An Audiophile’s Guide to Loudspeaker Efficiency

One of our primary goals at Future Audiophile is to introduce the hobby to new enthusiasts. It matters not if a listener is a teenager or someone closing in on retirement, we want to be able to help any and all involved in the audiophile hobby gain a more in-depth understanding of the concepts more seasoned veterans sometimes take for granted or gloss over too quickly. Many of the newly interested are unfamiliar with some of the more technical aspects of our hobby. In an effort to help explain what most of us already understand, Future Audiophile will occasionally publish feature articles on certain technical aspects of the audiophile process. Please understand, this article is intended for anyone who enjoys what a high-performance audio system can deliver, but is mostly unsure how such excellent sonics are achieved. This article, therefore, will try to remain very basic, yet still be informative. 

What Type of Speakers Do You Have and How Hard Are They to Drive?

Following the notion it is best to start at the beginning, let’s look at the various speaker types and how they function. Please note: we will only cover the four most basic types of speakers. There are many hybrid speaker designs but, for now, for simplicity’s sake, those will be omitted. Also, for simplicity’s sake, the description of how each speaker type works will be very minimal. A link to a more in -epth description of each speaker will be provided. 

Dynamic speakers are by far the most popular design for speakers used in the audiophile world. This design is identified by a round membrane in various diameters mounted inside a cabinet – usually a rectangle-shaped box. Called drivers, the larger sizes are woofers, which produce low-frequency sounds. Slightly smaller sizes, normally about three inches in diameter, will produce the middle, or midrange frequencies. A small driver, normally one inch in diameter, called a tweeter, is responsible for all high-pitched sounds. Dynamic speakers are the easiest to set up and position in a room for the best sonic presentation. This speaker design will normally be able to reproduce the full frequency range without too much trouble and, when correctly positioned, can fill a room with sound.

Planar speakers are made with magnets and a sheet of plastic material, normally mylar, embedded with a series of wires. When an electrical current reaches the magnets, they energize the wires and move the mylar sheet, thus causing air movement and music to be distributed into the room. Because the mechanics governing this air movement is so easily accomplished, many feel planar speakers produce a decidedly natural-sounding musical presentation. However, they typically have trouble producing very low bass frequencies and oftentimes will be supplemented by a subwoofer. Planar speakers like to be well into a large room and usually have a very narrow dispersion pattern. 

Electrostatic speakers are very similar in design to planars, except they use very thin strips of aluminum rather than mylar sheeting. Electrostatic speakers are also very accurate and, many feel, are highly lifelike in their sound. Most electrostatic speaker manufacturers incorporate a subwoofer into the cabinet to facilitate low bass production. 

Horn speakers are the oldest design on our esteemed list. Long before any other type of speaker design had been conceived, horn speakers were being used in abundance. Recently, at the Munich HIFI Show, Silbatone showed a vintage 1930s movie theater sound system, complete with horns, and it was physically gigantic, as well as an interesting look into the history of sound reproduction. 

Horn speakers function in a very similar fashion to a megaphone. They are normally very easy to drive, or operate, and they only require very nominal amounts of amplifier power to make them play – generally very loudly. There are two main drawbacks to horn speakers. One, it takes quite a large physical speaker to produce much in the way of low bass. The very early designs of horn speakers, long before the invention of stereo sound, saw horn speakers the size of modern refrigerators, or even bigger. The second drawback of horns is their tendency to sound like someone is speaking with both hands cupped around their mouth. Manufacturers of these types of speakers go to great lengths, and cost, to correct these two deficiencies. Anyone who likes to play music at obscenely loud levels will appreciate horn speakers and how efficiently they reproduce a musical signal.

What is Loudspeaker Sensitivity and Why Does It Matter?

Let’s face it, efficiency and sensitivity are important in everything we do, and speakers are no different. When we measure the amount of sound, we use the term amplitude to indicate how loud something sounds. The level of amplitude is measured in decibels (dB). Sound Pressure Level, or SPL, is a measure of the pressure variation, or sound pressure, caused by a sound wave relative to a reference value. It quantifies how loudly a sound is perceived. Normal conversation is about 50 dB, a rock concert is about 105 dB to 110 dB. Hearing damage and deafness will occur as the SPL, measured in decibels, increases above concert levels. It is always advised to limit how loudly music is played, especially when wearing headphones or earbuds.

