Hi everyone,
I have a question regarding the "edge" material (the one that supports the cone) of a woofer. I see that there are 2 kinds used in woofer construction. The first is a foam or rubber type that is half round (also used in subs) and the second is a paper-like corrugated thing.
What are the difference in sound in those two?
Thanks in advance,
JojoD
I have a question regarding the "edge" material (the one that supports the cone) of a woofer. I see that there are 2 kinds used in woofer construction. The first is a foam or rubber type that is half round (also used in subs) and the second is a paper-like corrugated thing.
What are the difference in sound in those two?
Thanks in advance,
JojoD
Hi,
The "edge" you refer to is commonly called the "surround". Take a look at this site for a quick explanation to the differences. It's not complete, but a starting point...
The "edge" you refer to is commonly called the "surround". Take a look at this site for a quick explanation to the differences. It's not complete, but a starting point...
?), please see the insert pic, that is what I am asking about.
Actually there are many different surround configurations, the most common being the foam surround. You can also get a butyl rubber and there is a cloth surround. The "accordain" edge can be a separate piece or part of the speaker cone.
As for sound the surround will affect it indirectly as their main purpose is to support the cone and keep it centered. The lighter the material the easier the cone many move (effeciency), also depends on the spider density (at the base of the cone on the back side). Anyway, more efficient speakers have lighter surrounds. High power speakers use butyl rubber or accordian edges. Butyl typically for subs and car applications. Musical instruments use accordian edges the most for power handling and ruggedness. The lighter material will help to promote the ability to reproduce delicate or quick notes.
As for sound the surround will affect it indirectly as their main purpose is to support the cone and keep it centered. The lighter the material the easier the cone many move (effeciency), also depends on the spider density (at the base of the cone on the back side). Anyway, more efficient speakers have lighter surrounds. High power speakers use butyl rubber or accordian edges. Butyl typically for subs and car applications. Musical instruments use accordian edges the most for power handling and ruggedness. The lighter material will help to promote the ability to reproduce delicate or quick notes.
jojo...edge/surround is a common term
instrumentel woofers are designed to operate over a wider frequency range than a regular woofer and are usually mated with a horn for upper frequencies
rubber surround drivers are usually used for high excursion/wattage drivers because of their rigidty
foam surround drivers offer advantages as they allow the cone to be able to react to transient peaks from the music but the foam does deteriate after time
pleated paper surround material is said to be the best but it has its limits as far rigidty and not really the best for high excursion/spl and life span is limited that is why paper cones and surrounds are treated to avoid this
thats a basic answer in laymans terms
DIRT®
instrumentel woofers are designed to operate over a wider frequency range than a regular woofer and are usually mated with a horn for upper frequencies
rubber surround drivers are usually used for high excursion/wattage drivers because of their rigidty
foam surround drivers offer advantages as they allow the cone to be able to react to transient peaks from the music but the foam does deteriate after time
pleated paper surround material is said to be the best but it has its limits as far rigidty and not really the best for high excursion/spl and life span is limited that is why paper cones and surrounds are treated to avoid this
thats a basic answer in laymans terms
DIRT®
what surround works best, depends on the application. Foam surrounds tend to be best for subs that go really low, accordian, or inverted half-roll (cloth/impregnated cloth my preference for these) being better if you want an extended range driver. More exotic surrounds -- such as those on the newer Fostex, are also showing up.
As always these interact with all the other bits in the driver, and as such should be evaluated as a whole unit.
dave
As always these interact with all the other bits in the driver, and as such should be evaluated as a whole unit.
dave
Hi,
Thanks for all the replies! I now have a general understanding of the material used for the woofer surround. So if I will use it for home hifi, I must use a foam surround woofer, but for PA, I must use the accordion type surround woofer. Am I correct?
Another thing that worries me is which of these will provide more low bass? Or will they sound the same? That is, using the same amp, or even the same box.
Thank you very much for bearing with me. I have been studying speakers for a long time now but still get confused
specially on the terminologies used. 
JojoD
Thanks for all the replies! I now have a general understanding of the material used for the woofer surround. So if I will use it for home hifi, I must use a foam surround woofer, but for PA, I must use the accordion type surround woofer. Am I correct?
Another thing that worries me is which of these will provide more low bass? Or will they sound the same? That is, using the same amp, or even the same box.
Thank you very much for bearing with me. I have been studying speakers for a long time now but still get confused
specially on the terminologies used. JojoD
Types of surrounds used and what surround actually does to a driver
Hi JojoD!
