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Re: group delay ?

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Posted by Dave Rat on March 09, 2002 at 12:10:58:

In Reply to: group delay ? posted by martin on March 08, 2002 at 14:55:53:


Interesting. I guess that would account for the "horn loaded sounds punchy" phenomenon. Though group delay is something I have not tested directly, the concept does seem to possibly make sense when the lows of the system depend on the resonance formed by the tuned enclosure.

The Rat Trap 5 system, though 15" and 18" are ported, may be less effected by this than other systems. The reason being is that we "under port" our enclosures. We do this to reduce that resonant sound that enclosure that are "optimally tuned" seem to exhibit. Additionally we over-damp the inside of the box. Lastly, we tune the 15"s below the xover cut off point so the ported resonance is not really an issue and the 18" are tuned so low that the efficiency at the tuning frequency is considerably lower in volume than that other subs.

The idea behind all this is that many of the acoustic environments that live show occur are overly resonant, combined with the resonance that occurs with amplified open mics. So in real world applications, resonant enclosure tend to aggravate the environment resonance.

Dave Rat

: Hello,

: I never heard a RAT System (i live in Europe Austria), but i heard a lot of ported boxes, where the lower frequencies seem to run behind the rest. I wonder if this is due to the huge group delay around the tuning frequency, or what else could cause this? Did not hear similar behaviour with closed boxes and horns. Especially with ported tops it seems they have this problem.

: And if i look at measurements (Burst), a closed one needs 1-2 halfcycles to reach full burstlevel, while the ported one needs 5-6. Which indicates slow response?

: Any ideas?

: Thanks
: martin

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