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Multi-Way Conventional loudspeakers with crossovers

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Old 21st October 2012, 12:24 PM   #401
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Quote:
Originally Posted by buzzforb View Post
......but should have good transient attack and clarity in midbass, which most people are talking about when they talk about bass
Yup! Thats what I think of as accuracy

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For the horns, i am choosing Iwata, becaus ei can diy one failry easily and will basically amount to cost of wood and time. Jmlc vs tractric is just a decision. Kohlbreck, the guy who measured the jmlc for lynn, is now listening to another horn. That tells me that the jmlc is not the undisputed end of th eline. Also, i fyou look at the ETF article i linked, while the JMLC and Kulwegen horns measured well, they were not chosen first in terms of sound. Go figure.
'just a dicision'?????? Its driving me loopy As for someone listening to something else........I wouldn't read that much into it. Going on the general populace of DIYAudio changing 'is just something we do' - sometimes changing up, sometimes down, and sometimes sideways!!!

As for the results/measurements they are interesting but as the competition was of different CD & horn combinations, none of which I'll probably ever own, it goes to prove nothing is, or should be, decided by measurement alone. As you said - Go figure!!

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Truth is, we won tknow till we try
Amen brother, amen
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Old 21st October 2012, 05:07 PM   #402
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Align the coils.
That will get you close. Then align the phase.
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Old 21st October 2012, 07:00 PM   #403
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It goes without saying that to align the voice-coils sounds like the right idea as far as time alignment is concerned, but that is only part of the story. While that approach seems simple enough in the end you have to look at what you have created by doing that. Think about that horn lens or waveguide sticking out in front of a bass driver directly below the waveguide. You have now created a large physical surface that is quite irregular in shape usually on top of the bass driver that the mids and lows are now going to reflect off of. The reflective properties of a waveguide hanging out there like that are going to be a real problem if you look at this as a reflective surface and not just as two completely disconnected devices. You won't have problem with the high frequency response as it is unaffected but you surly will with the lower frequency dispersion. If things were only simple things could be done so easy. In today's active electronic arena it would seem that it would actually be smarter to use a simple time delay to align the two acoustical centers rather than to physically move the waveguide forward to align the voicecoils which could be anywhere from a few inches on a short waveguide to almost a couple of feet with a long horn.
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Old 21st October 2012, 08:20 PM   #404
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Thanks guys

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Originally Posted by Pano View Post
That will get you close. Then align the phase.
How would one go about ascertaining the phase difference?

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In today's active electronic arena it would seem that it would actually be smarter to use a simple time delay to align the two acoustical centers rather than to physically move the waveguide......
That all makes sense. So with the CD behind the mid/woof, how do you go about ascertaining the delay needed to time align the drivers? I assume (again!) that you time align the CD to the mid/bass - don't know why, I just do
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Old 21st October 2012, 08:23 PM   #405
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How would one go about ascertaining the phase difference?
when you begin to feel uncomfortable and like getting sick
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Old 21st October 2012, 08:36 PM   #406
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I haven't drunk THAT much in years
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Old 21st October 2012, 09:22 PM   #407
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For phase you just have to measure. HOLMImpulse is a handy way to do that.
But you do want to know what the phase of your particular acoustic roll-off should be.
You can do the same looking at the impulse.
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Old 21st October 2012, 10:07 PM   #408
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Here is an example of how I do it with HOLMImpulse.

Let's suppose that you've built a crossover where the acoustic slopes (important, acoustic!) end up as 4th order Bessel at 800 Hz. What would the response, phase and impulse of an ideal Bessel 4th order look like? You can see them in the graph below.

You will notice that LP impulse peak lags the HP peak by 20cm. If your drivers don't measure like that, they are out of alignment/phase. On this graph the impulse is in dB mode, otherwise you'd hardly see the LP peak.

When I first started doing this I made the mistake of trying the line up the LP and HP impulses. Phase was never right doing that. One day it occurred to me to see what an ideal filter would look like - and that's what you see below. Of course real speakers are rarely that ideal, so you have to fudge, tweak and use your judgment. It's not all that difficult.
Attached Images
File Type: png bessel-4th-800.png (39.5 KB, 343 views)
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Old 22nd October 2012, 08:07 AM   #409
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thanks Pano.

So i'll need a mic and HOLMImpulse.

My crossover understanding is limited as I've only used 1st order.

I know that 1st order = 6db/octave - phase unchanged? 2nd order = 12db/octave - phase 180? 3rd order = 18db/octave - no idea! 4th order = 24db/octave - no idea! I understand low-pass, band-pass & high pass.

I've also been reading up on active vs passive & the 3rd way - PLLXO

Pano, you mention 'acoustic slopes (important, acoustic!)'. Dumb question I'm sure, but why do you highlight acoustic slope?

tnx for the help
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Old 22nd October 2012, 08:27 AM   #410
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My crossover understanding is limited as I've only used 1st order.
unfortunately passive xo and compression drivers are like oil and water
I fear you will get into trouble with that, and see no other way for you than going active
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