Speaker sensitivity is therefore a measurement of the decibel output any one speaker can produce, given a specific amount of power from the amplifier at a given distance. The universal standard is expressed in decibel output with one watt of power (1w) at one meter (1m) of distance. When you read about a speaker with a listed sensitivity of 88 dB, this means this particular speaker will produce a SPL of 88 dB with one watt of amplifier power at one meter of distance. Normally, sensitivity is simply expressed by most manufacturers as 88 dB. The wattage and distance references are implied. If fully expressed, it would read as 88 dB/1w/1m. 

It is important to realize this rating is based on one meter, or just over three feet. Normally, these readings are taken in an anechoic chamber and not in the real world. They are NOT a representation of completely filling an entire room with sound. These ratings will make choosing an amplifier a little easier. A horn speaker, for instance, may well have a sensitivity rating of 110 dB, while a less efficient design may barely be above 80 dB. For the most part, any sensitivity rating below about 85 dB is less efficient, and above 90 db is very efficient. So why does this matter? It helps when choosing an amplifier, which, when paired with a properly chosen speaker, will produce a pleasing and listenable sound.

Another relevant factor in how hard or easy it is to drive your speakers is impedance. This is best described as the amount of resistance the power amplifier will incur when trying to drive (or power) the speakers. Impedance is usually measured in ohms (defined as the level of electrical resistance between two points) and, the lower the impedance at which a speaker operates, the more difficulty the amplifier will have in driving them. For instance, most speakers will have an impedance rating of either eight ohms or four ohms. Some difficult-to-drive speakers will dip below four ohms, and there was a time when some really out-there designs operated at two ohms. Impedance ratings of two ohms in speakers these days, however, is a rarity. The lower the impedance, the more amplifier wattage it will take to properly drive the speakers. Most amps will have a listed output power of wattage at eight ohms, and also at four ohms. Normally, the wattage output doubles as the speaker impedance is halved. So, an amp rated at 200 watts of power at eight ohms may easily output 400 watts at four ohms. 

It is vitally important to pay attention to the speaker impedance and match that to the output power of an amplifier. Always consider an amplifier and a speaker as a partnership and not as individual separate components.  

Reproducing Music (or Sound) in a Room Isn’t as Easy as It Might Seem

If you have ever been in a Best Buy, or another big box store, and started playing around with the wall full of ubiquitous AV receivers with all the buttons and knobs, when you increase the volume, often, the louder it gets, the worse it sounds. Understand first that adjusting the volume knob on an amplifier and how loudly the music sounds in the room is not a linear or one-to- one ratio. In fact, it is probably best described as logarithmic, not a linear progression. 

Looking at the numbers, each increase of three dB of SPL in the room means the output power of the amplifier must double. Going from 70 dB to 73 dB means the amp must double its output. Go from 73 dB to 76 dB means the amp must double its output again. This doubling of an amplifier’s output power continues for each three decibels of increased SPL in the room. If it takes five watts of power to produce 70 dB, it will take 10 to produce 73dB, 20 watts to produce 76 dB, 40 watts to produce 79 dB and so on. If you have ever wondered why those big box store receivers sound progressively worse as the volume knob is increased, it is because of a simple lack of power and the inability of the amplifier to continue to double its output power. Let me restate a very important fact: amplifiers and speakers should be chosen as a complementary pair, not as individual pieces.

What is Headroom in an Amplifier and Why Does it Matter?

Because the loudness of a musical presentation in any given space is dependent upon a combination of the speaker and the amplifier, having sufficient amounts of output power enables a realistic recreation of recorded music. When a low-efficiency speaker is paired with a lower powered amp and the listener tries to play music at concert levels, the amplifier will very often overload. Called clipping, this is when an amp can no longer provide the necessary level of output power the speakers demand to faithfully and accurately reproduce a given musical passage. Clipping not only completely ruins sonic excellence, it may actually damage the amp and/or the speakers. Pairing a highly efficient speaker, one with a sensitivity rating of, say, 96 dB with an amplifier rated at 300 watts at eight ohms, and 600 watts at four ohms, will provide vast amounts of power. Generally speaking, it is seldom necessary to use more than 30 or 40 watts of amplifier power when listening to music. So why do we need so much power?  

