52 replies to this topic

[muzzy66]

Ahh, I thought you mean't don't need to T/A tweeters, becuase you can't identify timing on high frequencies - i getchya now!

As for moving the tweeter back for 'physical' time alignment (e.g. the Focal's), couldnt wavelength potentially be a factor?

I know that according to theory sound waves all travel at the same speed, however because low frequencies have a longer wavelength could this possible result in the low frequency reaching your ear before the high frequency does, even though they travel at the same speed?

For example, if you have a 10cm pole and a 1m pole heading towards you next to each other at the same speed, in theory the longer pole may hit you before the short pole does.

If sound signals worked in a similar fasion, could it be possible that the wave with the longer wavelength could reach your ear before the wave with the shorter wavelength, despite them travelling at the same speed - hence requiring extra distance applied in order to reach your ear at the same time?

Edit:

Just thought about it, and the results of the above 'pole test' would be dependant on the alignment of the poles. If they are aligned by centre (i.e. midpoint of one pole side by side with the midpoint of the other pole) then the longer pole would hit you first. However, if they were alligned by the front of the pole (i.e. front of one pole lined up with the start of the other pole) and launched at the same speed, they would in fact reach the target at exactly the same time (assuming everything else including speed is consistent).

Therefore, assuming speed is the same, the only thing determining which pole reaches the target first would be the initial allignment of the poles.

I assume that metaphorically, this whole 'alignment' of the poles is equivelent to the 'phase' or a sound wave.

If the longer wave and shorter wave leave the speakers at the exact same distance and the same time, they will essentially be in phase (moving side by side) and reach the listener at the same time.

If the longer wave is closer then the shorter wave (by say, 1cm) when fired, and they are fired at the same speed, then the waves will be slightly out of phase and the longer wave will reach the listener first.

Just had a uni assessment so my brain isn't all there, but am I somewhere along the right track at all?

[BMWTurbo]

muzzy66, on May 12 2008, 12:51 PM, said:

There isn't any need to delay the furthest away driver, because it's already the furthest away!

Sorry, I should have clarified that.. I meant all bar the 'furtherest' driver can use some TA, no point in TA'ing ALL including the furtherest as you'll only be offseting.

Edited by BMWTurbo, 12 May 2008 - 02:16 PM.

[SCorpion]

muzzy66, on May 12 2008, 01:41 PM, said:

snip

a driver only puts out one continuous wave. this wave consists of all the different frequencies that occur @ that instant in time.

SO, if i could build a driver that played every frequency, then there is no way the long wavelength could reach the ear before the short wavelength could because that would imply that there are two wave's with two different speeds.

one driver = one wave.

2 drivers = 2 waves.

so if we have 2 drivers then we need to ensure that the ear recieves 1 wave. so what we do is if there is one driver creating one wave closer to the ear than another driver we would then move the driver so that they are both aligned. suppose the drivers location is fixed, we electronically move the wave back so it aligns with the other driver. so the closest driver plays @ the exact instant in time that the wave from the furtherest driver passes the closest driver.

this is different to 'time alignment' due to crossovers etc. that was explained above

[~thematt~]

Be careful with that one wave statement Scorp, you'll confuse a lot of people!!

One wave, yes, but its actually not REALLY one wave at all. Its a combination of many waves, that are interacting with each other (and yet not interacting....). Visually, it is seen as a single wave.

And the pinnae is used more for vertical height cues then horizontal, still very important, but not as much so, given the fact that we developed through evolution as horizontal hunters as opposed to vertical ones (like birds).

Those frequencies, like mentioned, are related to their wavelengths, and its this length that becomes important. At 2kHz, the wavelength is 17cm, which is about the distance between ones ears. At 4kHz, that same wavelength becomes 8cm. This simply demonstrates that a wavelength makes a full cycle between one ear to the other, so phase differences are too obscure (as the phase can be anywhere up to 360 degrees out).

You'll actually find that localisation cues around 1.5 to 3kHz are very poor. There isnt really any dominant localising feature here, but as you get lower ITD's dominate, and as you get higher IID's dominate. However, when you combine the fundamental (below 1-1.5k) with its HOMs (above 3-4k) you can quite effectively shift localisation due to a combination of both at once (IF the reproduction is musical in nature - because of the natural ability of an instrument to have modes).

A tweeter though, isnt designed to play fundamentals. It has no suspension. Its a HOM unit, designed from the ground up to reproduce harmonics. Its ability to play into the ITD zone is very poor, because the distortion levels are too great, and if you use it properly, the crossover will be quite high. High enough to limit (or completely null) the effect of ITD's.

[SCorpion]

~thematt~, on May 12 2008, 04:18 PM, said:

Be careful with that one wave statement Scorp, you'll confuse a lot of people!!

probably. its how i think and that seems to confuse ppl, including myself

Quote

And the pinnae is used more for vertical height cues then horizontal, still very important, but not as much so, given the fact that we developed through evolution as horizontal hunters as opposed to vertical ones (like birds).

actually, i think ill go and re-try my pinnae test with a 10kHz tone outside to see if i can still localize it with one ear.

if i can, my theory will fit the explanation a lot better than the IID theory.

[Matt VIP]

real-world testing Scorpion?

not round here thanks mate...

[zion187reigneth]

i helped a dude TA his 4wd one day at the local shop and we changed the phase on the tweets using his HDX2, it produces a large noticable difference.I can change the phase on mine now and i cant tell.One thing i do notice when TA the tweets is vocals and how the lower voice and higher voice can be out of time.If u delay the tweets enough the vocals brighten up.

[MaFi0s0]

I need some help with TA.

Here is my situation, my TA goes only by 5cm steps, my midbass drivers are in the doors below the tweeters, and my tweeters are in the doors where the sideview mirrors are, one of my issues is I dont think I can TA the tweeters and midbass drivers separately.

I am not sure if I am ment to get the center infront of me or in the middle of the dash?
Anyway if I get it infront of me I notice the soundstage is low, if I get it in the middle then I get a higher soundstage but I feel as though everything is off to the left.

I have a problem with balance aswell, I have found that when I play pinknoise in the left and right speakers separately it is actually louder on the left even though my balance is neutral(vocals and hihats etc seem pretty much normal, it is only with pink noise)

I have come across so many inconsistencies which I put down to the acoustics and also the inability to time align the mids and tweets seperatly that it is making it hard for me to find out what is optimal at all.

My 2nd question, Should I time align my tweeters or mids? and what sound frequency or samples should I be using(treble, female vocals, male vocals, midbass?) Marty uses a female vocal but personally I find it more annoying for the beat to be off than the vocals.

I hope everything I said makes sense.

Edited by MaFi0s0, 19 August 2008 - 07:35 AM.