OK kids it’s (finally) time for what you all have been waiting for: the naked truth about speakers. I will probably make some enemies and lose some readers here. But so be it. Let’s start out by reviewing the goal of this blog: “To discuss producing, in a home environment, a sound field which is indistinguishable from the original live acoustic musical performance from which it was recorded”.

That’s important because if your goal is something other than this, what I have to share here may not be very helpful.   We have already spent some time discussing the space where your speakers will reside. For now I’ll limit my discussion to a classic 2 speaker (system) stereo in front installation. Speakers 101 is a prerequisite for Speakers 102, 103, 104 etc where we might cover more exotic installations. But we first need to understand some basic characteristics that a speaker system needs in order to convince you that “you are there” or “they are here”. This does not mean “better” or “worse” sounding. Those are subjective. The Holy Grail here is accuracy: A sound field which is indistinguishable from the original performance. We are out to deceive your brain. Audio sleight of hand.

A few starters:

 Factoid #1: Audio is not wine, people. There is nothing a speaker does that can not be scientifically measured in such a way to give a real picture of its ability to accurately generate a sound field in a given environment using the original performance as a basis of comparison. If one prefers to make measurements by virtue of biological transducers (listening with our ears), a “double blind” test is a perfectly acceptable substitute.

Factoid #2: A perfect copy of the original sound field is not required in order to be completely convincing. Thank your aboriginal brain for this. A few years ago Acoustic Research decided to do some marketing promotions where they invited listeners with all levels of expertise to a concert which featured a stage and musicians along with a pair of AR3’s which were, at the time, their best loudspeakers. The musicians would play a passage live and at some point stop at which time a recording of the same musicians (done in an anechoic environment) was fed through the loudspeakers. The listeners were then asked to identify the live Vs. recorded passages. Can you guess what the listener’s responses were? Some said they could identify a subtle difference in the sound between the two passages but were unable to come to a consensus of which were live and which were recorded. Howcum? Our brain has a poor ability to recall the details of a sound out of context. We can identify the roar of a saber toothed tiger. But the timbre or articulation of his roar is not relevant for survival. No different with a cello or piccolo. We can identify them. But beyond that it becomes tres difficult. More on this later. I digress. Suffice it to say that a perfect audio copy of what is being fed to the speaker, while very preferable, is not a requirement.

Factoid #3: The laws of acoustics (physics) have not been repealed. There are a ton of manufacturers out there that claim their stratospherically priced products incorporate some new technology which makes all previous designs obsolete. Hokum. You are certainly entitled to buy what ever it is that floats your boat. But be advised, there is no connection between how a speaker system looks and how accurate it is. Um, well, maybe there is a little connection. The more a speaker system looks like a sculpture or a space ship, the less likely it is to be accurate. And the more likely it is to empty your wallet.

     Factoid #4: The number of drivers (speakers) in a system is a poor indicator of accuracy. Indeed the old engineering axiom which instructs us that simpler is (almost always) better is very much in keeping here. The only things of importance to be convincing are how smooth and to a smaller extent how wide the overall frequency response is, how linear the dynamic range is over the loudness required for the material in the given listening space, and the uniformity of the spatial dispersion pattern.

 Factoid #5: There are many ways to arrive at the same metaphorical place. Speaker systems use many different driver and enclosure designs. They all work to one degree or another. Some better than others. From a purely theoretical perspective, they all seek to emulate a mass less pulsing sphere: an isotropic (point) source which radiates a wave front of any audible frequency equally in all directions. But who cares? Which is the best design and manufacturer and model? How do I tell? This brings us back to Factoid #1. By looking at the “specs” , one can determine the best choice. But a trip to your local audio purveyor is so much more fun. So let’s go. Really. Not to worry. We’ll do this together.

OK. But before we go speaker shopping though, we need to have a look at our listening room. Important things to consider are how large is your room, and how much amplifier power do you have available to drive your new speakers? The larger the room or the less power you have, the more efficient your speakers must be to provide the volume necessary to be convincing. That is, they must make your music louder than other speakers of less efficient designs. Some examples of efficient speaker designs are “horns” or direct radiators (traditional speaker cones) in a “bass reflex” (ported) enclosure.   If on the other hand, you are the happy owner of an amplifier or receiver that provides a robust amount of available power, or your listening room is modest is size, a less efficient speaker system may be your best choice. An “acoustic suspension” design will provide a powerful and accurate low end but will require more power to deliver a realistic sound pressure (volume). And it will do this from a relatively small enclosure. Which design is better for your system will depend on these issues.   In any case, our new speakers must also have a uniform dispersion pattern which means the sound level remains as uniform as possible over a 180 degree hemispheric pattern. This is especially important (and difficult) at the high frequency end of the spectrum. And / yes / this too can be measured and quantified.   Oh, and one more thing, the night before you go to the audio salon, go listen to some live music. It should be similar to what you will be playing at home, preferably a small acoustic instrumental or vocal ensemble. Remember what we said back in factoid #2 about our acoustic memory? It will help you to identify the most accurate speaker. Believe it. Only the facts here…

To be continued…

Hey kids / Have a look at this audio blog that was recommended by my good friend Raphael…

http://archimago.blogspot.com.au/

Just the facts. I love it!!

