Understanding Speaker Spec Sheets

Structure of a Speaker Spec Sheet

A spec sheet usually begins with the design type, followed by the measured values. Detailed spec sheets supplement the numbers with measurement curves and conditions, while short ones often only mention four or five values. Some specifications also appear under several names, such as sensitivity and efficiency.

The numbers show what a speaker is built for. They can only be directly compared under the same measurement conditions.

Design and Components

At the beginning, it usually states how many ways a speaker has. In a 2-way speaker, a woofer and a tweeter share the work; in a 3-way speaker, a midrange driver is added. The crossover in the speaker distributes the sound to the individual drivers. The crossover frequency indicates at which pitch the next driver takes over. Some spec sheets call this value the cut-off frequency.

In addition, there is information about the cabinet, such as closed or with a bass reflex port, as well as dimensions and weight. The cabinet type allows for initial conclusions about the bass. Dimensions and weight are primarily needed to plan the placement on a shelf or next to the TV.

Measurement Conditions

Many values in the spec sheet are measured in a room without reverberation, with a microphone at a fixed distance in front of the speaker. However, by no means does every manufacturer state which procedure they used for measurement.

If the measurement conditions are missing, values from different manufacturers can hardly be compared. Two speakers with the same wattage or the same frequency range can still differ significantly.

Frequency Response and Frequency Range

The frequency response describes how loud a speaker reproduces individual tones from low to high. In the spec sheet, it is usually listed as a range between two limit values; in detailed versions, it is also shown as a measurement curve. Strictly speaking, the frequency response is the curve, while the frequency range is just its start and end points. Some manufacturers also refer to the frequency range as the transmission range. For voices in TV audio, it is particularly important that the midrange frequencies are reproduced evenly.

Limit Values and Tolerance

A specification like “45 Hz to 22 kHz” states the limits of the range specified by the manufacturer. It only becomes meaningful with a tolerance, such as “±3 dB.” This tolerance means that the volume within this range deviates by no more than 3 dB up or down from the average.

If no tolerance is included, the speaker may already be very quiet at the limits. Some manufacturers list two ranges, for example, one for ±3 dB and one for −10 dB. The second range goes deeper, but at its lower limit, the bass is then significantly quieter.

Structure of the Measurement Curve

In a frequency response curve, the tones are from left to right, from low to high. The volume in dB is plotted upwards. A line that is as flat as possible means that the speaker reproduces all tones at a similar volume and does not emphasize any particular range.

Individual peaks and dips are normal. However, a dip between about 1,000 and 4,000 Hz causes voices to recede slightly, while a strong peak in this range can make them sound sharp. For the TV, this range is therefore more important than a particularly deep bass.

Impedance and Ohms

Impedance is the AC resistance that a speaker presents to the amplifier. It is specified in ohms and is particularly important for passive speakers that are connected to an amplifier or AV receiver. With active speakers and soundbars, the amplifier and speaker are already matched to each other.

Nominal Impedance 4 and 8 Ohms

The spec sheet usually lists a nominal impedance, for example, 4 or 8 ohms. The base value is determined by the wire of the voice coil that drives the diaphragm. Since the movement of the diaphragm and the crossover also play a role, the impedance changes with the pitch and is significantly higher at some frequencies. The nominal impedance is based on the lowest value in the frequency range used.

A 4-ohm speaker is not better or worse than an 8-ohm one. However, at the same voltage, it draws more power, which is also reflected in the sensitivity. Some spec sheets also mention the minimum impedance and the frequency at which it occurs.

Impedance Specification on the Amplifier

The amplifier or AV receiver also has an impedance specification in its spec sheet. It states which speakers it is designed for, such as “4 to 16 ohms.”

Many amplifiers also specify their power for two impedances, for example, 100 watts at 8 ohms and 140 watts at 4 ohms. The higher number then applies to 4-ohm speakers.

Power in Watts

The wattage specification is one of the best-known numbers in the spec sheet, but it is particularly difficult to compare. For a passive speaker, it describes the amplifier power the speaker is designed for. For active speakers and soundbars, it stands for the power of the built-in amplifiers.

