Acoustic Phasing importance for A-5

[drummerwill]

So I followed the diagram Fig 5A from the Altec Loudspeaker Phasing note for my 828 and 803/299 A5's. Right away I could heat a difference. the "image" became much clearer and "stageing". I put quote to emphasize we're talking about a PA system in a basement. I don't crank it and use low powered DHT amps.

All I did was reverse the polarity of the wires to my 515G's. When first got my 828 boxes I rewired the 515G's with new speaker wire I kept the positive (+) terminal to the right when looking from the rear on both LF and HF.

When I saw the phasing note all I did was reverse the LF leads and .... Wha-La !

The image I was getting was good but not like now. My 299A still overhang the 828 box now, but the horn fronts are about even with the front of the 828. Asethically it looks good like that.

But whats should I do go for even better phasing moving the 803 's forward more ? By the way all pictures of 803's I've seen show them near even with the front of 828's .

Better question is. What the optimum placement for 803/805s on 828's with regard to phasing ?
Thanks All!

[bfish]

If you have an RTA, first reverse the phase, then play pink noise with the mic a few feet away and at cab height. Then slip the horn forward or back to adjust for the deepest notch at XO. There's only a short range of movement (~2") where the notch appears, and tiny movements in that range will find the deepest notch. You should be able to get -6-8dB notch. Then return the phase to normal.

[drummerwill]

Thanks bFish

No I don't have RTA I as Hopeing I could do it by ear.

What is amazing is thatyou say it's only only a fraction of an inch withihn that 1"- 2" range that could make a difference!

Maybe I'll have to do the RTA thing!

Have fun!

[ngccglp]

Try to align the voice coil of the 299 to 19.3 inches from the front edge of 828. Then fine tune by 0.5 inch forward or backwards. For the 803 I think the horn will portrude out from the 828 but that's OK.

[drummerwill]

Thanks ng

Thats good info. 19.3 inch is about what I got. I'll check again and play with that 1/2".

Have fun!
Willie

[valhallax]

hey will.. irun the same setup here at home, an a-5 loaded with a 416-16c/ 299-16k. i also have an rta, a rane re27. my horns are mounted just like yours, with the horn mouth at the front of the cab. my sytem is however biamped using a rane ac23. i got to thinking that the time delay feature fot the mids might cure the off center driver configuration...it did. bt reversing the polarity of the 299, setting the rta at a 1db measurement, i was able to see the hole at the crossover point. the weakness off the rane crossover tho is that it doesnt show how much delay in milli sec, just min-max. it took the max delay to get the right results. i would note however that the results were more prevelant at 500 hz croosover than at 1200 hz. i started at 1200 and worked down to 500. i noticed you mentioned the 805 horn here, i have a set of those as well, hooked to my ex father-in-lawsb cabs, iset him up with. for my money the 803 is much smoother sounding..much. also about half as long. the 300hz horns are very long, as you well know.

[valhallax]

hey will.. irun the same setup here at home, an a-5 loaded with a 416-16c/ 299-16k. i also have an rta, a rane re27. my horns are mounted just like yours, with the horn mouth at the front of the cab. my sytem is however biamped using a rane ac23. i got to thinking that the time delay feature fot the mids might cure the off center driver configuration...it did. bt reversing the polarity of the 299, setting the rta at a 1db measurement, i was able to see the hole at the crossover point. the weakness off the rane crossover tho is that it doesnt show how much delay in milli sec, just min-max. it took the max delay to get the right results. i would note however that the results were more prevelant at 500 hz croosover than at 1200 hz. i started at 1200 and worked down to 500. i noticed you mentioned the 805 horn here, i have a set of those as well, hooked to my ex father-in-laws cabs, i set him up with. for my money the 803 is much smoother sounding..much. also about half as long. the 300hz horns are very long, as you well know.

[bfish]

Originally posted by valhallax:
...the results were more prevelant at 500 hz crossover than at 1200 hz...

<font size="2" face="Verdana, Helvetica, sans-serif">5 degrees of phase shift at 500Hz occurs with 0.376 inches displacement. For 1200Hz, only 0.157 inches causes the same 5 degree shift.

<font color="#FFFFFF" size="1">[ February 26, 2008 05:55 AM: Message edited by: bfish ]</font>

[bfish]

<font color="#FFFFFF" size="1">[ February 26, 2008 05:46 AM: Message edited by: bfish ]</font>