A. How do your Loudspeaker & Amplifier interact?
How do you evaluate the Sound Pressure Level in your Listening Room...
- Sound Level
The three following rules are used to calculate the SPL (Sound Pressure Level) in your room, depending on:
- The Distance between loudspeakers and listener.
- If we double our distance from the loudspeaker, we get -6dB SPL less.
- If we halve the distance we get +6dB SPL more.
- The Sensitivity of your loudspeakers.
A pair of loudspeakers yields Sound Pressure Level +6dB SPL more than one single loudspeaker.
- The Power output of your amplifier.
- Doubling the amplifier power yields +3dB SPL more, (if the input power of the loudspeakers allows it before their sound is distorted and operation is broken).
- Halving the level of amplifier power, yields -3dB SPL less.
- Sensitivity
The sensitivity of a loudspeaker is defined by the Sound Pressure Level it produces.
It is measured in dB-SPL/W/m with how many:
- dB-SPL the speaker produces at
- 1m distance, when driven with
- 1 W or 2,83V by the amplifier.
The higher the sensitivity, then:
- the louder the speaker sounds, driven by the same amplifier or
- the smaller the amplifier needed for the speaker to give a certain Sound Level.
What's the actual advantage of +3db?
A loudspeaker with 3db higher sensitivity, needs half the amplifier's power than the less sensitive one, in order to produce the same SPL.
As an example, our System-8 with 94dB sensitivity needs half the input power required by a loudspeaker of 91dB sensitivity, to produce the same SPL.
Therefore, if our System-8 needs 100 Watt for a given sound level, competitive loudspeakers of 91dB or 88dB need 200 or 400 Watt, respectively.
High sensitivity loudspeakers not only save you money on amplifier cost, but also give you lower distortion and better dynamics!
- Input Power
It's the continuous power (Watt RMS) that a loudspeaker can absorb from the amplifier without damaging itself. Usually, loudspeakers can absorb many times their rated input power, for very short time periods (in the order of milliseconds...).
If high input power is combined with high sensitivity, then the headroom of the speaker is greatly enhanced, permitting it to reproduce music at realistic levels without distortion or compression.
- Impedance
Impedance is the frequency dependent load, which the loudspeaker presents to the amplifier. It is measured in Ohm, the most common values being between 4 and 8.
An amplifier of 2x100Watt driving a load of 8 ohm, yields on average, some 2x150 Watt facing a 4 ohm load. You may also note that some amplifiers, even double their power output, as the Ohm load is halved...
- Dynamic range
Dynamic range is called the difference between the lower and the higher level of a particular musical performance or Hi-fi component.
The Dynamic range is higher for the most Powerful and the most Sensitive Loudspeakers.
B. What are the realistic Sound Levels you need in your Listening Position?
The following Table-1 gives you the SPL Sound Pressure Level values of various sound sources. This helps you to realize your SPL requirements.
Table-1
| Sound Pressure Level values (SPL) of various sound sources |
| Sound Source |
Sound Pressure Levels
(dB SPL, Weighted) |
| Rocket Launch |
194 |
| Jet Engine |
160 |
| Propeller Driven Aircraft |
140 |
| Threshold of Pain |
135 |
| Jet Aircraft Take - Off (at 60m) |
120 |
| Rock Concert (Peaks) |
125 |
| Symphonic Orchestra |
113 |
| Piano Solo Peaks (RMS, 1/8sec) |
110 |
| Piano Solo |
103 |
| Large Truck |
100 |
| Minimum Level for assessing Hi-Fi equipment |
96 |
| Noisy Office - Heavy Traffic |
80 |
| Train (at 30m) |
70 |
| Electric Vacuum Cleaner (at 3m) |
70 |
| Speech (at 30cm) |
70 |
| Discussion |
60 |
| Private Office |
50 |
| Quiet House |
40 |
| Recording Studio |
30 |
| Leaves Rustling |
20 |
| Hearing Threshold |
10 |
|
B. How do you calculate the SPL output of your Amplifier / Loudspeaker / Room combination?
The Table-2 gives the SPL values for a pair of speakers of 90 dB/W/m sensitivity. This pair gives 90+6= 96dB/W/m with 1Watt/channel from the amplifier and at 1meter distance from the speakers.
Following the 3 rules of previous page you know their output in various distances and with varying amplifier output.
Are your particular speakers more or less sensitive than the 90db speakers of the Table-1?
- If they are more sensitive giving e.g. 94 dB you add 4dB to every cell in the table.
- If they are less sensitive giving e.g. 88db you subtract 2db to every table cell.
Doing this simple calculation you will be able to determine the capability of your own set - up to reproduce lifelike sound levels.
Compare various Amplifier /Loudspeaker /Room combinations.
Table-2
| Sound Pressure Level of a Speaker Pair - 90dB/W/m sensitivity |
| Amplifier output |
1m -distance |
2m-distance |
4m-distance |
8m-distance |
| 1 W/ch |
96 |
90 |
84 |
78 |
| 2 W/ch |
99 |
93 |
87 |
81 |
| 4 W/ch |
102 |
96 |
90 |
84 |
| 8 W/ch |
105 |
99 |
93 |
87 |
| 16 W/ch |
108 |
102 |
96 |
90 |
| 32 W/ch |
111 |
105 |
99 |
93 |
| 64 W/ch |
114 |
108 |
102 |
96 |
| 128 W/ch |
117 |
111 |
105 |
99 |
| 256 W/ch |
120 |
114 |
108 |
102 |
D. Application example
Suppose you need at least 113db for realistic Symphony orchestra reproduction and your sofa is 4meters away from your speakers.
Table-2 indicates that with 90dB speakers you receive 114dB with amplifier output 2x256WattRMS at the distance of 2 meters.
At the 4meters distance the maximum output is only 108dB.
So you need speakers with at least 5dB higher sensitivity (113-108= 5).
Also the amplifier power must be higher than 256Watt in order not to work distorted around its limits.
Then of course the loudspeaker power has to be also about 300Watt in order to deliver safe and without compression and damage risk the music peaks.
- What is the alternative equal solution of a 92 db speaker?
In order to deliver the 3db lost by lower sensitivity it has to be driven by +3db more power. This equals two times 2x256W=512W/ch (according the second law above).
- What is the cost of such a 512W/ch amplifier?
- What is the cost of such a powerful loudspeaker driven safe by the 512Watt amplifier?
- What is the distortion of equipment driven so hard because of low sensitivity?
- What is the risk of breaking the above speakers driving them in realistic levels?
- What is the advantage of the high sensitivity both in Sound quality and cost?
Usually the room reflections boost some frequencies giving a few dB more. When you decide for your equipment and if you want your equipment to work safe without risk around it's limits, it's wise not to rely on this extra room gained dBs. Calculate your useful dB output according your equipment specifications.
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