An Improved Transmission Line Alignment

Most of my archive from that time is currently in storage, although since I need to head over there when I'm back on my feet I'll have a dig through. Monk (I think) did a 3-part piece. Bullock did some work & even a DOS model, but it only worked for untapered, undamped lines & I don't think was written up in SB, although my memory is hazy on that & I could be wrong. Rick Schultz did some work, although the latter part was mostly alignment tables derived from Augspurger. There were a couple of others but nothing significant on the math / physics front beyond those that I can remember. If there was, I'll have to seek it out as it would be good to have for the records.
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although since I need to head over there when I'm back on my feet I'll have a dig through. Monk (I think) did a 3-part piece.
It wasn’t very good IME.

Shultz’s work was going thru sims in Augspurger and then often making claims of inventing stuff many people were already doing.

I worked with him for awhile as well.

From 1937 some of the first work on thw subject:

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I don't know what the Hornresp model calls for in this design - in the designs I did and built, I put polyfil in the closed end and in the top down to the top edge of the vertical baffle. And the on the design that had the terminus on the front (very similar to this design) I did need egg crate to limit the higher frequencies coming out of the terminus opening.

I just noticed a smart thing on this build - the outer panels are Baltic birch, and the inside pieces are MDF. Makes a lotta' sense!
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Fact is B.F.'s claims for his speakers go way beyond
verifiable, and are largely invented marketing bluster.

Bud was a marketer first. I have heard many of his speakers. Even contributed to one. He did some very good loudspeakers (for the day), but his TLs would have been much better idf designed with a proper mideler (somethign that did not exist in his day) and like everyone else he guessed using classic design techniques and lots of real prototypes.

I have a very generic question can any one answer please.

in a TL do we need to tune the line resonance to driver resonance just like how we do in the ported box. I know both are different in many ways but is it usually the case that the line resonance to be tuned with the driver resonance so that the driver excursion at resonance is reduced?
I did extensive testing with different damping materials in my Impulse H2 inspired speakers. They are somewhat of a hybrid between a transmiisionline and horn speakers. The original H2 is a 3 way with hornloaded Seas 4,5 inch mid and Seas 8 inch woofer. In the woofer compartment there is no damping material. Since mine were 2 way I had to use some damping or else there was to much midrange echo inside the cabinets smearing the midrange.

I tried polyfill, sheeps wool and foam. Tried with small amounts and large amounts and placements of damping in all imagenable areas of the cabinets. What I found was that the bass was without a doubt the best with no damping material at all. But that was not ideal for the midrange. The best compromize was to use foam and as little as possible.

What I found with to much damping (and especially with wool and polyfill) was that I lost that crisp leading edge of bass notes. Kickdrum lost speed and articulation, as if there suddenly was a thick woolen sock over the hammer.

And in my other diy speakers with regular bass reflex tuning I have been using only foam. I like the bass better with foam. But there is always a trial and error period, and there certainly will be with these MLTL10's as well.
Impulse H2.jpg
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Will you tell us a little more about this design ?
For which drivers you design it ?
Dimensions ? Any response curve ? Group delay ? ......


Hi Elias,
This thread is about these MLTL10s, designed and generously shared by Neil.
A bit about the choice of drivers and crossover and the cabinet. A few years ago I bought some old Yamaha monitor speakers. The sound was more or less ok, but I thought I could beter them. After some discussion on various forums, a type of filter was proposed, developed by the BBC in the 60s and 70s, and used to this day by e.g. Harbeth, Spendor, Graham, Rogers, Stirling etc. After a bit of playing around with this, I've really got the feel for it.

For my MLTL10 build I will be using Scanspeak P21 and Hiquphon OW5.
So these old-fashioned Scanspeak (Vifa) P21 basses can seem like outdated dinosaurs seen through today's eyes. For example, if you look at the SB Acoustics bass/midrange, you get a much more modern design with a better motor, lower distortion, etc. for a very reasonable amount of money in my opinion.
But these dinosaurs have a few tricks up their sleeve that not many of the newer and more modern competitors have. If you look at suspension or transition between membrane and suspension, almost all of them struggle with resonances and in addition phase distortion here. Look at around 600-700hz for 8 inch woofers, about 1000hz for 6.5 inch and up to 1500hz for 5 inches. These old Vifas are almost free of this. And with the chosen filter topology, the crossover frequency will be around 3khz. Here again the dinosaurs are very well behaved in their upper working area. Both in terms of breakup and resonances, but also in terms of dispersion upwards in frequency. The membrane's design means that it has good dispersion further up in frequency than is common for many 8-inch speakers.
And then it has almost optimal TS parameters for such a relatively large transmission line cabinet.

With a crossover frequency of just over 3khz given by the filter topology, the list of candidates for treble was very short. You can prioritize completely differently when you crossover that high.
From my personal experience, I am a big fan of good soft-domes. Metal domes and other hard domes can sound good, with impressive reverberation and detail. But for me personally, I often like the "timbre" better in a soft-dome. Ribbon tweeters are other breeds that can be very good. But I think many of the constructions I've heard with them, integration with bass/midrange is a challenge. They are often sonically different, so even if they measure well, they often live a bit of their own life at the top there. Possibly a large ribbon tweeter that can be crossed over below 2khz would change my view on that. Or possibly a very light and fast 3-4 inch midrange would be a better match... But back to the OW5.
Oscar Wrønding (Hiquphon) was previously production manager at Scanspeak. After he left Scanspeak, he created these tweeters, he puts a lot of love into each individual product. They are hand-coated in many layers, measured individually and finally sold as matched pairs, and with each pair comes the measurement results for the exact pair you have bought. Due to their structure, they have a very good dispersion. They have low moving mass, no oil in the coil gap and are therefore extremely "fast". Independent measurements of csd, i.e. how quickly they "stop" after movement are extremely good. And so even though they don't have such a high thermal load capacity, they have an x-max (p-p) of 1.8mm so they can withstand a little beating. This results in a treble that has the sound of a good soft-dome, but can challenge other constructions in terms of speed and 'air'.

I have long wanted to try a transmission line project. When I realized that the P21 had nice TS-parameters for this construction, I just had to try it. The cabinet has a tuning of approx. 28hz, so this speaker will by all accounts go deep.
I have hired a professional cabinet maker to make the cabinets for me. We have discussed different options with regards to finish and aesthetics. The base or foot of the speaker is heavily infuenced by Graham LS6F, I really like that design.

There was leading time on the veneer, but the speakers should be finished in mid march. I will have the crossovers ready by then. Then there will be period of breaking them in and probably adjusting the damping material.
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