DIY Transmission Line Speakers

Update: I'm now offering crossover upgrades. Read more >

If you are looking for a high end transmission line kit, I recommend LSK TL6. (Not currently available, but soon to be redesigned from the ground up.)


Why choose this design over JV60 + TL box?

JV60 is a good value kit that with some mods can sound very good indeed - it is a smooth laid back sounding speaker that sounds even better with a good quality TL (transmission line) box. The crossover parts are cheapies and that is addressed with my assembled crossover upgrades. However, there are better drivers available and better design choices. The stock JV60 was designed to avoid failure when driven hard. One can remove the polyswitch protectors but the crossover point is a little high in order to optimise power handling over off axis response. Where very high output is desired, there are far better choices.

TL6 is about to be redesigned from the ground up. It will soon be a completely new design. New drivers. New crossover. New box. 





After selling my modified JV60 kit in a TL box, this is what the new owner had to say:

"I can't believe you parted with them, for any price. They sound as good as anything in the 3-5k range, amazing! We listened to some Focal Floor standers at [my local hifi retailer] a week back with the wife and we are both agree these are better. "

The Etude TL is a 2.5 way MTM floorstander with extension below 25 Hz in typical listening rooms. The bass is articulate and the overall sound is neutral with a slight mellow bias in the voicing. This speaker has been built by DIY enthusiasts all around the world.


If you have built the TL, please share some photos. 

Sonic preferences

In choosing a speaker to build, it's worthwhile to understand a little about your preferences. Some speakers are ruthlessly accurate and highly resolving. They will expose a poor recording without holding anything back and for many this means not being able to enjoy many albums. I have found the Linkwitz Orion to be in that category as well as Vaf Signature speakers. The Etude TL is a different type of speaker. It does not expose detail to the same extent and tends to be a little more forgiving with less than perfect albums. The sound is neutral and natural.


JV60 kit

This project is based on the JV60 kit which previously was sold in Australia through Jaycar. The kit included a pre-assembled crossover, drivers and damping material. The crossover shown here is a modified version in which the tweeter level has been adjusted and unnecessary parts have been removed. If you have this kit then some crossover upgrades are suggested.

Crossover upgrades

What is a transmission line speaker?

A transmission line (TL) speaker loads the woofer into a tapered tube which is filled with acoustic damping material. The line tunes the woofers to extend the bass lower. It also absorbs the midrange output from the rear of the driver and thereby minimises box coloration.
In effect, a TL combines the best of sealed and vented designs. A sealed enclosure allows more acoustic damping to reduce box coloration but allows no bass reinforcement. A vented enclosure doesn't allow sufficient damping to remove box coloration to the same degree. The result in either case is a compromise that isn't required in a TL speaker.





More info on wikipedia:
Wikipedia - TL

What's the catch?


The most obvious downside is enclosure size. A TL will normally be larger than a sealed or vented enclosure. However, if the line is folded, the size is still acceptable. Another issue is coming up with a design. It isn't quite as simple as a simple vented box.





The drivers


The drivers are well regarded Vifa classic units - Vifa D25AG a 1" aluminium dome and the Vifa P17 6.5" midbass. They are now discontinued, but currently still available in Australia.









How does it sound?


With the tweeter pad, the sound is smooth, open and relaxed. The midrange is natural and uncoloured and the bass is articulate and deep. Acoustic double bass sounds very natural. The bass tends to be natural rather than punchy, although this also depends on the room. It is perhaps slightly under-stated.


The Vifa D25 aluminium dome is one of my favourite tweeters. It has a nice smooth extended response and no hint of the harshness that some associate with metal domes. The Vifa P17 is a very well behaved driver and the box helps to keep coloration low.


Different music styles


I've always felt this speaker shines the most with vocal jazz music. Acoustic double bass is very natural on these. Norah Jones, Harry Connick Jr, Dianna Krall, and Natlie Cole among others stand out. Of course, any decent speaker will handle all types of music, but if your music preferences are more towards rock then this might not be the best choice. Where bass authority is important I suggest adding subs, but for dynamics and raw energy and high output you probably shouldn't be looking at a conventional floorstander such as these. You might instead consider an Ewave.


Recommended placement


Placement is an important to get the best result. Like every floorstander, this one requires breathing space. Bring them out from the front and side walls and toe them in so that they face the main listening chair. Ideally their offset from the front and side walls should be different to avoid boundary effects. At least 1m clearance is recommended. If you must place them closer then acoustic treatment should be used. 
When placed correctly, the sound image should float out in the middle of the room, extend behind the speakers and sometimes project out the sides as well. With your eyes shut there should be no sense that the sound is coming from two speakers. 


Use with subwoofers


Where more bass force and impact is desired, a sub is recommended. Be careful with your choice, to ensure that your sub is up to the task. You will also need to put in some effort at integration. It is much harder to get good bass from a sub because there are many more ways it can go wrong.


More about bass integration


I have used Rythmik servo subs with my TLs and recommend them highly. When integrated well they extend the bass deeper and the bass improves further.


Home Theatre use


Ideally for home theatre I would suggest a speaker with greater efficiency such as the Ewave. The higher efficiency is likely to mean spending less on amplification. Hence instead of adding power amps to your receiver, you may instead use more efficient speakers. However, the TLs are as good as any floorstander for home theatre and the crossover is ideally suited to building matching surrounds.