Paralel resistor

[jan]

Can anybody tell me the effects of a tweeter hooking up paralel with a resistor. And how will I calculate the value of the resistor.
People told me harshness would be reduced.

Thanks

[VictorG]

Um, now granted I'm no EE, nor do I claim to have any knowledge outside my own tinkering with my own speakers (trial and error style), but I would think that all that adding a resitor will do is change the relative volume of the tweeter in relation to whatever you are running for the bass/mid.

To correct "harshness" you prob want a capacitor to act as a high filter to take out the ultra high frequencies and add a supertweeter into the system to take over. This may be the solotion, maybe not, what does the "harshness" sound like?

B

[navin]

the reduction in harshness by using a parallel cap would largely depnd on the impedance curve of the tweeter also some tweeters like the SS 2905-9900 sound better without teh parallel resistor.

[Jay]

IMHO, harshness will happen if we drive the tweeter with too much power, and/or we feed the tweeter with too low frequency such that it approaches it's resonance. Harshness then will automatically be attenuated if we take away the power out of the tweeter, and/or (in most cases) we lift the crossover frequency or similar effort to take away low frequencies from the tweeter.

1. Paralleling the tweeter with resistor, no matter how big the resistor, will lower the total impedance. With lower impedance, the crossover frequency will be higher. This way the tweeter more likely to operate farther from it's resonance frequency, thus eliminating "harshness".

2. Paralleling the tweeter with resistor, no matter how big the resistor, will share the power between the tweeter and the resistor (though microscopic), and may reduce the "harshness" as well.

3. Compensation should be done as an integral part of the whole design. A change such as adding a parallel resistor with the tweeter will change the whole design (especially if the resistor is small enough). If the harshness is the thing to compensate, I think L-PAD is more appropriate to apply, as this doesn't change many important design parameters.

4. To use L-PAD, we add R1 in series with the tweeter such that this R1 share a small part of the power going into the tweeter. R2 is put in parallel with the tweeter to compensate the increase in total resistance/impedance due to R1. This, I think, assummes that the speaker impedance is purely resistive. There are lots of simple programs (on the net) to calculate R1 and R2 based on recognized speaker impedance and required signal attenuation.

5. I'm not sure (never experienced) if common tweeter can introduce "harshness" or resonance on the top frequency roll-off. Even if it is true, I'm afraid the side effect on sonic of the attenuation will be worse. To attenuate this "highish" frequency, IMO, you can use a zobel-like circuit (C+R in parallel with the tweeter). The C will choose the frequency (try 2u2 to 3u3) and R (try 2 Ohm to 3 Ohm) will attenuate the total impedance, or short the signal to ground.

6. If you insist to use the parallel resistor, why not try with 1K and then lower the value until you hear the harshness attenuated. Nothing fancy I guest, just don't use small power R.

7. If I have to include the "harshness problem" into my design process, I will not use the parallel resistor as my solution. I don't even like the L-PAD solution. I can accept R in series with the tweeter, but not in parallel. There's no technicall explanation here (as I'm no expert), just my phobia of anything that could possibly take away the sonic performance out of my system



__________________________________________________ _____________
"Am no expert, take my advice at yer own risk." - Sigmund Freud

[navin]

Originally posted by Jay
6. If you insist to use the parallel resistor, why not try with 1K and then lower the value until you hear the harshness attenuated. Nothing fancy I guest, just don't use small power R.

7. If I have to include the "harshness problem" into my design process, I will not use the parallel resistor as my solution. I don't even like the L-PAD solution. I can accept R in series with the tweeter, but not in parallel. There's no technicall explanation here (as I'm no expert), just my phobia of anything that could possibly take away the sonic performance out of my system

i too experinced the same with my 9900. the tweeter sounded like it was shouting when a 10ohm resistor was in parallel.

i had used the parallel resistor to damp the impedance peak making a notch filter (1.7mh, 64uf, 6.5ohm) was looking too expensive. how does one damp an impedance peak without resorting to a parallel resistor or nothc filter? any acoustic modification that can be made to reduce the impedance peak?

increasing the parallel resistor to 20ohm reduced the shouting problem but the problem surfaces when the volume is turned up.

[jan]

I think i`m just going to give it a try. I´ll let you know the outcome. Thanks guys.

[ChuckT]

Parallel resistors will increase the voltage handling and reduce the resistence.
This may or may not improve the proformance If you didn't use a high enough voltage resistor.
I believe the formula is 1 / ( 1/Rx + 1/Ry)

[Jay]

Originally posted by navin
i had used the parallel resistor to damp the impedance peak making a notch filter (1.7mh, 64uf, 6.5ohm) was looking too expensive. how does one damp an impedance peak without resorting to a parallel resistor or nothc filter? any acoustic modification that can be made to reduce the impedance peak?

Navin, I really have no background in scientific speaker design, only some Physics from universities and fun-(if not stupid)oriented DIY activities so I’m not qualified to answer your question, and I have some confusion regarding a notch filter implementation.

If I calculated it properly (a rough one indeed), the notch filter values you have mentioned is intended for the SS Revelator, where the resonance frequency is for the tweeter alone:

R = Re + (Qes * Re / Qms)
L = Qes * Rs / (2 * pi * Fs)
C = 1 / (2 * pi * Fs * Qes * Re)

IMO (just logical thinking), if we cross the tweeter at high enough frequency (at least 2K for the revelator, where Fs is about 500) to incorporate a woofer, and then we put the tweeter INSIDE an enclosure, the bump (or is it hump?) will often be shifted near the crossover frequency. In this case, it is more logical to damp the overall impedance peak (applying the filter in the input of the crossover), or at least not to use the raw driver parameters to calculate the filter.

As notch filter will create other problem if targeted at wrong frequency (what if the cure is worse than the diseases?) and that it is impossible to calculate the values by ears, I have never used a notch filter, but IMO the effect of the resistor in the notch filter on transient is not significant, even compared to zobel or higher order filter, because it operates in a narrow band (it’s effect is only on the bank account as in your case )

Opposite to the common notch filter, a notch filter by paralleling RLC and putting it in series with the driver is possible to do by ears. In some cases with woofers, I simply exclude the R for “better” transient.

As with acoustic mod to combat peak, I don’t think that it is necessary possible. But I prefer to damp the tweeter chamber and internally isolate the enclosure with the rest of the enclosure volume. And I don’t think that a peak in impedance (as long as the respond is linier and/or phase linier) should be a problem with good (MOSFET?) amplifier.

[mhelin]

Originally posted by navin

any acoustic modification that can be made to reduce the impedance peak?

You could use a waveguide, but it's difficult to build a DIY waveguide with right properties (btw. www.hifitalo.fi in Finland sells some waveguides for Seas 3/4" and 1" metal dome tweeters, AWSM-120 for 19 mm and AWSM-140 for 25 mm tweeter). If your tweeter has a back chamber you might try replacing the stuff inside with decent lamb's wool. Also you could try expanding the back chamber to lower the FS. If there are any changes you could also fit in new motor or cone / dome which would allow for longer throw (that has been done for an example with Dayton tweeters which were built with compatible Morel parts).

[navin]

thanks guys. i knew there were wave guides that could help. I prefer solving problems at the source and not addind fixes like notch filters.