Hi there,
I searched for past posts on these forums but couldn't find what I was looking for. I am trying to attenuate the tweeter in some bi-amped loudspeakers I have built.
The tweeter is 4 Ohms 91.5dB sensitivity
trying to match to an 8 Ohms woofer with a sensitivity of 86dB.
Which would be better, seeing as they are active speakers, an L-pad or single resistor? Everything I can find online seems to recommend an L-pad but assumes a passive design.
Also, does anyone know how I would calculate the resistor value? If a single resistor is fine I was thinking of hooking up a rotary switch with a few different values for fine control.
Any help would be much appreciated.
Thanks!
I searched for past posts on these forums but couldn't find what I was looking for. I am trying to attenuate the tweeter in some bi-amped loudspeakers I have built.
The tweeter is 4 Ohms 91.5dB sensitivity
trying to match to an 8 Ohms woofer with a sensitivity of 86dB.
Which would be better, seeing as they are active speakers, an L-pad or single resistor? Everything I can find online seems to recommend an L-pad but assumes a passive design.
Also, does anyone know how I would calculate the resistor value? If a single resistor is fine I was thinking of hooking up a rotary switch with a few different values for fine control.
Any help would be much appreciated.
Thanks!
Maybe Not
If they are active speakers, there is a good chance the tweeter is driven by a seprate amplifier that has its own level control. Otherwise:
L pad calculator - attenuation dB damping impedance decibel loudspeaker speaker voltage divider - sengpielaudio Sengpiel Berlin
Regards,
WHG
If they are active speakers, there is a good chance the tweeter is driven by a seprate amplifier that has its own level control. Otherwise:
L pad calculator - attenuation dB damping impedance decibel loudspeaker speaker voltage divider - sengpielaudio Sengpiel Berlin
Regards,
WHG
In an active design, the correct approach is to adjust the level in the active control. This assumes as WHG does, separate amps. You did not say anything about the speaker. I would not be surprised if some cheap active speakers have one amp and just a cap on the tweeter. Are you talking high end audio, PA or big-box store computer speakers.
If you are just cracking open the box, the just a series resistor should work fine as the amp is not driving a passive crossover and the impedance change will not change the transfer function. Amps like a litter higher load, so that is actually good.
If you are just cracking open the box, the just a series resistor should work fine as the amp is not driving a passive crossover and the impedance change will not change the transfer function. Amps like a litter higher load, so that is actually good.
Hi WHG,
Thanks for the quick response, yes the speakers are bi-amped so the tweeter has it's own separate amplifier, but I cannot find anything on the amplifier module itself (Hypex UCD180) to adjust the level. Is there usually a level control on amplifier modules?
Thanks for the link, I'm aware of the Sengpiel-audio calculator, the single resistor value seemed quite low so wasn't sure whether to trust it. The problem still remains though, do I actually need an L-Pad or a single resistor?
I have an active crossover before the amplifiers so the resistor or L-pad would be between the active crossover and the tweeter amplifier. So do the problems of the amp 'seeing' a constant load still apply to active designs?
Many thanks,
Matt
Thanks for the quick response, yes the speakers are bi-amped so the tweeter has it's own separate amplifier, but I cannot find anything on the amplifier module itself (Hypex UCD180) to adjust the level. Is there usually a level control on amplifier modules?
Thanks for the link, I'm aware of the Sengpiel-audio calculator, the single resistor value seemed quite low so wasn't sure whether to trust it. The problem still remains though, do I actually need an L-Pad or a single resistor?
I have an active crossover before the amplifiers so the resistor or L-pad would be between the active crossover and the tweeter amplifier. So do the problems of the amp 'seeing' a constant load still apply to active designs?
Many thanks,
Matt
Sorry, just posted in response to WHG before I saw your post tvrgeek.
They are high end studio reference monitors I built a while ago but haven't got round to tweaking. I currently have a single resistor in series with the tweeter but wasn't sure if this was correct or if I needed an L-pad. thanks for clearing that up!
The speakers are quite expensive scanspeak ones and the amp modules are Hypex UCD180 amps. Each loudspeaker has...
Input>>Active Crossover (2kHz)>>Separate amp modules for tweeter and woofer.
Woofer - Scanspeak 22w-8857t00
Tweeter - Scanspeak d3004-662000
P.S. Thank you very much for your help tvrgeek - I will just use a series resistor then to attenuate the tweeter! For some reason I stuck one in there ages ago but wasn't the right value (not attenuated enough) so I will use the sengpeil audio calculator to get the correct value.
