Basically, I'm designing a set of 3-way speakers with a vented woofer and a sealed mid/tweet chamber. I was thinking just to throw the XO components in the sealed chamber, which is quite small at about 0.1 ft^3, but then I got to wondering if there's such a thing as burning out XO components due to not enough cooling and getting too hot. They're not huge speakers or anything - just a pair of bookshelves rated under 100w rms.
Similarly, I've been asked to generally brainstorm some larger designs, which would be closer to 1,000w rms in a ~1 ft^3 sealed box. What sort of thermal limitations would I be running into with stuffing that much power into a small sealed box?
Similarly, I've been asked to generally brainstorm some larger designs, which would be closer to 1,000w rms in a ~1 ft^3 sealed box. What sort of thermal limitations would I be running into with stuffing that much power into a small sealed box?
Ask a car stereo install / repair technician whether overheating of crossovers can be a problem - short answer is 'effen ya' . I've seen the hot glue adhering a 10W sandcast resistor to the cheapie phenolic boards melted, along with scorching of the board and fracture of the resistors themselves. The numerous components on those little XO modules are packed into as compact a space a possible, and then often stuffed into locations with inadequate ventilation / thermal dissipation, so it's like an intentionally engineered failure mode.
.1ft^3 is pretty tiny box for sure, and I'd be inclined slightly increase volume of vented portion and place the XO as close to the vent as practical.
For the 1000W system, 1ft^3- really? but you might want to think about active and multi-amping for that
.1ft^3 is pretty tiny box for sure, and I'd be inclined slightly increase volume of vented portion and place the XO as close to the vent as practical.
For the 1000W system, 1ft^3- really? but you might want to think about active and multi-amping for that
First, if your parts are adequately sized (i.e. if you need a 10w resistor, use a 10w resistor) you will not have any trouble putting your XO anywhere in your cabinet. If you run your speakers with the XO on the outside, you should be able to touch every component (mostly resistors) with your finger and be nothing more than warm to very warm. Anything hotter and you need to go up a wattage rating on that component. Assuming you have it wired correctly and no dead-shorts anywhere.
To the 1000w question - I know of no system, except a stadium concert and even that doesn't do it RMS, where you would ever hit 1000w RMS, a system running 50w RMS would typically be 110+db from a 88-90db efficient speaker. That's hearing damage and extreme discomfort with exposure for more than a short period.
Add to that anything less than a subwoofer would not have the voice coil to stand up to that much abise and heat --- you won't be making that "design' a reality. Also 1-ft3 is not a large design, large would be 3-4 ft3 or more.
To the 1000w question - I know of no system, except a stadium concert and even that doesn't do it RMS, where you would ever hit 1000w RMS, a system running 50w RMS would typically be 110+db from a 88-90db efficient speaker. That's hearing damage and extreme discomfort with exposure for more than a short period.
Add to that anything less than a subwoofer would not have the voice coil to stand up to that much abise and heat --- you won't be making that "design' a reality. Also 1-ft3 is not a large design, large would be 3-4 ft3 or more.
It IS a thing. If you watch DIY boards you often see X brand speakers blew, resistors are toast kind of messages.
The last stage before buying parts for me is examining the transfer function to make sure my crossovers are doing what I think they are doing, and after that, examining power dissipation on each component. I use XSim to accomplish both.
By leaving ample safety margin I ensure I never have to worry about this. Also by using resistors which are incredibly thermally stable (Mills)
Best,
E
The last stage before buying parts for me is examining the transfer function to make sure my crossovers are doing what I think they are doing, and after that, examining power dissipation on each component. I use XSim to accomplish both.
By leaving ample safety margin I ensure I never have to worry about this. Also by using resistors which are incredibly thermally stable (Mills)
Best,
E
How do you measure power dissipation per component before ordering them and what would be defined by the 'safety margin'?
I would be buying components that I believe are of good quality. Mostly Dayton audio grade stuff from PE, I would imagine.
I would be buying components that I believe are of good quality. Mostly Dayton audio grade stuff from PE, I would imagine.
I have epoxied heatsinks to resistors, they need to be large enough to keep the temperature below that which will melt the epoxy of course.
Inductors also have resistance. Low DCR inductors are both larger and will dissipate less heat as well. Too high a DCR on a woofer inductor, for example, can result in shorted windings, maybe indicated by black spots on the enamel.
Inductors also have resistance. Low DCR inductors are both larger and will dissipate less heat as well. Too high a DCR on a woofer inductor, for example, can result in shorted windings, maybe indicated by black spots on the enamel.
Hi Kc,
Simulate your speaker in XSim. Set the amplifier output to the maximum reasonable level, and use the power dissipation charts to examine all components. If you see any device approach it's rated power dissipation, double it. 🙂
You can use the LM-1 design files as a free sandbox. Links from here:
A Speaker Maker's Journey: The LM-1 Bookshelf Version
Best,
E
Simulate your speaker in XSim. Set the amplifier output to the maximum reasonable level, and use the power dissipation charts to examine all components. If you see any device approach it's rated power dissipation, double it. 🙂
You can use the LM-1 design files as a free sandbox. Links from here:
A Speaker Maker's Journey: The LM-1 Bookshelf Version
Best,
E
Should also point out, space around high power components matters!
Resistors can put out a lot of heat, and even if they survive it, they may "cook" the circuit board or a nearby capacitor. So while over-rating a resistor (using 12W instead of 5W) will ensure the life of the resistor, it may still ruin a PCB or cap next to it. 🙂
Best,
E
Resistors can put out a lot of heat, and even if they survive it, they may "cook" the circuit board or a nearby capacitor. So while over-rating a resistor (using 12W instead of 5W) will ensure the life of the resistor, it may still ruin a PCB or cap next to it. 🙂
Best,
E
You will be fine with Dayton stuff. Use 10-watt resistors and you'll have no issues.
