Upgrading drivers in my 20" T39's.

[Bruce Weldy]

Just don't v-plate anymore since we went to stacking for the big shows.

How big is big for you Bruce? Which sub model and configuration are you stacking?

Bruce has 6 x T39 3012lf at 23 15/16" IIRC with Otops 12's and a T24 for drum fill if required, and places them based on coverage requirements...

The big shows in the park get the T39s ( 2-25" and 1-20") stacked on their sides split on the sides of the stage with the OT12s on top. I can get 'em about 48 feet apart. With a high pass of 47hz or so, there is a small null right in the middle of the crowd. But, the ease of setup and tear down is worth it.

Adding the 5th and 6th sub kinda' negated the v-plates, so this is a good solution for us.

[Keryn O'Shea]

... the ease of setup and tear down is worth it.

Adding the 5th and 6th sub kinda' negated the v-plates, so this is a good solution for us.

Excellent! Thank you

[Bill Fitzmaurice]

The V Plate makes the horn path a bit longer, but its main purpose is to make the total mouth area larger, which increases sensitivity at the lower end of the passband. Adding more cabs makes the total mouth area larger as well, so there's a point where any additional area from a V Plate has little to no effect.The V Plate is most effective when you only have two cabs.

[Bruce Weldy]

The V Plate makes the horn path a bit longer, but its main purpose is to make the total mouth area larger, which increases sensitivity at the lower end of the passband. Adding more cabs makes the total mouth area larger as well, so there's a point where any additional area from a V Plate has little to no effect.The V Plate is most effective when you only have two cabs.

One summer, when I only had 4 subs, I'd V-plate two per side and put the OTops on stands. It worked fine, but the additional setup time in 100 degree weather on concrete made the ease of stacking way more palatable.

With my sound business winding down.....I doubt that I'll ever use the plates again, but they did their job when needed. I'm not getting out of the business, just not chasing jobs any more. My work now is coming from running installed and band-owned systems where I show up with my iPads and maybe my mixer.

Still have my long-standing summer shows and a monthly Opry-style show. Other than those, it's rare that the trailer leaves the drive.

[Keryn O'Shea]

... The V Plate is most effective when you only have two cabs.

That's great info mate

[Seth]

I ran some numbers for you, Grant.

The calculated increase in maximum output based purely on:
- Xmax, 6.2mm to 8.5mm is 2.7dB
- Vd, 207.4cc to 321.12cc is 3.8dB
- Voltage Limit, 35V to 50V is 3.1dB

However, none of the simple calculations are really helpful without an accurately modeled or measured 2.83V response plot for the cab with each driver. One thing that sticks out between the two drivers is the DC resistance. In no way is it any sort of fact, but in my casual observation I've noticed that drivers with lower Re tend to have higher sensitivity in the plots I've compared. BP102's Re is 5.59Ω and KL3010LF's Re is 7.03Ω, which leads me to suspect that the KL3010LF may result in less sensitivity that could potentially offset some of the gains. But again, without and accurately modeled or measured 2.83V response curve, it's purely supposition. I'm convinced my Hornresp models aren't accurate enough to be reliable in this comparison. I wish they were, I'd post comparative graphs for you.

If you choose to upgrade, it would be great if you were able and willing to take before and after measurements.

[Grant Bunter]

I ran some numbers for you, Grant.

The calculated increase in maximum output based purely on:
- Xmax, 6.2mm to 8.5mm is 2.7dB
- Vd, 207.4cc to 321.12cc is 3.8dB
- Voltage Limit, 35V to 50V is 3.1dB

However, none of the simple calculations are really helpful without an accurately modeled or measured 2.83V response plot for the cab with each driver. One thing that sticks out between the two drivers is the DC resistance. In no way is it any sort of fact, but in my casual observation I've noticed that drivers with lower Re tend to have higher sensitivity in the plots I've compared. BP102's Re is 5.59Ω and KL3010LF's Re is 7.03Ω, which leads me to suspect that the KL3010LF may result in less sensitivity that could potentially offset some of the gains. But again, without and accurately modeled or measured 2.83V response curve, it's purely supposition. I'm convinced my Hornresp models aren't accurate enough to be reliable in this comparison. I wish they were, I'd post comparative graphs for you.