I was thinking if I hook up a rotary witch with some different values on, this would act as an EQ by changing the tweeter level - a 2kHz shelf. Not sure if this is a great idea though. I saw on some other studio monitors that they had a 2kHz crossover and a 2kHz shelf but not sure if this is how they acheived it. If so, would it have to be a 'break before make' or 'make before break' switch?
Thanks again, much appreciated.
They are high end studio reference monitors I built a while ago but haven't got round to tweaking. I currently have a single resistor in series with the tweeter but wasn't sure if this was correct or if I needed an L-pad. thanks for clearing that up!
The speakers are quite expensive scanspeak ones and the amp modules are Hypex UCD180 amps. Each loudspeaker has...
Input>>Active Crossover (2kHz)>>Separate amp modules for tweeter and woofer.
Woofer - Scanspeak 22w-8857t00
Tweeter - Scanspeak d3004-662000
P.S. Thank you very much for your help tvrgeek - I will just use a series resistor then to attenuate the tweeter! For some reason I stuck one in there ages ago but wasn't the right value (not attenuated enough) so I will use the sengpeil audio calculator to get the correct value.
I was thinking if I hook up a rotary witch with some different values on, this would act as an EQ by changing the tweeter level - a 2kHz shelf. Not sure if this is a great idea though. I saw on some other studio monitors that they had a 2kHz crossover and a 2kHz shelf but not sure if this is how they acheived it. If so, would it have to be a 'break before make' or 'make before break' switch?
Thanks again, much appreciated.
It's pretty simple really:
1) An L-Pad will lower the efficiency of the tweeter without changing the frequency response very much.
2) A resistor will lower the efficiency of the tweeter also. But it will be less effective at frequencies where the impedance is high. The net effect is that a resistor in series will tend to depress the frequencies between about 2khz and 8khz. But the rest of the bandwidth will be barely effected. This is because the impedance of the tweeter at resonance may be as much as 4x higher than an octave or two above it. And the impedance at 20khz may be as much as 2-4x higher than at 4khz.
A lot will depend on the impedance curve of the tweeter.
Here is the frequency response of a 3" midrange, with and without a resistor in series. See how the effect of the resistor is nearly zero at the resonance frequency of 60hz and in the top two octaves (5khz-20khz.)
1) An L-Pad will lower the efficiency of the tweeter without changing the frequency response very much.
2) A resistor will lower the efficiency of the tweeter also. But it will be less effective at frequencies where the impedance is high. The net effect is that a resistor in series will tend to depress the frequencies between about 2khz and 8khz. But the rest of the bandwidth will be barely effected. This is because the impedance of the tweeter at resonance may be as much as 4x higher than an octave or two above it. And the impedance at 20khz may be as much as 2-4x higher than at 4khz.
A lot will depend on the impedance curve of the tweeter.
Here is the frequency response of a 3" midrange, with and without a resistor in series. See how the effect of the resistor is nearly zero at the resonance frequency of 60hz and in the top two octaves (5khz-20khz.)
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Thanks for the info regarding frequency response.
I can see how this would be true in passive speakers.
I just want to be clear, is this the same in active speakers?
The resistor will be after the active crossover but before the amplifier, and the amplifier is only supplying the tweeter.
Many thanks,
Matt
I can see how this would be true in passive speakers.
I just want to be clear, is this the same in active speakers?
The resistor will be after the active crossover but before the amplifier, and the amplifier is only supplying the tweeter.
Many thanks,
Matt
You confused everyone when you mentioned an L Pad.
L Pads are only used for speaker attenuation after the crossover, rather than for attenuation prior to the amplifier.
For attenuation ahead of the amplifier you just need a simple potentiometer. Probably something in the 10k ohms to 50k ohms range.
David
L Pads are only used for speaker attenuation after the crossover, rather than for attenuation prior to the amplifier.
For attenuation ahead of the amplifier you just need a simple potentiometer. Probably something in the 10k ohms to 50k ohms range.
David
Hi Speaker Dave,
Thanks for clarifying! Is there a formula or online calculator to determine the value resistor I would need?
I'd like to try and get close to the correct value first to eliminate some of the guesswork.
Then once I have found the value I can just solder in a resistor.
Many thanks,
Matt
Thanks for clarifying! Is there a formula or online calculator to determine the value resistor I would need?
I'd like to try and get close to the correct value first to eliminate some of the guesswork.
Then once I have found the value I can just solder in a resistor.
Many thanks,
Matt
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