Bass Driver for a transmission line speaker

[haraldo]

View attachment 49393
Schöne Grüsse aus Österreich.
Happy to read about good memories of visits to Europe. Right now the clouds are gradually disappearing and the sun has returned.
In my mind the clouds on good TL design are also clearing. So, I now understand that the design frequency for the line/pipe is not fs, but around the middle of the frequency area which one wants to boost, seen the free air frequency response of the driver. https://audioxpress.com/article/thor-a-d-appolito-transmission-line/10034 provided a lot of information additional to that already given by TLS guy.

I read in other forums that the Thor seem to be a bad design with improper TL tuning and not really good bass response at all, am I wrong here?

 

[TLS Guy]

http://www.seas.no/images/stories/diykits/pdfdataheet/thor_measurement.pdf shows the final result of d’Appolito‘s Thor TL. In the very interwsting article linked above he writes: ”The resulting line produces a uniform 3–4dB bass response lift from 110Hz all the way down to 20Hz with less than 1dB ripple.” The effect of the port with the right amount of padding is from the article and shown below.
View attachment 49396
The design of d’Appolito is from 2002, when there was a lot more about knowledge about how to design a TL speaker.
The design of the housing can be seen using a link on http://www.seas.no/index.php?option=com_content&view=article&id=382:thor-seas-diy-kits&catid=66&Itemid=250 .
TLS Guy, do you have any remarks with regard to d’Appolito’s design of the Thor speaker? Do you know of any other published TL designs that are as good as this one?

Yes, that Thor design was the first to really use George Augspurger's TL model.

Soon after that was published, I built a pair of those Thor speakers for my late father on a trip to the UK. I was very impressed with them.

So when I came to design my new studio monitors back in 2005, the midline of those speakers takes a lot of inspiration from that design. Then I borrowed the late John Wrights idea of using two lines half an octave apart, and built the bass line around the midline. Since roll off is 12 db per octave, even though calculated F3 is 27 Hz, it has no trouble in room, going to 20 Hz and below. In fact with room gain you have to keep them tamed.

So the shorter line is run full range, but I give the Baffle Step Compensation to the upper driver in the basslines vai an active network. Both 10" drivers receive the sub output and LFE signal. The BSC is variable, and it is set at a different level in this new room compared to the last. This really enables speakers to be voiced to the position in the room. The cross from the receiver is only low pass to the bass line. The mid is acoustic only. In this room it sounds and measures best at 40 Hz, in the last room is was 60 Hz, so there was some overlap there.

Here is a picture of the drivers.

The port for the midline is just above the top 10" driver. The midline has to be configured differently to the Thor, as the Thor is rear ported. The bass line ports either side at the top.

Certainly the bass is deep authoritative, really tight and highly realistic. I have never heard more realistic bass reproduction.

 

[Paul N]

Yes, that Thor design was the first to really use George Augspurger's TL model.

Soon after that was published, I built a pair of those Thor speakers for my late father on a trip to the UK. I was very impressed with them.

So when I came to design my new studio monitors back in 2005, the midline of those speakers takes a lot of inspiration from that design. Then I borrowed the late John Wrights idea of using two lines half an octave apart, and built the bass line around the midline. Since roll off is 12 db per octave, even though calculated F3 is 27 Hz, it has no trouble in room, going to 20 Hz and below. In fact with room gain you have to keep them tamed.

So the shorter line is run full range, but I give the Baffle Step Compensation to the upper driver in the basslines vai an active network. Both 10" drivers receive the sub output and LFE signal. The BSC is variable, and it is set at a different level in this new room compared to the last. This really enables speakers to be voiced to the position in the room. The cross from the receiver is only low pass to the bass line. The mid is acoustic only. In this room it sounds and measures best at 40 Hz, in the last room is was 60 Hz, so there was some overlap there.

Here is a picture of the drivers.

The port for the midline is just above the top 10" driver. The midline has to be configured differently to the Thor, as the Thor is rear ported. The bass line ports either side at the top.

