Dual T18 vs Dual T39 (aka bass on the cheap)

[jbell]

OK, First let me say that this is going to provoke many people, and many won't believe me... I've just been unable to believe the response of my dual T18... so much so that I built a couple T39's just to compare.

Meter's don't lie.. I used a bench transformer (12volt 6amp) to get a 60hz sine wave, a beckman amp meter and volt meter. Both volts and amps were measured during load. You can fault my test method if you like, but rather than haul out all the gear, this is a simple gut check, and 60hz is a frequency that everyone can agree is needed in a sub.

I had a couple 55-1740's around, and they are one of the drivers (although not a bp102) that can work in a T39. So I built a couple 22" dual driver T39's. They look nice. And when I compare them with the published charts -- everything looks spot on. They were well broken in this morning, but I let them run all day just to make sure, cool off and then do the test... same reading this morning and afternoon, nothing changed.

So this test is between a pair of $25 dollar 55-2421's and 1 sheet of plywood vs. a pair of $23 dollar 55-1740's and 1.5 sheets of plywood. Total investment in either one is well under $100.


Here's the deal:

T39 9.78cu.ft. 12.2volts, 3.9amps, 47.5watts @60hz 113db/1M.
T18 4.75cu.ft. 12.2volts, 2.8amps, 34.0watts @60hz 117db/1M.

Not kidding. The dual T18 kicked the T39's butt, and not by a little, BY ALOT!!! AND look at the size difference.

I know I've said before the dual T18 is cubic inch per cubic inch the leader of all of Bill's cabinets... Now here's an apples for apples comparison that shows it verses a T39. This is intriguing enough to haul out the testing gear and do some sweeps.... will let you know.

[mty]

ThankS for your effort to bring this test to all us .

[WB]

This is intriguing enough to haul out the testing gear and do some sweeps.... will let you

This is very interesting. I like the apples to apples factor. Looking forward to the sweeps.

(I don't see any braces, are they braced internally?)

[Bill Fitzmaurice]

The comparison at small signal levels and 60 Hz isn't unexpected. Where you'd see a major shift to T39 is with a full sweep at 100 watts or better. At 300 watts with BP102s there'd be no comparison, T39 all the way.

[Mikey]

The results will definately be interesting.

How wide did you build that dual-driver T18?

I'm surprised you didn't throw an AT into this battle!

[jbell]

With the drivers used... The T18 will continue to outperform the T39. 55-2421's are 'rated' at 125watts, and 55-1740's are 'rated' at 150. Neither one would I want to push much over 25-35 volts on a continual basis. As it is, at 12 volts, I'm pushing 34watts across 2 drivers. (17 watts each)

yes both cabs are fully braced, except for mouth braces. (I want to put on grills, just hasn't happened yet) The T18 is 24" wide, and it's on it's side in the pic. BTW -- whoever first made panel 5 go past panel 6, and just 45 panel 6, instead of 56 degree... thanks.

With a single s2010 20" wide cabinet (what the spl charts are based on.) I'd be surprised if (with power compression) it could muster 121db@60hz, and the bp102 could only be a db or 2 above at most. Anyone want to measure and see if that's accurate? I know my T18 can get to 122 outdoors. So, I'm not so sure the T39 actually beats the T18 -- even with extra power thrown in. Which is really odd. bigger cabinet, more rapid/efficient flare... hmm... To beat the T18, it'd have to be dual bp102's.

I guess the one 'take away' from this, is to answer peoples questions if they 'have' to build 'on the cheap'

If you only have $100 total to spend.. it needs to go into a T18 with dual 55-2421's. Don't waste your time/money on T39's or T24's with the 55-1740 driver. And if you want another db and a half for free, add an extra wrap. When that's just not enough, scrape together another $100, build another dual T18 and v-plate them.

[klocwerk]

With the drivers used... The T18 will continue to outperform the T39. 55-2421's are 'rated' at 125watts, and 55-1740's are 'rated' at 150. Neither one would I want to push much over 25-35 volts on a continual basis. As it is, at 12 volts, I'm pushing 34watts across 2 drivers. (17 watts each)

buy once cry once. I for one wouldn't put that driver in a T39 if I put all the effort into making one.

I'm really curious to see a full sweep comparison.
Also, do you still have a single T18 kicking around you could compare?

