# Moving Air - Speaker question.



## Petey D (Sep 8, 2011)

Trying to get a handle on the concept of moving air as it relates to amp speakers. Not sure how it works, can somebody point me in the right direction?

My sense of logic tells me, that because I have a 210, with 20inches of total speaker surface area, my amp "moves more air" than a similar wattage (12w) 112. So how does that translate into volume or sound quality or what other effect does it have? What are the benifits of "moving more air?"

I've been thinking of ordering a set of these Ten 30's for my Vaporizer, http://qcomponents.ca/product.php?productid=2670&cat=34&page=1 would it be worth my while to do it, or would I be better off just going big with the Greenbacks? http://qcomponents.ca/product.php?productid=2619&cat=34&page=2

Thanks guys.


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## Swervin55 (Oct 30, 2009)

Unfortunately, I'm only able to contribute with the math. Surface area of a flat circle is a function of the diameter squared, so (2)-10" speakers (if they were flat) would have a total surface area of 157 sq in. Similarly, a single 12" speaker has 113 sq in of surface area (again if it is flat). The fact that speakers are cone shaped means the surface area is actually larger and dependent on the characteristics of the cone. But for simple comparison if the cone displacement is the same in each case, the (2)-10" speakers will push approximately 40% more air.


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## ronmac (Sep 22, 2006)

Not an easy question to answer. You certainly will not get a linear amount of increased "air" pressure (SPL) simply by adding more speakers to any given amplifier.


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## sulphur (Jun 2, 2011)

Does a more efficient speaker push more air than a less efficient one?

I know that they are louder.


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## jbealsmusic (Feb 12, 2014)

A speaker works by creating changes in air pressure as the speaker moves forward and backward, essentially pushing and pulling air. At 100Hz the speaker is pushing and pulling 100 times per second, at 500Hz it is pushing/pulling 500 times, etc. Our ears react to that air pressure, which is what we perceive as sound.

However, the concept of "moving air" is largely the same as the concept of something having more "mojo". People referring to something subjective that they like about what they are hearing from a certain cab/speaker, but they don't necessarily know how to articulate exactly what it is. They could be referring to their cab having more bass, better dispersion, or any number of other things.

The best way to find the right sound for you is to experiment. Try different speakers in different cabs until something has the colour/flavour that you like or that inspires you.


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## mhammer (Nov 30, 2007)

If my car is stuck in a snowdrift, who do I want to help me get it out: a 160-lb 5'7" guy who works out, or a 230lb 6'2" guy who spends his days sacked out on the couch eating burritos?

The air movement IS a function of the total surface area of the cone, but it is a function of a number of other things as well:

1) The cone surface area is a function of the shape and depth of the cone. A deep conical form actually has more surface area than a flat form with the identical diameter.

2) The "push" is a function of how hard you put your shoulder into it. So, a more compliant cone that has a lot of backward and forward movement to it can move more air than one of identical size/shape that is restricted in its "throw".

3) A heavier cone will respond more sluggishly than a lighter one, just as a small 6cyl compact will accelerate faster than a cement truck with a more powerful engine.

4) Voice coils, and the gap they fit in, are not all created equal. Other things being equal, a speaker with an efficient coil, sitting in a narrower magnetic gap, will produce more work output per input current/voltage than another coil dangling in a much wider gap. Differences in speaker efficiency often result from not only the size/strength of magnet used, but the manner in which the spider/basket allows for that coil to move back and forth with precision inside a smaller space, without rubbing against the sides and generating the sort of heat that can compromise it.

All toild, some speakers are more efficient than others of the same size. The air movement they produce is generally measured in terms of db sound-pressure level produced at 1 metre distance, with 1W of input. It is generally included in the specs for the speaker, and generally ranges between 90-105db...which is a VERY big range. If you have 2 speakers of the same size and wattage rating, with one having an efficiency rating of 97db and the other at 94db, the first one is moving a LOT more air than the second. That doesn't mean it necessarily _sounds better,_ since the overall efficiency is not the same thing as frequency response.


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## jbealsmusic (Feb 12, 2014)

mhammer said:


> 230lb 6'2" guy who spends his days sacked out on the couch eating burritos?


