At what point should I use speaker delays?

Discussion in 'Location Recording' started by katzenandguthrie, Sep 19, 2005.

  1. Hello all,

    This is my first post.

    My background is recording and broadcast and I'm just now getting in to live sound. There are some venues that I feel might need a second and third set of speakers because of the depth of the room. The second set would be about 75 feet back and the third set would be about 25 to 30 feet back from those. The venue is a Temple and most all of the sound is spoken word.

    Is there a general rule about when you should use delays?

    Thanks in advance for any input you may have,

  2. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Welcome to RO!
    Whenever you get more than 25-30 feet from the speaker, you will get a noticeable time delay. You can figure that sound travels at roughly 1100 ft/second. The audio projecting from the front speakers will reach the furthest-point in the back of the Temple in about 110 milliseconds. This is certainly discernable to the human ear and should be compensated.
    Ideally, you would have a delay/amp/speaker arrangement(with a 70-75msec delay,+/-) at the "middle' cluster, and a 90-100msec delay/amp/speaker rig at the rear. My bet is that you could get away with an 80msec delay/amp rig driving both the 'middle' speakers and the rears. This would mean less electronic hardware, and the shorter distance between the mid and rears would be all but negligible. REMEMBER: YOUR MILEAGE MAY VARY!!!
    Then to the hardware. Check out te Sabine Graphi-Q. This system is a combination 1/3-octave EQ, a Feedback Eliminator, time delay, and dynamics processor in one unit. Awesome for houses-of-worship.So is the Ashley Audio Protea (time/EQ) system...Check them both out!!
  3. Wow! Thanks for the quick response. I think I know where a delay is and I think it might be a Symetrix. It seems to me that the delay settings are in 'feet' so it might be a no brainer to setup. I'm going to take a look and post back later.
  4. sheet

    sheet Well-Known Member

    Let me clarify something for ya. I don't know about the statement about 25-30 feet from a speaker, delay, etc.

    I do know that this guy has to find the critical distance (Dc) from that speaker. That is going to be room dependant. So, at that spot, where the rooms delayed reflections overcome the direct signal, that's where the delayed speakers go. With about 1 ms per foot delay, and about 10dB down from the primary speaker, you will get the desired result.
  5. nak

    nak Guest

    sound is going to travel much faster inside a club being hotter.
  6. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Really.........? I have worked in both "bars" and "houses of worship" for longer than you have probably been on the face of this planet! I know that A/C ( or the lack thereof) will affect sound in some whacked ways (i.e., turning off the A/C to "assist" the fog machine activity may induce feedback nodes), but not the SPEED of it. Barometric pressure and humidity will also have a factor.
    BUT "much faster"!?!?!?! How much faster? Fill us in.....
  7. nak

    nak Guest

    ok... not MUCH faster.... (but still, its a difference you should keep in mind) sound moves at roughly 1130ft a sec at room temp. its moves faster and hotter temps. simple.

    but please, dont get all offensive about whether you are better than me or not, because i dont really believe you.

    but still all i am saying is that you shouldnt be worrying about time delays and what not. most "bars" and some "houses of worship" have bad acoustics. and no matter how much you try to compensate for the delay, its still going to sound BAD.

    before any of that, get better acoustics. this should be any venue's FIRST priority.
  8. sheet

    sheet Well-Known Member

    OK folks. This guy needs to be told about Critical Distance (Dc). At the church that I mix full time now, we have a Dc of 36". That means that the ambient sound of the room, through all of it's delays, slow decay time, etc., overcomes the direct sound at 36". If this temple is very live at all, delay rings may be required much more frequently than at a club, where the acoustics would have a lower RTC.

    The comment about a specific distance of 25' to 30' being a point of noticing reflections, decrease in volume, etc is bogus. It is hall, speaker system topology/placement and system sensitivity driven. There is no distance that can be thrown out as a rule.

  9. Pressure will have no effect at all, humidity very little. If you want to know how much faster, pick a temperature in degrees celsius (t) and do the calculation:

    speed of sound = 331.5 + (0.6t)

    Your result will be in meters per second. Multiply by 3.2808399 to get feet per second.


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