Altec 9844-8B

[Zilch]

And here's Steve's 806As on the N800-F HF filter:

[MrT]

Hi Zilch

Were the Red and Green measured with T filter? Active crossover do make a huge difference!

Thanks.

MrT

[Zilch]

Nope, no T-filters shown, only on Gary's 802s @126.

Biamping provides the headroom necessary to do the requisite compensation, active or passive.

Footnote: I am stunned by how similar Scott's and Steve's 806As measured @135. I had never previously juxtaposed them. It's as if I were remeasuing the same pair.

That's what 806As are on 811B horns, apparently. If someone measures them with a different result, I'd certainly like to know about it....

[MrT]

Nope. I did not go active. Not yet anyways. But I did finish putting up T filter to n800f. It sounds dramatically different. Better balanced, sound stage is better and I am really happy with the result. Time to enjoy the fruits.

Thanks guys. Thanks Zilch.

Tim

[Skywave-Rider]

Mr. T,
I'm happy you got the T-filter well integrated and apparently tweaked. If you get a chance, post some pics of the monitors.

[vuki]

Hey Zilch

Thanks for the analysis. I understand it better now. I know the RTA plot was done with the driver in a 120lt cab. The guy who provided the parameter xoed his at 1200hz. However, I did not understand how the value of these component correlates 3.9mh+8.2uf. Second order butterworth? I thought the crossover was some what close to n800f. It will be great to see skywave's findings.


Tim

Hi,

those are the measurements of my 2-way Altec (414z in 120 Lit. BR + 902 + 450Hz round tractrix). First graph is free-air parameter measurement. Second graph is far field in-room RTA measurement of 414z in "Petite Onken" enclosure (ca. 165 lit.) without crossover.
One cannot "file" crossover based on its components values because crossover "works" with real loudspeaker's freq. response which is all but textbook flat.

Regards,
Vuki

[MrT]

Hi Skywave

Here is what my speakers would look. I tried to stay with this plan as closely as I can. But this is for single 414. Yours may be different. Look through this sight if you are trying build your own enclosure. I hope this helps.

http://www.lansingheritage.org/images/altec/plans/1970's-lf-plans/enclosures06.jpg

Vuki. Thanks for dropping in and clarify your measurements.

MrT

[Zilch]

One cannot "file" crossover based on its components values because crossover "works" with real loudspeaker's freq. response which is all but textbook flat.

We'd like to buy or build textbook crossovers and have them work. They DO work, of course, but rarely all that well.

One would be hard pressed to find very many textbook crossovers among JBL products, and, as we've seen here, Altec deviated substantially from that path, as well....

[Skywave-Rider]

Parts arrived. Just tried to scavenge 16uf caps from old homebrew x-overs and learned a valuable lesson. That is: HOT GLUE IS #@%&ING STRONG. Just ordered a pair of those
Will do the N-800F measurements part 2 tomorrow.

[Zilch]

Yeah, hot glue's a bad idea until you're really, REALLY done. I never am, so it's cable ties on everything. The only way I succeed in breaking the glue loose is with a heat gun, utility knife, and a prayer that whoever used it did a crappy job.

I'm anxious to see how the "Helper" woofer thing operates in your setup.

Depending on where the 20 mH inductor kicks in, the main lowpass rolloff will revert somewhat to the 16-Ohm curve, which may work out because there'll only be one woofer playing in that region.

There are two options: 1) Run the helper with its inductor off the LF output of N800-F as normal, in parallel with the woofer not having the additional 20 mH, or, 2) Run the helper with its inductor directly from the crossover input, in which case the main woofer gets the full 16-Ohm voltage drive curve.

Try both, maybe....

[Skywave-Rider]

Hi,
I opted for comforters to reduce floor bounce. I’m having some fiberglass issues (in my throat right now -- probably from opening/closing the cabinet repeatedly and digging around in there); as for the bedding’s effectiveness, I don’t know. I additionally fastened some foam onto the ceiling in the bounce zone.

For nearfield measurements in 2.5 way I placed the mic at 3” from the baffle equidistant between both woofers and ports. For full range 3’ readings I offset the mic so as not to be centered on the middle vane, as Zilch pointed out that might create the notch we saw in the 3k region. I “think” this helped and I posted the RTA for benchmark “centered” on the vane and the offset pointed into the first sector to one side.

This time I did not have the opportunity to listen at all. I left the 20mH coils installed in N-800-F output mode, so this week I should roll them out and give a listen.

I have all the parts for the next crossover, but have not put anything together yet.

[Skywave-Rider]

OKhttp://www.youtube.com/watch?v=97CEcUEjJAE
Try removing the "OK" at the head of the above URL and paste it into a browser window.

Fun to watch the LF come up. Not very clear, though.
Nearfield with supercoil running from N-800-F output. HF is on a dummy load.

[Zilch]

Well, you've certainly got BASS in the 2.5 mode with the helper running!

Though the nearfield with one woofer @ 16 Ohms looks the best, remember that nearfield exaggerates the LF response. I think of it as reflecting how the response would sound with full boundary reinforcement.

Missing in your measurements is nearfield of the helper woofer running alone. Get that first when you go do more.

As suspected, the notch at 3K15 would appear to be coming from shadowing by the central vane of the 811B horn on axis. Mitigating the floor bounce seems to have helped, also. I've seen the HF roller-coaster response you're showing in my own measurements here; I believe it's the horn vanes doing that. We'll ignore all of that henceforth, unless some surprise appears.

Adding the helper woofer doesn't do anything to the main woofer response in the lowpass region (the top end of woofer response,) the reason being that the inductor impedance is apparently high enough at those frequencies so as not to alter the filter frequency or slope. We're therefore presently running on the 16-Ohm curve rather than the 8-Ohm one.

If we were to stay with N800-F, we might choose to alter the filter for optimum response blending of the two drivers in the crossover region, but I think we'll be preferring to work with the modified M19 crossover, once you have those built.

The HF is still running too "Hot," but I appreciate that you have some difficulty cranking that down due to intermittency in the stock crossover attenuation potentiometers....

[Skywave-Rider]

I can't believe I forgot to get the helper alone, Zilch....
Yes, bass! Thanks.

[Zilch]

Fun to watch the LF come up. Not very clear, though.

Nearfield with supercoil running from N-800-F output. HF is on a dummy load.

WAY cool, and quite amazing, actually, I must say. I am in full giggle mode here.

[Fun to hear the pink noise playing, too.... ]

I can't believe I forgot to get the helper alone, Zilch....

No problem; we'll get it next time. Both direct wired and on the N800-F filter, please.

We need to know that if we're going to tweak the bass extension....