Conversions and estimations
Sensitivity conversionSensitivity can be expressed as Power sensitivity, which is what WinISD uses for modelling, or a Voltage sensitivity.
Convert between them as follows:
Power sensitivity = Volage sensitivity - 10 * log( 8 / Re )
going the other way....
Voltage sensitivity = Power sensitivity + 10 * log( 8 / Re )
DVC drivers T/S Parameters
|Single Coil Driven||Both coils in series||Both coils in parallel|
|Re||Re *2||Re / 2|
|Le||Le * 2||Le / 2|
|Bl||Bl * 2||Bl|
|Qes||Qes / 2||Qes / 2|
|Power sensitivity ( dB per watt@1m )||+ 3dB||+ 3dB|
|Voltage sensitivity ( dB per 2.83V 8ohms @1m )||The same||+ 6dB|
My thanks to contributors at the diyAudio subwoofer forum and HTGuide forum for their help assembling this table
Resistive braking - one coil shortedWhen driving a Double Voice Coil driver via a single coil, the second coil can be shorted or have a resistor fitted. This causes resistance to movement which produces a modified value for Qms. Several manufacturers use this method:
- Ascendant Audio used to supply their "Atlas" driver, however it's no long available and the details of RDO operation have also been removed from their current website. It was originally shown with a 4 ohm driving coil and a 2 ohm control coil. They used either a dead short or a 1.5 ohm resistor across the control coil
- Searching some forums, I came up with a posting by Dan Wiggens of Avatar Audio, who states that for a driver with two coils (presumably identical), shorting the second coil causes the Qms of the driver to change to a value equal to that of Qes. Avatar Audio is now Adire Audio.
So, with the second coil open, you'd have a Qes of 0.8, and a Qms (unchanged) of 6.5, for a Qts of ~0.7.
Now, when you short the second (unused) coil, it essentially acts as an electric brake.
This will manifest itself by lowering the Qms to the Qes of a single coil: 0.8
So, you'll have a driver Qes (of the coil you're driving) of 0.8, and a Qms (of the shorted coil) of 0.8, for a combined Qts of ~0.4
One coil driven, other open, Qts = ~0.7. One coil driven, other shorted, Qts = ~0.4
President Avatar Audio"
It is this last method I explore with some of the DVC drivers. The T/S specs for this arrangement are identical to
a single coil arrangement except that Qms=Qes and Qts is re-calculated as per the formula at the top of this page.
On the subject of alternative arrangements for DVC drivers, you can also run the driver on just one coil. There are opposing views on the subject, although the consensus is that you can do it, but generally you would be better to use a SVC driver of the required impedence and power rating.
There's a great tutorial on DVC drivers at JL Audio, where they also point out the change in T/S parameters and power handling if only one coil is used.
You can see drawings of these different configurations, along with the conversions for one-coil-shorted and RDO, at f4ier
Cone AreaWhere Cone Area (Sd) is unknown, following estimations can be used
|Driver size||Cone Area (cm squared)|
Efficiency Bandwidth ProductEBP can be used as a predictor of which box type is mosted suited for a particular driver
EBP = Fs / Qes ---- if Qes is unknown, approximate as Fs / Qts
|50 or less||Best in sealed enclosure|
|50 - 90||Good all-rounder|
|over 90||Best in ported enclosure|