Audio equipment specs

chrisshennan

New member
Hey,

Sorry if this is in the wrong forum!

Any music tech tutors here?

I'm currently teaching a level 3 BTEC qualification and there's some areas I'm a bit unsure about.

I need to get the students to interpret audio equipment specifications, but i have no idea myself. yikes!

Any help would be great as i'd like to get stuck into this side of things myself and not just the DAW all the time

Chris
 
I suspect ecc83 will be along when it's morning in the UK and he will be a wealth of information.

However, may I suggest a book: "The Yamaha Sound Reinforcement Handbook" by Gary Davis and Ralph Jones should be the first reference book on the shelf of anyone getting involved with sound. Ignore the "Yamaha" and "Sound Reinforcement" parts of the title. The information in there is of use to any aspect of the sound industry. There's even a specific section on interpreting specifications and why, very often, manufacturers' specs are made meaningless by giving only half the story.

Highly recommended.
 
I am flattered by Bobb's mention! I must point out however that I am totally "self taught"!
I have been interested in electronics for well over 50 years and went into domestic electronics servicing at 16. Did "tech" and night school for my "Colour TV ticket" . I have always had an abiding love of music and an interest in recording and reproduction (MUSIC that is! Shut up that boy at the back!).

I think I can claim to have coined the bastardized phrase "Lies, dammned Lies and Specifications"? For they are SO often such. Maybe not downright untruths but not, "................, The whole truth m'Lud".

I do not have that book but shall hunt one down as soon as I am done here. I would strongly suggest a post to Sound on Sound forum where a group of "proper" graduate engineers will give you the very best advice I am sure.

Also, investigate "DIN 45-500" an attempt many years ago to codify "hi fi" specifications. Much maligned at the time for being well below many people's concept of a really high quality specification but it was a least a fair go!

Just bought the book.

Dave.
 
Hi,
I have a few music tech qualifications.
Do you want to list some specific areas or questions?

That said, I'm still just a hobbyist like most of the guys around here, and there are a few professionals too.
Plenty of people should be able to help. :)
 
That. The topic is just too broad to even know where to start.

Well, just a suggestion but I would start with a discussion about what is WRONG with many (most!) specifications as we get them?

E.g. units not specified.."rms" bloody watts when they should say "continuous sine wave power". Lack of dB limits to frequency "ranges" e.g. "response to 35kHz". What response? Flames?

Noise levels not tied to a gain level. Gains/inputs not tied to an output level (dBu or dBFS). Output levels not tied to a distortion level/load impedance. IMPEDANCE! All over the fekkin' shop!

No wonder noobs are confused when manufacturers all sing from different song books, many written by the tea boy.

If most of the audio companies advertised on UK TV the ASA would have their arses for breakfast!

Dave.
 
Thankyou so much everyone for the replies so far!

Considering the students are 16-18, i don't think its going to be all that involved to be honest!

If it's cool with you, ill copy and paste something from the unit specifications to see if anyone can make sense of it.


They need recommend equipment through the interpretation of audio equipment specifications

Equipment specifications: eg frequency range, frequency response, power bandwidth, sensitivity, signalto-
noise ratio, operating level, power rating/handling, RMS, peak, continuous, program, impedance;
analogue devices eg microphones, pre-amps, crossovers, power supplies, amplifiers, filters, loudspeakers;
analogue audio theory; Ohm’s law; voltage; current; resistance, power; decibels (dBu, dBV, dBSPL etc)

To achieve, learners will produce evidence that they can recommend equipment through correct
interpretation of audio specifications. It would be expected that a microphone, power amplifier and
loudspeaker be included to allow coverage important principles relating to common specifications such
as frequency, decibels, power and impedance. Evidence is likely to be brief but should explain what each
specification means. Evidence should be produced during classroom sessions to allow proper assessment
against the grading criteria.

To make things a little trickier, the course finishes in a few weeks, so it's more trying to get them through than spending loads of time on it if you know what i mean?

Is any of this making sense? :wtf:
 
Most of that sounds good but...

...unless it's on the syllabus I wouldn't worry quite so much about things like ohms law. As important as it is, I've never had to use it to interpret any part of an equipment spec.

