horn time alignment question

I'd like to clarify what exactly is needed for proper horn 'time alignment'? Is it just a question of having as close as possible alignment of the voice coils of the various drivers vs. the listening position or more complex? Jean Hiraga on his book on loudspeaker suggests that the alignment is not necessarily linked to the voice coil, but instead to some variable plane where the image would form within the horn throat, so that it require complete experimentation rather than a fairly straightforward locating all voice coils in a plane.

I'm using a 3-ways with a 15" bass speaker not horn loaded, a 2" mid with a round horn and 2405, aligning the voice coil of the mid driver with the bass would require significantly advancing this driver vs the front of the bass box, is this the way to go? I'd be interested in any advice on this.

Carolus, if you happen to read this, I'd like to have your opinion, I know you're pretty keen on this proper alignment,

Thanks all,

The time alignment is best done by experimentation. You can use pink noise http://www.moehrenbude.de/Moehre/mod...op=getit&lid=8 or a female voice to adjust the delay in an acoustical pleasing way.

In theorie there are some uncertainties. The speed of sound in air is much slower than in a cone for example. There are phase differences because of the frequency limits. And the overall frequency response is influenced by speaker, network and enclosure.

I did it twice when combining some cone drivers with a HF horn. It was not critical but clear for me (3000 Hz change over). On the basis of listening I made the decission for the placement of the horn - the mouth some centimeters ahead of the baffle.
__________
Peter

Hi Hoerninger and thanks,

If you are using pink noise (I have a generator in my RTA), can you describe what to listen for in doing the alignment? :o:

I have always had an idea how pink noise should sound (- maybe I have heard too much radio hiss in my youth by head phones ;) ). But I think it is an easy task to detect dips or peaks developed by two interferring speakers. You can shift one speaker as long as you want. If there is no difference then time alignment would be no issue - but it is. The only problem you will realize, your arms are too short from your listening position and a helper will soon be fatigued. (Some mechanical device could be helpful.)
__________
Peter

Altec procedure:

Wire the compression driver out of phase.

Move it back and forth for maxium dip in RTA at crossover.

Correct the phase connection of the compression driver.

Done.

Quote:

---

Originally Posted by Zilch

Altec procedure:

Wire the compression driver out of phase.

Move it back and forth for maxium dip in RTA at crossover.

Correct the phase connection of the compression driver.

Done.

---

Yea, that works.

Quote:

---

Originally Posted by scorpio

If you are using pink noise (I have a generator in my RTA), can you describe what to listen for in doing the alignment?

---

Any chance that device can measure Impulse? Listening for the subtleties with Pink Noise can be pretty trying - very subjective, IMO. And, the physical movements can be small, depending upon what is going on with your crossover(s). Better if you can measure the response, either as Zilch suggests, or using Impulse to quantify the difference.

No, all I have is a very basic RTA as part of a Berhringer 8024 - I am only using this to check response, not for 'correction'. It ain't capable of impulse.

I'll try the Altec procedure described by Zilch, even that could be a little difficult since this RTA is not very precise, and doen't have an averaged level, it's instantaneous, so it varies quite a bit, specially if I move around at the same time, but it should work. I don't think that I would personally be capable of noticing the difference in pink noise. I could probably hear differences, but certainly I couldn't tell what is the target to achieve.

Thanks all,

A simple phase inversion switch will demonstrate the difference, and it is huge.

Frankly, I often cannot tell which is "right" merely by listening, and have to see it on the RTA to know.... :dont-know.

Quote:

---

Originally Posted by scorpio

...since this RTA is not very precise, and doesn't have an averaged level, it's instantaneous, so it varies quite a bit, specially if I move around at the same time...

---

Yea, that's the tedious part of it. If your RTA has any Save memory, it is very helpful to take "snapshots" to compare to. If your RTA is on your laptop, you could do some screenshots, too.

Good luck - it's well worth it!

I followed the Rane ac23 manual when I set up my system,than fine tuned to my ear.in the picture(early design) I was using the 077's,than later changed to 075's.must say I liked the 075's better.when I designed the mounting board I put one of the 075's at ear level sitting,the other at ear level standing(5'10")adding about 8"-10" above the lens.I also moved the baffle board up to the very edge of the front of the cabinet,the lens hung over about 3".

Quote:

---

Originally Posted by jblwolf

I followed the Rane ac23 manual...

---

Here.Rane AC 23 manual

See my web site for a simple test procedure using a raised cosine test pulse. The tests pulses are used in the web site to test a Super Duplex crossover delay. They can also be used for other systems.
http://web.mac.com/donaldpatten
Don

That looks damned handy, Don - great presentation. Those are some great references for the Mac platform.

I too prefer using a pulse to align elements - the precision is much greater and there is real satisfaction in seeing the result of the applied delay on the wave forms. But not everyone has the means. Those products, however, bring the cost of entry down considerably, and DIY'ers should think about it. :yes:

You should also look at the Rane AC 24 manual.

Another concern that no one has mentioned...

I assume that you are referring to the big white horns in your avatar. If you start shoving these forward (to get the drivers in the same plane), you are going to have a big curved obstruction blocking at least a portion of the woofer and creating some spurious reflections off the back of the horn. This could be to the detrement of all of your hard work. :banghead:

Quote:

---

Originally Posted by toddalin

Another concern that no one has mentioned...

I assume that you are referring to the big white horns in your avatar. If you start shoving these forward (to get the drivers in the same plane), you are going to have a big curved obstruction blocking at least a portion of the woofer and creating some spurious reflections off the back of the horn. This could be to the detrement of all of your hard work. :banghead:

---

Yes, that's what it is, but if this becomes a problem, I'm thinking of building some sort of gantry to hang the horn to, this would also help me a lot in aligning the 2405 that you can't quite see on the avatar but is just sitting on top of the bass cabinet at the moment. This would also completely isolate these from the bass cabinet. I think I could even make it reasonably good looking. If I haven't done it yet, it's because of our common ennemy - time.

Thanks,