Called headroom, amplifiers with higher output power will have a much easier time of accurately recreating any one passage of recorded music. Consider, if you will, a recording of a symphony orchestra. You are listening to a very soft, very imitate flute solo. Without warning, the massive 50-piece orchestra comes in with the power of the horns and stringed instruments, and also the kettle drum and percussion, along with a pianist furiously pounding the keys. Were you in the concert hall in person, the power and forcefulness of this change in dynamic amplitude would be not only heard, but also felt. The difference in the amplitude of a soft musical passage and a much louder one is called dynamic range. And because the SPL is substantially increased, to faithfully recreate this on a home stereo, like it was in a live setting, and most certainly how it was recorded, you guessed it, the greater the demand on the amplifier becomes. The more output power your amp has in reserve, the more easily and more believably the recorded passage will be recreated in a home listening environment. This is what audiophiles call headroom and, generally speaking, the more of it an amplifier can provide, the easier it will have to work to deliver an immersive and believable musical experience. It also lessens the chance of overloading the amp, which may damage the amp, the speakers, or both. 

What Are the Main Differences Between a Hard-To-Drive Speaker and One That is Very Efficient?

High-performance, hard-to-drive speakers often prioritize accuracy, clarity, and detail over efficiency. This type of design will very often reduce distortion, which can be the cause of a less than natural-sounding musical presentation. Hard-to-drive speakers will usually offer an increased level of dynamics, or the power of a musical presentation, and will handle higher volumes more easily. They also tend to be better engineered with a higher level of build quality. 

Additionally, harder-to-drive speakers also require a more powerful amplifier and, potentially, a more expensive amp as well. They are much better suited to a high-output-powered, solid state, Class-AB amplifier, as opposed to a three-watt, single- end triode (SET) tube-type amplifier. Of course, here again, if a harder-to-drive speaker is being considered, be sure it will very easily pair with whatever the specifications are for the existing amplifier in use. Or, if replacing the amp is being considered, be sure it will easily and properly drive the speakers. 

Very efficient speakers, on the other hand, are more easily paired with lower-powered and oftentimes less expensive amplifiers. If a very low-powered tube amp is being considered, say, a three-watt SET amp, high-efficiency speakers are a must. An easy-to-drive loudspeaker system gives you acceptablesound with less power, broad amplifier compatibility, may actually offer cost savings, and not require as much space in the room. It may certainly be a smart choice for users who value simplicity and economy in their audiophile systems.

Final Thoughts on Loudspeaker Efficiency and Other Audiophile Loudspeaker Terms …

All audiophiles would love to have the feeling of awe and unbelievability a fantastic live musical experience provides. Go to a really fantastic concert and if, three days later, you are still amazed by the performance, this is exactly the feeling an audiophile wants from each and every listening session. There will never be enough slack-jawed, mic-drop moments in the audiophile hobby. 

It is therefore vitally important to understand how best to choose an amplifier and speakers, which will work in concert with each other, not an adversarial position. Newcomers to the hobby are well-advised to visit better AV dealers to become better informed if that is realistic or logistically possible. The Internet is awash with articles and videos on the speaker/amplifier relationship. Before you buy, do your homework. Read the specs on both the amplifier and the speakers. Be sure the amp will provide sufficient output power to drive the speakers as desired. Taking the time to be sure the components are best suited for each other is a safe approach. It is always best advised not to buy solely and exclusively based on price. Be sure your purchase is one in which all parts of the system – amp, preamp, sources, speakers and cables – are all on the same level of quality, complementary efficiencies, and the ability to produce a sonic presentation that will afford continued listening pleasure. When it works best, the listener will have a hard time shutting the system off and ending a listening session. When mismatched components are used, it is likely the listener will have to force themselves to listen to one more song. 

Be smart, be informed, and take the steps to create an immersive and pleasing musical experience. It certainly makes the hobby a lot more fun. 

What type of speakers do you use in your main audiophile setup? Are they hard to drive? Did that factor into your buying decisions? Share with us a little bit about your system, and we will post your comments below via our moderator.