T45 Driver advice

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Pabloaguas
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T45 Driver advice

#1 Post by Pabloaguas »

I bought these B&C 12bg76 sub drivers for my tuba 45 project, but am now beginning to second-guess if they are a good fit. We are going 16" wide, so without a hole in panel 5, I calculated the enclosure volume at 1.12 ft3. With this driver, that gives a QTC of .6 - which should be in the realm of good, tight bass, (which is what I want), with the sacrifice of a bit of efficiency (no problem I have good amp power). Also calculated the f3 at 69hz... which seems a little high...

As far as cutting the holes in panel 5 to double the enclosure volume, I hesitate to do this because when I simulate the B&C using speaker box lite, it shows the B&C hitting xmax prematurely at lower frequencies. Anyways, at this point it's really too late to do holes in panel 5, so I want to keep it in the 1.12 ft3 space (I want to do the jackplate in panel 5.

So, I'm second guessing myself because the popular lab 12 seems to have a lot less mechanical damping than the B&C. Also- I am wondering if the horn itself adds damping, thus dropping the QTC down even further.

Thanks for taking a look at the TS of this woofer and offering your opinion. At this point I'm wondering if I would be better off with the lab 12 or going for the higher-powered B&C 12bg100 and just muscling through the low QTC...

Thanks,
Paul
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Seth
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Re: T45 Driver advice

#2 Post by Seth »

Pabloaguas wrote: Mon Jan 25, 2021 1:40 am I bought these B&C 12bg76 sub drivers for my tuba 45 project, but am now beginning to second-guess if they are a good fit. We are going 16" wide, so without a hole in panel 5, I calculated the enclosure volume at 1.12 ft3. With this driver, that gives a QTC of .6 - which should be in the realm of good, tight bass, (which is what I want), with the sacrifice of a bit of efficiency (no problem I have good amp power). Also calculated the f3 at 69hz... which seems a little high...

As far as cutting the holes in panel 5 to double the enclosure volume, I hesitate to do this because when I simulate the B&C using speaker box lite, it shows the B&C hitting xmax prematurely at lower frequencies. Anyways, at this point it's really too late to do holes in panel 5, so I want to keep it in the 1.12 ft3 space (I want to do the jackplate in panel 5.

So, I'm second guessing myself because the popular lab 12 seems to have a lot less mechanical damping than the B&C. Also- I am wondering if the horn itself adds damping, thus dropping the QTC down even further.

Thanks for taking a look at the TS of this woofer and offering your opinion. At this point I'm wondering if I would be better off with the lab 12 or going for the higher-powered B&C 12bg100 and just muscling through the low QTC...

Thanks,
Paul
Hey Paul. Bill will be the guy to point you in the right direction here. Horns have little in common with standard sealed or ported enclosures, you wont be able to model it in speaker box lite. The driver you chose looks good except the Vas is about half of the minimum recommended value of 60-120L.

About panel 5, the first paragraph at the top of page 15 states "Panel 5 subdivides the driver chamber. Cut and install it. Note the holes, which allow air flow from the rear to the front of the driver chamber. Holes are used with all ten inch drivers and with twelves with an Fs spec of 35Hz and higher."

Your driver's Fs is above 35Hz, so I'd think you'd want to cut some holes in there. I'm sure you can get in there with something... right angle drill with a hole saw maybe. Perhaps a rotary or oscillating tool.

But, again, Bill will let ya know how well suited the drivers will be and the possible downsides of being out of spec.


The build is really looking fantastic. :thumbsup: I hope the Vas and solid panel 5 doesn't hurt the performance too bad. :fingers: If so, LAB12 would be your solution and you'd be able to put your jacks in panel 5. Otherwise, the 3012LF seems to be the go-to most of the time. But, that would mean putting holes in 5 instead of jacks.
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: T45 Driver advice

#3 Post by Bill Fitzmaurice »

Pabloaguas wrote: Mon Jan 25, 2021 1:40 am I calculated the enclosure volume at 1.12 ft3. With this driver, that gives a QTC of .6 - which should be in the realm of good, tight bass
You cannot apply calculations for a direct radiating enclosure to a horn. Horns do not have Qtc.
when I simulate the B&C using speaker box lite, it shows the B&C hitting xmax prematurely at lower frequencies.
Speaker box lite does not sim horns.

