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In the Forum: Audio Discussions
In the Thread: Constructing LF modules to the limits

Post Subject: Dynamic consistencyPosted by noviygera on: 9/30/2011

Romy the Cat wrote:
noviygera wrote:
p.s from my experience of having a 500 sq. ft. listening room with 7 ft. ceiling and having two 18" woofers in a infinite baffle configuration, it is not enough to pressurize the room. I am talking about low and medium listening levels. Four 18" would be just acceptable. Eight 18" woofers in infinite baffle will be good for a 500 sq. ft. room so there is your rough ratio according to my experience.

Herman, I would like to ask what methodological reasoning you uses to assess that your room of 500 sq feet having two 18" woofers in a infinite baffle it is not enough? Do you feel that not enough bass? You do not have more power or gain in your amplification? Do your drivers excurt too much? Do you hear too high distortions or compression? Do you have measurements in the room at the frequencies that you are interested in?

The reason I ask as I feel that 4x 18 inchers for 500sq feet room is certainly wonderful but it is nowhere near absolute minimum. A good pair of 416/515 drivers with moderate 40Hz would perfectly fine for 500 sq. ft. Sure the more drivers and more size is better but when we do it we just minimize the excursion of each driver and improve sound by spreading all problem across multiple transducers allowing each transducer to be not as good as a single driver. Anyhow, I would be interested to know how you came to the concussion you have came.

The caT

Romy,

I came up with the conclusion by following my personal reasoning of consistency in dynamics. I say personal because no one else I know explicitly agreed with this reasoning. It is simple reasoning. I believe that to have proper sound in any system the dynamics must be consistent from top to bottom, by this I mean not loudness of sound but output in terms of potential and even pressurization of room. For example, if we look at a musical instrument like a trumpet or violin or any percussion instrument, there is a natural correlation between pitch and size, they are proportional. A small trumpet plays a high pitch at the same scale as a large trumpet plays a low pitch. It would be unnatural to force two equal size trumpets to play different pitch equally, with the same power of input.

So I think same applies to any sound producer and that is why I reason that if my midrange horn (lets say it's a proper horn) has the volume of "x" than the midbass horn should have the volume "4x" and bass horn to have the volume "16x". But I cannot accommodate "16x" so as you are doing, I am using sealed boxes (well actually I am using infinite baffle) to replicate the potential of our ideal bass horn "16x" volume. This is just my theory and my best replication is to at the least replicate the mouth area of the bass horn.

The closest approximation of potential of a sealed bass channel to the potential of a bass horn is to replicate the mouth area with driver surface area. So lets just approximate the mouth area of a 20Hz horn(s). Just convert that to a number of 18" or 24" or whatever diameter woofers and you are at my best approximation of "ideal". But since this is all maybe a b.s. theory then what do we have in practice?

With two 18" in an infinite baffle I have enough output in decibels keep up with horns to a certain point but this almost worthless. because there is not enough potential. So what happens is there is no dynamic consistency and also no consistent pressurization of the room at different frequencies, specifically the bass range. Decreasing or increasing the output of the 18" subs does nothing to the rate of pressurization, as does changing the crossover type and point. I measured my system response but it does not show anything bad.

An extreme case of the worst solution would be to use two high excursion 8" woofers for the bass, just to make a point. However if the rest of the system was proportional to the bass section, lets say a 5" mid and 1" tweeter, than the 8" woofers would be in a situation of dynamic consistency, in my opinion.

In your sitation, it would be different again, since you are using huge midbass horns, your bass filler channel will be covering less than usual so maybe it's not as critical to get that range absolutely right. But still.. Do you have any more attic space available?

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