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T/S parameters for 6171

 
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awkwardbydesign
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Joined: 23 May 2007
Posts: 1
Location: Devon

PostPosted: Thu May 24, 2007 9:34 am    Post subject: T/S parameters for 6171 Reply with quote

Hi, I am new to this site, so I may have missed something, but does anyone know the Thiele-Small parameters for the B139- 6171 drive units?
I have 2 and can get 2 more quite cheaply, as I want to go isobaric (again!).
They will be used from about 150Hz down, with a 24dB active xover.
The rest will be handled by Ted Jordan's full (!) range units.
Thanks.
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ColinR
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PostPosted: Thu May 24, 2007 8:20 pm    Post subject: Reply with quote

With the "quality challenged" B139A, where out of "100 units you won't match a pair" - retired IMF contact.

It would be prudent as you're doing an isobaric design to measure each available drive units parameters and match up the best pairs.

Here are some numbers to start you off

Fs 25 hz
Mmd 43.5 grams
VAS 164 litres
Rscc 6.2 Ohms
Vl 0.56 Mh
Bl 12.3
Qms 5.5
Qes .4
Qts .37
SPL 84dB
Pe 100W
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speakerguru
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PostPosted: Fri May 25, 2007 9:02 am    Post subject: Reply with quote

ColinR wrote:
With the "quality challenged" B139A, where out of "100 units you won't match a pair" - retired IMF contact.


Let's not get too precious about T-S parameters. In any case, matched to within what? 10%? 1%? 0.1%? Even if the moving masses and motor strengths were exactly equal you would still have the variation in suspension stiffness of probably over +/-20% which comes from using doped cloth for the rear suspension and rubber front suspension, both of which vary with temperature, age and excursion. This applies to most speakers, not just the B139.

The suspension affects the resonance and all the the Qs scale up and down with the resonance, pro rata. None of which affects the low frequency response much, as in most systems the box air stiffness swamps the driver stiffness. It's the moving mass and motor strength which are important.

I suspect your IMF contact could have been referring to the high frequency break up modes of the B139 diaphragm which were many and various. By the 70s it was never used much above a few 100Hz. Thankfully I have never heard any of the earlier systems using the B139-T15 combination.
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ColinR
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PostPosted: Fri May 25, 2007 3:13 pm    Post subject: Reply with quote

Quote:
suspect your IMF contact could have been referring to the high frequency break up modes of the B139 diaphragm which were many and various.


Yup the ~415Hz one.

Why do you think the bass chamber behind the driver in the TLS80/Ref Monitor "reflex design" (your definition Twisted Evil ) is so large when compared with other designs that use the cube of the equivalent surface area.
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proffski
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Location: Tewkesbury UK

PostPosted: Sat May 26, 2007 9:04 pm    Post subject: B139 Reply with quote

My very last personal project with B139s used crossover of 100Hz, prior to that I thought that 250Hz was pushing it.
I was never happy with 400Hz with my first attempt so many years ago...
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