Thank you to anyone taking time out to read this post and any replies to it, its much appreciated.
Having had to take apart one of my semi omni directional speakers to bits earlier this year to replace a damaged woofer, I also took the opportunity to replace the original circa 1991 tweeters, resistors and capacitors with modern replacements with the same values.
Everything worked out fine and this gave me the confidence to move to the current phase which sees me replacing the original two tweeters and adding a third to hopefully give a fuller omni experience.
The new design will be as follows, 2 x Monacor SPH220HQs 8" woofers in an isobaric configuration directly wired to one of the three sets of binding posts, the woofers have no crossover.
The left & right firing tweeters are Visaton G 20 S and the forward firing tweeter is a Visaton G 25 FFL. The tweeters will have a basic first order crossover with the crossover being in the 6 khz region.
My friend has calculated the two G 20 S wired in series to the second set of binding posts will need a capacitor in the order of 1.63uf and the single G 25 FFL wired to third set of binding posts will need a capacitor in the order of 3.3uf.
But here's the $64m question, what size/value resistor do I need to include ahead of the each capacitor/s.I have done my best to search google and various forums for a formula or calculation but all that's happened is I have ended up dazed & confused.
All advice is welcomed because this is I think the last piece of my speaker redesign jigsaw. All the best Paul B
MONACOR: SPH-220HQ
G 20 SC - 8 Ohm | Visaton
G 25 FFL - 8 Ohm | Visaton
Having had to take apart one of my semi omni directional speakers to bits earlier this year to replace a damaged woofer, I also took the opportunity to replace the original circa 1991 tweeters, resistors and capacitors with modern replacements with the same values.
Everything worked out fine and this gave me the confidence to move to the current phase which sees me replacing the original two tweeters and adding a third to hopefully give a fuller omni experience.
The new design will be as follows, 2 x Monacor SPH220HQs 8" woofers in an isobaric configuration directly wired to one of the three sets of binding posts, the woofers have no crossover.
The left & right firing tweeters are Visaton G 20 S and the forward firing tweeter is a Visaton G 25 FFL. The tweeters will have a basic first order crossover with the crossover being in the 6 khz region.
My friend has calculated the two G 20 S wired in series to the second set of binding posts will need a capacitor in the order of 1.63uf and the single G 25 FFL wired to third set of binding posts will need a capacitor in the order of 3.3uf.
But here's the $64m question, what size/value resistor do I need to include ahead of the each capacitor/s.I have done my best to search google and various forums for a formula or calculation but all that's happened is I have ended up dazed & confused.
All advice is welcomed because this is I think the last piece of my speaker redesign jigsaw. All the best Paul B
MONACOR: SPH-220HQ
G 20 SC - 8 Ohm | Visaton
G 25 FFL - 8 Ohm | Visaton
Considering you may want different attenuation between the side and front tweeters, using L-Pad Attenuators would allow that without having to figure out the exact resistance needed for an unknown amount.
L-Pads allow from virtually no attenuation when "wide open" to completely off (infinite attenuation). Your single forward tweeter, being about the same sensitivity as the isobaric woofer pair may need no attenuation.
Being able to cut the side firing tweeters off completely would also allow you to revert to a "normal" presentation when an "omni experience" might not be desired.
With a first order 6kHz crossover, for usual music demands, the average power dissipated through the Lpad (or resistors) and tweeter would be somewhere around 20dB down from the peak program. Using 15 watt (or greater) Lpads or resistors should be adequate.
L-Pads allow from virtually no attenuation when "wide open" to completely off (infinite attenuation). Your single forward tweeter, being about the same sensitivity as the isobaric woofer pair may need no attenuation.
Being able to cut the side firing tweeters off completely would also allow you to revert to a "normal" presentation when an "omni experience" might not be desired.
With a first order 6kHz crossover, for usual music demands, the average power dissipated through the Lpad (or resistors) and tweeter would be somewhere around 20dB down from the peak program. Using 15 watt (or greater) Lpads or resistors should be adequate.
