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Old 18th November 2002, 01:31 AM   #1
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Default questions about spl ect...

ok, i commonly come across numbers for SPL, efficiency, and sensitivity, and i am getting a feeling that they are not measureing the same thing.

i've noticed SPL seems to be the lowest number of the 3, and efficiency and sensitivity are higher by 3dB or more. I'm beginning to think manufactures are advertizing something with units of dB and hoping people interpret it as another measurement that also has units of dB.

also, the same manufacturer makes a woofer that has a Re of 6.00ohms and the Z curve looks to be well above 8ohms for the intended freqencies, yet the woofer is labeled 6ohms.

someday i will stop asking questions and begin answering other's questions...
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Old 18th November 2002, 02:14 AM   #2
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Hi Chris,

It can be confusing at times, and the advertisers make things that much worse by using the terms incorrectly. These are terms as defined at the Infinity Loudspeaker web site.

Sound Pressure Level (SPL) - Acoustic measurement for sound output. Measured in dB, the readings are often "weighted" to reflect how human ears work.

Sensitivity - A measurement of the sound output of a speaker or speaker system's output relative to the power put in. Typically measured in dB at 1 watt of input, 1 meter away.

Efficiency - The measure of an amplifier or speaker's ability to convert input power to work. Expressed as a percentage.

Hope this helps,
Rodd Yamashita
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Old 18th November 2002, 02:51 AM   #3
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in you're experience, which is the most useful rating for chosing or not choosing a speaker. see, i am trying to set up a primarily SQ system in my car. not really a hi-fi system, but one that sound very good especially for the music that i like. the thing is that i like a lot of music, and not all of them play well with others. most music i like either has a lot of midbass(80-250 is my def), or bass(30-80 is my def).

I'm worried that i will either have too much or too little power for a given speaker. too much isn't a big problem, but since i'd like to at least factor in the different levels while designing the setup. There are entirely too many car setups with the bass overpowering the rest. that works for rap, but i listen to very little rap.
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Old 18th November 2002, 02:59 AM   #4
JoeBob is offline JoeBob  Canada
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The efficiency of a speaker effects your choice, but it doesn't effect the sound quality. There are some very nice sounding low-efficiency drivers out there as well as some great sounding high-effiency drivers, there are also horrible sounding drivers of all types of efficiency. I don't like super efficient drivers for they'll show every little bit of hum your system has. Drivers with too low an efficiency can't be used with class-a amps at resonable volumes and are therefore frowned upon for my use (for you this wouldn't apply since it's car audio). But you want you drivers to have an efficiency so that when paired with your amp they are capable of producing the SPL levels you desire without surpasing (preferably even coming close to) theur max SPL ratings. Hope that helps, but even if you've got a loud driver, it has to be a quality unit used correctly to sound nice, quantity isn't everything.
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Old 18th November 2002, 03:01 AM   #5
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Chris,

Stick with sensitivity since this is the most used term in evaluating a speakers output capability for a given input (usually SPL/Watt@1m). This way, if all your speakers have the same sensitivity, and all your amps have the same, or similar power, your speakers outputs will be balanced.

Rodd Yamashita
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Old 18th November 2002, 03:12 AM   #6
haldor is offline haldor  United States
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Hi Chris,

dB is shorthand for a ratio between two measurements. dB is used to describe the difference between two values using a logarithmic ratio which pretty much matches how our hearing works. Anything that can be measured (volts, amps, distance, time, babes, etc) can be expressed in terms of dB although dB is normally reserved for measurements of power or voltage (SPL is like an acoustic voltage). A negative dB value means that the number is smaller than the reference, a positive dB value means it is greater than the reference. In practical use, some level is picked as being 0 dB and all other values are relative to that one.

The formula for calculating the dB difference between two power readings (P1 and P2) is dB = 10 * log (P1 / P2).

Power is proportional to the square of Voltage (double the voltage and power x 4). This means that when calculating dB for voltage you use dB(Volts) = 20 * (V1/V2). SPL is treated the same as voltage so dB-SPL = 20 * (SPL1/SPL2)

To understand what a dB value means you have to know what it's 0 reference is. There are a number of standard reference points in common use. Some terms you may see include dBm, dBV, dBu and dB-SPL. Note, zero when referring to dB does not mean nothing, it just means this is the point that other dB measurements are relative to.

0 dBm = 1 milliwatt.

0 dBu = 0.775 V rms. This is the same voltage that results in 0 dBm when driving a 600 ohm load. Common pro audio voltage reference.

0 dBV = 1 volt rms. Common consumer gear voltage reference.

0 dB-SPL = Threshold of hearing. This is the faintest sound a typical young, undamaged ear can hear in the frequency band between 1 KHz - 4 KHz (the most sensitive range for human hearing).

dB can be confusing, especially if someone mixes zero references. Example: What is the difference in dB between the typical pro audio +4 dBu level verses the typical -10 dBV consumer level? Hint, the answer isn't 14 dB.

The reason why people use dB is it makes it easy to compare very small or very big numbers without having to deal with a lot of zeroes. It also matches how our human hearing perceives changes in sound levels.

Phil
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