T45 Driver advice

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Pabloaguas
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Joined: Tue Dec 22, 2020 2:31 am

Re: T45 Driver advice

#31 Post by Pabloaguas » Sun Feb 14, 2021 12:18 am

Got the DriveRack Venue 360!

So do I set up limiting by using test tones?

These woofers handle 500w, I'm going to have one per channel, so therefore 63v pushes 500w through (nominal?) 8ohms, so I would just measure voltage across the woofer several different test tones up to 63v and limit at the -db that produces 63v, right?

What about people saying that the horn itself raises impedance and to go with 10ohms and 70v?
Can I just play several test tones and set the db to the tone that produces the most power? Or, should I be looking at the published impedance curve of the driver from the datasheet and setting test tones for the frequencies of the lower-impedance parts of the curve?
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Seth
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Re: T45 Driver advice

#32 Post by Seth » Sun Feb 14, 2021 1:25 am

The driver is likely to run out of usable Xmax before hitting it's thermal rating. Just going off the Xmax of your driver, my guess is it's displacement voltage limit would likely be closer to that of the 3012LF, 50v. Pretty sure Bill would have to model the driver to give you a specific number, but 50v is where I'd put it without confirmation.

With the speakers disconnected and the amp gains turned all the way up, probe the amps speaker leads while playing a 60Hz sine wave and set the limiter. Then try to get the output to exceed your desired setting by reducing the signal attenuation and quickly flicking it up to maximum. If the output never exceeds your set value, you're good to go. If you see a blip above your set value, reduce the limiter threshold a little more and test again, until it never goes above the desired value.

Take a look at the last paragraph on page 23 of your plans. It talks a little bit about the difference between the speakers rating and displacement limits.

Also, remember to follow the high pass recommendations in the plans too.
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
Posts: 31
Joined: Tue Dec 22, 2020 2:31 am

Re: T45 Driver advice

#33 Post by Pabloaguas » Sun Feb 21, 2021 6:10 pm

So, what should I have these parameters set to? Should I just set to “auto” and leave alone or is there a more optimal setting?
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Bruce Weldy
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Location: New Braunfels, TX

Re: T45 Driver advice

#34 Post by Bruce Weldy » Sun Feb 21, 2021 6:38 pm

Pabloaguas wrote:
Sun Feb 21, 2021 6:10 pm
So, what should I have these parameters set to? Should I just set to “auto” and leave alone or is there a more optimal setting?
No one can tell you what settings to use.

You MUST use a voltmeter on the power amp output while playing a 60hz test tone with your mixer output run up to unity and your power amp all the way up. NO SPEAKERS Connected!

Then you adjust the limiter until the output is whatever your voltage limit is. Once you've done that, while watching the volt meter - push the master fader all the way up. If the voltage stays at your limit, then you've set it properly. If it runs past the limit, then something is wrong - start over.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
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."

Pabloaguas
Posts: 31
Joined: Tue Dec 22, 2020 2:31 am

Re: T45 Driver advice

#35 Post by Pabloaguas » Tue Feb 23, 2021 6:34 am

Bruce Weldy wrote:
Sun Feb 21, 2021 6:38 pm
Pabloaguas wrote:
Sun Feb 21, 2021 6:10 pm
So, what should I have these parameters set to? Should I just set to “auto” and leave alone or is there a more optimal setting?
No one can tell you what settings to use.

You MUST use a voltmeter on the power amp output while playing a 60hz test tone with your mixer output run up to unity and your power amp all the way up. NO SPEAKERS Connected!

Then you adjust the limiter until the output is whatever your voltage limit is. Once you've done that, while watching the volt meter - push the master fader all the way up. If the voltage stays at your limit, then you've set it properly. If it runs past the limit, then something is wrong - start over.

Yes, I used the multimeter, but had it connected in parallel with the driver. Why would I want to have the driver disconnected for that? Seems that I would want to measure the voltage drop on the driver rather than the voltage of the amp struggling to just push through a 10M ohm meter...

Did my test tones at 25,30,40,50, 60, 70, 80...

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Bill Fitzmaurice
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Re: T45 Driver advice

#36 Post by Bill Fitzmaurice » Tue Feb 23, 2021 7:42 am

SS amps deliver the same voltage into any impedance load,including the high impedance load of a meter. You can set the limiter with the driver connected, but the result is the same, and disconnecting the driver is just a wee bit quieter.

Bruce Weldy
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Joined: Fri Nov 27, 2009 11:37 am
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Re: T45 Driver advice

#37 Post by Bruce Weldy » Tue Feb 23, 2021 9:51 am

Pabloaguas wrote:
Tue Feb 23, 2021 6:34 am
Why would I want to have the driver disconnected for that?
Because if you didn't get the limiter correct, when you slam the master fader all the way up, you could fry the driver. Did you actually push the fader up to see if the limiter held? If not, then you don't know if you did it right.

We all harp on the limiter business because we are trying to save you from a big mistake. If you have questions about the procedures, it's a good idea to ask before doing it a different way and blowing up your gear.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
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."

