Sound direction

[Patthehat033 10+ year member]

I am confused on how sound works..

If a subwoofer produces sound by vibrating air. Then whenever sound vibrates off something wouldn't it change the sound that our ears can understand.

So for example, when the subwoofer beats, it is producing the sound of a song. But then a few seconds later when the air particles encounter an object (the back of the sub box, a seat, the panels of your car etc.) wouldn't the sound change, and it would not longer sound like the song?

That also leads me to the question of how much an enclosure makes a difference. Doesn't a subwoofer enclosure only affect sound waves produced by the back of the subwoofer?

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[daboyfrumdabx 10+ year member]

Well the waves from the front of the woofers will likely come into contact with the enclosure at some point (i.e. rear facing in a trunk). It also separates front from rear waves. I'm no expert on the science of boxes, but I believe it's safe to say that it affects more than just waves from the "back of the subwoofer"

 

[Phoenix Risen 10+ year member]

the enclosure dictates 90% of the sound that your system can be produced.

as far as the acoustical part of everything keep_hope_alive will be the man to answer the question.

 

[Patthehat033 10+ year member]

Bump.

 

[keep_hope_alive Premium Member]

I can answer your question, it will take some time to explain. I can make a first pass at it later tonight. I hope you like physics.

 

[Patthehat033 10+ year member]

//content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif Haha that would be awesome, take your time lol it's just knowledge!

 

[keep_hope_alive Premium Member]

Refer to the Master Handbook on Acoustics 5th Ed. for more information.

A speaker cone moves air molecules, the molecules vibrate in a sinusoidal matter. You can imagine these vibrating air molecules as waves with peaks and valleys of high and low pressure zones.

Music is a type of complex sound waves that are made up of many frequencies. Note that reflections do not change the periodic nature of sound, but the combination of the direct and reflected sound will change the sound we hear. The frequency content does not change, but intensity changes at some frequencies due to a combination of absorption and phase interference.

Note that the perception of pitch will change with loudness. Chords that seem discordant at low amplitudes can seem pleasant at higher amplitudes.

The enclosure does a few things,

First, it isolates the rear wave from the front wave. Without this, you would get cancellation that would render the sub inaudible. This is easy to prove to yourself by holding one in your hand and playing.

Second it creates back pressure that resists cone movement.

The enclosure also absorbs some of the sound energy, and the amount of absorption varies with frequencies.

But most importantly, the speaker/sub design itself strongly influences the acouatic performance it can achieve in the recommended enclosure. Vance Dickason delves into this subject in the 7th edition of the LDC section 0.70.

Does the environment of a speaker influence the sound that we perceive by the ear? Certainly. Yes.

 

[Patthehat033 10+ year member]

So then with like a ported box. Would it seem louder because of how fast the waves of sound are moving? So like the wavelengths would still be the same length a part but moving faster? Or do I have that completely wrong haha?

Also like when the rear and front waves are seperated. Would the back of the box make the rear waves go towards the front of the box? And then the waves would be going the same direction?

 

[keep_hope_alive Premium Member]

No, a ported box is louder because the rear wave combines with the front wave in-phase, giving 3dB gain. There is more to it than that, but in essence that is the jist. The tube length allows the rear wave to travel further.