Help with notch filter for Dayton RS150-4

[gleepoy]

Hi guys,

Is there a textbook notch filter solution for the Dayton Reference RS150-4 that can help me tame the breakup @ ~6.3KHz & 9.4KHz?
<A HREF="http://www.partsexpress.com/pe/showd...number=295-372">http://www.partsexpress.com/pe/showd...number=295-372</A>

I am trying to use these in a car audio application mated to Morel MDT-33 tweeters crossed over @ ~ 2KHz.

With an electronic 3rd order butterworth @ 2KHz, I can still hear the breakup. Perhaps it's because they are relatively on axis.

Should I use a parallel or series notch filter? Can I use one of the online notch calculators like this one?
<A HREF="http://www.mhsoft.nl/ParallelNotchFilter.asp">http://www.mhsoft.nl/ParallelNotchFilter.asp</A>

I would rather not buy a more sophisticated processor. I tried underlapping the x-over points without much luck.

Any help would be much appreciated.

Thanks guys.

Regards,
Gary

[Pete Schumacher ®]

> Hi guys,

> Is there a textbook notch filter solution
> for the Dayton Reference RS150-4 that can
> help me tame the breakup @ ~6.3KHz &
> 9.4KHz?
>
> <A HREF="http://www.partsexpress.com/pe/showd...number=295-372">http://www.partsexpress.com/pe/showd...number=295-372</A>
> I am trying to use these in a car audio
> application mated to Morel MDT-33 tweeters
> crossed over @ ~ 2KHz.

> With an electronic 3rd order butterworth @
> 2KHz, I can still hear the breakup. Perhaps
> it's because they are relatively on axis.

> Should I use a parallel or series notch
> filter? Can I use one of the online notch
> calculators like this one?
>
> <A HREF="http://www.mhsoft.nl/ParallelNotchFilter.asp">http://www.mhsoft.nl/ParallelNotchFilter.asp</A>
> I would rather not buy a more sophisticated
> processor. I tried underlapping the x-over
> points without much luck.

> Any help would be much appreciated.

> Thanks guys.

> Regards,
> Gary

Then you can't use a notch filter in parallel with the woofer since it produces an impedance near zero ohm at resonance.

Series is the way to go. The calculator you dialed up has the correct topology. Use a resistor of at least 100 Ohm to get any serious reduction of level at resonance.

0.5mH , 0.56uF, and 100 Ohm should reduce the 6KHz peak a good 10dB and 15dB at 9.4KHz.

[Max_Andrews]

A zobel circuit is cheap and will reduce a lot of that breakup trash.

[gleepoy]

Thank you for your help Pete!

Is there any way to tweak the values a bit? I can't find a 0.56uF value cap at Partsexpress or combination of caps (parallel or series) to come to 0.56uF.

How did you arrive at those values? I'm trying to learn what effect changing the values does. But the sites I found don't really explain it very well. Thanks Pete.

Regards,
Gary

> Then you can't use a notch filter in
> parallel with the woofer since it produces
> an impedance near zero ohm at resonance.

> Series is the way to go. The calculator you
> dialed up has the correct topology. Use a
> resistor of at least 100 Ohm to get any
> serious reduction of level at resonance.

> 0.5mH , 0.56uF, and 100 Ohm should reduce
> the 6KHz peak a good 10dB and 15dB at
> 9.4KHz.

[gleepoy]

Thanks for your response. I'll incorprate a zobel. Since Zobels are placed in parallel with the driver, can I go cheap with the components or should I stick with poly caps and air-core inductors? Thanks again.

Regards,
Gary

> A zobel circuit is cheap and will reduce a
> lot of that breakup trash.

[boso]

> Thank you for your help Pete!

> Is there any way to tweak the values a bit?
> I can't find a 0.56uF value cap at
> Partsexpress or combination of caps
> (parallel or series) to come to 0.56uF.

> How did you arrive at those values? I'm
> trying to learn what effect changing the
> values does. But the sites I found don't
> really explain it very well. Thanks Pete.

> Regards,
> Gary

You could parallel to smaller caps, PE has .10 and .47 caps that would combine to .57. Very close.
<A HREF="http://www.partsexpress.com/dayton-film-capacitors.cfm">http://www.partsexpress.com/dayton-film-capacitors.cfm</A>

[Max_Andrews]

Use a regular non-polar electrolytic cap and a non-inductive 10-watt or higher resistor, should only be about two bucks combined.

[Jeff B.]

> Use a regular non-polar electrolytic cap and
> a non-inductive 10-watt or higher resistor,
> should only be about two bucks combined.

a zobel will have no effect the response if he is using an electronic crossover

[Jeff B.]

> Then you can't use a notch filter in
> parallel with the woofer since it produces
> an impedance near zero ohm at resonance.

> Series is the way to go. The calculator you
> dialed up has the correct topology. Use a
> resistor of at least 100 Ohm to get any
> serious reduction of level at resonance.

> 0.5mH , 0.56uF, and 100 Ohm should reduce
> the 6KHz peak a good 10dB and 15dB at
> 9.4KHz.

Why include the resistor at all? Using a parallel notch in series with the driver to suppress out of band peaks shouldn't require any resistor. Let the voltage run into a very high impedance at the resonance frequency and use that to knock it down.

