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Old 20th July 2004, 06:13 AM   #1
JinMTVT is offline JinMTVT  Canada
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Question Subwoofer designs .. TL ? need help!

I am in the process of determining my next project.
This subwoofer is for my room ( 15 by 10 by 9 high )
and will accompany my DIY ESL pannels for music and diverse listening ..

I've been reading about difference deisgns for woofers,
one that i like is the Transfer line ...
After reading lots and lots of pages about this design,

i tried to think of my own.

What do you expert thinks about this quick sketch :


This is for a 15" driver tunned for 30hz 1/4wave ...
the total travel lenth ( center of path) is just short of 10'

I have no restriction for spacing ,
and my point is to get the best performance possible
with good SPL from this box. ( + have fun doing it )

This design tapers to 0.50 area of the 15" at the end

i am a total newbie to audio, so please let me know if im' wrong

my point in this design, was to tune the box
so the back wave of the driver will be in phase and at the same place as the front wave of the driver after passing trhough the enclosure. ( is that what we want? )

i thought that why would we loose all the power from the back of the driver ( is that correct to think so ? )
i guess that it can be used to reinforce the lower bass of the driver by phasing it with the front ??

1/4 wave length will phase it correctly at a given frequencie?
( and it's multiples?? )


If this design is not correct, please state why,
i wish to understand more and more

bye the way, my ESL will be crossed over at 500
( starting fade in at 400 )
so the woofer needs to work good up to 5-600hz



Also, from the TL design point,
would it be good to use a tapered tube
in the rear end of a mid driver that is only playing 1Khz + frequencies ??? would there be any benefits?
i mean by using a tube at the back of the driver, of a predetermined length ( the 1/4 wave of the lower Hz the driver is going to play? ) + stuffing, would there be any benefits over closed enclosure design ?

would be cool in a line array system! ??
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Old 20th July 2004, 01:05 PM   #2
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There is an inherent misstep when considering a TL as a sub and that is the size of the box. It's one thing to have a ten foot line that runs full range from 30 Hz to 20kHz, and quite another to devote the same amount of space to only 30-80 Hz. In your case running all the way to 600 Hz makes the project more sensible.

There is no need to to 'tune' for the phasing; the 1/4 wavelength pipe does that job. The pipe must be stuffed sufficiently to eliminate resonant nodes above the pipe frequency.

What's paramount is choosing the correct driver. Preferred T/S specs place the Fs the same as the line frequency or lower, the Qts between .5 and 1.0. The Vas determines the total line volume; for a tapered line with driver Qts of .5 a total line volume of Vas x 1.5 is appropriate. The size of the driver end and exit end of the pipe is determined by the line volume and the taper rate; a taper of 3:1 is average. Then make sure that the driver will still run flat to your crossover frequency and you're good to go.
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Old 20th July 2004, 02:21 PM   #3
kneadle is offline kneadle  United States
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Default References

In case you haven't seen these important resources:

Martin J King's site is indispensable. www.quarter-wave.com (is it down? Tuesday 9:19 CDT July 20, 2004).

A collection of stuff and some good links: www.t-linespeakers.org

And Bob Brines' site: http://www.geocities.com/rbrines1/

Good luck.

Dave
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Old 20th July 2004, 05:53 PM   #4
JinMTVT is offline JinMTVT  Canada
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i have seen most of these ressources , thanks

here is the sketch i wasn't able to include in my first post
( moderated? )

I tapered the design 2:1 but it could get more...

i would like to tune the box to the driver unit, as i have no restriction to the boxe at all ...

Is it correct to have the front exits of the driver and port near each other?

