Bass Driver for a transmission line speaker

[Paul N]

Thanks TLS Guy,
Our messages just crossed. Linear instead of conic hardly seems to make a difference.

 

[TLS Guy]

Thanks TLS Guy,
Our messages just crossed. Linear instead of conic hardly seems to make a difference.

That would be true. However, the minimal impedance of the speaker can not be less than the DC resistance R. That is why it can not be less than one.

Here is the impedance curve of my two KEF B139s in my rear back lines.

Since there are two drivers, obviously you have to double the numbers for one driver. So the impedance does not drop below four ohms, for the two, so the minimum impedance for one driver is 8 ohms.

Now for some speakers, especially some very high priced ones, that are incompetently designed, the impedance does drop below the DC resistance of the drivers.
This is absolute evidence that the crossover is in electrical resonance. Those speakers are amp busters and lousy speakers to boot. This is particularly prevalent in very high priced boutique speakers, by designers who have eyebrows for brains.

 

[Paul N]

That would be true. However, the minimal impedance of the speaker can not be less than the DC resistance R. That is why it can not be less than one.

Here is the impedance curve of my two KEF B139s in my rear back lines.

Since there are two drivers, obviously you have to double the numbers for one driver. So the impedance does not drop below four ohms, for the two, so the minimum impedance for one driver is 8 ohms.

Now for some speakers, especially some very high priced ones, that are incompetently designed, the impedance does drop below the DC resistance of the drivers.
This is absolute evidence that the crossover is in electrical resonance. Those speakers are amp busters and lousy speakers to boot. This is particularly prevalent in very high priced boutique speakers, by designers who have eyebrows for brains.

Do you have the B139 with fs 25 Hz, so the B139B, or the older version, which is a little bit bigger and has a bit lower fs?
Your impedance curve is showing a big peak at 60 Hz. What is the cause of this peak?
The specification of the B139B mentions different R values, nominal R is 8 ohm. Input Impedance is 7.2 ohm, but this R(E), and the others are coming from an electric circuit that is “equivalent” to the B139B. From what I have seen, the lowest impedance is most often slightly below Rnom. I thought that KEF‘s R(E) is the lowest impedance when operating with a normal signal. As far as I understand, they do not mention R(dc), which is the resistance of the driver when measured with a multimeter, I presume.

 

[TLS Guy]

Do you have the B139 with fs 25 Hz, so the B139B, or the older version, which is a little bit bigger and has a bit lower fs?
Your impedance curve is showing a big peak at 60 Hz. What is the cause of this peak?
The specification of the B139B mentions different R values, nominal R is 8 ohm. Input Impedance is 7.2 ohm, but this R(E), and the others are coming from an electric circuit that is “equivalent” to the B139B. From what I have seen, the lowest impedance is most often slightly below Rnom. I thought that KEF‘s R(E) is the lowest impedance when operating with a normal signal. As far as I understand, they do not mention R(dc), which is the resistance of the driver when measured with a multimeter, I presume.

I have the newest version. That impedance curve was generated with the driver in the TL enclosure. So the peak is the tuning peak.

In a properly damped TL, there should be one peak of impedance, as there would be in a sealed enclosure. There is a small peak at 25Hz, showing the line is slightly underdamped. When I moved from Benedict Lake to Eagan, I added a little more damping to the line. I have not run and impedance curve since.

I have dug up a copy of the original insert that came with the drivers. Min impedance is quoted as 6.7 Ohms, at 160 Hz. So that is likely correct as I measured it in the line.

They quote 6.6 as the DC resistance, but this is not correct. I have a number of them here and the DC resistance is 7.1 ohms. So that gives minimum impedance over R as 0.944, which is as close to 1 as makes no difference.

I hope this clears things up for you.

 

[Paul N]

I have the newest version. That impedance curve was generated with the driver in the TL enclosure. So the peak is the tuning peak.