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First off thank you for your reply. At a high level I know what an L pad does but in practical terms I confess to being clueless (sorry). Its pleasing to hear you say I might not need a resistor for the G 25 FFL, I am firmly in the "less is more" camp re circuitry and no resistor means no calculations etc.
As I read up further on L pads I am sure what you have written will continue to inform me ever more but right now I am struggling to understand a couple of things.
The first is must the two resistors in an L pad be of the same value ? The second is this, if the resistors are rated at say 15 watts each, what ohm rating should they be because I think I might have been mistaken in thinking the ohm rating was more important than the watts when sizing resistors.
As I read up further on L pads I am sure what you have written will continue to inform me ever more but right now I am struggling to understand a couple of things.
The first is must the two resistors in an L pad be of the same value ? The second is this, if the resistors are rated at say 15 watts each, what ohm rating should they be because I think I might have been mistaken in thinking the ohm rating was more important than the watts when sizing resistors.
The resistance (ohms) is what's important for them to reduce your tweeter level.
Watts is important to reduce the risk of damaging them, or starting a fire. Simply make sure they are large enough (power rating in Watts), and have sufficient ventillation. Check on them as you use them.
Watts is important to reduce the risk of damaging them, or starting a fire. Simply make sure they are large enough (power rating in Watts), and have sufficient ventillation. Check on them as you use them.
Sorry, my response previously should have included "variable" in front of "L-Pad", examples below. The variable L-pad automatically increases one resistance while reducing the other, resulting in the same nominal resistance while increasing or decreasing attenuation.
The "ohm rating" (resistance) determines attenuation in an L-pad. Without knowing the attenuation required, impossible to determine the resistor values required.
Attachments
Thanks guys, I am going to try a variable L pad because it's only true way of hearing it's effect. Given its almost impossible to calculate the attenuation in advance would anyone care to suggest a value to start with and then I will probably go up and down from the initial value and see where it all comes together.
" its almost impossible to calculate the attenuation in advance"- from the manufacturer's data, subtract the sensitivity of the woofer from that of the tweeter.
for the drivers in post 1, it seems you don't need any attenuation
for the drivers in post 1, it seems you don't need any attenuation
Sorry for the delay in catching up. Having now had the opportunity to read up on variable L pads I think that is such an elegant and flexible answer. A big thank you to everyone who replied especially Weltersys �� - I can't wait to to get going on this upgrade.
Voltage divider - loaded and open-circuit dB calculator damping volts potentiometer circuit impedance damping pad decibel dB voltage attenuator impedance bridging matching - sengpielaudio Sengpiel Berlin
Another calculator. Most variable L-pads are 8 Ohm but they also come in 16 Ohm. If you have a 4 Ohm driver, you could put a 4 Ohm series resistor between the driver and the L-pad for 8 Ohms. Of course, you have to take into account the additional attenuation.
To use the voltage divider and dB loss calculator, just choose an input level of 1 Volt to keep the math simple. If you let "Z LOAD" = 10,000, you will see the effects of attenuation. Then try Z LOAD = 4 Ohms, 8 Ohms, etc. to get an idea of the driver Z on the attenuation. Keep in mind that the crossover component values may need to be adjusted; there is no such thing as a pure 8 Ohm driver for example. Look at the spec sheets if available; the impedance rises with frequency, every driver is different in this respect.
Another calculator. Most variable L-pads are 8 Ohm but they also come in 16 Ohm. If you have a 4 Ohm driver, you could put a 4 Ohm series resistor between the driver and the L-pad for 8 Ohms. Of course, you have to take into account the additional attenuation.
To use the voltage divider and dB loss calculator, just choose an input level of 1 Volt to keep the math simple. If you let "Z LOAD" = 10,000, you will see the effects of attenuation. Then try Z LOAD = 4 Ohms, 8 Ohms, etc. to get an idea of the driver Z on the attenuation. Keep in mind that the crossover component values may need to be adjusted; there is no such thing as a pure 8 Ohm driver for example. Look at the spec sheets if available; the impedance rises with frequency, every driver is different in this respect.