Yup! Thats what I think of as accuracy
'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!!
Amen brother, amen
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.
Thanks guys
How would one go about ascertaining the phase difference?
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
How would one go about ascertaining the phase difference?
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
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.
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.
Attachments
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 180º? 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
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 180º? 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
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
impedance interfere with passive xo, and changes its function and resulting response, phase etc
and compression driver/horn combo is even worse, with multiple impedance ressonance peak
active is at least free of those speaker impedance issues
still have to deal with acoustic response tho
I guess those problems might have made the CD's bad reputation of sounding very harsh much worse than it deserves
and no doubt it will sound unbareably harsh if the xo is not functioning properly
on the good side, I don't think you need any fancy amplification for a CD
probably a simple low power chip amp will do fine, and be very simple
the remaining other drivers might still work with relatively simple passive xo
tnx tinitus.
So the passive crossover is passive in both directions - subject to the drivers impedance anomalies - just because it is designed to give the correct crossover freq. & slope , it may not due to the driver attached.
An active crossover is essentially line level (before amplifier) and not subject to driver feedback, stamping its exact filter upon the signal before amplification with no speaker level interaction.
This should also be true of a PLLXO?
So the passive crossover is passive in both directions - subject to the drivers impedance anomalies - just because it is designed to give the correct crossover freq. & slope , it may not due to the driver attached.
An active crossover is essentially line level (before amplifier) and not subject to driver feedback, stamping its exact filter upon the signal before amplification with no speaker level interaction.
This should also be true of a PLLXO?
Yep, this is the case AFAICT. I've tried both PLLXO and active via mini-DSP and it's much better than passive speaker-level Xover, at least at my design skill level.
IG
Altec all the way buzzforb?
The 288 is a 1.4 incher if I remember correctly. I read (http://alteclansingunofficial.nlenet.net/publications/techletters/TL_231.pdf) that the 288 starts really dropping of around 15k.
Response graph shows big drop. Are you going to prop it up with a s/tweeter or EQ the hell out of it?
be interested to see you construction of the iwata!
The 288 is a 1.4 incher if I remember correctly. I read (http://alteclansingunofficial.nlenet.net/publications/techletters/TL_231.pdf) that the 288 starts really dropping of around 15k.
Response graph shows big drop. Are you going to prop it up with a s/tweeter or EQ the hell out of it?
be interested to see you construction of the iwata!
Depends. I will probably allow for super tweet or small horn in design. May not need it. Prefer as little EQ as possible, but will do what is necessary. Here is my thread if you want to drop in. Ill stop polluting yours. Hurry up and get something. Its a build off!
Be forewarned. Lots of screwing around
http://www.diyaudio.com/forums/multi-way/221111-horn-tl-combo-7.html#post3211568
Be forewarned. Lots of screwing around
http://www.diyaudio.com/forums/multi-way/221111-horn-tl-combo-7.html#post3211568
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