TS Parameters
What is TS Parameters?
TS parameters are a logical, minimalist assortment of loudspeaker characteristics which can be used to predict the low frequency behavior of a driver in an enclosure ­ especially a vented enclosure.

The T in TS refers to A. Neville Thiele the Australian engineer who first defined these parameters and then used them to create 28 discrete alignments for vented box loudspeakers. The S in TS refers to Dr. Richard Small who refined and expanded on the work of A. N. Thiele. Referring to the precis of Thiele's first paper and excerpting:

"An investigation of the equivalent circuits of loudspeakers in vented boxes shows that it is possible to make the low-frequency acoustic response equivalent to the ideal high-pass filter or as close an approximation as is desired". In other words, Thiele has taken the guesswork out of vented speaker design with his parameters and equations into which these parameters are then entered.
Continuing: "The simplifying assumptions appear justified in practice and the techniques involved are simple." In other words real loudspeakers can be simply measured to yield these parameters and the measured results obtained from these speakers installed in cabinets (enclosures) are consistent with the results obtained from the equations.
Continuing: "The low frequency performance of a loudspeaker can be adequately defined by three parameters, the resonant frequency Fs, a volume of air Vas, equivalent to it's acoustic compliance, and the ratio of electrical resistance to motional reactance at the resonant frequency Qe. From these three parameters, the electroacoustic efficiency h can be found also. A plea is made to loudspeaker manufacturers to publish these parameters as basic information on their product."

In other words the small-signal performance of vented speaker systems can be fully predicted using only these three parameters. This paper was originally presented at the 1961 I.R.E. Radio and Electronic Engineering Convention, Sidney N.S.W. Australia. This was reprinted 10 years later in the US in the AES Journal. After the passage of nearly another decade TS data was being supplied by most driver Manufacturers on their products.

In general speakers with lower Qe and Vas maintain control in smaller boxes. Fs is the free air resonant frequency of the raw driver where cone mass and the suspension stiffness interact to form a simple resonant system. Modern computer programs embed these parameters into the appropriate equations defined by Thiele and Small to predict response shape and the impedance curve.

Other TS parameters predict how loud a speaker will play at various frequencies. Besides depending on box parameters (Vb and Fb) certain speaker parameters are important. Xmax, Pd and cone area (Sd) predicts the limits of loudness in the bass. The bigger, the better the bass performance is for all three of these parameters. The parameter Qe can be experienced along with Fs by gently tapping a speaker cone near but not on the dust-cap.

In order to hear this, the ear must be positioned very close to the cone. The dull hum or boom heard is at Fs. Placing a piece of metal like a key across the speakers terminals will change sound to a thud due to motor damping which reflects Qe. Vas is inversely proportional to the stiffness of the suspension and directly proportional to the area of the cone. That stiffness is easily observed by applying a gentle pressure to the cone as above. These three qualities are sufficient to predict how the speaker will produce low frequency sound in a specific enclosure.

There are up to thirty TS parameters and many equations describing how certain speakers will perform in certain cabinets. This information is available in the AES Journal as follows:

Thiele- Volume 19 number 5 and
Small- Volume 21 number 5,6,7,8

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