[guest60106]

I put this model together this weekend for a TL based on an AC-180F1D and a Focal TI-121. I already own the drivers from other projects. The AC driver is a dual voice coil and the fs is about 37hz. I thought I would try something I read about years ago written by one of the Focal engineers in Speaker Builder (I forget which issue) where a DV driver is utilized in a 2-way driver set-up, however, one of the voice coils is connected to the band pass section of a 3-way crossover and utilized as a midrange. This has always sparked my interest so it thought I would take a swing at it for fun. If I can’t make it work I can always wire it in a 2-way configuration. If any of you have experience with this, or the box design for that matter, feel free to chime in. The TL itself I designed based on material I have researched from M. King and also calculators from various web sights and software modeling. The cab is 40 inches tall, 8 inches wide and 15 inches deep (exterior dim). The line length is about 67 inches and is a constant cross section area close to driver cone area.

[sreten]

Hi,

Splitting the coils in the way you describe has no advantage.
You can wire them up in the same way as 2.5 ways.

rgds, sreten.

[guest60106]

Sreten,
You may very well be correct. I have not yet reached the point in the design where I am looking at crossover design nor do I remember exactly what the design topology was when I read about it years ago. For the last couple of evenings I have been sorting through the MJK derivations trying to solve an issue with this particular DVC driver. For some reason, when I do the hand calcs for a TL utilizing the AC-180F1D, the enclosure gets unusually large in both cross sectional area and line length. So far, it looks like I have isolated it to the driver BL factor but more analysis is needed on my part. The BL on this driver is listed @ 3.3 (no units given) which seems low (about 1/3) relative to other drivers I have modeled. I have not measured the driver. I will do this right after Christmas when I have them broken in. There is also the possibility of a mathematical error on my part, however, when I run other drivers parameters with hand calcs everything seems reasonable.

Again, this is my first swing at transmission line design. It is quite interesting and challenging. As with any design, I want to make sure the math is right before I move forward.

MLC

[sreten]

Hi,

Yes. I can see a very low BL will affect So/Sd as this is affected
by 1/(BL)squared and 1/(3.3)squared is a different kettle of fish
to say a more typical 1/(7 to 10)squared for typical 8" drivers.

Using a tapered line will give you more So and shorten the line.

I'm very suspicious of the specced 3.3 BL value.

Try defining your driver in WinISDPro (freeware) and see what
what BL number come out. Could be per coil so is actually 6.6.
which is the ballpark BL for a Qts=0.6 driver, (here 4 ohms).

Doesn't look the easiest driver to c/o to a tweeter,
IMO consider the mid/treble drivers here :
http://www.zaphaudio.com/ZDT3.5.html

rgds, sreten.

FWIW corner fillets should be good enough,
you don't want one at the mouth.

http://www.t-linespeakers.org/design/MJK-for-dummies/index.html
http://www.quarter-wave.com/TLs/Alignment_Tables.pdf
http://www.linearteam.dk/default.aspx?pageid=winisdpro

[Russell Dawkins]

MLC,
Years ago when I was building a lot of transmission line speakers, I developed a little trick which you might like to use.

For the curves in the corners you can use a type of floor linoleum that has an impact adhesive on the back.
You cut it to size (slightly undersize in the width), then heat it at low heat in an oven (140º or so).
With a rubber mallet or similar at the ready, you place it where you want it in the cabinet and whack the edges at the beginning and end of the curve with the mallet/hammer.

When it cools it will be rigid, due to the curve - probably more rigid than thin ply or any wood equivalent.
Of course, you have to work fast so it is warm when you bend it into place, and also the adhesive is more effective when warm.
I hope you can use this - I hope they still make this type of linoleum!

[Levi]

I am a fan of good TL speakers.  When designed properly, you will have the best clean full-range bass for such small drivers.  You will hear full-range sound even on low volume levels.  A perfect DIY project because you can tune your speakers to your room and ears. 

[guest60106]

Thank you Russell. That is a good tip. I was planning on using some flexible 1/8” veneer backed up by corner blocks but your idea sounds better.

I measured the divers last weekend. I will post the results as soon as possible. (maybe tonight?) I used a Parts Express woofer tester and my home computer. It was my first time doing this and I spent the entire day measuring all different kinds of drivers I had lying around so that I could understand the system and also get used to the data output scheme. I did this so that I could get used to spotting faulty data and also get an understanding of how the measurements are correlated. Being a mechanical engineer by trade, I have learned the importance of vast repetitions to get a feel for a new type of measurement system. Metrology is not a trivial field.

The metrology system from Parts Express has its short comings but over all I am pleased with the results (assuming the accuracy is fair. It was only $100). It crashed a few times and I had to recalibrate a few times but it told me a lot more about the drivers than I knew. That is what I was looking for.

The measurements I took on the AC-180 drivers were a bit shocking but not unexpected since I have read a few posts on Aurum Cantus quality control. I will post the results as soon as I can and welcome discussion. I have also been playing with MJK equations and looking harder at a tapered design. I will post some pics of the model soon. I want to start the build in the next couple of weeks if I can.

Sreten, your input is valuable. Please keep it coming.

MLC

[planet10]

The deflectors can actually be counterproductive. Without the deflectors you get a line expansion which acts as a low pass filter, subtle but real. Means that for the same ripple you can use less stuffing and get more bass.

dave