Comments on: Loudspeakers: Why are bass speakers way bigger than trebble speakers?

By: Kes

Kes — Thu, 07 Jan 2010 15:43:59 +0000

Bass speakers are not only larger but usually are enclosed in a box that helps resonate their low pitch. Resonation (efficient reflection of sound energy) works best when the size of the resonator is more nearly equal in size with the length of the soundwave (pitch). The treble speakers transmit higher pitches which are more energetic and penetrating and generally don’t need a special enclosure. The largest stops (pipes) of a pipe organ produce the lowest notes because the fundamental (lowest) wavelength is consistent with the length of the pipe (whether open or closed). The pitch of a bass drum is deeper the larger the drum with increased volume for the same reason.
References :
http://dev.physicslab.org/Document.aspx?doctype=3&filename=WavesSound_ResonancePipes.xml

http://images.google.com/imgres?imgurl=http://cache.daylife.com/imageserve/08ml6iafERfce/610x.jpg&imgrefurl=http://www.daylife.com/photo/08ml6iafERfce&usg=__NNylJlUs2UvYZD-Vq7o-2t639vo=&h=488&w=610&sz=73&hl=en&start=9&um=1&tbnid=-YmvcRTMA6lAjM:&tbnh=109&tbnw=136&prev=/images%3Fq%3Dgiant%2Bbass%2Bdrum%26hl%3Den%26sa%3DN%26um%3D1

By: charcinders

charcinders — Thu, 07 Jan 2010 15:09:59 +0000

It does have to do with the relationship between the size of the speaker cone and the length of the sound wave, and something called acoustic impedance. Here’s my conceptual understanding of it:

Sound is rapid fluctuations in air pressure, high pressure / low pressure / high pressure… etc. These travel out from the source as waves. The loudness of a sound depends on the sound pressure level, which is the difference between the highest pressure in the wave and the lowest pressure in the wave.

OK, let’s say you have a speaker cone. If you drive it with an audio signal it will move back and forward. When it moves out, it squeezes the air in front of the cone, causing a high pressure wave peak, when it moves in again it causes a low pressure wave trough. Now of course the speaker cone is open to the air, and air is free to move, so when the cone moves outwards to create the high pressure peak some of the air will just move out of the way.

However, air can only move so fast. If you drive the speaker at a very fast rate (high frequency) the air doesn’t have time to get out of the way, so you get a big difference in pressure between peak and trough. Big difference in pressure = loud sound. If you drive it at a slow rate (low frequency) the air has time to move, to equalise the pressure between in and out parts of the cycle, so you get a small difference in pressure, which equals a quieter sound.
Now if you use a bigger speaker cone, the air has further to go in order to get out of the way, so you can still get a good sound pressure level from it.

Now, you may ask, why doesn’t a good bass speaker produce an even louder treble (high frequency) sound? It is because you need energy to accelerate a mass, like a speaker cone. The higher the frequency, the greater the acceleration, and the more energy you need to move it. A big speaker doesn’t work well at high frequencies because there is not enough energy available in the electrical signal to move the cone very fast.
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By: Technobuff

Technobuff — Thu, 07 Jan 2010 14:30:59 +0000

I think it’s more a case of treble speakers being smaller that bass speakers. They need to be less massive, to vibrate the cone at the high end of frequencies.
Woofers are bass, not treble also.
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By: theradioham

theradioham — Thu, 07 Jan 2010 13:57:59 +0000

To deliver the same amount of acoustic energy at low frequencies, more air must be moved in each cycle, necessitating either a large cone area, a long throw (large movement) or both. In essence, if you halve the frequency, you only have half the number of cycles to deliver power, so more must be put into each one. Extending the motion of the cone beyond certain limits is difficult, due to limits of the cone suspension, so it is more effective to use larger cones.

To deliver higher frequencies efficiently and accurately, the tweeter cone must be lighter and more rigid, to avoid resonaces within the cone.

"Full range" speakers use a variety of methods, from a small "whizzer" cone attached at the centre, while the larger cone flexes and does not drive at higher frequencies, to a simple rigid varnished area in the centre.
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By: gintable

gintable — Thu, 07 Jan 2010 13:35:59 +0000

The answer is that the wavelength in air of low frequency (bass) sounds is longer than the wavelength in air of high frequency (treble) sounds.

Octave 3 is typical of bass notes. Wavelengths in air of octave 3 notes are on the order of 5 meters long.

Octave 5 is typical of treble notes. Wavelengths in air of octave 5 notes are on the order of 1 meter long.

Even wavelengths in the materials of the speaker equipment fit this trend, except that they are not equal to air-based wavelengths of the same note. Within the speaker, we need the sound waves to be able to have constructive interference patterns and resonate, to get the desired sound more efficiently. As a result, bass speakers are built larger than treble speakers.
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