Finally! Omni 12 Tall Boy build

High power and fidelity from an easy to build cabinet.
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Tom Smit
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Re: Finally! Omni 12 Tall Boy build

#211 Post by Tom Smit »

24w power supply? Might that explain the imbalance of low to highs?

Cyclone deputy?
TomS

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Seth
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Re: Finally! Omni 12 Tall Boy build

#212 Post by Seth »

Mid to woofer needs 0.63ms delay between them. Not sure which.
Screenshot (242).png
Mid to tweeter needs 0.08ms delay between them. Not sure which.
Screenshot (243).png
Might take a little juggling to figure out which driver needs no delay and which needs the most. If the mid is not the baseline that doesn't need any delay, the one that needs the most is actually going to need both of those figures combined, 0.71ms.

It's confusing. We'll work it out when you get there.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Bill Fitzmaurice
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Re: Finally! Omni 12 Tall Boy build

#213 Post by Bill Fitzmaurice »

Less than 2ms is inaudible.

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Seth
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Re: Finally! Omni 12 Tall Boy build

#214 Post by Seth »

Bill, I'm a little confused... 180º out of phase at 2.5kHz is 0.2ms. 1.25ms at 400Hz, also 180º out. Both less than 2ms and both dead cancellations at their respective frequencies. Inaudible?
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Seth
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Re: Finally! Omni 12 Tall Boy build

#215 Post by Seth »

... At about -2dB from 100% summation, I could certainly see anything less than 2ms at a subwoofer crossover point being inaudible.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Bill Fitzmaurice
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Re: Finally! Omni 12 Tall Boy build

#216 Post by Bill Fitzmaurice »

Seth wrote: Sun Feb 19, 2023 9:28 am Bill, I'm a little confused... 180º out of phase at 2.5kHz is 0.2ms. 1.25ms at 400Hz, also 180º out. Both less than 2ms and both dead cancellations at their respective frequencies. Inaudible?
Audible if you have two sources playing the same frequency at 180 degrees apart, which doesn't happen thanks to the crossover. What's of concern with time align is the perceptible arrival time difference of the two sources. At 500-800Hz, where we're most sensitive to it, the minimum detection threshold for the average person is 2 to 3ms.

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Seth
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Re: Finally! Omni 12 Tall Boy build

#217 Post by Seth »

Ah. I'm talking phase alignment, you're talking time alignment. Understood.
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Bill Fitzmaurice
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Re: Finally! Omni 12 Tall Boy build

#218 Post by Bill Fitzmaurice »

They are related. There's a specific procedure to time align the HF horn atop an Altec A7 with the woofer horn. The HF horn polarity is reversed, placing the drivers 180 degrees apart. A 500 or 800Hz tone is played through the system, depending on the crossover. The horn sled is moved forward and backward until a sound meter shows minimum output, indicating perfect time align. The HF horn polarity is then returned to normal.

Bruce Weldy
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Re: Finally! Omni 12 Tall Boy build

#219 Post by Bruce Weldy »

Bill Fitzmaurice wrote: Sun Feb 19, 2023 5:58 pm They are related. There's a specific procedure to time align the HF horn atop an Altec A7 with the woofer horn. The HF horn polarity is reversed, placing the drivers 180 degrees apart. A 500 or 800Hz tone is played through the system, depending on the crossover. The horn sled is moved forward and backward until a sound meter shows minimum output, indicating perfect time align. The HF horn polarity is then returned to normal.
When we used A7s back in 1977, time align just meant the show started when it was supposed to. :mrgreen:

We just stacked the horns on top where they wouldn't fall off.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

CarterKraft
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Re: Finally! Omni 12 Tall Boy build

#220 Post by CarterKraft »

I still don't have time for a lengthy response but I appreciate those calculations, and all the other "teach a man to fish" work you have put it.
It was worthwhile doing the "tuning" as you described to get a feel for what it takes to sound correctly (on paper).

There is a LOT going on with this project, most of it is a first for me, and likely many of you aka running on 24w of power, cordless tool batteries etc.

Each time I mess with it I get more comfortable with the DSP, there are a lot of booby traps in that regard. If I had a regular pro-sound EQ this would be MUCH easier I think. The "turning of knobs" on a computer screen then having to "flash" the board to try and keep the adjustments real time is super challenging as you can continue to make adjustments with out the DSP responding, then when you write the instructions again ALL the instructions you were adjusting hit at one time and the response curve is trash again...
Hard to explain but I would describe it as a flaw in the DSP software/hardware.

Having said all that, in its current state it just doesn't sound very good, I don't know if my settings didn't stick and it reset after a power cycle or just the crowded listening environment of my shop is tailoring the output, either way I will get it outside in the correct area and perform the tuning once more (should be much easier now) and see where that gets it. I don't mean to say tuning it made it worse, it helped immensely in the mid/top end, but something is off in the woofer, likely all caused from the erratic operation of the DSP.

The good news is my wife was WOW'd when she saw it finished. She was very impressed and said that definitely looks like I bought it...
Weldon Carter

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Seth
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Re: Finally! Omni 12 Tall Boy build

#221 Post by Seth »

Oh man... Tuning isn't real time? That could seriously be a PITA. We'll get it there though. I'm on board as long as you are.

I love that your wife had such a great reaction. You've put a lot of time and energy into this project and it does, in fact, look fabulous. You deserve the kudos. :thumbsup:
Build in process - 2 WH6, one Alpha 6a loaded, one PRV Audio 6MB250-NDY loaded

Two 2x6 shorty SLA Pro's
One T39, 16", 3012LF loaded
Tall AutoTuba, 20" wide, 2x 8" MCM 55-2421
TruckTuba, 8½" wide, 2x 8" MCM 55-2421

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Tom Smit
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Re: Finally! Omni 12 Tall Boy build

#222 Post by Tom Smit »

+1...to Seth's words.
TomS

Grant Bunter
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Re: Finally! Omni 12 Tall Boy build

#223 Post by Grant Bunter »

Well, it seems the hitch at this point is relying on the DSP on the onboard amplifier.

Is it worth exploring a more failsafe method?

Where did this come from? I've been researching heavily into repair of DCX 2496's (mostly the problem is power supply). In my search there was a great thread with a 12V power supply for the DCX auto use.

What I was thinking. For DSP the DCX 2496 Crossover/limiting/ 10 band PEQ on the V1.17 or later etc
A couple of 12V power amps. Rehousing in the cab is perhaps the biggest hurdle, but will end the war...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

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Tom Smit
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Re: Finally! Omni 12 Tall Boy build

#224 Post by Tom Smit »

Very interesting suggestion there Grant.
TomS

CarterKraft
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Re: Finally! Omni 12 Tall Boy build

#225 Post by CarterKraft »

Grant Bunter wrote: Wed Feb 22, 2023 1:12 am Well, it seems the hitch at this point is relying on the DSP on the onboard amplifier.

Is it worth exploring a more failsafe method?

Where did this come from? I've been researching heavily into repair of DCX 2496's (mostly the problem is power supply). In my search there was a great thread with a 12V power supply for the DCX auto use.

What I was thinking. For DSP the DCX 2496 Crossover/limiting/ 10 band PEQ on the V1.17 or later etc
A couple of 12V power amps. Rehousing in the cab is perhaps the biggest hurdle, but will end the war...
That is a possibility but before I went to that trouble I think I would just build the passive crossover and try it like that.
Its not a loss or anything at this point, I have heard it sound much better, I just need to undo whatever I did to cause the problem.
Weldon Carter

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