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Thread: Audio equipment specs

  1. #11
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    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.

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    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.
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    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.

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    Quote Originally Posted by ashcat_lt View Post
    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.
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    Quote Originally Posted by ecc83 View Post
    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.

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    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.

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    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.

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    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.

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    Quote Originally Posted by chrisshennan View Post
    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.

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