I mostly sit at a computer desk actually.:sFun_dancing:


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## greco (Jul 15, 2007)

jbealsmusic said:


> The best way to find the right sound for you is to experiment. Try different speakers in different cabs until something has the colour/flavour that you like or that inspires you.


I agree with jbealsmusic. *Speakers are so subjective* and the sound you will obtain from them will depend on many variables (e.g., the cab they are in, cone material (i.e., paper vs hemp), magnet type (i.e., ceramic vs AlNiCo) and the list goes on and on). A new speaker will also typically sound differently after it has been "broken in" by several hours of playing through it.

Changing speakers could very likely make a big difference to what you presently are hearing from your amp. However, IMHO, you just have to take the plunge and try a few. You might want to consider buying used speakers as they are often broken in and sell for much less than the cost of new speakers. 

Good Luck with your search.

Cheers

Dave


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## High/Deaf (Aug 19, 2009)

I always thought 'moving air' was one of those semi-meaningless statements, like haunting mids.

Cabs with multiple speakers sound different than single speaker cabs because of the design. The speakers are all doing the same thing and interfering with each other. Hi-fi and SR companies spend lots on cross-over technology so this doesn't happen with reproduction systems, as the tweeter and mid start to overlap. The two devices covering the same frequencies lead to alot of phase and frequency/level problems. But it is desirable (at least to some) for musical instrument amps.

A vertical 212 is a little different than a horizontal 212 and a 412 is a whole 'nother animal. You don't really hear the sound of the cabinet until a get a number of feet away from it, where the comb filtering occurs. Close mic'ing a speaker in a 412 doesn't give you the same sound as mic'ing the cabinet from 20' away (which is impractical for live use). I think this is more the 'moving air' reference than actually moving more air (which to me means more amplitude or louder). But it is hard to explain sounds in words.


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## Steadfastly (Nov 14, 2008)

This article basically puts it in a "nutshell".










[h=3]How Speakers Work[/h]Speakers produce sound! You already know that, but do you know how they work? This article will guide you through a conceptual overview of how speakers convert an electrical signal into sound. No matter what you are told, no matter how pretty they look, no matter how fancy of words people use, speakers just make sound. Although the explanation of what they do is simple, how speakers work, and how to make them work well, can be extremely complicated. Gaining knowledge about how speakers work will better help you understand how a speaker functions, as well as help you become an informed buyer when you purchase audio equipment.
[h=4]How is sound made?[/h]Sound is a phrase that typically refers to frequencies that the human ear can hear (20Hz -20,000Hz). Sound is created by the fluctuation of air pressure caused by the movement and/or vibration of a given object. When an object moves or vibrates, it transmits the kinetic energy to the air particles around it. The most common analogy for this is to visualize waves in water. Frequency is the word we use to describe the length of a single wave. The frequency is affected by the speed of vibration of the sound-creating object. Slower vibrations equate to lower-frequency sounds. Faster vibrations make higher-frequency sounds.








​As stated above, the human ear can hear frequencies from 20Hz to 20,000Hz (20kHZ). When a sound's frequency is on the lower end of our hearing scale (down near 20hz), we hear deep/low notes/sounds we commonly call Bass. When the frequency is up near 20kHz, we hear high-pitched sounds we commonly call Treble. We call the middle ground frequencies Midrange. Those of us who are fortunate enough to be able to hear most of these frequencies know that we are surrounded by sounds at all times; the world is a noisy place.
Humans are capable of creating sounds in many ways. Most of us can make sound with our vocal cords. Some of us are able to use our hands or lung power to make instruments produce sounds. Babies cry for their parents, children bang on plates, teenagers scream at their parents, and some of us use our knowledge of science to create eqiupment that can reproduce sound; speakers! We are all deeply connected to sound in many ways. Knowledge of how we create sound, and incororate it into our daily lives, will help you notice phenomena that you never knew were there.
[h=4]How do Speakers make sound?[/h]A speaker's function is fairly simple. A speaker converts electrical signals into acoustical energy: sound. By moving back and forth, the speaker increases and decreases the air pressure in front of it thus creating sound waves. Below is a basic diagram of a speaker.