Certainly the bass is deep authoritative, really tight and highly realistic. I have never heard more realistic bass reproduction.

Funny, I was already thinking about a separate TL for the mid speaker. With ”the mid is acoustic only”, do you mean it is not filtered, except that sub and lfe aren’t fed to it?
As far as a folded TL is concerned, is it not better to assist the soundwaves by rounding the corners? When I was building our house, the plumber said that he tried to avoid 90 degree bends, by using 2 45 degree bends. I would be surprised if aerodynamics of the interior of the cabinet are of no concern to the sound quality of the speaker.
Has Joe d’Appolito ever heard your speakers?

 

[Paul N]

Thank you for the lovely photo. Makes me want to visit home.

I hope to start some speaker builds some time next year. Probably try something small for my computer desk-top, or one of Dennis Murphy's designs, either the BMR Monitor or the ER18MTM TL design using these drivers from Meniscus. The ER18MTM is pretty well regarded and there is a good discussion thread in the forums from when one of the members built a pair.

Your welcome. I am always a bit disappointed by stand alone small speakers, even if they go low. In a surround setup, it is different. I looked at the Paul Kittinger design you presented a link to and do not understand why he calls it a TL and not a bass reflex. Maybe TLS Guy can shine his light on it. The drivers are nice, but quite pricy in my view. This might be a nice read for you https://www.tnt-audio.com/casse/kerr_acoustic_k300_e.html

 

[ryanosaur]

Your welcome. I am always a bit disappointed by stand alone small speakers, even if they go low. In a surround setup, it is different. I looked at the Paul Kittinger design you presented a link to and do not understand why he calls it a TL and not a bass reflex. Maybe TLS Guy can shine his light on it. The drivers are nice, but quite pricy in my view. This might be a nice read for you https://www.tnt-audio.com/casse/kerr_acoustic_k300_e.html

I've had a few conversations with Paul K. I cannot speak for him, obviously. I do know that he is fond of the Mass Loaded Transmission Line and a majority of his designs follow this principle. He wrote to me once that all things being equal between a TQWT and a MLTL, the MLTL will always have a smoother response in the lower octave(s).
I'm certain there will be debate about this... it's just what he has found in his time designing Speakers and therfore his preference.
The key item in a MLTL is that the Port/Terminus still has to allow air to pass without audible sound or chuffing. My Mains are one of his designs and they do quite well. I would like to see a test between the Phil 3 Bass cabinets and the new BMR Tower which is also an MLTL using the same driver (8" Revelator) and the same tuning (25 Hz).

Regardless, I've seen many people write off all TQWTs and MLTLs as just a poor and overly complicated version of a bass reflex design: that they have little to no value to offer. I disagree with this sentiment quite strongly.

An interesting side note is that Paul also believes that the best Bass Reflex designs should involve Quarter-Wave Theory. The BMR Monitor is an example of this in practice. While I do not understand exactly how the modeling is applied, the port is optimized in placement/size (my understanding) to take advantage of that principle. For those who have experienced the BMRs, I think all would agree that there may be something to this as every comment I've heard discusses the strong output the BMR has down into the mid/low 30s. A marvelous achievement in a .75cu.ft cabinet with a 6" Scan-Speak Classic woofer.

 

[Paul N]

I read in other forums that the Thor seem to be a bad design with improper TL tuning and not really good bass response at all, am I wrong here?

From the frequency response curve, one can only be impressed. Maybe because the port is on the back, it is more critical where you place the Thor. Also see TLS Guy’s remark. Further there is the matter of taste and expectation. If one expects the Thor to be great and to produce a lot of bass...

 

[Paul N]

I've had a few conversations with Paul K. I cannot speak for him, obviously. I do know that he is fond of the Mass Loaded Transmission Line and a majority of his designs follow this principle. He wrote to me once that all things being equal between a TQWT and a MLTL, the MLTL will always have a smoother response in the lower octave(s).
I'm certain there will be debate about this... it's just what he has found in his time designing Speakers and therfore his preference.
The key item in a MLTL is that the Port/Terminus still has to allow air to pass without audible sound or chuffing. My Mains are one of his designs and they do quite well. I would like to see a test between the Phil 3 Bass cabinets and the new BMR Tower which is also an MLTL using the same driver (8" Revelator) and the same tuning (25 Hz).