On the other hand, I WOULD include a section on what's needed to make a spec meaningful. For example, most mics or speakers you find will have a spec like "Frequency Response 40Hz to 18kHz" but unless they include something like +/- 2dB it doesn't tell you anything. That monitor could be down by 20dB at the 40Hz end and still make the claim.

Similar applies to everything. If an amp is rated at 200 watts but the don't tell you how they were measuring it, the number is meaningless.

There are pot holes like this all over so-called specifications.

(FYI, you'll find a useful section on interpreting specs in that book you've ordered. I should warn you that it's not a book to sit down and read cover to cover--use it more like an encyclopedia and check the index for the bits you want/need to know. I'll also warn you that some sections have some pretty high level maths--but you certainly won't need this for the class--unless they misbehave and you want to freak them out. Or is that "freq them out" in an audio forum?)
 
It is not often that I disagree with pal (if I may call you that?) Bobbsy but..

Ohms Law to me is at the root of specifications. Hon' Bob mentions "200 watt amplifier". The student can have no idea what 200 watts is unless they have a firm grounding in the electrical units of volts, amps, ohms and watts. Then, since we are (I think?) pointing up some of the flaws in quoted specifications you need to know some electricals to spot for example when an amplifier is claimed to deliver more power to the speakers than it draws from the mains supply!

I would honestly get the students to work through a few simple "find power/resistance/current" problems before unleashing decibels e.g. on them.

Ohms Law is also fundamental to the Signal Transfer system we now use, i.e. NOT image matched 600 Ohms. Get them to calculate some losses in systems of various source and sink impedances.

Dave.
 
I suppose it depends on a lot of things but simply teaching the students what Bobbsy and ECC just said could probably tick several boxes.
If they have a basic understand of how several measurements and statistics are dependent on other factors, and can give examples, that says quite a lot.

I can tell you how much my re20 weighs, but If I don't mention that I weighed it on the moon it isn't much use to you.

"They need recommend equipment through the interpretation of audio equipment specifications"
If you can cut that down a little further, do you know specifically what they'll be asked?

If the questions are going to be pretty basic then I doubt everything in your list can be addressed.

I guess I'd be wanting to explain what the various common signal levels are, what balanced/unbalanced signals are, a basic understand of ohms law and measurement references,
and then ask for a few practical setup demonstrations.

Maybe a detailed description of the signal chain for recording line, DI, and mic level inputs, and a description of the equipment required to address a large crowd in a concert hall?
Those can cover the various analog output levels, amplification stages, impedance, sensitivity, polar patterns...all sorts of things.
 
Oh yeah shit! If you've got a quiz or test for this course you should post it! (unless maybe it's a copyright infringement thing). It would be fun to see all these know-it-all's wrong answers. ;)

No but seriously, we could reverse engineer (pun intended) a course pretty quickly from that.
 
It would be fun to see all these know-it-all's wrong answers. ;)

Warming up my typing fingers as we speak. ;)

I remember the college assessments. It wasn't even almost about a demonstration of knowledge. It was a demonstration of being able to mention the right thing.
Maybe that was just my college. :p
 
It is not often that I disagree with pal (if I may call you that?) Bobbsy but..

Ohms Law to me is at the root of specifications. Hon' Bob mentions "200 watt amplifier". The student can have no idea what 200 watts is unless they have a firm grounding in the electrical units of volts, amps, ohms and watts. Then, since we are (I think?) pointing up some of the flaws in quoted specifications you need to know some electricals to spot for example when an amplifier is claimed to deliver more power to the speakers than it draws from the mains supply!

I would honestly get the students to work through a few simple "find power/resistance/current" problems before unleashing decibels e.g. on them.

Ohms Law is also fundamental to the Signal Transfer system we now use, i.e. NOT image matched 600 Ohms. Get them to calculate some losses in systems of various source and sink impedances.

Dave.

Lol...I thought of putting a "but Dave will disagree" in my post and now wish I had.

