Altec 9844-8B

[MrT]

I don't know how many times I read this thread. Finally, I got it. I keep going back to the online calculators which does not explain anything. But this thread does.

Further, no VHF high but all mid. Thus the warmer sound or is it the age or even both? I don't hear mosquito anymore.

Many many thanks.

Over and out.

Tim

[Skywave-Rider]

Thanks Zilch!
I’m trying to arrange getting in there late in the week to do the next round.

I just realized that I have been referring to polarity of driver connections as “phase.” I believe I should have said “reversing polarity” when swapping the 902 connections.

I calculate the floor bounce to be about 18.6 wavelengths at 3150 Hz, so I think that puts the reflected wave at almost 180 degrees out at that frequency. But I don’t trust my math. Nor should anyone else.

Fiberglass first,

hopefully new diaphragms are not called for.

[MrT]

Hey Skywave

Once again, I thank you for letting me into your thread. Your graphs revealed so many things. Awesome! To me this is the most helpful thread for 414s. My 2 cents.

Enjoy your speakers. Play some music and let us know how they sound.

Thanks.

Tim

[Skywave-Rider]

Thanks, Tim.
Maybe one day I'll live in something bigger than a studio apt. and will be able to take them home, LOL.

[Skywave-Rider]

I calculate the floor bounce to be about 18.6 wavelengths at 3150 Hz, so I think that puts the reflected wave at almost 180 degrees out at that frequency. But I don’t trust my math. Nor should anyone else.

Just double checked my math....WRONG.
I think it's only about 70 degrees difference in phase between direct and floor bounce at that freq. Forget I said anything....

[Zilch]

Circuit's posted at #118. I checked it in simulation; should work.

DCRs for inductors are provided. Use 0.8 mH for L2.

LP1 is balance with LF, then set LP2 for VHF level.

I like some of the JBL compensation curves better, but we're sticking with Altec here....

Unfortunately there was no extra time to listen much, but I rigged mono signals to both the 2 and 3 ways. No time to listen with contour filter. The 2 way sounded great compared to the 3 way. Much more balanced mids, highs were actually better, less smearing there. Sounded well extended too. The 3 way was horn forward and “pointy” in that range. Sounded like it had less bass, and rather irritating in comparison.

I suspect you're looking at the HF response you measured and saying, "SHEESH, that's HORRIBLE!"

Well, look again. If that notch weren't there, you'd be +/- 2.5 dB, and it's sounding nice to boot....

Here's what I got with Gary's 802-8Gs using the T-filter. Look familiar?

You're damn close, is what:

[Skywave-Rider]

I like some of the JBL compensation curves better, but we're sticking with Altec here....

So you're saying I can't put a DC bias on the network?!?!

Is this inductor OK for the low end leg of the circuit:
http://www.partsexpress.com/pe/pshow...number=266-910
A "magnetic" core coil. It specs perfectly for both inductance and DCR.

Do you think I should buy all the parts to build a pair or make one as a test mule?

Cool!

[Zilch]

Is this inductor OK for the low end leg of the circuit:
http://www.partsexpress.com/pe/pshow...number=266-910
A "magnetic" core coil. It specs perfectly for both inductance and DCR.

Do you think I should buy all the parts to build a pair or make one as a test mule?

That's the one I spec'd, yes. The others you'll find are 18 ga Jantzens, I believe.

Build a pair. If they suck, with some minor rewiring, you'll have a nice pair of brand new Model 19 crossovers to sell to a Valencia upgrader.

[And a couple of spare parts.... ]

[Skywave-Rider]

If that happens, the spares will go into my burgeoning "crossover cart."
Thanks again Zilch.

[Zilch]

One more thing, Skywave. When you disconnect one of the woofers, short its terminals. Otherwise, it will behave as a passive radiator.

It'll still do that, to a limited extent, but will be heavily damped by the dynamic braking effect of shorting it on the cone movement.

[Skywave-Rider]

Thanks Zilch. I'm re-reading "Valencia" and this thread to try to conform all that has happened. Thanks for the shorted woofer tip, I understand backwave emf.

Need to ask: I'm assuming I should present a 16 Ohm dummy load in parallel with the in-circuit woofer to fake a nominal 8 Ohm impedance for this test. Am I right? Or do you really want to see what a 16 Ohm woofer will do with the N800F? [It's safe to say I won't even have parts for the M19"Z" clones by the time I do this test.]


More questions/confusion to follow.