Regardless, I've seen many people write off all TQWTs and MLTLs as just a poor and overly complicated version of a bass reflex design: that they have little to no value to offer. I disagree with this sentiment quite strongly.

An interesting side note is that Paul also believes that the best Bass Reflex designs should involve Quarter-Wave Theory. The BMR Monitor is an example of this in practice. While I do not understand exactly how the modeling is applied, the port is optimized in placement/size (my understanding) to take advantage of that principle. For those who have experienced the BMRs, I think all would agree that there may be something to this as every comment I've heard discusses the strong output the BMR has down into the mid/low 30s. A marvelous achievement in a .75cu.ft cabinet with a 6" Scan-Speak Classic woofer.

I read about your mains being very nice speakers. Will look into the BMR monitor. Thanks.

 

[TLS Guy]

From the frequency response curve, one can only be impressed. Maybe because the port is on the back, it is more critical where you place the Thor. Also see TLS Guy’s remark. Further there is the matter of taste and expectation. If one expects the Thor to be great and to produce a lot of bass...

It is true, that Joe did reduce the line volume Pv somewhat for cosmetic reasons. This probably compromises output a little. However it is a really good sounding speaker.

I think the major problem is that there were a lot of prebuilt kits, but they were done in a way that it was impossible to stuff the line correctly and that is crucial.

The ones I built for my father were really good speakers.

As far as mass loaded lines, I'm not in favor of them. They really have much more in common with ported reflex enclosures then an organ pipe. The impedance curve and the fourth order roll off scream bass reflex alignment.

I did toy with those years ago, and used a passive radiator in place of the port. This is the JW Jupiter. Not a speaker to be proud of, but you live and learn.

A properly designed TL, and I stress that, is in a league of its own. The problem is that so very few have been properly designed. It has taken me a lifetime to really get the hang of it. George Auspurder's work really took out the guesswork and I'm hugely indebted to him. If it were not for his work, I know I would not have the speaker system I now enjoy.

 

[Eppie]

Your welcome. I am always a bit disappointed by stand alone small speakers, even if they go low. In a surround setup, it is different. I looked at the Paul Kittinger design you presented a link to and do not understand why he calls it a TL and not a bass reflex. Maybe TLS Guy can shine his light on it. The drivers are nice, but quite pricy in my view. This might be a nice read for you https://www.tnt-audio.com/casse/kerr_acoustic_k300_e.html

Thanks for the link. It may not be obvious from the photo but the US$671.48 is for both sets of drivers (6 in all) and the crossovers. The Kerr Acoustic K300 you linked to is $2995 pounds or US$4118. A comparable speaker in the US would be the Philharmonic BMR Monitor ryanosaur mentioned (which also uses a ribbon tweeter) for US$1700-$1900 per pair or US$2400-2600 in premium finishes from Salk Sound. The drivers and crossover for the BMR Monitor are US$972.24 for the pair for those that want to build their own. The BMR Tower looks to be very promising judging by the initial measurements.

 

[haraldo]

Do any of you guys have any experience with the Troels Gravesen TL designs .... there are some on his site that also seem to be quite cool

All of the following are TL's
Some of them also employ TL for the midrange

Jenzen-NEXT

Jenzen CA

Ellam-FLEX-3W

Jenzen-Illuminator

 

[Paul N]

Thanks for the link. It may not be obvious from the photo but the US$671.48 is for both sets of drivers (6 in all) and the crossovers. The Kerr Acoustic K300 you linked to is $2995 pounds or US$4118. A comparable speaker in the US would be the Philharmonic BMR Monitor ryanosaur mentioned (which also uses a ribbon tweeter) for US$1700-$1900 per pair or US$2400-2600 in premium finishes from Salk Sound. The drivers and crossover for the BMR Monitor are US$972.24 for the pair for those that want to build their own. The BMR Tower looks to be very promising judging by the initial measurements.

