Another PVC Pipe TL thread,, - diyAudio
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Old 18th August 2011, 06:38 AM   #1
geepee is offline geepee  Australia
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Default Another PVC Pipe TL thread,,

Hi, yesterday i was cleaning out my garage and I came across some stuff that I had stashed away and forgotten all about..

5 Tang Band W3-593SFs and a whole bunch of 90mm PVC pipes and fittings. I have decided to play around with the idea of a TL for these little speakers again.

I have a copy of a spreadsheet made by Henkjan ages ago that uses MJKs alignment tables. Putting the specs (Fs 110Hz, SD 32 cm2, QTD 0.58, BL 3.7, RE 6.6) in gives me a 734mm line, Zd of 256mm and and SO/SL (1-1 taper) of 153.8cm@ (4.81 * SD). Now my 90mm PVC has an area of 60cm2 which is about 1.87 * SD. When I use the spreadsheet to wind the SD down to match my pipe, it gives me a modified line length of 750mm.

Bear in my my total budget for this experiment is $0 so i would like to use the pipe and fittings I already have. Will reducing the crossectional area by that much (60%) make this pointless or will it be ok? I am not expecting miracles with such a small speaker but I see it as a good learning experience. Also, do I have to tune the pipe to the Fs of the driver? Can it be tuned lower? lowering the tuning on the spreadsheet reduces the required cross sectional area, making the pipe longer of course but i can live with that.

Any advice would be appreciated..



George
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Last edited by geepee; 18th August 2011 at 06:50 AM. Reason: spelling
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Old 18th August 2011, 06:58 AM   #2
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I would not significantly reduce the required pipe xSection.

You could parallel 3 pipes.

dave
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Old 18th August 2011, 03:25 PM   #3
GM is offline GM  United States
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Vas?

Anyway, assuming a reasonable 1.5 L, We need ~5 L for a ~77 Hz T/S max flat tuning as a minimum net Vb the way I figure these things, so with CSA = 60 cm^2 = ~83.33 cm pipe length + [60/pi]^0.5*0.613 = ~2.68 cm end correction = ~86 cm acoustic length = ~34400/4/86 = ~100 Hz tuning, so should be plenty big enough for 110 Hz.

Making the pipe long enough to support 77 Hz = ~34400/4/77 = ~111.69 - 2.68 = 109 cm long/~6.54 L to lower F3 and/or increase tuning options, including converting it into a MLTL of best compromise in-room tuning.

Of course use the correct Vas in a T/S box program to get the appropriate net Vb required.

GM
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Old 19th August 2011, 01:03 AM   #4
geepee is offline geepee  Australia
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Thanks GM. will do some more math. VAS is 2.67l (going by the manufacturers specs..)

The good news is that using the pipe and fittings it is pretty simple to change the line length, driver position and stuffing.

Will have a play on the weekend and see how I go!

G
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Old 19th August 2011, 01:19 AM   #5
sreten is offline sreten  United Kingdom
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Hi,

Somebody correct me if I'm wrong :

1) Line length looks good for a reasonable listening height.

2) So you could use a pipe open at both ends, this effectively
half's the length and doubles the CSA ? Basically a tall inverted U,
or even very tall and straight, driver near the middle of the pipe ?

3) Having the two paths different lengths is actually good for smoothing.
Detune the average half pipe length to get the half pipe Sd you require ?

4) I'd guess a tight 180 degree bend is not a standard part ......

rgds, sreten.
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Old 19th August 2011, 04:04 AM   #6
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Quote:
Originally Posted by geepee View Post
Thanks GM. VAS is 2.67l
You're welcome!

Hmm, the other specs plus this Vas equates to an impossibly low Qes and negative Qms value, so one or more spec values are bogus.

GM
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Old 19th August 2011, 04:31 AM   #7
GM is offline GM  United States
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Quote:
Originally Posted by sreten View Post
1) Line length looks good for a reasonable listening height.

2) So you could use a pipe open at both ends, this effectively
half's the length and doubles the CSA ? Basically a tall inverted U,
or even very tall and straight, driver near the middle of the pipe ?

3) Having the two paths different lengths is actually good for smoothing.
Detune the average half pipe length to get the half pipe Sd you require ?

4) I'd guess a tight 180 degree bend is not a standard part ......

rgds, sreten.
Greets!

The longer one does for me, but the shorter one seems to be what most folks around here prefer.

No, an open pipe is a 1/2 WL resonator, so will need to be ~twice as long for a given Fb as a stopped [one end closed] pipe which is a 1/4 WL resonator. As such, having them at two different lengths makes no difference unless the bend is very restrictive, then they tend to break down into individual 1/2 WL resonators unless the driver is positioned in the bend, turning them into ~ individual 1/4 WL resonators that will average out their separate tunings somewhat. FWIW, tuning them an octave apart has worked well for me.

Don't know of a preformed pipe bend tight enough, so a small cab to act as a filter chamber with two large, TL length vents is what I've done.

GM
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Old 19th August 2011, 05:39 AM   #8
geepee is offline geepee  Australia
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Quote:
Originally Posted by GM View Post
You're welcome!

Hmm, the other specs plus this Vas equates to an impossibly low Qes and negative Qms value, so one or more spec values are bogus.

GM
Its the same driver thats been used in a few designs around here... the TABAQ comes to mind..
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Old 19th August 2011, 05:58 AM   #9
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Well, you listed BL as 3.7 instead of the published 3.17 which would close the gap a bit, but it's academic since 3.17 is way too high based on the other specs. Don't know any specifics of other designs, but if not designed from measured specs I'm betting the cabs are either smaller or larger than they need to be depending on which specs were used.............

How does using a BL = 2.83 N/A change your TL design?

GM
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Old 19th August 2011, 06:57 AM   #10
geepee is offline geepee  Australia
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Quote:
Originally Posted by GM View Post

How does using a BL = 2.83 N/A change your TL design?

GM
It increases the required CSA to around 8 * SD from around 6 * SD and increases the box volume from 16 to around 19 liters...

G

Last edited by geepee; 19th August 2011 at 06:57 AM. Reason: spelling
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