Ideas on how to improve the Thor transmission line speaker

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After getting excellent help in this forum ive decided to build a transmission line speaker. Ive thought most about seas thor speaker:

Now I want to improve the design of the thor. Or more correctly to tweak it. I dont have the skill to computersimulate new designs and dont have the time or means to build and rebuild several to find out what tweaks would be worthwile. So my goal now is to find tweaks that very very likely will improve the sound and then go for them.

Ive put together a list of own ideas. I would be very happy to get your views on them, or if you have other worthwile ( safe ) ideas to improve the sound. Thank you:

My ideas:
1. Move the treble a little to the side to lessen baffle difractions. ( i just dont know how much. one option is to move it as far as the slim cabinett allows you too. ) Madisound has a version of the Seas Odin speaker with the treble offset to the side. Both trebbles should be moved towards each other.

2. Strengthen cabinet. Glue 4cm solid oak board to the baffle. glue 2cm oak board to sides, back and top. This will create a 6.5 cm baffle that should be very stable. I know this seems excessiev but the extra thickness also allows me to round the corners and keep the nice oak finish.

Im also thinking of adding 1cm diameter oak rods horizontally at different heights to improve the strength of the cabinett. These will steal a little of the overall volume but will make the cabinet very rigid.

3. Increase the diameter of the rounded corners. The corners in the design shall be rounded to a diameter of 19mm. I want to increase this to 50mm. The extra thick baffle allows this. My hope is to get less difractions from the cabinett when i use the larger radius. ( i will also get a nicer look. )

4. Put the filter in a box outside the speaker. Modify it so you can trí-wire it with three sets of speaker terminals. Use best possible components. Does anyone have an idea what type of components to use? The reason for putting the filter outside the box is making it easier to later build an active filter and then feed the speaker from two or three power amps.

5. Build a stable heavy foot. I want to build a concrete foot that i screw the speaker down too. I will use a slightly larger footprint than the wood foot in the design. I also want to use high quality speaker feet in the concrete foot corners. Another idea is to add lead shots in the concrete mix to add to the weight. Im working on a design for this. My influence is the linn speaker feet. Very heavy and stable. nice!

6. Does anyone have experiances of adding supertweeters to existing speakers. Do you know of any good brands? ( not too expensive as im not totally convinced that there is a real benefit.. )

One could add one and design a filter to start giving the supertweeter power at 20kHz and work it up to its limit. The merge will not be perfect ( at all ) with the current tweeter as the frequency response is a bit erratic around 20kHz. I dont want to impose a lowpass filter on the normal tweeter just to add those batlike frequencies.

what do you think?
Me again. I have posted a couple of further replies that touch on some of this on the original thread, so I will only answer the additional stuff.

1: I like this idea. use a golden mean ratio to determine centre position of tweeter if possible (may not be due to baffle width.

2: Can't hurt, ecept thet you want to make sure there is no aerodynamic restriction behind the driver due to the thicker baffle. Make the driver cut-outs in the 'rear' or 'inside' baffle as large as possible. Router a chamfer on the inside of the oak baffle.

The 1' oak rods should increase the box stiffness and have a side benefit of giving you something to support the stuffing.

3: OK

4: Yes! Put the crossover outside of the enclosure. Inside, microphonics will compromise it's performance.

5: Large foot=good idea. Simpler than concrete, might be to laminate two sheets of your 40mm oak together, and shape the edges to suit your taste. Maybe 50mm radius like on the baffle?
Concrete can ring, and it's more difficult to attach the cabinet and spikes to.

6: Two suggestions for a supertweeter. <a href="">Fostex FT 17H</a> and <a href="">Visaton TL 16H</a>. The Visaton is about 5 times the cost of the Fostex, but I have used the Fostex with good results on Goodmans and Tannoy 15" Golds. I have had trouble downloading the pdf from there in the past, but I will email it to you if you like.

The Fostex is 98.5 dB sensitive, so pad it down heaps, add a series cap for crossover around 17kHz and adjust the positioning on the top to time align. IMO, it's a worthwhile addition for the small cost (Fostex).

I don't want to sound like a stuck record, but you are going to spend a lot of money modifying a very 'average' design. Your time, effort and $$ may well be better spent elsewhere.

Thanks for your input.

thanks a lot for your input Brett. Im now very interested in doing the Ariel speaker and Ill think Ill go for that one.

I was very impressed by the different Ariel sites. Its clearly visible that they have a huge following and a long history of incremental improvements.

I still think about adding the oak casing for a nice finish. Would look SOOO nice in my living room!! ) What conerns me with this is that if I add a 4cm oak board on the baffle Ill prolong the transmission line with 4cm.... That dont sound so hot..

If I dont do the solid Oak casing of the cabinett i dont know how to get a nice wood finish. I think its very difficult add veneer by yourself and get a nice result.. Perhaps paint it...

What will you do Brett?
I am new to this forum and ran across this thread while doing a search for "speaker feet."

I am almost done building the Thor Transmission Line speaker that you are referring to. I know your last post on this was almost a year ago but I thought you'd be interested to hear what another maniac has been doing to this design.

Because of the time demands of my job, I've been working on these speakers for about 2% per week and I almost ready done.

I started with an MDF cabinet that was double-walled on the front -- two 3/4" pieces of MDF glued to each other. Then I veneered both sides of 1/4" MDF and glued them to all sides (except bottom) of the speaker cabinet (total thickness 5/16"). The bottom MDF panel was hardened and leveled with West System epoxy which just soaked in the MDF. The show face veneer is Bubinga Pommele. With a rabbeting bit, I routed out a 1/2" x 1/2" groove on all edges so that I could glue solid strips of Bubinga along the edges and then 1/4" radius corner round them. Also, next to the edging on some of the edges I inlayed solid Gaboon Ebony.

In tests with a prototype that a friend built, we found that the tweeter had to be mounted flush, not surface mounted, or the entire response curve was thrown off. To preserve this, the speaker portion of the face was veneered with black dyed Poplar veneer (1/16") while the lower part of the face has the Bubinga/MDF sandwich in the format of a Golden Rectangle. This created a 5/16" ledge that the speaker grill could also recess into.

I decided to locate the crossover on the back of the speaker and to build a solid Bubinga base which is a very dense wood -- nothing like concrete with lead. However, with the modifications, these speakers already weight about 85 lbs with the components in them.

The crossover box is located in the lower back and protrudes 2.75 inches (8" x 8" x 2.75"). I extended the base beyond this by 1/2" for a total depth of 18" thus protecting the crossover box as well. Since the base is 14.5 wide, I plan to mount to skateboard wheels in cutout slots in the rear of the base. These wheels will be off the floor until the speaker is tilted back on to them.

I also added a solid Bubinga handle just up from the crossover box. This acts as a "roll bar" to protect the crossover box in combination the extension of the base. The handle makes it easy to pick up the speaker should that become necessary (one hand on handle and the other in the rear port).

My final task is to find the right isolation feet. I am trying to avoid spikes (w/protective floor disks). I would prefer a something more floor friendly but I don't want to compromise this design. I see no alternative to spikes as yet (at least as a sane price).

So that's my story. Next week a satin catalyzed lacquer finish will be sprayed on them and I will assemble the electronics.

If you'd like a photo or two when it's done, send me your email address and I'll shoot one off to you. Likewise, I'm happy to offer any woodworking advice if you need it.

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