In a properly damped TL, there should be one peak of impedance, as there would be in a sealed enclosure. There is a small peak at 25Hz, showing the line is slightly underdamped. When I moved from Benedict Lake to Eagan, I added a little more damping to the line. I have not run and impedance curve since.

I have dug up a copy of the original insert that came with the drivers. Min impedance is quoted as 6.7 Ohms, at 160 Hz. So that is likely correct as I measured it in the line.

They quote 6.6 as the DC resistance, but this is not correct. I have a number of them here and the DC resistance is 7.1 ohms. So that gives minimum impedance over R as 0.944, which is as close to 1 as makes no difference.

I hope this clears things up for you.

Thank you Mark for your patience with me!
Why have you tuned your TL’s at 50 Hz? Has it something to do with your placement of the B139B in the TL? I thought that TL‘s are normally tuned at fs of the driver. How does the frequency response of your TL’s look like?

 

[TLS Guy]

Thank you Mark for your patience with me!
Why have you tuned your TL’s at 50 Hz? Has it something to do with your placement of the B139B in the TL? I thought that TL‘s are normally tuned at fs of the driver. How does the frequency response of your TL’s look like?

Another misunderstanding. That peak of impedance is associated with the Fp the tuning frequency. Since the line is underdamped slightly you can see the tuning frequency Fp. It is at the low point of the saddle at 35 Hz.

It is just like a ported enclosure, where there is a saddle shaped impedance curve. The lowest point of the saddle is the tuning frequency of the box, but is NOT f3.

Here is a picture I pulled off the net which shows what I mean.

Since you ask here is the FR of those lines with two B139s in each line.

For what it is worth, here is the FR of those speakers.

The amp to the bass drivers was probably set a little hot in that measurement, however that is by ear where it seems to sound optimal. It actually seems f3 is 27 Hz rather than the calculated 30 Hz.

That speaker uses first order crossovers for the 900 Hz and 5 KHz crossovers. Design started in 1979. I had a lot of help from the folks at Dynaudio, as they were designing this monster with first order filters at the same time. Communications were snail mail and phone back then!

So your misunderstanding is a common one. Tuning frequency and f3 are NOT the same. For both ported and TLs the same applies. Fb will be above F3 and so will fp.

I hope this clears the matter up for you.

 

[Paul N]

Mark, you have given me a lot to think about. I will be going on our summer holiday (in Austria, we love the mountains, which we do not have).
I hope you do not mind teaching me more about building an excellent TL speaker. Anyway, thanks again for your willingness to share your knowledge with this newby.

 

[Eppie]

And a thank you from the lurkers too. Very interesting discussion.

 

[TLS Guy]

Mark, you have given me a lot to think about. I will be going on our summer holiday (in Austria, we love the mountains, which we do not have).
I hope you do not mind teaching me more about building an excellent TL speaker. Anyway, thanks again for your willingness to share your knowledge with this newby.

I know you don't have mountains in Holland. We had a family holiday in Belgium/Holland when I was 17. I loved it. It was the year I got my first driver's license. We took the car ferry over to Ostend. I did a lot of the driving for the family. We had an Austin A 60 estate, which was a real lump of lead.

It was just like this one, but white.

So that was my first experience of driving on the right side of the road. However the steering wheel was also on the right! So overtaking was a problem. My wife and I spent a few days in Amsterdam on our way back from Italy celebrating our 25th wedding anniversary. I spent a lot of time trying to find out what the Dutch meant by Beer and Schnapps. In my teens our boat was moored in a boat yard in Frindsbury Kent on the River Medway. There are a pub right there, and Dutch seaman would often lean over the wall as I worked on the boat, and ask where they could find Beer and Schnapps. I had to tell them I did not have a clue, and I'm sure the publican did not either. They seemed greatly annoyed. So in Amsterdam it still took me a long time to find what they had been asking for. As I suspect you know, it is Heineken with a chaser of Jacob Genever which is a potent gin that is extracted from the deep freeze before serving. Apparently this was favored by Dutch seeman according to the publican.

