Sound Pressure and Sound Power - what's the difference?
www.parkerjonesacoustics.com

... The difference between sound pressure and sound power can be tricky to get your head around. For predicting noise levels from noise polluting sources like plant, it is very important.

As a consultant, I'm often verbally quoted noise levels by clients, i.e. this unit has a level of 60 dB'. Unfortunately, based on that alone, I can't do a great deal, without making a lot of assumptions. If you tell me it's 140 dB I know it's going to be very loud and problematic! But at 60 dB, depending on the situation, it's difficult to assess the risk.

What is a sound pressure level (SPL)?

A sound pressure is the pressure deviation from atmospheric pressure caused by a sound wave, in pascals. The sound pressure level (SPL) is a logarithmic measure of the ratio of a sound pressure over a reference sound pressure (corresponding to the hearing threshold of a young, healthy ear), quoted as a dB. If these two pressures are the same, we have an SPL of 0 dB.

A sound pressure level is what we can physically measure using a sound level meter. Most noise level parameters in a report are based upon an SPL, albeit they are mostly adjusted in some way, i.e. weighted to a single number (dB(A)), or a level difference such as a Dw.

A sound power level (SWL) is theoretical. A sound power is in Watts (W), a sound power level like above, is in dB, a logarithmic ratio of the sound power over a reference sound power. W for Watts, hence SWL (as SPL is already taken!) I'll explain more shortly.

Why do we need sound power levels (SWL)?

The sound pressure level (SPL) depends on distance, the position of the source and the environment, i.e. reflections from the ground, or if inside the surfaces of the room and therefore the reverberation time and volume of the room. So if we measure the SPL of a fan unit inside a plant room, and move this fan outside, the SPL is unlikely to be the same because of more sound energy escaping into the atmosphere. Similarly, if the unit is in the corner of a room, condensing sound radiation by the surfaces close around it, and then move this unit into the centre of the room on the floor, where it radiates more hemi spherically, the SPL will be different. Simply moving further away from a sound source, will reduce the SPL, particularly noticeable when outside.

If we take a large plant enclosure, with many different machines from different manufacturers, who all give us noise data as a sound pressure level, but all measured at varying distances, some in a lab, some outside, some in an anechoic chamber (or very often not referencing how it was measured at all which is effectively useless data as it could be measured at 1m or 10m!), we'll have a hard time predicting the sum of noise levels from our plant enclosure.

The sound power level (SWL) helps us around this. It is not dependent on distance, position or environment. This is the crucial difference. It is a theoretical value; it is not directly measurable. A noise source will have the same sound power irrespective of where it is placed. It gives us a level playing field to directly compare two sound sources. Predicting the noise levels from our plant enclosure is now much simpler, we can apply the same calculation to all of our equipment. ...

How Loud Is a Data Center? How Far Does the Noise Travel?
www.lsars.com

... Continuous noise from cooling fans and transformers reaches 60 to 80 dB at the property line. Generator load tests can be heard up to a mile away. The defining problem is the 24/7 nature of the noise, not the peak loudness. ...

Big, noisy and coming to a town near you - why the data centre backlash is growing
www.bbc.com

... Until a few years ago many of us may have been blissfully unaware of what a data centre was.

These giant, warehouse-like buildings power virtually all our internet activity, from our web searches and emails to movie downloads and online banking.

They are at the heart of the AI boom, housing the advanced computer chips and servers needed to run services like ChatGPT and Claude.

But the speed at which they're growing, the enormous amount of electricity they consume and concerns about their environmental impact are fuelling a public backlash around the world.

In the US, they've become a huge issue ahead of the midterm elections on 3 November, with both Republicans and opposition Democrats coming out against their development.

It's putting opponents of data centre expansion on a collision course with US President Donald Trump, who has dismissed the pushback as a "sick conspiracy", even as public anger grows.

Here's what you need to know about the data centre boom, and why opposition is growing.
They are growing rapidly

There are about 12,250 data centres around the world, according to Data Center Map, a company that tracks both operational and pre-operational sites.

That's up sharply from 2021, when there were around 8,000 operational sites.

As the chart below shows, data centres are most densely clustered in the US which has 4,767 sites. It is followed by Europe, where the UK and Germany lead.

Data centres have typically been located near to cities where it's easier to access high voltage power lines or water resources for cooling. But as they get bigger, more are being built in rural areas. ...

[good links and maps in the article]

Quotes on Cap and Trade and Energy
www.instituteforenergyresearch.org

... "Under my plan of a cap and trade system, electricity rates would necessarily skyrocket. . . .

Because I'm capping greenhouse gases, coal power plants, natural gas -- you name it -- whatever the plants were, whatever the industry was, they would have to retrofit their operations. That will cost money. They will pass that money on to consumers."

- - - President Barack Obama, January 2008

So is your memory indicative of what fmr Pres Obama actually said?

It seems to have a deficiency.

As a corollary, should this most august forum rely upon your memory in the future?

Oil companies report sky-high profits thanks to wartime crude prices
www.npr.org