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  »  New  Macondo's Axioms: Horn-loaded acoustic systems..  No wonder...  Horn-Loaded Speakers Forum     72  399775  07-29-2007
08-17-2010 Post does not mapped to Knowledge Tree
KS
Posts 9
Joined on 08-07-2010

Post #: 1
Post ID: 14261
Reply to: 14261
Time alignment of drivers
fiogf49gjkf0d
Hey I read around here of the importance of time aligning drivers, and am trying to build it into my horn frame, but I'm starting to wonder, if tweeter frequency wavelengths are around and inch long, wont I completely loose any alignment if I sit half and inch forward of back in my chair? I've never noticed the music to all of sudden start to sound sound shite if I move back 1/2" in my chair with my previously time aligned speakers. I'd appreciate any enlightenment in this regard.

K.S


08-17-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 2
Post ID: 14263
Reply to: 14261
Aligning drivers vs shifting one's head
fiogf49gjkf0d
Try thinking about it like this: Moving your ears 1/2" closer to all drivers in the system is not the same as moving a single driver 1/2" closer to your ears.

jd*


How to short-circuit evolution: Enshrine mediocrity.
08-17-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 3
Post ID: 14264
Reply to: 14263
A little homework for everyone.
fiogf49gjkf0d
Yes, Jessie, in a way right – we align the summits to the same frequency from two drivers in the same period. Why he is right “in a way” in such case? Well, become in Jessie’s example there is an interesting hidden bug. I would like to offer everyone to looking at Jessie example and try to find the bug along with find out a way to deal with the issues. I will give a tip: the bug will manifest itself a bit different in context of Jessie’s playback and my playback.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-17-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 4
Post ID: 14265
Reply to: 14264
Closer to the bug ?
fiogf49gjkf0d
To save people from researching the differences between Romy's and my systems, I'll note the principal differences here, ignoring our ongoing mid-bass projects, which will be different, but both are incomplete, so not yet in the picture.

As concerns this discussion, the main differences would be as follows:
 
DSET amplification in Romy's case (in essence, a dedicated amplifier for each driver), vs essentially full-range amplification in my case, though I do use a second pair of amps for lower-bass. I don't see how DSET vs full range could make a major difference with regard to time alignment, but I'm ready to listen.
 
A very likely place for the "interesting bug" to hide would be in implementation of HF. Romy uses a custom-made ribbon driver, where I use a compression driver (EV T350) playing into its own small horn; easier to align with the other channels than a ribbon-type HF driver, which has a different dispersion pattern. This could be a clue... Yes, HF dispersion; I think this might be it.

Kitty-Bug.jpg
 
Another difference (and this could also be it) is in implementation of MF. Romy uses his main MF channel to cover most of the MF frequency range, then uses what he calls a "fundamentals channel" in a narrow bandwidth at the lower end of MF, with some attenuation (correct me if I've got that wrong). I split MF more equally between the two channels with no attenuation. It is logical that if I were to mess with alignment of these channels, the misalignment would be more apparent, as the lower-MF channels in my case are more easily heard, and need to be very strictly aligned with upper MF, and upper MF with HF; the whole lot referencing the upper-bass driver. 

Though used differently, our upper-MF channels consist of the same drivers and horns; S2 into 400 Hz tractrix. Romy's fundamentals channel uses an S3 into a 250Hz tractrix; my lower MF uses an S2 into a 180Hz tractrix.
 
Finally, Romy uses what he calls an injection channel (direct-radiating MF driver from Tannoy Red mounted in custom sealed enclosure) to inject tone and color into the presentation. I know this is not where the bug is hiding, but I'll mention it anyway. If I remember correctly, this channel is run with quite a lot of attenuation. I'm not sure exactly what frequency range it covers, but it uses a 10" driver, so it can only be lower-MF and below. I like to tell myself that my way of using the lower MF channel (and metal-suspended diaphragms) gives me the tone and color I'm looking for.
 
