Thor Kit: Anyone build it?

[MJK]

The Thor design is not a very good TL. The cross-sectional area is too small for the two woofers. The bass output is limited by this small cross-sectional area, the enclosure effectively chokes off the lowest bass. There was a very good thread over at DIYaudio about the Thor design and a few alternate designs were provided that enhanced the bass performance. If the Thor cabinet had been made bigger the bass would have been deeper and louder but at the expense of commercial appeal.

 

[TLS Guy]

The Thor design is not a very good TL. The cross-sectional area is too small for the two woofers. The bass output is limited by this small cross-sectional area, the enclosure effectively chokes off the lowest bass. There was a very good thread over at DIYaudio about the Thor design and a few alternate designs were provided that enhanced the bass performance. If the Thor cabinet had been made bigger the bass would have been deeper and louder but at the expense of commercial appeal.

That issue is addressed by Joe d'Appolito. You can build the line according to the calculations from Ausperger's tables if you want. It is true there is a slight mismatch between VAS and Vp in the Thor design. I agree with Joe, however that this trade off is not excessively critical.

There is a lot of nonsense on the DIY forum, about this issue. If you look at it though, they are increasing output at the expense of correct damping. They are clearly under damping.

You have to look at the work of the developers Bailey, Fried, Radford and Wright to really understand this. There has been a huge amount of confusion since. G.L. Ausperger did make an important recent contribution.

 

[MJK]

I don't agree with d'Appolito and definitely don't agree with Bailey/Bradbury's work. Bailey and Bradbury messed up TL theory for over 30 years with the moving fiber myth. In my opinion, the Thor TL is way too small and the bass performance could be improved significantly with a larger enclosure. I think d'Appolito missed by not following Augspurer's tables more closely and not accounting for dual drivers correctly. As far as the DIYaudio forum, there is good and bad info on all forums and you need to weed through the posts with a critical eye.

 

[TLS Guy]

I don't agree with d'Appolito and definitely don't agree with Bailey/Bradbury's work. Bailey and Bradbury messed up TL theory for over 30 years with the moving fiber myth. In my opinion, the Thor TL is way too small and the bass performance could be improved significantly with a larger enclosure. I think d'Appolito missed by not following Augspurer's tables more closely and not accounting for dual drivers correctly. As far as the DIYaudio forum, there is good and bad info on all forums and you need to weed through the posts with a critical eye.

The F3 of the Thor is 41 Hz. Roll off is 12db per octave. You can think what you want, but that is excellent bass performance for a pair of 7" drivers! Just try and name speakers with such a low bass output with those size drivers. They will be few to none, to say nothing of the uncolored bass quality achieved by the Thor.

In summary the bass output from the line is really at the practical limit of those drivers. As you can see from the data the frequency response is ruler flat. If you did increase bass output, the response would no longer be flat and would not be a pleasant low Qtc system.

The only way to smoothly extend the bass reach is to transition to another driver system as I did. I leaned from John wright that tuning two lines wound around each other tuned around half an octave apart produces best results.

 

[WmAx]

Do not cross brace internally, if you do, the pipe will not work. You can make the walls thicker if you want by using 1" mdf. If you put in internal braces, I can assure you, you will ruin the speaker. I have built enough pipes to know..

Thicker MDF alone is not sufficient. The constrain layer construction I specified will be far more effective as compared to simple increase in wall thickness. As for bracing, I suspect you can easily add in steel 3/4" tubing crossed, that is epoxied to angle iron that is adhered to the side walls as the anchor points; I can't see how this small dimension cross piece can appreciably effect the line behavior.

The fact of them being non resonant refers to the tuning of the pipe with correct aperiodic damping, as stated earlier in the thread.

But this only refers to the air pressure behavior. The physical vibration that collects at the driver end of the pipe from air pressure excitation to the panels, and the physical driver vibration transmitted from driver frame to baffle, will make the entire cabinet vibrate substantially. Accelerometer data demonstrates that a typical TL cabinet has no better panel resonance behavior as compared to any moderately braced standard cabinet(which are both completely insufficient).

But, most people are accustomed to some cabinet resonance in their sound reproduction I suppose; but I won't ever accept it.

