Fast, fun, Inexpensive OB project

[Johno]

To John B, my enormous thanks for the design and your willingness to share and teach at the same time. Ditto to Pano.

I have just now finished building my Manzanitas at long last, and I am now listening while the last coat of varnish dries. Very impressed first up with how good they sound, so clear etc etc etc compared to my old 3 way, base reflex corals. They look good too, even if I say so myself.

I have followed the recipe fairly closely (I started with C = 5u6 but have 6u and 6u2 on standby) but the main change was to use air cored inductors and 2mm wire.

I soon found out 2mm is quite challenging to wind. So I designed and built a coil winder with enough torque to wind very tightly. (used a windscreen wiper motor from the wreckers and a home made pulse width controller to give a variable speed drive and re-wired the foot pedal from the sewing machine). The 20mH coils are both 19.95mH and about 0R9 after stripping off about 10 of the over-wind turns. Similarly the 2mH measured 2.04mH and 0R3. Weight is 5kg and 1.2kg. Measurement frequency 1kHz.

[Moondog55]

Nice coils
You may have the start of a small cottage business there

[Pano]

Great work on the speaker and on the coils! That may be the biggest crossover coil I've ever seen. Very glad to hear that you are enjoying the speakers.

FWIW, this thread passed 250,000 views last week. How about that? We need to convert more of those views into bulids.

[Russell Dawkins]

Originally Posted by Pano

That may be the biggest crossover coil I've ever seen.

Are you looking at the spool of wire that the coils are wound from?

Nice tightly wound coils there.

[Johno]

I have used an ordinary 5mm iron coach bolt to hold the 20mH coil in place and I will try to find a non magnetic stainless or brass equivalent to finish off properly. While measuring I checked the impact of the iron bolt - it adds only 0.4mH to the 1kHz inductance.

However I do not know what effect it would have at the operating frequencies and currents, nor if there will be any saturation effects. Does anyone have experience in this area?

Quote- You may have the start of a small cottage business there -
I guess I am open to requests, there is enough copper left for 2 more pairs. The 36kg mother reel cost me over AU$550 and that was a clearance price for a part used reel.

Quote - Nice tightly wound coils there
Thanks, I used the Brooks approximation for minimum copper length which gives a square profile - equal turns and layers. It was very challenging to get a perfect lay like that and I suspect there is a vastly diminished return on the effort. What you see is the first coil. The bobbin for the next one was made 2 turns larger but for some reason I could only fit one then zero extra turns on alternate layers. With extra spaces between each turn the lay became uneven and the finish was nowhere near as professional. However the roughy only had 5 extra turns on it get the same inductance.
My understanding is that excess inter-winding distance in an air core only affects the net inductance and not frequency or current responses of the solenoid - is this true?

[Pano]

Originally Posted by Russell Dawkins

Are you looking at the spool of wire that the coils are wound from?

He-he, no. I was looking at the inductor in back of the speaker. It looks as big or bigger than the Peerless woofer magnet.

[Pano]

BTW, I really like what you did with the sides and legs. That's something I had discussed with John B a couple of years back, as so many people objected to having to put the Manzies on a stand. Building the stand into the sides is a great way to do it.

[Juhazi]

"Building the stand into the sides is a great way to do it."

Often the most obvious way is the way to do!

If you can't hide a thing, make art of it!

[Russell Dawkins]

Originally Posted by Pano

He-he, no. I was looking at the inductor in back of the speaker. It looks as big or bigger than the Peerless woofer magnet.

I think the biggest crossover coils I've seen were in the passive crossover for the Fried Model H: (!!)
model H.png

[c2cthomas]

Originally Posted by Johno

and re-wired the foot pedal from the sewing machine).

Would you put me in you will for when SWMBO discovers this ???