# Time and dispersion



## oabeieo (Feb 22, 2015)

I don't want to start a topic to sit on the boards as a useless topic. So I'll do my best.

Since the onset of dsp and the control over the signal has much improved over the last 10 years horns haven't changed. The design of the horn doesn't call for any time correction between each other ( left delayed against Right). 

I've tryed both sizes of horns and always had a much wider sound when there is no delay against each other. Being the ends of the drivers are where most the energy is directed and the ends are argueably the same PLD or only a couple inches diffrent from left horn to left ear and right horn to right ear. So upon that principal I've never seriously used delay to try to overcome any time diffrances. When there's no delay the sound from both sides is wide and deep. The center is formed by the close proximity of the ends of the horns and usually stays smack dab in the middle between them. 

Now if I use a tape measure and measure from the ends I get a PLD of about 4".
If I apply 4" worth of delay the high vocals (about 2-4k) range come much more pin point center. But as I add delay the width begins to compress as well (Below 2k especially) Sonically no delay sounds more correct. 

I've heard some say a few inches of delay is OK and some say don't use it and it's a eq problem. 

So my question is; if it is OK to use delay , how much and under what circumstances, and why? Or , should delay between horns just not be done because it messes with its dispersion (which is noticeable)? 

Does horn axis have any play in this or is it more a crossover reigon thing? Like bringing the horn crossover up high enough so wavelength is short to better manage time via amplitude. Or does having the horn more off axis worsen time and phase? Should horns be pointed slightly upwards in some cases, or one pointing slightly up and the other level of even pointing slightly down? We have all experienced the right horn give it self away issue would pointing it downwards a couple degrees make sense? 

I realize there meant to work off axis , and being there not ever going to be completely perfect PLD there's going to be a polarity flip at x frequency. Should time controls be used to help critical polarity flips? of course frequency and PLD decides what band the flip will be which is why some of us run out horns above 2k. or is reversing the speaker electrically still the best option for those circumstances. 

Is there a device passive or active that has the ability to flip polarity only at a passband and flip it back otherwise? 

Overarching question , is a deviation from the reccomended mounting and setup ok or should that stay a constant and use good ole fashion eq and polarity to fix responce and phase incoherencies and whatever limits the eq controls have is what your stuck with?


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## thehatedguy (May 4, 2007)

An all pass filter will change phase at a certain point that you define.


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## oabeieo (Feb 22, 2015)

thehatedguy said:


> An all pass filter will change phase at a certain point that you define.




Okay you got my attention. How could I define that passively so I can tinker .

Let's say a flip at 800-1k with a wide Q


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## oabeieo (Feb 22, 2015)

A passive 12db high pass set a oactave below the active hp should get me 180° of rotation , the low pass side is confusing, if I built a low pass at 20k it would give e 180 degrees rotation on wrong side of filter. And I want to rotate it back around 2k 


Maybe two resistors in series with a cap and coil in parallel


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## thehatedguy (May 4, 2007)

They are a PITA to do passive.


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## T3mpest (Dec 25, 2005)

Personally for me one click of my t/a put my horns back in phase I was not afraid to do that. When setting T/A I'd time align it to the mids and then confirm phase at the xover point. If it was off, I'd back it forward and back one step and see if either of those fixed the phase issue. 

In my last install I remember horns out of phase with one another sounded the best.


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## sqnut (Dec 24, 2009)

The need to time arrival does not vary with the types of drivers you use, timing is timing. Horns don't need less TA for a given PLD than say normal cones. I'm not sure how even a kick panel install can give only a 3-4" PLD between L&R, but a 4" PLD means the sound from the near horn would arrive 0.3 m/s before than that from the far side. The ear is sensitive down to 0.01m/s and beyond when it comes to timing difference. A 0.3 m/s difference is more than sufficient for the precedence effect to kick in, and pull the image towards your side. You're definitely not getting a wider stage

TA drivers does not narrow the width. For any given install configuration, the max perceived width comes when you have the timing and response balanced for L&R.