We should get this right from the beginning. You don't need to select a subwoofer based on its surround material for an application. What we can do is make generalizations on what is in the industry.
Accordian - typical of pro sound woofers
Rubber and Surround - typical of commerical home subwoofer drivers
The material used for the surround does not relate to how much "bass" you will get from the driver at all. The surround is part of the suspension system, which includes the spider as well. So their main job is to provide the restoring force for the cone and keep the voice coil centered over the pole piece. The suspension system describes the mechanical damping of the driver, which is made up from the stiffness of the spider and the surround. The suspension system and cone weight make up the term Qms. Assuming cone weight is kept equal, then a stiffer surround raises the resonant frequency of the woofer, and the looser the surround lowers the resonant frequency.
That means that the material of the surround has nothing to do with the amount of bass extension you will recieve.
The surround also has absolutely nothing to do with the efficiency of a driver. Efficiency of a driver is strictly related to cone weight and motor strength. Compliance has nothing to do with it either . If you do the substitutions in Fs, Qes, and Vas with the physical parameters (Cms, Mms, BL, Re, Sd, Le) you find that Cms cancels out. At the T/S parameter level, there is a dependency on compliance; however, Fs and Qes are also dependent upon compliance, too. So when you do the full physical parameter derivation, Cms cancels out and you're left with just Mms and BL.
In terms of high frequency extension, the issues involved here is really cone weight and and cone size. Heavier cones are less able to extend high, and larger cones suffer breakup modes earlier which cause both frequency response anomalies up high (and their corresponding phase shift) and also introduces more distortion up high. Some of this distortion can be offset by use of things such as copper shorting rings, higher precision, and many of the other things that pro drivers incorporate. If you look at the distortion ratings, you'll also notice that good pro drivers have much, much less distortion than commercial drivers. The surround will actually impact the high frequency response too, but no where near as much as the two aforementioned things.
As a final note - you certainly can use accordian-surround woofers for subwoofer applications. I personally use an 18LW1400 pro sound driver in a 300L vented cabinet with a -3db point of 23Hz. It has an accordian surround. The JBL 2245H 18" is also another really great subbass driver, which a free air resonance of 20Hz and an accordian surround too. I don't use them because they have accordian surrounds, but rather because the best pro drivers have extremely low distortion, excellent linearity in all areas, and great motor control.
But the point is - you should not select a woofer for an application based on the material used to make the surround. Secondly, the surround doesn't set the efficiency of the woofer either. The surround does alter HF response somewhat, but only marginally - and the modifications it does may be better or worse depending on how it has been implemented. The real purpose of the surround is to keep the voice coil aligned over the pole piece and provide the restoring force of the cone. The stiffness of the surround will also set the resonance frequency of the woofer, and also the mechanical damping of the woofer (Qms, and therefore it affects Qts too, just like Qes does).
Adrian
Hi JojoD!
We should get this right from the beginning. You don't need to select a subwoofer based on its surround material for an application. What we can do is make generalizations on what is in the industry.
Accordian - typical of pro sound woofers
Rubber and Surround - typical of commerical home subwoofer drivers
The material used for the surround does not relate to how much "bass" you will get from the driver at all. The surround is part of the suspension system, which includes the spider as well. So their main job is to provide the restoring force for the cone and keep the voice coil centered over the pole piece. The suspension system describes the mechanical damping of the driver, which is made up from the stiffness of the spider and the surround. The suspension system and cone weight make up the term Qms. Assuming cone weight is kept equal, then a stiffer surround raises the resonant frequency of the woofer, and the looser the surround lowers the resonant frequency.
That means that the material of the surround has nothing to do with the amount of bass extension you will recieve.
The surround also has absolutely nothing to do with the efficiency of a driver. Efficiency of a driver is strictly related to cone weight and motor strength. Compliance has nothing to do with it either . If you do the substitutions in Fs, Qes, and Vas with the physical parameters (Cms, Mms, BL, Re, Sd, Le) you find that Cms cancels out. At the T/S parameter level, there is a dependency on compliance; however, Fs and Qes are also dependent upon compliance, too. So when you do the full physical parameter derivation, Cms cancels out and you're left with just Mms and BL.
In terms of high frequency extension, the issues involved here is really cone weight and and cone size. Heavier cones are less able to extend high, and larger cones suffer breakup modes earlier which cause both frequency response anomalies up high (and their corresponding phase shift) and also introduces more distortion up high. Some of this distortion can be offset by use of things such as copper shorting rings, higher precision, and many of the other things that pro drivers incorporate. If you look at the distortion ratings, you'll also notice that good pro drivers have much, much less distortion than commercial drivers. The surround will actually impact the high frequency response too, but no where near as much as the two aforementioned things.
