Double Bass What Does Speaker Surround Do?

[Steve Freides]

A silly question, maybe, but what does speaker surround do? It seems rather an inexact sort of thing - if, in principle, the cone was rigid (probably not the right word - stiff?) enough to be completely controlled by the magnet, would surround even be necessary? Would a speaker without an connection at the edge of the cone, perhaps a smallish speaker, work satisfactorily? Would sound quality be impaired, or longevity, or both?

Just curious and not yellow.

-S-

 

[greenboy]

The tolerances of a voice coil are really tight, and the cone and coil needs to travel only in and out on the z axis without crashing - deviating on the x axis and y axis of the gap. Nobody has yet come up with a better method that's actually affordable. It's actually amazing how well these things work, actually!

EDIT: Really I'm talking of the spider here too.

 

[DukeLeJeune]

The surround also helps damp the bending waves that propagate from the apex (voice coil) to the rim of the cone when the cone is used above its pistonic region. The surround dissipates some of that energy so that less is reflected from the rim back down to the apex.

And, if you didn't have a surround of some sort, the out-of-phase low-frequency energy on the back side of the cone would pass around the edges of the cone and you'd have a very weak, farty low end. This happens when the foam surround rots away on an old speaker, but fortunately re-coning is usually possible.

 

[fdeck]

A silly question, maybe, but what does speaker surround do? It seems rather an inexact sort of thing - if, in principle, the cone was rigid (probably not the right word - stiff?) enough to be completely controlled by the magnet, would surround even be necessary? Would a speaker without an connection at the edge of the cone, perhaps a smallish speaker, work satisfactorily? Would sound quality be impaired, or longevity, or both?

Just curious and not yellow.

-S-

Like Duke says, the surround serves to keep air from passing in and out of the cabinet. It's like the piston rings in a gas engine. You can minimize the effect of the surround by using a driver with a stiff cone and floppy surround. In most bass speakers, the cone is controlled primarily by the air pressure in the box.

 

[Steve Freides]

Thanks, folks.

So on an older speaker with, e.g., maybe an inch or two of surrounding missing from a 12 inch driver, it's probably not going to have a huge effect because most of the damping and most of the air blockage will still be taking place?

NB - I don't have anything like this, just curious.

Is the surround material specific to the driver, to the diameter or the speaker, or something else, e.g., if you wanted to redo the surround, exactly how DIY is it? Again, just curious to know, e.g. If I cam across something old that seemed to work but the surround was damaged, is this the kind of thing I could fix myself? I'm sure I couldn't replace a speaker cone, but if the surround is basically just rubber that glues on, well...

If there's any not terribly techie reading on this subject, feel free to point me in the right direction. I just want to know how this works, e.g. if I ever built my own cabinet, does the surround come with the driver, how do you size the hole in the cabinet and how much space does the surround take up - that sort of thing.

Thanks again.

-S-

 

[greenboy]

A fair amount of home audio enthusiasts get into replacing surrounds because some older drivers that are considered desirable have deteriorated foam surrounds.

With MI/SR drivers it's arguably pretty important to use like materials as found in the stock/OEM driver formulations so that the T-S parameters stay within tolerance. Guys can recone or replace surrounds, but professional reconers are a little more likely to have the materials/kits on hand and get the desired results.

Parted or ripped surrounds are guaranteed to adversely affect driver-in-enclosure parameters, and bass instruments are definitely going to take a performance and durability hit if the surround is not doing its several jobs.