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## Eric Stevens (Dec 29, 2007)

I have been using delay since 1995 in my Sable. It was only on the left and right in the EQ but it has always helped to improve the image focus. I found it best to use it in small amounts to improve the phase rather than delay to align left to right. So I would everything as good as possible then use the delay to further focus the images. Always i was in the .2 to .5 Ms range with a PLD of I think 11" in the Sable.


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## oabeieo (Feb 22, 2015)

Eric Stevens said:


> I have been using delay since 1995 in my Sable. It was only on the left and right in the EQ but it has always helped to improve the image focus. I found it best to use it in small amounts to improve the phase rather than delay to align left to right. So I would everything as good as possible then use the delay to further focus the images. Always i was in the .2 to .5 Ms range with a PLD of I think 11" in the Sable.


Thank you for confirming my doubts .


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## oabeieo (Feb 22, 2015)

sqnut said:


> The need to time arrival does not vary with the types of drivers you use, timing is timing. Horns don't need less TA for a given PLD than say normal cones. I'm not sure how even a kick panel install can give only a 3-4" PLD between L&R, but a 4" PLD means the sound from the near horn would arrive 0.3 m/s before than that from the far side. The ear is sensitive down to 0.01m/s and beyond when it comes to timing difference. A 0.3 m/s difference is more than sufficient for the precedence effect to kick in, and pull the image towards your side. You're definitely not getting a wider stage
> 
> TA drivers does not narrow the width. For any given install configuration, the max perceived width comes when you have the timing and response balanced for L&R.


Yeah horns are a bit diffrent. 

If I measure from motor to motor it's about 12"PLD , however the horn bodies are exactly the same so it's safe to discount the distance inside the horn and use the exit to measure PLD . The part of the exit that has the most energy is the end of the horn torwards the middle of car, if I measure left ear to right side of left horn and right ear to left side of right horn PLD is only 4" . 4" subsequently dialed in on the TA makes center pop out perfectly. 

whats wierd is when TA is added a lot of ambiance and width gets eaten up. 
And it's done this on more than one install.

I really been trying understand how to ajust the horns so there isn't a polarity flip below 2k. PLD makes up part of the reason but I dare to suggest diffrent axis at listening position has some rule over it as well. I want to explore more into maybe moving the driver side horn point towards me and passanger side torwards the floor to even out responce a bit that way being there so cross firing it might get us to where there won't be a need for reversing a horns speaker wire.


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## SPLEclipse (Aug 17, 2012)

I think Patrick Bateman wrote in one of his posts that the apparent point source of a horn will be further back in the throat for higher frequencies and further into the mouth as you get lower in frequency. Considering that phase alignment becomes more important as you go lower in frequency, this could be why your TA numbers are what they are.


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## thehatedguy (May 4, 2007)

Sounds like Eric was doing more to mitigate the group delay in the XO at the XO points.


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## oabeieo (Feb 22, 2015)

SPLEclipse said:


> I think Patrick Bateman wrote in one of his posts that the apparent point source of a horn will be further back in the throat for higher frequencies and further into the mouth as you get lower in frequency. Considering that phase alignment becomes more important as you go lower in frequency, this could be why your TA numbers are what they are.


My TA numbers are non existent and sounding good.

So I'm not sure what your saying. But I'll take a stab at it, yes the lower frequency goes the more the mouth shapes the wave front.
I was curious more about the axial responce of the horns together. 
The driver side seems to be more off axis than the passanger , from the drivers seat. I was wondering if slight adjustments to the tilt (not the tow) of the drivers can help get the polarity flip at lower frequencies back or more in phase throughput the entire bandwidth. 

I was reading about geddes horns having a hole on axis and how folks were tilting them to get them to play right and a bell went off. What if we play with the tilt? I thought I would ask before I go playing around with mounting. 
I'm sure it's been explored , that's why I asked


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## oabeieo (Feb 22, 2015)

thehatedguy said:


> Sounds like Eric was doing more to mitigate the group delay in the XO at the XO points.


That's basicly what I understood as well. And it works, 
Seems if you take TA past a certain point the cross fire gets screwed up.


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