To match speakers to an amplifier, check three numbers on the speaker's spec sheet: impedance, sensitivity and recommended amplifier power. Choose an amplifier that is rated for the speaker's impedance, whose power per channel sits comfortably inside the recommended range, and remember that a more sensitive speaker needs less power to play just as loud. Get those three right and almost any decent amplifier will drive your speakers well. This guide explains each number, with real figures from the Wharfedale range.
1. Impedance: will the amplifier drive the speaker safely?
Impedance, measured in ohms (Ω), is the electrical load the speaker presents to the amplifier. Most home speakers are 4, 6 or 8 ohms. A lower number asks more current from the amplifier.
- Nominal impedance is the headline figure. Wharfedale often lists it as, for example, "4Ω (8Ω compatible)", meaning the speaker works with any amplifier designed for 8 ohm speakers.
- Minimum impedance is the lowest point the load dips to at certain frequencies. If it is below about 4 ohms, as on some larger speakers, choose an amplifier that is specified as stable into 4 ohms.
Most modern stereo amplifiers and AV receivers handle 4 to 8 ohm speakers without any problem. The check matters most with very small amplifiers, older receivers and multi-room amplifiers driving several pairs.
2. Sensitivity: how loud will it play?
Sensitivity tells you how loud a speaker plays from a fixed input, measured in decibels (dB) at 1 metre. The higher the number, the less power it needs.
The rule of thumb: every 3 dB of extra sensitivity halves the amplifier power you need for the same volume. Compare the Crystal CR4.1 at 86 dB with the Elysian 4R at 92 dB: 6 dB apart, so the CR4.1 needs about four times the amplifier power to play as loud as the 4R.
One thing to watch when comparing spec sheets: most Wharfedale speakers are measured at 2.83 V, but the heritage models such as the Linton and Denton are measured at 2.0 V. A 2.0 V figure reads about 3 dB lower than the same speaker would at 2.83 V, so those speakers are more sensitive than the number suggests.
3. Recommended amplifier power: how many watts?
Every Wharfedale speaker lists a recommended amplifier power range, for example 20 to 100 W for the Diamond 12.1i. Choose an amplifier whose output per channel, at your speaker's impedance, falls inside that range, ideally in the middle to upper part of it.
More power than the minimum is a good thing. It gives headroom, so peaks in music and film play cleanly. A small amplifier pushed to its limit starts to clip, and clipping is harder on tweeters than a larger amplifier used at a sensible volume.
Wharfedale speakers: the numbers side by side
| Speaker | Sensitivity | Nominal impedance | Minimum impedance | Recommended amplifier |
|---|---|---|---|---|
| Crystal CR4.1 | 86 dB | 8Ω compatible | 4.3Ω | 20 to 60 W |
| Diamond 12.1i | 88 dB | 8Ω compatible | 4.0Ω | 20 to 100 W |
| Diamond 12.3i | 89 dB | 8Ω compatible | 5.0Ω | 30 to 150 W |
| EVO 5.2 | 88 dB | 4Ω (8Ω compatible) | 3.2Ω | 25 to 120 W |
| EVO 5.4 | 90 dB | 4Ω (8Ω compatible) | 4.3Ω | 30 to 200 W |
| Aura 2 | 88 dB | 6Ω (8Ω compatible) | 3.5Ω | 25 to 150 W |
| Aura 4 | 89 dB | 4Ω (8Ω compatible) | 3.1Ω | 30 to 200 W |
| Elysian 2R | 89 dB | 4Ω (8Ω compatible) | 3.6Ω | 25 to 250 W |
| Elysian 4R | 92 dB | 4Ω (8Ω compatible) | 3.2Ω | 15 to 250 W |
| Linton | 90 dB (2.0 V) | 6Ω | 3.5Ω | 25 to 200 W |
| Super Linton | 90 dB | 6Ω (8Ω compatible) | 3.9Ω | 25 to 200 W |
| Denton 85 | 88 dB (2.0 V) | 4Ω | 3.8Ω | 20 to 120 W |
Sensitivity is measured at 2.83 V and 1 metre unless marked. Figures are from each product's specification page.
Putting it together: three examples
- A small room with Diamond 12.1i. 88 dB and 20 to 100 W. A 40 to 60 W per channel stereo amplifier is plenty for a study or bedroom.
- A lounge with EVO 5.4 floorstanders. 90 dB, a 4 ohm nominal load and 30 to 200 W. Choose an amplifier rated into 4 ohms with around 80 to 150 W per channel for effortless headroom.
- Elysian 4R in a large room. 92 dB means it plays loud from modest power, but its 15 to 250 W range and 3.2 ohm minimum reward a high-quality amplifier with plenty of current.
Other things to check
- Room size. A bigger room, or sitting further away, needs more power for the same volume. Allow more headroom for open-plan spaces.
- AV receivers. The power figure is often quoted with only two channels driven. With five or seven channels running, each gets less, so lean towards speakers with higher sensitivity or a receiver with power to spare.
- Speaker cable. For most homes, 1.5 mm² (16 AWG) cable is fine for short runs and 2.5 mm² (14 AWG) for longer runs or 4 ohm speakers. Keep left and right lengths the same.
- Subwoofers and active speakers have their own built-in amplifiers, so they do not draw on your main amplifier. See what size subwoofer do I need?
Frequently asked questions
Can an amplifier be too powerful for my speakers?
Not in normal use. A more powerful amplifier simply has more headroom. Damage comes from playing far too loud, or from a small amplifier distorting, not from the amplifier's rating itself.
Can I use 4 ohm speakers with an 8 ohm amplifier?
Wharfedale speakers marked "8Ω compatible" work with amplifiers designed for 8 ohm speakers. For speakers with a minimum impedance near 3 ohms, choose an amplifier that is specified as stable into 4 ohms.
What does speaker sensitivity mean?
How loud a speaker plays from a standard input, in decibels at 1 metre. Each 3 dB higher halves the power needed for the same volume.
How many watts do I need?
Choose an amplifier whose output per channel falls inside the speaker's recommended range, ideally in the middle to upper part. For most rooms that means 50 to 150 W per channel.
Do I need an amplifier for Wharfedale speakers?
For passive speakers, which is most of the range, yes. Subwoofers and active speakers have amplifiers built in.
Want a second opinion on your system? Contact us with your speakers, amplifier and room size, or book a demonstration at a Wharfedale dealer.
