Timing Measurements

[Chris A]

I wonder how audible a 4.8 ms delay is?

It's a real miracle how once something is confirmed through measurements it becomes "painfully" audible to some folks..

If you look at the bottom of the third page of the now-famous Richard C. Heyser review of the Khorn from 1986, the effects of the time misalignments of the three drivers (bass bin, midrange, tweeter) are described in terms of the disturbances in subjective listening tests.  Heyser of course was the initial proponent of ETC and other time-based tests of loudspeakers.  Those new tests enabled understanding of what human ears already heard but couldn't identify the causal factors to be:

https://community.klipsch.com/index.php?app=core&module=attach&section=attach&attach_id=36543

I find that once the time misalignments are corrected, there is a timbre shift of the speaker--for the better.  It's easily demonstrated using the Dx38s on my Jubilees and on the center tri-amped Belle in my room.  It's not subtle (to my ears).

Edited August 19, 2014 by Chris A

[jcmusic]

I wonder how audible a 4.8 ms delay is?

Craig

I have confirmed the delay with a measurement but I can't hear it. Now I can for sure hear the difference in the sound quality since aligning the mid and tweeters. The difference is huge.

It's a real miracle how once something is confirmed through measurements it becomes "painfully" audible to some folks..

[jcmusic]

My math tends to be terrible, but I think at 400Hz (going from the woofer to mid, you are almost two cycles behind the mid, with one wavelength at 2.5ms.) 

 

The difference between the mid and tweeter is far more critical, as the wavelength at 4500Hz (newer Khorn crossover freq. between mid and tweeter) is a fraction over 3 inches. If the tweeter were placed on the top of the cabinet and moved to the back of the cab to line up with the K55, you can easily tell when they are lined up.

 

Bruce

Bruce

That is exactly what I did except I used REW to measure to get the timing exactly correct.

[Rudy81]

In all honesty, I'm not sure I can tell when my drivers are aligned or not.  I have not spent time trying to discern the difference.  In measuring the alignment at the crossover frequency, there is clearly a db loudness difference as well as a difference in phase when not aligned.  

I have been happy just aligning the LF and HF drivers only.  My SPUD clones and RSW-15s are considerably slower than my mains and I'm not willing to push back my mains (in time) far enough to match the subs.  

I would suppose a truly discerning listener would be able to tell the difference.  I'm not one of those.

[CECAA850]

I have been happy just aligning the LF and HF drivers only. My SPUD clones and RSW-15s are considerably slower than my mains and I'm not willing to push back my mains (in time) far enough to match the subs.

I'd think changes would be more noticeable higher in the spectrum as you've noticed.

[mark1101]

How do you use REW to "measure" the required delays?

[Chris A]

BTW: I believe that the timbre shift heard when time misalignments are present--is due to "zero lobing error" (scroll down to the section on "Time or Phase Correction").

Mark, I believe that deconvolution to produce an impulse response from an up-sweep within REW (the "impulse" view) will give you a time delay - and if the sweeps are done separately for each driver, a characteristic time delay is determined, as long as the microphone position and room temperature both don't change.

I calculate the path length difference from the bass bin to the midrange, and the midrange to tweeter (for a 3-way loudspeaker), then plunk those into the channel delays for the midrange and tweeter channels (typically).  When I run REW up-sweeps using the FR and phase view, I can see the remaining phase misalignment between the two horn/drivers.  I can then fine tune the delays by varying each delay one at a time, then look at up-sweep FR and phase to eliminate the FR dip at crossover and minimize the phase disruption by looking at the un-smoothed phase curve: and it works like a charm.

Edited August 20, 2014 by Chris A

[Rudy81]

I have been happy just aligning the LF and HF drivers only. My SPUD clones and RSW-15s are considerably slower than my mains and I'm not willing to push back my mains (in time) far enough to match the subs.

I'd think changes would be more noticeable higher in the spectrum as you've noticed.

