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Hi Guys,
I have the above speakers and a pair of replica A7 cabs made from very good grade plywood to the factory plans.
I have a pair of 811B horns....
My question is about the X-Over frequency - should I go for 800 cycles or 1200 cycles?
If I buy a pair of 511bs will I be able to use the 902s at 500 cycles?
I have a brand new pair of GPA's replacement diaphragms installed in the 902s
Thanks
Winders
O.K I have learnt a bit from the Altec literature that I found.
I see that my confusion is all centred around a 'loading cap' that I need to install in order to use the 902-8A at 800 or 500 cycles.
It looks to be a plastic or phenolic cap that is inserted before the outer cap.
Are these avialable is the next question - I will check with GPA.
Winders
What is your intended application?
Do your 902's have 7/8 or 1 inch throats?
Which "factory plans" were your cabinets built to?
More specific information should get you more responses.
Personally, with that driver combination my suggestion is to forget about a passive network and actively bi-amp. To my ears the 902 sounds "strained" when pushed much below a 1khz XO point, your mileage may vary.
Intended aplication - Domestic Audio system.Quote:
Originally Posted by bowtie427ss
Plans for LF Cab - Altec Lansing as attached.
Yes that is the sort of info I am also looking for - users experiences with 1200/800/500 cycle crossovers using the 902 (with/without loading cap).
I have not used/setup a VOT system yet so I am looking for advice from folks that have been there and done that.
At this moment in time I have no loading caps so I am steering towards the 1200 cycle X-Over point.
Winders
I second the 1200 choice.
And if I could add a vote for biamping...biamped systems just sound better to me, yer mileage may vary. ..and all that stuff...
It's a lot more hassle though.
I'm not sure I agree with your thoughts on loading caps.
I believe they were designed for higher output applications like movie houses. In a home hi-fi application, they are not really necessary, and for that reason are often not used by these folks. Loading caps are not rare, so you could experiment with and without to see what you prefer.
Since you probably have the home hi-fi 902 diaphragms from GPA, I would assume you would like the drivers without loading caps.
Most factory applications using these components were crossed at 800 but many folks like the higher x-over point. I believe the venerable Model 19 was crossed at 1200 and many consider this the hallmark of Altec home application systems.
Quote:
Originally Posted by robertbartsch
On loading caps, virtually all Duplexes use them, so many home systems Do have them. It is not as simple as you think.
All later apps had the 1200 Hz crossover, you will find most 902's crossed at 1200 not 800. You are confusing with older systems.
Have you a schematic, tube possibly, that you like?Quote:
Originally Posted by Old Guy
Getting 4 really nice output transformers might be a daunting task. Maybe Triode Electroncis SCA 35 set with EL-84s? Then pay $500 for a quad of Telefunken? Man I could get caught up in this big time if I'm not careful. There are lot's of nice sounding guitar tubes but I haven't an idea in the world about hi-fi. Maybe Valve Art? Do they make a EL-84? They make a nice KT-66 but in my opinion it's too fragile in guitar amps. On and on.
What?Quote:
Originally Posted by bowtie427ss
The small format drivers all had the same throat size. They all mate to the same horns. Confused by this comment.
1200 hz works well. Find some N1201-8A or M19 crossovers and be happy. These are much better than the older 800hz units. You can tweak mid vs high, and they are quite good.
You will tweak active x-overs forever.
Domestic use, this works well. You don't need loading caps.....felt in the rear cover is best. Loading caps were meant to limit over excursion......if you get it that loud in your home, your ears will bleed.
BTW, Dickenson says the 902-8a is the best sounding HF driver, and I agree.
Ron
Quote:
Originally Posted by RonSSS
Thanks guys.
Ron yes I have now a copy of the Model 19 X-over and will build that as I see it has addressed quite a few issues and can be tuned to taste as opposed to changing crossovers infinitum!
I guess a Model 19 cab would have been better then but one can change the porting/Fb of the 825/A7 cab quite easily by way of the front "boards" - so I think I will give it a go like that first.
Best
Winders
I once believed this too.Quote:
What?
The small format drivers all had the same throat size.
There are 7/8 inch throat horns that mate with these drivers as well.
Here's a 7/8 inch throat 902.
http://i107.photobucket.com/albums/m...7ss/902-8A.jpg
Quote:
Originally Posted by RonSSS
100% agreed the loading caps are not needed at 1200.
At 800 maybe. I would be cautious
If you wanna take the driver down to 500, you better
1 Add loading caps
2 Derate the power
I know you are aware of all this, just some readers might not be.
As you said, the caps were used to limit excursion, which is not caused just by power.
The 902 may be the best from 1200 up.
