laurenc319 Posted January 19, 2006 Share Posted January 19, 2006 Hi, from a thread on Audiogon "01-19-06: Audiokinesis I agree with the posts pointing out that a high efficiency system usually has better dynamic contrast than a low efficiency system. Let me try to explain why. It's a nasty little secret almost nobody talks about. Theoretically, a loudspeaker's output will increase by 3 dB for a doubling of input power. In practice, this is ALMOST NEVER true. The reason is power compression (also often called thermal compression), and its primary cause is voice coil heating. As you increase the power going into a voice coil, it heats up. As it heats up, its resistance increases. As its resistance increases, more of the power going into it goes into overcoming that resistance (heating it up still more) and less goes into actually producing sound. Let me give a few numbers as an example (drawing on measurements posted by Bill Roberts on Audio Asylum). At normal volume levels, the typical 86 dB efficient speaker may well only give you an average of 2.5 dB increase in loudness for a doubling of input power. So let's say you have an 86 dB efficient speaker playing at 80 dB average volume level, and along comes a +20 dB peak (quite common). This speaker will compress the peak and you'll only get about +17 dB. On the other hand, a high-efficiency system (say 96 dB efficient or higher) usually has negligible power compression at normal listening levels, and will more than likely give you the full +20 dB that the peak calls for. Once again, this is a generalization - I'm sure there are exceptions, but unfortunately this is something nobody measures and includes in their specifications. Differences in the power compression characteristics of the various drivers within a speaker often cause the tonal balance to change with volume level, with woofers typically suffering from more power compression than tweeters and therefor many multiway systems sound dull at low volume levels and bright at high volume levels as they've been optimized to sound right at medium to medium-high volume levels. On another note, bass reflex loading only increases efficiency in the region of the port tuning. It does nothing for midband efficiency. The reason why bass reflex speakers are usually more efficient than sealed box speakers is that the driver parameters most suitable for reflex loading include a more powerful magnet system, which is what raises the midband efficiency. Hope this helps some. Duke" seems to make sense to me Larry Quote Link to comment Share on other sites More sharing options...
crazytubepower Posted January 19, 2006 Share Posted January 19, 2006 Makes sense to me as well... Duke made my speakers, he is a great guy and very knowlegable... Quote Link to comment Share on other sites More sharing options...
Deang Posted January 19, 2006 Share Posted January 19, 2006 All true. Quote Link to comment Share on other sites More sharing options...
MarkBK Posted January 19, 2006 Share Posted January 19, 2006 Yes, true for the most part. Voice coils do heat up and I cannot recall anyone ever listing this heat value in specs. The most common reason for speaker damage is underpowered speakers. The source sends a clipped signal which causes the voice coil to heat at a faster rate than intended - when that occurs - the voice coil heats up faster than it can dissipate the heat - and the voice coil starts to cook. Give it enough time to be exposed to a clipped signal or one that has a very large DC value and poof! the coil seizes up - bye bye speaker (and other stuff in the food chain if not caught in time). One of the more interesting voice coil designs was from Tannoy - a dual layer voice coil - outer coil looked fine but the inner coil burnt and that could only happen if the speaker was overdriven in some way. Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted January 19, 2006 Share Posted January 19, 2006 The dreaded sigmoid response curve for most objects in motion with resistance. I lost it today when talking to a guard at work about this response, and his eyes were glazed over until an idea come to him....he blurted out "It's just like human sexual performance!" ... in mixed company. Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted January 19, 2006 Share Posted January 19, 2006 JBL list's the Power Compression figures for thier drivers .. typically around 1.5% Quote Link to comment Share on other sites More sharing options...
MarkBK Posted January 19, 2006 Share Posted January 19, 2006 JBL list's the Power Compression figures for their drivers .. typically around 1.5% Raw frames - yes - but do they list the Compression for their finished cabs? I don't recall seeing that listed. Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 19, 2006 Share Posted January 19, 2006 Horn loaded drivers have the same power compression issues that direct radiators have....they just happen to start exhibiting it at higher SPL's. In other words voice coil temperature correlates directly to the power output of the amplifier. A horn gets you what, a 10dB increase in efficiency? So horns can play 10dB louder than direct radiators for the same levels of power compression. Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 19, 2006 Share Posted January 19, 2006 JBL list's the Power Compression figures for their drivers .. typically around 1.5% Raw frames - yes - but do they list the Compression for their finished cabs? I don't recall seeing that listed. They don't need to...the driver is going to exhibit the same power compression for the same power level regardless of the enclosure - the SPL at those points might be different, but it's easy to account for it. It gets a bit more complicated when you try to take into account mechanical compression, but the speaker is usually operating within the mechanical linear range (even at loud volumes). Quote Link to comment Share on other sites More sharing options...
Duke Spinner Posted January 20, 2006 Share Posted January 20, 2006 i saw this Late .. thanks, Who ... Quote Link to comment Share on other sites More sharing options...
D-MAN Posted January 20, 2006 Share Posted January 20, 2006 The speaker maximum wattage rating is the VC ability to SAFELY dissapate heat before failure. As the VC heats up from increased current flow, it tends to work less efficiently and effectively in the magnetic field, which is called heat (or power) compression. That is, at a certain power level, no more excursion will be achieved and may even lessen. DM Quote Link to comment Share on other sites More sharing options...
3dzapper Posted January 20, 2006 Share Posted January 20, 2006 "A horn gets you what, a 10dB increase in efficiency? So horns can play 10dB louder than direct radiators for the same levels of power compression." Closer to the range of 15 to 20 Db increase in efficiency Who. Rick Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 21, 2006 Share Posted January 21, 2006 "A horn gets you what, a 10dB increase in efficiency? So horns can play 10dB louder than direct radiators for the same levels of power compression." Closer to the range of 15 to 20 Db increase in efficiency Who. Rick Ummm...K-33 in the cornwall is 98dB? Lascala and khorn are 104dB? I know sensitivity is different than efficiency though...isn't a 15" driver more on the order of 92dB? I forget. I know it's going to depend on the horn anyway (narrower bandwidth = more efficiency, and wider bandwidth = not as much more efficiency) Quote Link to comment Share on other sites More sharing options...
Spkrdctr Posted January 22, 2006 Share Posted January 22, 2006 I would caution that the author needed to move his SPL numbers higher to get the heating effect. Playing in the 1 watt range will not cause any heating. But as far as generalizing, he did a good job. Once again, a good case for buying Klipsch speakers if you want a more "realistic", you are there sound for instruments. Especially solo instruments. Quote Link to comment Share on other sites More sharing options...
Griffinator Posted January 22, 2006 Share Posted January 22, 2006 If nothing else, this would explain the gap between the K-Horn's max output SPL vs. its max power handling capacity... Quote Link to comment Share on other sites More sharing options...
Audio Flynn Posted January 22, 2006 Share Posted January 22, 2006 Makes sense to a trogladite like me. Quote Link to comment Share on other sites More sharing options...
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