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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: that part I apparently failed to convey that I knew posted by Mart on January 14, 2007 at 19:33:09:
Hi
I’m not sure about your question, Q is used in many places.
You mention filters, a closed box response is a 2nd order filter, a Q of about .6 is a low group delay alignment .7 is a normal Butterworth and 1 or more accents the low cutoff with ringing. A vented box would be a 4th order alignment.You mention reactive parts L’s and C’s, cool.
Your driver has a motor, which converts current into force and the motors Velocity is converted in to a Voltage proportional to Velocity.
This motor force is applied to a moving system which has mass and is held by a spring.
The spring force is made of two separate springs, one is the driver suspension, and the other is the springiness of the air in the box.
After being “converted†by the motor, the moving mass appears to be a parallel capacitance and the spring force appears to be a parallel inductance, both of which are separated from the input terminals by the motor’s Rdc, a series resistance.
For a small radiator, to have “flat responseâ€, the radiator velocity must fall at a rate (6 dB / oct) which compensates the radiation resistance slope for a small radiator.
This compensating filter slope is made by the parallel capacitance driven by the series resistance which forms a first order slope.
The corner frequency is the box resonance, the Q of that corner is set by the proportion of reactive elements compared to the resistive ones. In the case of the speaker, one has the high Q resonance of the mechanical system if driven with no electrical connection and then one has the Qt dominated by electrical damping when driven normally.
When you increase the spring force by putting the drive in a smaller box, you raise the resonance and (since you made the reactive part larger) raised the Qt(b).
When you raise it to .6 to 1, you have a typical sealed box alignment.
Damping factor is simply the ratio of the source impedance to the load impedance.
This matters at the low cutoff of a woofers response but a DF much greater than about 20 to 40 is an imaginary improvement.
You can easily raise the Q of a driver by adding a series resistance (which reduces the electrical damping).
Best,Tom Danley
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Follow Ups
- Re: that part I apparently failed to convey that I knew - tomservo 17:17:05 01/15/07 (0)
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