# T/S parameters... what are they good for?

11868 Views 11 Replies 10 Participants Last post by  Caiman
What are T/S parameters and what do they mean? I get asked this all the time and I think well, it really isn't so important to know what they mean but rather what do they tell you about a speaker's performance?

The quick answer I'm going to give you is that T/S parameters don't tell you anything about how a speaker performs. If you've read the articles here on transient response and non-linear distortion, you already know that THESE are the things to look at when evaluating a speaker's performance.

So what can you learn about a speaker by looking at it's T/S parameters? Well, assuming that the manufacturer gives you accurate specs (keep in mind that all drivers will deviate somewhat from their manufacturer's specs), T/S parameters can tell you 2 things.

1. The efficiency of the driver using the following formula:

1 watt spl at 1 meter in decibels = 112+ 10 * log (9.64 * 10^-10 *fs^3 * vas /qes) ... for example 90db @ 1w/m sensitivity.

2. And the low end frequency response of the speaker at low levels of power, in a given enclosure. I recommend reading the Winisd/box modelling article here for more info on the use and limitations of T/S parameters, when designing and modelling enclosure+speaker frequency response.
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Is there anyway we could get a rough explination of Box Q effects...as well as FS and QTS effects.

As i slightly understand what box Q means, but not sure how its determined....As well as different effects of QTS of a driver, and applications of each QTS parameter, if at all possible.

Also how can we tell how strong a sub is going to be in the sub 40hz region, as i'm looking for a sub that can really put out down low, pretty flat from 60hz down to a good 20hz, as i'm wanting that low end rumble, and i just don't seem to be getting it as much as i beleive i should..
Is that a base ten log?
Q in general is a loss ratio. basically imaging a swingset or pendulum. it will swing back and forth for a long time and at the same rate. this corresponds to a high Q.

ok, so add some friction to the moving parts and they'll slow down. friction converts the energy to heat. this is actual use of energy and eventually the swing will stop. this is lower Q.

take a woofer now. normally it will want to move at a given frequency, and has a Qms related to how much it favors moving in that manner. Qms will show up when you look at a free-air impedance plot. if you use the electomagnet to stop the woofer you can get a signifigantly lower Q, Qts.

from this perspective you can see that a high Q means highly favoring one note, while a low Q means favoring a wide bandwidth. once you port a woofer, you actually intoduce a second Q and F resonant effect. you can use this second resonator to give a boost. the port will have a Q as well, and a low Q port will give a smaller boost, but will do so to more frequencies.

i saw one of my old posts. almost though someone else was pretending to be me...

for high SPL it is beneficial to have high Q values, as a high Q corresponds to low loss.

edit -- this is more of a generalization. i am not saying to look for high Qts speakers.
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So would the T/S parameters be good for modeling a HT theater speaker, specifically, one of those Polk Audio in-wall speakers, to figure out if one should build an enclosure for the midrange driver in the wall or not?
it would be easier just to cut a hole in a box top[ie- a shoe box ] and put the speaker face down on top of box to hear difference.
from this perspective you can see that a high Q means highly favoring one note, while a low Q means favoring a wide bandwidth.

for high SPL it is beneficial to have high Q values, as a high Q corresponds to low loss.

edit -- this is more of a generalization. i am not saying to look for high Qts speakers.
This made it worth waking up and getting out of bed today. Ive been lost when it comes to Qts and trying to figure it out for quite a whole now.

THANK YOU!
This made it worth waking up and getting out of bed today. Ive been lost when it comes to Qts and trying to figure it out for quite a whole now.

THANK YOU!
Ummm...that post was from 4 1/2 years ago
and yet 4 1/2 years later it made someones day
when 1 says a high qts in general is better, what would you say a good qts number is. you say look for a high qts, but what exactly is a good number for qts in a ballpark
I really like the Klippel tests published here and, as a noob in this forum, I'd like to thank everyone involved.
jblw10... the question you are asking is not that simple to answer. Your best bet would be to read up about harmonic oscillation and its variants, simple, damped, and forced. As usual, Wikipedia has a succinct writeup. Look up "Harmonic oscillator".
There you will see that the critical amount of damping equates to a total Q of 0.5, although this, in and of itself, is not all there is. You will be needing some understanding of calculus if you want to dig deeper. Q is a qualitative measure of how much energy is lost every time an oscillator completes one full oscillation.
Roughly speaking, a driver is characterized by its own Q, which has an electrical part and a mechanical part. The electrical part is much more significant, because it is the smaller of the two, and is added to the mechanical part in inverse form. Once a driver is mounted to a cavity, its mechanical Q changes because the air in the cavity gets coupled to it. This changes the overall Q, and the new total Q is what now characterises the system's behavior.
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In addition to what npdang states in his initial post, Thiele/Small is a set of parameters that characterize small-signal behavior only. They presuppose that a whole host of variables (Bl, compliance, etc) remain constant, which is of course true only when dealing with small displacements. They are not descriptors of the quality of performance. Still some of them may describe driver quality indirectly. The Bl product, for example, is a pretty good indicator of magnet strength and, since magnets are expensive, sometimes it can indicate whether a manufacturer has been penny-pinching.
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