If you choose to upgrade, it would be great if you were able and willing to take before and after measurements.

Thanks for your efforts Seth.
I did ask Bill because he should have those plots, with the modelling software he uses.

As far as Re goes I reckon it misses out as a singular variable, because it doesn't account for AC reactance in the driver.
Just in case you didn't know, or for others, Re by AES standard should be equal to or greater than 80% of total impedance.
So one could almost argue that the Re of the BP102 means it should be classified as a 6 ohm nominal impedance driver.
It's probably called an 8 ohm driver because that was in keeping with it's right at the start design brief.
Re represents the lowest impedance in an impedance plot with a 0 Hz DC input, not near Fs.
It's unusual enough for any 2 drivers to have Fs at the same frequency, and similarly Re will be at a different impedance.
I think that skews comparative analysis.

My understanding is that sensitivity is of much less importance than design in horn enclosures, and more significant in direct radiators, hence the quote "it's the design, not the driver, that dictates response" which I often quote.

There's always exceptions, but point in case is Lab12 vs 3012lf. The lab 12 should win (and does, ever so slightly) in the same enclosure, because it has greater Xmax, greater Vd. It also has lower Re and sensitivity than the 3012lf. Obviously, the 3012lf has lower Xmax and Vd, but greater Re and sensitivity.
You might expect the Lab12 to beat the snot out of the 3012lf, but it doesn't. It has the same voltage displacement limit.

It always comes back to voltage displacement limits for me.
And IIRC, the top 2 most important criteria for those limits are Xmax and impedance in order of importance, with other variables following.

Perhaps the greatest thing about this proposed change isn't so much the increase in output, for me it's not having to run separate limited outputs for subs with different drivers. Everything will be able to be limited to 50V, meaning I can simplify my setup.

I don't know if my time frame will allow me to do measurements at this time...

[Seth]

Thanks for your efforts Seth.

You're welcome buddy

As far as Re goes I reckon it misses out as a singular variable, because it doesn't account for AC reactance in the driver.

You're absolutely correct that it doesn't account for reactance. But again, just in casual observation, it occurs to have value as a "singular variable" and if you think about it, it makes a bit of sense. Well... it seems to make sense to me. But, I'm not as pragmatic as you are.

Just in case you didn't know, or for others, Re by AES standard should be equal to or greater than 80% of total impedance.
So one could almost argue that the Re of the BP102 means it should be classified as a 6 ohm nominal impedance driver.

Looking at the impedance graph for the BP102 looks like it's minimum impedance is roughly 6.5, just above the 6.4 Minimum to be considered an 8Ω driver.

Re represents the lowest impedance in an impedance plot with a 0 Hz DC input, not near Fs.
It's unusual enough for any 2 drivers to have Fs at the same frequency, and similarly Re will be at a different impedance.
I think that skews comparative analysis.

It's my understanding that Re is purely the DC resistance of the coil, completely independent of any frequency spectrum or resonant frequency, which would coincide with a Zero Hz input signal.
But yeah, I'm not convinced it's un-noteworthy. And also not convinced it's a reliable predictor either. Just an observation that has, so far, been reliable.

My understanding is that sensitivity is of much less importance than design in horn enclosures, and more significant in direct radiators, hence the quote "it's the design, not the driver, that dictates response" which I often quote.

I think you're right that the overall response is mostly dictated by the cab design, however I'm fairly certain driver selection has an impact on sensitivity.

There's always exceptions

100% agree

Perhaps the greatest thing about this proposed change isn't so much the increase in output, for me it's not having to run separate limited outputs for subs with different drivers. Everything will be able to be limited to 50V, meaning I can simplify my setup.

That sounds like a good plan and your logic seems solid to me. Simplification of setup and operation is always a good thing.

I don't know if my time frame will allow me to do measurements at this time...

Sniffle sniffle... okay.

[Grant Bunter]

Well, 4 x picked up yesterday.
Got a discount, so overall pricing was better than if I bought OS.
Bonus, no freight to me. A 15 minute drive each way pfft.

Looking forward to getting home when treatment ends to burn them in and try to fit them...

[Seth]

That's awesome Grant

Now, the question becomes... what to build to put the BP102's in? Hahaha