Personally, I find the RS150 to not work well with notch filters due to the wide bandwidth of the break-up. Instead I find it best tamed with simpler higher order crossover circuits. Like the 3rd order I used in the pic below.

Jeff B.

[Andy_G]

> a zobel will have no effect the response if
> he is using an electronic crossover

hmmm.. are you certain about that ?
I see that the decreased resistance (wrt the actual speaker impedance) caused by the zobel as the frequency rises would cause increased power from the amp, but this increase in power would be used by the zobel, I assume, so that means the driver sees no difference.
But are any phase issues introduced by the zobel ?

[Pete Schumacher ®]

> Why include the resistor at all? Using a
> parallel notch in series with the driver to
> suppress out of band peaks shouldn't require
> any resistor. Let the voltage run into a
> very high impedance at the resonance
> frequency and use that to knock it down.

> Personally, I find the RS150 to not work
> well with notch filters due to the wide
> bandwidth of the break-up. Instead I find it
> best tamed with simpler higher order
> crossover circuits. Like the 3rd order I
> used in the pic below.

> Jeff B.

Sure, you could do without the resistor altogether. I just thought the overall response looked a little better with the resistor in. PCD is really nice!!! The values for this notch filter provide a fairly wide bandwidth however, and like I said, knock down the broad resonance bump at least 15dB at 9.5KHz.

[Pete Schumacher ®]

> hmmm.. are you certain about that ?
> I see that the decreased resistance (wrt the
> actual speaker impedance) caused by the
> zobel as the frequency rises would cause
> increased power from the amp, but this
> increase in power would be used by the
> zobel, I assume, so that means the driver
> sees no difference.
> But are any phase issues introduced by the
> zobel ?

Since the zobel is in parallel with the woofer and is driven by the same voltage source, there will be no effect on the frequency response at the woofer terminals.

[unknownuser]

> Is there any way to tweak the values a bit?

Certainly. Tweaking the values of the parallel trap circuit you are using can be tricky though, because all the components influence all the others.

Lowering the cap value OR the inductor value raises the frequency affected by the filter. Raising either lowers the frequency.

Lowering the cap and raising the inductor will widen the notch, the opposite will narrow it. Keeping the product of uF and mH the same will keep the center frequency of the notch the same.

Raising the R or removing it completely (infinite resistance) will deepen the effect.




(Originally posted by: BFB)

[Andy_G]

> Since the zobel is in parallel with the
> woofer and is driven by the same voltage
> source, there will be no effect on the
> frequency response at the woofer terminals.

I can see that now. I was looking at it in terms of impedance as seen by the amp. That does change, but of course it equally countered by the draw of the zobel. Therefore no change.

[Jeff B.]

> Since the zobel is in parallel with the
> woofer and is driven by the same voltage
> source, there will be no effect on the
> frequency response at the woofer terminals.

Thanks for clarifying my garbled statement. I need to quit making quick posts on my way out the door to work in the mornings, unless I have time to reread them.

[Jeff B.]

> I can see that now. I was looking at it in
> terms of impedance as seen by the amp. That
> does change, but of course it equally
> countered by the draw of the zobel.
> Therefore no change.

Not exactly. If you use a Zobel the amount of power delivered by the amplifier will change. It will actually be greater due to the lower impedance at the higher frequencies affected. However, solid state amps are constant voltage sources and these swings in impedance do not impact the frequency response as delivered by the amplifier, and therefore the frequency response will not change either.

Now, voice coil inductance may impact the frequency response of the driver causing it to roll-off earier, but adding a zobel does not change this. The inductance is still present in the motor, it just isn't seen by the amplifier due to circuit being there to compensate for it.

I wonder if people who use Zobels realize this? Zobels do not remove voice coil inductance, they simply compensate for it in order to benefit other parts of the circuit. The effect of the inductance on driver response is still present.

Jeff B.

[Andy_G]

> Not exactly. If you use a Zobel the amount
> of power delivered by the amplifier will
> change. It will actually be greater due to
> the lower impedance at the higher
> frequencies affected. However, solid state
> amps are constant voltage sources and these
> swings in impedance do not impact the
> frequency response as delivered by the
> amplifier, and therefore the frequency
> response will not change either.

But a change in impedance must surely change the current, hence power, generated by the amplifier, and this excess current/power must go somewhere, ie the zobel.

So putting a zobel on a driver directly connected to an amp, while it does not change the frequency response, it does increase the load on the amp, wastefully.
Now trying to figure if it has any affect on things like damping etc ???

[Jeff B.]

> But a change in impedance must surely change
> the current, hence power, generated by the
> amplifier, and this excess current/power
> must go somewhere, ie the zobel.

> So putting a zobel on a driver directly
> connected to an amp, while it does not
> change the frequency response, it does
> increase the load on the amp, wastefully.
> Now trying to figure if it has any affect on
> things like damping etc ???

Yes, it does draw more current, which goes into the Zobel. And if an amp has any high frequency damping issues then the Zobel will have an affect on it.

[Andy_G]

> Yes, it does draw more current, which goes
> into the Zobel. And if an amp has any high
> frequency damping issues then the Zobel will
> have an affect on it.

This is what I suspected, thanks Jeff.