I need to see some of these speakers that need XO cooling and heat sinks, they must be way better than mine, since I have never needed any of those things, LOL!
I need to see some of these speakers that need XO cooling and heat sinks, they must be way better than mine, since I have never needed any of those things, LOL!
I've a pair of Dahlquist DQ-10s here where the 4Ω 15W resistors in each grew hot enough at some point to set the masonite crossover board on fire. Yes, on fire, one hot enough to burn a hole completely through underneath them, leave soot around the back and drive the prior owner to dousing the crossovers with water to put the flames out. Fortunately, the Dahlquists had an externally mounted crossover board and not an internal one, but they're a good example of the importance of being smart about these things.
High power, small sealed box, Pro drivers & DSP = success!
Oh yes you can, and with fantastic results!
A few caveats though:
(1) Ditch all passive crossovers and replace with a high quality DSP active crossover. £250 up to £5,000 depending on quality of DSP, A to D and D to A conversion. This one is an absolute giant killer... DriveRack PA2 | dbx Professional Audio
(2) Ditch all ports / transmission line / ABR / vents.... They all suck & blow) out of phase with the direct wave front.... But thats another story.
(3) Ditch all audiophile drivers and use high performance Pro audio drivers and use real high power amplifiers.... This means big £££ and is why most people dont follow this path.
Here are a few examples of high power / small sealed air volume designs which deliver low distortion, accurate bass / midrange with outstanding reliability.
(1) 900 watts into 24 litres (28 litres = 1 cubic foot). Simulation & driver spec of the RCF 15N 401, this is a killer bass / subwoofer solution.
More in a mo... files too big.
Cheers
Derek.
Oh yes you can, and with fantastic results!
A few caveats though:
(1) Ditch all passive crossovers and replace with a high quality DSP active crossover. £250 up to £5,000 depending on quality of DSP, A to D and D to A conversion. This one is an absolute giant killer... DriveRack PA2 | dbx Professional Audio
(2) Ditch all ports / transmission line / ABR / vents.... They all suck & blow) out of phase with the direct wave front.... But thats another story.
(3) Ditch all audiophile drivers and use high performance Pro audio drivers and use real high power amplifiers.... This means big £££ and is why most people dont follow this path.
Here are a few examples of high power / small sealed air volume designs which deliver low distortion, accurate bass / midrange with outstanding reliability.
(1) 900 watts into 24 litres (28 litres = 1 cubic foot). Simulation & driver spec of the RCF 15N 401, this is a killer bass / subwoofer solution.
More in a mo... files too big.
Cheers
Derek.
RCF Mid bass version
Here is the mid bass version, the RCF MB 401.
Compared to the LF 401 it's a couple of dB down in output at the lowest frequencies but only needs 18 litres of air and has a superb Mms / Bl ratio of 3.8 (100g Mms with 26.1 Bl) allowing it to be crossed over as high as 1,200Hz, with around 800Hz being optimal.
Note the very low Qts yet is still hits 97dB at 20 Hz....Without any room gain, which adds 6dB to 9dB gain with back wall or corner placement respectively.
This driver makes a great two way / stand mount when paired with a good full range / broad band driver.... Crossover anywhere between 80Hz and 800Hz depending on required SPL, low end power handling of full range driver and Eq to suit ones sonic preferences using the DSP.
Cheers
D.
Here is the mid bass version, the RCF MB 401.
Compared to the LF 401 it's a couple of dB down in output at the lowest frequencies but only needs 18 litres of air and has a superb Mms / Bl ratio of 3.8 (100g Mms with 26.1 Bl) allowing it to be crossed over as high as 1,200Hz, with around 800Hz being optimal.
Note the very low Qts yet is still hits 97dB at 20 Hz....Without any room gain, which adds 6dB to 9dB gain with back wall or corner placement respectively.
This driver makes a great two way / stand mount when paired with a good full range / broad band driver.... Crossover anywhere between 80Hz and 800Hz depending on required SPL, low end power handling of full range driver and Eq to suit ones sonic preferences using the DSP.
Cheers
D.
Precision Devices PD 158
This is one I built up as part of the development of my RED driver.
Able to run in tiny air volumes with a midrange to die for, yet still has that gorgeous easy low end that only comes with 15 inch drivers barely moving.... under 1mm +/_ cone movement and still solid to 33 Hz.... Left hand piano is so accurate and lifelike!
Hope the above inspires someone to take the plunge!
Cheers
D.
This is one I built up as part of the development of my RED driver.
Able to run in tiny air volumes with a midrange to die for, yet still has that gorgeous easy low end that only comes with 15 inch drivers barely moving.... under 1mm +/_ cone movement and still solid to 33 Hz.... Left hand piano is so accurate and lifelike!
Hope the above inspires someone to take the plunge!
Cheers
D.
Spec sheet on PD 158
File too big to post... Here is the link to the PDF on the Precision Devices PD 158.
http://www.precision-devices.com/file-downloads/PD158-DATASHEET-310114.pdf
File too big to post... Here is the link to the PDF on the Precision Devices PD 158.
http://www.precision-devices.com/file-downloads/PD158-DATASHEET-310114.pdf
Having seen crossovers burst into flames - I think cooling is a good idea. 
Of course that was P.A. speakers with 100s of watts pounding them. Seems much less likely in home use.
But as Erik says, use XSim to look as power in the various parts. That will give you a good idea of what's going on.
Of course that was P.A. speakers with 100s of watts pounding them. Seems much less likely in home use.
But as Erik says, use XSim to look as power in the various parts. That will give you a good idea of what's going on.
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