TB W4-1320 twin driver TL for 2A3

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I plan to make TL speakers for my 2A3 tube amp. I would like to have high sensitivy and good low end extension. I came up with the idea of using two TB W4-1320 in serial in a simple transmission line box.

I would like to build a 36" tower with two drivers in the front about 1/3 from the top. The cross section area of the tower is about 35 inch^2. The bottom is either open or with a tuned port. The width of the front baffle will be 7".

I have a few questions:

1. I choose two TB W4-1320 because I want higher sensitivity and no crossover. Can I put two together in this design? Is the cross sectional area too small for two of them?

2. Is this length OK? Or should I make them into a folded design and double the line length? The simple design is easier to make.

3. To get higher sensitivity for a 2A3 amp, I would like to wire the drivers in serial and use the 16 ohm output tap of the amp. Since W4-1320 is rated at 89 db, I should get 95 db with two of them. I assume the 16 ohm output tab will work perfectly with two drivers in serial. I should still get my 3.5 watt power from my 2A3. Am I correct?

3. Do I need baffle diffraction correction for this design? Can I avoid using one by building a round baffle (14" diamter) around the drivers?

4. Should I put a port at the bottom or simply with an open end? I believe a port can lower F3. If I use a port, what would be the right size? I have seen 3" diameter at 1" length. Is it good for this design?

I would appreciate any help.

Bing
 
Anyone that would like to correct me if I am wrong, please feel free to do so. When you say wired in "serial" I assume you mean series? If so, then no you are not correct. If you wire the drivers in series you will effectively halve your impedence. Two 8 Ohm drivers in series will give you 4 ohms. IF you were to wire in parrallel, then you would attain the 16 ohm rating you were speaking of.
And as for your amp, no you won't get the 2.3 watts. If the amp is rated at 2.3 watts in to 8 ohms then you will be reducing the wattage by using the 16 ohm tap. On this one I am not sure about how much you will lose though. Hope this helps.
Tom
 
I must have my thinking wrong. Say, one wire from positive on the amp goes to the positive on both speakers and the negative goes to the negative on both speakers. IS this not parallel? In series the positive goes to the positive on one speaker the negative of that speaker goes to the positive of the next. and the neg of that speaker goes to the neg of the amp.

SMACKS FOREHEAD VERY HARD> Geez, I feel like an idiot. I just answered my own thought. Hehe I knew that. I think I need sleep. Doh!

TOm
 
I don't think you will be happy with such low sensitivity speaker drivers at the power level you have available. I recently built a 3.1 watt/ch SET amp and discovered it takes rather herculean sensitivity speakers to be really enjoyable. Have you considered something in pro sound drivers? Perhaps a large coaxial? One of those could work nicely in a TL enclosure.
 
And with a 7" baffle, you're going to have some serious roll off pretty high . . . you'll need BSC which will kill what sensitivity you have.

Only thing I can think to do with a pair of those drivers would be to mount them as bipole so you won't need the BSC and then wire them in parallel so you'll have more watts to push into the 4ohm load and simply make your box a straight BR (most TB drivers are fairly well designed for BR enclosures . . . mores the pity).

Kensai
 
Kensai said:
And with a 7" baffle, you're going to have some serious roll off pretty high . . . you'll need BSC which will kill what sensitivity you have.

Only thing I can think to do with a pair of those drivers would be to mount them as bipole so you won't need the BSC and then wire them in parallel so you'll have more watts to push into the 4ohm load and simply make your box a straight BR (most TB drivers are fairly well designed for BR enclosures . . . mores the pity).

Kensai


Kensai,

He has a tube amp with an output transformer with Z taps. The use of four or sixteen ohms will deliver the same power to the speakers.

Bing,

For sensitivity think big enclosure. You could do something really impressive if you don't try to fight the laws of physics. If it were a BR box I'd be looking in the 5-10 cu.ft. range and fairly high Qts coaxial driver in the 12-15" range. Don't hesitate to search the drivers from the 50's and 60's that were designed this way for low power tube amp use. If you can find/afford a pair of Altec 604 coaxials I'm quite sure you'd be pleased. EV, Jensen, Tannoy and others made some decent and high sensitivity coaxials back in the golden age.

Asking here for advice was a good start. Now research will pay dividends.
 
All,

After some more searching on the net, I decided to try the concept out with my current particle board TL. The size of the TL is 7" wide, 7" deep, and 36" tall. The bottom is open with no port. It is a very simple design with straight pipe no folding.

I mounted a Parts Express NSB 4" driver that is slightly modified and a spare 4" VersaTronics mid woofer. The VersaTronics can only go up to 10 KHz. It can go lower than the NSB but is less sensitive. The NSB is mounted about 5" from the top and the VersaTronics is mounted 12" from the top. Both drivers are in the front.

Since I do not have any testing facility, I did my adjustment by listening. When I connect both drivers parallel, the sound is a bit scratchy. I ended up adding a 1 mH inductor in series with the NSB driver and parallel that with the VersaTronics directly.

I also removed bottom 1/3 of the polyester stuffing to "let out" some mid-low frequency from the bottom end.

The set-up as is does not play very loud, but for one single speaker, it is loud enough for me. It lacks the high end extension slightly. Otherwise, it is very nice sounding in the mid range. I am sure once I got my TB W4-1320s, they will be louder (89 vs. 86db) and with better high end extension (20 KHz vs. 14 KHz).

The most amzing part is the bass. With one NSB, I got some bass but not outrageous. Thus, I did not believe TL is good for 4" driver. With the additional 4" VersaTronics, the bass comes strong and deep.

I pulled out my 2A3 amp and connected the speaker for a quick try. As far as I can tell, the speaker works fine with the 8 ohm tap from the 2A3. Again, I don't expect loud music coming from this speaker. I don't play rock and roll with my 2A3 any way. But the potential of this design is there.

When I compared this speaker with my stanadard 6.5" Vifa 17PJ BR speaker, I could not belive my ears! I can hear the bass that was not produced by the Vifa before. I am now a believer of TL.

One thing that I could not confirm is the lobing effect caused by two drivers in the front. I don't know mounting the two drivers next to each other will make it better. I tried to stand up and sit down to detect the lobing effect but could not decide whether I hear anything different with music. I normally sit about 6 - 10 ft away from the speaker. I may need to play some test tones or pink noise to determine whether lobing is an issue or not.
 
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