Speaker impedance 101: What are speaker ohms?

Active speaker SoundLink Revolve+ II sitting on outdoor table with food

You might not be too familiar with the term “speaker impedance,” which essentially means the electrical resistance of a device. But it’s a crucial factor in speakers, AV receivers, and amplifiers. Impedance is measured in ohms and can seriously affect your audio quality.  The higher the ohm rating, the more it resists the incoming signal or sound. In simple terms, higher impedance means you’ll need more power to drive it.

But what are speaker ohms exactly, and why should you care? Read on to learn more.

What are speaker ohms?

Getting a handle on speaker ohms is easier when you’ve got a basic grasp on how speakers work. When you’re in the market for a new set, you’ll likely come across terms like ohms, power handling, watts, amps, and voltage. But when it comes to speaker impedance, it’s the ohm rating that really matters.

Picture the speaker as a pipe, channeling sound as your music passes through it. The bigger the pipe, the more sound it can let through. When it comes to speaker design, low-impedance speakers are like a wide pipe, enabling a greater flow of electricity or sound.

The lower the impedance or ohm rating, the less resistance there is, which allows the speaker to transmit the electric signal or music more effectively. This means a 4-ohm speaker, also often called a low-impedance speaker, can process music or sound that could potentially over-circuit and seriously damage an 8-ohm amplifier.

What can be even more confusing is that the speaker ohm rating can change depending on the frequency it’s handling. For example, when you play a deep bass tone, speaker impedance could jump up to 8 ohms, but a sharp high tone could drop it down to just 2 ohms. According to the Audio Engineering Society (AES), loudspeakers can draw currents up to six times greater than their speaker impedance rating.

Your average home stereo system speaker will likely have a rating of 4, 6, or 8 ohms, and you can usually find the impedance rating on the back of the device. And remember, ohms apply to outdoor speakers too, not just indoor speakers.

Bose Music Amplifier on a table with a turntable

Ohms are crucial for determining both volume and sound quality, but they only apply to passive speakers, which draw power from an external amp. For clear and distortion-free audio, opt for high-impedance speakers like the Bose Virtually Invisible 791 In-ceiling Speakers II and Bose 251® Environmental Speakers, which are both rated at 6 ohms.

 But don’t worry, most Bose products are active speakers, so you can select whichever speaker you prefer without having to be concerned about speaker impedance. This even includes our soundbars, so you can enjoy hassle-free sound in your living room without worrying about ohms.

Pairing speakers and amplifiers

When you’re shopping for a set of matching speakers and amplifiers, compatibility is key. For example, you shouldn’t pair a 4-ohm speaker with an 8-ohm amplifier as they won’t connect properly. With a matching amplifier, you can confidently crank up a speaker to its highest power and volume, knowing it will effectively process and deliver sound.

While high-end speakers often come equipped with safeguards to shut down the amplifier before doing damage, not all products on the market offer this feature. Be especially mindful of tube amplifiers, which are prone to damage when not matched correctly with speakers. While some amplifiers and A/V receivers offer a mode for selecting different impedance settings, these options are less common.

When you have an 8-ohm speaker with an 8-ohm amplifier, you've hit the sweet spot, and the amplifier should be able to handle any volume or level of sound that the speaker is capable of. Four-ohm speakers are generally considered higher quality, but they must be paired with an amplifier that can handle the increased sound and volume capacity. This also applies to headphones and desktop computer speakers. Another AES study mentioned how impedance provided insight into certain electronics' acoustic design and performance.

Well lit living room with Virtually Invisible 791 In-ceiling Speakers II

When connecting multiple speakers to one amplifier, there are different calculations you need to consider depending on if you’re connecting them in a series, in a chain link, or in parallel. Make sure to calculate the ohm rating correctly for each scenario to avoid short-circuiting the amplifier.

Making smart shopping decisions

After all this, you may feel like you're in the technical weeds, but understanding the impedance and ohms of your electronics can help you better care for them and can improve your audio setup and sound. Make sure to keep these important terms in mind, especially when shopping for new speakers or amplifiers.

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