The B&C DCM50. Can it replace the K55 driver?

[Al Klappenberger]

I did give some thought to the idea of a 1.4 or 1.5 inch horn and driver. The idea was really to have a better choice of drivers. There was a long list of 2 inch options but not nearly as many 1.5 inch ones. It was pretty obvious that market forces were going to dictate the choice too. The buzz is 2-inch. Like I mentioned earlier, what the market wants is what the market gets. What's really the "right" thing is usually secondary except to the technically savvy minority!

I did some tests with the Altec 902 on the Altec horn a long time ago too. I'll have to look to see if I still have the plots.

Al k.

[Al Klappenberger]

Guys,

Now here's a radical idea. The throat of the K400 horn has enough "meat" in the throat that it could be drilled out to 1 inch diameter. I have heard through the grape-vine that PWK actually designed this feature into the K400. I don't know for sure if that's true, but it sure looks like it to me. The JBL 2426 driver comes with an adapter on it to make it fit the standard 3 bolt mounting pattern of a 1-inch horn. Under that adapter, which is supposed to unscrew, is the threads required to screw right on to the K400 horn. I think it might take some machine shop to do the drilling. I really doubt it is worth doing though. The K400 is still an old exponential horn and outmoded no matter what driver you put on it.

BTW: the throat actually measures .70 Inch.

AL K.

[cjgeraci]

I concur with the slammer

I had an Altec 902-16B that bested the K55 on my cornscala dbb's. Also had it XO'ed at 400Hz......not even an extreme slope network.

Slammin also used to crank the 902 with a -6dB slope network at XO 400 Hz. It survived somehow.

j

JC, were you guys using that Altec in a two way setup? I just looked at the specs and it claims 500 to 20 kHz! That's impressive.

, passave

Rudy,

At one point I think JC ran the 902's in two way above Jub-clone bass bins. I know that Seti ran 511b's/902's above Jub-clone bins two way. I heard them both and without any EQ there was nothing missing in the HF to my ear I use the 902's in three way with passave nets and a JBL2404 tweeter for the sizzel on the top. Just my taste.

Hope that helps

tc

'

Me too - love my 902s (actually new Great Plains 902s). I have used 902s up front with Al's one inch Trachorns with no EQ and to my ears, they go all the way out enough to satisfy me, without a tweeter. I used to cross my 902s over at 500 hz back in my (Khorn alone) days, but now I cross mine over at 800 hz (because I can in my current setup). So, I cannot speak to them at 400 hz. I have heard some nice two-inch drivers, but I still also love the sound of the 902s. VMMY.

Come to think of it - - no more tweeters in my setup, front or rear.

But.....don't currently have any sweeps of the 902/Trachorn combo. That will have to wait until I get through pile of "work" at work for the next couple of weeks.

Carl.

[Al Klappenberger]

Guys,

The race is on. All the contestants are here. I start the instrument tests tomorrow.

BTW: The K55 looks ratty, but it's the good solder-terminal, 2-piece phaae plug version.

Al K.

[Al Klappenberger]

Here is the plot I did on the Altec 902-8 on an Altec 811b horn. Excuse the vertical scale. It's 10 dB / Division but uncalibrated for absolute SPL. That plot was done before I know how to do that.

AL K.

[Rudy81]

Al, can you tell me how to properly read the x axis on your plots....I'm slow, in the back of the class as usual.

[Al Klappenberger]

Rudy,

The plots I have posted up until now are on a linear scale. 0 Hz to 20 KHz on the right. Each vertical line is 2000 Hz. These were done with a very old Spectral Dynamics analyzer. I have a newer one now, an HP 3563a. It will have better scales and Log capability. Hopefully it will be easier to figure out.

Al K.

[Al Klappenberger]

I was able to do a swept impedance test on the B&C driver on the bench, so I don't have to wait until tomorrow to do that. I would call it 10 Ohms, not really 8. I like that.

Al K.

[IB Slammin]

I use the 902's in three way with passave nets

What is your horn? Tractrix or 511?