-Chris

 

[MJK]

The F3 of the Thor is 41 Hz. Roll off is 12db per octave. You can think what you want, but that is excellent bass performance for a pair of 7" drivers! Just try and name speakers with such a low bass output with those size drivers. They will be few to none, to say nothing of the uncolored bass quality achieved by the Thor.

Have you personally measured that result? I just ran the numbers and in my estimation best case F3 is no lower than 50 Hz, probably closer to 60 Hz, and it is rolling off and quickly approaching a 24 dB/octave slope. Don't believe everything the manufacturer puts on their website.

 

[legion1capone]

Is there any cabinets out there that you can buy suited for the thor kit?

 

[TLS Guy]

Is there any cabinets out there that you can buy suited for the thor kit?

http://www.audioxcel.com/audioXpress Thor Review.pdf

http://www.madisound.com/catalog/index.php?cPath=35_40_401_276

 

[TLS Guy]

This one is also mostly great.

Which one?

 

[R-Carpenter]

I am not sure about Thor but I always wanted to build transmission line. Thor driver compliment was never very affordable nor was my personal preference.
I just finished building a very similar TL, call it Thours if you will with the objective to go through same calculations as Joe D'Appolito did.
Drivers were Usher 8945A and Hiquphon OW4
It sounds incredible. I've attached FR data, just one of the files.
Design was done with wise tutelage from TLS.
I am now working on second generation with slightly different drivers.
Mark, BTW, what say you to the anechoic measurements of Thor on Seas web site. It does look like it starting to roll off at about a 100hz. Is that an artifact of measurements and in this case summed up MLS data is actually more accurate?
Roman.

 

[R-Carpenter]

trying to attach
here we go it worked.

 

[TLS Guy]

I am not sure about Thor but I always wanted to build transmission line. Thor driver compliment was never very affordable nor was my personal preference.
I just finished building a very similar TL, call it Thours if you will with the objective to go through same calculations as Joe D'Appolito did.
Drivers were Usher 8945A and Hiquphon OW4
It sounds incredible. I've attached FR data, just one of the files.
Design was done with wise tutelage from TLS.
I am now working on second generation with slightly different drivers.
Mark, BTW, what say you to the anechoic measurements of Thor on Seas web site. It does look like it starting to roll off at about a 100hz. Is that an artifact of measurements and in this case summed up MLS data is actually more accurate?
Roman.

I think the reason is that the SEAS measurement is just a near filed measurement and the port output has not been summed to the woofer output.

Joe addresses this issue in his article.

CLIO works in the time domain and
produces both amplitude and phase response
data. The woofer and port responses
are measured separately and
then added, taking proper account of
phase and woofer/port area differences
to get the complete low-frequency response
of the line. This process is described
in detail in Chapters 4 and 7 of
my book, Testing Loudspeakers5. Photo
1 shows the lab setup for testing and
trimming the line.
When measuring the port near-field
response, you must place the microphone
in the plane of the port exit.
The port measurement is then corrected
by multiplying it by the square root
of the ratio of port area to the combined
area of the two woofers. This
correction is:
After correction, the port response is
added to the two woofer responses
to get the complete near-field TL
response.

 

[R-Carpenter]

You mean far field without port response summed up?
Seas response looks similar to Dayton 4 inch full range driver without the hump between 16kHz and 20 kHz. It can't be that a speaker with a pair of 7 inch W18s rolls off at 200 just as a 4 inch driver would.
Have you measured either of the Thors you build by any chance?

Lets not forget that D'Appolito was designing a system for Seas to show off their drivers and obviously had some limitations in terms of size and appearance of the speaker.

 

[AmadeusMozart]

Thicker MDF alone is not sufficient.
-Chris

Actually the BBC did a study that thicker material may have more resonances than the thinner materials and is harder to dampen.

(Factors in the design of loudspeaker cabinets. H D Harwood, R Mathews, BBC RD 1977/3)

 

[AmadeusMozart]

Martin King has promoted what he calls a mass loaded TL in recent years. He has published a modeling program. I personally do not regard those as TLs. I think they are specialized ported enclosures. I think he has added to the confusion of an already confused area, for people who have not studied this form of loading in depth..

Completely agree! Besides this he himself is confused about modelling and is trying to fit the real world to a software model that he has created.

If the real world does not comply with his software then he assumes that the real world is wrong because "computers don't lie". As the Tui ad here in New Zealand goes: "Yeah right".

AM