Hi Lon,

"My pipe diameter is standard 4" with the fittings.

So you probably have an S0/Sd of about 1.6 which is a littrle low but not too bad. As a TL's area gets bigger the bass resposne gets better. I have found that this effect starts to reach a diminishing return at about S0/Sd = 3. The classic rules of thumb recommended S0/Sd = 1.25 which in my opinion is too small and chokes the bass response.

I bet you are learning a lot and having a great time in the process.

>> Yes, lack of tools meant that I had to find a design without much cutting that
could be done with a hand saw. But I am still mathmematically challenged.

If I were to recommend a classic TL per my understanding of the topic, I would recommend the length I previously posted and a pipe diameter of at least 5 inches. If you could find a way of mounting the driver 20% to 33% along the length you would get additional improvement. Maybe a "T" could be used.

>> Ok. So a speak made this way could use the 6" diameter PVC at 40" of length using
the information from the previous post as a guide(?)

The issue that I had when making my initial length was: How does downfiring into
carpet affect what is heard? I could understand downfiring onto a wood floor
but carpet would have to absorb the energy of the sound would it not? So then I
got onto the idea of getting the pipe pointing forward like the driver. That was on the
single length tube. Then I used the longer length, cut it down and bent the tube
up with a fitting at the open end identical to the elbow for the driver.

6" pipe at 40" is going to look like a narrow trashcan sitting in the living room...
or maybe two of them. Sonotube is no decorator's dream either, but someday I
am going to fool with that depending on how the current work goes.

So you probably have an S0/Sd of about 1.6 which is a littrle low but not too bad. As a TL's area gets bigger the bass resposne gets better. I have found that this effect starts to reach a diminishing return at about S0/Sd = 3. The classic ruls of thumb recommended S0/Sd = 1.25 which in my opion is too small and chokes the bass response.

I bet you are learning a lot and having a great time in the process. If I were to recommend a classic TL per my understanding of the topic, I would recommend the length I preciously posted and a pipe diameter of at least 5 inches. If you could find a way of mounting the driver 20% to 33% along the length you would get additional improvement. Maybe a "T" could be used.

"I had wondered how SPL effects pushing the sound through such a long length... or which of the parameters addresses the issue of
pushing the sound through a long length."

The sound does not really get pushed through the length. The pipe responds at discrete frequencies that are related to the length. At these frequencies the air in the pipe resonates, attenuates the driver's motion, and almost all of the sound comes form the pipes open end. This is similar to a BR but at more frequency values.

I used a sonotube for my test TL and it worked great. I('ve) seen many TL designs using sonotube both tall straight ones and folded ones using nested tubes of different diameters.

>> Where are examples of the nested tube approach? These would be new to me.

If you can cut cardboard easily and glue joints that are air tight then sonotube would probably be as flexible to use as the sewer pipes. Nothing wrong with cheap and easy.

>> The next tool I will get is a spin saw. RotoZip is the commercial name and there's
examples of their use here in AudioRoundtable. I've made a homebrew spin saw using
an electric handrill, a drill guide (type found at Sears) and RotoZip(c) bit. I've
found that using this rig makes little dust and what waste is created goes down
more than up into the air. There's some holes in the drill guide which I've used
as centers to cut circles. But I am limited to using this rig for the 3 circle diameters
available. The spin saw comes with an adjustable circle guide.

To conclude, you said up there that a 3/4 wavelength pipe
would be a total of 10 ft. What could I expect by adding on
another short length to go the full 10 ft. distance?
Would anything be gained?"

I have no idea how a 3/4 wave pipe would work and if there is an advantage or disadvantage to using one. I always try to keep things small. TL's tend to be big enclosures and I struggle building big boxes and getting up two flights of stairs form the basement to my listening room.

>> I am asthmatic. I live on one level. So the things you are saying applies
to me as well. Small tools, low dust levels, and minimal lifting. At age 56
I have no work and would like to learn something I can do at my own pace.

"Since the 3 ft. 4" length for a TL is pretty close to
my shorter tube, I'm thinking that the driver should
be on the shorter length which would be closer to listener's
sitting height and the back tube would be open and may
not even need an elbow for "directionality" if I'm
reading what you're saying correctly. In that configuration
it'd prob'ly look more like a calliope."