[Mikey]

Although it really does sound compelling, I think the jury's out until more thorough testing is completed.

I wonder how well your DD T18 would handle bass guitar. With a DR200, O10.5, or OT12 on top, it might be a cool little rig.

Two "stock" single-driver T18s would perform even better than a 24" double-driver T18 (more mouth area), yet combined, they'd still take-up less pack space than a 20"w T39.

[MYork]

I don't have the plans for a T18, but I do have two Tuba24s with HL-10C drivers, and the build looks the same. I also have a Titan48 with 2 x HL-10Cs. These were for bass guitar use. In comparing the two cabinets, I preferred the Titan over the Tuba because the Titan was a lot cleaner/crisper throughout the range of the sub. I don't have any measuring equipment; I just played an mp3 of bass solos and compared. Mark

[jbell]

I built a T18, and was disappointed enough in it, I roasted hot dogs over it... (burn barrel) so no comparisons...

In order for a T39 to be more compelling that a T18, it would have to be 10db louder than with my 55-1740's. Somehow I don't think bp102's are going to do that. The reason I say 10, is T39 is currently 4db down, and twice the size. I can fit 2 dual T18's in the same space.

some one with bp102 loaded T39's willing to share what they do at 12,28,56 volts? full sweeps aren't necessary, if you have a spl meter, just a test tone and a volt meter is enough.

[Mark Coward]

Do you still have the passive x-over in the T18?

[jbell]

passive cross is external, and for this test, no it wasn't hooked up. When I get some time this weekend, I can do some real tests, I'll do with and without.

edit:
hooked up the T39 to my home stereo (typical home of the T18) and had a bad peavey W-bin flashback... ran it up till it phlatted-out (is that a word?)

T18 beats it hands down, in spl, and playing lower, and overall sq. (even tried combo of passive/active cross with T39, didn't help much at all) double checked for leaks, it's tight. Only explanation is it needs time to loosen up. I remember my dual T18 needing a couple weeks before it really started sounding good. Either that, or 55-1740's just sound like crap in a T39.

I'm bummed, I only lack panel 10 & 2nd side on the other T39... not sure what to do with it now. I was hoping to use this as a personal PA with a couple o10.5's

[RubiconProSound]

Two "stock" single-driver T18s would perform even better than a 24" double-driver T18 (more mouth area), yet combined, they'd still take-up less pack space than a 20"w T39.

I'll measure both of mine but I don't have a transformer floating around to make the comparison. What would be a good benchmark for comparing? I'm thinking pink noise band passed in the 30~100Hz range; one pass at 1 watt, and one pass just below limit (28 to 30 volts?)

I've got some wood laying around maybe I could build a dual driver version in the next few weeks before John and I have our "RTA party".

[jbell]

something must be terribly wrong with my T39 that I built. It sounds right, don't hear any leaks. (I could even hear on my T18 when I didn't have it sealed 100% tight around my wire exits... so I know what a leak sounds like) I've built a dozen or so tuba / titans, so I've got the whole PL thing down pat. It just seems like you can push and push, and nothing comes out of the T39. People love them for a reason, so it must be me.....

As a comparison, my experimental OT( http://billfitzmaurice.com/phpBB2/viewtopic.php?t=6023 ) is db for db as loud at 60hz as my T39, when tipped down facing the ground (6" block on one side for floor load) They are both 110 db at 12volts. (which shocked and amazed me, btw) In this case it was free space, not in front of my garage door, which originally gave me 113 for the T39.

what's up with that?

any suggestions on what could be wrong with my T39, other than me using MCM 55-1740 drivers?

[moo]

something must be terribly wrong with my T39 that I built.

... any suggestions on what could be wrong with my T39, other than me using MCM 55-1740 drivers?

Have you checked and double checked that all of the drivers + wiring etc have the correct phase?
I use a speakon with bare ends and a 9v battery, and check that every driver pushes outwards with the correct polarity before sealing every thing up.
It may also be worth cabling up the whole rig with the access covers off, and exchanging the amp for the bare ends +9v battery to test all of your cables for correct polarity.
You may be surprised to find one / some of the cones moving in the wrong direction.
Just one out of phase driver will destroy low end response and make everything sound muddy.

Moo.