Monday, June 21, 2010

"Small Thor" ML-TL Transmissionline speaker project

I was really inspired by the thread at diy on Seas Thors. Thor uses very expensive Seas drivers like W18E001 woofers and T25CF002 "MILLENNIUM" tweeter mounted in a D'Appolito (MTM) configuration. These drivers are beyond my budget & reach. So here in this experiment, the idea here is to build a similar TL based on the budget minded drivers. Here i am using locally procured speaker drivers & crossover.

In this modified design there is a solid brace behind the driver ( Mid-woofer magnets should fit tightly to notch) this transfer & distribute the energy from the driver to the back of the cabinet & the other one runs parallel with the baffle notch. Brace needs to be filled with random holes. It has 4" long & 3 " dia port at the back. I have used two 19mm MDF boards for the cabinet.

Sandwiched two19mm boards for the front baffle  using PVA glue (Fevicol)        


Marking for driver cutouts

Done with the marking......

Driver holes cut using jig saw

 Marking for countersink holes

Countersink holes done.........

Test fitted the drivers.......looks perfect !!!

Cutting circular holes on the brace

Holes almost done..............

Cabinet almost ready

Fitted the drivers & crossover

Closeup of xover

Filled the upper half of the cabinet with Dacron fibre

Here are the TS parameters of the mid bass driver.

Woofer size : 6.5”
Motor :          120MM magnet with 8MM top and bottom plates
Polepiece :     31.5MM
Voice Coil :    32MM Dual Layer wound in 32Guage wire
Spider :          100 MM wide and 10MM tall
Cone :            Air Dried with Rubberised Form Surrounds

First set of them without any hours on them (or max less then 1hr)

Re :6.8487
Fs : 47.3723Hz
Zmax :186.0971 Ohms
Qes :0.3228
Qts :0.3109
Qms :8.4475
Le : 0.7287
Vas : 25.8084 L
BL : 8.7027
Mms : 11.9917g
Cms :941.2622
Sensitivity :90.546@ 1M /1W

Second Test results after some brief burn-in using 25Hz Sine wave

Re :6.844
Fs : 47.42Hz
Zmax :186.72 Ohms
Qes :0.3244
Qts :0.31
Qms :8.5251
Le : 0.7287
Vas : 25.8084 L
BL : 8.82
Mms : 12.398g
Sensitivity :90.88@ 1M /1W

After 5 Hours of 25Hz sinewave

Re :6.88
Fs : 43.8792Hz
Zmax :177.1931 Ohms
Qes :0.3000
Qts :0.2883
Qms :7.4175
Le : 0.7308
Vas : 26.9775 L
BL : 9.2001
Mms : 13.3713g
Cms :983.8979
Sensitivity :90.546@ 1M /1W

After 3 day's of listening of the “Small Thor” i think i can now make few comments on the result.
The main objective was to get better bass out of the cabinet, after 6 hours of listening with NAD 314 & Pioneer SA 9100 amps, speakers sounded excellent with lot of bass, good mids & clar high's but the second cabinet was bass shy. After inter changing the bass driver it sounded like the first cabinet, so it's important to test the drivers before they are bought. Stuffing dacron also plays a role here, i did experiment with it to see how much stuffing to use, to keep the bass reinforcement, but kill off the losses higher up. When i got one side working, i pulled out the stuffing & weighed it, and the same amount of dacron was stuffed in the other cabinet (approximately stuffed 300 grams of dacron per cabinet).
I played jazz, 80's disco & indian classicals, i am pretty pleased with result. Drivers are still new so they may sound different after burn in. I really enjoyed building this small thor, it is truly worth the effort


Blogger Keerthi said...

How much does it cost to make a set of these?

July 2, 2010 at 4:08 PM  
Blogger Anil said...

Hi keerthi, it costs around 15 - 17 k

July 2, 2010 at 5:28 PM  
Blogger Windowshopper said...

very well. some great time n effort being put in there.


March 17, 2011 at 4:47 PM  
Blogger shivap said...

nice speaker diy. locally procured drivers? pls let me know which make and how much it costed?

August 25, 2011 at 11:18 AM  
Blogger SS18w4531g00 said...

Thats as much as a TL or any kind of transmission line as I am Queen Elizabeth. This is a standard D`Appolito design with very wrong placement of polyfill and too much spacing between the midwoofers leading to severe comb effects on the vertical plane. And with no information on the design itself - line simulation and graphs, measured response, driver parameters (a TL works best with drivers wiht Qts of 0.45-0.6) and etc, its pretty pointless loss of bandwith to post it. Your build quality otherwise is very good, go to one of the specialised forums for audio and read mroe about transmission lines and loudspeaker design. Loudspeaker cookbook is a very good start for beginners, I`d highly recommend you read it. Besides, the Thor is ok but its price performance is not good. Not sure why D`Appolito (he designed this in his early days)settled on a MTM design for a transmission line.

October 10, 2017 at 2:40 PM  

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