As a final note - you certainly can use accordian-surround woofers for subwoofer applications. I personally use an 18LW1400 pro sound driver in a 300L vented cabinet with a -3db point of 23Hz. It has an accordian surround. The JBL 2245H 18" is also another really great subbass driver, which a free air resonance of 20Hz and an accordian surround too. I don't use them because they have accordian surrounds, but rather because the best pro drivers have extremely low distortion, excellent linearity in all areas, and great motor control.
But the point is - you should not select a woofer for an application based on the material used to make the surround. Secondly, the surround doesn't set the efficiency of the woofer either. The surround does alter HF response somewhat, but only marginally - and the modifications it does may be better or worse depending on how it has been implemented. The real purpose of the surround is to keep the voice coil aligned over the pole piece and provide the restoring force of the cone. The stiffness of the surround will also set the resonance frequency of the woofer, and also the mechanical damping of the woofer (Qms, and therefore it affects Qts too, just like Qes does).
Adrian
microscopic quibble
Adrian, the 2245H has a foam surround, not accordian. As you so correctly said, though, it makes not a whit of difference- what matters is the driver parameters, not how the driver manufacturer achieved those parameters.
One other minor quibble- the surround does normally provide some restoring force, but most of the restoring force normally comes from the spider. That's why one can refoam drivers without seriously changing the T-S parameters.
Adrian, the 2245H has a foam surround, not accordian. As you so correctly said, though, it makes not a whit of difference- what matters is the driver parameters, not how the driver manufacturer achieved those parameters.
One other minor quibble- the surround does normally provide some restoring force, but most of the restoring force normally comes from the spider. That's why one can refoam drivers without seriously changing the T-S parameters.
Hi SY!
> Adrian, the 2245H has a foam surround, not accordian. As you
> so correctly said, though, it makes not a whit of difference-
> what matters is the driver parameters, not how the driver
> manufacturer achieved those parameters.
Your absolutely right. It must have slipped my mind, I guess it did not occur to me that the 2245H was not accordian. The idea behind it still stands though, as you've acknowledged.
> One other minor quibble- the surround does normally provide
> some restoring force, but most of the restoring force normally
> comes from the spider. That's why one can refoam drivers
> without seriously changing the T-S parameters.
Nonetheless, the suspension system is made up of the spider and surround, which is why I've decided to write it. And it still does contribute to the restoring force of the driver, but certainly the spider takes the most control here.
Adrian
> Adrian, the 2245H has a foam surround, not accordian. As you
> so correctly said, though, it makes not a whit of difference-
> what matters is the driver parameters, not how the driver
> manufacturer achieved those parameters.
Your absolutely right. It must have slipped my mind, I guess it did not occur to me that the 2245H was not accordian. The idea behind it still stands though, as you've acknowledged.
> One other minor quibble- the surround does normally provide
> some restoring force, but most of the restoring force normally
> comes from the spider. That's why one can refoam drivers
> without seriously changing the T-S parameters.
Nonetheless, the suspension system is made up of the spider and surround, which is why I've decided to write it. And it still does contribute to the restoring force of the driver, but certainly the spider takes the most control here.
Adrian
Excellent post indeed!
macky888,
You have have just cleared a lot of thoughts in my mind but also stirred up some more questions (hope you guys don't mind). I thank you for explaining it in such simple terms.
Generally, I have now grasped the idea between the surround and the spider (is it also called diaprahm?).
More questions...
1. In layman's term, what is the meaning of "resonance frequency"? (which the surround sets as you said.)
2. What is mechanical damping? Pls in simple terms.
3. If heavy cone weight relates to efficiency, then smaller woofers like 8" - 12" are more efficient than 15"s or 18"s? Did I get that right?
4. I saw a Crown 18" woofer with a "double magnet", why did they use double magnets? More power handling?
Again, thank you for bearing with me. Maybe instead of "Woofer edge question..." as a title, I think "Woofers for dummies" is a lot more appropriate.
Regards,
JojoD
macky888,
You have have just cleared a lot of thoughts in my mind but also stirred up some more questions (hope you guys don't mind). I thank you for explaining it in such simple terms.
Generally, I have now grasped the idea between the surround and the spider (is it also called diaprahm?).
More questions...
1. In layman's term, what is the meaning of "resonance frequency"? (which the surround sets as you said.)
2. What is mechanical damping? Pls in simple terms.
3. If heavy cone weight relates to efficiency, then smaller woofers like 8" - 12" are more efficient than 15"s or 18"s? Did I get that right?
