A Question About Time Alignment

You are correct, all frequencies being played travel at different speeds to your ears

BS

they travel at very different speed so the higher sounds need to be delayed and the lowest played first

BS

This is like high school science stuff.

If it it did work like you say, then the lightening bolt would a crack and woofer notes arriving later. But roll of thunder is more likely stuff we cannot see happening above the clouds.

Related is the issue of keeping your speaker wires the same length. The lengths we use are very small relative to signal speed, but, I still follow the rule. Makes a big difference using expensive cable.

I am pretty sure that the speed of sound is relatively constant at a given temp.

The speed of light is also a constant, and the speed of electricity is usually a bit slower than the speed of light for most cables.

The main reason to keep the cables the same length is more for resistance and the other electrical parameters like inductance and capacitance.
It has nothing to do with the shorter cable getting the sound to the speaker faster, slower or at an equal speed as the longer cable.

Time Cohesion is making sure that the sound from the tweeter gets to your ears at the same time as the sound from the woofer. Lets say theres a piano sitting 10 feet in front of you and a cello sitting 6 feet in front. The sound of the cello hits your ears faster than the sound of the piano. Its the ratio of the speed that needs to be conserved by the speaker. This can only happen if the time cohesion is tuned perfectly. 

The master has spoken.

Not exactly… master.

If the piano and the cello are playing the same note, or using a full range driver, then they are already tome coherent from a single driver.

And the cello will still arrive 4 msec before the piano.

If it is a piano playing many notes then we want them all to be time coherent with each other. That is a harder to do with multiple drivers, but pretty common these days.

There is no “ratio of speed”, as the speed of sound is the same for cellos and pianos.

The time it takes for the low notes to arrive at your ears is slower than the highs no t because they are inherently long but because the voice coil of the woofer is mounted behind the baffle whereas for the tweeter it is mounted almost about the same level as the baffle hence the tweeter is closer to yours ears than the woofer.

Maybe instead of “slower”, do you mean “delayed”?

The former is speed/velocity, and later seems more like time/distance.

in colloquial speech fast or slow refers to time. For example fast food refers to food that is prepared quickly. There is no mention of distance in that.

@kenjit but we’re not talking about cables being like a pizza, or how quickly KCF gets a bucket ready.
It started off with time alignment, and then went towards the speed of sound… so it seemed like a technical discussion rather than a colloquial one?

 

Monopulse Loudspeakers here in the UK have made this time alignment issue their main selling point for decades.

The designer Allan Hendry has been stating that impulse precision is hard wired into our evolution for survival itself and thus it’s importance cannot be overstated.

Everytime I’ve listened to Monopulse speakers they did seem to be easy on the ear, very listenable for long durations. That led me to also wonder whether they are onto something.

If so, does that mean most others aren’t?

http://www.monopulse.co.uk/

Technically having a good impulse response means having higher fidelity.

There many speakers that do it, but it is easier to have speakers that may not be so good.

@hifidream Steve, your post was great except for the velocity being a function of the frequency.

I can see how one might think that the velocity is a function of frquency as t links like this show v = freg * wavelength

let’s just round off the speed to 1 foot/millisecond.
And at a 1000 feet away the 1Hz takes a second to travel it.
what amount of time does 20Hz take to arrive?
And what amount of time does 20kHz take to arrive?

I have no doubt you MiniDSP sound good, and I suspect that the tweeter to woofer delays are on the order or inches or fractions of a millisecond.

if the speed was a function of frequency the the lightening crack would sound like a descending chirp from 20KHz down to 20Hz.
But it doesn’t, we see the lightening and we hear the crack a bit later. When it is so close that it is almost simultaneous our we also tend to crap our britches.

Lets get back to the OP’s question.

It seems to me, however, that live music isn’t time aligned. Suppose I’m playing the piano and you’re sitting across the room. When I stretch out my left hand to hit the low notes, those notes travel along the same long, slow wavelengths as the notes from Wilson’s woofers. Similarly, the treble notes I play with my right hand move quickly through the short wavelengths. The notes from the piano are naturally out of alignment.

There is not “slow and quickly” happening as the frequency changes.
The notes all travel at the same speed across the room.

If the woofer and the tweeter are both involved, with say a note in the middle of the cross over, then we want both of those to be launched so as to arrive at the ears in unison.
Hence this is fractions of an inch or a few inches at most.

One usually either steps the speakers spatially, or with a tilt, or uses a DSP to align them electrically. And each sample of a 44.1 kHz signal is roughly a 1/4” from the previous or next sample.

Don't move your head even one inch while listening or your whole time alignment will be off.

I’m more worried about my chakras being aligned… 😋

Would it be correct to say that some form of time alignment starts at the source?

@4krowme no. Microphones and electronics generally close to perfect.

The speaker dominates time and phase alignment by orders of magnitude compared to everything else.