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Seth
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Re: T45 Driver advice

#4 Post by Seth »

T45 Recommended Specs for 12" drivers / B&C 12bg76 Specs

Fs 20-50Hz / 44Hz ..............:thumbsup:
Qts 0.25-0.50 / 0.41 ...........:thumbsup:
Min Xmax 4.5mm / 9.5mm ....:thumbsup:
Vas 60-125L / 32L ...............:thumbsdown:


Bill, I'm curious... what would be the effect of the low Vas? And then also not cutting the holes in panel 5 to accommodate the Fs?
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: T45 Driver advice

#5 Post by Bill Fitzmaurice »

Vas too low requires making the rear chamber smaller, which he has done by not having the holes.

Pabloaguas
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Re: T45 Driver advice

#6 Post by Pabloaguas »

Thanks Bill. So it sounds like the woofer will work well then?

I'm just wondering if I would gain anything by changing it out for a Lab 12? (other than gaining 10lbs)

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Re: T45 Driver advice

#7 Post by Seth »

On the surface, it seems like that driver may work out okay then. Sensitivity and extension wouldn't suffer too much?


B&C 12bg76 Vd 496cc
Lab12 Vd 658cc
Difference = 162cc in favor of the LAB12 at roughly 33% more Vd than the B&C 12bg76.

Other than an extra Vd, does the LAB12 offer enough benefit in his case to suggest purchasing a pair of LABs instead?

I'm guessing the voltage limit would be about the same with the B&C driver. But, I've got nothing to base that on other than it's reduced Xmax and increased nominal impedance compared to the LAB12.
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: T45 Driver advice

#8 Post by Bill Fitzmaurice »

It's more or less equivalent to the 3012LF.

Pabloaguas
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Re: T45 Driver advice

#9 Post by Pabloaguas »

Seth wrote: Mon Jan 25, 2021 2:24 pm On the surface, it seems like that driver may work out okay then. Sensitivity and extension wouldn't suffer too much?


B&C 12bg76 Vd 496cc
Lab12 Vd 658cc
Difference = 162cc in favor of the LAB12 at roughly 33% more Vd than the B&C 12bg76.

Other than an extra Vd, does the LAB12 offer enough benefit in his case to suggest purchasing a pair of LABs instead?

I'm guessing the voltage limit would be about the same with the B&C driver. But, I've got nothing to base that on other than it's reduced Xmax and increased nominal impedance compared to the LAB12.
So, basically the lab12 has 33% more output then?

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Seth
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Re: T45 Driver advice

#10 Post by Seth »

Pabloaguas wrote: Mon Jan 25, 2021 3:32 pm
Seth wrote: Mon Jan 25, 2021 2:24 pm On the surface, it seems like that driver may work out okay then. Sensitivity and extension wouldn't suffer too much?


B&C 12bg76 Vd 496cc
Lab12 Vd 658cc
Difference = 162cc in favor of the LAB12 at roughly 33% more Vd than the B&C 12bg76.

Other than an extra Vd, does the LAB12 offer enough benefit in his case to suggest purchasing a pair of LABs instead?

I'm guessing the voltage limit would be about the same with the B&C driver. But, I've got nothing to base that on other than it's reduced Xmax and increased nominal impedance compared to the LAB12.
So, basically the lab12 has 33% more output then?
Yes, but that only equates to roughly 1dB premium in peak output, on the limiter. 1dB is noticeable in an A/B comparison, but not very. If you're not on the limiter you'll never know the difference. If you're constantly on the limiter, you need to build more cabs anyway. Up to you if 1dB is worth the hassle/money. IMO, at this point, it's not. It looks like the ones you have will work out just fine. I'm happy for you about that. Good news.
Last edited by Seth on Mon Jan 25, 2021 4:18 pm, edited 3 times in total.
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

Grant Bunter
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Re: T45 Driver advice

#11 Post by Grant Bunter »

Hi, and welcome from me as well :)
Pabloaguas wrote: Mon Jan 25, 2021 3:32 pm So, basically the lab12 has 33% more output then?
No, it won't have that much more output in a horn.
At best, if your B&C drivers are most like an Eminence 3012lf, the lab 12 would have a couple of dB extra output. Not worth the weight IMHO.

