I have some frequency extension questions

[SuBXeRo]

so for example, when you read bass extension diwn to 18 hz +/- 3db, what does that exactly mean. How loud is 0 db if thats the point you are working from? What is the range below -3db? I suppose this same goes for towers speakers. I notice some are +/- 1db and so on. I just dont understand the concept of what 0db is in refernece to the rest here.

[russ69]

A db is a unit of power. In your example, 0 db is the reference level and is without definition or level. +/- 3db means that the response is within that range at that frequency. Or in other words the frequency response does not vary more than 3 db at 18 hz.

[SuBXeRo]

but what is the 0db reference point, is this something that can differ between manufacturers and there is is batha fodder when comparing brands?

[willland]

but what is the 0db reference point, is this something that can differ between manufacturers and there is is batha fodder when comparing brands?

Whatever the tester decides. Some testers use multiple reference volumes like 85dB, 90dB, 95dB, 100dB, 105dB, etc.

Like these subwoofer tests taken from AVTalk.

http://www.avtalk.co.uk//showthread.php?t=10999

http://www.avtalk.co.uk//showthread.php?t=15240

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Frequency Response: +/-3dB points: 17.3Hz -> >150Hz

Bill

[Quiet_Hollow]

so for example, when you read bass extension diwn to 18 hz +/- 3db, what does that exactly mean.

That means the frequency response from 18Hz on up will deviate no more than plus, or minus, 3 dB SPL from their stated one watt-meter dB SPL value...

In a nutshell, it gets really F***'n low, and is smooth on it's way down there. Notice we can't say "how loud?" from just this statement alone.

How loud is 0 db if that's the point you are working from?

The originator of the test should state this if the plot is referenced to 0 dB. For example, the response graph from a La Scala, as it comes from a Klipsch brochure, will be referenced to 0 dB, but Klipsch states right below the chart, "0 dB equals 100 dB SPL". +3 dB SPL would equate to a peak response somewhere in the speaker's passband of 103 dB SPL, and -3 dB SPL would equate to 97 dB SPL respectively if using the statement from above. Likewise, if the vertical axis of the chart is plainly marked off in nice increments like 80 dB, 90 dB, 100 dB...etc. it's that value then.

In a nutshell...if the chart says 0 dB, then you're gonna to have to hunt a little for the factoid that tells you what "zero" actually is, in dB SPL.

What is the range below -3db?

Depends on the chart.

I notice some are +/- 1db and so on. I just dont understand the concept of what 0db is in refernece to the rest here.

Got charts? We can John Madden this real quick like.

[wboffthelake]

I have always had the same questions and thoughts about this. A spec of a certain frequency, + / - a certain number of dB, by itself, tells you nothing about how loud the speaker is actually reproducing that frequency.

For example, my RF-83s are spec'd at 29 Hz, +/- 3 dB. OK, fine, but just how loud (how many dB) is the speaker at 29 Hz?

I have not come across a response graph for the RF-83. Based on what is said above, specifically "will deviate no more than plus, or minus, 3 dB SPL from their stated one watt-meter dB SPL value", since the RF-83 is rated at 100dB sensitivity, does that mean that the speaker produces 29Hz at somewhere between 97dB and 103dB?

[JJkizak]

The old telephone spec was "0" DBM equals 1 milliwatt with 600 ohm termination. This is what every old telephone channel was designed for and you could hear the other end just fine.

JJK

[Quiet_Hollow]

A spec of a certain frequency, + / - a certain number of dB, by itself, tells you nothing about how loud the speaker is actually reproducing that frequency.

Right, it only gives you a rough idea of a speaker's capacity to emit sound in that spectrum.

I have not come across a response graph for the RF-83. Based on what is said above, specifically "will deviate no more than plus, or minus, 3 dB SPL from their stated one watt-meter dB SPL value", since the RF-83 is rated at 100dB sensitivity, does that mean that the speaker produces 29Hz at somewhere between 97dB and 103dB?

Correct. Be mindful that this is an assumption that the consumer (we) are forced to make based on the provided (limitied) data, and is subject to marketing.

Typically, the lowest response value reported is the speaker's official
-3 dB point...in a nutshell, where response truly starts to nosedive.

An actual response chart trumps a statement any day, but also be respectful of the fact that even a frequency response chart cannot disclose the entire "quality" of the reproduced sound

For example, my RF-83s are spec'd at 29 Hz, +/- 3 dB. OK, fine, but just how loud (how many dB) is the speaker at 29 Hz?

Two things to mention here.

1. dB SPL is a ratio of actual air pressure to a specific reference value air pressure. To measure dB SPL is to measure the average change in air pressure over time.

Cool, because that means the higher the number the louder, right?

2. No. Unfortunately, percieved loudness is a psycho-acoustic phenomenon. It's a derivative of how your body actually receives and processes information about it's environment. It's a combination of a whole bunch of factors and it is possible to trick the "human ear" to certain degrees.

The most important question to answer is, "How loud does it need to be for me?" Until you establish that for yourself, the numbers are useless.

It's a little bit like maxing out before starting a weightlifting program or testing the waters with a tape measure and a thermometer instead of using your toes.

A good way to start is buy or rent an SPL meter and start walking around with it. Take it to concerts, the airport, subway, hifi sotres, etc. Make a mental note of what's too loud or too quite. Attach numbers to what you hear. If you go to hi-fi store, bring a CD or record that has some test tones. Listen to what they sound like. Ask yourself, "How do they really compare to what I experience outside of the listening room?" Doing this will only save you money in the long run.