Having heard it crossed lower, I disagree it is better than an 802 tangerine from 800 up, and at 500 no contest the 802 wins.
they are different, the 900 series bandwidth is shifted upward. Different is not always the best, it depends on other factors.
Not suggesting over the M19 xover suggestions, and no knowledge of how they relate electrically, but if desiring selectable, in order to adjust to taste, you may want to research / purchase one of the N-1285 series...Quote:
Originally Posted by Winders
e.g.
http://www.altecpro.com/pdfs/vintage...%20Network.pdf
In the pic, above, could the 7/8ths inch exit hole have been produced by inserting a 1/16th inch thick sleeve into a normal 1 inch exit hole?
If so, could the sleeve be readily removed?
I think this is an excellent idea.Quote:
Originally Posted by gearfreak
Ron
I only have a guess here, but the 900 series drivers have a much shorter throat, so perhaps when mated to an earlier horn, the reduced diameter makes a better match. Just a thought.Quote:
Originally Posted by mah
I don't think you would want to remove the sleeve.
As far as lower crossover freq and over excursion, I would not think this to be an issue in domestic applications using low power. I can blow my ears out with 10w total to a pair of A7's in my living room, I never cared for the 500hz crossover anyway.
Ron
I have one of these with a loose tangerine, when time allows i'll dig into it and try to get a couple pics that should probably show that the throat/pole piece is a single machined part.Quote:
Originally Posted by mah
As you can see in the pic i posted above, it appears that they only made front plates with 1 inch holes and this throat/pole piece has a bit of a nose machined on it that fits into the 1 inch front plate hole.
I don't think it's a sleeve, besides being an additional part a sleeve would have to be tapered both inside and out making it a fairly complicated part to machine(read expensive) and since these are of the generation that adopted the plastic tangerine phase plug for it's low production cost above all else, i think it's important to factor in cost effectiveness when trying to determine how the assemblies were produced.
FWIW, these are from 9842 monitors which use the MR931-12, the drivers mate perfectly to the horn's 7/8 inch throat, with not so much as a "bump" and the joint between driver and horn, which is my understanding of a proper fit.
I'm pretty confident that the engineers knew what they were doing and designed all of these components to observe constant and proper flare rates. I don't think they can be mixed and matched to the extent a lot of folks do and still obtain the same results as when the proper components are mated.
Just my .02..............
Drat this foggy old brain...:doh:Quote:
Originally Posted by bowtie427ss
I remember a conversation with some of the really whiz bang Altec people one of my trips out there in 72-ish.
But I think John Hilliard, referencing small formats...said something like "the horn flare starts in the driver".
Now that's drifting back, and I wonder if in the thin design they just moved that part out to the horn...
It sure sounds like he was talking about something along these lines..
GM- any observations?
Where is GM? Not seen him on the forums lately. Hope he's OK.
He posted here earlier today and just posted at diyAudio.
Well I finally got to measure the units and indeed they are not an inch but 7/8th of an inch.Quote:
Originally Posted by bowtie427ss
And here is the other conundrum - the 811 Horns that they mate with are 1inch diameter at the throat - meaning they are a mismatch.
The conundrum being that they were clearly or seemingly clearly factory set like this - the gaskets etc gave me the impression they had not been separated prior to my taking them apart......
So I have a mismatched setup and I am now pretty stumped - this may be the end of the road for the Altecs unless I resort to machining options...
Or can folks confirm the existance of 7/8" 811 sectoral horns?
Hmmmm :(
Winders
This may be the lesser of two evils. I think where you can really have the potential for audible problems is if the driver were 1 inch and the horn 7/8. That would leave a small flat face that could reflect energy back into the driver throat.Quote:
the 811 Horns that they mate with are 1inch diameter at the throat - meaning they are a mismatch.
In your situation it may be possible to "smooth" that transition by just adding a second gasket and carefully sanding/cutting the gaskets to more or less continue the flare rate of both throats.
Quote:
Originally Posted by bowtie427ss
I'll look into this - it might be worth machining up a phenolic adaptor say 1/4" thick - the studs seem long enough....
But I have no idea what this means to the FR and its still a cobbled system - has anyone got a pair of 811B Sectoral horns with 7/8 inch throats that they want to sell?
Cheers
Winders
Ditto!!! Not only run the risk of audible problems but the reflected energy puts an undo strain on your diaghram from the reverberating sound pressure's back into the diaghram.And will eventually cause the fragile diaghram to fail.Quote:
Originally Posted by bowtie427ss
Understood... better in that there is no reflected energy going 7/8ths to 1" but still a significant discontinuity and a discontinuity in the throat of any horn is a no no.....Quote:
Originally Posted by Altec Best
Need to ascertain how many systems are thus afflicted and still yet to see an Altec 7/8ths adaptor or a horn with a 7/8ths throat!
