PDA

View Full Version : Box size in relation to sound output and power input



jcarver
05-28-2012, 07:13 PM
So first this may be better to be moved to one of the discussion forums because its only theoretical talk as I donít really have this problem. If so someone just say so and Iíll 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 Iíve been giving some thought to how box size, sound output, and power input all relate to each other and Iíve come up with some grey ideas of how it all connects but Iíd like to get a clearer picture. Here are some of the things Iíve 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 isnít 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 Iíve seen and donít completely understand as well as real world testing but Iím wondering if those can be manipulated a little to work in our favor. Hereís what Iím thinking.

In this scenario letís say we have a 12Ē 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 letís 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 letís 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.

jcarver
05-29-2012, 12:43 PM
wow no one wants to take this one on lol

surreal
05-29-2012, 12:56 PM
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
05-29-2012, 01:38 PM
First, sound is not produced by moving air.

http://images.wikia.com/illogicopedia/images/c/c1/ORLY.jpg

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
05-29-2012, 10:28 PM
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
05-29-2012, 10:48 PM
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
05-29-2012, 10:52 PM
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
05-29-2012, 11:21 PM
[QUOTE=surreal;8045041] 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
05-29-2012, 11:45 PM
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
05-29-2012, 11:48 PM
Sound is more like pressurization than air flow.

Moble Enclosurs
05-30-2012, 01:18 AM
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. :D. 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
05-30-2012, 01:22 AM
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
05-30-2012, 01:28 AM
Oh no, I foresee quite the debate ITT.

Moble Enclosurs
05-30-2012, 01:30 AM
Oh no, I foresee quite the debate ITT.

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

jolly_26
05-30-2012, 01:45 AM
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!

murph
05-30-2012, 01:49 AM
between who? Buck and Mobile Enclosures are making pretty much the same point. And **** arguing with either of them!

Someone will come and skimp through thinking they "know it all". This will lead to stupid responses that make no common sense. People may mistake the poster for a troll, but truly they know the man who did it just does not know what he is talking about.

Chriszle
05-30-2012, 01:29 PM
My tweets must not be too loud then, cause they don't "move" any air... The sound they make is vibrations. "Moving air" has more so to do with frequency than anything else.

Moble Enclosurs
05-30-2012, 01:48 PM
My tweets must not be too loud then, cause they don't "move" any air... The sound they make is vibrations. "Moving air" has more so to do with frequency than anything else.

Loudness is measured in different forms. The loudness you refer to with your tweeters is based on intensity (w/m^2) and distance, not frequency based. Moving air as far as compression is concerned is of course the factor of the measurement of Pascals, or pressure converted directly to SPL, but dB reference is related to both intensity and pressure in all forms.

you are confusing the terms and relationship between the two.
The intensity is based on energy, so if your tweeters produce a directive high energy transfer, they will be loud to the ear based on vibrations yes. But in sub frequencies, we also have the psi relation to pressure in measurement terms. Moving air can be accomplished without an acoustical source, and it can be metered just the same output, such as blowing into a meter. But the intensity, or energy, from the sound is another form of measured "loudness" to a meter. Both are relative to their own units of measurement and both can be transformed into the form of dB logarithmic output (better for audible accuracy).
Pressure is related to a 3d field of all dimensions, where as intensity is a directive source of transfer from point a to point b. It uses all planes as pressure, but is again, measured differently.

Your reference to "loud" in the sense of a tweeter has not much to do with the dB pressure units of measurement more so it does with intensity units of measurement. Therefore, tweeters can hit say, 120dB a lot easier than one may think without moving an inch. Vibrations and fluctuations or oscillations as we call it, take the same form of transferred energy into two related fields of acoustics.

Do not confuse the two.

Moble Enclosurs
05-30-2012, 01:53 PM
Don't get me wrong though, as far as frequencies are concerned, the main form of concentration of energy has to do with time (ms) which is directly related to frequency changes, so yes, it has to do with frequency differences also, but all forms of sound take a certain amount of pressure to move. The fact that frequencies of higher scale have less time between a neutral state between positive and negative wave formation, they tend to produce less pressure and more intensity, and vice versa for the lower frequencies. Why do you think 1kHz is used for a lot of testing purposes? It is a good balance between the two factors.

Buck
05-30-2012, 02:20 PM
Sound is created by compressions and rarefactions, high pressure zones basically followed by vacuums/extreme low pressure zones. These basically are drastic differences causing a lot of rapid turbulence in the air, a lot of crazy pressure changes. That's why a sub keeps going up and down, it's pressurizing it's environment to the frequency of the sound consistently.

Air is just a medium in which sound (the energy of sound) is transferred.

Chriszle
05-30-2012, 02:24 PM
Thanks for the clarification. That makes sense to me.

Moble Enclosurs
05-30-2012, 02:36 PM
CHeck this out too. It gives a basic understanding other than just words. ;D Sound is a Pressure Wave (http://www.physicsclassroom.com/class/sound/u11l1c.cfm)