4. I saw a Crown 18" woofer with a "double magnet", why did they use double magnets? More power handling?
Again, thank you for bearing with me. Maybe instead of "Woofer edge question..." as a title, I think "Woofers for dummies" is a lot more appropriate.
Regards,
JojoD
Hi Jojod!
> You have have just cleared a lot of thoughts in my mind but
> also stirred up some more questions (hope you guys don't
> mind). I thank you for explaining it in such simple terms.
Not a problem.
> Generally, I have now grasped the idea between the surround
> and the spider (is it also called diaprahm?).
Actually, the diaphram is just the cone and dustcap of the driver. What we have is a few things that make up the electrodynamic driver:
1. Motor system - this is the magnet, and everything that comes with it. EG: Pole piece, frontplate, air gap, voice coil, and other various things that manufactures may include.
2. The Diaphram - this is the cone and the dustcap.
3. Suspension system - this is the spider and the surround
> 1. In layman's term, what is the meaning of "resonance
> frequency"? (which the surround sets as you said.)
There are a number of resonances in different systems. But the one I was referring to is the term fs, which is the free air resonant frequency of the driver. The free air resonant frequency is set by the stiffness of the suspension system and the weight of the cone assembly.
Why do drivers have a resonant frequency? Lets assume that the cone assembly is a rigid piston, this is suspended from thre frame by a spring. This "spring" is the suspension system, the spider and the surround. Anything where there is a mass suspended by a spring will have a natural frequency where it vibrates. On our loudspeaker driver, that is called fs, the free air resonant frequency. So the resonant frequency is the result of a balance between the total vibrating mass and the stiffness of the suspension. If the mass is increased, then the resonant frequency decreases because the system is more sluggish. Decrease the mass, and the resonant frequency increases. If the stiffness of the suspension system is increased, then the resonant frequency also raises as a converse effect. Likewise, if the stiffness is decreased, then so does the resonant frequency. Hence, the drivers free air resonant frequency is a ratio of stiffness to mass.
> 2. What is mechanical damping? Pls in simple terms.
Mechanical damping is described as the mechanical Q, or the term Qms. The driver has the terms, Qes, Qms, and Qts which is a combination of the two. They all refer to the damping of the driver at resonance.
Qms is a term used to describe the damping through mechanical means. Cone mass and the force provided by the suspension system are related to this, it acts much like a spring such as the shock absorber on a car.
Qes is a term used to describe the damping through electrical means. It is the ratio of series motor circuit resistance to the square of BL. That means all circuit resistance (including Re, the speaker cable, the amplifier, and any other filters etc in the path) form togethor to make this figure.
Qts is a combination of the two, they are literally parallel forces. So this describes the total damping of the driver.
These parameters form a huge part in how the system responds. I won't get into that, so I'll just describe damping - which is just how much it can damp cone motion at resonance. In free air, the driver will "ring" at its resonant frequency. This overring describes just what the name suggests - its decaying parts of the cycle that are still being played (so the cone is still moving) even after the signal is removed. It is an unwanted artifact. The driver provides damping to attenuate this (in effect, increasing cone control), and so does a correctly designed box. Higher Q values describe a condition where cone control is less, and there is a tendancy for it to ring. Lower Q values describe a damped condition where the cone is more controlled.
> 3. If heavy cone weight relates to efficiency, then smaller
> woofers like 8" - 12" are more efficient than 15"s or 18"s? Did I
> get that right?
Efficiency is made up from both moving mass and motor strength. It's a matter of force (BL times current, thus the Re dependency) trying to move mass (Mms). Thus you need to consider both items when determining efficiency of any given driver.
> 4. I saw a Crown 18" woofer with a "double magnet", why did
> they use double magnets? More power handling?
Those "double stacked magnets" are really made so that longer voice coils can be employed. The magnet still performs the same functions as before - its not even something that you should look for, and a double magnet does not make it any "better" either than another driver which does not have a double magnet. Although, many novice builders will think this. You'll see a general trend between manufactures and terms which don't mean anything, but they attract customers with no proir knowledge of it because it sounds cool.
Adrian
> You have have just cleared a lot of thoughts in my mind but
> also stirred up some more questions (hope you guys don't
> mind). I thank you for explaining it in such simple terms.
Not a problem.
> Generally, I have now grasped the idea between the surround
> and the spider (is it also called diaprahm?).