My XO between the LF and Oris driver are set near 200Hz, so maybe that is why I cannot detect the difference by ear.  However, the difference is clear when using REW to check the phase alignment and/or sound level at the XO point.

[Ski Bum]

how would you know when it was in the correct position anyway?

whenever I see aftermarket tweeters sitting on top of cabinets, they are always towards the back  of the cab... tell tale?

Schu,

Yes towards the back because the idea is to vertically line up the voice coils. The sound stage opens up and everything kinda clears up because there is less smearing of the sound.

What about the resulting comb filtering?  Mounting the tweets in such a way, firing across a reflective cabinet top, has quite audible effects, and none good IME.  

[Marvel]

What about the resulting comb filtering? Mounting the tweets in such a way, firing across a reflective cabinet top, has quite audible effects, and none good IME.

I could never hear it on my LS tops. I tried different materials on the top and found, to my ears, no discernible difference.

Bruce

[jcmusic]

Well I have room treatment and honestly I have not heard any negative effects. The sound has gotten a lot better clearer and the sound stage has gotten much bigger.

[mark1101]

BTW: I believe that the timbre shift heard when time misalignments are present are due to "zero lobing error".

Mark, I believe that the deconvolution integral to produce an impulse response from an upsweep within REW (the "impulse" view) will give you a time delay - and if the sweeps are done separately for each driver, a characteristic time delay is determined, as long as the microphone position and room temperature both don't change.

I calculate the path length difference from the bass bin to the midrange, and the midrange to tweeter (for a 3-way loudspeaker), then plunk those into the channel delays (midrange and tweeter channels).  When I run REW upsweeps using the FR and phase view, I can see the remaining phase misalignment between the two horn/drivers.  I then fine tune the delay by varying the delay and looking at upsweep FR and phase at the crossover points to eliminate the FR dip at crossover and verify by looking at the un-smoothed phase curve: works like a charm.

Wow.......you use a microphone to try and set a time delay on driver path lengths?  I have learned by using the same stuff in my rooms that a large % of the sound picked up by a microphone in your room is reflected sound.

I would not do what you are doing to set driver path length delays........

What you seem to be attempting is to do is acoustically align drivers..........which seems based at least partly on reflected sound.  You must have some interesting results.

Do your delays mirror Roy's or come close?

I use a much higher technology method............its called a tape measure.  My processor allows you to enter the path lengths in "feet".  I can get it down to inches with "tenths".  I just measure the length of each driver from voice coil to horn entry and the processor creates a time delay in "seconds" (milliseconds in my case).

Without an oscilloscope everyone is approximating anyhow.  But "close enough" works very well.  When I switch off the delay the room clouds up and snaps into cripsy clarity when I re-engage.  Very noticable........Works well.

[Chris A]

Mark,

I'd recommend reading on pulse compression techniques (e.g., "chirp radar") using sine wave upsweeps (or downsweeps).  An exact analog is used in reflection seismology and it's called Vibroseis.  It does its work in highly reflective environments because it knows when certain frequencies should be there and when they shouldn't.   I spent 6 years designing and testing machines that most people call "ground shakers". 

So yes, it works, and that's why REW, Audyssey, YPAO and other audio tools don't have to use impulse injection to find time delays.

Chris

Edited August 19, 2014 by Chris A

[Chris A]

Do your delays mirror Roy's or come close?

I use a much higher technology method............its called a tape measure.  My processor allows you to enter the path lengths in "feet".  I can get it down to inches with "tenths".  I just measure the length of each driver from voice coil to horn entry and the processor creates a time delay in "seconds" (milliseconds in my case).

Without an oscilloscope everyone is approximating anyhow.  But "close enough" works very well.  When I switch off the delay the room clouds up and snaps into cripsy clarity when I re-engage.  Very noticable........Works well.

I haven't changed the HF delay setting for the Jubs because they are great, but I had to find the correct delays for the Belle bass bin-midrange and midrange-tweeter delays.

