Compound Transmission-line

delfi

Member
2007-08-27 10:13 am
Anyone with knowlegde or experience with using a small sealed chamber and extra compound-driver between the main driver and the transmission line, as described in these two patents:

TRANSMISSION LINE LOUDSPEAKER WITH COMPOUND DRIVER
http://www.wipo.int/pctdb/en/wo.jsp?wo=2000016588

Push-pull transmission line loudspeaker
http://www.patentstorm.us/patents/5815589-fulltext.html

I know T+A used systems like this back in the early 90’s.

Without increasing cabinet volume, I guess a compound driver will better the systems transient respons, raise sensitivity, and give more “dynamics & size” to bass and lower mids as compared with conventional systems?

Any drawbacks?

Does the extra/auxiliary driver has to be smaller than the radiating driver (as in old T-+A speakers) ??

Will the distance between the two cones and the trapped air introduce phase cancellation at certain frequencies thereby also limiting bandwidth to maybe 300-500Hz ??



Stein S
 
Hi Stein,

delfi said:
Anyone with knowlegde or experience with using a small sealed chamber and extra compound-driver between the main driver and the transmission line, as described in these two patents:

TRANSMISSION LINE LOUDSPEAKER WITH COMPOUND DRIVER
http://www.wipo.int/pctdb/en/wo.jsp?wo=2000016588

Push-pull transmission line loudspeaker
http://www.patentstorm.us/patents/5815589-fulltext.html

I know T+A used systems like this back in the early 90’s.

I designed such a system a few years ago (2001), somebody approached me with the idea and he had four Focal 13" woofers on hand. I had derived the equations needed to model an Isobaric enclosure design in the late 1980's so I programmed them into one of my MathCad TL worksheets and gave it a try.

Basically the Isobaric driver arrangement allows you to decrease the cabinet size by a factor of two, in a TL this means the length stays the same but the cross section is one half the required area for a single driver. The results were a tapered ML TL that was quite compact for a 13" diameter woofer. It went flat to 30 Hz and the feedback I received was very positive.

In reading the first patent, I am amazed that they were allowed to patent this design. Isobaric alignments of drivers have been around forever and there have been commercial speakers using the concept. I remember a very good AES paper on Isobaric speakers that I used to derive my equations and it predates this patent by a lot of years. The description of how the TL works also leads me to believe they are still counting on moving fibers to shorten the length. It would appear that the technical understanding of TL's is not very good. I don't believe they could enforce this patent.

Without increasing cabinet volume, I guess a compound driver will better the systems transient respons, raise sensitivity, and give more “dynamics & size” to bass and lower mids as compared with conventional systems?

I don't think any of those things are true. The main advantage is smaller enclosure size.

Any drawbacks?

The additional cost of two drivers per side and complexity of build. You have to be careful when sizing the trapped volume of air and the frequency range being fed to the woofers. You can get a second set of resonances of the drivers seperated by this air spring if the volume is too large or the driving frequency is too high.

Does the extra/auxiliary driver has to be smaller than the radiating driver (as in old T-+A speakers) ??

No, it could be bigger, smaller, or identical. I used identical because it made the design simple. I did look into using two different drivers and rolling the rear driver off above the fundamental cabinet resonance. I don't remember the results of all of the studies, it was too long ago.

Will the distance between the two cones and the trapped air introduce phase cancellation at certain frequencies thereby also limiting bandwidth to maybe 300-500Hz ??

Yes, all kinds of nasty things can happen if the air volume and drivers combine to produce a resonance at higher frequencies. The MathCad models showed a lot of these things fairly accurately so you had to be careful with the design.

Hope that helps,
 

delfi

Member
2007-08-27 10:13 am
Thanks, Martin

If anything looks to good to be true….

In any case, I will build a prototype with each W18E supported by a L18s inside each line (I have an Ariel-inspired 3way today with double W18Es). The main problems are resonanses in the air trapped between the two drivers, and phase-problems between the two cones in midrange?

In that case I will limit the volume, and cross the W18 (and L18) low, around 500-700Hz to the mid driver (Seas MCA11).



Stein
 

Thawach

Member
2007-12-13 9:48 pm
Hi martin


You explain very good. i understand.

sometime i would like to build isobaric speaker.
But i don't know about transient of it.
The sensitivity i had known.
I ask you that about the transient of it.
is it better than vent box systems?
I had ever seen M&K iso speaker as a long time . that time
i understand that it's the best transient for the large driver.


regards

;) /Thawach
 
Thawach said:
sometime i would like to build isobaric speaker.
But i don't know about transient of it.
The sensitivity i had known.
I ask you that about the transient of it.
is it better than vent box systems?
I had ever seen M&K iso speaker as a long time . that time
i understand that it's the best transient for the large driver.

If I understand your question correctly, you are asking if the Isobaric alignment has a better transient response compared to other enclosure alignments. I don't see any reason why it would have a better transient response. Depending on the driver and the type of enclosure design, the transient response can vary between different designs and I don't believe one type of enclosure is necessarily the best all of the time.