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-   -   Here's an interesting TL pipe question ??? (http://www.diyaudio.com/forums/subwoofers/95252-heres-interesting-tl-pipe-question.html)

Fish Chris 29th January 2007 07:58 PM

Here's an interesting TL pipe question ???
 
I was already considering a 10ft to 14ft pipe anyway. Probably 10" in diameter, and I will have almost no choice but to mount it horizontally, next to the ceiling.......

But I just had an interesting thought; How would it change things if most of the pipe, and the drivers themselves, were in the next room over, and only the open end of the pipe came into the listening room, through a perfectly cut hole in the top of the wall (then sealed around the pipe) ???

In other words, kind of a cross between a TL design, and an IB design ?

Just wondering if this might help, hurt, or have no effect either way ?

Your thoughts please,
Fish

lndm 29th January 2007 08:56 PM

No, it wouldn't hurt at all, but I would have reservations.

Modern thinking about transmission lines suggests that pipes are typically not needed to be that long. Have you built one before and do you know what to expect?

Fish Chris 29th January 2007 09:14 PM

Hello Indm....
 
No. I have built a bunch of tuned port enclosures, and a few sealed ones, mostly for car audio, with just a few for the home, but no TL pipes.

I have been researching the heck out of TL's though, both here on this forum, as well as all over the Internet. It's pretty confusing really, as I have found so much conflicting info. For instance;

I have heard that horizontal pipes are not recommended, AND that they are perfectly okay....

I have heard that the pipe diameter should be no less than the driver diameter or slightly more (like 100% to 110%) AND that a 10" diameter is just about right for most 15" drivers.....

I have heard of successful TL pipes as short as 6ft, and as long as 12ft (14ft if you include the small attached enclosure at one end).

Here on this forum, GM supplied me with a chart which takes driver specs into account. It shows that a 9.7" diameter pipe, by 168" (14ft) would work optimumly with a 15" Dayton Titanic...... but you don't think so ?

I'm certainly not arguing with you Indm, I'm just trying to make sense of all of the conflicting info on TL pipe design.......

Peace,
Fish

Oh BTW Indm, GM also supplied me with a calculator for a "quarter wave" pipe, which is only about 6ft in length. I believe the 168" pipe is for a half wave design.... more efficient ?
Can you imagine how long a "full wave" pipe might be ? ;-)

lndm 29th January 2007 09:58 PM

Re: Hello Indm....
 
Quote:

Originally posted by Fish Chris
Here on this forum, GM supplied me with a chart which takes driver specs into account. It shows that a 9.7" diameter pipe, by 168" (14ft) would work optimumly with a 15" Dayton Titanic...... but you don't think so ?
I have respect for what GM has to say and wouldn't question it.

It's just that in my experience (I have built TLs for 4, 5, 6.5, 8, 10 and 12" drivers) I found that the old rule of thumb in tuning the pipe to the drivers resonance often produces weak pipe output. I just wanted you to be aware of this before you punched holes in your walls or you might be punching holes in your walls :clown:

Transmission lines have come a long (very long) way in the last less than a decade (although some would say that some smart cookie knew it all along :)). You will have a job to eliminate all of the out of date information that you come across.

With regards to the response of a given pipe (much to the disdain of some), I feel you'd get useful answers from a simulator. You might look toward forum member MJK http://www.quarter-wave.com/ for example.

Fish Chris 29th January 2007 11:00 PM

Thank you Indm.....
 
I guess if the quarter wave pipes were 95% as efficient as the half wave design is, I'd be okay with this. In fact, this would even allow for verticle placement of a couple pipes (one for each of my two 15" subs).

Yes, I have been to http://www.quarter-wave.com/, but all of the examples I saw over there, were for "folded horn" TL's. While I am just really intrigued with the simplicity, and unusualness of a great big pipe organ type of sub woofer horn :-) I couldn't find a straight up "plug in the driver specs, and get a pipe length and diameter", simulator on this site. Is their one that I'm overlooking ?

