How Speakers and PA Systems Respond 

If you ever went to an outdoors event like a street fair where recorded music was being played, chances are it didn't sound that good.

The music has simply no boundaries to create reflection and bass frequencies are not felt well.

A record that was mastered with a minimum compromise on the dynamics will sound much better than the record that had its dynamic range squashed (a very loud record). This compunds the problem.

Why? The human ear perceive much better mid frequencies (between 800Hz to 5 kHz or so) and most of those squashed records have mild distortion in the mid frequencies and apparently, they move no bass frequencies at all.

That doesn't mean that there are no bass frequencies in them; it means that the sound of these bass frequencies were flattened and therefore, there is hardly any speaker movement.

When the music is blasted though those big horns, the record with the fuller dynamics will sound best.

Speaker movement.- every speaker has a cone that has "excursions", which respond to low frequencies, the more the cone travels or expands outwards, the more air it will "pump" out.

Excursion.- A movement from and back to a mean position or axis in an oscillating or alternating motion.

A record with high peaks on the bass frequencies will generate longer excursions to the speaker cone. 

If you are still not convinced, let’s take this theory to the other end. Let’s say you are now at a nightclub.

The music is being blasted with high power amplification systems (10,000 watts or more) and your mix (pay attention hip-hop people) sounds really loud, but then comes another mix and WOW, now that’s a great and exciting sound. 

Nothing wrong with yours, after all, you heard it in your car and it sounded fat and louder than the others, hmm... but, why did that mix in the club sounded better?

You get a hold of a copy of that mix that was played, you take it to your car and realize that mix is lower in volume than yours but it's fuller with dynamics! 

Of course, in night club situations, a DJ is supposed to level the music as he makes his transition from record to record, so what was happening is that the mix that was louder and fading out of the DJ’s main house mix was being replaced at equal power by the one with superior dynamics and even though that mix is at a 'lower RMS level' {by say, about 3 dB or so} it was leveled by the DJ as he mixed it in. In addition, since it had more 'kick' presence due to increased low frequency peak transients, it had more speaker movement than the other.

See example 1: The cone expands longer and pushes more air density. Check the shape of that excursion from the dynamics point of view at the bottom of the pic.

The average level of this signal is about -2 dBFS

Now, look at example 2:

Even though the louder signal is more than 2 dB louder in average , it doesn't creates much of a movement to the cone and therefore not much air displacement (The distance of the oscillating body of air in the room from its central position).

And, although they both have plenty of RMS power, example one is for sure more dynamic.

Now, see the bottom of the pic on example 2. It looks like the shape of the dynamics is nothing but a big block of flattened frequencies.

The average level of this signal is about -3 dBFS

Having said all that, only a mad person or an uninitiated mastering engineer would master a pop ballad or a soundtrack instrumental like a grunge, metal or hip hop record, right?

Edward Vinatea
Audio Engineer

If you need more information, go to our general discussion forum to sign up and to post questions or create a new topic.

If you need more information, go to our message board to post questions or create a new discussion.