T/S Parameters explained

[dave_Edwards 1]

Prior to 1970, there were no easy or affordable methods accepted as standard in the industry for obtaining comparative data about loudspeaker performance. Recognized laboratory tests were expensive and unrealistic for the thousands of individuals needing performance information. Standard measurement criteria were required to enable manufacturers to publish consistent data for customers to make comparisons between various loudspeakers.

Thiele-Small Parameters

In the early seventies, several technical papers were presented to the AES (Audio Engineering Society) that resulted in the development of what we know today as 'Thiele-Small Parameters'. These papers were authored by A.N.Thiele and Richard H. Small. Thiele was the senior engineer of design and development for the Australian Broadcasting Commission and was responsible at the time for the Federal Engineering Laboratory, as well as for analyzing the design of equipment and systems for sound and vision broadcasting. Small was, at the time, a Commonwealth Post-graduate Research Student in the School of Electrical Engineering at the University of Sydney.

Thiele and Small devoted considerable effort to show how the following parameters define the relationship between a speaker and a particular enclosure. However, they can be invaluable in making choices because they tell you far more about the transducer's real performance than the basic benchmarks of size, maximum power rating or average sensitivity.

Fs------This parameter is the free-air resonant frequency of a speaker. Simply stated, it is the point at which the weight of the moving parts of the speaker becomes balanced with the force of the speaker suspension when in motion. If you've ever seen a piece of string start humming uncontrollably in the wind, you have seen the effect of reaching a resonant frequency. It is important to know this information so that you can prevent your enclosure from 'ringing'. With a loudspeaker, the mass of the moving parts, and the stiffness of the suspension (surround and spider) are the key elements that affect the resonant frequency. As a general rule of thumb, a lower Fs indicates a woofer that would be better for low-frequency reproduction than a woofer with a higher Fs. This is not always the case though, because other parameters affect the ultimate performance as well.

Re--------This is the DC resistance of the driver measured with an ohm meter and it is often referred to as the 'DCR'. This measurement will almost always be less than the driver's nominal impedance. Consumers sometimes get concerned the Re is less than the published impedance and fear that amplifiers will be overloaded. Due to the fact that the inductance of a speaker rises with a rise in frequency, it is unlikely that the amplifier will often see the DC resistance as its load.

Le--------This is the voice coil inductance measured in millihenries (mH). The industry standard is to measure inductance at 1,000 Hz. As frequencies get higher there will be a rise in impedance above Re. This is because the voice coil is acting as an inductor. Consequently, the impedance of a speaker is not a fixed resistance, but can be represented as a curve that changes as the input frequency changes. Maximum impedance (Zmax) occurs at Fs.

Q Parameters---------Qms, Qes, and Qts are measurements related to the control of a transducer's suspension when it reaches the resonant frequency (Fs). The suspension must prevent any lateral motion that might allow the voice coil and pole to touch (this would destroy the loudspeaker). The suspension must also act like a shock absorber. Qms is a measurement of the control coming from the speaker's mechanical suspension system (the surround and spider). View these components like springs. Qes is a measurement of the control coming from the speaker's electrical suspension system (the voice coil and magnet). Opposing forces from the mechanical and electrical suspensions act to absorb shock. Qts is called the 'Total Q' of the driver and is derived from an equation where Qes is multiplied by Qms and the result is divided by the sum of the same.

As a general guideline, Qts of 0.4 or below indicates a transducer well suited to a vented enclosure. Qts between 0.4 and 0.7 indicates suitability for a sealed enclosure. Qts of 0.7 or above indicates suitability for free-air or infinite baffle applications. However, there are exceptions! The Eminence Kilomax 18 has a Qts of 0.56. This suggests a sealed enclosure, but in reality it works extremely well in a ported enclosure. Please consider all the parameters when selecting loudspeakers. If you are in any doubt, contact your Eminence representative for technical assistance

Vas/Cms--------Vas represents the volume of air that when compressed to one cubic meter exerts the same force as the compliance (Cms) of the suspension in a particular speaker. Vas is one of the trickiest parameters to measure because air pressure changes relative to humidity and temperature

[adirevolvo 0]

wow, i just learned way to much...and its all stuff i've wanted to know for a long time but never seen explained in one place so THANKS!

[ghs_wrestler189 0]

That was an excellent description, now they aren't just letters to me

just kidding. I did know a few, but now....ALL!

[sandt38 448]

2 thumbs up Dave.

Great amount of info in 1 spot.

I have a stickeyed thread on CAT (we call it George, I linked it here for you) where we discuss everything from simple to advanced (although at this point we have reached beyond the simple on the thread) audio information. There was a question about all the TS params, explained in detail, yet simpple enough for the layperson to understand. I feel this is the finest example of that I have ever seen. Do you mind if I copy this and add it to that thread, giving you full credit of course.

[dave_Edwards 1]

2 thumbs up Dave.

Great amount of info in 1 spot.

I have a stickeyed thread on CAT (we call it George, I linked it here for you) where we discuss everything from simple to advanced (although at this point we have reached beyond the simple on the thread) audio information. There was a question about all the TS params, explained in detail, yet simpple enough for the layperson to understand. I feel this is the finest example of that I have ever seen. Do you mind if I copy this and add it to that thread, giving you full credit of course.

no problem---I try to educate as many people as I can that will listen.

Dave

[sandt38 448]

Thanks Dave, it has been added.

Seth

www.s-fs.com

[ANeonRider 3]

Adding this little big of motor reading:

http://ldsg.snippets.org/motors.php3

[Aaron Clinton 2,372]

I have to port the RL-p, but the RL-i 8 could go ported or sealed with great success

[joebangaa 0]

uh, why would underpowering damage a speaker

[Supa_c 1]

I dont know but people do it every time they get new speakers in their car and run them off the H/U

[dave_Edwards 1]

it isn't running them with less power----it is the morons that try to play them too loud with no real power.

[Supa_c 1]

But but...i like clipping