Passive crossover idea

[Tubetec]

I found some very large motor and welder/ transformer terminal boards in the scrap at work .
I was thinking of repurposing some of these as crossover boards for my Dynaudio Bookshelf speakers . Whats in there is very basic ,but there are better crossovers for these drive units published by Troels Gravesen . Theres many almost depleted reels reels of larger gauge magnet wire which are surplus at work ,so get stacked and left aside , I can wind up any size inductors I want on my break ,with the bosses full permission of course ,
Id like to wind some very high powered coils from fat wire , as its all going to be housed externally from the speaker,so  there is no space constraints , I can get a bag of the usual binding posts and make it so I can sub out each component in the crossover
on test ,with no soldering . I found a large bag of mixed size wooden thread/ yarn spools from China ,four sizes and the smaller ones could be simply lathed to allow more copper to  be wound on , once wound they could be varnished and baked so everything is rock solid , a simple wooden dowel in the bobbin would allow easy mounting on thick bakelite board .

I'm using a very strong power amp on these speakers ,Hafler Xl 600 ,so 460 w into 4 ohms ,both channels driven . probably considerably  more with just one channel . So I might aim for these crossovers to handle 1000w , seeing as coppers no object ,why the hell not . Theres a good range of motor run foils in the right in the ballpark for what Im doing as well , 250 volts ac, wire ended ,stud mount , I can very easily extract matched pairs from the large boxes of stock also .

Does anyone know a good program for speaker inductor design ? .

 

[Tubetec]

I found a neat calculator for air cored inductors, you spec the coil lenght and diameter of the former, the AWG of the wire and the inductance you want  ,it calculates everything else ,         

Resistance ,wire lenght ,weight of wire , number of turns per layer ,no of layers ,its quick and easy .

I ran some simulations of inductors I want for the Dynaudio 15w75 crossover , going all air cored amounts to almost 2kg of copper per speaker , just for the low pass section  ;D

https://www.diyaudioandvideo.com/Calculator/AirCoreInductorDesigner/

Seeing as theres lots of surplus 'end of reel' copper in work ,and any extra I need I can get at trade (about 10 euro's a kilo) , its looks like its worth doing , I should be able to do it for less than 100 euros all up ,including caps and hardware .
We have a cable bin full of used heavy duty mains cables ,two, three, four, and five cores rubber jacketed , upto 2.5mm2 per core . The terminal blocks on the boards Im going mount the components on can take 100amp or more , so I could go for even heavier cable for the connection from the amp to crossover , automotive thick speaker multistrand would be another option , but heavy duty mains /industrial would be just as good if a bit less manageable

 

[Tubetec]

Inductance 1.21 mH
DC Resistance 0.18 Ohms
Wire Gauge 12 AWG
Wire Diameter 80.8 mils (1 mil = .001 in)
Coil Length 3 in
Coil Inner Diameter 1 in
Coil Outer Diameter 2.29 in
Average Turn Diameter 1.52 in
Wire Length 110.97 feet
Copper Weight 2.19 pounds
Turns 278
Levels 7.49
Turns/Level 37.13


Inductance 2.2 mH
DC Resistance 0.38 Ohms
Wire Gauge 14 AWG
Wire Diameter 64.1 mils (1 mil = .001 in)
Coil Length 3 in
Coil Inner Diameter 1 in
Coil Outer Diameter 2.15 in
Average Turn Diameter 1.47 in
Wire Length 149.06 feet
Copper Weight 1.85 pounds
Turns 388
Levels 8.29
Turns/Level 46.8


Inductance 0.1 mH
DC Resistance 0.13 Ohms
Wire Gauge 16 AWG
Wire Diameter 50.8 mils (1 mil = .001 in)
Coil Length 3 in
Coil Inner Diameter 1 in
Coil Outer Diameter 1.2 in
Average Turn Diameter 1.05 in
Wire Length 31.29 feet
Copper Weight 0.24 pounds
Turns 114
Levels 1.93
Turns/Level 59.06

Looks like there could be as much mass in copper as in the speakers themselves at the rate Im going , still though worth it for the fun of it and because we can . 

