Planning a very large TL design

[darkmatter]

I have been thinking of building a really big TL system something rather larger than the TDL RSLS I owned over 20 years ago.

The large resulting cabinet size will not be an issue!!

I have the space to house it and have been considering drivers, though would welcome comments on suitable bass drivers 15" plus.

I have 4 18" JBL 2245 units which might be suitable I will use 2 drivers per side (force cancellation) per side, as per the illustration below which shows a smaller 2 x 12" system.

The JBLs have a have a nice low 20Hz resonance but haven't modeled them yet, but I will be using King/Augspurger modeling software.

An externally hosted image should be here but it was not working when we last tested it.

My design will be considerably larger than the above.

Any suggestions would be great.

Thanks

Simon

 

[planet10]

Your TL could use some improvements. You do need to model it.

1/ seat of the pants it looks a little small
2/ you are not taking advantage of using a Zd to kill the 1st unwanted harmonic
3/ the deflectors at the top corners can be left out
4/ it is going to be tippy without wider outriggers

5/ push-push is very good, it dramatically reduces the load on the box

dave

 

[darkmatter]

Your TL could use some improvements. You do need to model it.

1/ seat of the pants it looks a little small
2/ you are not taking advantage of using a Zd to kill the 1st unwanted harmonic
3/ the deflectors at the top corners can be left out
4/ it is going to be tippy without wider outriggers

5/ push-push is very good, it dramatically reduces the load on the box

dave

Thanks Dave for the thoughts and suggestions, very useful pointers including the use of a Zd

Please note that the illustration is not my design, mine will be somewhat wider and considerably larger. With a youngster in the house stability will be important.

I will consider very carefully where to position the drivers, the line type and the vent.

This is a very rough idea, and will I am sure evolve over time.

Thanks

Simon

 

[Fenalaar]

Positioning the drivers at one end and the port on the other gives you problem with the harmonics. Ideally, you want the driver(s) a distance from the end.

As planet10 says, the deflectors are unneccessary for a TL, and you need more taper.

You can download Leonard Audios free Transmission line software to model the enclosure. For discussion and tips and tricks, you may want to visit Martin Kings discussion group, quarter-wave on groups.yahoo.com

Johan-Kr

 

[pkitt]

I would add a suggestion to use considerably more taper than what's depicted in the example drawing you showed. Like optimizing Zd, a larger taper ratio will also smooth out the response ripples. It will also shorten the necessary line length but that might make the box shorter and deeper than you prefer for a form factor.
Paul

 

[zedda]

If you tune at 20hz, what do you do with the 40hz resonance?

For planet ten, what do you mean for "push push reduce the load on the box?"
reduce the oscillation?
The distance from woofer to the line output or the distance from each woofer don't create a cancellation?
Or the distance is equal to a higher frequency wavelenght that is crossovered?

 

[planet10]

what do you mean for "push push reduce the load on the box?"

As a driver moves there is a reactive force which directly feeds energy into the cabinet. This is the largest source of energy that can cause box resonances. If you have 2 tightly coupled drivers with the same electrical/acoustic phase and opposite mechanical phase (push-push) then the other driver cancels a significant amount of the energy normally feed into the box, greatly reducing the energy that could cause resonance.

As an experiment we built a (smallish) sealed push-push sub with SDX10 drivers out of 15mm baltic birch (well braced). To get the cabinet to resonate, i had to turn the system up to louder than i'd ever play it, then turn the satelittes off and increase the volume another 10-12 dB and i was able to get the top to resonate (likely the bottom if it wasn't sitting on the floor). Finish will be a constrained layer, so these will be fairly immune to any resonance.

dave