| 4pi with altec 807? [message #63163] |
Mon, 14 June 2010 16:47  |
geezer
Messages: 5
Registered: June 2010
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Esquire |
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Hello Wayne
I been gathering parts for a 4pi build and stumbled upon a pair of old altec 807 horns. The horns are a bit big to fit in to the box so I was thinking of putting them on top. Are the box dimensions critical? And if so which ones shall I stick too?
Best regards
/Anders
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| Re: 4pi with altec 807? [message #63172 is a reply to message #63170] |
Tue, 15 June 2010 14:10  |
Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA
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Illuminati (2nd Degree) |
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A number of us have, in the past, used the older 4Pi crossover with 811s and other horns with drivers that include the 806 and 902. We all used bigger boxes than Wayne, 3 1/2 to 4 1/2 cubic feet tuned to 40 Hz, because that's what we had, mostly from the JBL Tent Sale at that time.
Heres a 3 1/2 cu ft JBL 3677 cabinet with a 4 1/2 cu ft behind it and the 811 just peeking out above. If you do a search here for Speakerman57 you'll find a lot of discourse between Ron and Wayne about implementation. I just held Ron's coat 
(Wayne, you believe all that goes back nearly 10 years? Yikes!)
After several years of this, I built the dead stock 4Pis with the new crossover and couldn't be happier. Ron's still out there, with Beryllium, this time.
Happiness is:
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| Re: 4pi benefits [message #63179 is a reply to message #63178] |
Wed, 16 June 2010 18:49 |
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Wayne Parham
Messages: 18783
Registered: January 2001
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Illuminati (33rd Degree) |
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Actually, as much as I like the Altec 811 horn, there's no way to get the polar response right, or even close. You can make the on-axis response right, but not off-axis. So you have to sit with the speakers directly facing you for them to sound good.
While that may seem to be a non-issue, it is actually really important because if the sound isn't balanced in all directions, then reflections have the wrong spectral balance. The total energy in the room - what you hear is made up of this total energy - is actually an aggregate of sound radiating in all directions, not just the sound that points directly forward from the speaker. So the goal is balance of the reverberent field, not just the on-axis response.
The problem is that long neck on the 811 horn. The lower region, from about 800Hz to 4kHz or so, radiates from the horn pretty evenly at all angles defined by the mouth. At the low end, it's actually wider than that. But as sound frequency rises, the pattern becomes more narrow. The higher frequencies are only present straight forward on-axis, and cannot be heard off-axis at all. That long narrow throat makes the sound beam at higher frequencies.
All of my loudspeakers have constant directivity as one of their design goals. If you'll stick with the stock plans, what you'll gain is nice smooth response over a nice wide 90°x40° pattern. I gave you a brief overview of why that's important in the paragraphs above, and in the link below, there are several threads with more detailed information. I've also included a link to the response (both on-axis and off-axis) of the four π loudspeaker. You'll notice it's nice and smooth over a wide range of angles, and that's no easy feat. It's more complicated to make performance good over a large area, and there are more competing priorities to balance. That's why it's nice to be able to leverage the R&D I've already done, but to do that, you'll have to build what's shown the plans.
By the way, you're right that the driver and port position can have an effect on lower midrange response, mostly in larger cabinets. The positions set how the standing waves line up. The goal is to keep acoustic radiators near zero crossing positions, so internal standing waves aren't audible. But that's not the only thing that matters where position is concerned. In fact, it's not even the main thing. The main thing is acoustic flight time, the path lengths between sound sources and listeners. These distances combine with electrical phase from the crossover to set the overall summing between sound sources. You can find more information about that at the link above.
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| Altec 811B horn and 807 driver [message #63186 is a reply to message #63179] |
Thu, 17 June 2010 10:41 |
spkrman57
Messages: 522
Registered: May 2009
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Illuminati (1st Degree) |
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First off I must agree with Bill and Wayne as far as using the 811B horn will be less than ideal unless you toe them in to the listeners position and that limits how many people will be able to hear the system like it should.
I still have that situation and then some since I use round horns which beam like a laser, but will image like not other horns if you can stand a micro-sized sweet spot.
I would also like to point out that the 807 driver if stock has a "symbiotek" diaphram and HF response will be limited. Installing a aluminum diaphram will help, but driver to use if you want Altec (or Great Plains) is the 902 with "Tangerine phase plug" and aluminum diaphram.
Regards to all!
Ron
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| Re: Altec 811B horn and 807 driver [message #63189 is a reply to message #63186] |
Thu, 17 June 2010 14:00 |
geezer
Messages: 5
Registered: June 2010
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Esquire |
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Thanks for all the replys. It´s been very informative and have most likely saved me alot of unnecessary work and dissapointment.
I just orderd a pair of H-290 horns, so I could get started. I will for the moment stick with the 807 driver as I already have those and then later upgrade.
Thanks again!
/Anders
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