I think that this experiment would answer the question above. Try the two different length and see what you hear. Maybe one will be far superior to the other. The proof is in the listening.

>> That will be my next step: reverse the construction keeping the same lengths
and test individually. Then after that, add some additional length out to 10 ft
of length total.

Hope that helps,

>> It certainly does, though I don't know if I will ever be able to apply theory
over intuition and listening experience. Bill Schultz' followup article in
_audioXpress_ on Alpha t-lines should provide some additional clarification.

>> I have scouted the Tangbands and Fostex extensively and I use the FE87e in
my computer setup. I use the FE87e's in some doctored mini enclosers from an
old Nakamichi shelf system. Being in Wisconsin, Madisound is within driving
distance or fairly inexpensive shipping.

lon

I think a 40 inch long piece of 6 inch diameter PVC would work well. Having the open end near the floor should not be a big problem, you might try using a 12 inch square wood base and mounting the pipe 3 or 4 inches above the base on attached legs. I have seen similar things done many times without any hints of poor performance resulting.

I remember seeing a sub done this way on the DIY Forum, I think. Basically it was something like a 12 inch diameter tube with the driver at one end near the floor. The sond came up this tube and then wnet back down a 15 inch tube mounted concentric ans paced about 3 or 4 inches above the end of the inner tube. The sound then exited the outer annulus near the floor. This arrangement was a different way of folding the line in half.

I am also waiting to see the next alpha TL article from Schultz. I have communicated with him a few times and we have swaped ideas. He approaches TL design and alignment a little different so it is always interesting hearing about his results.

Martin

So the outer 15 in tube was capped on the top? I'm trying to visualize this thing: 12in. driver facing up at the floor attached to
a tube (what length I wonder?) Then a 15 in. tube inserted over it
with little legs or something keeping it off the floor. The top would have to be capped then ennit?

Ceramic tiles would work well on a base too I think.

I've made the switch on these tubes putting the driver on the
shorter lower front tube and the open end with an elbow at the
rear. On the other one I put an extra length of pipe on
the rear portion with no elbow like a smoke stack. Too early to
say if this is practical plus it is not cut to a specific length.
Overall the length of that one from throat of the terminus to driver is... omigod 9 ft 9 in... just shy of the 10 ft 3/4 wave length.
If I put the elbow back on I'd have it all.

Soundwise, I have no test equipment so not sure about that last one up there. I spoze I should figure out what I have here by calculation but the 8.5 length is the closest thing to 'fitting a room' that I've come up with and sounding good to boot. I'm starting to get curious about how a different driver would sound.

Your description of the nested sonso-tube sub is correct. I don't remember the details but the builder was very happy. I think that you could find details in the DIYAudio forum Loudspeakers subforum if you go back far enough. I think it was at least a year ago.

As for your PVC pipes. You are on uncharted ground as far as I am concerned so I am looking to hear about your impressions. Does a 3/4 wavelength pipe offer any advantages over a 1/4 wavelength pipe. I have no idea.

Martin

Anyway, being pretty isolated socially from any other hobbyists I have no effective gauge of what I'm hearing. The first impression I
have of making the toobz length nearly 10 ft overall is that
effective listening is put too far out. In other words, just like
my 8.5 ft straight pipe open at the front bottom, you have to get
way back in order to appreciate the lower frequency reproduction...
with considerable volume.

The folded U-shape has given the most satisfying listening
experience.

other thing to try is going in the other direction: shorter.

I will follow up with the link (when I find it) of another approach.
It'd be good if all the tubes were archived in the same place but
I guess not many are doing this kind of building.

if u have a picture you need to show on a forum
draw it in MSPAINT,save as say a 16colour bmp,then resave as a GIF or PNG file(png is less distorted)email it to me, and i can save it on my webspace then ppl can see the pic to get the idea :-)

basshornguy(at)yahoo.co.nz

Cheers!

That's "Lon" and hello. :-)

My drawing talents wouldn't be up to the job. But
over time I'd like to show how the design progressed. That's easy
to do since all that needs to be done is reassemble the parts
a few times.

There's a small amount of webspace that's available at
my ISP account. It's just getting a proper image into it.

lon@athenet.net