model 19 clone box for my A7 500Hz components?

[kipduff]

Hi Kiduff -

Been following along with your progress. How about some pics of what you are working with? I know, I know - if you've seen one . . . but photos sort of personalize the experience for us.

Keep us updated!

GeeDeeEmm

So here is the original eBay listing that I turned into PDF. In the eBay pictures, they appear original grey- I think he took them before he painted them. In the second link where I'm discovering that the XOs are screwed, you can see now they are a very dark grey. I'm building panels to mount behind original XO mount area to adapt the '66 XOs temporairily. Just received some Cardas Patented Binding Posts which I will try out in these. It's amazing how many binding posts that are out there- and I don't really like any of them. Russian MBGOs on their way for quick XO repair. I will post more later with questions. These are in pretty good shape I think. Mostly 5/8" particle board- back is 3/4" as are some other panels.


Dropbox - A7:828 cabinets bought off eBay 2017 09 21.pdf
2017 09 29 2981 testing.jpg
Dropbox - 2017 09 29 2983 XO disassembled.jpg

[kipduff]

http://www.lansingheritage.org/image...ign/page15.jpg


http://www.lansingheritage.org/image...ign/page16.jpg

Regardless, I've learned the hard way never to trust polarity markings because in my then teen youth I thought the Altec distr. was 'jerking my chain' about never trusting them, so long since been ignoring them, using a battery or impulse test to find which terminal attached to 'battery +' blows a piece of toilet paper or similar forward/away from the driver face [compression stroke in acoustic speak, rarefaction stroke on intake] as opposed to the diaphragm's relationship to the motor and mark it 'positive' or '+' with something that will stand out at a glance. Ditto anything polarity centric if you have to use any sort of magnifying glass to see tiny markings and/or didn't pay attention when replacing them .


As you can see, Altec's way can be quite confusing, especially as to when to reverse polarity; better to understand the basics, i.e. for each XO slope order there's a 90 deg phase shift [lag], so with a 2nd order the HF is lagging behind 180 deg out of electrical phase, but if you reverse the HF's polarity, it's now in phase, though still lagging in time by however many milliseconds [ms] of the XO frequency [~SoS/(4/slope order)/XO frequency].


Note that all of this for HIFI/HT is kind of bogus due to small room acoustics and other variables like the acoustic center of a compression driver rests on its phase plug and moves forwards/backwards with frequency on a point source, so only accurate at one frequency; plus a point source starts with a 90 deg phase lag relative to a compression driver, so either the acoustic centers need to be gapped an extra 90 deg relative to a compression driver or use a 3/2 slope order XO.


Historically then, the typical DIYer tried swapping polarity of a speaker's HF [mids, then HF to mids for three way] and whichever one sounded best was the right one regardless of markings, theory.


Explanation of Time Aligned and Linear-Phase? - diyAudio


You're welcome!

GM

Thanks GM. Will take me a while to digest this obviously.
I am making a MSWord NOTES document where I cut and paste web info for easy access- and this post is going in there for future reference.

On this subject- just got back my re-coned/regaussed 604-8Hs from GPA. Broke em in a little with about 4 hours of a break-in disc I have. Just tried them with the polarity reversed from indication on the GPA N-604-8A XOs. Seems better. I will let them break in and do another A-B. New suspension on these seems stiff- I believe Fs is now about 33Hz- original Fs on 8H is 28Hz I believe.

[GM]

You're welcome! Ran out of time to include physical offsets, but this procedure works well enough for positioning a horn or finding the ~correct XO point for a fixed position: https://audioroundtable.com/misc/Altec_AN-9.pdf

GM