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Old 18th March 2006, 05:16 PM   #1
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Default TL design questions from a newbie.

NOTE:
This is a branch of my "simple designs" thread. They're valid questions, though.

1. Sonotube woofers: Can these be done with a folded transmission line, or using a shorter pipe and woofer, perhaps made of PVC? I don't have the room for a full sonotube!

2."Straight tube" transmission lines.
http://melhuish.org/audio/DIYTQ7.html
I'd like to see if I can find some spare drivers to make a pair of these as my first DIY speakers. They're simple, and cheap!
I was wondering, though, how I could calculate the correct length of pipe, and how I should mount them. Should the pipe be braced to keep it from "ringing"?


3. Folded transmission line
You can see what I mean under the "babysnakes" section.
http://www.t-linespeakers.org/projec...son/index.html
How do I figure out the required lengths, and how to fold it? I'd like to try a folded TL design, possibly with the speaker at a right angle to the loops of pipe so that I could mount it on my wall. (I have a small room, and not much floorspace).

4. Batting
I'm still confused as to how and where I can and should use this.

5. Portable designs
The biggest appeal of PVC pipe (to me, anyway) is the durability and resilience; you can drop PVC without damaging it. Would anyone mind helping me find a design for a simple, portable speaker design? Quality does'nt have to be amazing; I just want a portable speaker to use with my laptop, and I can't afford a Tivoli PAL. (Stereo is'nt important; you only really hear one channel with most tiny stereos, anyway.)

Thanks,
Joe.
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Old 18th March 2006, 06:35 PM   #2
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Default Re: TL design questions from a newbie.

Greets!

1) If you mean a tube within a tube, yes, since you're creating a tapered quarter wave tube (TQWT), which can be further mass loaded with a vent (ML-TQWT).

2) Either use Rick Shultz's Alpha TL math http://homepage.mac.com/tlinespeaker...TL-article.pdf or check MJK's Classic Alignment charts http://www.quarter-wave.com/Theory/Alignment_Tables.pdf

Use his worksheets to sim their response and/or fine tune them if you want.

3) Fold it as you want, just make sure you ~maintain the flare through the bends.

4) It's a personal preference thing, so experiment to find your acceptable trade-off between the tube's hollow and/or too lively sound Vs bass attenuation.

5) Yes, it's more durable, but transmits more of the impact to the driver, so may not be the best material to use if you're a klutz. As for a design, check out the various threads on small ~FR drivers. There's some suitable designs.

GM
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Old 18th March 2006, 07:37 PM   #3
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Reading those made my mind try to explode. Remember, contrary to what some EEs say, audio engineering is not an easy thing to do.
I don't have access to woodworking equipment, so I think I'll go for a plain-tube design, such as Guiuseppe Pipitone's "periscopes".

http://melhuish.org/audio/DIYTQ7.html


I'm going to try ordering a pair of Hi-Vi B3S's as soon as I'm no longer swamped with work. That way, I can tinker with "periscope" style designs, and compare them to the speaker design you reccomended.

Anyway, here's (even more) questions:
1. What diameter of pipe do you reccomend for the 3" drivers? 3" pipe is cheap and convinient; but smaller pipe would work if I doubled it back on itself.
2. How long should the pipe be for a single B3S?
3. What's the best way to mount a speaker on to a piece of wood or MDF? I was thinking that I could cover a ring of stiff styrofoam (Bluecor) in epoxy, with the side glued to the inside of the tube, and the front glued to the actual piece of wood/MDF. That way, it would dampen vibrations, and I'd save myself a lot of trouble.
4. Can you reccomend a small woofer? I'm also a bit confused on the reccomended length of tube; I'd like to keep it as small as possible. (Think "Bose-Small", but without the pricetag.)

I'm sorry about the need for "spoon-fed" information, but I'm a high school student, and I've yet to take physics yet. I'd just like to try bodging together a pair of speakers so that our cheap-tastic home theater setup does'nt sound so bad, and maybe a pair for my robotics team.
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Old 19th March 2006, 02:12 AM   #4
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Greets!

1) The driver's size doesn't have any bearing on the pipe's CSA (cross sectional area), it's aunction of it's Fs, Vas, and Qts.

2) Forget 'B*** small, you want that small, buy B***: Design a Bose-beater

A TL's length is a function of the desired Fp (aka Fb in a box alignment and Fc in a horn's). Historically, it was based on the driver's Fs, but in recent years anything goes now that there's a program to ~accurately sim them. Anyway, read this thread and my fencepost MLTL should serve your needs except for size: Advice: a fence post for a full range?

3) Cut the proper size hole, chamfer out the backside so the driver can 'breathe' and install a handmade cardboard or similar gasket to seal it between it and the baffle. Some folks use thin closed cell insulation tape or non-hardening putty instead.

4) My background/preference is cinema/prosound drivers, so I don't keep up with the latest n' greatest consumer/DIY offerings, but I have a pair of Adire Extremis 6.8s that are right impressive and should be adequate in a small BP (bandpass) alignment of around 1 ft^3 gross, though at $100 plus shipping may be over budget.

The Apex Jr. Super 8 has gotten some good reviews and is cheaper, but I don't know if they will sell you only one: http://www.apexjr.com/speakerstuff.html (scroll down).

GM
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