Why?
Because drivers in horns need to have voltage displacement limiting to protect them from blowing. Exceed the voltage, blow the driver.
To that end, you need to use DSP, either in the amplifier, or outboard like a DBX driverack, or the Behringer DCX2496, or similar.
This aspect isn't desirable, it's mandatory...
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...

Pabloaguas
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Re: T45 Driver advice

#12 Post by Pabloaguas »

Grant Bunter wrote: Mon Jan 25, 2021 4:05 pm Hi, and welcome from me as well :)
Pabloaguas wrote: Mon Jan 25, 2021 3:32 pm So, basically the lab12 has 33% more output then?
No, it won't have that much more output in a horn.
At best, if your B&C drivers are most like an Eminence 3012lf, the lab 12 would have a couple of dB extra output. Not worth the weight IMHO.

Why?
Because drivers in horns need to have voltage displacement limiting to protect them from blowing. Exceed the voltage, blow the driver.
To that end, you need to use DSP, either in the amplifier, or outboard like a DBX driverack, or the Behringer DCX2496, or similar.
This aspect isn't desirable, it's mandatory...
Grant, do you think that the "clip limiter" built into my QSC RMX 2450 would be a sufficient voltage limiter? The RMX 2450 is rated at 450W (0.1%thd) and 500W (1%) and includes an optional "clip limiter" that is activated by a dip switch. The only info from qsc is "The limiter only responds to actual clipping, and automatically
compensates for load and voltage variations. Clip limiting is generally recommended, especially to protect high
frequency drivers."

Do you think that if the power of the amp and driver are matched, that the clip limiter would sufficiently protect the driver?

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Seth
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Re: T45 Driver advice

#13 Post by Seth »

To clarify a little on what Grant and I have said...

Volume, to a listener is somewhat subjective. But, it's fairly standard to reference an increase of 10dB (measured) as twice the perceived volume/output. However, doubling the Vd of a driver is measured as 3dB. So, while 33% more displacement does equate 33% more measured output... measured, it would only equate to about 1dB, when it takes 10dB to be perceived as twice as loud.

So, as perceived by the listener, that additional 33% displacement only means a increase in volume that is just barely perceptible.
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

Pabloaguas
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Re: T45 Driver advice

#14 Post by Pabloaguas »

Seth wrote: Mon Jan 25, 2021 4:42 pm To clarify a little on what Grant and I have said...

Volume, to a listener is somewhat subjective. But, it's fairly standard to reference an increase of 10dB (measured) as twice the perceived volume/output. However, doubling the Vd of a driver is measured as 3dB. So, while 33% more displacement does equate 33% more measured output... measured, it would only equate to about 1dB, when it takes 10dB to be perceived as twice as loud.

So, as perceived by the listener, that additional 33% displacement only means a increase in volume that is just barely perceptible.
Got it!

I think the B&G is the clear winner with almost double the force factor (bl) of the lab12... should translate to tighter bass, right?

So what about the limiting on my amp... sufficient for voltage protection?

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Re: T45 Driver advice

#15 Post by Bruce Weldy »

Pabloaguas wrote: Mon Jan 25, 2021 4:26 pm
Grant, do you think that the "clip limiter" built into my QSC RMX 2450 would be a sufficient voltage limiter?
No, no, a thousand times no..... :mrgreen:

There are a few amps that have true limiters in them - that one doesn't. You'll need a real limiter that you'll set with a voltmeter. The best option is a driverack. Don't try to use an old stand alone limiter as it can be changed with a knob on the front - not safe.

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."

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