Anyway Indm, like I keep saying to anyone who has built successful TL pipes, here are the subs I'm strongly considering: http://www.partsexpress.com/pe/pshow...number=295-420
{found then on e-bay a week ago for only $149 each, too !}

And again, I'm looking for lots of bass in the 20 to 40Hz range, with an upper cutoff of between 50Hz and 100Hz... not sure on that aspect yet, as it will depend on whether or not I keep the sub that comes witrh my HTiB, for use as a mid-base driver.

With all respect to other peoples opinions of course, if it were you, how would you design a pipe(s) for two of these subs ? Length, diameter, stuffing ? (keeping in mind I can only get sono-tube in increments of 2"... so 8", 10", 12", etc.

Thank you,
Fish

bjorno 30th January 2007 01:05 AM

2 Attachment(s)
Quote:

You will have a job to eliminate all of the out of date information that you come across.
I applaud that comment.:)

Quote:

Here on this forum, GM supplied me with a chart which takes driver specs into account. It shows that a 9.7" diameter pipe, by 168" (14ft) would work optimumly with a 15" Dayton Titanic...... but you don't think so ?
Why not!

b

1(1)
:)

lndm 30th January 2007 01:54 AM

Re: Thank you Indm.....
 
Quote:

Originally posted by Fish Chris
With all respect to other peoples opinions of course, if it were you, how would you design a pipe(s) for two of these subs ?
bjourno's simulation seems to have done the work for me :) A flat impedance and a response falling gently to be 10dB down at 20Hz which will blend well with the room gain of many typical listening rooms. Quite similar to the infinite baffle response. Not bad.

You say you want a crossover at 50-100Hz? Whilst this can be done you may find it a little close to the low end rolloff to come together simply. You may want to go active or increase the frequency.

On the other hand if I were to design a text book TL without having a simulator I would probably do this:

Pipe frequency of 50Hz or 5'8"
Pipe volume of 2.7' ^3 with the start of the line at 4 times the area of the mouth.
3dB down at 38Hz

This may give you a line that suits the driver well but you'd need to consider the suitability of the resultant system for your room. My first guess though is that it may suit you.

Cameron Glendin 30th January 2007 10:37 AM

Hey Chris, that driver looks a lot more like it, than the Alpine featured in the unhappy chappy thread.

Useing more than one sub tube in your room is a good idea, more even sound than one, room issues ect.

Although my design is old way, ie fs is the length, The results are very impressive and compared to bass reflex, quite easy to get.

If you want to go up to 100hz, it might be a good idea to place the driver either 1/3 or 1/5 the length of the tube for a smother response up higher, similar to boses acustic wave cannon.

I look forward to details of your success soon.

Personally my gut reaction would be not to vent the speaker from the other room. Sound from the front of the cone is as loud as the rear and the idea is to re enforce the lowest frequencies with the combined sound of both, the pipe is to shift the phaseing so that they match. '

Im just speculating! as I don't truely understand the theory. Its quite possible that the shake will pass through the walls. I know at the cinema, that people hear/ feel it through the concrete floor, in the shopping arcade downstairs!!!!!!

bjorno 30th January 2007 02:48 PM

2 Attachment(s)
15" TitanicMKIII again.

b

1(1)

Fish Chris 30th January 2007 05:13 PM

Hey Bjorno....
 
I REALLY appreciate all the great help, with the graphs and such. The first two were of a bit too small file size for me to be able to read the text very easily.... But this latest one is perfect. In fact, I have printed it out, and tacked it to my cork board, right here beside my PC.

Hey, you've already helped more than I could have even asked for (I suspect that doing these graphs must be fun for you :-)

But if you get a few more spare minutes, and if you don't mind, how would the graph for a straight "quarter wave" pipe compare to the longer "half wave" pipe you have posted here ?

And the one that would be even tougher for me to ever figure out..... With both of my Titanic 15"s {because I'm definately getting two of them, to be powered with a nice, big Crown Amp} attached to the bottom of one pipe, like this one: http://www.teresaudio.com/haven/subs/place.jpg (Half wave, or Quarter.... not really sure)

Thanks so much again,
Fish


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