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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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Propeller Head Plaza Technical and scientific discussion of amps, cables and other topics. |
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In Reply to: Re: I'm just not sure about one thing posted by Pat D on November 27, 2006 at 18:15:15:
http://www.rythmikaudio.com/servo_tech.htm
http://www.jblpro.com/pages/general_faq.htm#What is "power compression"?
http://www.nearfieldacoustics.com/whiteppr.pdf (read the section on dynamics where they state that even small compression effects in the bass can have big effects on perceived loudness).
http://www.klippel.de/download/bin\AN12 - Amplitude Compression.pdf"Don’t Make a Bad First “Compressionâ€
All these SPL ratings are 1w/1m ratings. “But what type of performance can I expect if I apply more than 1w of input electrical power to my subwoofer?â€Well, it’s quite simple: you suffer from compression. There are two types of compression to be concerned with:
1. Thermal/Power
2. BLAs electrical power is applied to a voice coil, the voice coil heats up. This causes an increase in the Resistance of the voice coil, also known as Re. This is referred to as thermal or power compression.
As the voice coil moves out of the gap, motor strength (also known as BL) begins to drop. The further the voice coil moves out of the gap, the lower BL drops. As BL decreases, output drops as well. A 30% decrease in BL will cause a 3dB decrease in acoustical output.
Now which is worse? I guess you could say that depends. Thermal/Power compression is typically a slower process. Because music is very dynamic, it does take a few seconds for the voice coil to increase in heat, and therefore, a few seconds for the voice coil’s resistance to increase. Once this voice coil is hot, it takes 10-30 seconds to cool back down. As you can see, once the voice coil has become hot, the effects of Thermal/Power compression are fairly constant.
On the other hand, BL compression is a "quicker" issue. A voice coil can move right out of the gap and back into the gap in a single second. As excursion increases, it only gets worse. It is quite obvious that BL compression is the more serious issue of the two.
Don’t Make a Bad First “Compressionâ€
All these SPL ratings are 1w/1m ratings. “But what type of performance can I expect if I apply more than 1w of input electrical power to my subwoofer?â€Well, it’s quite simple: you suffer from compression. There are two types of compression to be concerned with:
1. Thermal/Power
2. BLAs electrical power is applied to a voice coil, the voice coil heats up. This causes an increase in the Resistance of the voice coil, also known as Re. This is referred to as thermal or power compression.
As the voice coil moves out of the gap, motor strength (also known as BL) begins to drop. The further the voice coil moves out of the gap, the lower BL drops. As BL decreases, output drops as well. A 30% decrease in BL will cause a 3dB decrease in acoustical output.
Now which is worse? I guess you could say that depends. Thermal/Power compression is typically a slower process. Because music is very dynamic, it does take a few seconds for the voice coil to increase in heat, and therefore, a few seconds for the voice coil’s resistance to increase. Once this voice coil is hot, it takes 10-30 seconds to cool back down. As you can see, once the voice coil has become hot, the effects of Thermal/Power compression are fairly constant.
On the other hand, BL compression is a "quicker" issue. A voice coil can move right out of the gap and back into the gap in a single second. As excursion increases, it only gets worse. It is quite obvious that BL compression is the more serious issue of the two."
A well designed voice coil system shouldn't move out of the gap unless very long excursions are happening so thermal is the bigger problem at realistic volume levels.
Almost every speaker maker in audio is concerned with the effects and not many mention FR at all. Could it be because compression affects realism in sound more than FR abberations, perhaps?
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- Other sources of information - morricab 09:05:17 11/29/06 (0)
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