Guide to Speaker Specifications

June 2, 2006

By Sherlock Ohms

Perhaps the most misunderstood of all home theater elements is that of the loudspeaker. With today’s Web-savvy, knowledge-thirsty customers comes the challenge of shopping for speakers by specifications and price. And this shouldn’t be viewed as burdensome, but rather as another piece of the puzzle and learning process to make your overall home theater experience even better.

Many argue that buying a loudspeaker without ever personally auditioning it would be quite reckless. However, given the vast number of loudspeakers in today’s market understanding specifications and using them to narrow down the field of search isn’t a bad idea.

The Web can be a valuable resource for such searches, and volumes of information, however beware that not everything you read on the Web is factual. Stick with companies you know and trust and you’ll avoid the snares of creative marketing.

"While many consumers today look first at the “Power Handling” spec of a speaker, this is actually not an important consideration at all."


With this in mind, it is most important to understand the specifications of a loudspeaker, so that you can better gauge where your audition time will be best spent.

While many consumers today look first at the “Power Handling” spec of a speaker, this is actually not an important consideration at all. The two most important specifications (and often the least understood) are the Nominal Impedance and Sensitivity Ratings. PSB Speakers takes the Sensitivity Rating a step further by including the Voltage Sensitivity Rating.

Sensitivity
Sensitivity is most easily defined as the speakers’ ability to effectively convert power into sound. The traditional way of measuring a speakers’ sensitivity is using the standard of 1 watt/1 meter. Meaning a microphone is placed 1 meter away from the speaker to measure the sound output (in decibels) with 1 watt of sound played through it.

There is much room for error (or imposed error) with this type of measuring system and some manufacturers today take advantage of this.

Voltage Sensitivity
Because today’s solid state amplifiers do a good job across the board of maintaining a voltage output of 2.83 volts, many companies consider this as their standard of measurement. Here again, 2.83 volts are inputted and measured at 1 meter. [Note: 2.83 volts into an 8 ohm load is equal to 1 watt. Ohm’s Law: Power (watts) = Voltage (V) x Current (I) or Power = V_/R (impedance in Ohms)]

Because a speakers’ efficiency in transforming (transducer) power into sound is greatly determined by the impedance of a speaker, (see more on impedance below) 2.83 volts becomes greater about 1.5 watts at 6 ohms (as many PSB Speakers are rated.) and 2 watts at 4 ohms — a 3dB increase. (Read more on the importance of a 3dB increase below.)

Now let’s look at the Sensitivity Rating of a speaker, since many speakers are still rated this way today. Basically Sensitivity is the speakers’ ability to efficiently use the amplifiers energy to create sound. This spec is rated in decibels (dB), but how it’s measured is also important to know. Consider a speaker with a Sensitivity Rating of 87 dB. The standard for achieving this rating is 1 watt/1 meter. This means the speaker will produce sound at the volume of 87 dB, measured by a microphone placed 1 meter away when it’s given the input power of 1 watt. (Typically, the input sound is 1 kHz.) A typical PSB loudspeaker has a minimum Sensitivity Rating of 87 dB and this is considered quite efficient. While many of today’s mass-marketed loudspeakers range closer to 84 dB, PSB speakers “average” Sensitivity is quite high and some PSB speakers boast a Sensitivity Rating of up to 90 dB which is quite rare and quite good!
Consider this: If 0 dB represents the threshold of hearing, then what are other common volume levels of sound?

A Whisper: 15-25 dB
Home or Office Background Noise:
40-60 dB
Normal Speaking Voice:
65-70 dB
Orchestral Climax:
105 dB
Rock Concert:
120+ dB
Pain Threshold:
130 dB
Jet Aircraft:
140-180 dB


Think about this for a moment; it takes twice the amount of power to produce an increase of only 3 dB in sound volume. That means, given the example of the PSB speaker above, an amplifier with 100 watts of power would need 200 watts of power to increase from 84 dB to 87 dB!

All this time you must temper your requirement for amplifier power (and therefore, the maximum potential output level) with the knowledge that, when asked, most people will say that they think they hear a doubling in perceived loudness or volume when the amplifier power is turned up 10 dB (=10x). Just think about that. This knowledge sheds some light on the needs for a speaker/amp combination that plays loud enough and sounds “true to nature” – the way it was intended when the music was recorded. For example, using the chart below, if you are listening to a speaker with a Sensitivity Rating of 87 dB, when played with 4 watts of power, it will produce 93 dB. Therefore, to perceive twice the volume, you will require 40 watts (10x) which will equal an SPL of 103 dB.