The problem with using only measured path lengths is that you are ignoring the relative phase of the drivers (with their horns) at the crossover band.  Using REW will allow you to get dead on, correcting for this source of error, too.

By the way, there is a freeware application that turns your computer into an audio-quality oscilloscope - TrueRTA.  I used that, too, using square waves at the crossover region-- to check for issues.  That method is much noisier, however.

Here is evidence that Roy's delay settings are correct, but using REW (the same way that Roy set the delay in the chamber):

Edited August 19, 2014 by Chris A

[Daan]

One day.... when my two braincells have grown to three [ when that even will happen in the first place].... then I hope to understand what you guys do with measurements....

I only have my wife's ears and mine, but we do use time-delay in our two-way system and it's a bit like the icing on the cake for us.

[Don Richard]

It's a real miracle how once something is confirmed through measurements it becomes "painfully" audible to some folks

It's more like a problem is heard, then measurements are made to confirm the existence of the problem, and to point toward the solution to the problem. When a correction is made, measurements are made to verify that the problem has been solved. Kinda like when someone sends a dead amplifier to you for repair, you measure some voltages to get an idea of what to fix.  

[Chris A]

One day.... when my two braincells have grown to three [ when that even will happen in the first place].... then I hope to understand what you guys do with measurements....

I only have my wife's ears and mine, but we do use time-delay in our two-way system and it's a bit like the icing on the cake for us.

Much of this is done for setting loudspeaker delays automatically using Audyssey and YPAO, etc. using exactly the same techniques.  All we're doing is using the technique for single loudspeakers, and all you really need to buy is a calibrated USB microphone, a microphone stand, and an active crossover.  You probably already have a laptop or desktop computer.

Edited August 20, 2014 by Chris A

[mark1101]

Do your delays mirror Roy's or come close?

I use a much higher technology method............its called a tape measure.  My processor allows you to enter the path lengths in "feet".  I can get it down to inches with "tenths".  I just measure the length of each driver from voice coil to horn entry and the processor creates a time delay in "seconds" (milliseconds in my case).

Without an oscilloscope everyone is approximating anyhow.  But "close enough" works very well.  When I switch off the delay the room clouds up and snaps into cripsy clarity when I re-engage.  Very noticable........Works well.

I haven't changed the HF delay setting for the Jubs because they are great, but I had to find the correct delays for the Belle bass bin-midrange and midrange-tweeter delays.

The problem with using only measured path lengths is that you are ignoring the relative phase of the drivers (with their horns) at the crossover band.  Using REW will allow you to get dead on, correcting for this source of error, too.

By the way, there is a freeware application that turns your computer into an audio-quality oscilloscope - TrueRTA.  I used that, too, using square waves at the crossover region-- to check for issues.  That method is much noisier, however.

Here is evidence that Roy's delay settings are correct, but using REW (the same way that Roy set the delay in the chamber):

I never knew how Roy actually derived the delays for the Jubilee, even though I was watching.     Glad someone paid attention.

[mark1101]

I have always used TRU-RTA.  I need to get REW and fool around.

[Max2]

I just purchased a set of Beyma tweeters a month or so ago to go in my K's.   I made a little make shift box to hold them upright and tried flush with the top hat and raising them 4 inches. I put them back, forward, centered, you name it.  Now my ears are well below what a 45 year olds should be, but the differences were very subtle or at least my ears thought they were    Anyway, I was relieved that I didn't notice anything positive because that solo tweeter would have been an eyesore on top.  One thing though, my Volti mids are good deal shorter than the stock 401's, so maybe my timing was off a tad less than normal and I wasn't going to hear it in the first place.  It may be best for me to steer clear of any REW software and it linking's, because I really don't need another audio aspect to be obsessed over....especially a response chart telling me what correct sound is supposed to be instead of what sounds good to my ears. I guess ignorance is bliss