Annihil-8

dynamo

First I want to say thanks to hifiside for opening this door to a whole other aspect of the hobby for me. I had always wanted to try to diy my own woofers but never felt it would be worth it. I built an 8” woofer using some of the parts resources he listed and I had a blast doing it.

So I know that there is a lot of math and science to transducer development, none of what I have any clue about. I took some educated guesses and dumb luck and ended up with a part that was what I wanted.

I was hoping to build a heavy duty woofer but not quite a sub. I used what was effectively a sub motor and spider with a short for a sub but long for a woofer copper coil on kapton, with a light poly cone and soft surround. 

The result worked for what I need. I’ll post parameters and some measurements when I can. It is an 8 ohm driver, 84 dB, 9.5mm overhang (30mm winding length). Biggest downside is the 4 layer 2” coil with no motor treatments makes for a 4.4mH inductance at 1k, but playing it full range laying on the floor it really doesn’t sound ugly.

It models well, flat to 30ish in 1ft3 ported. F3 of 26.6, within Xmax to 150w down to about 28 hz. The motor is deep, pole is extended, and spider is stiff, so it should never bottom or jump the pole. I was beating it pretty hard with no enclosure to soften the suspension a little and had no mechanical issues.

It is no where as clean as hifiside’s assembly and has none of the cool custom parts he machines, but was fun and worked so well for me I am building a quad for a pair in the bottom of some multi-way towers. 

 

Please forgive the random pic order.

jr@mac

I sense a trend. Any way to glue a copper ring on the pole piece? 

hifiside

Fucking sweet! Careful it can get out of hand fast!

hifiside

I still have more boxes to organize and put away.

howard

Very cool, gentlemen!

6thplanet

So the surround was already glued to the cone? What glue did you use for the rest of the build?

rjj45

MOMOFUKU!

ani_101

What's the 2 of hearts doing in the coil?

jr@mac

That's a shim.

dynamo

jr@mac said:

I sense a trend. Any way to glue a copper ring on the pole piece? 

There definitely is, I just don’t have one big enough. The largest copper washer at the hardware store was 1/2” and that was only about 1.5 across, so too small. I bluetacked one in anyway and it made no measurable difference in dats. I also tried a sleeve of copper foil but was too thin to make a measurable difference either.

dynamo

hifiside said:

Fucking sweet! Careful it can get out of hand fast!

I can tell already, quite addictive!

dynamo

6thplanet said:

So the surround was already glued to the cone? What glue did you use for the rest of the build?

It was on the cones I used. All other pieces are done with a thick black CA (superglue) and a spray accelerator. I think it is just CA and rubber. I glue the surround to the frame and the dust cap with a liquid rubber glue.

dynamo

ani_101 said:

What's the 2 of hearts doing in the coil?

Just like JR said, I used cards to shim the gap between the pole and coil to make sure everything is centered when I glue the moving parts together.

dynamo

Thanks for the comments guys. It is kind of a nice winter project as it can be done in the warm house. Without scavenging used motors, it isn’t cheaper than buying a commercial driver, but it’s more fun! I’m really happy with its combo of power handling, excursion, and small box size (.75 ft3 is about the minimum, 1ft3 is about perfect).

dynamo

Hifiside, where did you source the trim ring on your (beautiful) Novice build?

ani_101

dynamo said:

Hifiside, where did you source the trim ring on your (beautiful) Novice build?

AFAIK, DIY mdf ring, painted black and press fit... 

hifiside

ani_101 said:

dynamo said:

Hifiside, where did you source the trim ring on your (beautiful) Novice build?

AFAIK, DIY mdf ring, painted black and press fit... 

Ani is right. Cnc’d my own.

dynamo

Awesome, looks great!

dynamo

The parts even come wrapped in newspaper so I can keep up on current events:

hifiside

dynamo said:

jr@mac said:

I sense a trend. Any way to glue a copper ring on the pole piece? 

There definitely is, I just don’t have one big enough. The largest copper washer at the hardware store was 1/2” and that was only about 1.5 across, so too small. I bluetacked one in anyway and it made no measurable difference in dats. I also tried a sleeve of copper foil but was too thin to make a measurable difference either.

I made mine from flat sheet of copper which is not cheap. As far as just adding a copper cap to the pole, machining it as perfect as I could it lowered Le from 1.7 to 1.2. I have a friend who is a professional machinists and I have him currently making me copper sleeves. My plans are to take a 1.89in pole 4 layered motor and make it into a 2.02in 2 layer motor with copper sleeve and cap, still reading up on outer modulation rings. I’ve built around 30 drivers so far and this sounds like the next step for me. 

dynamo

Good info, thanks. Having access to a machinist seems key to taking this to the next level. Combine that with a magnetizer and a press and you could make any motor you like! 

The copper sheet is a good idea. I tried playing around with some copper pipe but wasn’t able to make anything worthwhile come of it. 

dynamo

With your rolled copper sheet did you just solder the joint to complete the circuit?

hifiside

The machinists is using copper tubing. The sheet copper I used was .20” thick. 

PWRRYD

Hmmm?   As cool as this stuff is, I must resist.  I have all the machines at work and the skills to make all this happen.  Unfortunately my project A.D.D. is already way out of control

dynamo

Nothing new, just getting around to posting the specs for these. They are definitely more suited as a sub, based on the lower sensitivity and high Le. That said, they have 10mm of vc overhang and will handle 200 watts in 1ft3 at xmax.