The UK, has kept to the Roman way of doing things, as they marched on the left, as most people are right handed, so that way they could have their swords at the ready, to smite enemy columns.

The French had to be awkward, and changed it to the right. During the early post civil war years, America was enamored with the French, Pierre Charles L'Enfant being the architect of Washington, which is why our capital city, has such a French feel to it. The US ended up driving on the right because of that connection.

Anyhow enjoy your time in Austria. I have only been in the part that used to be Austrian, but was given to Italy after WW I. I went to visit Gustaf Mahler's composing shack. The whole area was stiff with German speaking people prancing about in Lederhosen. They seemed a bolshy bunch to me, upset to be in Italy and not Austria.

 

[Eppie]

That car reminds me of my grandfather's Cortina wagon, another lump of lead. I'm from Austria originally but emigrated when I was quite young. Moved back at the age of seven for one year and then back to Canada again permanently. Wish I could visit there more often. Last time was 2016 when we visited Prague and Budapest and made a side trip to Vienna for a few days to meet up with family.

It's funny how the languages intermix along the borders in Europe. When we visited Switzerland there was just enough German mixed into the Swiss language that I could generally make out what they were saying. I don't think I've ever heard an Austrian called bolshy before though.

On an audio side note, my cousin runs the restaurant / concession at the new (2012) Muth Theatre in Vienna, located on the grounds were the Vienna Boys Choir live and rehearse. She told me it had some of the best acoustics in the world and got us comp tickets. She was right. We were in the balcony and there were singers on the stage and also some boys in the balcony for accompaniment. The boys down on the stage sounded just as clear and loud as the ones near us on the balcony. Simply wonderful.

 

[TLS Guy]

That car reminds me of my grandfather's Cortina wagon, another lump of lead. I'm from Austria originally but emigrated when I was quite young. Moved back at the age of seven for one year and then back to Canada again permanently. Wish I could visit there more often. Last time was 2016 when we visited Prague and Budapest and made a side trip to Vienna for a few days to meet up with family.

It's funny how the languages intermix along the borders in Europe. When we visited Switzerland there was just enough German mixed into the Swiss language that I could generally make out what they were saying. I don't think I've ever heard an Austrian called bolshy before though.

On an audio side note, my cousin runs the restaurant / concession at the new (2012) Muth Theatre in Vienna, located on the grounds were the Vienna Boys Choir live and rehearse. She told me it had some of the best acoustics in the world and got us comp tickets. She was right. We were in the balcony and there were singers on the stage and also some boys in the balcony for accompaniment. The boys down on the stage sounded just as clear and loud as the ones near us on the balcony. Simply wonderful.

I suspect the Austrians in Austria are not bolshy. However, I strongly detected that they had the mentality and "chip on the shoulder" of subjugated people which they are.

It was probably not helped by the weather. It absolutely pissed down due to a stationary front in the gulf of Genoa. After that we were booked in Verona, but travelling south it seemed to me that the skies were clearing south of the Po river. So we went to Bogna, and found a wonderful hotel. We found a nice restaurant, and asked the waiter for La lista (menu). He replied "In Bologna, es la lista orale". So as neither of us were at all fluent in Italian, we put ourselves in their hands. They made a tremendous fuss of us, and brought out course after course of the most delectable food we have ever eaten.

The next day we spent in St. Peter's Piazza. The was an elderly gentleman who ran a wonderful record store stacked with best CD collection I have ever seen. He spoke good English. I told him that I did not find a CD I would not be happy to own. There was absolutely no rubbish in the whole store. When I congratulated him on his inventory, he replied: "Ah, but it only gives me pleasure to sell beautiful music!"

No wonder Italy is considered the cradle of western civilization.

