Advert Response.
Our latest advert “Have you got a hi-fi system or just an overpriced music centre” has elicited quite a strong response. We’re pleased about this because, on the one hand, we feel very strongly about the subject and on the other it shows the huge passion and commitment of audiophiles generally. It seems to us that, disagreements aside, we all share the same passion.
We’d like to explain the scientific facts (laws of physics) and our consequent position.
The Laws of Physics
The following are not made up or some marketing company’s weird fantasies. They are scientific fact backed up and endorsed by the foremost technical journalists in the world. In alphabetical order; John Atkinson (Editor of Stereophile) Robert Harley (Group Editor for Absolute Sound, ex Technical Editor of Stereophile. He really knows his stuff and has written books about it), Keith Howard (deeply knowledgeable and experienced Technical Journalist in the field of, well, anything technical) and Paul Miller (perhaps the foremost technical reviewer in the world, current Editor of Hi-Fi News).
- Sound pressure level (SPL) attenuation over distance. It’s really quite simple: SPL attenuates by 6dB at each doubling of the distance from the starting point. Therefore a particular loudspeaker’s SPL at 1 metre is 6dB less at 2 metres. At 4 metres that level is reduced by a further 6dB so the resultant level is now 12dB less than the starting point. To reiterate these figures are not made up: they are scientific facts.
- dB watts. This is probably the single biggest cause of all the misunderstandings. Historically, amplifiers have been measured in watts and that is how people understand them. The trouble is that watts are a linear scale of heating with no direct or intuitive relationship to the subjective, listening-level experience. Each dB step is, near enough, 1.25893 times the starting power. If you start with 100 watts, 1dB more than that is 125.9 watts. Another dB up is 158.5 watts and another dB is 200 watts. Each doubling of power is 3dB. The point about all this is that amplifier makers talk about increases in watts which look good on paper but in practice are of little significance. You can see (and hopefully work out for yourself) from the above that if you look at amplifiers in dB watts, rather than conventional watts, you form a rather different view about the power and its relationship to price and subjective performance.
We have been going on about amplifier power and dB watts for the last 10 years.
- dB what is it? We know that the vast majority of you know exactly what dB’s are but we thought we’d like to explain it for those who aren’t so familiar with the technical concepts. A dB (decibel) is the minimum change in sound pressure level that the human ear can differentiate UNDER IDEAL CONDITIONS. This is really, really important. The vast majority of listening conditions are far from ideal and as a result most people will not be able to discern 1dB difference between levels. Our experience shows that virtually anybody can hear a 3dB difference under almost any circumstances. Far fewer people can hear 2dB, but all the audiophiles we’ve met can hear it easily. 1dB, ahh! That’s another matter. Under carefully controlled circumstances yes it can be heard. But, with a few little distractions in the background, such as tea cups, conversation, or telephones, the 1dB difference becomes inaudible.
The point is that, in terms of amplifier power, 1dB is rather a lot but in subjective listening terms it’s almost nothing. To get an appreciable difference in listening level you need at least 2dB or 3dB to be sure. That means virtually doubling the amplifier power to hear any difference.
Okay that’s all the beyond dispute scientific laws of physics.
Now for the subjective bits.
The whole discussion hinges around dynamic range and peak level. Do you think your hi-fi system should be able to produce 95dB, 100dB, 105dB 110dB peaks?
We know for a fact that concert hall peak sound pressure level (SPL) for a medium sized symphony orchestra is 109-110dB. For a big symphony orchestra or rock concert the levels are much higher.
The real question is what you think your hi-fi system should be able to reproduce at your listening position, in your home.
We think that 105dB peak (about 5dB less than you’d hear in a concert hall) is pretty reasonable. You may not agree and that’s fine. You pay your money and you take your choice.
However, at Musical Fidelity, we believe that a hi-fi system should be able to produce at least a 105dB peak if it is to be reasonably accurate.
We think that a hi-fi system should be able to produce a sweet, clear, neutral sound, with a convincing sound stage and realistic dynamics. For us, the musical experience is one of passion and commitment, life and death. We feel it that strongly. We’re pretty convinced that most audiophiles are the same.
For us, the visceral life and death experience comes not only from the content of the music but its dynamic physical impact.
It is physically impossible for a low powered amplifier with insensitive loudspeakers to produce that visceral impact.
And here is where the controversy starts... You can easily calculate a hi-fi system’s peak SPL capacity at your listening position. You can use the formula above (scientific fact, remember) to work out your loudspeaker’s effective sensitivity at your listening position. Remember to add back the 3dB because you have two loudspeakers in the room, because each doubling of power gives you 3dB more level. If you put a second loudspeaker in a room (doubling the level again) you have added 3dB to the level. Therefore, if your listening position has caused the SPL to attenuate by, say, 12dB the fact there are two loudspeakers means that the effective attenuation is 9dB.
