New DIY MTM Towers designed by Dennis Murphy and Paul Kittinger

[Sailor Mike]

Some info about bass alignment with a SET amp.
The higher output impedance of a valve amp, particularly a SET, will raise the Qes which then raises the Qts. This affects the bass alignment, typically it causes a hump in the response at very roughly 100Hz.
Fortunately this can be fixed, by calculating Qes and then modelling in Winisd, adjusting the port tuning to improve things.
I have posted how to do this in Diyaudio, multi way speakers, a thread 'SET Friendly MTM, Seas ER18RNX and 27TDFC'.
Using Winisd, different box frequencies can be tried and results for frequency response and group delay can be seen, and tuning changed to reduce the hump while keeping group delay below 10mS, as suggested by an expert. In my case, 30Hz looked good and the result sounds good.
Winisd will also find the port length for you.
This process is highly recommended if you want to use these great speakers with a SET amp. I can't say if it's worth doing for a PP valve amp which should be fine as is, but if anyone has an issue with bass quality it might be worth doing the maths and modelling it.

I do hope people (Dennis in particular) do not take this as in any way criticising this excellent speaker! It is not meant that way; it's just a tip about matching them, as matching amp and speakers is important.

 

[BigArtoo]

Hi, I am trying to understand this design.
I am struggling to see the "transmission line" in this design. Could someone explain it? I see a traditional bass-reflex box only. In other words, what is the length of the TL in this design?
Does anyone have the source simulation files from WinISD or Hornresp?
Are there better plans of the box than what is seen on the first page of this tread?

 

[everettT]

Hi, I am trying to understand this design.
I am struggling to see the "transmission line" in this design. Could someone explain it? I see a traditional bass-reflex box only. In other words, what is the length of the TL in this design?
Does anyone have the source simulation files from WinISD or Hornresp?
Are there better plans of the box than what is seen on the first page of this tread?

You won't find the simulation files as I'm sure that Paul used Martin Kings software. Also, it's a quarter wave transmission line and they can closely resemble a bass reflex box. Paul has been doing these a long time and his work is excellent. I own both TLs and bass reflex from him via Salk Sound.

Link to Martin's site

Quarter Wavelength Loudspeaker Design

Derivation and Correlation of a General Acoustic Model for a Fiber Filled Transmission Line Loudspeaker.

www.quarter-wave.com

 

[TLS Guy]

Hi, I am trying to understand this design.
I am struggling to see the "transmission line" in this design. Could someone explain it? I see a traditional bass-reflex box only. In other words, what is the length of the TL in this design?
Does anyone have the source simulation files from WinISD or Hornresp?
Are there better plans of the box than what is seen on the first page of this tread?

They are what is known as mass loaded TLs, and you are right, but they have more in common with a bass reflex design than pipes. It does reduce enclosure size which is the attraction, but the penalty is fourth order rather than second order roll off, although F3 will be a bit lower. The big penalty is that Q can not be well controlled as only a truly damped aperiodic line can give you essentially non resonant reproduction. The other issue is that the number of drivers with T/S specs optimal for aperiodic TLs is limited. The optimal ones are the KEF B 139, back in production from Falcon acoustics, and some of the SEAS Excel drivers. I was playing my rear surrounds the other day, that have two KEF B139s in each line. You would have sworn there was a potent sub playing, when there was no such thing. They could shake the floor and vibrate your chest cavity without difficulty.

 

[BigArtoo]

Thank you TLS Guy.
It was my understanding that these speaker boxes were designed using Martin's worksheets. I have never seen them but I heard they are pretty accurate. I was hoping that someone tried to reproduce the original design using either WinISD or Hornresp, hence my question.
I've build a couple of TLs in the past but never an MLTL. And from what I know MLTL still should look like a pipe with the only difference being the output section of a constant diameter tuned to the same frequency as the pipe. Essentially, a pipe tuned to Fres with an output looking like a BR port tuned to the same Fres as the pipe. I do not see this in this box. What I see is a standard BR.
I am planing to build another one and while doing a research I came across this thread. I like the design as it is fairly simple but the drivers used here are rather exotic and hard to get hold of in Europe. I see that B139 can be bought in UK, but it is expensive and import taxes are not helping.
So for my next diy project I plan to build either this design or Ekta-TL by Troels. And in either case I will be looking to replace the drivers with something easier to get hold of and less expensive.