Old, old, PVC pipe design...

[Ronmeister]

Hi All,

After searching this, and other, forums I hope I'm not re-hashing old topics... here goes!

In the 80's there was a design floating around in DIY circles consisting of a small 4" mid/bass paired with a Tweeter both from KEF. The enclosure consisted of a 4" PVC tube inside a 6" PVC tube, effectively creating a transmission line of sorts. I've attached a drawing I rendered from memory.

A few questions:

1) Does anyone remember this design? It was posted in a HiFi Magazine that was distributed in the early 80's in Holland. I believe the magazine went out of business in the mid 80's. I recall the reviews of actual builds of this design were very positive.

2) Is this a design worth pursuing? So much progress has been made in the past 25 years... It would seem a fairly easy build, leaving a lot of room for creativity and individualism, not to mention unit choice (two way, singly driver...).

3) If it is worth pursuing what units would we use?

[AuroraB]

Well- it is kind'a late and my brain is tired, but if circle A is a solid disc - how on earth will you excite the line part ???? All I see is a small closed box on a resonant, ringing stand....???
If A and B had the same open crossection hole, we could be getting somewhere, though....

[rtirion]

The design was made by John van der Sluis.
A moderate construction effort was required.

The slots in the outer tube were not that easy to make
and required some patience to get right.

Original speakers were Focal (W) and Audax (T)
I still own a pair. Even have contruction details.
I think the model name was L-50. First appeared in a magazine
Audio & Techniek around 1982.

You can reach John at www.audio.nl (I am not affiliated in any
way to John).
He even has some succesors / to this design.

[rjb]

There was another designed by Rex Baldock of HiFi news, called a tricolumn.. Basically a Voigt Tapered design, a number of scaled models for different size speakers were published in the period 1959-62. It used PVC tubes he acquired as off-cuts, but also he experimented with other materials including paper tubes, rolled plywood and steel (with a paper liner,glued inside).

For example the 8" model was a 36" tube 8 12/16 ID. (Diam due to what he could get, and not critical). Open at the lower end and set about 1" above the floor. The top end sealed with an 8" full range speaker mounted pointing upwards. A reflector could be used if desired.

Inside was a 4 3/4 ID tube offset to one side, 25" long, sealed at the lower end, and cut at the top with a 45 degree angle to clear the speaker.

The result was a tapered cross-section in three steps, closed at one end, open at the other, with the speaker set 1/3rd from the open end.

Frequency responses were published for 4 cheap speakers available at the time including Elac, Wharfdale and Goodmans. Naturally these varied with drive unit, but for example an impedance plot for a unit with a high Q peak at 55Hz open air, showed two lower peaks at 30and 100 Hz, with the upper one reduced considerably by damping.

For such a simple,cheap and high WAF enclosure results were good. I threw one together and at the time thought it OK, as good as a BR with the same unit, but with slightly less (but cleaner) bass.

However using MJK calcs and specific driver parameters should produce a design constructed similarly but with better results

[PeteMcK]

take the last dot off that URL for his latest designs.

Here's how I did it a few years ago - before I knew anything about TL design (I intend to re-visit these someday using what I've learned from MJK in the interim), not so elegant as the above design, but a bit easier to build:
Karlson-slotted pipes

[Ronmeister]

Originally posted by rtirion
The design was made by John van der Sluis.
A moderate construction effort was required.

The slots in the outer tube were not that easy to make
and required some patience to get right.

Original speakers were Focal (W) and Audax (T)
I still own a pair. Even have contruction details.
I think the model name was L-50. First appeared in a magazine
Audio & Techniek around 1982.

You can reach John at www.audio.nl. (I am not affiliated in any
way to John)
He even has some succesors / to this design.

That's the one! And that's the magazine! I can't believe how badly my memory deserted me. The name of the magazine, the units... etc. The designs on John's website do conjure up memories of the "L-50".

Thank you so much for taking the time to reply!

[rtirion]

YGM