Time alignment

zedda

Member
2014-07-05 1:50 pm
gaeta
Hy
I have a pa system with:
Dbx driverack pa+
Handbuilt sat with 15ndl76 and hf10at on 270*270mm horn 60*40°

Active three way

The center of woofer is 1,70meters high from floor,
And the horn center is 33,6cm higher
The horn depht from baffle to driver is 23cm...
The woofer depth is only 4cm from baffle to dome

I can delay only the woofer, is correct?

But the max delay is only 10ms...

How I can calculate the optimal delay?
If is bigger than 10ms, is better set 10ms or turn off the delay?
 
10 ms is 11... feet BTW. ;)

Zedda, are you talking of the delay between woofer and tweeter ? This would be around 20 cm (it is actually frequency dependant). Once you get your acoustical slopes sorted you can just invert one driver and vary the delay until the deepest possible suckout at the crossover frequency is reached. The delay with the deepest suckout is the actual delay. You then keep this setting and switch the inverted driver back to normal.

Regards

Charles
 
I'd use 0.55 ms delay on the woofer channel as a starting point. Calculation:

Speed of sound in air at 22 degrees C is 345 m/s (34501 cm/s). The net depth of the horns vs. the woofer that you described is 19 cm, I believe.

19(cm)/34501 (cm/s) = 0.00055 s

You didn't mention the crossover frequency between the woofer and horn. This will tell you the relative wavelength mismatch at center crossover frequency, uncorrected. For instance, if it is 800 Hz, then:

relative phase angle = 158 degrees

Chris
 
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You cite all good reasons for optimal t.a. in a pair of audiophile speakers, but public address speakers????

Time alignment is much more common in PA systems than it is in hifi these days. Above a certain size and price level, you'll find it in every system. All the digital crossover/processor units have the facility, and factory settings for speakers all use it.
 

zedda

Member
2014-07-05 1:50 pm
gaeta
Most people don't calculate it, they measure it. Measurement tools such as SmaartLive include the ability to measure time. http://www.rationalacoustics.com/

The dbx have a rta input for microphone...
If I use the automatic calibration with a undefinied microphone (I have a set of three mic thomann) can I delete the equalization parameters and use only the auto time alignment?

Or can I use the dayton imm-6 with an adaptor?

Thanks :)
 

zedda

Member
2014-07-05 1:50 pm
gaeta
I have a big problem.... in the middle of the dance floor (open space) the medium frequency is cancelled...
The distance from left and right speaker is the same...
Same thing when I turn the speaker looking the center of the floor...
And when I walk on the floor the sound is very innatural, and change with my position...

When I tested the speaker in my house there isn't this problem...

For camouflage the problem I turn the right speaker look right and the left speaker look left...

The change of sound when I walk on the dancefloor was resolved... but in the middle there isn't sound...

What can I do? :( :( :( :( :(