Polars Plots for Altec Multicells? - Page 2 - diyAudio
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Multi-Way Conventional loudspeakers with crossovers

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Old 15th February 2013, 01:13 PM   #11
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Thanks for that GM! That's the type plot I was thinking of. There should be one for most of the common Altec Multi-cell horns. Very useful info.
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Old 15th February 2013, 03:54 PM   #12
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You're welcome!

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Old 15th February 2013, 04:41 PM   #13
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My ears were burning.

The only plots I have are the measurements 1803B horn cells. If you need polar plots then befriend GM. He's our best resource here.
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Old 15th February 2013, 05:00 PM   #14
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Originally Posted by steve71 View Post
That looks good, I like that concept. But if I were to make the mouth of the bass horn that large, the beam width would be less than 90 deg at 300hz - or am I missing something?
Bass horn beam width at 300 Hz will be largely dependent on the horn throat angle, not the mouth angle.
My PA uses optional waveguides which extend the 26.5 wide 90 degree horn to 53 inches wide.
The dispersion remains a uniform 90 degree pattern, the waveguides extend pattern control about an octave lower.
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Old 15th February 2013, 05:04 PM   #15
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Cal,
Sorry if I made your ears burn. I thought that you were the man with multi-cells! Have you done a sweep across the cells or just an individual cell? I though that they use to have this information in my old AES Journal papers on loudspeakers but my old copy is somewhere in storage. If I remember correctly they are not nearly as smooth as some seem to think, on average they may be good at dispersion but on a smaller scale I want to remember that they are rather rough in a polar response sense.
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Old 15th February 2013, 05:10 PM   #16
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Weltersys,
The use of the wings you are talking of would also lower the effective loading of the horn mouth and this would be another advantage of using such extensions.
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Old 15th February 2013, 05:18 PM   #17
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Quote:
Originally Posted by steve71 View Post
On axis it sound good playing down to 300hz so it would be nice to cross that low.
Having "Been there, Done that" you'd have to define "nice".
To sum up a few years of work and pulling my hair out:
  • Q: Why would you want to cross that low?
  • A: Because I want to cover as much as I can with the horn.
  • Q: Why with the horn?
  • A: Because it sounds better than the woofer.
  • Q: Does it really? Or do you just think it does?

I found that it does not. That is probably not entirely the fault of the horn, the compression driver is important, too. Even with the robust Altec phenolic drivers like the 291 "Giant Voice" running that low does not sound great. Remember that at some point output will drop and distortion will skyrocket. You want to stay far away from that point, unless you are using very steep crossover slopes, which have their own problems.

After a lot of experiment, measurement and listening, I've found that 1.4" drivers are just better sounding crossed at ~600Hz or higher. Although they will play lower on the right horn, you do need the extra octave (or more) below the crossover point to stay out of high distortion. Even if they will play down that low, you probably don't want to use it for high fidelity.

Honestly, most good 15" woofers sound better in that range than the compression drivers. Placing the crossover point where it actually sounds best, not where we hope it will sound best, is best practice.
It took me years to learn that.
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Old 15th February 2013, 05:43 PM   #18
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Pano,
I second that opinion on the crossover point of the 1.4" compression drivers and even more for a 2" for other reasons. I didn't want to get into a verbal joust so I kept my mouth shut. In pro-audio PA applications this is why I originally developed cone driver mid-range horns to cover this region. The sound of a compression driver that low at any kind of level is just not a nice sound. Besides the fact that you could easily overload the compression driver and watch a whole PA worth of diaphragms go up in smoke back in the day with passive crossovers. From what I remember the aluminum diaphragms did sound a bit better than the phenolic ones but would break easier in use than the phenolic. We developed 10" cone driven mids just to take this out of the equation and to improve the mids so much over just 15" horn bass bins and a horn top.
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Old 15th February 2013, 05:47 PM   #19
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Yep. I'm fond of a 10" cone with a horn for PA mids, too. Works great.
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Old 15th February 2013, 07:04 PM   #20
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Yep. I'm fond of a 10" cone with a horn for PA mids, too. Works great.
Yup, first time I heard 10" or 12" cone mids compared to JBL 2440s at 500 Hz was a real ear opener, never went back to low crossover compression drivers since 1978.
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