The many resistor reviews and comparisons I've read usually include Dueland, Mundor, Caddock and a few others but I've never seen the Dale wirewound power resistors included. Is this type of Dale resistor considered not appropriate for crossovers?
The Dale resistor marked RH will have some inductance. Dale also makes wirewound non inductive resistors marked NH
I mounted them on heatsinks in my first outboard XOs. I also used them without heatsinks in another outboard XO and I can't feel any heat in either XO. Bottom line is, I think I wasted money and energy implementing heatsinks on the first design.
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See the data sheet. To be capable of anywhere near the rated power dissipation, a suitable heat sink is necessary.
Or else buy a resistor sized x2 to x3 larger than the actual needed power dissipation.
Or else buy a resistor sized x2 to x3 larger than the actual needed power dissipation.
In my application nothing is getting warm in either XO so I don't understand how your remarks relate to my posts.
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And just to be clear, my trying to improve a crossover is, to me, nothing more a than an interesting and pleasant diversion with no siginificant consequences. My work as an aerospace engineer was much more than a diversion.
I just measured the R and L of several Dale RH resistors. The inductance of the 2 and 2.2ohm are almost identical and the inductance of the 1ohm 15X larger. Is this difference to be expected?
RH-10 10W 1ohm 1% R=1.020 L= 5.3uH
RH-50 50W 1ohm 1% R=1.016 L= 5.34uH
RH-50 50W 2ohm 1% R=2.017 L= 0.3uH
RH-50 50W 2.2ohm 1% R=2.224 L= 0.4uH
The different construction of various ohm and power values will yield varying inductance as well.
Here is an article that shows an empirical formula for the inductance that depends on the coil diameter,
the coil diameter squared, number of turns squared, and wire length. Not easy to guess what the value
of L is without calculating it. Or, maybe they deliberately labeled 2 ohm NH as RH, due to low stock in RH.
https://www.omnicalculator.com/physics/helical-coil
Here is an article that shows an empirical formula for the inductance that depends on the coil diameter,
the coil diameter squared, number of turns squared, and wire length. Not easy to guess what the value
of L is without calculating it. Or, maybe they deliberately labeled 2 ohm NH as RH, due to low stock in RH.
https://www.omnicalculator.com/physics/helical-coil
Your question specifically mentioned a
POWER resistor.
Which implies power dissipation, hence heating.
If not, what´s the point?
with due respect, nothing in that haphazardly built crossover with squiggly wires (all same colour) and parts hot glued here and there to a piece of plywood suggests mouth opening NASA quality.
Must certainly do its job, but not so sure it merits bragging.
As of wirewound resistor inductance, in depends strongly on winding geometry.
I wind my own, out of Constantan wire.
Cylindrical ones are quite inductive; zigzag "wound" on a flat pieced of Micanite, not that much, because effective coil area is minimized.
I use 0.5 mm thick Micanite.
IF needed, I can wind them in two parallel but opposite direction paths and then inductance practically self cancels to a very low value.
I read several Dale spec sheets and couldn't find any info on the wire size or length. Regarding resistor inductance effect in a crossover, should a small value, like 5.3uH, be included in a crossover design?
I'm not bragging. Only added the pics to show resistors mounted on heatsinks and resistors not on heatsinks. And, whether I listen to the Firebird at a loud level or Miles playing a ballad at a quiet level, the resistors never get warm to the touch.
It's likely too small to affect the crossover near the audio range, with a time constant around one uS with 10R.
So I could have done what many do which is drill holes near wires leaving the various components so the XO looks like a very neat assembly of passive components. I doubt that has any effect on the sound and I question the effect of different colored, squiggly wires on the sound.
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Hi Henty, I think you have spent quite some thought on your Crossover design and component blayout and even though the power resistor doesn't get hot and you might feel that you've wasted your time, I think you should be very happy with the work done to complete the project. Perhaps at a ;later date, you might try different power resistors to see if it makes any difference to the sound regardless if the power resistors are inductive or not
I designed the first XO, for my Sound Dynamics 300Ti speakers, about ten years ago. The layout was based on what I thought would be optimal location and orientation for the four air coils. I used the same basic inductor layout, for the P6 XO, with coil axes at 90deg. angles to each other.
What you can't see in the photo is that all components are tightly secured to the plywood base with heavy duty cable ties.