I could also cite Romy's direct-radiating mid-bass arrays, or my lower-bass enclosures, but the bug is not living in the LF world... There are many more differences (for example I listen to much better music than Romy), but none of these would allow the "interesting bug" a place to hide... I say he is living in difference between our HF drivers.

jd*


How to short-circuit evolution: Enshrine mediocrity.
08-17-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 5
Post ID: 14267
Reply to: 14265
Do not let yourself to be distracted with differences.
fiogf49gjkf0d
Yes, I implied the different between my and you tweeters that would make in my case the bug to be larger in amplitude. HOWEVER, even in context of ONLY my or ONLY your system the bug still exists, irrelevant to the fact that our systems have differences. BTW, you did not mention what you think the big is.


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-17-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 6
Post ID: 14268
Reply to: 14267
Naming the bug
fiogf49gjkf0d
Comb filtering in the HF/MF overlap?

jd*


How to short-circuit evolution: Enshrine mediocrity.
08-17-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 7
Post ID: 14269
Reply to: 14268
To remind the homework
fiogf49gjkf0d

Of cause the Comb filtering is there like in any reputed itself louspeker but it s not the problem that would manifest itself in your case. Remain you that “your case” was the following:

“Moving your ears 1/2" closer to all drivers in the system is not the same as moving a single driver 1/2" closer to your ears.”

The tip would be that in the acoustic systems that have the configuration like yours and mine the exposure to the bug will be particularly vulnerable. Reminding the homework:

1)      What is the bad

2)      Why Romy's system is more susceptible to the bug then Jessie's

3)      How to deal with the bug.

The caT


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-17-2010 Post does not mapped to Knowledge Tree
KS
Posts 9
Joined on 08-07-2010

Post #: 8
Post ID: 14271
Reply to: 14269
An experiment
fiogf49gjkf0d
I should have said UP or Down in the listening chair. Toward and away from the speakers will also do it, unless you're sitting midway between tweeter and mid of course, but not to the extent of up/down will.

I just did an experiment with some fishing line. Sitting about 12' away from time aligned driver where the tweeter is ±1.5' from the mid, if I move down in my listening chair by 2" I achieve perfect phase misalignment (i.e 180 out of phase) at my tweeter crossover point of 10k.

Can you guys hear these comb filtering anomalies if you slouch in your chairs?

As far as time aligment goes and delay goes, I came upon this (source unknown) which would seem to suggest tweeters need about a 2' offset before lack of alignment is audible:

Frequency Threshold of Audibility
8 kHz 2 msec
4 kHz 1.5 msec
2 kHz 1 msec
1 kHz 2 msec
500 Hz 3.2 msec


Comments welcome.
08-23-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 9
Post ID: 14289
Reply to: 14263
OK, about the “bug”
fiogf49gjkf0d
While a listener moves let say a few inches closer to an acoustic system like Jessie’s or mine then sh/e does not move closer to ALL drivers. Macondo is vertically piled up multiple drivers and when a listener head move closer to speaker then it most likely doe it at MF level. So, the distance to MF driver changes but the distance to other drivers is changing at different ratio. The image below explains it: The distance L1 in respect to the distance to MF will not be the same as the distance L2 in respect to new distance to MF. Now, continuing to play with homework work game, we have 2 questions left: why my Macondo is more susceptive to this then Jessie’s speaker and how to deal with this problem. 

Aproximation_Bug.GIF




"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-23-2010 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 142
Joined on 06-12-2009

Post #: 10
Post ID: 14292
Reply to: 14271
Time alignment of drivers and crossover slopes
fiogf49gjkf0d
I think clearing this up this may be of benefit to other users who are building multi-way horns.

Let's say I've got two horns mounted on a frame. There's a high horn above and a mid horn below and they are physically time aligned, meaning the magnets of the drivers are about at the same vertical axis.

I want to cross them over (either passive or active or line level passive) at 2kHz.

I want to try 6db/octave slopes and 12 db/octave slopes for SQ comparisons sake.

