Transmission Line Isobaric Subwoofer for home. - Page 2 - AVS Forum
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post #31 of 41 Old 10-14-2013, 10:14 PM
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for isobaric, the parameters change. how they change depends on whether you go parallel wiring or series wiring. i'm not sure if you get a different result in hornresp either way.

for isobaric drivers in SERIES:

motor force doubles. but motor force is bl^/2, so twice that value means bl increases by root 2 (1.414) all other things equal.

re doubles.

sd is just the sd of a single driver, so stays the same.

cms is the suspension compliance, so it gets reduced by 50% with two drivers. twice the suspension, twice as stiff. compliance is opposite of stiff.

rms doubles.

le doubles.

normally, all of this results in a dramatic reduction in sensitivity (6db :-0 ), but preserves the same frequency response shape of a single driver in a cab twice as large.

not sure what the result will be in hornresp. could be better. could be worse.

good luck and interesting experiment!

something like this would seem like a real winner for a pair of inexpensive, weak motored, assymetrical bl field, drivers with lots of excursion that otherwise wouldn't work in a horn loaded environment.
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post #32 of 41 Old 10-14-2013, 10:35 PM
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not sure why I get totally different results than you do with the basic model in hornresp.

-25cm seems about right for the combination.

otherwise, the two look totally different.

I was going to confirm our hornresp models before then changing up the t/s parameters for isobaric loading, but can't even confirm the basic model.





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post #33 of 41 Old 10-14-2013, 10:47 PM
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doesn't seem to correlate with your measurements too well though. :-(




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post #34 of 41 Old 10-15-2013, 10:10 AM - Thread Starter
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Thanks for the feedback. I will post my txt file later which may help to match up the two simulation. I too will adjust the speaker parameters but for parallel isobaric and see what difference it makes.

I have to reselect 2p each time I open the program even after I import. So should be more convenient in the long run.

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post #35 of 41 Old 10-15-2013, 05:38 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

not sure why I get totally different results than you do with the basic model in hornresp.

-25cm seems about right for the combination.

otherwise, the two look totally different.

I was going to confirm our hornresp models before then changing up the t/s parameters for isobaric loading, but can't even confirm the basic model.





Here is the output parameter files. The only difference I can see is that you used a 2P where as I used a 2p. Doubt it would be case sensitive but maybe the way the pop up features were calculated???

ID=29.00
Ang=1.0 x Pi
Eg=2.83
Rg=0.01
Fta=0.00
S1=1650.00
S2=750.00
Con=61.60
F12=0.00
S2=750.00
S3=250.00
Con=64.60
F23=0.00
S3=250.00
S4=500.00
Con=66.10
F34=0.00
S4=500.00
S5=500.00
Con=47.50
F45=0.00
Sd=506.00
Bl=10.23
Cms=4.86E-04
Rms=3.22
Mmd=51.35
Le=2.40
Re=7.00
Nd=2p
Vrc=0.00
Lrc=0.00
Fr=0.00
Tal=0.00
Vtc=0.00
Atc=0.00
Pmax=250
Xmax=8.0
Comment=12W1-8 Measured T&S parameters. IsoTL

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post #36 of 41 Old 10-15-2013, 06:36 PM
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must be a bug. i'm running v28. you have v29.

i'm getting the same thing with your numbers that i posted last night. eek.gif

guess i'm not going to be much help on this one. eek.gif



that said, it was worth doing because i learned why scoops aren't more popular than they are. eek.gif

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post #37 of 41 Old 10-15-2013, 06:50 PM - Thread Starter
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I converted all the speaker inputs to a parallel isobaric configuration based on what I think they should be. Result was the same as my previous trial.

Sd remains the same. (This was one reason why i went this route to keep the enclosure size smaller)
Vas is 50% - Combined isobaric speaker has twice the moving mass, half the compliance because of the doubled suspension. This changed Cms in Hornresp.
Mmd increased as it is calculated from Vas. Went up by 213% eek.gif
Re is 3.5 Ohms as each speaker measures 7 ohms individually.
Bl remained the same. It is using Cms and Re so it seems the adjustments I made offset each other. I used the same Qes value as previous sims.
Rms doubled. Again it is based on Cms. I used the same Qms value as previous sims.
Le is 50% for two inductors in parallel.
Nd is default. I.e. 1 speaker - normal configuration.




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post #38 of 41 Old 10-15-2013, 06:54 PM - Thread Starter
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Quote:
Originally Posted by LTD02 View Post

must be a bug. i'm running v28. you have v29.

i'm getting the same thing with your numbers that i posted last night. eek.gif

guess i'm not going to be much help on this one. eek.gif

that said, it was worth doing because i learned why scoops aren't more popular than they are. eek.gif

Could be a bug? idk but thanks for checking into it.

My lingo is lacking. What is a scoop??? rolleyes.gif

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post #39 of 41 Old 10-15-2013, 07:04 PM
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roughly the same idea as what you have.


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post #40 of 41 Old 11-27-2013, 04:14 AM
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Hi Gaugster

Must say this is a great design.

Many years ago i built a isobaric small bass reflex subwoofer with two 8" woofers to my 5.1 system.

This was scrapped and the woofers was put in the storage.

Last week I was looking around the web trying to find some idéas for a horn or TL subwoofer and reuse the speakers.

That's when i found this nice forum and project.

I used the Peerless CSH217 8 ohm woofers and design similar to your. Outside measurements approx 700*300*420 (H*W*D)

I'm surprised by the deep bass it produces, and the first test was very impressive. :)

I want to complete with 2 horn/bass reflex hybrid design speakers with fostex FE126En for a 2.1 setup.

 

BR

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post #41 of 41 Old 11-27-2013, 04:21 PM - Thread Starter
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This Forum is a great place for inspiration! The low bass response has inspired me to get a calibration software / setup to document my results.... a work in progress!

Ps - Thank You!.

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