Back thataway several posts I opined that the most important component in your audio system is the recording engineer responsible for capturing the original musical performance. It’s a fact, kids. So now what’s next? Surely it’s time to think about D to A converters, or low distortion speaker cables made only with organic oxygen free copper, or yada yada yada. Nope. The second most important audio component in your system is your listening room.

Since the goal is (repeat again after me) to produce the most believable sonic image of the original, we need to be able to transmit this sound to your ears from your speakers in the most accurate and uncolored way possible. This means we need to keep from adding or subtracting any sound levels that were not part of the original. The truth is, our ears are not too smart. But our brains will instantly call fowl if the spectral balance is messed up.

So how do we go about dealing with this? There are several things to consider about the room (and the space within it) which will have a huge effect upon how convincing the sonic image is to our brains. Let’s take them one at a time.

First, we need to understand a bit about room acoustics. Walls are required in most rooms. Sonically they can do good things or bad things. Which they do depends upon their construction, dimensions, and placement relative to one another. I will spare you the math associated with how to answer this question in favor of some general do’s and don’ts:

• Parallel walls are bad;
• Curved or non parallel walls are good;
• Sloping ceilings are good;
• Sloping floors are good for sound but can be dangerous;
• Avoid a room where walls (including the floor and ceiling) are equal or multiples Eg: 10x10x10 is the worst possible; 10x20x10 is nearly as bad;
• Having large heavy objects in the room is good (unless they are the listener);
• Walls should be rigid. 16″ on center studs and drywall is not a wall at 40 Hz;
• Room size is also dependant upon your speakers and available amplifier power. More on this later too;

OK Second, we need to determine the optimal location for your speakers. The distance between your speakers and a rigid surface (such as a wall or floor) will have a big effect upon bass response. Um, no. The speakers will respond almost the same no matter where you put them. What I should say is, it will have a big effect on how loud and the how smooth the bass sounds to you depending upon where your ears are in the room. Again there is a ton of math you can use to determine this but for most folks there are practical considerations about where your speakers end up in your home environment (such as marital bliss). So more do’s and don’ts:

• Putting speakers deep in corners of the room is very bad. It’s scary in there for them;
• Sitting on the floor is bad (if you are a speaker);
• Speakers need some distance between them. For now let’s just consider a classic 2 channel stereo system.  A good starting point is the distance between them should be roughly the same as the distance to your ears;
• Let your speakers away from the wall. They like to join the party;
• Try to maintain an equal distance between each speaker and an adjacent wall. Symmetry is good;

Remember: All this is primarily about the bass reaching your ears. For a simple classic two speaker system, it matters not how much you spend on “technology”. No amount of equalization will cure a bad listening room acoustic problem. The uniformity of  amplitude across the low end of the spectrum as well as the absolute low frequency limit will both be highly influenced by the room shape, construction, contents, where you are, and where your speakers are in it. This is laws of physics folks. Get used to it.

Middle and high frequencies are a different problem for room design. They react to their surroundings in quite a different way from the low end. Bass energy tends to go through surfaces easily. Middle and especially high frequencies are easily reflected by hard surfaces and much more readily absorbed especially by soft materials such as rugs or drapes. In general, at least some broad surfaces should have damping (rugs, drapes, wall hangings). The exact amount of these soft acoustically absorbent materials will depend upon your speakers and the size of the room. Too much softness and the sound will lack openness and sparkle. Too little softness will mean unpleasantly bright and hollow audio. Given the right balance, the sound from the loudspeakers will reach your biotransducers (ears) in tact and with the least amount of coloration from your listening room. Listening trial and error will carry the day on this one.

Next time: Speakers 101

Sooo we are stuck with having to be sonically transported to the place where the recording was made / “You Are There”. This presents a whole different list of psychoacoustic problems. First off there is a vast difference between recording a symphony in a concert hall, and, say, a jazz trio in a club. The concert hall is huge compare to the club. Reflections from the concert hall will be slow compared to the jazz club because of the time it takes for the sound to reflect (we call this “Ambience”) from the large hall. We have to rely on the skill of the recording engineer to select the best microphones and place them in such a way that they will pick up a convincing balance of direct sound and ambience. He really is the most important component!

OK. For now let’s pretend we have the amplifier power and speakers to handle the dynamics of both. How do we handle the problem of our reflected sound in our listening room? Won’t this additional “return” confuse our ears and make the sound seem unnatural? Or do we have to haul our system outside where there are no walls or ceilings?

Hold on. There is good news kids. If we listen in a reasonably small area, several things happen. We find ourselves relatively close to the speakers. In this “near field” environment, the ratio between the direct sound from the speakers to the reflected sound from the room is quite low. Your ears will not be aware of the small amounts of “room” acoustics choosing instead to “believe” the much louder near field energy. And with it comes the ambience which has been recorded from the concert hall along with the direct sound from the instruments. “You Are There”. More good news: There are things you can do to your listening room to improve things further.

Next time: “The Second Most Important Component”