TB W4-1320 twin driver TL for 2A3

[Bing Yang]

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

[Harderror]

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

[Bob Brines]

Originally posted by Harderror
.... 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....

Nope. That's backwards. 8 -- 8 = 16, 8||8=4.

Bob

[ttan98]

Basic Electricity:

Parrallel speakers lead to half impedance ie 4 ohms
Series speakers lead to double impedance ie 16 ohms.

check the text...

[Relax]

yeppers:

Parallel wiring:

R1 + R2/(R1 * R2)

Series: R1+R2



Same formula no matter what.

[Harderror]

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

[Bing Yang]

Yes, they will be connected in series.

Can anyone answer my question on transmission line design and the SPL that I will get?

Can I put two drivers in one line?

[rcavictim]

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.

[Kensai]

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

[rcavictim]

Originally posted by Kensai
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.