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Grimani SPL rule of thumb

Dzhaughn

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Audioholics recently posted a 105 minute video chat session of experts (including the estimable Sean Olive) on improving speaker measurements, particularly how to communicate them to residential users. It has many interesting points.

At 37 minutes or so, he posts a slide for "sound level capability." This is his "ballpark" method for estimating sound level for the average residential home theater room, good to +/- a few dB. It says, to paraphrase

For a 3000 ft^3 room, Seat SPL = Sensitivity (at 2.83 VRMS ) - 7 dB.
For 6000 ft^3 room, Seat SPL = Sensitivity - 10 dB
For 9000 ft^3 room, Seat SPL = Sensitivity - 13 dB

At 100W, add 20dB; At 200W, add 23 dB; at 400W, add 26 dB

So a 100W amplifier and a speaker with 85dB sensitivity will produce around 98 dB for a listener in the typical 3000 ft^3 room.

I can't recall such a clear model for estimating amplifier and speaker requirements.

So, how reasonable is it? If it's not reasonable, what's the next change to make?

The entire discussion is at:

 

aac

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It depends too much on DI, room absorbtion, etc. It'll be very strange to think if speakers had the same resulting sensitivity in a living room and something like non-environmental studio.
Probably for speakers he installed and rooms he built or measured it is correct.
Here is some more food for thought for you. Emperical knowledge I assume too.
correct-monitors-direct_sound_dominance-chart.jpg
 
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Koeitje

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Can you translate that from freedom units to meters (or liters, since a m3 is a 1000 liters)?
 

Koeitje

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aac

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I hope you've changed the speedometer in your car over to m/s and the thermostat in your house to kelvin.
I'd like that for some drivers, maybe they would've realized how dangerous some of their behavior is.
 

Jim Matthews

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I just don't find it very useful to talk about feet and other arbitrary units on a science focussed forum.
I know, it's such a chore to use a readily available conversion online.

I prefer Angstroms and degrees Kelvin, myself.
 

amirm

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One issue is the real sensitivity of a speaker. Speaker sensitivity is proportional to frequency response. Since that varies, so does sensitivity. Manufacturer sensitivity numbers are usually wrong so you can't do such math. If you use our measurements where we show it, you still have to device if you are using mid band sensitivity or bass where most of the loudness is.
 

EJ3

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It's on the chart: 55 cubic meters is approximately 1,950 cubic feet. If you would like to check it's accuracy manually:
Units of length:
The four US customary units that are in everyday use are listed below, along with their SI equivalents based on the definition of 1 yard as 0.9144 meters:
  • inch (symbol: in) – 0.0254 meters
  • foot – 0.3048 meters
  • yard – 0.9144 meters
  • mile – 1609.344 meters
Units of area:
Square feet, square inches, square yards, etc., are units of area commonly used in UCS, but the only area measurement in the system that is not related to one of its lengths is the acre, which is equal to 4,046.873 m2.
Units of volume:
UCS uses many different measurements of volume. It uses some general units of volume, as well as volume measurements specifically for dry or liquid volumes. Below are some, but not all of these volumes, and their SI equivalents.
General approximate units of volume:
  • cubic inch (in3) – 0.0000164 meters3
  • cubic foot (ft3) – 0.0283 meters3
  • cubic yard (yd3) – 0.765 meters3
 

MZKM

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One issue is the real sensitivity of a speaker. Speaker sensitivity is proportional to frequency response. Since that varies, so does sensitivity. Manufacturer sensitivity numbers are usually wrong so you can't do such math. If you use our measurements where we show it, you still have to device if you are using mid band sensitivity or bass where most of the loudness is.
Yep, I haven’t updated my database since like February, but as of then the average difference has been -1.5dB, though some companies are more honest than others.
 

Koeitje

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I know, it's such a chore to use a readily available conversion online.

I prefer Angstroms and degrees Kelvin, myself.
Angstroms are pretty cool, since fit in perfectly with meters. 1 Angstrom is 10^-10 meters. Perfectly consistent across the board.

Kelvin is just an offset of 273.15 (I could be off for the decimal part, doing this from the top of my head), apart from that its the same scale as Celsius. An increase of 1C is the same absolute increase as a 1K increase.

So if you are trying to prove a point at least use more arbitrary metrics than these. May I suggest feet, inches, yards and miles?
 

izeek

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It's on the chart: 55 cubic meters is approximately 1,950 cubic feet. If you would like to check it's accuracy manually:
Units of length:
The four US customary units that are in everyday use are listed below, along with their SI equivalents based on the definition of 1 yard as 0.9144 meters:
  • inch (symbol: in) – 0.0254 meters
  • foot – 0.3048 meters
  • yard – 0.9144 meters
  • mile – 1609.344 meters
Units of area:
Square feet, square inches, square yards, etc., are units of area commonly used in UCS, but the only area measurement in the system that is not related to one of its lengths is the acre, which is equal to 4,046.873 m2.
Units of volume:
UCS uses many different measurements of volume. It uses some general units of volume, as well as volume measurements specifically for dry or liquid volumes. Below are some, but not all of these volumes, and their SI equivalents.
General approximate units of volume:
  • cubic inch (in3) – 0.0000164 meters3
  • cubic foot (ft3) – 0.0283 meters3
  • cubic yard (yd3) – 0.765 meters3
dang, now they'll have to do the math.
 
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Dzhaughn

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Can you translate that from freedom units to meters (or liters, since a m3 is a 1000 liters)?

I could, but I find using metric length units reduces the dynamics, staging, and rhythm. This is because of the simple integer ratios between the driver size and room dimensions.
 

Haint

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Sounds like a hard thing to quantify as it seems the presence (or lack thereof) and significance of room treatments would significantly alter the cubic foot rules of thumb in the formula.
 
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Dzhaughn

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Sounds like a hard thing to quantify as it seems the presence (or lack thereof) and significance of room treatments would significantly alter the cubic foot rules of thumb in the formula.

No, it's not that hard, it's just not exact. Stick a speaker and a mic some rooms and measure. Any real estate agents around? They've got access to so many rooms, just pop in a monitor and a microphone.

A standard deviation to go with the point estimate would be nice.
 

hardisj

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The CTA-2034 has a section on specifying max SPL. With good stuff.

I feel like Anthony is kind of trying to reinvent the wheel with his specifications (referencing his chat with the Audioholics last week). Maybe I'm being too harsh with that statement; I don't intend to be. I just feel like there's a push to repackage specs when the majority of manufacturers aren't even packaging them at all as it is.
 
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