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Author Topic: Arrival Time  (Read 2256 times)

Canute J. Chiverton

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Arrival Time
« on: August 24, 2013, 10:25:06 am »

Lets see if my question will make any sense. I am looking for thoughts here.
Specifics: Lets suppose a DJ has a system set up on each corner of a 40ft square Dance Floor.  Room is 100ft w by 300ft long. Dance floor is centered along the short wall.  Someone is standing in the middle about 150 feet from the center of the short wall.
System comprises of a Two way Box (With 10" Woofer like a QSC K10) on top an 18" sub on bottom. Two way configuration. We may for the sake of argument consider this an acceptable alignment/placement as far as typical DJ setups go.

Question is, Will changing the tops also change the arrival time of those Mids and Highs Frequencies relevant to where that person or other persons may be standing? In other words, will it take a shorter time for the Mids and Highs to arrive, if it was a Two Way 15" box on top?

What formula if any determines Power, Deployment, Coverage, size of transducers etc to achieve the best possible overall sound not just for one sweet spot? (In this case I included it only as a reference) For this exercise consider the temperature as excellent.
« Last Edit: August 24, 2013, 12:51:59 pm by Canute J. Chiverton »
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Tony Mitchell

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Re: Arrival Time
« Reply #1 on: August 24, 2013, 05:04:41 pm »

If both the sub and the mid/high are reflex boxes and postioned with the sub beneath the mid/high, no time alignment should be necessary.    If the sub is horn loaded, the reflex box should be delayed to the horn length.   If the sub is placed back behind the mid/high, then likewise.

The size of a driver does not influence the speed of sound.

If, by "centered along the short wall", you mean the 40' x 40' dancefloor is against the wall at one end of the room, I'm imagining the mid highs (K10s you say, they're 90deg horizontal) positioned against said wall in either corner of the dancefloor, probably somewhere between 45deg and 60deg offset to the wall.   The person at the half way point (150' from the wall and slightly more from each source) is not going to hear anything particularly useful from either source, the loss will be somewhere between ~(34dB) if on axis vertically and a significantly greater loss if the mig/highs are positioned up high and pointing down on the dancefloor.

To achieve the "best possible overall sound" in a space this size, a distributed system is the way to go.   High SPLs on the dancefloor and BGM levels elsewhere in the room.
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Doug Fowler

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Re: Arrival Time
« Reply #2 on: August 24, 2013, 09:50:04 pm »

If both the sub and the mid/high are reflex boxes and postioned with the sub beneath the mid/high, no time alignment should be necessary.

Sorry, that is not the case.  The phase shift caused by the LPF on the sub channel causes misalignment, and should be accounted for. 
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Mac Kerr

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Re: Arrival Time
« Reply #3 on: August 24, 2013, 10:03:06 pm »

Lets see if my question will make any sense. I am looking for thoughts here.
Specifics: Lets suppose a DJ has a system set up on each corner of a 40ft square Dance Floor.

Where are the speakers pointing? If they are pointing in at the dance floor, like would be common with a DJ, they will be pretty useless to get anything but boom and reverb to the rest of the room. If you want a DJ on a dance floor and good PA coverage in the rest of a big room, you need 2 systems.

Mac
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Tony Mitchell

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Re: Arrival Time
« Reply #4 on: August 25, 2013, 03:23:55 pm »

Sorry, that is not the case.  The phase shift caused by the LPF on the sub channel causes misalignment, and should be accounted for.

Thanks Doug, I have just read up on the topic & that makes sense.  Interesting stuff.
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Paul G. OBrien

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Re: Arrival Time
« Reply #5 on: August 28, 2013, 09:28:19 pm »

Lets suppose a DJ has a system set up on each corner of a 40ft square Dance Floor.  We may for the sake of argument consider this an acceptable alignment/placement as far as typical DJ setups go.
I know this isn't your question by those are the first and second mistakes.


What formula if any determines Power, Deployment, Coverage, size of transducers etc to achieve the best possible overall sound not just for one sweet spot?
There is no single formula but providing "the best possible overall sound not just for one sweet spot" or in other words the most even coverage will be from the smallest possible point source that is equidistant from all listeners. Now speaker technology has not advanced enough to allow something the size of a pin head to produce the whole audio spectrum at usable sound levels in open air so you're gonna have to use traditional audio transducers, but best results will be achieved with them clustered together and positioned overhead so that no matter where you are on the dance floor you're roughly the same distance from the cluster. If flying speakers is not possible then take the second best approach and put them in a cluster at ground level but again at a distance away from the dance floor to achieve a response similar to the overhead cluster.
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