Perhaps an even better illustration (as stated before) is that many home theater speaker systems today have a Sensitivity Rating of 80 dB to 84 dB and some are even worse. PSB Speakers tend to average around 87 db (with some as high as 90 dB). If you’ve got a speaker with a Sensitivity Rating of less than 85 dB, you’re going to need a fair amount of power to achieve a reasonable sound level.
Here’s a simple chart to give you an idea of how power relates to speaker volume. These numbers aren’t based on any particular manufacturer amplifier or speaker, but rather just to give you a simple point of reference for a speaker with a Sensitivity Rating of 87 dB.

Power in watts
Volume in dB
1
87
2
90
4
93
10
97
20
100
40
103
100
107
200
110
400
113


As you can see from the chart above, you can get a fair amount of volume (dB) out of as little as 32 watts of power (continuous) for a speaker with a Sensitivity Rating of 87 dB.

You will notice as you look at amplifier specifications that some offer variable power ratings based on the Nominal Impedance, listed in Ohms. Here again we are revisiting the idea of efficiency from another perspective.

Impedance
Quite simply, Impedance is the speakers’ resistance to power or impeding the flow of power. Generally speaking, the majority of today’s loudspeakers are rated at an Impedance of 8 ohms. And this is the standard specification for which many amplifiers are also rated—meaning their power delivered into 8-ohm loads.

Many higher-end speakers and amplifiers are rated at 4 to 6 ohms. Understand that some amplifiers cannot drive speakers at less than 8 ohms for any sustained period of time. This will eventually cause the amplifier to fail.

PSB speakers all bare a Nominal Impedance rating of 6 ohms, which on their own make them quite efficient. However, when coupled with their outstanding Sensitivity Ratings, this makes for an incredibly efficient loudspeaker with headroom far greater than most speakers offered today. This is just one of many factors that make PSB Speakers some of the most critically acclaimed, highly sought after brands on the market.

A New Understanding
Now that you understand some of the basics as to how specifications relate to a speaker, let me again stress the importance of auditioning speakers in person before you buy them. While there are many factors in which manufacturers account for when designing loudspeakers, it is still more of an art than a science.

Several factors will affect a speaker’s performance which cannot be accounted for. Consider that nearly every single room, including size, volume, shape, and materials which inhibit or enhance sound, is different.

That said, the measurements we discussed cannot account for an anomaly known as “Room Gain.” Speakers are tested and measured in anechoic chambers—rooms that are sound proof and have little or no sound reflections whatsoever. No room in any home meets this criterion. This is done (in part) to isolate the speaker during testing.

Direct or reflective sound (reverberation) or sound reflecting off the boundaries of a room is often described as “sound power.” Sound power is the sum of all energies combined; including amplifier power, speaker volume, reflective and non reflective sound, and so on. Additionally, this does not take into account the abilities of the listener—remember, at home, your ears are now the microphone. And some are better than others.

When most people are asked what they want or expect out of a premium sound system, their answer is almost always “more power.” Now that you understand that the perception of more power can be directly related to the ability of the loudspeaker itself, the real question is “what should I expect out of my sound system?”

"Expect a sales associate to tell you what to listen for, but not how it should sound to you."


The answer is simple—nothing but the best for your personal tastes and needs. Expect a sales associate to tell you what to listen for, but not how it should sound to you. When auditioning speakers, it is in your best interest to bring your own source material, if at all possible. After all, this is the music or movie(s) that you are most familiar with and will, therefore, provide the most revealing demonstration.

Now that you understand some key loudspeaker specifications, you will be better prepared as you shop for and audition loudspeakers. This will also help you to understand the working relationship between speaker and amplifier and better equip you to determine your needs.

Remember, buying loudspeakers should be a fun process for you. Take your time and audition as many speakers as you wish until you feel comfortable with your choice. Expect that the speakers will sound better in the comfort of your own home and be sure to make your purchase with a retailer who has a return policy that will allow you to audition them in your own home.

Good speakers will last you a couple of decades and should be considered an investment.

Good luck and good listening!





Comments (1)

2011-07-30 08:36
Rubens - Brazil

Hi Sherlock, long time since you have been writing this article. I have been searching speakers for myself and for my son - replacement ones - but as far as we go searching more lost indeed. For isntance, our new amp heads are up to 4,8 and 16 Ohms speakers. Wich one is going be better for quality, power and raliability? How undesrtand sharts? and so....
I need for myself a spkeaker fro a smooth jazz and I am not sure how choose as soon as most brands says that they are also good for blues, rock and so.

Thanks, Rubens

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