Of course i will use stuffing in the box


Where can i find an explanation of all the drivers's specs ?
all thoose Qs Ts Fz whatever i don't understand at all



Quote:
here is no need to to 'tune' for the phasing; the 1/4 wavelength pipe does that job
what is the point of the TL design then ?
i thought that we were "tunning" for phase matching
at a certain frequency to help reinforce the runnout of power?

i'm not sure i get it then ..

what other enclosure designs would give me good performance
of the sub similar to TL ?
IS there a better enclosure design than TL ? for a 20-600hz woofer?

hope the pic works this time
thanks all again!
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Old 20th July 2004, 08:58 PM   #5
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I don't want to seem condescending, but it seems that you are trying to put your cart before your horse. Knowing what Fs, Qts , Vas and so forth are is the most basic of information when it comes to building speakers, and if those terms are completely foreign to you then you're not ready to roll your own. Successfully designing and building speakers from scratch is a skill that takes years to achieve.

Before you waste a lot of time and money I'd suggest you first invest in a good book on the subject, Vance Dickason's is the benchmark, and then start your building efforts with a kit. You'll get a far better result and many fewer headaches. Cruise the Madisound, Parts Express and Zalytron sites for kits; there may be other sources closer to you so that you don't get screwed on the shipping costs.
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Old 20th July 2004, 10:50 PM   #6
qi is offline qi
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Quote:
Where can i find an explanation of all the drivers's specs ?
all thoose Qs Ts Fz whatever i don't understand at all
http://www.diysubwoofers.org/define.htm#tsparam

Regards and good luck
Joe
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Old 20th July 2004, 11:48 PM   #7
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Quote:
Originally posted by JinMTVT
here is the sketch i wasn't able to include in my first post
Not very effective use of the cabinet volume, any ration of tapered line fits perfectly into an appropriate sized rectangular box....

An example i did earlier (based on MJK tables for a Peerless CX176)... for a sub you really need to take advantage of all the geometry tricks to improve the lines low-pass function because stuffing isn't as effective at low frequencies. That is why this one has a large taper ratio and drivers offset from the closed end.

dave
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Old 21st July 2004, 01:50 AM   #8
JinMTVT is offline JinMTVT  Canada
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Ok
i know that i should know all of those parameters and understand everything before trying to design a unit.
But i do not have the time to wait to get all that information.
Then a driver is never really lost in any not good enclosure right?

And the material costs are not exceptionnaly big for a press wood + stuffin built enclosure

I am trying to least as fast as possible,
but if it is not worth the effort i should just buy a good sub?

Or is there a possiblility that with all the available information on here and the internet, i can build myself a high performer at
a few times lower price than comercially available ?
( i don't see why not, since this forum is so popular? ;p )

neway ..this is not the point of the thread

i'll try and cathch up with what i need to know asap!!!!


so here is another quick sketch ..

that's what i thought would be the good way to design TL
enclosure, but nobody seems to do it this way
( size limitation ? )
this is 8foot long total ..approz 3:1 taper

i want to know , what is good and what is bad about that kind of design ( without taking measyurements or preceise technical numbers into account..i want to understand the TL thing.. )

here it is! thanks again alll!
i'm learning quicker by reading post and replys here than searchin the net for answers
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Old 21st July 2004, 01:54 AM   #9
JinMTVT is offline JinMTVT  Canada
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also, since we are talking about enclosure designs

i have this subwoofer presently :

Mirage BPS 150i

wich is a powered sealed bipolar subwoofer ..

what do you guys thing about bipolar?
waht are the real advantages?

i've seen a few here talk about dipole arrangement,
but what about bipolar?

this one sounds pretty good a low levels, ani't boomy,
fast responce to music changements ..
but no more than that !

thanks
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Old 21st July 2004, 02:03 AM   #10
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Quote:
Originally posted by JinMTVT
Mirage BPS 150i

wich is a powered sealed bipolar subwoofer ..

what do you guys thing about bipolar?
waht are the real advantages?
I'm a big fan of push-push bipolar subs like the Mirage... the big advantage is active vibration cancellation, improving the downward dynamic range, and reducing the vibrational load on the box.

Your drawing still has the driver on the end, particularily for a subwoofer you need to take advantage of what an offset can do.

What you have drawn is basically half of a "coffin" woofer .


Click the image to open in full size.


dave
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