Box size in relation to sound output and power input

[jcarver 10+ year member]

So first this may be better to be moved to one of the discussion forums because its only theoretical talk as I don’t really have this problem. If so someone just say so and I’ll post it there. If not this may help clarify things for me and possibly others. Please try to read the full post before replying.

So I’ve been giving some thought to how box size, sound output, and power input all relate to each other and I’ve come up with some grey ideas of how it all connects but I’d like to get a clearer picture. Here are some of the things I’ve seen reference which may or may not be true.

• Smaller box = higher power handling, or as some call it less efficient. In either case the why isn’t important only that it takes more power to reach full excursion of the sub.
  
• Larger box = full excursion on less power
  
• If the box is to big the sub gets sloppy and slow to return.
  
• If the box is to small the internal pressure forces the sub back out too quickly.
  

Given those to be true (if they are), I was thinking about the manufactures recommended box sizes and how they come to those number. Obviously they use a mathematical equation that I’ve seen and don’t completely understand as well as real world testing but I’m wondering if those can be manipulated a little to work in our favor. Here’s what I’m thinking.

In this scenario let’s say we have a 12” speaker that is rated at 500w in a 2.5cuft box. Ideally you put 500w to it in this box and you reach its RMS potential. Now let’s say we up the box size to 3.0 or 3.5 etc, and its power handling goes down. Based on my understanding of how a subwoofer works you get sound output by moving the air. So in this bigger box let’s say we reach the full excursion at 400w due to the oversized box. It should be moving the same about of air right? Would this mean the sound output would be the same in terms of SPL on less power? If not why not? Sound quality aside on this by the way, I know the wrong box size can mess with how it sounds.

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[jcarver 10+ year member]

wow no one wants to take this one on lol

 

[surreal 10+ year member]

Many inconsistencies there. First, sound is not produced by moving air. Play your sub full tilt at tuning. Does the sub move much? No. Is it making sound? Yes!

Also, there are tons of things to be considered like resonance, response peaks, excursion changes through the frequency range, etc to answer such a broad question.

 

[hispls 5,000+ posts]

First, sound is not produced by moving air.

Please explain how soundwaves are created then?

OP are you talking about sealed or ported box? "Rated" power handling is typically not determined by mechanical limits (since as you say box and frequency would determine that), and IMO most manufacturers "reccomend" box based on as small as possible (since that's what people want) that will give reasonable response.

 

[surreal 10+ year member]

Sound is a form of energy of which requires a medium to travel through..

A good example is the one given - is a sub louder at its highest point of excursion? Heck no.. in fact, likely quieter as the way people achieve this is by playing under tuning and out of the enclosure passband, incurring response rolloff.

Pretty sure you already know that though..

And, in my opinion, manufacturers recommend oversized boxes generally, to give the heavy low end response people are looking for. This is mostly true of higher end subs that take smaller enclosures (E.g. DD) Take DC for example, equally strong and comparative subs and they have smaller box recommendations. Its all subjective..

 

[jolly_26 10+ year member]

Sound is a form of energy of which requires a medium to travel through..A good example is the one given - is a sub louder at its highest point of excursion? Heck no.. in fact, likely quieter as the way people achieve this is by playing under tuning and out of the enclosure passband, incurring response rolloff.

Pretty sure you already know that though..

And, in my opinion, manufacturers recommend oversized boxes generally, to give the heavy low end response people are looking for. This is mostly true of higher end subs that take smaller enclosures (E.g. DD) Take DC for example, equally strong and comparative subs and they have smaller box recommendations. Its all subjective..

Sound waves involve the movement of air. Pretty basic stuff there bro. Sound waves are longitudinal waves in the form of moving high and low pressure bands. No, the air from right in front of the sub does not move to your ears to make you hear it, but it moves the air directly in front of it, causing waves of high and low pressure which travel through the air. Causing it to move. Ever seen a hair trick? Also usually mainstream manufacturers recommend small boxes and reasonably high tunings, from what I have seen at least.