I have used both.

tc

[jwc]

Al,

That 902 sweep looks like a fall under 1000Hz. But this horn is the 811!!!

On the B&C....I might be reading that wrong but it looks like the impedence is going nuts below ~450Hz. Help me out there.

jc

[Guest David H]

The JBL 2426 driver comes with an adapter on it to make it fit the standard 3 bolt mounting pattern of a 1-inch horn. Under that adapter, which is supposed to unscrew, is the threads required to screw right on to the K400 horn. I

Exactly right, it is very difficult to unscrew, but the adapter is removable and will thread onto the original K-400.

[Al Klappenberger]

JC,

I should have expand the area below 400 Hz to study that. I would expect the impedance to go bananas below the cutoff of the horn. That's the idea behind the horn cutoff being place 1/2 octave below the crossover. I'm doing several things at once here, so I broke down the impedance test. I will rig it back up sometime later and look at the Zo down low. It's worth doing.

EDIT (later) I repleced the linear scale Zo plot with the same range using a log scale. It's a lot easiere to see below 400 Hz now.

Dave,

Yes, I have tried to get the adapter off the end of the JBL 2426 driver and wasn't able to do it without using tools that I thought might cause damage to the driver. I chickened out since I really didn't need it off anyhow!

Al K.

[Bacek]

Here is the plot I did on the Altec 902-8 on an Altec 811b horn.

Does any one has plot of 902 on tractrix horn?

[seti]

These are measurements I made of the gpa 902 on a 511b last year.They are obviously not professional curves. These were made to get me in the ballpark not to be taken as gosple. I got better at it later on but this was consistant. Mic @ 3ft. The GPA902 and 511b is a wonderful sounding combo. It made me want a pair of Altec Valencia's.

In my research I found 902 curves published with varying curves some dropping around 500hz some around 1000hz. They all went out to almost 20khz.

I did find this info in some 902 documentation.Not sure if this was for pro or consumer.

It would be nice if great plains audio would produce curves for all their drivers. I really want to check out their current 604. That is on my want list.

[seti]

At one point I think JC ran the 902's in two way above Jub-clone bass bins. I know that Seti ran 511b's/902's above Jub-clone bins two way. I heard them both and without any EQ there was nothing missing in the HF to my ear I use the 902's in three way with passave nets and a JBL2404 tweeter for the sizzel on the top. Just my taste.

Hope that helps

tc

The HF was great on the 902/511 although the sweet spot was a little narrow but great in my room.. Nothing missing to my ears. No if you like them bat slayers that may be a different story. My HF hearing stops dropping off around 18khz.

[deafbykhorns]

Here's some plots of a 1,5" driver comparing the TruExtent to stock diaphrams.

476BE / 2451

Reference:

http://www.audioheritage.org/vbulletin/showpost.php?p=276155&postcount=11

[Blvdre]

Can't remember who posted this originally, and I believe the 902 was mounted to a 511:

[jwc]

Can't remember who posted this originally, and I believe the 902 was mounted to a 511:

That curve looks similar to the one I did. Slow loss of output under 600Hz. But that curve went a tad lower.

jc

[seti]

Can't remember who posted this originally, and I believe the 902 was mounted to a 511:

I think that is the one sfogg posted a while back. That looks really good. I'd like to have a collection of the various 902's to listen and test to. It would be cool to have a BE diaphragm for the 902.

[Al Klappenberger]

Here is the results on the sensitivity tests on the three drivers.

The B&C has a little less sensitivity than the the JBL but it's hotter then the K55.

The plots were done with wideband pink noise and are not anechoic. The dip at about 3000 on the B&C may not be real. There is a trick to approximate anechoic measurements in an ordinary room that my new analyzer is capable of. I have only tried it once and I am not sure I can do it right. I am going to try that next. If it works, I'll post the results and explain how it's done.

I place the mike 1 meter from the drivers rather then the mouth of the horns considering the 2-inch horn is shorter.

AL K.