Speaker Specs 101: Impedance, Sensitivity, Resonant Frequency

Editor’s note: this blog from 2022 was updated in 2023 with additional information.

It can feel like there is an overwhelming amount of data when you’re trying to figure out what you need in a loudspeaker. Looking at the spec sheet can be intimidating, but not all those numbers matter equally. When it comes down to it, there are a handful of specs that are critical to understand to get the speaker that’ll do what you need it to. Here are the ones to focus on.

Impedance

Impedance is about how much electrical energy is needed for a speaker. It’s important because it helps determine what kind of amp you need to supply that power. Impedance is measured in Ohms and most speakers will be rated at 4, 6, 8, or 16 Ohms by their manufacturer. The lower the impedance, the more electrical current a speaker draws from the amplifier. Impedance really comes into play when you have more than one speaker working off an amp. This is because speakers that are wired in parallel draw more power.

In designing a multi-speaker system it is worth considering how bi-amping can improve overall performance.

Power Handling/Ratings

This number is usually given in watts and may also be called a speaker’s wattage rating. It tells you the theoretical limits the speaker can handle in terms of electrical power and is closely related to volume. A large speaker could be 1000W or a small one could be under 1W. The full sound system in a stadium could be several hundred thousand watts. There is no one standard way to establish a speaker’s power handling, so make sure you communicate well with your speaker manufacturer about what your needs are.

Klippel, the global leader in speaker testing, has introduced a new offering called Klippel Endurance Test (KET) that covers multi-channel long-term, power, and accelerated life tests for quality assurance. This testing is a good way to confirm power handling specifications.

Frequency Response

Different speakers are good at handling different frequencies. This is why there are subwoofers, woofers, midranges, tweeters, etc. Knowing the frequency response ensures your speaker is good at what you need it to be good at (or your combination of speakers is accomplishing what you want in your sound system). Frequency response is shown as a graph or chart with Hertz (Hz) – the measure for frequency – on the X-axis and amplitude (dB SPL) on the Y-axis. The peaks and valleys on the graph tell you where the speaker is overplaying or underplaying specific frequencies relative to how they are intended.  

Resource: The Difference Between a Midrange and a Full Range Speaker

Sensitivity

Sensitivity is the relationship between the wattage going into a speaker and the volume coming out of it measured, at a specific distance away from it. It’s closely related to power handling and impedance. Sensitivity will tell us how loud a speaker will get with a given amplifier. To standardize sensitivity, it’s a measure of the volume (in dB) at 1 meter away from a speaker when 1 watt of power is being fed into it. Speakers frequently have a sensitivity of around 87 dB. A speaker is considered excellent if it has a sensitivity rating above 90 dB.

Resonant Frequency

This tells you the lowest frequencies a speaker will function well at. It’s impacted by the materials and design of the cone and the speaker’s driver. In general, if your speaker will be handling lower tones you’ll want a lower resonant frequency. This number also comes into play when considering enclosures and whether they may “ring” at the frequencies below the resonant frequency of the speaker. One way to lower the resonant frequency of a speaker is by incorporating a port into the enclosure design. 

Qts

A spec related to resonant frequency is the Total Q (or Qts) of a speaker. This unitless decimal tells you how the inner workings (spider, voice coil, magnet, etc.) are moving when the speaker is at its resonant frequency. It takes into account the electrical properties and damping effects of the driver. The Qts can inform decisions about speaker enclosures. A Qts below .4 means a speaker should be put in a ported enclosure. A Qts above .5 means it’s better suited for a sealed box. 

Small Signal Parameters

Influential research papers on speakers written in the 1970s led to the establishment of Thiele/Small Signal Parameters (abbreviated T/S parameters, or TSP). These numbers tell you how a speaker performs at low frequencies. They can also help speaker manufacturers determine the best enclosure for a speaker. 

Large Signal Parameters

These data points are important for understanding how a speaker operates under higher power levels. This information can be helpful in figuring out the limits of a transducer and in preventing distortion.

Loudspeaker manufacturers must use high-tech testing tools to accurately measure how a speaker is performing. This is the only way to get data for many of these specs. Download the guide below if you want to understand the numbers that go into evaluating a speaker on a deeper level.

This video, the first in a series on Designing and Building a Loudspeaker, explains how a manufacturer makes decisions around materials and design to meet a customer’s specifications for a speaker.

 

Download this free guide to help you build you loudspeaker acumen

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