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How to Estimate DB At 1 Meter By Volume Knob for Active Speakers?

DVDdoug

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This is what's frustrating, if you have several inputs being used in the KEF Wireless 2, optical/wifi/Bluetooth/HDMI/analog input, I doubt the input volume is all the same especially for the analog input.
Nothing is (usually) calibrated at home. Movie theaters are calibrated (for a certain seating position) and pro recording studios are calibrated. There is a standard for calibrating your home theater but I suspect it's too loud for everyday use so most people probably turn it down, loosing the calibration (for everyday listening).

I don't even know if the KEF Wireless 2 analog input is for headphone or line level, given it's a regular 3.5 mm stereo jack.
Both. They are pretty-much interchangeable except that headphone outputs are capable of driving headphones (lower impedance) and headphone outputs always have a volume control, whereas line outputs sometimes don't.

I think the only real way to measure it is to look at the spec sheet, see the power output at the amp output, do some math and figure out the DB value if you're using a preamp to your amp. Line levels are not constant with preamps and with active speakers, what the heck are we supposed to do with different sources coming in?
Turn it up to whatever level makes you happy and if you aren't hearing distortion everything is good! ;)


Why are we testing speakers at 96db and 86db? I can't imagine most people listen to speakers above 60db. Is it just marketing to get better noise measurements?
With specs & testing we are concerned with the peaks which are higher than the average loudness. The short term peaks aren't necessarily perceived as "loud" or "louder", but they can cause audible distortion if you push your amplifier or speakers into distortion. Bass also requires more power (and big woofers). Amir made a video - How loud is loud?



1. What settings I should use for accurate SPL readings in REW using the UMIK-1 with calibration file?
I've never used REW but once you've loaded the calibration file you'll get accurate readings. ...But I don't know if there's a setting for A-weighting like a regular SPL meter.

2. Is there a math equation I could use and what is it if I'm outside of an SPL meter when listening to speakers outside of my home such as a store and friends house? I had believed most potentiometers are either linear or logarithmic.
No, because everybody has a volume control.

3. Given that most tests are at 1 meter from 1 speaker vs 2 speakers, how much more DB does 2 speakers vs 1 make when determining loudness when making a speaker buying decision?
Double the power is +3dB.

4. Given that most tests are at 1 meter, what difference in db does distance make as you go past 1 meter?
The inverse square law says double the distance is -6dB. (That's "worst case" outdoors with no reflected sound.)


5. When looking at the optimal loudness for volume, does noise generally go up at lower volume levels for amp noise but goes down for speaker noise?
The noise from an amplifier or active speaker is (usually) constant. So it's more noticeable with silence or low volumes and the signal-to-noise ratio gets better at higher volumes.

6. If using a physical preamp or streaming wirelessly (Bluetooth and wifi), does noise generally stays constant at the preamp to amp stage. If this is true, shouldn't we max out our preamp or streaming minus a few DB to stop clipping at the DAC or preamp input, to reduce noise at speaker output? In other words nearly max out Bluetooth or preamp analog input signal to get the least amount of noise to the speaker?
If you have a preamp (or other source) with a volume control, the noise from the preamp generally goes up-and-down when you change the volume. But it depends on where the volume control is in the chain. Of course, adjusting the digital level doesn't affect any noise generated on the analog side.

7. Does speaker cabinet resonance go down as volume goes down or is it linear or logarithmic or just random based on volume level?
Resonance doesn't change with volume but it might seem worse at higher volumes. Good speakers shouldn't have any noticeable resonance.
 
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sigbergaudio

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I guess my question specifically after giving this a lot of thought are the following;

1. What settings I should use for accurate SPL readings in REW using the UMIK-1 with calibration file?
2. Is there a math equation I could use and what is it if I'm outside of an SPL meter when listening to speakers outside of my home such as a store and friends house? I had believed most potentiometers are either linear or logarithmic.
3. Given that most tests are at 1 meter from 1 speaker vs 2 speakers, how much more DB does 2 speakers vs 1 make when determining loudness when making a speaker buying decision?
4. Given that most tests are at 1 meter, what difference in db does distance make as you go past 1 meter?
5. When looking at the optimal loudness for volume, does noise generally go up at lower volume levels for amp noise but goes down for speaker noise?
6. If using a physical preamp or streaming wirelessly (Bluetooth and wifi), does noise generally stays constant at the preamp to amp stage. If this is true, shouldn't we max out our preamp or streaming minus a few DB to stop clipping at the DAC or preamp input, to reduce noise at speaker output? In other words nearly max out Bluetooth or preamp analog input signal to get the least amount of noise to the speaker?
7. Does speaker cabinet resonance go down as volume goes down or is it linear or logarithmic or just random based on volume level?

Still a bit unclear what you're trying to achieve or figure out.
  1. C-weighting, the SPL is calibrated automatically with UMIK-1.
  2. no
  3. With active speakers like yours, you'll get 5-6dB more with two speakers.
  4. 6dB loss each time you double distance
  5. Didn't understand that question
  6. In reality amplifier noise is likely inaudible whatever you do in the chain you are describing. Many active speakers have some audible noise/hiss, in that case it can be a good idea to reduce the gain of the speakers if possible.
  7. Cabinet resonance volume will follow the volume of whatever you're playing, and will be frequency specific, so the severity of the resonance will depend on the amount of energy at the specific frequency that is triggering the resonance.
 

antcollinet

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I actually do have a RadioShack SPL meter someplace in storage and the Minidsp UMIK-1 and trying to learn how to use REW. What settings on REW do I need to measure the SPL accurately, because I know you can increase gain in the software. This also confuses me because the computer analog levels using the analog output (headphone jack) to the KEF Wireless 2 will also determine how loud you will be playing the speakers in REW. Do I MAX out the output in REW? I'm using a laptop vs my desktop which has optical/coaxial/balanced line level (4 volts at line level for the Antelope Audio Zen Q), but I would need to buy some seriously long cables to hook it up to my desktop.
Connect the Umik, make sure the cal file is loaded, set it as the input, and open the SPL meter.
 

staticV3

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Using a smartphone is usually no better than guessing. Most of those apps are useless unless you can choose the specific smartphone you use.
It seems like there exists a way for smartphone manufacturers to firmware calibrate their mics so that accurate SPL readings are possible, even with generic Apps, without manual calibration.

See here:
 

MrSoul4470

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It seems like there exists a way for smartphone manufacturers to firmware calibrate their mics so that accurate SPL readings are possible, even with generic Apps, without manual calibration.

See here:
I'm not saying it's not possible, but simply downloading some SPL Meter app and expecting accurate SPL readings is not realistic. You'll most likely just measure crap unless you have a calibrated meter to varify that what the app measures is approximately correct. Don't blindly trust those apps.
 

NTK

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I'm not saying it's not possible, but simply downloading some SPL Meter app and expecting accurate SPL readings is not realistic. You'll most likely just measure crap unless you have a calibrated meter to varify that what the app measures is approximately correct. Don't blindly trust those apps.
The NIOSH Sound Level Meter App when used with an Apple iPhone or iPad is sufficiently accurate.


 
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