I cannot find any Altec literature referring to such a beast...
Seems I might be in the market for a 1" pair of Ferrite 902-8A's (if they exist) - Diaphragms are not critical as I have a brand new pair from GPA...
Or I am looking for a pair of 811's with 7/8ths throat - again if they exist..would Altec make a horn in two throat sizes with same part number...
Would Altec make two types of 902-8As with same part number - this whole thing makes no sense....
Or I make a proper adaptor out of fibreglass resin .... to mate 7/8ths to 1".
Hmmm... weird that Altec did this....
Winders
TA DA!!!!!Quote:
Need to ascertain how many systems are thus afflicted and still yet to see an Altec 7/8ths adaptor or a horn with a 7/8ths throat!
I cannot find any Altec literature referring to such a beast...
MR931 HORN
Interestingly, while the GPA website says their current model of this horn is designed for drivers with a 1 inch throat aperture, their data sheet specifies a 7/8 throat on the horn. My guess would be the website gives just a generalization to avoid confusion. Maybe TWW can clarify for us.
FWIW, my 9842 902's/MR931's, and factory gaskets are all precisely mated at 7/8".
I can only guess, but my suspicion is that early 902's were probably 1 inch, but as the Mantaray horns began to replace the 811 and 511 sectorals they were revised to a 7/8 throat while the more industrial aimed 908's and 909's retained a 1 inch opening............ purely a guess on my part. This is another chapter that should be covered in Bill H's book when he writes it.Quote:
Would Altec make two types of 902-8As with same part number - this whole thing makes no sense....
Again you provide excellent info thanks - have to admit I was looking in the sectoral horn '511/811 arena' for a 7/8ths interface as I am making an A7 replica...Quote:
Originally Posted by bowtie427ss
I guess given that I have expended so much money and time already that I should simply make an adaptor - next will be to try and ascertain the curve.....
Thanks again - most helpful!
Winders
Yes I think all Altec 811B's and 511B's are 1" throat aperature. the 7/8" is for the newer Mantarays and newer 902's to name a couple, Bowtie's right on.:Nodding:
I have a 908-8A here ( serial # 00915 ) that sports a 7/8" exit .Quote:
Originally Posted by bowtie427ss
That supports your contention that you're guessing about the above .
<> cheers
ps ; not that it matters , nobody's going to lose an eye over this 1/8" difference . :p
On the contrary I think if thats the case then they 'cocked' it up and 1/8th certainly makes a difference especially as a discontinuity at the throat, as we all know, is not good.Quote:
Originally Posted by Earl K
They went to great lengths to make adaptors for 1.4" to 1" for this reason.
Now how much it matters well who knows.....
Winders
I received an e-mail from Todd an apparently this is the way it was done - 7/8ths to 1inch.
For my own peace of mind I will make a 7/8ths to 1inch adaptor spacer out of 5mm thick phenolic and continue with the project although I must say I am wondering if the Model 19 cab might be a better route even if it means leaving the A7 cabs in dust gathering mode...
But the project will now proceed.
Winders
Thats what i'd do.Quote:
For my own peace of mind I will make a 7/8ths to 1inch adaptor spacer out of 5mm thick phenolic and continue with the project
I love them both for entirely different reasons. The A7 has dynamic attack that is 2nd to none, for some program material and my listening preferences this can really "float my boat".Quote:
I must say I am wondering if the Model 19 cab might be a better route even if it means leaving the A7 cabs in dust gathering mode...
With other program material and different listening moods it's the very well balanced extension into the lowest octave, and well refined HF response of the Model 19 that can equally "float my boat".
19's have a pretty steady demand, if you built them and didn't like them, you could always find another home for them, and you'd have an opportunity to compare them to A7's in your own listening environment.
Thanks...Quote:
Originally Posted by bowtie427ss
I was attracted to the A7/825 cab due to the horn loaded bass driver and the M19 seemingly gets away without this... I guess I will get the A7's running and then decide...
Winders
Just remember, it's only a horn down to ~100hz, below that roll-off is fairly steep. On their own, i really like the A7 for big band, and vintage jazz/blues. For more modern stuff and even hard rock i need smoother and more extended bottom octave response. I augment my A7's with a quad of emilar EW15-8B woofers in ~15 ft3 boxes, with enough amplifier, they can almost track the midbass dynamics of the A7's at my preferred listening levels.:2thumbsup:Quote:
I was attracted to the A7/825 cab due to the horn loaded bass driver
Yes, my feeling at the moment is I can try lowering Fb as the 825 cab baffle boards lend themselves to this readily - so to try a lower bass reflex freq would be relatively easy - how it works - hey who knows!Quote:
Originally Posted by bowtie427ss
Cheers