Seth
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Re: T45 Driver advice

#38 Post by Seth » Tue Feb 23, 2021 4:30 pm

If you're setting the limiter with the driver connected, best practice would be to start with the limiter threshold turned way down and slowly increase it until you see 50v. That way you're not starting at the full power the amplifier is capable of and working back. I've always used 60Hz to set, simply because that's someone else told me to when I learned, along with a story about how most/many/inexpensive DMM's read 50/60Hz best. Whether there's any truth to that or not... don't know, don't care. However, it makes sense to me that if you're setting the limiter with the speaker connected, using a frequency that's not at the bottom of the cabinet's passband would add a little buffer and margin for error, being less likely to experience over-excursion.

In all reality, you're not likely to melt a coil with short term voltage the creates marginal over-excursion. Even long term could probably be endured by most drivers, depending on the content and how long term were talking. I'm no expert, and really, it seems you have a better grasp on some of this subject matter than I do. But, I'll share my take on it anyway. If the driver goes into gross over-excursion, you run the risk of hitting Xlim and bottoming out the coil on the backing plate or damaging the spider or surround... whichever occurs first. That's not really the main issue a limiter targets. When the coil extends beyond the magnet flux two things occur. The motor structure starts to lose control of the cone movement and adherence to the signal is compromised, aka distortion... which you probably wont hear, so no real big deal there. However, another thing that occurs as the coil progressively leaves the magnets flux is the impedance starts to drop off toward that of the coils DC resistance and more and more of the amplifiers power is converted into heat in the coil than cone movement the more it's pressed beyond Xmax. I'm pretty sure that's the most desired effect of using a limiter... Reducing excessive residual heat buildup in the coil. But, I could be slightly off base in that, or not have my facts straight.
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

Bruce Weldy
Posts: 7450
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: T45 Driver advice

#39 Post by Bruce Weldy » Tue Feb 23, 2021 6:14 pm

Seth wrote:
Tue Feb 23, 2021 4:30 pm
If you're setting the limiter with the driver connected, best practice would be to start with the limiter threshold turned way down and slowly increase it until you see 50v. That way you're not starting at the full power the amplifier is capable of and working back. I've always used 60Hz to set, simply because that's someone else told me to when I learned, along with a story about how most/many/inexpensive DMM's read 50/60Hz best. Whether there's any truth to that or not... don't know, don't care. However, it makes sense to me that if you're setting the limiter with the speaker connected, using a frequency that's not at the bottom of the cabinet's passband would add a little buffer and margin for error, being less likely to experience over-excursion.

In all reality, you're not likely to melt a coil with short term voltage the creates marginal over-excursion. Even long term could probably be endured by most drivers, depending on the content and how long term were talking. I'm no expert, and really, it seems you have a better grasp on some of this subject matter than I do. But, I'll share my take on it anyway. If the driver goes into gross over-excursion, you run the risk of hitting Xlim and bottoming out the coil on the backing plate or damaging the spider or surround... whichever occurs first. That's not really the main issue a limiter targets. When the coil extends beyond the magnet flux two things occur. The motor structure starts to lose control of the cone movement and adherence to the signal is compromised, aka distortion... which you probably wont hear, so no real big deal there. However, another thing that occurs as the coil progressively leaves the magnets flux is the impedance starts to drop off toward that of the coils DC resistance and more and more of the amplifiers power is converted into heat in the coil than cone movement the more it's pressed beyond Xmax. I'm pretty sure that's the most desired effect of using a limiter... Reducing excessive residual heat buildup in the coil. But, I could be slightly off base in that, or not have my facts straight.
Not discounting anything you said - but bottom line - don't set the limiters with the speaker plugged in .... period. Even if you don't get too much excursion, you are still sending a constant signal at somewhere close to full power to the driver while you are setting the limiter - that creates heat quickly since the driver never gets a chance to rest or cool.

6 - T39 4-25" 2-22" 3012LF
4 - OT12 2512 Melded/NSD2005
1 - T24
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."

Seth
Posts: 1432
Joined: Thu Sep 10, 2009 8:06 pm
Location: Sacramento, California, USA
Contact:

Re: T45 Driver advice

#40 Post by Seth » Tue Feb 23, 2021 11:43 pm

Yup, we're on the same page...
Seth wrote:
Sun Feb 14, 2021 1:25 am
With the speakers disconnected and the amp gains turned all the way up, probe the amps speaker leads...
Bruce Weldy wrote:
Sun Feb 21, 2021 6:38 pm
You MUST use a voltmeter on the power amp output while playing a 60hz test tone with your mixer output run up to unity and your power amp all the way up. NO SPEAKERS Connected!



I think it's a case of leading a horse to water or Paul's too smart for his own good... which I can personally relate to both, being that way myself. Sometimes I don't listen until I blow shit up. Then in a moment of reflection, I say to myself, Bill/Bruce/Grant (etc.) was right after all. :bash: Nothing wrong with being that way IMO (other than the financial cost. LOL). Just a way some peoples minds operate. However, the people that do operate that way, but don't own up to it and blame everyone else when things blow up drive me nuts... dumb asses. :cussing:
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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