This article covers everything about speaker and the technologies associated to it. Knowing those things will help you in deciding a suitable speaker system, headphone, earphone, or any gadget, which has sound as a predominant feature.
Speakers are devices that convert analog audio signals (electrical energy) into sound waves (mechanical wave energy). The electrical signals have power and voltage factors, and sensitivity is based on one or both of these factors.
☼ Sound
As sound waves reach our ears, they cause vibrations in our ears and the air molecules around our ears. Our sense of hearing effectively converts these sound waves into electrical impulses that are sent to and understood by our brains.
☼ Sound unit Decibel
Decibels are a unit-less expression of the ratio of one value of a power or field quantity to another on a logarithmic scale.
Every 6 dB increase effectively doubles the amplitude of the sound wave. A 6 dB decrease, then, effectively halves the amplitude of the sound wave.
☼ Frequency Response
The audio signals that are sent to a speaker driver are alternating currents. These AC signals mimic the shape of sound waves, and it is the job of the speakers to convert the AC signals into their coinciding sound waves.
Audio signals typically have frequencies within the audible range of human hearing (20 Hz – 20,000 Hz) though they may have more limited or even extended bandwidths.
The accuracy in which the headphones will reproduce the audio signal across all frequencies is given as the headphones' frequency response.
☼ Signal to Noise Ratio (SNR)?
There is always a very small amount of noise from the electrons whizzing around inside a speaker amplifier. A signal-to-noise ratio (SNR) is a measure of signal strength (desired signal) relative to background noise (undesired signal).
Typically expressed in decibels (dB), the ratio value can be zero, a positive number or a negative number. A signal-to-noise ratio over 0 dB indicates that the signal level is greater than the noise level. The higher the ratio, the better the signal quality. For example, a signal with SNR of 40 dB will deliver better audio quality than a signal with SNR of 20 dB.
☼ Sensitivity?
The sensitivity of a headphone is a specification that is used to measure the power of a driver to convert electrical audio signals into sound. It is measured in dB SPL (decibels of sound pressure level) per unit of power. The higher the sensitivity rating of a speaker, the louder its audio will be with a certain amount of input power wattage.
Headphone sensitivity ratings typically fall between 90 dB SPL/mW and 105 dB SPL/mW. This is a great range for headphone sensitivity.
Sensitivity values are often calculated against a 1 kHz sine wave with a power of 1 mW (1/1000 of a Watt).
Headphone jacks typically provide between 10 and 20 mW of output power. This power can be lowered with volume control. Most dedicated headphone amplifiers can provide power between 10 mW and 2 W depending on the specific headphone being used and the amplifier's design.
For example, the sensitivity of the JBL 700BT headphone is 102 dB at 1 mW (milli-Watt) from the source at a frequency of 1 kHz.
This means the JBL headphone will produce 102 dB of audio by using one mW of power. Want 105 dB audio from the headphone? You will need to provide two watts of input power to the headphone. This is due to the fact that every additional 3 dB of volume requires double the power. Similarly, to generate 114 dB audio, this JBL headphone will require 16 mW input power at a frequency of 1 kHz.
| if sensitivity is 102 dB at 1 mW (1 kHz), then |
| to generate 105 dB will require 2 mW input power |
| to generate 108 dB will require 4 mW input power |
| to generate 111 dB will require 8 mW input power |
| to generate 114 dB will require 16 mW input power |
Headphone sensitivity below 85 dB is very poor in terms of audio loudness. Hence, speaker sensitivity in the range of 100 dB is very good and should be sought after.
Low frequencies require a bit more energy, so headphones will generally require more energy than the sensitivity rating may suggest in the low-end.
Why manufacturers don't produce speakers that are as sensitive as possible? The cone in a woofer/driver could be lightened to improve sensitivity. But this likely results in a more flexible cone, which would increase overall distortion. And when speaker engineers go about eliminating unwanted peaks in a speaker's response, they usually have to reduce sensitivity. So it's aspects like these that manufacturers have to balance out.
But with all things considered, choosing a speaker with a higher sensitivity rating is usually a better choice. You may end up paying a little bit more, but it will be worth it in the end.
☼ Efficiency
Efficiency is the measure of the sound pressure level when standard power (1 mW) is supplied. Efficiency ratings can be given as dB SPL per mW (dB/mW).
dB SPL (Decibels sound pressure level) is used in both sensitivity/efficiency calculations.
☼ Rated Power 50W, 300W, 700W, 1000W…
The power specification – measured in watts – refers to how much power the speaker is designed to safely receive from an amplifier before it starts to distort.
If a speaker is driven too hard, it distorts and gets very hot. If so, you may permanently damage the speaker, and it could become unusable.
if the speaker specification says maximum power of 130 watts, you don’t really want to hook them up to an amplifier rated at 1000 watts output. This is because it probably won’t take much to get that amplifier to send more than 130 watts and potentially damage the speaker. Having said that, as long as you are careful with the volume control, then you can pretty much drive any set of speakers with any amplifier – regardless of its power.
If the 130-watts maximum power is average (or RMS), the speaker would comfortably handle a peak power signal from the amplifier of around 300 watts. However, if the 130-watts value is a peak value (sometimes called peak music power), the average power it can handle would be more like 70 watts.
RMS and peak values are entirely different things, and it is important to compare like with like if you are matching the power of an amplifier to a set of speakers.
Let's say a soundbar, rated at 250 W, is putting out 30 watts-per-channel in actual use. If the soundbar uses very cheap drivers — let's go with 82 dB sensitivity — then the theoretical output is about 97 dB.
☼ Impedance
The amount of output voltage is dependent not only on the volume control of the output device (smartphone) but also on the impedances of both the source (smartphone) and the load (headphones).
Impedance is measured in ohms (Ω). It basically tells us much power the headphones will need to get to a reasonable listening volume. Higher headphone impedances require stronger audio signals to move the driver.
Headphone (load) impedance values are fixed while the audio source (smartphone) impedances vary from device to device. Source impedance variation may alter the potential power transfer between the source and load and, therefore, affect the volume of the headphones. However, the sensitivity rating (let's call it volume per power) will remain the same.