Reading about subjective opinions of sonic qualities in resistors are well, take it with a grain of salt.
Generally the ratings go up the more expensive and fancy looking they are.
Like duelund carbon with silver leads 30$ for a 'wonder resistor'.
Is it the high 2nd order distortion people like?
10-20% change in resistance over 50 degrees °c thats great about them?
Or is it the instability from heat/effect over time, and moisture etc, changing the value over time just like electrolytic caps that is so great?
Or is it simply from the marketing/price and looks the 'improvement comes.
Just a rant and a example )
Subjective opinions is just that.
And carbon resistors are generally not in use any more for these reasons and more.
Generally the ratings go up the more expensive and fancy looking they are.
Like duelund carbon with silver leads 30$ for a 'wonder resistor'.
Is it the high 2nd order distortion people like?
10-20% change in resistance over 50 degrees °c thats great about them?
Or is it the instability from heat/effect over time, and moisture etc, changing the value over time just like electrolytic caps that is so great?
Or is it simply from the marketing/price and looks the 'improvement comes.
Just a rant and a example )
Subjective opinions is just that.
And carbon resistors are generally not in use any more for these reasons and more.
The OP's question was a good one and deserves a serious, engineering based answer.
When I've needed a power resistor, I've always favored the type pictured because they are simply more believable than those that look like over grown non-power resistors. They are made to be screwed down to something as opposed to being suspended in free air for better air circulation and avoiding contact with a combustible base. They don't require a heat sink but can make use of one depending on actual power handling and anticipated ambient temperatures.
I promised an engineering based answer so I downloaded a data sheet of an example of that type of resistor and found the following at the bottom of it - derating curves based on ambient temperature and heatsink vs no heatsink. You can simply look at graphs, consider your ambient conditions, and make a judgment. It pays to overdesign with power resistors because if you don't they can get uncomfortably - even dangerously hot on a wood base in a hot climate without air conditioning. Home audio is obviously more forgiving than aerospace but it pays to be conservative.
The hardest thing to know is the actual power dissipation requirements. In general, a spice simulation is required. Its seldom worth the effort and even then that is a lot task of someone not trained in the art. For an L-pad, its easy as the amplifier's output is across the resistor pair and ohm's law suffices. I use Vituix and I see it recommends a power rating for Rs in a parallel RLC circuit where there will be significant dissipation but not for a series RLC where dissipation is significant only at or near resonance and then only at a low duty cycle for audio.
If you are concerned about the inductance, you can model it in the XO program and see if the L makes a difference in the response. Usually though, its easy enough to find a non-inductive resistor.
When I've needed a power resistor, I've always favored the type pictured because they are simply more believable than those that look like over grown non-power resistors. They are made to be screwed down to something as opposed to being suspended in free air for better air circulation and avoiding contact with a combustible base. They don't require a heat sink but can make use of one depending on actual power handling and anticipated ambient temperatures.
I promised an engineering based answer so I downloaded a data sheet of an example of that type of resistor and found the following at the bottom of it - derating curves based on ambient temperature and heatsink vs no heatsink. You can simply look at graphs, consider your ambient conditions, and make a judgment. It pays to overdesign with power resistors because if you don't they can get uncomfortably - even dangerously hot on a wood base in a hot climate without air conditioning. Home audio is obviously more forgiving than aerospace but it pays to be conservative.
The hardest thing to know is the actual power dissipation requirements. In general, a spice simulation is required. Its seldom worth the effort and even then that is a lot task of someone not trained in the art. For an L-pad, its easy as the amplifier's output is across the resistor pair and ohm's law suffices. I use Vituix and I see it recommends a power rating for Rs in a parallel RLC circuit where there will be significant dissipation but not for a series RLC where dissipation is significant only at or near resonance and then only at a low duty cycle for audio.
If you are concerned about the inductance, you can model it in the XO program and see if the L makes a difference in the response. Usually though, its easy enough to find a non-inductive resistor.
Attachments
The sound improvement I realized, ten years ago, by using the outboard XOs with the Sound Dynamics 300Ti convinced me that inductor positioning and the of quality of XO components can make significant, cost effective improvements. Bottom line is I listen to the $500 Sound Dynamics 300Ti with outboard XOs much more than my $5,000 B&W N803 speakers.