What you put in doesn't always come out

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Thank you for all the replies to yesterday's question about loud levels and compressed sounding peaks. I would say that the response was about 50/50 that you experienced what I was writing about and my guess about those differences would be the type of music you listen to, the room size, the type of speakers, your loudness levels and the size of your amp. There are a lot of variables going on as you would imagine. I've been to enough listening environments to have heard the gamut from great sounding SET systems of only a few watts to mega systems of many watts and they are all different. Some of the SET setups I have heard sounded great on certain kinds of music but dreadful on others. I've noticed, for example, that many SET owners choose their music carefully rarely playing anything with high average value - like my Pink Floyd example - and concentrating their selections on high peak value music like classical or jazz. On big well powered systems with lots of drivers, like the Infinity IRS I am hoping to acquire, just about anything big sounds effortless if you have enough reserve amp power to make it sing. And this brings me to the subject of today's post, the speaker's ability to remain linear with level. Loudspeakers, just like phono cartridges, are mechanical devices with very defined limitations when it comes to extremes. This means that as a loudspeaker driver (or phono cartridge) gets close to the maximum level the distortion rises as the amplitude becomes non-linear. This is due to the nature of how these magnetically based motors work. As you approach the limits of the drivers excursion a number of problems arise, but the one we're most interested in is that the output of the driver is no longer linear - meaning it produces decreasing amounts of loudness for a given input signal - and we want it to produce a constant output vs. input. You can see an example of this in the graph where the Linear System line is what you want for a given input and the sloping line is what the speaker is doing at its output. To overcome this you can inject more power if you know where this is going to occur - or you can build a different type of loudspeaker - one that has many drivers doing very little individually but a lot as a whole. Big line sources like the Pipe Dreams, IRS, Genesis I and so on have a better chance of never getting close to this compressed state because you have so many drivers working at lower levels you rarely ever get to the compressed state. Tomorrow let's start delving into SET power amps. many of you have asked me to say a few words about them.
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Paul McGowan

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