# Compound driver's Ts calculation

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#### Tyimo

Hi!

I was calculating some compound drivers (two different kind of bass driver) TS and BR box (in the way as Thorsten suggested: paralleling the Qes, Qms, Qts, Fs, Re and summing the Vas and Sd)
and I got a much biger box volume for the compound drivers than I would have a separate calculated dimension.
Is it O.K so?
Greets:
Tyimo

#### Don Hills

It is not OK. Modelling the effects of two different kinds of driver in one box requires the use of a program that will allow entering the parameters of the two drivers separately. I have not seen Thorsten's suggestion, but I suspect he was thinking of the situation where you have two identical drivers in the same enclosure.

#### Tyimo

Hi!
I have not seen Thorsten's suggestion, but I suspect he was thinking of the situation where you have two identical drivers in the same enclosure.
No, it was two different kind of bass driver. "Afterburner" project.
I will try to find the original article.

#### Tyimo

I can't find the original article where this paralleing technique was suggesting.
But here is something:
http://www.quarter-wave.com/General/Two_Drivers.pdf

For the standard configuration of two drivers in one
enclosure, the following equivalencies are listed.
fd = remains the same as the single driver
Qtd = remains the same as the single driver
Vad = is twice the single driver value
ZVC = impedance is half if the drivers are wired in parallel
= impedance is doubled if the drivers are wired in series
SPL = +6 dB if the drivers are wired in parallel
= unchanged if the drivers are wired in series

But what about if I use different kind of drivers in one enclosure???

#### Tyimo

Thanks Ron!
That is it.
So my question is still the same:
The calculated compound driver needs bigger box than the two independently calculated would need. Is it O.K.???

#### Don Hills

The answer is still the same: Yes and no.
"The calculated compound driver needs bigger box than the two independently calculated would need."

Yes. This is logical, for example if you have two identical drivers the required volume is twice that needed for one driver.

" Is it O.K.??? "

As a general rule, no. The two drivers will "push each other around". There may be some combinations of driver that do happen to work together, but you will need a simulation program that allows specifying the two drivers' parameters separately.

#### PeteMcK

re:"It's a load of crap, if you ask me" - I've used it, & it works, if the drivers aren't too dissimilar....

#### Tyimo

Yes. This is logical, for example if you have two identical drivers the required volume is twice that needed for one driver.
No. I meant so, that for example the X driver would need 20L and the Y driver would need 30L box volume ( independently calculated) than the total volume would be 50L. But! The compound driver with the calculated Ts parameters will need 80L!

#### Tyimo

re:"It's a load of crap, if you ask me" - I've used it, & it works, if the drivers aren't too dissimilar....
Yes, I agree. Thanks!

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