​As you can see, there are not many parts. However, minimal variations in each component can have dramatic effect on the speaker's performance.
The Essentials: Cone, Suspension, Magnet, Voice Coil, and Frame.
The cone is the main moving mass of the speaker. The larger the cone, the more mass and surface area a speaker will have. The more surface area a speaker has, the more air it can move. The more air it can move, the louder the speaker can get; In a nutshell.
NOTE: Accurate, High frequency replication requires smaller specialty drivers; tweeters.
The suspension and the spider keep the voice coil aligned and act like a spring when the speaker is in motion. The suspension pulls the cone back to the center position when it moves back and forth. If there were no suspension, there would be nothing to hold the voice coil and cone in place. The rigidity, composition, and design of the suspension can greatly affect a speaker's performance. Below is a diagram of how a speaker's suspension works.








​The magnet structure is what creates the standing magnetic field. This standing magnetic field gives the voice coil's generated field something to push off of. A strong standing magnetic field allows greater cone motion potential. The stronger this field is, the further it spans thus allowing a voice coil's field more to push off of. The entire action is similar to the idea behind a solenoid. The below diagram demonstrates the voice coil's relationship with the standing magnet field.








​The voice coil and standing magnetic field are what makes the cone move. When an electrical current/signal from from an audio amplifier (alternating at the same frequency as the sound that created it) is put into a speaker's voice coil, the voice coil generates an alternating magnetic field. The alternating polarity of the voice coil causes it to be repelled-from and attracted-to the standing magnetic field. This action of alternating attracting and repelling causes the cone (attached to the voice coil) to move! When the cone moves between 20Hz-20 KHz, the speaker makes sound that we can hear!
All of the above components are held together by the frame. The voice coil is connected to the cone which is connected to the frame via the suspension and spider. The magnet structure is held in place by the frame. The frame keeps the family together and it has to be strong to keep everyone together when things start moving. Without anyone of these crucial components, the speaker would not exist.
[h=4]What is a driver?[/h]







Drivers are specialist. Drivers are speakers that have a certain job to fill and that job is voicing a certain range of frequencies. There are traditionally three types of drivers: Woofers, Midrange, and tweeters. Woofers specialize in producing low frequencies and are the largest of the drivers. Midrange drivers specialize in producing midrange frequencies. Tweeters specialize in producing high frequencies.
Sub-woofers, which you may have heard of, are special drivers that focus on replicating very low frequencies; many of which we can't hear. This driver's purpose is to add the shake, rumble, and roll to a listening experience. Sub-woofers can bring a home theater system closer to sounding and feeling like a movie theater sound system which adds to your home theater experience. Sub-woofers can also make music listening feel like a live experience. Live music experiences are typically experienced at louder volumes where you can feel the bass and impact of the instruments. Subwoofers replicate this sensation but without the other frequencies being at high volume which can be uncomfortable to your ear.








Although there are many different types, styles, and sizes, speakers just make sound. Knowing how they make sound can add a new dimension to a listening experience. Much like knowing a little bit about how a car works may change your driving habits, knowledge about speakers can help you operate them more efficiently. We hope this article helps you understand speakers a little more and gives you a little more confidence when you go out and purchase them.


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## jb welder (Sep 14, 2010)

Moving more air is kind of slang, but it pretty much has to be louder. Is a 50W marshall head not louder into 2 cabs than 1? Either way the amp is putting out the same power, but the 2 cabs "move more air" than the single one.
As far as the spl thing, doubling amp output power gives 3db boost. If you can find a speaker that is 3db more efficient than the one you are currently using, it will give you an increase in loudness that is the equivalent of doubling your amplifier power. Either way you are getting a 3db boost.
So changing speakers is always the easiest way to make big changes to your sound.


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## mhammer (Nov 30, 2007)

In an era where people are more likely to listen to music through Beats than through AR-4a or Smaller Advents, a lot of common knowledge about speaker cabinet design and efficiency tends to have been lost.

So, a refresher from an old fart....

The speaker cone moves both forward AND backward. It pushes air in both directions. The manner in which that air movement is put to use is a function of the cab design. If the cab redirects, and makes use of, the _backwards_ air movement, such that it comes out in the direction of the listener, then the listener hears the sum of the two kinds of air movement. This will produce a high sound pressure level, providing the phase of the forward and backward air movement is aligned. If they are not aligned, such that redirected backwards movement is out of phase with the forwards, then they will partially, or completely cancel out in air.

