I finally designed and built my first crossover!

[sreten]

Yeah 1 cuft is ridiculous for a 4" driver, even for 2,

You should be looking at a sealed box, reflexing will just give
you a boom box. Sealed box 0.3 cuft for 2 drivers Q = 1.

And you'll need BSC, has to be near 6dB or you won't match
the tweeter sensitivity, here you don't have much choice.

Build your subwoofer it its a learning exercise, with the box
volume far better optimisations in terms of efficiency and
extension are possible with suitable drivers.
An isobaric is -6dB in efficiency and maximum output.

No commercial manafacturer has ever sold a reflexed isobaric.
You'll find near identical performance possible with a single
driver at double the efficiency as impedance is double.

Also for a good match with the TB's you"ll need two V/J's in parallel.

sreten.

[Jim85IROC]

I suppose building a sealed box would be smarter... I just was hoping to get usable bass out of these without a sub. But hey... these are "experimentation" speakers, so I'll try a few different configurations.

I'm still thinking about the sub, and it seems that with active equalization, doing a non-isobarac enclosure would make sense, but without having the ability to build the active filter makes it hard to get the low frequency extention without a huge box or going isobarac. I can understand why OEMs don't use an isobarac design. With their resources, building an active filter to compensate for a small enclosure is much less expensive than using a 2nd woofer.

But... I just went back and looked at my design. There was one thing I didn't notice until now... port length.

With a 2" port, I'm going to need a length of 26". That'll be hard to fit into an 8" cube.

With a 1" port I'll need a little over 6". A 1" port should make plenty of port noise!

I think I just bought 4 $6 paper weights.

[Jim85IROC]

Damn!

I just realized that I've done all this box modeling with the other 4.5" jbl/vifa. The one I ordered is a piece of junk!

I guess I'll be sending some of this stuff back. :-/

[SimontY]

Oops!

[Jim85IROC]

It may not be all that bad. I called PE but they already shipped it. If I build a narrow enough box, I may be able to use the big bump below 900hz as a baffle step compensation.

If not, they'll make nice Christmas presents!

[Jim85IROC]

I didn't plan to bring this thread back from the dead, but now that it's being referenced in another "NSB" thread, I wanted to provide an update.

After Jeff B released his excel crossover program, I plugged all of my data into it to see what things looked like compared to my crude spreadsheet design. Surprisingly, my crossover modeled flat to +/- 4.5dB over the bandwidth range. Better than I thought, but I could also see why the mids were so "shouty". The 6dB/octave cap wasn't sufficiently attenuating the bump at the low end of the tweeter's spectrum.

I added a shunt .15mH inductor on the tweeter circuit, and also added a series 2 ohm resistor with the NSBs to flatten out a lower midrange bump. Of course, the 2 ohm resistor is going to raise the qts, so I may not have actually gained anything... we'll see. It'll be easy enough to remove if necessary.

I haven't listened to the new crossover yet (hopefully tonight), but here is a schematic. According to Jeff B's spreadsheet, this models flat +/- 2dB over the spectrum.

[random_id]

Can you fill me in on the spreedsheat you are talking about?
I've tried to search, but I can't find anything on the forum.

I just want to make sure I'm not missing some cool tool.

Thanks

[Jim85IROC]

It's been discussed extensively at the madisound forum. Currently it's not available because he pulled it to work out a couple bugs.