Plan For Transmission Line Speaker Cabinet Using 8" Main Driver

[walpurgis]

Here's a design for a reasonably compact, quarter wavelength transmission line speaker using an 8" main driver. I drew this up about twenty years ago and it's all in imperial measurements. The effective overall length of the acoustic line is a little over five feet, giving a port cut off of around 35Hz, taking into account the roll off below this point, with a decent lowish resonance bass/bass mid unit, there should be useful output to 30Hz or below. I actually built this and got some very solid deep bass output. Don't forget you will need damping material, the bulk of which should go towards the wide (driver) end of the acoustic line, but don't go mad or it'll spoil the sound. If you use a full range driver, you won't need a tweeter, if you need to fit a tweeter mount it on the lower front panel as close to the upper main driver as possible. It's my own design and there's no copyright, so feel free to use it as you like. Any questions, just ask!

http://i59.tinypic.com/2lxjadl.jpg

[hoopsontoast]

Have you taken into account the driver specs? VAS and Qts should be essential for a TL speaker design, as well as FS for the line length if you are going 1/4 wave tuning.

[walpurgis]

Have you taken into account the driver specs? VAS and Qts should be essential for a TL speaker design, as well as FS for the line length if you are going 1/4 wave tuning.

It is a general layout, something I drew up a long, long time ago. Are you suggesting it is unuseable? I'd say there are many drivers that could work here, I had good results using a low resonance Audax paper coned unit.

[hoopsontoast]

It is a general layout, something I drew up a long, long time ago. Are you suggesting it is unuseable? I'd say there are many drivers that could work here, I had good results using a low resonance Audax paper coned unit.

I am not suggesting its unusable, just unlikely to be optimised for a specific driver that you may want to use. Generally you would prefer drivers with a 'higher' Qts say between Qts: 0.35-0.5 for a TL speaker. With the closed and open end area ratio 10:1 (IIRC) and the start area at the closed end around 2x sd.

[walpurgis]

I am not suggesting its unusable, just unlikely to be optimised for a specific driver that you may want to use. Generally you would prefer drivers with a 'higher' Qts say between Qts: 0.35-0.5 for a TL speaker. With the closed and open end area ratio 10:1 (IIRC) and the start area at the closed end around 2x sd.

Yes I'm aware of driver Qts implications and the ratio between wide & narrow line ends and comparative driver area vs. port size, etc., but none of this is quite 'set in stone' and a fair bit of variation and bending of rules often pays off in my experience. I've found for instance, that drive units that work in horn enclosures, also work well enough in well proportioned reflex cabs and lightly damped acoustic columns/transmission lines. Generally speaker units with generous magnets and good self damping (the type I prefer) . I've never 'computer modelled' anything on a speaker (although I'm certain I could). I started building speaker systems before PCs were ever made. Mind you, so did Lowther and Klipsch for instance and their old models are still on sale. The old Cambridge R40 & R50 speakers did not exactly stick to accepted practice for TL designs either, but worked very nicely.

[vvbunglevv]

Hi Walpurgis( system wouldn't allow me to pm you)
Sorry to resurrect an old thread , I'm interested in building these enclosures...would you have any more details, images etc regarding construction method please?
In particular your image states "front and rear panels to be removable" is this a requirement? Would driver removal provide enough access for wiring , damping etc?
Thanks
Mike

[walpurgis]

It's just something I drew up about thirty years ago. Everything can be changed, such as whether panels are removable or not, it's up to you. I no longer have the data I worked from, but the line length is around five feet, so bass extension should be decent.

[vvbunglevv]

Many thanks, I'll give it a go after I've built my turntable.