The sound wavelength @ 2kHz is about 7 inches. 6db crossover have a 90 deg. phase shift; 12db crossover have a 180 deg. phase shift.

And the QUESTION IS:
Switching between 6db and 12db crossovers slopes (and other slopes like 18 and 24db), do I also need to physically move the mid and high horns in relation to each other to have proper time alignment? Or should I leave the horns the way they are?

thank you,
Herman
08-24-2010 Post does not mapped to Knowledge Tree
jessie.dazzle


Paris, France
Posts 456
Joined on 04-23-2006

Post #: 11
Post ID: 14299
Reply to: 14289
Icarus & parallaxis
fiogf49gjkf0d

The presence of this "bug" is clear. Apparently your Raal tweeter is somehow making your system more vulnerable to the issue than mine. I'll refrain from guessing exactly why, as I'm not familiar enough with the dispersion pattern of this tweeter or ribbon drivers in general.

I have to admit that I have a kind of superstitious aversion to mixing driver types (that rely on different ways to generate SPL) especially across the HF/MF transition; this same aversion extends to filter slopes.

jd*




How to short-circuit evolution: Enshrine mediocrity.
08-24-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 12
Post ID: 14300
Reply to: 14292
Sorry, I do not get you.
fiogf49gjkf0d
 noviygera wrote:
I think clearing this up this may be of benefit to other users who are building multi-way horns.

Let's say I've got two horns mounted on a frame. There's a high horn above and a mid horn below and they are physically time aligned, meaning the magnets of the drivers are about at the same vertical axis.

I want to cross them over (either passive or active or line level passive) at 2kHz.

I want to try 6db/octave slopes and 12 db/octave slopes for SQ comparisons sake.

The sound wavelength @ 2kHz is about 7 inches. 6db crossover have a 90 deg. phase shift; 12db crossover have a 180 deg. phase shift.

And the QUESTION IS:
Switching between 6db and 12db crossovers slopes (and other slopes like 18 and 24db), do I also need to physically move the mid and high horns in relation to each other to have proper time alignment? Or should I leave the horns the way they are? 

Herman,

I completely do not understand what you ask. The physical aligning of magnets is absolutely irrelevant. The crossover slopes are irrelevant. Why would you need to do switching between crossovers slopes? All that you need to alight is the arrival time of the summits of two sinusoids in the same period. I think the best would be not just tell you how to do it (it was told many times before) but to encourage you to listed your multi-way with and with alignment and to learn what the auditable difference might be.

The Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-25-2010 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 142
Joined on 06-12-2009

Post #: 13
Post ID: 14304
Reply to: 14300
Clarification
fiogf49gjkf0d
 Romy the Cat wrote:


Herman,

I completely do not understand what you ask. The physical aligning of magnets is absolutely irrelevant. The crossover slopes are irrelevant.

OK.
 Romy the Cat wrote:

Why would you need to do switching between crossovers slopes?

I want to listen to both 12db/octave and 6db/octave passive versions and see which one sounds better. And keep the one that sounds better.
 Romy the Cat wrote:

All that you need to alight is the arrival time of the summits of two sinusoids in the same period. I think the best would be not just tell you how to do it (it was told many times before) but to encourage you to listed your multi-way with and with alignment and to learn what the auditable difference might be.


Let me clarify:

I am trying to move away from my DSP crossover to a passive crossover. Currently I have a DSP crossover @ 2Khz @ 12db/octave.
I will make two versions of the passive crossover: a 12db/octave and 6db/octave version. I have the capacitor and inductor values calculated.
So I need to know when I switch to the passive crossovers, do I also need to re-align the horns?  If so, would you recommend listening to the system and moving one of the channels (lets say the highs because it's easier to move) until the sound becomes coherent?
Then let say I switch the crossover slope, do I have to re-align them again?
The summits must be aligned at the listening position, right?

