If you're building an audio system, I've got three questions you can ask that will help you to choose
the perfect speakers. The answers to these three questions will be your guide to understanding the
features and specifications, so that you feel confident you're making the right decision.
Speaker spec sheets can be difficult to navigate, especially if you're not used to looking at them.
You've got to be careful, because some specifications might actually mislead
you into thinking that a speaker is much more powerful than it actually is. You'll learn how
you can find and understand some of the key specifications that you should be considering
when choosing your speakers. It's best if you can start the process of designing a sound system with
a clear understanding of the goal. Here are the three questions to ask before getting started.
Where will the audience be located? I think this question is the best place to start. Is this a
listening system for one person, 50 people, or a thousand people? If there's only one listening
position, you know where the listener will be at all times and that means that you can optimize
the system to sound best at that exact position, maybe even employing a stereo or surround setup
to make the experience even more immersive for that listener. When designing a sound system for
a larger audience, just providing even coverage can be a challenge. A sound system can really only
be optimized for one point in space, so you'll have to make some sacrifices when optimizing the
system to sound good throughout a larger audience area. In a speaker's technical specifications,
you might find a coverage angle that describes the vertical and horizontal angle that sound
disperses from the speaker. There's only one angle listed for this particular speaker - 75 degrees.
That means that both the vertical and horizontal coverage angles are 75 degrees, but the vertical
and horizontal angles aren't always the same. Some speakers even have variable coverage angles.
If a listener steps outside of the speaker's coverage pattern, it will start to sound dull
to that listener because high frequencies are more directional than low frequencies.
It might seem like the wider the coverage angle, the better. However there are several reasons why
this isn't necessarily true. One reason is that you'll usually be aiming for a consistent level
throughout the listening area and the sound from overlapping speakers will add together
at the point where they overlap. The areas where the speakers overlap will be louder
and the areas covered by just one speaker will be quieter. Not only will the speakers add together,
but they'll also cancel out at some frequencies because of phase interference.
I've got another post that goes into much more depth on why this happens, but the result is a
change in the frequency response of the system. Obviously, designing a home theater system is
much different from designing a PA system for a music festival or a paging system for a building.
In a surround sound system, the goal might be for the various speakers to work together to create an
immersive experience for a single listener. While addressing larger groups, the approach as a whole
might change to groups of distributed speakers that address smaller portions of the audience.
The second question should be, "Where should the speakers be located?".
Unfortunately, the question is most often, "Where can the speakers be located?". The best location
for a speaker, in terms of sound quality, might be directly in front of the audience. However,
if the speaker obstructs the view of the audience, it doesn't really matter how good it sounds.
The speaker will need to be placed somewhere else where it won't obstruct any important sightlines.
The reality is that it's commonplace for visual aesthetics to be prioritized over sound quality
and, in most situations, you won't be able to place the speakers in the absolutely ideal
position. Paying attention to the coverage pattern of the speakers not only helps to provide sound
where it is needed, but it also helps to reduce sound levels outside of the listening area.
This could be used to prevent sound from leaking into nearby areas or to prevent
unnecessary reflections off of nearby walls. It's important to understand the relationship
between the coverage pattern of a speaker and the placement of a speaker. Naturally,
the coverage area becomes larger at longer distances from the speaker.
While a ceiling speaker with a 135-degree coverage pattern might cover a 14-foot diameter from 8-foot
ceiling height, that same speaker could cover a 24-foot diameter from a 10-foot ceiling height,
because there's more distance for the sound to spread out before reaching the listener.
That means more speakers are required to cover the same listening area
when the ceiling height is lowered. The same goes for surface mounted speakers. A 75-degree pattern
might seem narrow at short distances, but a 75-degree speaker on each side of the stage
might cover the entire audience if there's enough distance between the speaker and the audience.
Often fill speakers will be used to cover the areas not fully covered by the main speakers.
The third question to ask is, "How loud does the system need to be?". If you know the location of
the listeners, the location of the speakers, and you have a target level for the listening
position, you're off to a great start. To give you an idea of what the target level should be,
let's take a look at this chart. I usually aim for a music system target between 80 and 100 dB
SPL at the listing position. Having that extra headroom is unnecessary in many situations,
but I'll leave that up to you to decide. This is a good time to mention a pair of specifications
that help us to understand how loud a speaker can get: sensitivity and continuous power capacity.
The speaker's sensitivity tells us how loud the speaker will be if supplied with a given amount of
power. Most often, you'll see something like this. When one watt of power is applied to this speaker,
you can expect 97 dB SPL measured from one meter away from the speaker.
The speaker's continuous power capacity describes how much power can be supplied to the speaker
consistently over time without causing damage or permanent change. Speaker companies will
often boast the much higher peak power capacity, which merely describes the maximum momentary power
that can be supplied to the speaker without damage. I think comparing speakers based on
continuous power capacity is much more useful in almost every case. Let's take a look at how
sensitivity and power capacity are related. If this speaker is capable of producing 97 dB SPL
at one meter away with one watt of power from the amplifier, how loud will it be when supplied with
500 watts (its continuous power capacity)? This formula will help us to answer this question.
By the way, many of the formulas and charts you'll see in this video can be found in the
Audio University article on decibels. Power 1 is our wattage from the sensitivity specification.
Power 2 is the continuous power capacity - 500 watts. This formula can be solved using
a scientific calculator like this one. I'll leave a link to this one in the description below. The
formula tells us that the difference between 1 watt and 500 watts is nearly 27 decibels.
So, by adding 27 to the 97 from the specs, we can calculate that the speaker is capable of producing
124 dB SPL at one meter. With this information, we can determine if a speaker is capable of
achieving our target level at the listening position. The inverse distance law states that,
with every doubling of distance, there's a 6 dB loss in level. This is another reason why it's
so important to know where the speaker will be in relation to the listening position. Let's say we
plan for the speaker to be placed about 10 meters away from the listener. This time, we're going to
use the non-power decibel formula, because we're comparing distance rather than power.
Distance 1 is our starting distance that we found in the sensitivity specification - one
meter. Distance 2 is the distance between the speaker and the listening position. This formula
tells us that there will be about a 20 dB loss over that distance. So, subtracting 20 from 124
tells us that the speaker will produce 104 dB SPL at the listing position. That
means that the speaker is certainly capable of providing adequate level to listening position.
If the speaker couldn't get loud enough at its continuous power capacity, you'd need
to choose either a more sensitive speaker or a speaker with a greater power handling capacity.
I think it's always best to choose speakers first
and then find an amplifier that will provide enough power to those speakers.
If you're ready to learn how to choose the right amplifier for your speakers,
check out the video that's on your screen now. I provide you with a simple guideline for choosing
an amplifier and explain why it's so important to match your amplifier to your speakers properly.
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