New Heathkit AS101 owner - First post.

**alancohen** · November 20th, 2012, 05:52 PM

Originally Posted by Alien_Shore

Alan,
I have many of the same questions as you (and others) are recently posing here.
In my research, I've found that the topic is very complex and there aren't many good articles published for the layperson. Take a look at this thread where I've linked some of the better articles that I've found. It will provide a start at least in understanding some of the fundamentals of horns and the science behind them.

That's some pretty heady stuff there. Honestly, I don't think I even want to understand it all. At my age there is only so much room left on the old hard drive. If I let too much more in there I might lose vital data...like my name.

This is an example of what leads to my confusion. Here is a data sheet on the 1225A HF cabinet. On the first page it says the 805B horn "operates from 800Hz to beyond audibility". http://altecpro.com/pdfs/vintage/Spe...%20Systems.pdf

Then down below it says the 1225A enclosure, with only the 805B horn in it, has a frequency range from 300Hz to 8000Hz. That makes no sense to me.

I'm now in the camp of just try it and see what happens. I know my 806A CDs go down to 500Hz. I'm going to tune my crossover that low and see what I hear. If I like it, who cares, right? If not, I'll adjust it until I do. The good thing is I know what sounds good...to me at least. I have a sound in my head that I'm trying to achieve. I really don't care what the numbers are.

**cradeldorf** · November 20th, 2012, 09:14 PM

Originally Posted by alancohen

That's some pretty heady stuff there. Honestly, I don't think I even want to understand it all. At my age there is only so much room left on the old hard drive. If I let too much more in there I might lose vital data...like my name.

This is an example of what leads to my confusion. Here is a data sheet on the 1225A HF cabinet. On the first page it says the 805B horn "operates from 800Hz to beyond audibility". http://altecpro.com/pdfs/vintage/Spe...%20Systems.pdf

Then down below it says the 1225A enclosure, with only the 805B horn in it, has a frequency range from 300Hz to 8000Hz. That makes no sense to me.

I'm now in the camp of just try it and see what happens. I know my 806A CDs go down to 500Hz. I'm going to tune my crossover that low and see what I hear. If I like it, who cares, right? If not, I'll adjust it until I do. The good thing is I know what sounds good...to me at least. I have a sound in my head that I'm trying to achieve. I really don't care what the numbers are.

I couldn't agree more, I have seen so many conflicting pieces of literature That I too decided to just go with my own instincts, Altec doesn't appear to be any more educated than the people on this board. And since were on the subject I'll never deal with GPA again either.

**VolvoHeretic** · November 21st, 2012, 12:00 AM

Originally Posted by cradeldorf

And since were on the subject I'll never deal with GPA again either.

Color me confused...?

On a lighter note, just like some are better than others, there is no such thing as a bad Corvette. I might not own the best Altecs, but they both sound wonderful and I am glad I wound up with them.

**cradeldorf** · November 21st, 2012, 02:46 AM

Originally Posted by VolvoHeretic

Color me confused...?

On a lighter note, just like some are better than others, there is no such thing as a bad Corvette. I might not own the best Altecs, but they both sound wonderful and I am glad I wound up with them.

I just was not happy with the service I received, And my VW Beetle would take out that Volvo!!

Sorry OP for hijacking your thread.

**voice of the theater** · November 21st, 2012, 09:59 AM

Originally Posted by cradeldorf

I couldn't agree more, I have seen so many conflicting pieces of literature That I too decided to just go with my own instincts, Altec doesn't appear to be any more educated than the people on this board. And since were on the subject I'll never deal with GPA again either.

Sorry to hear that you had bad luck with GPA. They've reconed Altec 421's for me in my old P.A. speakers that I used to own and have also re-foamed Altec woofers for me, and every time the work they did was flawless. I also bought two spare diaphragms from them that I plan to store in case I ever need them. Their diaphragms are the real deal--you just can't get "real" Altec diaphragms anywhere else.....

**gearfreak** · November 21st, 2012, 12:23 PM

Originally Posted by alancohen

...gather the curve of the horn structure is tuned to maximize a certain frequency range, but what would happen if you put a 500Hz signal into an 811b horn, assuming the driver itself could handle it? Of course a sound would come out, but what would be happening to it to make it undesirable? Inquiring minds want to know.

I may have missed the original post about undesireability... so maybe this is not entirely on target.
I think the overall point is that the horn will not load the driver below Fc. This creates an impedance mismatch. So you loose efficiency, perhaps to the point of no sound coming out.

Take the analogy to the next step and think of it this way.

If you strapped a 15" woofer to an 811, would sound come out? Yes.
Would 30hz come out? Probably: 'not really'.

**alancohen** · November 21st, 2012, 02:04 PM

Actually, GF, your post is exactly on target.

I guess the first thing is I don't get how a horn by itself, basically an inert flared tube, has an "impedance" at all. I understand the impedance of AC current in a circuit, but how does this apply to a horn? I assume it has something to do with sound waves moving in an air medium through a restricted space.

I gather that the lower the frequency, the longer the sound wave so it makes sense to me that the length of a horn could influence frequency efficiency, but length seems to be irrelevant in that shorter horns can still be rated lower than longer horns of a difference shape. I don't get it.

The good news is at this point I don't have to. I have what I have as far as equipment and you gotta dance with who you brung. I'm just trying to figure out what the ramifications are of trying to put 500Hz through an 811B horn. I'm going to try it anyway and see what I hear. It will either sound better to me or worse. It's a luxury to know why, not a necessity.

**VolvoHeretic** · November 21st, 2012, 02:16 PM

Someone here once told me that I would probably blow-up the diaphragm in my 32B horn using the 500hz 501-8A crossover because the horn wasn't loading the diaphragm at those low frequencies. Hasn’t happened yet, but I can’t remove the loading cap screws out to look and check if the diaphragm is aluminum or a symbiotic and am too lazy to take the whole horn out of the box to really get at the screws.

**alancohen** · November 21st, 2012, 02:34 PM

Yeah, but the diaphram is in the driver, not the horn. I can see that trying to push 200Hz into my 806A drivers that are rated for 500Hz might create problems. But putting 500Hz through a driver that's rated to 500Hz, but blowing through a horn "rated" and 800Hz, is a different animal.

The question is what happens to the 500Hz signal from an 806A driver when it goes through an 811B horns?

Here's the scenio: I have two 806A compression drivers (rated down to 500Hz). One is bolted to an 811B horn (rated at 800Hz), the other to a 511B (rated to 500Hz). I put the same 500Hz signal through both. The 806As are supplying the signal equally..yes? What happens to the signal as it goes through the horn and what SPL comes out the business end? I assume the 811B will produce a lower dB level at 500Hz than the 511B. If so, how much lower and do I really care?