Altec 9844-8B

[Skywave-Rider]

I’ve redone all my measurements in a more systematic way as Zilch suggested. Thank you for all your guidance on this Zilch, your expertise has been invaluable and is greatly appreciated.

I returned to the Studio room, and added more sound blankets. I also kept the pink noise levels consistent excepting for the woofer/port close micing. I was extremely careful about the speaker/mic positions. All tests were done at tweeter on axis from a distance of 3ft from the front of the cabinet (except for close woofer test.) I used only one side of the amp. The last session gave me a lovely few days of ear ringing, so I grabbed my range muffs. Best Idea I had all week

I used dummy loads when removing drivers from the tests because I found there was always some output even at minimum settings. Additionally, as Zilch suggested, this was needed for taking the woofer out of the equation, since there is no L-pad for that.

The tweeters are moved forward such that both horn bells are aligned. Although this should mean phase problems due to time alignment, the whole rig sounds much better this way. No more blankets on the top.

Here’s the setup:

Dummy loads are 8 Ohm, non inductive, L pads remained at this setting.

I found after I did all the image cutting and pasting, that there are no big discrepancies between the drivers in both speakers and I think the response is very similar.

I don’t know what I can realistically expect from the crossover. But I would like to improve it as much as is possible. I don’t know how good or bad the curves appear to you guys. I want to learn and am open to your suggestions.

Here are the curves:

[Zilch]

Well, there it is. The mid phase is correct, but, with the tweeter in this position, you need to reverse its phase. Do you see that?

And also that reversing the phase of the woofer produces the same notch between it and the mid as reversing the mid?

That's occuring at 630 Hz, it looks like, and I'm surprised the mids are playing so strongly down at 400 Hz. Your crossover designer may recommend a change to that particular filter.

The woofers are indeed rolled off below 50 Hz. As you have reported, there's no extended bass to be had here; need subs for that. You might achieve better balance with what's there by dialing down the mids and tweets more. It's looking somewhat "forward" overall.

The notch at 3.55 kHz is in your mid/horn combo, apparently. Do your new rear caps have felt or foam damping in them?

I don't normally run RTA pink noise so loud as to require muffs, though that certainly gives good signal to noise performance.

You should be able to observe the notch between the mid and tweeter increase and decrease as you move it back and forth from the front. It'll repeat in multiples of the wavelength at crossover.

Your results are certainly much better, and I would say also more reliable, now that you have the variables under control....

[Skywave-Rider]

Yes, it looks much smoother, the ~3k notch has become a mere depression with the phase reversal between mid & tweeter. But there's that 4K spike, it looks bad, doesn't it? Must be approx 5 dB. And it's a narrow Q. If I moved the tweeter front/back slightly, do you think that spike would move or be cut? If I had the speakers home, I'd try that right now. So I'll play with the tweeter positioning, I should be able to move it a few inches without getting into reflections off the top -- at that wavelength were talking short -- and try to get the best notch and see what happens to the spike.

Oh wow, I realized ur editing ur post as I type, so I'll hold off a while until the final version...

[Earl K]

Hi Skywave-Rider,

Zilch has covered a lot of points / here are some more ;

I don’t know what I can realistically expect from the crossover. But I would like to improve it as much as is possible.

- From my perspective, you do need to do a bunch of crossover redesign, to make that 3-way setup listenable for long term listening .

I don’t know how good or bad the curves appear to you guys.

- Honestly, IMHO ; those FR curves are fairly mediocre looking.

(i) Overall, the lowpass section is not performing as designed with those "text-book" values. The woofer section has a 3 db down point that is in the 1250 hz area ( rather than the 800 hz area as originally intended ) .
- You may just want to keep this lowpass section "as is" ( live with it ) & focus on fixing the hipass section on the 902/811 horn circuit .
- Here's one reason "why" you didn't achieve a 800 hz lowpass on those woofer pairs .


