January 2022

Think Of Your Loudspeakers As An Air Pump
Roger Skoff writes about a helpful new way to regard your system.
Article By Roger Skoff

  Christmas, Hanukkah, Festivus, or whatever else your winter gift-giving holiday may have been is now over, and Santa or some other friendly spirit may have brought new toys or goodies for you to play music on or to make your music listening even more enjoyable. Either way, here's a thought that might help you to get the most out of the new stuff – or even the old stuff, in case Santa brought the Lamborghini instead of the new audio gear you really wanted.

The first thing to remember is, even though what we listen to is music, and that music (and sometimes even the gear we play it on and/or the room we play it in) can have a strong effect on our emotions – the truth is that what's making the music for us is just an air pump, the equipment to power it, and the space for it to work in. And don't, incidentally, let the thought that there are two speakers lead you astray: Whether one (for mono), two (for stereo), or even five or seven (for Home Theater), however many speakers there may be (including all of the drivers they're made up of), they're all working together to create just one complex pattern of pressure waves to constitute our musical experience.

Yup, it's all pressure waves.

By this point, it's doubtful if anybody – except, possibly, little kids, whose tabula rasa ignorance is boundless – don't know that what we hear as sound is just a series of alternating pressure waves passing to our ears through a conductive medium. Because we are air-breathing creatures, living in an air environment, we normally think of that medium as being air, but the passage of sound works the same way for water, for concrete, for steel, or for anything else other than a hard vacuum, where nothing can be passed along simply because there's nothing there to pass it.

In fact, some of those things just named (water, concrete, and steel) pass sound faster, and maybe even better than air, so that, if there were such things as fish audiophiles, and they had audio systems, they might enjoy even better sound than we do. As a matter of fact, it's known that whales and dolphins -- not really fish, but still living in a water environment – hear a much broader range of frequencies than we do and can communicate sonically over distances of miles without any equipment at all, just because of water's greater sound conductivity.

Have you seen those Newtonian toys, where a row of steel balls is suspended from a frame, and when you bang the first ball in line against the row of balls behind it, the last ball in line moves, while the rest stay in place, motionless?

Although intended for a different purpose entirely, those toys can provide the perfect way to explain why sound passes faster through a denser medium than a less dense one: All you have to do is to imagine them set up differently, with the balls farther apart:

If, instead of all the balls on the frame being suspended in such a way that, when all are at rest, each is touching the one(s) in line next to it, you set it up so that the balls are suspended at some uniform distance apart from each other, it will act more like sound in a less dense medium. Before the first ball in line can transfer its energy to the second, it will have to travel the distance to the second ball and impact it. Then the second ball will have to travel the distance to the third ball, transfer its energy, and cause the third ball to move to, and impact the fourth; and so on, through as many balls as there are in the line, with each distance traveled slowing down the process and potentially resulting in some incremental loss of energy.

That's how it is with the travel of sound, too, with the molecules of whatever the medium may be replacing the balls, and the spacing between them providing the distance of travel. In a denser medium, the molecules will be closer together, and in a less dense one they'll be farther apart, and the differences in distance between molecules will correspond with differences in the speed of sound in the various media.

Where that gets important to your musical enjoyment is when (as Norman Varney, to my knowledge, first made plain to the audiophile public), music can make its way to your ears through more than just a single medium, at more than just a single speed, to arrive at more than just a single time.

The way that works is this: When a speaker is playing music, it's pumping pressure waves into the room, with (depending on the frequency of the sound and the speaker's single-driver and composite [all drivers] dispersion pattern), some of those waves impinging directly on your ears (first one and then the other unless the speaker is directly in front of you) and some of the remaining pumped energy spreading through the room, to bounce and re-bounce off the walls, and perhaps eventually reach your ears at later times, each such time depending on the size of the room, the placement of the speaker, and the number of bounces needed to get to your ears. Oh, and multiply that figure by at least two, for your two stereo speakers, or more, if you have more speakers or if each speaker system has more than just a single driver.

Right there you have multiple arrival times for each speaker, just through the air, with the direct waves being heard first and the indirect ones arriving at various later times, to smear the musical presentation.

And there may also be other sounds coming to you even sooner:

Do you recall what I said about denser media having a higher speed of sound? Well, the floor of your listening room is certainly denser than the sir your listening room is filled with. And (here comes Newton again) as your speakers are pumping pressure into the air, they're also, either directly or through their stands, vibrating your floor, too. "For every action, there's an equal and opposite reaction" is Newton's Third Law of Motion, and he said it even before there were speakers to say it about!

Where it gets interesting is that, being denser than air, your floor has a higher speed of sound than air, so sound carried to you through your room's floor may arrive at your ears before the sound comes to them directly through the air!  That means that, instead of the sharp pluck of the single note with clearly defined attack and decay transients that the musician is playing on your recording, what all those multiple delivery paths and times of arrival may be giving you is some formless, music-less blob of sound.

The way to fix that is to acoustically treat your room with diffusers and absorbers to minimize secondary air-borne arrivals and to isolate your speakers from the floor – not with coupling devices, like tiptoes, but with isolators, like EVPs. Your speakers are air pumps, and that's all they should be if you want to fully...

Enjoy the music!

Roger Skoff