Audiophiles: Stereo System Thoughts - Page 3
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This is a discussion on Audiophiles: Stereo System Thoughts within the Electronics/Car Audio forums, part of the Interior Mods category; If you think of the drivers as mechanical devices with defined excursion limits, overdriving them can and will damage them ...

  1. #31
    He simply abides. SD_GR's Avatar
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    If you think of the drivers as mechanical devices with defined excursion limits, overdriving them can and will damage them mechanically at least. This can happen either due to poor signal choices from the user and/or due to poor enclosure design. A great way to do this is to take a speaker, select a very good amplifier with good power output, and feed it the actual canon shots recorded in the Telarc version of the 1812 Overture at full gain. OTOH to picture what clipping does to a driver look at a driver not only as a mechanical device, but as an energy converter. When the signal is clipped the driver's efficiency at generating heat increases. Some people explain this by asking to visualize the cone not moving when the signal is clipped (at the plateaus). The energy goes into heating the voice coil(s) instead. This is a backwards way of looking at a driver but it makes sense when the end result is smoke.

    The reason I said that in practice RMS power ratings don't matter is that in practice they do no exist, at least not with any definition I can understand given the little physics I can follow. RMS describes current or potential difference -- the alternating current equivalent of a direct current that yields a given amount of heat for a load (for a sine wave this can be calculated as the peak multiplied by the inverse of the square root of 2). I see no way of describing power in terms of RMS values -- only potential difference or current (granted, they yield power, but unless someone can clarify then I'll stick to my thinking).

    In any case I question devices rated as X power, when X is enough to run a saw mill, the device also states that it only draws a fraction of the claimed output power to run itself, plus generate heat due to inefficiency, and all this depends on a stiffening cap, a simple alternator, and a car battery (to be fair I question similar claims when the devices uses the mains voltage -- you know, when a 110 or 220 V device in the home claims to produce 0.5 kW but uses... 50 W from the mains to do so).
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  3. #32
    Registered User Heide264's Avatar
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    Quote Originally Posted by SD_GR View Post
    When the signal is clipped the driver's efficiency at generating heat increases. Some people explain this by asking to visualize the cone not moving when the signal is clipped (at the plateaus). The energy goes into heating the voice coil(s) instead.

    The reason I said that in practice RMS power ratings don't matter is that in practice they do no exist, at least not with any definition I can understand given the little physics I can follow. RMS describes current or potential difference -- the alternating current equivalent of a direct current that yields a given amount of heat for a load (for a sine wave this can be calculated as the peak multiplied by the inverse of the square root of 2). I see no way of describing power in terms of RMS values -- only potential difference or current (granted, they yield power, but unless someone can clarify then I'll stick to my thinking).
    SD, some pretty good points. I'll post my thoughts.

    Whenever somebody says clipping, I think of signals. Be it from the head unit or the amp. Just flat topped/bottomed sine waves sort of deal. When dealing with drivers, I more so call it over driving. There are two main issues at hand... over driving, and under driving. Some believe that the flat line high/low signal from clipping causes the mechanical device extra stress. I personally do not believe this is so, and have never seen any damage from it as long as the drivers are rated higher than the amp's clipping level. My main issue is over driving a speaker. I have seen many speakers blown as we all know they do. If the amp does not flat line at the speakers rating, the driver may be able to handle it being over/under the rated power for a short period of time, as long as it isn't held in that position (ex, clipped signal above the speakers rating). Since drivers tend to still mechanically function above their power rating (including the magnet) a bit before letting the excess off into heat, it is much easier to let it go without noticing. When an amp/hu clips signal, you hear distortion. When drivers are at their max... sometimes you do, sometimes you don't.

    RMS can describe many things, not just voltage or current. You are correct that when dealing with standard 60Hz A/C, it is shown that the RMS of the A/C yields a good way to relate it to DC. In my classes RMS is a huge pain in all honesty. Some calculations require peak, some RMS. I think of RMS as an average of A/C stuff in simple terms (can't use a true average, or you'd have 0). The bottom line is that it really doesn't matter what you rate something in normally, but it does have to be consistent. That factor of 1.41 between the two does cause issues. I generally prefer RMS information, because it shows what the driver can constantly provide. Peak ratings could just be a spike that it can handle and then needs to cool off after for example.

    Basically, compare apples to apples and oranges to oranges.

    Also, for RMS conversions, you have to be careful. You can divide by 1.41 (2^.5 or sqrt 2 ) on a sine wave to get it. That is normally the puzzle. You need to find a way to make what you are dealing with a standard sine wave. When multiplying different sine waves to get different values, you run into issues. Say for example Power. It is two sine waves multiplied together (P = I * V). If your voltage or current are out of phase or has ANY DC component, which it normally is/does, it does not come out to a standard sine wave in practice many times. I can actually go into some more detail if anybody wants or has any questions. My power conversion class basically burned a lot of this into my brain, and it is still a bit hazy here and there. A lot of signals you actually divide by sqrt(3) for example to find component ratings.
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