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angsuman 14th July 2006 06:46 AM

Series resistor placement
 
2 Attachment(s)
Hey, I'm working on a new 3-way loudspeaker project.
I have no measurement tools yet except a multimeter, and will get a microphone soon. I use Passive Crossover Designer to design a crossover.

MY question is the placement of the series resistor. When i modeled the crossover i assumed it was with the resistor placed between the crossover and the driver. However i recently noticed it was actually with the resistor before the crossover. When I corrected this I was horrified by the response. This graph shows the frequency response of the midrange bandpass filter with the series resistor placed before the crossover. The second graph shows it with the resistor placed after the crossover as conventional wisdom would indicate. What is going on here?? Is this correct?? Also while it can be done will there be major problems by placing the resistor before the crossover.

angsuman 14th July 2006 06:49 AM

2 Attachment(s)
Heres the second graph. Notice how it's just bizarre, oh I also should have mentioned i'm using 3rd order electrical crossovers on both high and low pass.

lndm 14th July 2006 09:43 AM

The impedance phase of a driver can give unexpected results, such as the peak you see. I think I'd wait to work with measured results.

The series resistor is curious. There could be a good reason for it. Could you post a schematic?

sreten 14th July 2006 02:57 PM

Hi,

As you can see the source and load impedance of a filter is critical.

You cannot move the attenuation resistor from load to source or
vice versa without affecting the frequency response, the filter
needed for each case will be quite different.

For a bandpass midrange placing the resistor before the c/o
is the safest option as it will act as a current limit if any c/o
parallel capacitors go short.

It also makes the the response relatively impervious to amplifier
damping factor and the effect of different loudspeaker cables.

:)/sreten.

angsuman 14th July 2006 03:22 PM

Oh thank you for the replies. Oh so having the series resistor before the crossover will not affect damping factor? While I haven't done any measurements since i don't have equipment yet I listened to test tones and with the series resistor placed between crossover and driver I can hear a very high peak between 4-5khz just as the graph shows. When I change the resistor to before the crossover the peak isn't there anymore so i'm pretty confident in the simulation.

My crossover is a 3rd order bandpass filter, i'll try to post a schematic soon. I"m curious as to impedence phase, I've heard it mentioned before, but i'm not sure how to import that into PCD. How does impedence phase affect a loudspeaker?

lndm 15th July 2006 01:06 AM

Quote:

Originally posted by angsuman
I'm curious as to impedence phase, I've heard it mentioned before, but i'm not sure how to import that into PCD. How does impedence phase affect a loudspeaker?
First of all, if this is not your cup of tea, it is perfectly possible to start with a text book passive design and tweak it into a good design.

Text book passive crossovers work properly when driving an 8 ohm resistor. Not only does a speaker not behave like a resistor in so far as the impedance varies with frequency (its magnitude), it behaves capacitively and inductively as indicated by these variations, and by its phase. Impedance magnitude and phase are a team and should be worked with together.

Importing into PCD is a matter of measuring the data and creating a zma file for PCD to use.


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