- The pic above shows the raw impedance curve for a single 414-16z ( & I emphasize, "curve" ). You'll see that the woofers' impedance is only 16 ohms over a very narrow frequency area. The area along this curve where the cap is doing it's filtering , is actually more like 25- 30 ohms ( or 12.5 to 15 ohms when two 414s are paralleled ) . This pic is from This Thread at A.A. . ( I know I've linked into it, half-way through ).
- I'd suggest that you read the whole thread .

(ii) The 315 hz midrange spike ( from the twin 414 woofers ), definately needs to be tamed. Perhaps Zilch can suggest a "parallel type" LCR notch filter ( inserted "inline " , to notch it out some.

(iii) The hipass on the horn circuit ; your pic shows a 3 db down point ( Xover area ) in the 500 hz range.
- I'd suggest you take it up to 1250 hz, to match the existing lowpass on the woofer .

(iv) The UHF ; Well, at it's best, the 902a can get to up around 10K in a pretty linear fashion ( when a RC "bypass circuit" is implemented ). I would then roll in the tweeter at around 10K ( at either 18db or 24 db per octave ) .
- Such a high point will undoubtably loose most of that "hump" that you see below 10K ( in the raw tweeter RTA ) .

I want to learn and am open to your suggestions.

Okay, I've just made some suggestions ( of a few remedial actions that I would want to implement if I owned that setup ) .



ps ; I'll leave the rest to Zilch

[Zilch]

I'll leave the rest to Zilch

I've suggested that Convergence might have some recommendations.

It's 902s with Symbiotic, Earl, I believe, yet to be confirmed. If they were 806s, with which I am somewhat familiar, I might be able to be more helpful. Clearly the 902s have the same excessive midrange response, which must be tamed. How they behave at the high end, I don't know, but Skywave can easily determine that by bypassing the lowpass portion of the midrange filter.

Gonna go read the AA link now. I don't know 414 from a hole in the ground....

[Earl K]

It's 902s with Symbiotic, Earl, I believe, yet to be confirmed. If it were 806s, with which I am somewhat familiar, I might be able to be more helpful. Clearly the 902s have the same excessive midrange response, which must be tamed. How they behave at the high end, I don't know, but Skywave can easily determine that by bypassing the lowpass portion of the midrange filter.

Yes thanks, I've noticed my mistake and I'll edit it appropriately .

[CONVERGENCE]

Altec drivers don't like reverse polarity. So that design might not be suitable . Make a polarity check of your woofers with a 2.5 volt battery.
The speakers should be pushing not pulling just in case.

Bi amping again with todays prices is considered a real improvement over those passive networks especially with 3 way designs.

Most Passive 2 way networks from Altec VOTT will use the same values as the computerized models. On the other site we have not encountered such problems cause most owners have replaced the caps in their speakers with outstanding results.
.

The reason for reverse polarity in a 3 way butterworth design has to do with phasing of HF driver.

There are pro calculators around 100$ these will give you the right values according to RTA of the speakers.

..........................

[Skywave-Rider]

Altec drivers don't like reverse polarity. So that design might not be suitable . Make a polarity check of your woofers with a 2.5 volt battery.
The speakers should be pushing not pulling just in case.

Hi Convergence. I did check the woofers in that way when I was sorting out the wiring. Positive voltage gives forward motion of all woofers.

I wish I could do math. Gonna be reading a while....

[Zilch]

Bring this forum over to http://www.hostboard.com/cgi-bin/ult...b=forum&f=3729 and see what the experts will say.

Yeah, well, I just posted over there.

[Rereading THIS thread, now, to figure out how it came to this....]

Edit: O.K., Skywave, do this: Hook up your factory crossovers and make the same measurements without the tweeter. Let's see the woofers and mids alone, and running together. Do nearfield on the woofers again, as well.

Also, what is the model of the stock crossover, and do we have the schematic somewhere? Provide what component values you can from your originals, please....

[Skywave-Rider]

I just found this shot of the rear panel (the speakers are an hour commute from home -- thank God for digital cameras provoking indiscriminate photos.)

BTW, I am truly grateful to everybody who has helped. Can I say that again? Just did. And let's get along..........

