What is it exactly that is under so much pressure?

[ChalleB]

• hermetic woofers that function under high pressure
  
• pressure sealed to give ”levels associated with a rocket launch"
  
• “If you could get inside the Phantom, it would be like standingnext to a rocket during launch.”
  
• To name only one, the maximum air pressure inside the enclosure is 20 times higher than in a conventional speaker box. This pressure is equivalent to 174dB SPL,which is the acoustic pressure level associated with a rocket at launch... 
  
• Devialet uses a modified version of the sealed-box design where the drivers fire into the unit's hemispheric resonance chamber (which takes 1.2 tons of compression force to seal, by the way). Because it's blasting a speaker each into only 3 liters of air, the sound pressure in each chamber reaches levels which Devialet claims to exceed 174dB. That's roughly the sound pressure level of a rocket firing from 1 meter away, and 20 times the pressure inside the typical sealed-box subwoofer.
  
  Sorry, but could someone please explain to me exactly what it is that is under so much pressure?
  Is it the casing which is under pressure? or is it the speakers? 
  and will it explode if i try and open it  ?
  
  
  
  
  
  
  

[Confused]

No, it won't explode if you open it. Although I'm sure it won't help any future warrantee claims if you do.

Funnily enough, my lawnmower did actually explode this week, taking out the windows in three adjacent houses. This occurred when I was filling it up with petrol, although we did have a bit of laugh about this when I remembered that I'd sold my petrol mower and bought an electric one.

[ChalleB]

I realise (hope) that it won´t explode , but I´m just interessted in understanding exactly what it is that is under so much pressure?
everyone is talking about rockets taking off, but what are the physics, what is it exactly that is under so much pressure?

[Jean-Marie]

pressure is used in the expression 'Sound pressure'. They say that the Sound level inside is 170 dB SPL (SPL stands for Sound Pressure Level) which is equivalent to the SPL developed by a Saturn V rocket at take off.

For sure this is impressive to have an 8'' woofer with +/- 26mm action in a 6 liter closed enclosure!

[Rufus McDufus]

The marketing department are under pressure.

[Confused]

Although Rufus' answer is slightly flippant (and quite funny), I think he has a point. Very many things in normal life exist under very high pressures. Road bicycle tyres can run at 8 times atmospheric pressure, the combustion chamber of your car nearer 50 times, fire extinguishers higher than that and so on.

Devialet are doing a rather strange thing and quoting a sound pressure level, which is a measurement normally used to denote how loud something sounds, in a location where it would be difficult to locate a microphone, let alone a human ear. Plus, sound pressure levels follow the inverse square law, so it would be more meaningful if Devialet quoted the actual pressure in bar or psi if they wanted to boast about what is going on inside a Phantom. Who worries what the SPL is inside a car combustion chamber? After all, this is a very tricky place to stick your ear when the engine is fully assembled and running.

Undoubtedly, the pressure inside a Phantom is higher than you would find in a "normal" loudspeaker, and this explains why the egg shape is used, and why the bass "imploders" are dome shaped. For internal pressures, the sphere is by far the best shape, a cylinder is also quite good, but even a cylinder needs to be twice the thickness of a sphere for a given pressure. Large rectangular boxes are a very bad shape for internal pressures, but this is not too much of a problem for normal speakers because the pressures are not that high, in particular if you have a bass port, it is hard to pressurise something with a big hole in it. I guess you could do some very cleaver calculations, based on the internal volume of the Phantom, the degree of air compression you would get from the rapid movement of the drivers, but it should be noted that these pressures are transient, the Phantom has a hole in the front of it, effectively venting to atmospheric pressure.

So who is going to be brave and send a query to Devialet asking what the actual internal pressure inside a Phantom during one of it's 170dB moments?

I must stop now, I appear to be writing a load of annoying nonsense. (I wonder if they have any jobs going in Devialet's marketing department?)

[Womaz]

The marketing department are under pressure.

Brilliant

[nigelb001]

The marketing department are under pressure.

I think the software development department is also under extreme pressure

[Pleyel]

I don't think a Phantom would explode if you open it, as I don't expect any static pressure difference vs outside air.

I have no idea about how the 1.2 ton force to seal the box is meaningful for us, beyond being a parameter of  the manufacturing process.

Regarding the internal pressure, I did the math earlier when this figure was released, and could confirm:
Nominal volume is 3 liter (for each woofer). Excursion is +/-12 mm, as read on the web.
Volume change, each way, is 1.2 cm * pi * (10 cm)^2 = 377 cm3 = 0.377 liter peak
Relative volume change is 0.377 / 3 = 12.6% peak (+/-12.6%)
PV = nRT => assuming temperature is constant, relative pressure change = relative volume change = +/-12.6%
Rounding atmospheric pressure to 10^5 Pa, amplitude of pressure = 12.6 kPa pk
RMS pressure = peak pressure / sqrt(2) = 8.9 kPa RMS
https://en.wikipedia.org/wiki/Sound_pres...sure_level = 20 * log10 (pRMS / 20 µPa) = 173 dB
So the 174 dB in Devialet's white paper looks correct, and pretty unusual in less loud and/or compact speakers.
Hope it helps.

[Jean-Marie]

I don't think a Phantom would explode if you open it, as I don't expect any static pressure difference vs outside air.

I have no idea about how the 1.2 ton force to seal the box is meaningful for us, beyond being a parameter of  the manufacturing process.

Regarding the internal pressure, I did the math earlier when this figure was released, and could confirm:
Nominal volume is 3 liter (for each woofer). Excursion is +/-12 mm, as read on the web.
Volume change, each way, is 1.2 cm * pi * (10 cm)^2 = 377 cm3 = 0.377 liter peak
Relative volume change is 0.377 / 3 = 12.6% peak (+/-12.6%)
PV = nRT => assuming temperature is constant, relative pressure change = relative volume change = +/-12.6%
Rounding atmospheric pressure to 10^5 Pa, amplitude of pressure = 12.6 kPa pk
RMS pressure = peak pressure / sqrt(2) = 8.9 kPa RMS
https://en.wikipedia.org/wiki/Sound_pres...sure_level = 20 * log10 (pRMS / 20 µPa) = 173 dB
So the 174 dB in Devialet's white paper looks correct, and pretty unusual in less loud and/or compact speakers.
Hope it helps.

deleting my previous answer as it appears that I was wrong and Pleyel was right. My bad not to have verified before replying.

Jean-Marie