Cone area and surround for a subwoofer

[flakko 5,000+ posts]

i asked a knowledgable person about how the cone area/surround ratio on a subwoofer effects the output and this is the response i recieved:

It is a half truth about the cone area. The purpose of a surround asused in a wide bandwidth woofer as opposed to a narrow bandwidth SUB

woofer is to terminate any unwanted phasing irregularities as high

frequencies leave the coil and travel up the cone. They need to have a

brake so they do not go back down. Is a long excursion sub, as long as

there is no air passing through the surround and as long as it does not

cave in at high pressure, it is considered part of the cone. If it

moves forward with the cone, it will have to move air along with the cone

will it not? The tone quality of some subs are degraded when the surround type and size exhibits unwanted resonances or dampens the cone vibration too much or collapses in a sealed box causing distortion and loss of SPL.

discuss. i am interested in all yall opinions. //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Click to read more...

 

[squeak9798 5,000+ posts]

I've never heard that a surround is part of the cone. Every source I've talked to/read from has always determined effective radiation area (Sd), in any driver, to be either the area of the cone plus 1/3 of the surround (most used method, as far as I am aware), or area of the cone plus 1/2 of the surround (I believe RE, for example, uses this method).

The actual formula for Sd is:

Sd = (3.1416 x D^2)/4

where "D" is the diameter of the cone plus 1/3 of the surround (or 1/2 if that be the case)

I can't imagine they would toss this formula out the window for different drivers, i.e. only apply the method to mids and not to subs. I would think it would be a standardized measurement, as with anything used for comparison and calculation purposes.

 

[squeak9798 5,000+ posts]

And after I typed all that up, I'm not really sure whether or not I misread the question?

What exactly is the question again?

But, I guess if the question was about wide roll surrounds have decreased output due to smaller radiation area (Sd), I think the ole formula for Vd (Sd * Xmax) is pretty foretelling of your answer given my above post. If you think about it, if a sub is excurting 28mm, the entire surround is not likewise excurting 28mm. Only the portion closest to and terminating against the cone would move the entire excursion distance. The further you move towards the outter diameter, the less the surround is moving in relation to sub excursion all the way out to the point where the surround mounts to the basket, which would have very little (almost no) movement as the cone moves in and out.

This, I believe, is the reason they only calculate a portion of the surround into the effective radiating area, and why having a wide-roll surround WOULD affect output compared to a less wide surround (more Sd)

 

[PV Audio 5,000+ posts]

planar or parabolic, the cone is the piston, not the surround. of course it does depend, but the EFFECTIVE piston area is does not include the ENTIRE surround.

 

[PV Audio 5,000+ posts]

i find it funny that whoever wrote that was just rambling unnecessary facts to try and sound smart when the basic question could have been asked in a single sentence.

 

[flakko 5,000+ posts]

i was talkin to craig smith from zooss (dist of treo and such) and asked him about that GZ nuke i just purchased and the lack of cone area due to the massive

surround and how the subwoofer compensates for the smaller cone area.

i just wanted peoples opinions on that statement.

 

[squeak9798 5,000+ posts]

And after I typed all that up, I'm not really sure whether or not I misread the question?
What exactly is the question again?

But, I guess if the question was about wide roll surrounds have decreased output due to smaller radiation area (Sd), I think the ole formula for Vd (Sd * Xmax) is pretty foretelling of your answer given my above post. If you think about it, if a sub is excurting 28mm, the entire surround is not likewise excurting 28mm. Only the portion closest to and terminating against the cone would move the entire excursion distance. The further you move towards the outter diameter, the less the surround is moving in relation to sub excursion all the way out to the point where the surround mounts to the basket, which would have very little (almost no) movement as the cone moves in and out.

This, I believe, is the reason they only calculate a portion of the surround into the effective radiating area, and why having a wide-roll surround WOULD affect output compared to a less wide surround (more Sd)

Just to be sure you caught my edit //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

Not sure if it answers your question or not.

 

[squeak9798 5,000+ posts]

planar or parabolic, the cone is the piston, not the surround. of course it does depend, but the EFFECTIVE piston area is does not include the surround.

It DOES include a portion of the surround.

 

[flakko 5,000+ posts]

Just to be sure you caught my edit //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif
Not sure if it answers your question or not.

i tink that kinda answers my question. it makes sense....

comparing to my rlp, while the rlp has more SD (around 20mm more), the Nuke's VD is significantly more due to the xmax. right? so the SD DOES include some of the surround

now whats really interesting is what he said about low and high bandwidth speakers... care to comment on that squeak?

 

[PV Audio 5,000+ posts]

It DOES include a portion of the surround.

yes i know, that's why i said effective //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

 

[squeak9798 5,000+ posts]

i tink that kinda answers my question. it makes sense....
comparing to my rlp, while the rlp has more SD (around 20mm more), the Nuke's VD is significantly more due to the xmax. right? so the SD DOES include some of the surround

I don't know the Xmax of the Nuke....but, if it's Sd*Xmax is higher than the Rl-p's Sd*Xmax then yes, it has a higher Vd //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif

now whats really interesting is what he said about low and high bandwidth speakers... care to comment on that squeak?

It pretty much functions the same in either driver. It's two primary purposes are to keep the VC former centered over the pole piece and to provide a damped termination for the cone to decrease and dampen cone resonances and vibration modes. The main difference is that in subwoofers you aren't going to experience as much cone resonances and such, so it won't have as big of an impact in that area between the two different types of drivers (higher/wider bandwidth vs. subwoofers). In higher/wider bandwidth drivers, the type of surround used (in terms of thickness and material) can and does have an effect on the response of the driver. In subwoofers, it doesn't make as much of a difference. The surround also provides a little compliance to the speaker...on average 20% of the compliance is provided by the surround, the other 80% by the spider.

 

[flakko 5,000+ posts]

ah it make sense now //content.invisioncic.com/y282845/emoticons/biggrin.gif.d71a5d36fcbab170f2364c9f2e3946cb.gif

good info sqeaky!