A time-aligned top end for the Khorn

[Al Klappenberger]

crd,

"you certainly are an overly sensitive person aren't you."

About certain issues. I certainly am!

Al k.

[djk]

"The Emilar horn looks interesting. What IS the purpose of the unusual
throat? Is that splained somewhere? "

http://www.aes.org/aeshc/pdf/how.the.aes.began/cohen_wide-angle-dispersion.pdf

The wave is allowed to expand in the vertical direction only, then the direction of expansion is changed. The wave-front expansion is restricted vertically, and is released horizontally. The result is that the horizontal pressure that builds up in the first part of the horn causes the wave-front to expand more as it reaches the second part. That it is restricted in the vertical plane helps further.

Because the wave-front expansion is to be exponential all the way, the discontinuity at the flare reversal point (where the expansion changes direction) is small. In addition, the change of curvature
at the flare reversal point is made smoother in practical horns than what is shown in the figure.

This class of horns was patented for directivity control by Sidney E. Levy and Abraham B. Cohen at University Loudspeakers in the early 1950s. The same geometry appeared in many Western Electric horns back in the early 1920s.

[jcmusic]

After reading through this post I am wondering how important is time alignment in a small room, say 15x22x9???

Jay

[Guest David H]

I have a small room myself approx 12D and 20W, and I use an active crossover for time aligment. In my opinion it is an audible improvement.

Dave

[mark1101]

My room is 18 ft. wide.........OK so my speakers take it all up. To me.......time alignment has made a huge difference in clarity.

[mikebse2a3]

My room is 18 ft. wide.........OK so my speakers take it all up. To me.......time alignment has made a huge difference in clarity.

Wow!....hey Mark is this your latest system configuration..???

I would add based on my experiences so far that a combination of steep crossover slopes along with time alignment does offer an increased level of clarity through the crossover region. Another benefit of steep crossover/time alignment is the loudspeaker system now has a more stable polar control pattern through the crossover region for better integration in the listening room.

mike tn

[jcmusic]

I have a small room myself approx 12D and 20W, and I use an active crossover for time aligment. In my opinion it is an audible improvement.

Dave

Dave, What about before you set the delays? In setting the time delays in this room could you hear an audible improvement?

Jay

[Guest David H]

I have a small room myself approx 12D and 20W, and I use an active crossover for time aligment. In my opinion it is an audible improvement.

Dave

Dave, What about before you set the delays? In setting the time delays in this room could you hear an audible improvement?

Jay

I have to say yes, it was a definate improvement in clarity. Since then I have moved the drivers so I no longer need the delay, and amazingly enough the rule of thumb about lining up the magnets is very close to accurate.

Dave

[Coytee]

Mark, that's so nuts in such a good way!

[Y]

So that midrange is the replacement for the XII I presume. Is it a bona-fide K402 that's been modified or is it slightly (or greatly) different than the 402?

It's got a 10" driving hanging off the back? Need to post some backside shots.

[Al Klappenberger]

He's kidding us. It's the fancy anechoic ceiling treatment that's the real secret! []

Al K.

[mark1101]

The subs are JC's ex-subs......Titan 48 horn subs. The mid bass modules are Roy's new KPT-305s created from a K402 horn with an 8" driver on it. That shot may be the first anyone has laid eyes on them. I'm not positive but I believe I'm the first to own them. OK enough for now........I don't want to high Jack. But I will reiterate the processor delaying the various horns made all the difference in the world to me. You can listen to that big system in near field and it is pure heaven. Very clear and coherent. The ceiling treatment is special acoustic treatment with very careful placement as you can see (smile).

[Al Klappenberger]

Mark,

Don't worry about hijacking this thread. Now that Dave Harris is going to send me the new elliptic tractrix horn he just made I expect to start a new thread. When I get the parts for the Linkwitz-Riley network I'll be testing it and the DCX50 driver on that horn instead.

BTW: I just heard from Solen. They will be shipping the parts I need for the crossover prototype today. I should have them next week!

Al K.

[Al Klappenberger]

Guys,

I just discovered something very interesting about the B&C DCx50 driver. The two driver sections are OUT OF PHASE with each other! I don't understand why B&C did this, but both of the drivers I have are the same way!