Herman

08-25-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 14
Post ID: 14307
Reply to: 14304
First vs. second order crossover and alignment
fiogf49gjkf0d

 noviygera wrote:
I want to listen to both 12db/octave and 6db/octave passive versions and see which one sounds better. And keep the one that sounds better.
Herman,

It depends what you would like to listen. If you would like to assess how a given driver/channel sound with first and second order then do not need to worry about time alignment for most of the cases. If you concern what happened with imaging and other fine element of channels performance then an alignment need to be done.

 noviygera wrote:
I am trying to move away from my DSP crossover to a passive crossover. Currently I have a DSP crossover @ 2Khz @ 12db/octave.
I will make two versions of the passive crossover: a 12db/octave and 6db/octave version. I have the capacitor and inductor values calculated.
So I need to know when I switch to the passive crossovers, do I also need to re-align the horns?  If so, would you recommend listening to the system and moving one of the channels (lets say the highs because it's easier to move) until the sound becomes coherent?
Then let say I switch the crossover slope, do I have to re-align them again?
The summits must be aligned at the listening position, right?

OK, I see now. a few things you need to consider. 2Khz @ 12db/octave is not the same as 1Khz @ 6db/octave filter of the 1.5Khz filter. Then might be mathematically would give you the same cut off but my experience indicate that each driver/enclosure have own reactance to those changes. There are many variables in place here, and it the cheval is horn-loaded then there are even more variables.   Then there is more complexity. When you get to second order filters then the question is what kind filter it would be. Bessel filter have constant phase and very much resembles the first order filter but with faster roil off. However you will be able to write Bessel profile only if you have fixed load impedance or if you use passive line-level filtration. If you filter at speaker level then the impedance will be running in there wild and only God knows what kind filter Q will be effective at any given moment. You might find it noticeable or not, however.

When you switch from one filter to another then you misalign your channels, even if you move your filter a few cycles up or down you misalign your channels and you need to do it again. You do not need to ask me. Whatever method of time aligning you use – pulses or RTA it will clearly indicate to you that any change of crossover set channels in misalignment. Yes, you need to align at the listening position but do not go overly crazy over it as at the most parts you shall be able to make judgment about first vs. second order just by listening approximately-aligned delivers. After you make the decision, then you fine-align them.

BTW, you shall be able to make a decision about the first vs. second order crossover base upon use of your DSP crossover. That is what the DSP crossovers are very good and comfortable for.

Rgs, Romy the Cat


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-25-2010 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 142
Joined on 06-12-2009

Post #: 15
Post ID: 14310
Reply to: 14307
Will get to work on it.
fiogf49gjkf0d
Romy,

Thank you for constructive suggestions, they will be very useful tonight. I am slowly getting the hang of this system tuning and observation approach that you advocate.

I do not have separate identical amps (or one multi-channel) for separate speaker sections yet. So that is why I want to start with a passive speaker lever crossover. Then to get the proper amps and switch to a line level crossover. So far I use different amps with my DSP, none of which are particularly good.

Best regards,
Herman
08-25-2010 Post does not mapped to Knowledge Tree
Romy the Cat


Boston, MA
Posts 9,538
Joined on 05-28-2004

Post #: 16
Post ID: 14314
Reply to: 14310
Beware of the highpass caps
fiogf49gjkf0d
OK, good luck with your experiments. Be advised however that if you use capacitors for high-pass speaker lever crossovers then those caps need to be aged. The amplitude of this effect wary from cap to cap but  all of them in one way or other would need a good week or two to be able to performer at their max quality, So, do not make any concussions immediately.
 


"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche
08-25-2010 Post does not mapped to Knowledge Tree
noviygera


Chicago, IL
Posts 142
Joined on 06-12-2009

Post #: 17
Post ID: 14316
Reply to: 14314
Capacitors
fiogf49gjkf0d
Ok, understood. By the way, Dayton Metallized Polypropylene capacitors are fine for this experiment right? I don't have to buy expensive ones just to have a good idea of the passive crossover sound quality? I hope not.

-Herman
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