August 15, 2009

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.


  1. Hi,
    This is a great design, I'd love to try it. Have been wanting to do TL for a while now. You said the Vifa drivers are discontinued -- do you know of any other Vifa/Peerless/etc drivers that would suit? I'm also based in Melbourne - know anywhere where I could pick these up? Now that the weather is picking up, would be nice to spend a couple of weekends putting these together. Would just be difficult to choose the finish!


  2. Last I checked the Vifa drivers were in stock at Jaycar.

  3. Hey,
    Yeah, which is interesting since the drivers are no longer made by Tymphany. Are they just coming out of an OEM in China now?

    Anyway I have sourced 4 x P17 and 2 x D25, arriving next week. So in a few weeks when the weather is on the improve, will build an enclosure as you describe here! Minus the curvature, though.
    I'll let you know how it goes, though I don't have a big room to put it in really, I live in a small Victorian-era terrace house that is narrow. Anyway thanks for this article. I have been reading some of the stuff on and there is seemingly more detailed mathematical analysis than actual audio speak. Your blog entry makes it very simple.

  4. You might be right, I have no idea.

    Look forward to seeing how it goes.

  5. Hi,
    I really like your design and I am very keen to try it. I currently work at a Jaycar store. A few months back we started stocking the vifa drivers again but still don't have the complete JV-60 kit, only the premade enclosures. I'm waiting out for the whole kit as it is cheaper than buying all the bits individually! Should have them in a few weeks hopefully.
    Thanks again for the great article and design,

  6. Yep, built them. See my words and link to pics from Red-Spade gallery page:

  7. Hello, this link isn't working:

    Could I see it please? I have a couple P17 woofers...

  8. Hi Christopher,

    I've taken that page offline because I need to get permission to publish some of the content. Send me a message via the contact form (under feedback on the right) and I will dig up some info.

  9. Hi Paul.
    Thanks for sharing your knowledge.
    Read your DIY Transmission line blog with interest. I'm seeking to build speakers predominately for classy home theatre system at minimal cost. I want to build 4 plus a centre speaker and I also want to add a 12 inch active sub (I have long wanted to build the NHT 1259 sub variously described with praise on the web, with a plate amp but I have procrastinated so long the 1259's do not appear available any longer - I'd be grateful if you could suggest an alternative DIY sub to go with your Transmission Line JV60's). I bought a pair of vifa kit speakers from Radio Parts in the early 80's and still love them for my (2 channel) music. I'm very handy and I have a serious woodworking hobby, so cabinet construction is basic for me, even your curved boxes. Unfortunately with all my talents, I am an electronics (and speaker design) numpty. I don't feel capable of altering the standard JV60 crossovers - it's gobbledy-gook to me! Can you suggest where I can take the standard ones to get a professional to modify them? Conversely if anyone else with the necessary electronics skills (but lacking the woodworking side of things) is reading this and wants to partner up then feel free to email me. Based in SE Subs of Melbourne....
    I suspect I'm asking a stupid question here (so humour me) but I assume you can't just flip these speakers on their side to use as a centre channel speaker? Assuming I can't, can you suggest how I can modify a JV60 for this purpose to go with the TL's?
    Whilst I don't understand speaker design, I do understand how air (and sound waves???) moves through tubes. I know about this because of dust extraction related to woodworking and efficiently moving particles through a vacuum system. From this I know that air moves much more efficiently and with less friction in tubes (or channels) when there are smooth transitional curves when direction is changed. To this end, would there be an acoustic benefit in your TL box design if the internal base of the transmission line at the bottom (where you have the access hatch) was curved rather than simply blocking the corners with 45 degree ramps. If there was a benefit to speaker design (i.e. reversing the sound / air around the bottom of the baffle and back up to the vent at the top of the box), then this could be achieved by cutting a half circle out of multiple pieces of 19 or 25 mm thick mdf then gluing them together to fill the entire base of the boxes? Also the lower edge of the baffle could be rounded over on both edges with a round over router bit so there are no sharp edges / corers to interfere with a smooth transition around the bottom of the transmission line. What do you think?

    Best wishes,

  10. Hi Gordon,

    I've responded to this via email.

  11. Hi Paul,

    I have read with interest your blog regarding constructing Transmission Line speakers using the Jaycar JV60 kit.

    I am a novice when it comes to speaker construction but am keen to build this.
    However I am a little unsure of how to interpret your diagram.