[Zilch]

We want 16 Ohms. MrT posted his measurements of 16-Ohm 414s on N800-F. They don't look bad; let's verify them. We can try it again later with M19Z, as well.

Where I'm going with this is a 20 mH Super Q in series with the "helper" woofer. We don't know the in-box woofer impedance curve, so it's hard to be precise with respect to what frequency that's going to bring it in. They're not cheap at $32+ apiece, but, if you're feeling flush, spring for that and give it a try, as well.

It's a technique used in several JBL products, including the latest flagship Everest II, to extend the LF response some, and these 9844-8Bs may benefit from that, so long as the single woofer response blends well with the HF at crossover. Yes, you'll lose the double-woof SPL, perhaps as much as 6 dB; that's a tradeoff only you can assess based upon how they sound and your intended application for the speakers.

A major upside is that you don't have the two woofers interfering with each other off-axis (horizontal) at higher frequencies. Wavelength at 1 kHz is 13.5", no? So with a 6.75" differential distance to the two woofers, you've got full cancellation at that frequency. It's simple triangulation to figure out how far off-axis that would be, depending on listening distance.

For caps, I don't see much point in paying a premium for 1%. When I play with the values in the sims, nothing changes much with such small differences in values. I just use the stock Solens, without bypass caps. If you like the sound of the cheaper Daytons, use those....

[Skywave-Rider]

After hearing your explanation, I really want to try the "helper" woofer concept. The potential for extending the low end is cool, but I really like the possibility of having better horizontal phase coherency in the mids. And now that the super tweeter is off the table, imaging is tightening up. But I was thinking, in the crossover region, with the current design, the transition from horn to woofers is basically a vertical shift, and vice versa. Using one woofer may make the transition somewhat horizontal, which might be a compromise, but a better one. Am I looking at that correctly? However, the 811B is so wide at the mouth, this issue may not mean much.

I had assumed the Everest 2 used double vertical woofers. Just checked it. Wrong. It's beautiful. Wide horn mouth. It's a modern 9844 with mini supertweeter, LOL.

Decision made. I'm buying those 20 mh megacoils.

By adding the coil we are shifting the power distribution by relieving the helper woofer from some amount of mids, tbd. But the 414 will only go so low, so is this technique a trick to add a little emphasis where it starts rolling off?

And I just thought that the helper woofers should be the ones to the outside, far left, far right.

My intention for these speakers is for eventual home use. I will also try them for mixing music, but nothing abusive because I have a warped perspective and they are beautiful -- to me they really are......
I am also interested in the history of the technology and I know a lot of music was recorded and mixed on monitors like this; I want that experience. My career goes back to the age of Uries, I guess.

Probably the only other speaker I lust after at this point (besides those Everst IIs!! ) is a 604E, because of the Gold Star studio connection. But not sure if I've ever heard them.

Enuf rambling.

[Zilch]

By adding the coil we are shifting the power distribution by relieving the helper woofer from some amount of mids, tbd. But the 414 will only go so low, so is this technique a trick to add a little emphasis where it starts rolling off?

Yes, and because it's only 6 dB/octave, depending on the woofer impedance curve where the action is, it may bump up the bottom end, generally, as well. Whether you'll like that or not depends in part on how you use them. As nearfield monitors, you'll probably want that; consider it baffle step compensation. At home, perhaps, too; it may obviate the necessity of using subs with them, depending upon your room placement and listening preferences. A simple toggle switch in your final design will allow you to switch among the three operating modes in situ.

Again, all of this is speculative. We're just not going to know until you perform the requisite measurements. For this, set up nearfield with the RTA in average mode. Run just the one woofer until the curve is stable, then kick on the second one with the inductor and watch the curve gradually lift down there, in full giggle mode. It should go up 6 dB; 3 dB from summing, plus another 3 dB from mutual coupling. Finally, measure the "helper" woofer alone to see what and where it's actually contributing to the system response.

[More RTA fun.... ]

[Zilch]

I heard 902s are one of the better Altecs. And that they are clean and crisp. I've never auditioned them myself. But the graphs are saying a lot. On the other hand, I heard that 806As are warmer and smoother. Further, I did hear that 806As don't go up high.

For the 806A owners following this thread, we have earlier discussed their limitations in comparison Skywave's 902s with larger magnets and tangerine phase plugs. Here's a direct comparision of Gary's similar 802s versus Scott's 806As on Altec horns, unfiltered:



And here's Steve's different pair of 806As measured 7 months later, along with how they perform when actively crossed and 10 dB compensated, i.e., pushing the CX3400's "CD Horn" button: