Series, L-Pad, and RL Circuit

[Lojzek]

The only way it is possible to adjust the level of the tweeter
without shifting the crossover frequency (of the tweeter)
is with a L-pad.
-cT

Not that it matters much, an Lpad changes XO frequency
if we can agree XO fr is a junction where two slopes intersect.

LR 2nd order, attenuation -1dB on tweeter.

 

[Sonce]

I have some large three way speakers with rising tweeter response and they're killing me from 9kHz and up.
there is a 2ohm resistor used in series before the crossover to attenuate the tweeter.
My question is what is the next logical step in fixing this? Do I get rid of the series resistor and try an L-Pad instead? Or do I leave the series resistor and build an RL circuit to compensate?

Please draw the tweeter filter schematic and post it here, it is the only way to find the best fix.
Otherwise, keep 2 ohm resistor and try serial RC in parallel with tweeter, as recommended by giralfino. C has big impact on reducing high frequencies, R not so - you can use R=2.2 ohm fixed.

 

[speaker dave]

You have found that lowering tweeter level enough to get the top octave right means too low a level at the bottom. You might try some small value inductors in series with the tweeter to tilt it down. Perhaps a series RC leg in parallel with the tweeter. Try something like 2 to 5 uf in series with 1 or 2 ohms, both across the tweeter terminals.

Good luck

 

[Dissi]

Although I thought an RL (resistance and induction) in series would tame some rising response starting at a specific frequency? You're recommending an RC in parallel instead. I take it they both work but differently?

I never have seen a L in series to a tweeter, but parallel RCs many times. Nevertheless, the idea is absolutely correct and might, depending on case, even perform better. At least it will yield a high impedance in the upper frequency range and make your amp much happier than a parallel RC, especially when the series resistor only is 2 ohm. Those RCs often are questionable IMO.

 

[Jay]

there is a 2ohm resistor used in series before the crossover to attenuate the tweeter.

Not clear. Two possibilities: 1) Resistor is before tweeter crossover 2) Resistor is before (tweeter & woofers) crossover.

It is unlikely the second one, which is usually used to get good impedance or to achieve "tube sound".

For the first one, 2 Ohm is too small to affect tweeter response (especially to elevate tweeter response, is very unlikely). If you can hear differences with 2.5 Ohm, it is probably the different resistor brand, no?

Here is similar thread:
http://www.diyaudio.com/forums/multi-way/242206-lpad-v-single-resistor.html

 

[cT equals piD]

What he is referring to is usage of a resistor between the amplifier and dividing network portion of the xover. Yes the resistor is part of the xover network, but being to one side or the other of the dividing network portion has differing affects on the outcome.

Just so that we are talking about the same thing here, I'm assuming that we are discussing a parallel crossover.

When you say to one side or the other of the dividing network portion, do you mean the entire crossover network? My impression is that the discussion is about the high-pass filter section for the tweeter only.

Dickason, in his cookbook, discussing what he calls driver attenuation circuits, says that if you use a series resistor for attenuation, then you must recalculate component values of the crossover to account for the increased driver impedance. Apparently he lumps the series resistance together with the driver impedance. Do you disagree with him in making that statement?

Regards,
cT

 

[Jay]

Dickason, in his cookbook, discussing what he calls driver attenuation circuits, says that if you use a series resistor for attenuation, then you must recalculate component values of the crossover to account for the increased driver impedance. Apparently he lumps the series resistance together with the driver impedance. Do you disagree with him in making that statement?

Wolf said differing effect. The resistance before a crossover, you cannot lump into total driver impedance (unless first order). You need bigger resistance (compared to before driver) before the crossover to affect the tweeter, in a different way.

 

[cT equals piD]

Wolf said differing effect. The resistance before a crossover, you cannot lump into total driver impedance (unless first order). You need bigger resistance (compared to before driver) before the crossover to affect the tweeter, in a different way.

IMO that is all nonsense. It makes no difference where the resistance is placed in the loop that is between the output terminals of the amplifier and includes the driver, it is still in-series with the driver. Also, the quantity of resistance that is in-series with the driver (affecting a definite amount of voltage division with the driver) doesn't vary at all no matter where in the loop it's located.

Higher than first order filters are affected by a series resistor as any order of filter has reactance in-series with the driver.

Regards,
cT

 

[cT equals piD]

Not that it matters much, an Lpad changes XO frequency
if we can agree XO fr is a junction where two slopes intersect.

LR 2nd order, attenuation -1dB on tweeter.

Okay, good point. Then what would be more correct to say is that the proper application of an L-pad allows for correcting unequal sensitivity of a pair of drivers without making it necessary to change the values of the components of the filter.

 

[tinitus]

Not that it matters much, an Lpad changes XO frequency
if we can agree XO fr is a junction where two slopes intersect.

LR 2nd order, attenuation -1dB on tweeter.

yes
and not only has the xo point moved up
but the -6db condition have also changed

I have suspected this for some years now
strangely it is not very well known

thanks for showing it so clearly

which reminds me of old Snell speakers
they had adjustable L-pads
and those speakers could change from average to sublime, just by adjusting the tweeter L-pad
I was surpriced to experience this
unfortunately it also tells that many may never have experienced their full potential
funny thing, actually

scary to think about the many L-pads in a speaker like Infinity Kappa 9

 

[Jay]

IMO that is all nonsense.

Why use opinion? You can post a picture from any simulation software to prove your points. It may just a miscommunication as it is pretty basic issue.

 

[Lojzek]

tinitus,

you're welcome.

 

[cT equals piD]

Yes you can have a resistor before and use that single resistor as an attenuation resistor and be very effective vs using a conventional L-pad after the network.
Later,
Wolf

From the little bit of study that I did today, at the very least, a series resistor between the amplifier and a 2nd order filter changes phase of the driver at the crossover frequency from what it should be to obtain a flat response through the crossover region. Also I found that with the 2nd order filter, there IS a difference in how the series resistor affects attenuation at the crossover frequency depending on the position of the series resistor.

Regards,
cT