-
I've seen several discussions in the past concerning front-to-rear alignment of 511 horns/drivers, but I don't remember seeing any discussion of alignment of large format horns/drivers on A7 cabinet. It looks as though if I align voice coils, the large horns and sleds will be ready to topple off the top. Should I reverse polarity? Anybody have experience with this? I have no access to analysis equipment so I only hope to get close. Are there any rules-of-thumb, wives tales, or folklore that would help.
-
Hi Charles,
Is there a way you could mount the large horn to a platform of some kind and mount that to the cabinet, with it hanging over a bit? You would get your alignment but would that look OK to you? Why not mount it to a temporary platform and move it back and forth to see how much difference you notice and make your own judgement. If you look at my big system under the heading in this forum "Trying again for the link" you'll notice the coils from the upper woofers are not in line with the big woofers, but I'm not too worried about it because they are higher in the air and therefore further from my ear than the larger woofers so...does that mean that in fact they are in alignment or at least close to it?
As you said there is much discussion with ths topic.
Cheers
Cal
-
Cal, I will be using a Rane active crossover in my biamped system. Can I aliegn the drivers electronically with the Rane?
-
Hi Igor,
Does your unit have a time delay circuit?
Cal
-
How long is a wavelength at 500 Hz?
-
Here is the link to the same rane I have. I assume the time delay in the picture is what you are asking about.ebay sale
-
Greetings All,
Here is an excellent site and article regarding phasing:
http://www.soundpractices.com/images/phase.pdf
Later . . .
-
Hi all,
The Rane AC22 has an all-pass filter in the low pass section to provide up to 2mS of delay.
BTW, the Rane AC22/23 are EXCELLENT units http://www.hostboard.com/forums/
Calculating wavelength (a little high school physics):
Assuming speed of sound is 343.8 metres/sec (at sea level)...
wavelength = velocity (speed of sound)/frequency
= ( (metres/sec) / (cycles/sec) )
= (343.8 M/S) / 500hz
= 0.687 M (or 27 inches)
The Rane AC22's delay can easily compensate for the length of a 511.
BobR
BobR
-
I'm sorry but I can't see a time delay circuit on those buttons and I may be getting a bit over my head here. My experience with active crossovers is very limited.
In order the falsify the coil alignment don't you have to delay the sound to one of the drivers? In this case it would be the woofer as the tweeter is hanging out the back of it. The speed of sound at around 330 m/s means that at a difference of 5 cm the time delay should be 0.0001515/sec.
Am I in the right neighbourhood here?
Cal
-
Charles,
If you're using a stock Altec crossover, aligning voice coils is a pretty good starting point. Move the HF section back-and-forth until you get so near a flat response at crossover as possible.
Nearly all Altec passive crossovers (N-500, N-800, etc.) are plain 2-pole Butterworth affairs and have two attributes that you ought to consider: (1) LF and HF outputs are 180 deg. out-of-phase, and (2) they will never sum flat (to a flat frequency response, that is). As I mentioned in a previous post, stock Altec passive crossovers were very primitive and pretty awful...
Igor has perhaps the best solution: bi-amplification using an active crossover with an LF delay. What's more, you may use a crossover with Linkwitz-Riley filters that have excellent phase and transient behaviour and that DO SUM FLAT. Try that with a single-pole or Bessel filter...
BobR
-
Guys you're way beyond me.
I asked for help in flying a kite and it seems to me you guys are building a space shuttle. I realize that perfection is the goal of some, but the pros that used to install these in theaters, I'm sure, had some general guidelines for their installation. That's all I wanted to know. I appreciate all other suggestion/solutions, but I'm not there yet; maybe later. I'm fiscally restricted and spousally constricted. Just wanted to know how to move 'em back and forth for optimal performance. I hope you understand.
-
Cal,
The AC22 has a continuously-variable control for LF delay, which is a fancy way of saying it's got a dial that goes from 0 - 2mS of delay. It would be better if it went to `11' ;-)
And you're right - you do have to delay the LF section, though by a bit more than 5cm if you're considering a 511 or large-format horn (i.e. - 805, 1005, etc.).
BTW, your calculation for the time delay of 5cm is correct.
BobR
-
Hi Charles,
I have a pair of 311-60 horns sitting on top of my A7 cabinets. I have plywood "sleds" that the horns rest on. They are just half inch thick plywood panels in the outline of the horn. They let me slide the horns forward and backward to get the alignment right, and yes, the alignment is very important and makes a big difference in the sound. For my system, I find that having the two front corners of the 311-60 hanging 4 inches ahead of the cabinet is about right. I don't know what woofers or horns you are using but if you make the sleds and experiment, you will be pleased with the results.
Regards,
-
Dave,
I have 311-90 horns on one pair and 1005's on the other pair. The 1005's are on sleds and I'm now putting the 311-60's on sleds. Thanks for your reply, it's exactly what I was looking for.
-
Charles, I am peicing together my system from baught parts. I had the Advent and the dynaco st35, and the KLH sub. I would have to buy the altec crossover and the Rane cost me $99.00 on ebay. So I am not really going overboard. I don't know how much the altec xovers are but the cost diff between them and the Rane cant be that much for what the diff is sound will be.
-
>I realize that perfection is the goal of some, but the pros that used to install these in theaters, I'm sure, had some general guidelines for their installation.
====
Beyond aligning VCs, bad assumption until the previously referenced procedure gained some acceptance, but then along came bi-amping/electronic XOs with adjustable delay and it became a knob adjustment.
Assuming you're using a stock Altec 500Hz/2nd order passive, then there's a ~13.56" pathlength phase difference between the LF/HF (~(13560/500)/(360/180)), so find the ~center of the LF's VC in the vertical plane and mark it on the top of the cab. Find/mark the center of the HF's VC on the compression driver. Prop the HF horn up and move it aft as required to get the LF/HF VC center marks 13-9/16" apart. The HF driver should be somewhat behind the cab. With LF+ going to terminal (1), HF+ goes to terminal (2) since its VC is in front of the diaphragm. This puts them both moving ~in-phase at the XO point.
This will get you within a 1/4WL. It will be off some due to the acoustic centers not being at the center of the VCs, but I've done alignments this way and compared them to the more precise way, and at 500Hz I can't hear enough difference to bother, but you can use a test CD with a 500Hz tone on it in lieu of an RTA and using the alignment procedure and your ears in lieu of a mic, fine tune it if your hearing is acute enough.
Or you can line up the VCs in the vertical plane, reverse the HF wiring and put some of those safety poles in front of the speaker to keep folks from banging into the horn jutting out in front of the cab. http://www.hostboard.com/forums/
Better still, get some A4s and lay them down on their side, then you can align the VCs without the HF horns extending beyond the front of the cab. http://www.hostboard.com/forums/
GM
-
Speaking of A4's
Cal's big speakers need a new home
Cal's underused speakers