    1. If I follow the example given, and tune it for 40 Hz, then the Line Length = 2.15m. I assume I divide this by 2 and add the dimension "x" to arrive at the height?

    2. Should the whole folded column have acoustic damping material, or only that part where the drivers are mounted?

    3. Is the acoustic damping material applied to one of the internal surfaces, or is the whole space filled with it? If so, do you tightly fit it into the space?

    4. It appears from your diagram that the lower end of the internal baffle has a piece attached at right angles. Is this correct? I thought that it would simply be smoothly rounded, to minimise air disturbance as air moves in the tube?


  12. 1. Nope. The height is based on the line length being folded around. x indicates 3 dimensions that are the same.

    2. Around the first half is fine - dacron or similar as filling. The part behind the drivers is the most important.

    3. Lightly filled ... you might line it as well.

    4. Takes more effort to do it as you say and it's not needed.

  13. So are you saying that the height is half the Line Length, which for 40 Hz would be 1075mm? i.e. the dimension "X" does not determine the height?

  14. Almost. When you get the line length as required for the given tuning, the actual height of the box will work out a little different to half the line length. I think the actual height of mine worked out to be around 1200mm tall.

  15. Hi paul, You mention the cross sectional area is pretty important, i was just wondering how wide the internal dimention of the box is in your build?

    Not great at doing the numbers and stuff to work it out for myself but say using 100mm and 200mm for depth of the channel at the top (two ends back and front respectively) what width internal should i use 210-230 or is that external?

    Also in your diagram there is a little tick on the end of the internal baffle / seperator thing is that required? what are the specs on it?

  16. Mine were 230mm x 1200mm x 360mm external. At the end of the line there is just an opening made thicker.

  17. For those who are interested, the Vifa P17 is now manufactured by Scan-Speak (it's really the same driver made by the same people in Denmark) and is known as the "classic": ScanSpeak Classic P17WJ00 6.5" Woofer. Here in the US, carries it for about US$75.

    I've been building a TL using a single P17 for about ten years now. I've built about five or six pairs for friends. This is an exceptional woofer. It really shines in TL applications providing a nice, liquid, detailed bottom end. What I love most about the PW17 is it's extended upper midrange. I use all of the woofers response allowing it to roll off naturally and cross the tweeter in at about 4-5khz. The result is a total lack of phase-related problems in the upper mids. That does wonders for vocals.

    Paul, nice design!

  18. I've recently purchased a JV60 kit from a Jaycar stockist. He discounted it to $630. The standard kit seems to be great value for money.

    The original ported design provides a similar level of bass to my 12" accusound active sub, but the jv60s with the sub turned off is much more suited to listening to music. (The 200w active accusound sub is fine for movies but not quite right for music)

    At higher sound levels, the tweeter is really over the top. I agree with Paul on the need for an l-pad for the tweeter.

    I'll likely try the crossover upgrade first and will probably try a transmission line box. Even if my construction effort is a bit less attractive than the original enclosures, I'm curious about what the components sound like in a TL box.

    1. I was in Jaycar yesterday and picked up the vifa speaker kit for $450 on sale for Nov.

  19. At this point I'm actually considering offering a TL kit, with a new TL box and some drivers that I think may be a little better.

    One of the limitations of this speaker was that it could become strained at higher levels. I now suspect part of this is related to the crossover, both the quality of the parts as well as the absence of padding.

    Considering putting together an online store with crossovers that can be purchased for the JV60.

    1. If you do offer better crossovers for the JV60s I'll be interested.

      I'll keep an eye out.

  20. Neil, I offer them already, I just don't have an online store set up where you can click "buy it now!" Send me a message via the contact form link (top right side) if you would like to buy crossovers assembled.

  21. Paul, on your blog on DIY TL SPeakers you mention "With the tweeter pad..." - is this a tweeter pad that is part of your modified cross-over, or a suggestion that a pad be added to the standard Jaycar cross-over?

    From the information on this page, it looks like the intent is to provide enough information to come up with their own specific dimensions based on your diagram. Would someone building these speakers need to study up on T/L design a bit and calculate things like the line length, or is the intention that there should be enough information on the diagram to build the enclosures? I wasn't quite sure about this.

    Thanks for info regardless, looks like an interesting project and has got me thinking!


  22. The tweeter pad is added to the crossover.

    Shortly a similar TL speaker will be available again as a kit via LSK:

    Due for a redesign methinks!


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