BillFitzmaurice.info

Hi fellows,

This is a noob odyssey here: mine! I'm building an Omni15FR with an APT-80 tweeter and 3015LF. I already made several mistakes like a too big and too low hole for the horn. The cab is almost finished (missing access panel) and sounds great in mid-high. this section is louder than my previous 4 Ohms cabinet with the same amp setting (so 1/2 power due to impedance change). The clarity of the sound is amazing. Of course I can't judge the key bass reflex until it's closed...

I had a concern with the glue (PL is not easily available in France), so i used Sika 11FC+ that seems to be good for airtight. Please tell me that i have not screwed it up

I'm wondering about airtight questions. Does the seal of the speakers is only done with tnuts and speakers' gasket ? (i sanded the panel a bit before). For the access panel, i'm not sure to understand how the airthight is done. this must be after the drying of the gasket since we want to remove it after. I tried to make a 2/3mm cylindrical silicone gasket, but i'm guessing that this is a bad idea. Any help ?

Here're some pictures of my work so far :

Certainly even the French will have some product they use between windows and window frames? Something like this:

Nice to see the inside of one of these things for a change. The Omnis are definitely not the prettiest of the BFM cabinet designs -- I'd definitely opt for grilles and probably foam backing -- but I bet it sounds great. A true full-range cab.

People seal them however they need to. Some of the drivers have decent gaskets that do well enough alone. Others use weather stripping. Still others just caulk the thing to the wood. Do what you have to do to get them airtight, but if you do something (semi-)permanent, be very careful with your drivers!

I think where you will (possibly) have the most problem getting a seal is right at the front where you scewed off with your ?jigsaw. The spot I'm talking about is at the top of your bass driver hole, near the uppermost T nut, in the center.

If you can't get enough of your driver gasket covering that particular area, I'm not sure what you will have to do...

By the way, great first build and welcome to the Forum

Thanks for the answers.

I closed it today thanks to Rune's comment. The back is air tight.

When i increase the low frequences, i can hear some little and short cracks & pops. They must be leaks. Most of them are located in the woofer's gasket. I may not have fastened it enough, i was not sure. If it's not a loosen issue, they I bet that you are right, Grant.
The jigsaw mistake is not much important as I could move the woofer few mm out of it, but there's a small gap just behind. If i can't seal it efficiently, i'll have to make a wood gasket (6 to 10 mm would be enough, imho).

I'll see after resolving those if there are others. Maybe a screw in the driver. It will be hard to make tons of tests as neightbours are already complaining

Sir Nickity. Yes I'm also in favor of a grid in front to hide the ugly face.

rainbass wrote:When i increase the low frequences, i can hear some little and short cracks & pops. They must be leaks. Most of them are located in the woofer's gasket. I may not have fastened it enough, i was not sure. If it's not a loosen issue, they I bet that you are right, Grant.

To find your leaks, get a short length of plastic tubing about 6 to 9 mm wide on the inside, run a 30 hz sine wave into the cab at 10 Volts, put one end of the tube in your ear and run the other along the seams. Leaks will produce a distinctive and unmistakable highpitched sound.

If you tighten the speaker screws a little bit at a time, you'll find that you can get a lot more compression on the gasket than you think at first.

A bit of hot glue can plug pinpoint sized gasket leaks pretty nicely. Be sure to get the nozzle close to the gasket or that small bit will turn into a larger amount.

Hello,

Fastening the woofer solved the problem. I made test with the head of my SWR WP 15 (200W with 4 ohms). Very deep and clear tone. I tried also a 500W 4 ohms Trace Elliot head. Better sound but less power despite the 300/350W on a 8 ohms load. I don't understand.

Finaly i went with a Markbass LM Tube and it kicks asses. It's still unfinished, i'll add the carpet later.

Two gigs and great pleasure. I had a bit of distorsion in deep lows on the first one. Maybe it's because of the vibration of the amps on the top of the Omni15. The amps were moving few centimeters on every notes. No problems on the second gig.

All other bassists were kind of surprised by this ugly piece of wood that was so loud and so clear.

A carpet finish will make it look a lot better; most importantly, it's sounding that good!

rainbass wrote: Maybe it's because of the vibration of the amps on the top of the Omni15.

That indicates not enough bracing or too much bass EQ, or both.

thanks Bill. On the second gig, we had an"anti-slide" temporary carpet and a guitar amp. Nothing moved, better sound. Where would you add bracing ? on the top of the horizontal bracer ?

another picture :

I'm not familiar with the O15, but how about the back panel?

What do you mean Greg? The silicone gasket has been removed and replaced as proposed earlier. It's has been closed since, of course.

rainbass wrote:thanks Bill. On the second gig, we had an"anti-slide" temporary carpet and a guitar amp. Nothing moved, better sound. Where would you add bracing ? on the top of the horizontal bracer ?

I can't see in your picture how the top is braced, but if the top is vibrating it needs additional bracing. If you braced it per the Sketchup model it shouldn't vibrate unless you're using way too much bass EQ.

something close to that :



Maybe the connection between bracers only amplify it.

It not huge huge vibration. Just enough to move small object like the 6 pounds markbass amp. It will move far less with carpet on it. Maybe the bad connection to the ground plays its part too.