Here is a paste up of the scope displays of the two drivers with the mike in the same place. The two are nicely in time, but one is inverted compared to the other.

I inverted one driver and compared their phase shift from the driver to the mike. The phase difference between the two drivers is about 25 Degrees at 9 KHz. That amounts to about 1/10 of an inch!

The inversions is very easy to compensate for though. You need only swap the connections to one of the two drivers!

The plots are below.

Al K.

UPDATE: I have to back off of the 1/10 inch statement. Moving the mike back farther from the horn reduced the phase difference. There's something here I don't completely understand! [:S] The slope of the phase with frequency is always nearly the same between mid-range and tweeter drivers no matter the distance to the mike though. Phase slope is "group delay", so that implies time alignment.

UPDATE 2: After a few hours of head-scratching:
Group dealy = (pi * dPh / 180) / (2 * Pi *dF)
From the plot:
the mid-range shifts 360 Deg over 940 Hz = 1.06 mSec.
Tweeter shift 315 Deg over 940 Hz. = .913 mSec.

The difference is 1.73 mSec.

speed of sound is 13,397 In/sec * .000129 sec = 1.73 In. That seems to much!

But: 1/9000 Hz = .000111 Sec.
The two are almost the same! Could the reversed phase be to compensate for group delay difference at their suggested crossover frequency of 9 KHz?

DJK, HELP!

UPATE 3: After another couple of hours:

I think I'm kidding myself! [+o(]

[Al Klappenberger]

BUMP for reference by a new thread - part 2

Al K.

[Islander]

I have a small room myself approx 12D and 20W, and I use an active crossover for time aligment. In my opinion it is an audible improvement.

My room is 18' deep by 19' wide (or 30' wide if you consider the half-wall on one side) and setting the active crossover/processor for time alignment gives a subtle but noticeable improvement.

[DrWho]

Here is a paste up of the scope displays of the two drivers with the mike in the same place. The two are nicely in time, but one is inverted compared to the other.

Looks to me like they both start in the same direction?

There is definitely some time-domain dependant behavior happening with the tweeter since the amplitude is changing with time. The amplitude shift is coming in at ~1.25kHz, so that might be related to the Fs of the tweeter driver? Or maybe it's taking some time to fully pressurize the throat? There also appears to be a reflection happening ~11" after the intial signal arrives at the microphone. Are you just using 5 cycles for your stimulus, or is there more happening before the scope capture? The midrange might be a little bit underdamped up that high too. Its period isn't staying very consistent...

Btw, the slope of the phase change should be independant of polarity (assuming a linear and symmetric motor design).

Also, the amount of cone displacement needed to achieve the same SPL with two different diameter drivers is going to be different. Couple that with the natural uncompensated frequency response and you're gonna end up with different phase slopes. Adding EQ to flatten out the response of both drivers over the region being measured will make the phase difference a bit larger actually (since the tweeter is gonna need boost as you go lower).

This is why the frequency response of the speaker needs to be part of the filter design...it's even better when the speaker is minimum phase because then fixing the amplitude also fixes the phase response. If you're compensating for amplitude variations due to reflections, then you're not gonna have a nice phase response, which will be most apparent with transients (assuming that it is audible).

[Elso Kwak]

The close proximity of the 2 drivers will give intermodulation effects. Paul Klipsch published a paper about that:

A note on Modulation Distortion: Coaxial and spaced Tweeter-Woofer Loudspeaker Systems.

To quote:

"A loudspeaker radiating high frequencies in close proximity to a loudspeaker radiating low frequencies is observed to be subject to modulation distortion."

[djk]

Does that apply in this case?

PWK was comparing a T35 mounted on the cabinet face to a co-axially mounted T35 in the 15TRX, the woofer being able to create a great deal of modulation of the tweeter waves reflected (and modulated) by the woofer cone.

[DrWho]

I can't see how the distortion would be any greater than a single driver covering the same bandwidth...except maybe the decreased radiating area of the ring radiator is gonna need more excursion, and the types of suspensions used in those situations tend to be less linear. I think the throat distortion is more likely to dominate though.