 

[Eppie]

I've only been to Italy once, as a teen. My great uncle took my parents and I to Venice. All he could speak was "aqua minerale" so we ended up drinking it everywhere but he was pleased as punch to say it. Great coffee there too. He loved history and museums and was a fountain of knowledge. Didn't need a tour guide as he seemed able to describe almost everything. I think I got my love for classic art and architecture from him. I can spend hours walking through museums and churches. My kids, not so much, but I try.

Story goes that my great uncle was in Italy when WWII ended. Had to walk all the way back to Vienna. Can't imagine how long that would have taken. The train ride from Vienna to Venice was long enough.

Italy is (or at least was) at the top of my list for countries to visit next. Little interest in Rome as it's become crowded with tourists, but been hankering to go to Tuscany and get some rustic food. Probably visit Florence. My late uncle said that was one of most beautiful cities in Italy to visit.

 

[lovinthehd]

I've only been to Italy once, as a teen. My great uncle took my parents and I to Venice. All he could speak was "aqua minerale" so we ended up drinking it everywhere but he was pleased as punch to say it. Great coffee there too. He loved history and museums and was a fountain of knowledge. Didn't need a tour guide as he seemed able to describe almost everything. I think I got my love for classic art and architecture from him. I can spend hours walking through museums and churches. My kids, not so much, but I try.

Story goes that my great uncle was in Italy when WWII ended. Had to walk all the way back to Vienna. Can't imagine how long that would have taken. The train ride from Vienna to Venice was long enough.

Italy is (or at least was) at the top of my list for countries to visit next. Little interest in Rome as it's become crowded with tourists, but been hankering to go to Tuscany and get some rustic food. Probably visit Florence. My late uncle said that was one of most beautiful cities in Italy to visit.

I enjoyed Firenze quite a bit, didn't get to go out in the countryside much, tho, was there on business a coupla times. The food, wine and coffee are all so good there.....

 

[Paul N]

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.

 

[Paul N]

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.

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?

 

[haraldo]

There is something "different" with the bass from a proper TL
There are hardley any TL subwoofers out there and those there is, are insanely priced IMHO

Thanks @TLS Guy for sharing that program ... I would like to go into "modelling mode" to see if I should replace my Audio Physic subwoofers.....

Currently I am having 4 stacked Audio Physic Rhea II subwoofers, there is an active 10" and a passive 10" driver in each... it´s really great, but great can always become better

 

[Paul N]

There is something "different" with the bass from a proper TL
There are hardley any TL subwoofers out there and those there is, are insanely priced IMHO

Thanks @TLS Guy for sharing that program ... I would like to go into "modelling mode" to see if I should replace my Audio Physic subwoofers.....

Currently I am having 4 stacked Audio Physic Rhea II subwoofers, there is an active 10" and a passive 10" driver in each... it´s really great, but great can always become better

Why stack them? Do they not work against each other?

 

[haraldo]

Why stack them? Do they not work against each other?

No, a lot of people do that around here, by stacking them you get more bass pressure, all drivers play in phase, twice the cone area, better room loading as the drivers trigger different standing waves (being at different physical positions in the room). Going from two subs to 4 subs stacked is a clear step up for me

Those who tried 4 subs this way never seem to go back to simply two subs...
I reckon this could be a large TL with the similar driver geometry on the front

I seen stacks up to 8 subs in two towers ... 4 in height, with all subs being set at exactly same settings....

 

[Eppie]

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.

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.

 

[Paul N]

No, a lot of people do that around here, by stacking them you get more bass pressure, all drivers play in phase, twice the cone area, better room loading as the drivers trigger different standing waves (being at different physical positions in the room). Going from two subs to 4 subs stacked is a clear step up for me

Those who tried 4 subs this way never seem to go back to simply two subs...
I reckon this could be a large TL with the similar driver geometry on the front

I seen stacks up to 8 subs in two towers ... 4 in height, with all subs being set at exactly same settings....View attachment 49397

Nice picture. I suppose you are not sitting in your living room? I have read that some Dutch audiophiles have a sub in each corner of their living room, but never of them stacking subwoofers.