RMS, Nominal, and Peak Power

Nominal and RMS power handling are measured with a continuous signal over a long period. For nominal power handling, a noise signal is used; for RMS power handling, a steady tone is used. Both values are significantly below music and peak power and are the most comparable. Music and peak power refer to short, loud passages and are therefore much higher.

For soundbars and small systems, the power of all built-in amplifiers is often added together. A specification like “300 watts total power” therefore usually refers to several channels combined and often to short peaks. If the measurement method is not mentioned, it says little about how loud the soundbar actually plays.

Watts and Volume

Twice as much power only makes a speaker 3 dB louder. You only perceive about 10 dB more as twice as loud. To achieve this, the speaker needs about ten times the power. In the living room, a few watts are therefore usually sufficient at normal volume. The high specifications in the spec sheet primarily concern short, loud passages in movies and music.

Sensitivity and Efficiency

Sensitivity indicates how loud a speaker plays with a fixed, small amount of power. In the spec sheet, it is also called sensitivity level or efficiency. Strictly speaking, efficiency is the ratio of sound power output to power input, but in spec sheets, the term is often used for sensitivity. For everyday assessment, sensitivity is usually more helpful than the wattage. Together with the amplifier power, it shows what volume a combination reaches.

Specification in dB at 2.83 Volts and 1 Meter

The sound pressure is measured at a distance of one meter in front of the speaker while a voltage of 2.83 volts is applied to it. This corresponds to one watt of power at 8 ohms. The spec sheet then says something like “87 dB (2.83 V/1 m),” sometimes also “87 dB/1 W/1 m” or “dB SPL.”

A 4-ohm speaker mathematically draws twice the power at 2.83 volts, i.e., two watts. Its sensitivity is therefore about 3 dB above that of an 8-ohm speaker with the same efficiency. When comparing, the impedance must therefore be included.

Significance for Volume

A higher sensitivity means that an amplifier with less power is sufficient for the same volume. This applies when comparing two speakers, provided both values are based on one watt or both speakers have the same impedance. On the other hand, the value says almost nothing about sound quality.

Total Harmonic Distortion

Total harmonic distortion describes distortions that are added to the original tone during playback. In addition to the actual tone, a speaker also emits overtones that were not contained in the signal. THD relates these additional components to the original tone.

Specification in Percent or as THD

In the spec sheet, the distortion factor is usually given in percent, often under the abbreviation THD. A value of 1% means that the additional overtones together reach one hundredth of the sound pressure of the original tone. Their level is thus around 40 dB below the actual tone. The specification can only be meaningful if the volume and frequency range of the measurement are included.

THD in Everyday Life

For speakers, the THD is usually higher than for amplifiers, especially in the bass and at high volumes. In the living room, values around one percent are hardly noticeable at normal volume. Distortion becomes audible rather when small speakers are expected to reproduce low tones very loudly, such as during explosions or loud film music in action movies.

Spec Sheets for Soundbars, Subwoofers, and Active Speakers

Anyone looking to improve the sound on their TV usually deals with soundbars, subwoofers, or active speakers. Their spec sheets are often shorter than those of passive speakers. Specifications such as impedance or sensitivity are often missing because the amplifier and speaker are permanently paired.

Soundbars

For soundbars, the focus is usually on total power, the number of channels, and the connections. The channel specification shows whether a dedicated center channel is available. This is the case with 3.1 or 5.1, but not with 2.1. With a center channel, voices come from a dedicated speaker in the middle and often sound somewhat clearer, but this only helps to a limited extent against a poorly mixed voice track. If you primarily pay attention to voices, you will still find more clues in the channel specification than in the wattage.

The frequency range of a soundbar often ends at the bottom between about 60 and 100 Hz. Deeper tones are then handled by a subwoofer, if one is included.

Subwoofers

For a subwoofer, what matters most is how far down it reaches and at what frequency it hands over to the other speakers. This crossover frequency can often be adjusted; values between 80 and 120 Hz are common. The wattage specification here refers to the built-in amplifier and is comparatively high because low tones require a lot of power.

Active Speakers

Active speakers already have the amplifier built in. The spec sheet therefore lists the amplifier power per speaker or for the pair together, often separately for the tweeter and woofer. For connecting to the TV, the inputs are also important, such as an optical input or HDMI ARC.