Hi Eppie,
the link was not to promote the Kerrs, but to show that for a small speaker, a TL can also be very interesting

 

[Paul N]

Do any of you guys have any experience with the Troels Gravesen TL designs .... there are some on his site that also seem to be quite cool

All of the following are TL's
Some of them also employ TL for the midrange

Jenzen-NEXT

Jenzen CA

Ellam-FLEX-3W

Jenzen-Illuminator

Well not first hand, but from what I have read, like https://techtalk.parts-express.com/forum/free-classifieds/54892-jenzen-seas-er-ca-troels-gravesen-tl-design his designs are worth looking at. I might consider building the Jenzen Next cabinet, but no way I am going to spend so much money on the crossovers that he designed. Bi-amping and finding a cheap filter for the mid and high is what I am thinking about.
TLS Guy, what do you think of the cabinet design of the Jenzen Next?

 

[Eppie]

Hi Eppie,
the link was not to promote the Kerrs, but to show that for a small speaker, a TL can also be very interesting

Yes, a different approach to the BMRs. Would be interesting to compare the two.
Ah, more links to check out. Haven't seen the Gravesen builds before.

 

[ryanosaur]

Haven't seen the Gravesen builds before.

I love looking at his designs and builds. There is so much cool info on that site, it's almost impossible to find some things twice!

 

[ryanosaur]

I love looking at his designs and builds. There is so much cool info on that site, it's almost impossible to find some things twice!

I should add, I aspire to have my XOs be as clean and organized as his look. I have nothing against Active designs, but when I build my next XO (and I will), I want it to look more like his do just as a matter of pride and craftsmanship.

 

[Eppie]

I should add, I aspire to have my XOs be as clean and organized as his look. I have nothing against Active designs, but when I build my next XO (and I will), I want it to look more like his do just as a matter of pride and craftsmanship.

I like his idea of using a terminal strip down the centre as a common connection point. Nicely laid out.

 

[ryanosaur]

I like his idea of using a terminal strip down the centre as a common connection point. Nicely laid out.

Yes. The Solder Tag Strips are great. I adapted that to my first XO Mod project. I bought small ones (3 tags each) which allowed me to place them as necessary and not waste so much material or space. Using his technique of connecting a copper wire across a few tags is a marvelous way of avoiding a huge solder ball when connecting multiple leads to hook up wire, for example.
I used 2 or 3 on my XOs at places with common connections. It really made the process much more orderly for my first time. Yes it adds labor time to work them in, but the reward in orderly layout and simplicity of soldering is huge.

 

[Paul N]

Y

I love looking at his designs and builds. There is so much cool info on that site, it's almost impossible to find some things twice!

Yes, its quite impressive.

 

[Paul N]

I should add, I aspire to have my XOs be as clean and organized as his look. I have nothing against Active designs, but when I build my next XO (and I will), I want it to look more like his do just as a matter of pride and craftsmanship.

Are you good at designing XOs? I have no experience in that field at all.

 

[TLS Guy]

Well not first hand, but from what I have read, like https://techtalk.parts-express.com/forum/free-classifieds/54892-jenzen-seas-er-ca-troels-gravesen-tl-design his designs are worth looking at. I might consider building the Jenzen Next cabinet, but no way I am going to spend so much money on the crossovers that he designed. Bi-amping and finding a cheap filter for the mid and high is what I am thinking about.
TLS Guy, what do you think of the cabinet design of the Jenzen Next?

The crossover is the absolute heart of a speaker. You don't find a cheap filter. Off the shelf crossovers do not work ever. You have to design them custom from the ground up. That is probably the most difficult aspect of speaker design. All crossover have to be custom to the T/S parameters, acoustic responses, and power bandwidths of the drivers.

The first issue is driver selection. That is the first step. If you pick drivers out of thin air, you are very likely to find that the design and build of a crossover for that combination is not even possible.