Speaker kit experiments - an archive of the Jäger Speaker development

[kgoss]

Doc talks about it in his post on April 3

[Rocketman248]

Ah, nice.  I missed that part.  Thanks!

[Doc B.]

Went a little off the deep end the past couple of days playing with a potentially silly idea for the diffraction felt we will put on either side of the kit speaker tweeters. Have no clue if it will work better, worse, or just the same as a strip of felt or shark's teeth shapes like most everyone else tries. Anyway, I like the look. After 9 hours working out a quadratic residue diffusor cell layout that would fit and function at the frequencies of interest and getting the shapes into the CAD software yesterday, the actual cutting of the pieces took just a few minutes. After a few hours of swearing at the laser cutter software today, that is. At least with my past CNC experience I knew that was coming. Will be comparing these against straight strips of similar felt tomorrow.

(https://scontent.fsnc1-2.fna.fbcdn.net/v/t1.0-9/18057639_10210107926388436_8674783926921917921_n.jpg?oh=5c1c38e71b5401e517a5537e30ab54b8&oe=5982E913)

[debk]

looks cool!
Interested In hearing how it sounds

Debra

[Doc B.]

Wow, this setup really works! A distinct improvement in image stability over straight strips of the same thickness and type of felt. Sometimes you have to go with your instinct.

(https://scontent.fsnc1-1.fna.fbcdn.net/v/t1.0-9/18198535_10210113588809993_6605375143002291526_n.jpg?oh=afa238a1cea92fba7eabb90039ac142b&oe=598465E8)

[johnsonad]

 Very cool and much better looking!

[Doc B.]

Here's the more or less final version of the speaker kit impedance compensation network. Wood board with pressed in solder eyelets is laser cut in house. No solder traces to mess with the sound.
(https://scontent.fsnc1-2.fna.fbcdn.net/v/t1.0-9/18765654_10210364114992991_5360152913320854501_n.jpg?oh=73a4e75580c40dc53de7efeac44612d5&oe=59B06662)

[johnsonad]

Nice work!

[Rocketman248]

Nice and neat.  Lookin' good!

[Hank Murrow]

Dear Paul Joppa;

Could you explain what your "bridged T" network does for the new speaker?

I am sure there are many on our Forum who would be interested in how you developed it. PB says it works a treat!

I hope to hear it myself in late June.

Cheers, Hank in Eugene

[Paul Joppa]

Dear Paul Joppa;

Could you explain what your "bridged T" network does for the new speaker?

I am sure there are many on our Forum who would be interested in how you developed it. PB says it works a treat!

I hope to hear it myself in late June.

Cheers, Hank in Eugene

Sure. It's a long-ish story though ...

First, the woofers are Zobeled to give them a constant impedance with frequency. (That's a simplification; the lower woofer is cut out so only the upper one is active in the crossover region - but the end result is close to 8 ohms in the audio band.)

The woofer itself has a resonance at a bit over 5kHz, with about a 4dB peak. Above the resonance it falls at 12dB per octave. By using a suitable notch filter, that is made to be a 6dB/octave roll off from 2800Hz to around 10kHz. The bridged-T is a form of notch filter that maintains constant input impedance at all frequencies, which is needed for the crossover itself to work into. It has 4 resistors, 2 caps, and 2 inductors - more complicated than the usual RLC notch.

The woofer crossover combines with the 6dB/octave to give something very close to a 4th order Linkwitz-Riley function at the 2800Hz crossover.

[Doc B.]

Kelvin got the production impedance compensation networks installed in the cabinets Wednesday. The improvement was one of those "whoa, didn't expect that!" kind of things. Yesterday I got the external passive crossover boards laser cut, and today I built them out and installed them. I cannot explain why since the part values are pretty much the same as the crossover and network prototypes, but the speakers have taken a very big jump forward with these production prototypes. It's getting pretty wonderful. If you think you have heard them at their best, you haven't yet. I suggest you come by tomorrow and listen 12-3.

[Paul Birkeland]

It has 4 resistors, 2 caps, and 2 inductors - more complicated than the usual RLC notch.

I've studied lots of speaker designs, and I've never seen a speaker level bridged T filter used before.  (This is where PJ steps in and provides a link to an obscure JBL design that used one!)

[Paul Joppa]

I've studied lots of speaker designs, and I've never seen a speaker level bridged T filter used before.  (This is where PJ steps in and provides a link to an obscure JBL design that used one!)

The bridged-T is (was) commonly used in line-level studio gear before WWII, which used matched impedance connections. That came about from telephone technology, probably because phone lines were used to connect the studio and/or concert hall to a radio transmitter. Once gain became cheap and negative feedback became common, studios transitioned to low source impedance/high input impedance. I've never seen it in a speaker crossover either. I suppose the cost of twice as many components was off-putting. Today, commercial designers are more likely to us computer optimizations to achieve a good approximation to the desired target function, using as few component$ as possible.

For this design, I wanted to separate the eq from the crossover, and give the eq a constant input resistance to make it more flexible with different amps - looking ahead to the possible use of active crossovers. (I did a similar thing with the tweeter eq, but it's simpler.) This also makes the crossover design straight out of the book, so it's easier to understand, and also regular commercial active crossovers could be used. (We'll have one ourselves of course, but our customers are often independent minded and/or experimental.)

[Hank Murrow]

Dear Paul Joppa;

I am heartened by your decision to separate impedance matching circuits from the Xover circuit. This means I might be able at some point to make use of my XM-9 Marchand fourth order three-way Xover somehow. Previously, i used it to cross between a Linaeum tweeter, a 5 inch Vifa T-line, and a Focal 10" Kevlar T-line. wonderful speaks, but not sensitive enough for my Custom BH 2A3 amp. My electric piano in front.

Cheers, Hank in  Eugene