Wisdom of 4-way Studio Monitors

[boputnam]

I found this interesting, and while it may be common to many, perhaps it will engender some dialogue (maybe not...).

The so-called "Second Decade" is the range that serially troubles live sound applications - it is the range where fundamental frequencies and related harmonics conspire to ruin attempts at feedback-free, clear live sound. This is a notoriously difficult range to "tame".

I noted with interest this is largely (but not precisely...) the range where JBL engineers employed the mid-bass transducer (10-in in the 4343 and 4345, and 12-in in 4350 and 4355). Adding that transducer element into the mix, allowed JBL the opportunity to "trim" (in sailing parlance...) that troublesome/resonant frequency range within the network. Clever...

Oldmics, got any thoughts? Giskard - you were around in those legendary days, hey? Don? What was the thinking...?

[Ian Mackenzie]

Interesting cross fertilisation of academia but not quite.

Are you still smokin from your last GIG, its amazing what sturs the thought processes


The previously posted pdf Inside the Studio Monitor explains the ins and out quite well.

Ian

[boputnam]

Yea, I said "not quite", but there likely are design reasons for that. Well, I remain intrigued...

And no, on the Green Cloud.

[4313B]

Originally posted by boputnam
What was the thinking...?

That girls in skirts slit to the hip dancing to Kool and the Gang playing over six JBL 4343's wasn't a bad thing at all.

[whgeiger]

Bo,

Some appropriate notes follow:
(These are meant to be targets to shoot at.)

System Ways
1) A single high quality driver may achieve pristine performance within about one decade of the audio bandwidth.
2) So, to cover the audio spectrum, a 3-way loudspeaker system becomes a minimum requirement.
3) If, in this setting, efficiency is to be traded for bandwidth, then to adequately cover the entire audio spectrum, a 4-way (or more) system is required to make the trade.

The Critical Decade
4) By far the most critical decade is the second, as it is this region where hearing is acute and most capable of detecting imperfections in the reproduced sound.
5) While paragraph (4) expresses an acoustic truism, in many cases, reproduction of the speech range is not placed at the top of the loudspeaker design totem. This is exemplified by the presence of crossover frequencies well within the boundaries of this band of frequencies.

The Power Decade
6) To reproduce the first decade and slightly below it, requires large air displacements from muscular drivers driven by energetic amplifiers. Here there is simply no viable alternative to substitute.

The Gossamer Decade
7) Here the acoustic signal is ‘forced’ into a beam by the driver as its power response falls even though its on-axis response may remain constant. In this band, use of an acoustic lens, coupled with equalization has been unexplainably abandoned.

Regards,

WHG

[boputnam]

Originally posted by whgeiger
The Critical Decade
4) By far the most critical decade is the second, as it is this region where hearing is acute and most capable of detecting imperfections in the reproduced sound.
5) While paragraph (4) expresses an acoustic truism, in many cases, reproduction of the speech range is not placed at the top of the loudspeaker design totem. This is exemplified by the presence of crossover frequencies well within the boundaries of this band of frequencies.

Hey, Bill...

Bingo! Thoughtful stuff, particularly #4, and #5. The last few months of live engineering have caused me to more critically think about just that. The second decade is where acoustic hell will present itself, if you're not on top of it. Standing waves fundamental in that range present their harmonics in the Third decade, so they need be first tamed in the Second.

What I find odd, is that JBL's engineering of a 4-way system suggests they were very aware of the importance of the Second decade, yet in the case of the 4345 they crossed-over at 290Hz!

Can you imagine a system today taking an 18-in LF up to that crossover point?

[subwoof]

Wisdom indeed....

When I began in this buisness, subs were usually located far away from the "cluster" ( IE: auditorium ) because of limited weight issues ( we had to use big old metal / wood horns back then ) and the rule of thumb was to set the system LF crossover like this:

Put a male voice with plenty of low end ( jim nabors, greg lake, etc ) into JUST the LF amp and bring the crossover point up until you could *just* hear the persons voice then back it off ( to a eq cf if possible )

This way voice reproduction would not be time / location altered and they even had a name for this:

Acoustic Dismemberment.

And funny thing - it is usually in the range of 225 to 300 Hz depending on how much on-axis the listener was to the subs.

But the probable reason for the choice of 290 was that's about as low as the 2122H can go in a sealed chamber and have it's natural roll-off match the roll-in from the 2245H with the internal passive crossover and the ( then ) current analog electrical types.

Remember that the acoustic orders add to the electrical...