Can I Put 3 Ohm Speakers in a 6-8 Ohm Receiver?
By Frank Guthrie
People like to play music, often loudly, from their home audio receivers, and sometimes they desire to have a more powerful sound to listen to. One might ask, "Can I change the speaker, which is a 6-8 Ohm, to a 3 Ohm and get a more powerful sound?"
Speakers are electromagnetic mechanical devices. They are designed to meet a wide range of criteria. Most are designed with a round appearance, but some are rectangular or oval. From a functional point of view, they convert an electrical current (the audio signal) into mechanical movement. An electrical current flows through a "voice coil" (many turns of wire), which generates a changing magnetic field. The voice coil is closely centered around a stationary permanent magnet. As the permanent magnetic field does not vary, the coil wants to physically move due to the interaction of the magnetic fields. The voice coil is connected to the "speaker cone," which moves (vibrates) the air we breathe and thus creates the sound we hear.
The voice coil is one of many critical parts of a speaker. It is wired to the power output section of an audio amplifier, which provides sufficient electrical current for the voice coil. The speaker design and the audio amplifier must be matched together so that the available current from the amplifier is suitable for the speaker being used. If the amplifier is too powerful, the speaker will be damaged. If the speaker can handle much greater power than the amplifier can provide, then the sound will be weak and perhaps distorted. The technical term related to the amplifier and speaker matching is "speaker impedance" and it is measured in "Ohms."
Audio amplifiers convert weak audio signals into powerful currents that "drive" the speakers. That "power" is rated in watts---the same rating one will see on a light bulb. The term "watt" or "wattage" represents the amount of power that is available or being used in a circuit. A small hand-held receiver will not have much audio power, whereas larger receivers can be real power houses.
Selecting the Proper Speaker
If the receiver was designed to use a 6 to 8 Ohm speaker, then changing the speaker to a 3 Ohm type will demand more current from the audio amplifier. This might damage the amplifier or cause the sound to be distorted for lack of proper current through the speaker. Conversely, there is no benefit in changing the speaker to a 16 or 32 Ohm style, as the speaker will not demand enough current from the amplifier, and the sound might be weak. Also, most audio amplifiers use a design technique called "feedback" that helps to stabilize the performance of the amplifier. This feedback is often connected to the speaker circuit in some manner, and changing the speaker type might affect the amplifier stability.
What to Do
For best performance and safety, keep the amplifier and speakers matched. Better receivers that have external speakers will provide a printed specification for the speakers. If you want "better sound," use high quality speakers with the proper Ohm rating. The only other solution is to invest in a better receiver and speakers that meet your needs or expectations.
Frank Guthrie is a technical writer living near Chicago. He has 45 years of experience writing consumer and industrial product manuals and creating engineering level documentation. His knowledge of electronic circuitry provides uncommon insights.