Also, OP, there is a lot more to it than just what you have said, and it gets very complicated very quickly.

 

[itsblown 10+ year member]

Sound is a form of energy of which requires a medium to travel through..A good example is the one given - is a sub louder at its highest point of excursion? Heck no.. in fact, likely quieter as the way people achieve this is by playing under tuning and out of the enclosure passband, incurring response rolloff.

Pretty sure you already know that though..

And, in my opinion, manufacturers recommend oversized boxes generally, to give the heavy low end response people are looking for. This is mostly true of higher end subs that take smaller enclosures (E.g. DD) Take DC for example, equally strong and comparative subs and they have smaller box recommendations. Its all subjective..

You understand that the medium in which the sound is moving through in this case would be air correct?

 

[hispls 5,000+ posts]

is a sub louder at its highest point of excursion? QUOTE]
It should be rather high excursion at the loudest frequency in sealed, dipole, or infinite baffle alignment, though much of cone excursion to SPL relationship is based on frequency anyway. The reason a woofer generally moves least in a PORTED alignment at tuning is because the port is acting like another woofer that is exactly in phase with the driver.... so between the port and woofer more air is ejected (and moving).

Just pointing out another generalization that could be addressed if OP was more specific.

 

[surreal 10+ year member]

The medium is normally air, yes.. duh. But not exactly moving, but more so vibrating.

Saying sound is produced by "moving air" is completely misleading.

At tuning, actually the sub its self moves very little air.. most all sound at this point radiates from the vent instead of the cone - they are both radiators.

But yes, were taking this too far - a bit of good fun! Going to sleep though and likely wont return for awhile..anywho.. goodnight guys!

 

[Buck 5,000+ posts]

Sound is more like pressurization than air flow.

 

[Moble Enclosurs 10+ year member]

Sound waves involve the movement of air. Pretty basic stuff there bro. Sound waves are longitudinal waves in the form of moving high and low pressure bands. No, the air from right in front of the sub does not move to your ears to make you hear it, but it moves the air directly in front of it, causing waves of high and low pressure which travel through the air. Causing it to move. Ever seen a hair trick? Also usually mainstream manufacturers recommend small boxes and reasonably high tunings, from what I have seen at least.
Also, OP, there is a lot more to it than just what you have said, and it gets very complicated very quickly.

Yes. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif. Here is a great example of what happens to a sound wave......Ever see a piece of wood drifting in from the ocean on a windy day? The wood is the particle movement of sound, just not at a constant speed as sound is, and the air molecules, depending on the density and temperature, will aid in the traveling of the sound wave at its speed of sound.

Pressure and intensity work two different ways to create the effects of sound, but both are related in terms of measurements and identification of what is going on with each positive and negative movement of the wave.

 

[Moble Enclosurs 10+ year member]

The medium is normally air, yes.. duh. But not exactly moving, but more so vibrating.Saying sound is produced by "moving air" is completely misleading.

At tuning, actually the sub its self moves very little air.. most all sound at this point radiates from the vent instead of the cone - they are both radiators.

But yes, were taking this too far - a bit of good fun! Going to sleep though and likely wont return for awhile..anywho.. goodnight guys!

There are two types of sound travel here and both occur. The movement is from the kinetic energy transfer, which is in fact a movement from one point to another. The vibration is of concentration for the key to movement of the energy of the sound wave, or the flow per-say. SO, technically both do occur. it's just what occurs to what is the confusion for most.

 

[murph 10+ year member]

Oh no, I foresee quite the debate ITT.

 

[Moble Enclosurs 10+ year member]

Oh no, I foresee quite the debate ITT.

Im game lol. Heading to bed now, but tomorrow Ill catch up ;D

 

[jolly_26 10+ year member]

Oh no, I foresee quite the debate ITT.

between who? Buck and Mobile Enclosures are making pretty much the same point. And **** arguing with either of them!