What is meant by Voltage Drive?

[ngccglp]

Hi, Would like to request for an explanation of the meaning of voltage drive and also how to interpret the below graphs. Thanks. :p

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=15380&stc=1&d=1146736547

[Robh3606]

For all intents and purposes they show the attenuation curves for the networks. Those are the curves with and 8 ohm load connected. Voltage drive is just a name for the filtered signal you get for each driver after the network does it's job.

Rob

[DavidF]

Hi, Would like to request for an explanation of the meaning of voltage drive and also how to interpret the below graphs. Thanks. :p

http://www.audioheritage.org/vbulletin/attachment.php?attachmentid=15380&stc=1&d=1146736547

In terms of interpreting what you see in the graphs you have the electrical response of the xover as mentioned by Rob. This electrical output as shown feeds the drivers. Each driver has its own acoustic response. The total system response is the combined effect of the electrical (xover) and the acoustic response (driver).

In the example you attached notice that the peak response of the two upper drivers is lower than the two lower drivers. The upper drivers are both horn loaded compression drivers which are far more sensitive than the woofer and mid cone drivers. If you were to plot the acoustic response of all four drivers without crossover you would see that the acoustic response peaks for the upper drivers is much higher.

In addition to attenuating the upper driver’s response at a given xover frequency the overall output of the drivers also has to be lowered in relation to the output of the lower drivers.

The xover filter in the attachment includes attenuation circuits on the two upper drivers to significantly lower the electrical output coming out of the xover. So when the higher driver acoustic response for the two upper drivers is netted to the lower electrical response the effect will be to bring all four drivers to a similar average output sensitivity.

You might have a different situation as when the woofer has a rising response beyond the intended xover point of 800Hz. A standard xover filter calculation would not factor in the rising resonse characteristic. So the actual xover design would need a tweak or two to provide a shallow attenuation as frequency rises to compensate for the rising woofer response from a point well below the theoretical xover point. This kind of response tweak would show two "knees" in woofer electrical response. One about 150-200Hz that diminishes a few decibles up to the second knee of 800Hz at which point the electrical response falls off much quicker. The combined frequency response of the woofer would then appear flat up to 800 Hz (actually just a little lower) and falling off above about at the intended 6 or 12 dB (or higher) per octave roll off.

[gferrell]

Now that was a great explanation. You should copyright that one David!

[ngccglp]

Hi Guys,

thanks a lot for the excellent explanation. I understand now why the voltage drives are lower for the compression drivers I.e. to compensate for their higher sensitivities.

Cheers.