Plastic TLs

[Geoff H]

I have mentioned on a few other threads my intro into TLs. After a bit of testing with 3" driver placed on top of 29" of 80mm PVC, suspended from a camera tripod, I hacked the rear satellite housings from an Altec Lansing ACS45, and glued them to 30" of 50mm PVC tubing. I am not using the original Altec drivers, as the suspension is a bit stiff.

The drivers are from a Packard Bell - Diamond Audio Technology PC multimedia set. I have no details of these, and guessed the Fr to be about 130 Hz. I suspect they may be a bit lower, thus the longer tubes. 90-20KHz

They sound great. Bass is thin, but what can one expect from a 3" driver? I estimate 10db down at 50 Hz. But what is there is smooth. No sign of one-note boominess. Midrange and transients are great. I haven't noticed undue ripple in the midrange, though still have a bit too much midrange from the open end - more damping needed.

I started with 2 cotton nylon blend socks in the 80mm tube. Now have a piece of tontine and a sock in each tube.

The system is definately better the the original plastic tuned port BRs. I am still using the amp that was mounted in one of the cases.

Bang for bucks? Plenty. Everything I had on hand, except the 50 mm PVC. Found that on the side of the road a few days ago. It had TL written all over it.

Next stage is to try tapered plugs/fine tuning the length, then a mounting foot.

Once the're finnished, they will be the rear satellites on the main system. (classic Hefner type bridge) So bass and power are not a big issue.

They would also be ideal as near field monitors. Spaced 80cms, listening on the apex,

[Geoff H]

A few errata.

ACS 45 should read ACS 54. The fr of 90-20K is on a label, no db ref. They go up to my limit, 17K or so. I don't worry what happens higher up.

[Spasticteapot]

Schweet. I need to try some of these!

[Geoff H]

After much listening to these marvels, I decided to convert to a folded TL. Rather than using bends to make a u-turn, I went concentic. A length of 80 mm pipe would provide the same cross-sectional area as the 50mm, with the 50mm inside. Glued to a timber base.

The bits waiting to be glued:

[Geoff H]

The almost completed unit. Will probably get a coat of matt black.

[Geoff H]

The annular grooves in the base locate the tubes. The smaller was cut with a hole saw. The larger was cut using a arbor in the base, mounted on a drill press, with an 5/32 drill. Poor man's mill/router!!

Before cutting, I checked the resonance. By setting up a telescoping section, I could adjust the length with music playing. What's needed here is a bit of 12 bar with good solid walking bass. Simply adjust the length to get a flat response over the bottom octave on a bass guitar.

I then checked the fr, 103 Hz. My method gave 32 - 33 inches. the finished length is 32.25. So does the formula!

The bass has come up a bit and less phase shifting around the room, most likely due to the port and driver being closer.

I haven't worried about BC yet, I'll probably build that into a surround decoder.

To me, it's not so much a question of what enclosure for a given driver, but what driver will work in a 1/4 wave TL. I'm hooked. I might even part with my Altec 411s.

[kneadle]

Originally posted by Geoff H
After much listening to these marvels, I decided to convert to a folded TL. Rather than using bends to make a u-turn, I went concentic. A length of 80 mm pipe would provide the same cross-sectional area as the 50mm, with the 50mm inside. Glued to a timber base.

The bits waiting to be glued:

Wow, very innovative solutions to some distinct problems. I appreciate that. Congratulations.

Dave

[planet10]

Now you have me thinking about annualr cyclindrical TLs again. Lotsa pipe here.... and construction is simple. It doesn't take advantage of driver offset thou... have to think on that. Zd of 50% should be achievable easily thou.

dave

[Pano]

Very clever! I have a lot of cardboard tubes at work, might have to try it.

But how did you suspend the inside tube? It doesn't go all the way to the bottom, right?

EDIT: Never mind! Found the photo that shows the holes in the bottom of the small tube.

[Geoff H]

Hi Dave, I just hit the wrong button, and nearly reported you.

I have thought about the offset. I have 2 more of those shells. I could cut a shape in the pipe, and hold the shell in a jig of somesort and run a hole saw to match the pipe. I bit like line boring. Getting a grip on the plastic without crushing it is the problem. Then I could sit down in front of a good DVD, with a file. Beats knitting!

I think I found the limit of these things this morning. Not happy with Pink Floyd at realistic levels. Too much bass energy for them. Yet on most recordings happy to show 90 dB at 2 metres on a 4 watt /ch amp