 

[boji]

You post was too lonely given all the research you're doing. I have nothing to contribute but a thumb's up.  ;D

 

[Tubetec]

Cheers Boji ,

 

[gyraf]

*like*

 

[Tubetec]

I've run the sim on a few inductors of the same value ,but different dimensions , ,keeping the inner diameter smaller seems to give better value ,ie less copper for a given inductance , I dont understand what +/-'s are  with larger vs smaller diameter coils ,maybe someone in the know could enlighten me. . Of course I could do all this with active crossovers , I already have a couple of old but nice BSS xovers , but Im really tempted to try the heavy engineering solution instead , passive high pass on the inputs to the amp ,and passive freq split with lots of copper at the output , then active x over on the bass . I've been a big fan of fully actively crossed over speaker for many years , but Id like to try fully discrete at least on the mid highs , BSS 355 can handle the bass ,even though its only 48khz sample rate ,thats still plenty for handling frequencies upto a few hundred HZ .The bass end will be a pair of behringer truths per side , wired directly into the woofer amp from the crossover .

 

[Tubetec]

Is there anything to be gained from using very thick cables ,maybe 25mm sq per conductor  to interconnect the speakers and crossovers , Im not talking high end snake oil hifi cables ,just brute force and ingnorance mm sq , wheres the sensible limits to the amount of copper you throw at it , both in the cables and crossovers ?

460W per channel into 4 ohms is what the power amp makes , I'm constructing formers for the inductors from upvc pipe , the sky is the limit on the materials , as much of the copper I can get at cost or from scrap/leftover reels etc .There is also quite a lot of scrap welding transformers that could be broken down and large gauge coils trimmed and  reused as air cored inductors, , typically  these use 5mm or more diameter  copper wire on the secondary

I hear cries of 'selfindulgence' from the more cost conscious already , scrap copper is more or less free to me , so why not push the boat out ?

 

[Tubetec]

So I made up some formers from plastic pipe and used large nylon spacers at either end  , rolled up .1 mH  in 12awg during lunch today,
Using the calculator I posted before , I wound 84 turns  of 12 awg  turns onto a former of the given size, 2inch long by 1 inch diameter , sure enough when I measured with the LCR after,  0.105mH and resistance was bang on the money  too ,so that program is accurate.

Initially for simplicity I just cut a few standard lenghts of tube to wind onto , but now I see I can actually tailor the lenght of the former to the gauge of the wire , so that if axial mount is needed an odd number of complete layers makes mounting easy , where if radial suits better an even number of layers makes more  sense  .

I might as well give these babies a dunk in the varnish tank to solid em up a bit , there is several types of textile tape wrap I could use to bind them but Im not sure if its  necessary .

I would show pics but unfortunately my camera card adapter has vanished  without trace.

 

[Tubetec]

I went with black textile wrap , excuse the very poor quality of the pic .
The larger of the two was supposed to 1.2 mH ,came out at 1.02mH, the coils splipped on the former after winding and hence the doughnut shape , the wrapping material is strong and allows the coils to be  well tensioned into shape, I can probably live with the slight frequency shift caused by a value 20% low ,both these were done with 2.13 mm or 12 awg , the larger one is well over a kilo in weight , I found some good looking motor run box  caps in a range of values suitable very suitable for crossovers eg 1, 1.2, 1.5, 1.8 and up , less than two euros each ,  massive bakelite  blade fuse holders will be repurposed  as terminal blocks to mount things up on , I was thinking of trying automotive jump lead cable  as hook up wire from amp to crossover  easily available in ratings of hundreds or thousands amps most of it with fine stranded copper and silicone insulation ,100watt metal clad wirewound  resistors also only a euro or two each might give them  try .