Actually, the diaphram is just the cone and dustcap of the driver. What we have is a few things that make up the electrodynamic driver:
1. Motor system - this is the magnet, and everything that comes with it. EG: Pole piece, frontplate, air gap, voice coil, and other various things that manufactures may include.
2. The Diaphram - this is the cone and the dustcap.
3. Suspension system - this is the spider and the surround
> 1. In layman's term, what is the meaning of "resonance
> frequency"? (which the surround sets as you said.)
There are a number of resonances in different systems. But the one I was referring to is the term fs, which is the free air resonant frequency of the driver. The free air resonant frequency is set by the stiffness of the suspension system and the weight of the cone assembly.
Why do drivers have a resonant frequency? Lets assume that the cone assembly is a rigid piston, this is suspended from thre frame by a spring. This "spring" is the suspension system, the spider and the surround. Anything where there is a mass suspended by a spring will have a natural frequency where it vibrates. On our loudspeaker driver, that is called fs, the free air resonant frequency. So the resonant frequency is the result of a balance between the total vibrating mass and the stiffness of the suspension. If the mass is increased, then the resonant frequency decreases because the system is more sluggish. Decrease the mass, and the resonant frequency increases. If the stiffness of the suspension system is increased, then the resonant frequency also raises as a converse effect. Likewise, if the stiffness is decreased, then so does the resonant frequency. Hence, the drivers free air resonant frequency is a ratio of stiffness to mass.
> 2. What is mechanical damping? Pls in simple terms.
Mechanical damping is described as the mechanical Q, or the term Qms. The driver has the terms, Qes, Qms, and Qts which is a combination of the two. They all refer to the damping of the driver at resonance.
Qms is a term used to describe the damping through mechanical means. Cone mass and the force provided by the suspension system are related to this, it acts much like a spring such as the shock absorber on a car.
Qes is a term used to describe the damping through electrical means. It is the ratio of series motor circuit resistance to the square of BL. That means all circuit resistance (including Re, the speaker cable, the amplifier, and any other filters etc in the path) form togethor to make this figure.
Qts is a combination of the two, they are literally parallel forces. So this describes the total damping of the driver.
These parameters form a huge part in how the system responds. I won't get into that, so I'll just describe damping - which is just how much it can damp cone motion at resonance. In free air, the driver will "ring" at its resonant frequency. This overring describes just what the name suggests - its decaying parts of the cycle that are still being played (so the cone is still moving) even after the signal is removed. It is an unwanted artifact. The driver provides damping to attenuate this (in effect, increasing cone control), and so does a correctly designed box. Higher Q values describe a condition where cone control is less, and there is a tendancy for it to ring. Lower Q values describe a damped condition where the cone is more controlled.
> 3. If heavy cone weight relates to efficiency, then smaller
> woofers like 8" - 12" are more efficient than 15"s or 18"s? Did I
> get that right?
Efficiency is made up from both moving mass and motor strength. It's a matter of force (BL times current, thus the Re dependency) trying to move mass (Mms). Thus you need to consider both items when determining efficiency of any given driver.
> 4. I saw a Crown 18" woofer with a "double magnet", why did
> they use double magnets? More power handling?
Those "double stacked magnets" are really made so that longer voice coils can be employed. The magnet still performs the same functions as before - its not even something that you should look for, and a double magnet does not make it any "better" either than another driver which does not have a double magnet. Although, many novice builders will think this. You'll see a general trend between manufactures and terms which don't mean anything, but they attract customers with no proir knowledge of it because it sounds cool.
Adrian
macky888,
Ok, now I'm really getting somewhere in the study of speakers. Thanks!
However, local manufacturers of speakers here in my country does not provide any specs about the woofers they are selling. That is partly the reason why I am trying to understand how speakers work.
Ok, back to business... long voice coils, does that mean that the cone excursion (Xmax I think) increases or it doesn't? High excursion is preferable right?
I was almost fooled by that double magnet thing, thanks for the advice.
JojoD
Ok, now I'm really getting somewhere in the study of speakers. Thanks!
However, local manufacturers of speakers here in my country does not provide any specs about the woofers they are selling. That is partly the reason why I am trying to understand how speakers work.
Ok, back to business... long voice coils, does that mean that the cone excursion (Xmax I think) increases or it doesn't? High excursion is preferable right?
I was almost fooled by that double magnet thing, thanks for the advice.
JojoD
High excursion means more output at low frequencies. In theory, it can result in better linearity, but I'd be suspicious right from the get-go of any driver sold without specs. That's an indication of a manufacturer that's either trying to pass off something knowingly inferior or not in control of their build process and materials.
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