early next week. I was hoping to get it Friday and get another build going for the second. Now that I have the design aspect down, it shouldnt take more than a good Friday night to cut and assemble (a 12 pack of beer, good music, and Im ready)

A good rock n roll type enclosure? I listen to a mix of Metal and underground rap with a few good well recorded recent rap songs mixed in. I will say, I was slightly hesitant about how this design would do with the double kicks I love in my metal tracks and I will say it certainly does NOT dissapoint

how do you think the tempest will improve on that? I think quite well

Mike, how do you feel about standing this thing up with the mouth on the top as opposed to on the floor?

lilmike or anyone else that might know.....I have a version 2 mfw-15 amp that I got for my original mfw-15 as a replacement spare. It is sitting in a box and I don't think I will ever be needing it as I have one of the original first ten mfw-15's that were ever made and is still working like a charm.

I need the upper control panel and combine them together could I jimmy-rig a full working amp in order to use it for an f-20 build?

Would there be any real difference between my original mfw-15 and the f-20 in regard to output/sound quality?

Also does anyone know if there are mfw-15 drivers still available still?

Thanks all,
Aaron

I double boxed about 25 more last weekend if you need any for this project.

that's good to know, although is it relevant to compare 1w spl behavior when most instances at those frequencies the power will be at the thermal rating of the driver? what does the horn do at 12hz 250w and no high pass? where do the lines cross on that comparison? Wouldn't it be making all kinds of bad sounds by then?

All the above are posed as questions, and based on possible misconceptions

This is a strictly theoretical question as my wife would probably put rat poison in my meat loaf if I added a second box.

Having said that, how would you orient the mouth of two horns side by side in the front of the theater.

And on another somewhat off topic question, where would I get some good black velvet to cover these in. Even with them painted flat charcoal black I am getting a reflection off the top of it due to the fact it sits just below the bottom frame of the screen.

And to close... We had a birthday party last night for my daughter and had around 30-40 people over. At one point I had them racked and stacked like sardines last night watching Avatar. The sub left them all slack jawed from the impact it makes in my space. And I learned something. 25 people is about the right amount of acoustical treatment for my space. They are good bass traps.

This is what I used to frame my DIY AT screen.

http://cgi.ebay.com/BLACK-PLUSH-TRIP...30359658222080

Moto

Do they have JoAnn Fabrics down there? They have a Royal--something or other black velvet that I used in my theater.

I used this too, but you might want to go for something a little bit higher quality. for box this size that will probably see a little more wear and tear, check your local fabric shop and see what they got... it may cost a little more, but it should also hold together better than the triple velvet.

well in the three locations I want to try out, the ceiling is at 8 ft. so I have three feet from the top of the mouth to the ceiling. it is also a drop ceiling so who knows what else that entails...

in two of the locations, the riser I have my second row seating on would basically cover the mouth, therefore standing it the other way up might benefit. This would also help to put the access panel with the speaker wire coming through it against the wall (will look much better that way for sure)

Im pretty sure I could fit two across the front with my towers on top, but then the towers would be significantly taller than they should be (Tweeter would be ear level standing instead of sitting)

I think the main problem I am having is the front row is just too close the cab as it is, pulling it away from the front row a bit, and either tucking it in the bar area (which would be a great corner load) or midway in the room beside the second row might help to even response. Obviously I want my seat to sound the best

I have done some placement experimentation in my room and found with the mouth facing into the room rather then corner loading it's less localizable. However, corner loading gave me a 6-7db gain (Once, I build a second for the other corner it will fix the localize issues and balance the room).

I am using a Behringer a500 amp right now and it is sufficient power with just one channel. However, I can clip the amp at exactly -0 (reference level on my receiver) so maybe a little more power would be nice or when I build the second it will give the extra headroom needed. I can peg my RS SPL meter at 126 DB at 21hz test tones. I haven't used any EQ yet and by ear it is pretty darn flat. I am gonna try and get some REW measurements this weekend.

I'm trying to get another MFW from Erich ASAP to start building on a second.

Great design LiLMIKE!

Btw, I've heard both the THT and now the F-20. The tonal quality seems alittle more
solid with the F-20. I dunno if this is due to the design or the room differences or the sub itself. But I can definitely detect a different tone.