Posted on Wed, 25 Jul, 2018
Posted by Bob

Hi-Fi and Speaker Specifications, what do they mean and how do we interpret them? Understanding what impedance, sensitivity and power specifications really mean.

Building a Hi-Fi system can often be a confusing and mind-numbing exercise in understanding paper specifications which often, don’t make much sense. Impedance, sensitivity, power rating; often these terms seem to have more in common with a physics textbook than listening to music!

Worry not though dear reader, as in today’s Audio Affair Blog, we aim to demystify the world of Hi-Fi and speaker specifications!

Hi-Fi and Speaker Specifications

Hi-Fi and Speaker Specifications

“Why is it important to know what all of those numbers and jargon words mean? It’s all sales speak anyway right? Surely the most important thing is how my Hi-Fi kit sounds?”

It’s a common statement, and in some respects, a valid one; there’s only so much one can glean from specifications written on a website or in an owner’s manual. Every piece of Hi-Fi equipment and every loudspeaker has its own sound and character; one which can only really be appreciated by listening to it in person.

With that said, Hi-Fi and speaker specifications can tell you an awful lot about how to best combine pieces of equipment together. We often talk about how important it is to match one’s amplifier with one’s chosen loudspeakers. Understanding the Hi-Fi and speaker specifications can turn that process from guesswork into repeatable and enjoyable matched component setups.

Speaker Specifications

Let’s look at loudspeaker specifications first; your loudspeakers are the final link in the Hi-Fi chain and one of the most critical components to get right in any Hi-Fi setup. A loudspeaker is a complex device, but one with a simple purpose: to turn electrical energy into acoustic energy.

When we look at the specifications for loudspeakers, we’ll often see various units of measurements employed: db, Ohms, Watts. That’s because these are units which measure acoustic and electrical energy; understanding how they’re stated will tell us an awful lot about how the loudspeaker converts electrical energy into acoustic energy.

We’re going to use two different loudspeaker models to use as examples: the Tannoy Prestige GRF, and the ATC SCM11. Both excellent loudspeakers, but designed for different purposes and at very different price-points.

Sensitivity

This is a really crucial piece of information to understand; sensitivity tells us how efficient a loudspeaker is at converting electrical energy into acoustic energy. If we look at the sensitivity rating for the Tannoy GRF, they are quoted as 95db at 1metre. In comparison, the ATC’s are quoted as 85db at 1 metre.

Putting this simply, this means that with 1 Watt of input power, and standing one metre away, the Tannoys will generate a sound pressure level of 95db, and for the same 1 Watt input power, at the same distance, the ATC’s will generate a sound pressure level of 85db. So, what does this tell us?

This tells us that the Tannoys are significantly more efficient in turning electrical energy into acoustic energy. In fact, due to various complex calculations, the Tannoy speakers would be exactly twice as loud as the ATC speakers, for the same input level. This means that we would need to choose our amplifier very carefully if using the ATC loudspeakers.

Frequency Response

Here’s another important piece of information; the frequency response of a loudspeaker tells us the range of frequencies (sometimes called the bandwidth) a loudspeaker is able to reproduce. It may also give us information on how accurately those frequencies are reproduced.

Let’s look at the Tannoys again; they quote a frequency response of 24Hz to 27kHz. What does that mean exactly? Hz is a measurement of frequency; it’s the number of times a second a waveform moves back and forth. 1Hz means it moves once a second, 27kHz means 27 thousand times a second!

The range of human hearing is roughly 20Hz (which is very deep notes like the pedals of a church organ), through to 20kHz, which would be something like cymbals or the very highest notes of a female opera singer. If we look at the frequency response of the Tannoy GRF’s then, we can see that they comfortably encompass all the frequencies the human ear can perceive.

Comparing the ATC SCM11, we can see that have a frequency response of 56Hz to 22kHz, quite remarkable from a much smaller speaker enclosure that costs much less money. They don’t go quite as deep as the Tannoy GRF, but are impressive for the size; how do they achieve this though?

If we go back to looking at speaker sensitivity, you’ll remember the ATC SCM11 speakers are much less sensitive than the Tannoy GRF’s. This is partly because the large cabinets of the Tannoy GRF allow the speaker drivers to behave much more efficiently. Also, the crossovers of the ATC SCM11 will likely be designed to “dump” large amounts of energy at certain frequencies, to allow them to be more accurate.

Hi-Fi Specifications

Just like with loudspeakers, there are some common specifications used in Hi-Fi components, which can give you an idea, in advance, as to how they’ll perform as part of your system. This is especially important with regards to power amplifiers because as we’ve seen, some loudspeaker designs require a lot of power.

Power Output and Resistance

Power output is one of the most commonly quoted specifications there is; it’s also one which is often misunderstood and is crucial when understanding how an amplifier will interact with your chosen loudspeakers. We’re going to use two very different amplifiers as examples: the Sugden A21 SE, and the Primare I35.

Sugden & Primare

An amplifier’s main purpose, as the name implies, is to amplify (make bigger) electrical signals. It’s, therefore, to be expected that in order to quantify the amplifier’s ability to do this job, we’ll be using terms related to energy and electricity: Watts and Ohms. The Watt is a unit of power, whilst the Ohm is a unit of electrical resistance.

The Sugden A21 SE is quoted as being able to deliver 30 Watts per channel into 8Ohms; that means that when presented with electrical resistance to the value of 8Ohms, the Sugden A21 can provide 21 Watts of power output. In comparison, the Primare I35 is able to deliver 150 watts into the same 8Ohm load.

What happens if the loudspeakers we have are rated at 4Ohms resistance though? Well, thanks to Ohm’s law, the amplifier power output will double. The opposite is also true, however – if you had an amplifier rated to provide 50 watts into 4Ohms, then the output power would halve!

Looking at the naked specifications of the two amplifiers then, you might think that the Primare I35 is a better amplifier because it can generate much more power; as ever that’s not the whole story! The Sugden operates in pure Class A¬†and has a 100% analogue signal path; in comparison the Primare uses Primare’s UFPD Class D technology.

Both amplifiers will sound very different, and in order to perform to their best, should be accompanied by loudspeakers of the correct power handling and impedance.

Golden Rules of Amplifier and Speaker matching

There are some easy rules to follow when pairing amplifiers with loudspeakers:

  • Choose an amplifier which generates more power than the recommended minimum for the loudspeakers
  • Choose an amplifier which delivers its maximum power output with the rated impedance of the chosen loudspeakers
  • Don’t pair low sensitivity loudspeakers with low power output amplifiers
  • Do pair a low power output amplifier with high sensitivity loudspeakers
  • Choose a pair of loudspeakers with a frequency response which suits the kind of music you’re likely to listen to

 

Alternatively, if all of this is still rather confusing (and it is a lot to understand), feel free to ask for our advice. Our years of experience will guarantee that we can select a system with the right Hi-Fi and speaker specifications to suit all tastes. Remember, at the end of the day, the most important factor is how your Hi-Fi sounds.

We’re always happy to set up our extensive stock of demo equipment for potential customers to come and listen for themselves. Hearing is believing!

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