Yes, Ohm's Law is likely one of the very first thing you need to learn in any electronics course--but, as per the original post, what's wanted is a short course on interpreting audio specifications. It's rare--if ever--that I need to use Ohm's Law when evaluating manufacturers' specs for audio gear, at least at a first pass. The tricks used by manufacturers to talk about things like amp power or frequency response are the bits that everyone NEEDS to know before making a purchase or integrating one bit of gear with another.

Beyond that, the OP says he only has a few weeks until the end of the course anyway, hence my suggestion to stick to the totally practical stuff rather than getting into underlying theory.

That's my story and I'm sticking to it!
 
Heh! I would counter that Bobbs by saying that Ohms Law is SO deeply integrated into yours and my brains that we unconsciously "weigh up" specification claims against it?

Bit like the resistor colour code?. Can't see yellow and not think Four!

Dave.
 
cheers Bobbsy,
Yes you're correct here. Only a few weeks left so it's going to be more like me getting them through this unit (hopefully) than delivering anything on it.
All i need is something like a questionnaire relating to it.

In the course spec, it says they must "recommend equipment through the interpretation of audio equipment specifications with a degree of independence".
It also says "It would be expected that a microphone, power amplifier and loudspeaker be included to allow coverage important principles relating to common specifications such as frequency, decibels, power and impedance. Evidence is likely to be brief but should explain what each specification means."

SO, looking at it from a 'they just need to pass point of view' i think that the above just needs to be covered and things like Ohm's law could probably be left out.
 
Even the title throws me off a little though. When it says "recommend" it gives me the image of someone working in a music shop.
 
cheers Bobbsy,
Yes you're correct here. Only a few weeks left so it's going to be more like me getting them through this unit (hopefully) than delivering anything on it.
All i need is something like a questionnaire relating to it.

In the course spec, it says they must "recommend equipment through the interpretation of audio equipment specifications with a degree of independence".
It also says "It would be expected that a microphone, power amplifier and loudspeaker be included to allow coverage important principles relating to common specifications such as frequency, decibels, power and impedance. Evidence is likely to be brief but should explain what each specification means."

SO, looking at it from a 'they just need to pass point of view' i think that the above just needs to be covered and things like Ohm's law could probably be left out.

Even with the limited time that still more fun than anything I got to do in school. A few thoughts:

First, before even thinking about the actual gear, they need to consider both what sort of audio this is needed for (big difference between something the school principal can use to give a speech at a podium or a rock band. Similarly, the size and shape of the room need to be considered. From this consideration will come things like type of mic needed and the SPL and coverage angles needed from the speakers.

Once all that is decided, they can start looking at specs. For the person speaking scenario (or maybe even things like a folk or opera singer) you might consider some form of small condenser mic. For the rock band, you're into handheld dynamics with a lot of rejection of stage wash. In this discussion you can talk about those different types of mic and also introduce aspects like pick up pattern and frequency response.

After the mic, although it's not on your list, will almost certainly come a mixer--you'll need some form of mic pre amp anyway. A large thing to consider on a mixer is the number of mic and line level inputs you need and (if you want to get complicated) the number of Aux outs for monitors. You might mention mixers with effects vs those without, whether a USB out is needed for recording and the analogue vs digital decision.

At that stage, I'd probably jump to speakers since the choice there kind of determines the amps needed. Indeed, you might want to discuss passive vs. powered speakers. To decide on the speakers you need, there has to be a consideration of the room size and SPLs you need for your application. Any decent speaker should also give dispersion angles (say 80 degrees horizontal and 40 degrees vertical) to allow you to see if the speakers will give relatively even coverage of the room. If you want to be nasty, you can make them think about the height of the hang and any angle you need there.

Once the speakers are determined, the power requirements of the speakers will dictate what you need by way of an amp. This could range from none (for powered speakers) or the spec for amps to drive the speakers properly. In this you'll likely get into speakers efficiency (sound output from 1 watt input measured at 1 metre up to maximum power handling and therefore max SPL. You'll have to have lots of chat about the various cheating ways to describe amp power.

As mentioned above, one of the biggest things to talk about are the spec items often left out that turn a so-called spec into a sales brochure.

I don't envy you!
 
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