car cabin room

[sma]

Hi,

I am install Vifa P13WH10-04 woofer+ Vifa D26NC tweeter at my car audio.I am use RTA for make the crossover and already get good cutting point at 3500 hz .the response already linear between woofer and tweeter.

The problem is at 1.25khz frequency is peak 3 db.
I think this is because car cabin acoustic.because when the microphone put front of the speaker,the response is okay,but when the microphone put at driver ear position the 1.25khz is peak.

Is somebody people know how i can reduce this frequency peak?I don't want use active equalizer since will reduce the sound quality.

so please advice me with other method.is possible use passive crossover additional schematic for reduce this 1.25 khz frequency?
or use acoustic way like difffusor for break this frequency boost.

Please advice.

[roger2]

There is a way to cut specified frequencies using passive components. It is a circuit called a "notch filter". I have used these filters on drivers with peaky response...in fact when time permits I intend to make notch filters for the front speakers of my car which are a bit too strong around 4K.

I learned how to design passive notch filters from two books I have by David B. Weems. The book titles are "Great Sound Stereo Manual" and "Designing, Building and Testing Your Own Speaker System". These books were published by Tab Books in 1990...I would guess these are still available, either one will give you the information you seek. Or try Google...the info may be online somewhere.

A notch filter of this type consists of a capacitor, a coil, and a resistor wired in parallel to each other. This circuit is then inserted in series with the positive lead to the driver(s) which has a frequency that needs to be attenuated.

In your case, since the offending frequency is 1.25K and the tweeter is crossed at 3.5K, I would say that a notch filter should be placed in the leads to each of the woofers, after the crossover (between the crossover and the woofer).

The resistor in the circuit determines the amount of attenuation (depth of the cut). The capacator and coil determine the frequency (center). The books offer no method for varying the width of the notch.

The formulae are as follows:

C=1/(33 x f) for an 8 ohm driver
C=1/(16.5 x f) for a 4 ohm driver

After you have C, find L as below:
L=0.025/(f x f x C)

NOTES:

f= frequency
C= capacitance in Farads NOT microFarads (you must convert)
L= inductance in Henrys NOT miliHenrys ( you must convert)

Use trial and error to find the value of the resistor that gives you the desired attenuation. Experiment with values from about 2 ohms to about 30 ohms...but the few times I have made these the resistor values that I ultimately decided on were usually in the 4 - 10 ohm range I believe. (the larger the resistor the greater the cut).

Use quality passive components...mylar caps at a minimum, no electrolytics. Make certain that the voltage ratings on all components are high enough not to burn out.

Hope this helps

[sma]

Thank u roger,i will let u know the result