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Timing Measurements


jcmusic

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Yesterday after taking some measurements of all my drivers which are well balanced across the board, I did notice that the woofer is about 4.8ms behind the mid/tweeter. Is there nothing that can be done to correct this other than going active? Did I read some where about some delay being in the xover?

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Yesterday after taking some measurements of all my drivers which are well balanced across the board, I did notice that the woofer is about 4.8ms behind the mid/tweeter. Is there nothing that can be done to correct this other than going active? Did I read some where about some delay being in the xover?

You can try talking to Al K. on his website, but I know of no reasonable all-pass filter designs that can produce 4.8ms delays. Digital loudspeaker processors can, however. 

http://www.ebay.com/sch/i.html?_trksid=p2050601.m570.l1313.TR0.TRC0&_nkw=Behringer%20DCX2496%20Ultradrive

http://www.ebay.com/sch/i.html?_odkw=Behringer+DCX2496+Ultradrive&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XElectrovoice+Dx38&_nkw=Electrovoice+Dx38&_sacat=0

http://www.ebay.com/sch/i.html?_odkw=Electrovoice+Dx38&_osacat=0&_from=R40&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XElectrovoice+DC-One&_nkw=Electrovoice+DC-One&_sacat=0

http://www.ebay.com/sch/i.html?_odkw=Ashly+crossover&_osacat=0&_from=R40|R40|R40&_from=R40&_trksid=p2045573.m570.l1313.TR11.TRC1.A0.H0.XAshly+processor&_nkw=Ashly+processor&_sacat=0

Edited by Chris A
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Yesterday after taking some measurements of all my drivers which are well balanced across the board, I did notice that the woofer is about 4.8ms behind the mid/tweeter. Is there nothing that can be done to correct this other than going active? Did I read some where about some delay being in the xover?

How, specifically, did you measure the drivers' time delay?

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Yesterday after taking some measurements of all my drivers which are well balanced across the board, I did notice that the woofer is about 4.8ms behind the mid/tweeter. Is there nothing that can be done to correct this other than going active? Did I read some where about some delay being in the xover?

How, specifically, did you measure the drivers' time delay?

Hi Rudy,

I used REW and it's impulse feature, doing one driver at a time on each side. So that's six total measurements.

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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.

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The reason I asked is that over the last few years as I have become more comfortable and slightly more knowledgeable about measurements I have noted some issues which might give you some problems.

For example, if you are taking the measurements using the passive crossover, you will likely have some delays not a result of driver location.

Also, I have noted that the most accurate results have resulted when I measure the drivers using the same frequency range.  That is, if I measure the woofer from 50-3000khz, I need to measure the next driver up the chain in the same range.....which means, if you are measuring an HF compression driver, you need to be careful due to the low signal you will be sending to the driver.

In my case, with an active crossover, I can custom tailor the tests as desired. My best results, as compared to physical measurements have been done in that manner.

Granted, I am in no way an expert on the subject and have often asked more knowledgeable members for help.

I just didn't want you to spend a lot of time tracking down a timing issue that may have some other factors involved than just driver distance.

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Hey Rudy,

Thanks brother I appreciate the thought, I think I am good though even though I have a 4.8ms delay from the woofers. All six drivers measure almost exactly the same, the tweeters and mids are dead on with each other so I guess I will live with the 4.8 delay. Unless down the road i decide to go active!!!

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"I wonder how audible a 4.8 ms delay is?"

Depends on the frequency.

At the midrage crossover point it's very audible when you fix it.

Digital delay is the only fix.

If the horns are deeper than the woofer, then an all-pass delay will fix it.

all-pass.gif

I've done the above (balanced) with dual 12's, it's stunning.

Some B&W models use the unbalanced circuit (tapped inductor on a common core).

Edited by djk
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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

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