I believe the original N-800Fs are "potted." I'll look for a schematic. When I cut out the wiring I left just enough to reconnect in just such a circumstance. But those orig. caps have got to be crap. I will take NEW measurements using the OLD crossovers in 2 way. Actually it sounds like fun to see what the RTA will look like.

Zilch, do I need to really remove the N800s and melt out the wax? I guess it depends on finding the schematic. The reason I'm asking is because I understand a lot of the Altec documentation is not what was actually used in manufactured product.

Regards,
Vin
That's my name which u may use if u like.

[Zilch]

Zilch, do I need to really remove the N800s and melt out the wax? I guess it depends on finding the schematic. The reason I'm asking is because I understand a lot of the Altec documentation is not what was actually used in manufactured product.

Nope, we know N800-F (N-800F, N-800-F) pretty well. I just posted the link on the Altec Forum. Ironically, it was one of their members who had the original document:

http://audioheritage.org/vbulletin/s...31&#post160631

Member Bfish over there indicates that crossover was used in many Altec dual-414 designs despite the lowpass filter being used for 16-Ohm drivers in other products such as Valencia 846A. See also Malibu and Carmel.

In theory, it's "wrong" for use with 8-Ohm HF drivers, as well, but Altec engineers had more of a way of getting this stuff right than us textbook theorists sometimes give them credit for. Let's see how it behaves in comparison to what you presently have.

If you feel ambitious, you may want to read that thread in its entirety. Adding a tweeter is not necessarily the best answer to extending the HF. If you want to stick with your Altec HF drivers, the Model 19 (and others) "T-filter" compensation may get you where you want to be more seamlessly. Read the next post there.

Shine a flashlight into the throat of your 902 drivers. Do they have the orange plastic "Tangerine" phase plugs? If so, the prospects for success are good. We need to resolve the woofer and crossover frequency issues first, tho....

[Skywave-Rider]

Awesome. Yes, I know the 902 has good HF extension with the aluminum diaphragm, which I have. And I do have the tangerine phase plug as well. Several members, the first of which was Tom Brennan, tried to persuade me not to go 3-way. To my ear, the original setup was not open sounding, however. (But admittedly, that's listening to an aged crossover.) So I thought it would be fun and instructive to try 3 way. And it is.

I think I have photographed every inch of that speaker but inside the wax laden crossover. I will read that post. And I will reconnect one of the N-800Fs as soon as I am able. Cool.

[Skywave-Rider]

Nope, we know N800-F (N-800F, N-800-F) pretty well. I just posted the link on the Altec Forum. Ironically, it was one of their members who had the original document:

http://audioheritage.org/vbulletin/s...31&#post160631

Haha, ur a funny guy, Zilch...

[Skywave-Rider]

There are pro calculators around 100$ these will give you the right values according to RTA of the speakers.

Do you mean crossover design software? I was thinking about that. There's one Parts Express sells which seems to be popular. Unfortunately (fortunately) I have a Mac, but I can find a place to run that I'm sure. There's no way I'm going to build speakers from scratch given my living arrangements, but for the price it might be good for a guy with no mathematical abilities -- me

I don't know if you guys know what the Regents exam is, but it is (or was) required in NY high schools. Big end of the year exam in every subject, state sponsored. You don't get a "Regents Diploma" if u don't pass. The year I had to take the Regents in Algebra (or whatever the one above that is) I knew I was doomed. I studied my ass off. My friend tried to tutor me, but he was a numbskull as well. My brain is not wired right for numbers. But I wasn't going down without trying. And tried I did.

Well what happened was one of the few really lucky things that has ever happened to me. (Besides building this crossover, LOL.) That year, some angelic thieves stole the Regents exams, I don't know why, perhaps they were academic kidnappers holding out for ransom? Who cares. EXAM CANCELED. NO MAKEUP REQUIRED. Haha. I did not have to take that frigging test. And here I am, for better or worse.

[Skywave-Rider]

I have 902 drivers with aluminum diaphragms. My covers (which have felts) say 902-Bs (which I believe are Symbiotiks) but I don't have Symbiotiks. Those were the stickers GPA had available.

I am reading all your posts.