Then all you have to do (!) is to convert your amplifier power to dB watts. You can consult our charts or, if you don’t believe us, you can work it out for yourself. The multiplier of 1.25898 is a constant. You can easily do a chain calculation using a constant on any calculator. To calculate the peak SPL your system is capable of, take the loudspeaker sensitivity (more on this one later) and deduct the listening position attenuation factor, then add to that your amplifier’s power in dB watts. 50 watts = 17dB watts, 100 watts = 20dB watts, 200 watts = 23dB watts and 400 watts = 26dB watts. Put these figures together and you’ll end up with your system’s peak SPL capacity.
Many of you won’t like the results. Nor do we. We have been going on about the dynamic range and peak SPL for the last 10 years and nobody seems to have paid any attention. The result is that the vast majority of hi-fi systems cannot physically produce a realistic peak SPL.
Some people have accused us of insulting their amplifiers’ quality. This couldn’t be further from the truth. An individual amplifier of any power can be as high quality as you want but unless it is paired with an appropriately sensitive loudspeaker it will be impossible for that amplifier to produce realistic hi-fi dynamics. It’s just the laws of physics. If you have a 50 watt amplifier and you want a 105dB peak then you must use a 95dB sensitivity loudspeaker. There’s no way round this, it’s just the laws of physics.
So who’s to blame!
Well, nobody specific. The point is that in order to produce a particular peak SPL you need to match your system. The problem is that magazines talk about amplifiers in watts (as do amplifier manufacturers), which mean little when related to loudspeaker sensitivity.
If, for example, you wanted a 105dB peak at 10 feet using a 50 watt amplifier you would have to have a loudspeaker with 95dB sensitivity. They are available, you know, but they cost quite a lot. So a small amplifier can produce the correct SPL but it has to be paired with the right type of loudspeaker.
If you wanted to go at it the other way round, with a loudspeaker which had the sensitivity of 87dB, and you wanted the same peak SPL at the same listening position, you would need an amplifier of about 350 watts to achieve that result. The speaker might be somewhat cheaper than the 95dB sensitivity one but then the amplifier would be a lot more expensive. You use your ears, you pay your money and you take your choice.
Loudspeaker sensitivity (insensitivity)
The vast majority of loudspeakers overstate their sensitivity by 1 or 2dB. After all 1 or 2dB doesn’t sound very much, does it? But when you look at it in amplifier terms, it has a huge effect on the power required to achieve a particular peak SPL. 1dB = 25% more power.
We have found that the top brands such as B&W, Wilson or Vandersteen can be relied on to produce pretty accurate specifications, but even they can vary by the odd dB. Other manufacturers, particularly high end esoteric brands, regularly overstate their loudspeaker sensitivity. This has a huge effect on the total peak SPL capacity of the system.
Our advice to anybody buying an expensive loudspeaker is to make sure that you carefully check its real sensitivity from technical measurements in either Hi-Fi News or Stereophile.
So what’s the best way to go? High sensitivity or high power. For what it’s worth our experience shows that higher sensitivity loudspeakers have more immediacy and visceral impact. If you take two systems which are capable of the same peak SPL, but one has a low sensitivity loudspeaker with a high powered amplifier, and the other has a higher sensitivity loudspeaker but with a lower powered amplifier, the system with the higher sensitivity loudspeaker will always sound more alive and immediate.
Summary
Non debatable science, laws of physics.
- Sound pressure level attenuates at the rate of 6dB with each doubling of distance.
- Having two loudspeakers in the room reduces that attenuation by 3dB.
- Unless you recalibrate watts it is all but impossible to work out the particular system’s peak transient SPL capacity.
- Measured concert hall peak SPL at a reasonable position is 109/110dB.
- The quietest concert hall level is probably muted solo violin which is about 62dB.
Semi-science.
The reverberant field is different in every room with every loudspeaker but it does have an effect. The reverberant field is the sound which we perceive in front of us and is a result of both the system and its room reflections, non linearities and standing waves. This is how and why small amplifiers can appear to fill the room with sound. What you’re actually hearing is the system, its reflections and standing waves in the room and, most strangely of all, its distortion adding to the reverberant field effect making it sound fuller.
This is why, in some instances, the systems with small amplifiers can seem to have a fuller reverberant field than high powered amplifiers which are not clipping.
Matters of opinion.
How much peak level do you need in a listening room? We think that 105dB peak is a minimum for a real hi-fi system. We base this on concert hall figures. After all a hi-fi system is supposed to be able to recreate the live musical experience.
If you don’t think that a 105dB peak is necessary for a real hi-fi system that’s fine with us. It is, after all, just a matter of opinion.
Below are a couple of useful charts to help you in your quest for getting the most music possible from your hi-fi system.