Which driver?

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Posts: 25
Joined: Mon Jul 16, 2012 7:32 pm

Which driver?

#1 Post by nivlek » Sat Dec 01, 2018 1:29 pm

Greetings everyone!

I've got all the plans from about 2014. Trying to decide on the most appropriate bass horns to build. Its mostly between the T-39 and the T-49. It will be mostly used for portable live sound applications. I'm also leaning toward the O-top 12 for the top boxes.

I noticed that in the SPL charts, in the T-39 section, that the 4th chart down has a 30" wide horn with a 3012 LF driver. A powerful horn. I like it.

The 10th chart down has a 12" driver in a 30" wide horn, (being compared to a typical 8 x 10 sealed cabinet).

The two horns though, have somewhat different curves.

The question from me is: Which driver was used in the horn in the 10th chart down? Was it the Delta 12 LF?

I like the shape of the curve even though it may not be as loud as the 3012 LF horn.

Thanks for the info.


Grant Bunter
Posts: 6408
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia

Re: Which driver?

#2 Post by Grant Bunter » Sat Dec 01, 2018 3:07 pm

Don't get too excited about the SPL charts, and looking for differences. There's slightly different scales in the 2 charts you mention (number 4 goes to about 110dB, number 10 goes to 120dB), but mostly, the response at various frequencies is pretty much the same.

This is because it's not the driver that dictates response, it's the design.

In other words, whatever driver you use, response will be much the same.
What changes with driver choice is maximum output capability
The BP102, and the Delta12LFA, are both displacement limited to 35V, or +20dB in maximum output above the baseline chart.
The 3012lf (and the 3010lf), and the lab12 are limited to 50-55V(depends on the plans you have), or +26dB above baseline in maximum output.

That extra +6dB is the same as a doubling of cabs, so, one eg 3012lf loaded cab will have the same maximum output capability of 2 x S2010 loaded cabs.

Then start adding more cab width, and the differences in baseline output start to get more pronounced as well.

In the end, driver selection can be based on budget, but the 3012lf is king in the T39. Buy once, cry once.

28" wide is the new 30", for a number of reasons.
I can tell you from personal experience that 2 x 28" wide 3012lf loaded T39's go louder than 4 x 20" wide BP102 loaded cabs.

Before you build, get free updated plans:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" BP102 , 2 x 28" 3012lf.
WH8: x 3 with melded array.
Bunter's Audio and Lighting "like"s would be most appreciated...

Posts: 25
Joined: Mon Jul 16, 2012 7:32 pm

Re: Which driver?

#3 Post by nivlek » Sun Dec 02, 2018 6:54 am

Thanks Grant!

That is a very thorough response and great advise. I like the "buy once cry once" philosophy too.

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