Consequently, when a closed-back cabinet is used, and the backwards air movement is redirected out front, the redirection is not haphazard, but will involve a port designed to result in the least objectionable cancellation. I suspect the term "move air" comes, in part, from what you feel when you put your hand over such a port at any appreciable volume. The port is smaller than the speaker-cone surface area, so the effect is identical to putting your thumb over the end of the garden hose: the water is being squeezed through a smaller space, and comes out higher pressure.

Open back cabs allow the backward air movement to be largely wasted. It will reflect off any surfaces behind the amp (or off the floor if tilted back), but it isn't being redirected forward to the listener in any deliberate way. As such, all other things being equal, closed-back cabs with a port will "move more air" (in usable fashion) than an open-back cab.

Smaller "practice" amps are a kind of special case. In the world of budget practice or introductory-level combo amps, there is little profit margin, and lots of competition, so manufacturers look for ways to cut production-costs and turn that 4.5% profit into 5%. One of the ways they do this is by small adjustments to the cabinet. An inch less depth, height, and width can have a meaningful impact on the cost of the lumber involved, the cost of the packaging that the amp needs to be shipped and sold in, the shipping weight, the cost of the space required to keep all that inventory, and so on. Unfortunately, it can also have an impact on the resonance of the cab, the amount of bass the amp appears to produce, and the perceived loudness of the unit. Just about any $70 amp that has 3-band EQ, gain and master, and an 8" speaker, can sound MUCH louder if transplanted to a more appropriate cabinet.

Bottom line: the air that the speaker moves is always a function of what the speaker is sitting in.


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## Steadfastly (Nov 14, 2008)

mhammer said:


> Just about any $70 amp that has 3-band EQ, gain and master, and an 8" speaker, can sound MUCH louder if transplanted to a more appropriate cabinet.
> 
> Bottom line: the air that the speaker moves is always a function of what the speaker is sitting in.


Mhammer, that makes perfect sense but it brings a question to mind. There must be a limit to the size of the cabinet where there is too much space/air for the speaker. Is there any specific guidelines or rules for this that you are aware of?


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## mhammer (Nov 30, 2007)

There are, but I couldn't point you to them. Generally, when you see specs for any speaker, it will include some info on optimum cabinet volume, although that may be more a property of hi-fi woofers and such. You can find speaker-cab design software, but again, that tends to be geared towards music reproduction, rather than instrument cabs.

The volume calculations presumes that a) it's not going to be open back, and b) you have some notion of the resonant frequency of the speaker, the compliance and such. With respect to B, part of what a sealed cab does is provide some back-pressure to effectively stiffen a speaker that has deliberately flexible foam surround. We may think of a cab as essentially empty, but the air particles still constitute "stuff" that the speaker pushes against.


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## Petey D (Sep 8, 2011)

Thank you for all the info, I've got a much better handle on the whole concept now.

Mhammer metioned ported closed back cabs, but what about a closed back cab that dosen't have a port, is the backward moving air "wasted" because it dosen't really have a place to go?


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## mhammer (Nov 30, 2007)

1) The M is for Mark. I _gotta_ start signing my posts!

2) The backward air movement is sort of "wasted". On the other hand, in comparison to an open-back cab, it isn't cancelling out anything, and it does provide a sort of "push back out" when the cones move forward again.

It's a bit like a swing, in a sense. Nobody is standing in front of the child on the swing to push them back to you. But when you push them hard from behind, they swing back harder and you can put more "shoulder" into pushing them forward again. The cone compresses the air particles inside the unported cab, when it moves backward, and the air particles give that sucker a shove forward for a little more low-end oomph.

I think it is also fair to note that the sealed cabs we are often familiar with are 4 x 12 cabs, which get even more oomph by having a larger enclosed volume, hence a lower resonance, and ability to reproduce big bottom.


Ooops,
Mark

Somewhere out there, your public or nearby college/university library has the 1st or 2nd edition of _The Audio Cyclopedia_, by either Howard Tremaine, or Glen Ballou (depending on edition). Covers just about everything, from the basic physics of hearing and neurology of the auditory system, right up to digital recording, and the physics of just about everything in between. I've spent many wonderful hours with it in past.

Books - they're good for you. It'll be under the TK section, using the Library of Congress code.


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## Petey D (Sep 8, 2011)

Thanks _Mark._


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