# scratching my head over the Thiele/Small parameters of this speaker



## Justin Zazzi (May 28, 2012)

This is an older model Hi-Vi 12" woofer that was donated to me for experimentation with building a 3-way speaker. My goal is to measure the Thiele/Small parameters and model an enclosure with them. I have done this by hand before with pretty good results using the method found at this website. Then to be double sure and also because gadgets are cool, I bought a Dayton DATS V2 model to measure the T/S parameters again. I also have a few specs off the back of the speaker itself. These are all summarized in the table below:


```
Back of   By Hand   DATS
      Speaker
Fs	29hz    39hz      38hz
Qts	0.37    0.77      0.81
Qes	        0.94      0.91
Qms	        4.18      7.35
Vas	        113L       89L
Dia             250mm     250mm
```
My question is, should the Qts be so drastically different from the spec printed on the speaker from the manufacturer? If my measurements are accurate, then what the heck kind of enclsoure should I build? Both of the sealed and vented enclosure modeling tools I have give me ridiculous values like negative enclosure volume or say the QTS is too high.

Also, this is not the only woofer I have with high Qts values. I have two other models (a generic 5" with dual voice coils and a generic 3") with Qts of 0.67 and 0.96! Is this a product of the woofers sitting in a garage for years, or possibly being exposed to moisture in that environment?


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## lurch (Jan 20, 2014)

i n t e r e s t i n g !

would you mind taking some pics of this beasty for us ???


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## Justin Zazzi (May 28, 2012)

The big woofers are on the top left and top right
The smaller woofers are not in these photos.


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## Justin Zazzi (May 28, 2012)

On a whim, I decided to try and "break in" the woofer with a low frequency, high amplitude tone for a while. After three hours I measured it again, and both the Qts and Fs have lowered some. I'm guessing more time excercising the woofer will yield better results? We'll see.


```
Back of   By Hand   DATS     3 hours later
      Speaker
Fs	29hz    39hz      38hz     35hz
Qts	0.37    0.77      0.81     0.73
```


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## lurch (Jan 20, 2014)

OH !
and both hi-vi's are giving the same results ??

im no expert but i would say that the suspension ( especially spider ) has gone soft
on them. 
or the magnets have lost gauss.

those qts numbers seem very high for a woofer that looks to belong in a ported
enclosure. the original 0.37 seems to be a much more realistic number.


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## Justin Zazzi (May 28, 2012)

lurch said:


> OH !
> and both hi-vi's are giving the same results ??
> 
> im no expert but i would say that the suspension ( especially spider ) has gone soft
> ...


If the suspension has gone soft, then the resonant frequency should lower. At least, this is how it was taught to me in school when examining resonant systems.

I'm not sure how a loss of power in the magnet would affect things, but I don't think it would change the resonant frequency or the behavior at resonance. There are only three things that can according to the equations we studied: moving mass (unchanged), spring constant (spider and surround), and damping resistance (something about coil inductance or damping factor?). The magnetic strength would be on the other side of the equation, I think, that effects amplitude of the oscillations.


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## Beckerson1 (Jul 3, 2012)

Usually your going to read higher if thing haven't worked themselves in. If your going to build a box based off its true TS specs I'd let them loosen up and go from there.


Your spring constant will change slightly new vs worked in. Your spider and surround will be softer.


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## lurch (Jan 20, 2014)

yeah, agreed. 
look like i was editing my post whilst you sent this last one in. 
see above ^^^^^ LoL.


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## Beckerson1 (Jul 3, 2012)

lurch said:


> yeah, agreed.
> look like i was editing my post whilst you sent this last one in.
> see above ^^^^^ LoL.


Lol


This is what people refer to as breaking drivers in. Basically your letting the driver stretch it's legs. Basically (I'm not old and not referring to anyone as being old) the same concept as what happens with age to the human body. Been sitting for a while and have that stiff feeling. Get moving and it gets better usually. This case it's new parts that need loosened up.

Now I can't explain why Qts went up.

Use the specs on the driver as a reference. From the factory it's hard to say how accurate it is. You may find your driver doesn't quite meet those numbers.


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## lurch (Jan 20, 2014)

well i'm old. 
i feel just like those poor hi vi's. 

nap time ......


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## Justin Zazzi (May 28, 2012)

I gave the woofer an additional 3 hours of exercise and the Qts and Fs values have not changed any further. I feel like I'm stuck with a useless driver here.

What sort of enclosure can be built with a driver that has a Qts of 0.73?


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## brumledb (Feb 2, 2015)

What if you raised Qtc(I am assuming you are shooting for .707)? One of the constraints of sealed enclosure designs is that Qts must be lower than the highest acceptable Qtc.

Infinite Baffle?


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## Justin Zazzi (May 28, 2012)

brumledb said:


> What if you raised Qtc(I am assuming you are shooting for .707)? One of the constraints of sealed enclosure designs is that Qts must be lower than the highest acceptable Qtc.
> 
> Infinite Baffle?


All good points, but my application was supposed to be a floor-standing 3-way speaker for the home. I can't do infinite baffle as such.

It might work IB-style in a car or in some other kind of home/attic installation, but I don't have room in the car or need anything like that.

Thanks for your input!


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## brumledb (Feb 2, 2015)

Why not? Google "open back speaker tower"

Trio15 TB Open Baffle Speakers - PureAudioProject

This design would probably really get people's attention.


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## Beckerson1 (Jul 3, 2012)

brumledb said:


> Why not? Google "open back speaker tower"
> 
> Trio15 TB Open Baffle Speakers - PureAudioProject
> 
> This design would probably really get people's attention.


I like


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