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How important is the speaker surround (suspension)? Defects a problem?

mononoaware

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#1
Recently bought a pair of Fostex FE103NV drivers which are now made in china.

When opening the boxes and inspecting them I noticed 2 small defects on the inverted surround (both had 2 defects each in random spots).
Like if you gently pushed from underneath with the tip of your finger, except they are deformed like that permanently.
They are very minor and can only be seen under the right light, but still they are defects.

I have seen many photos of previous generation FE103 series drivers and I have never seen this defect.

I am an easy going person so I just screwed them into the enclosures and they work so that's fine, I will purchase replacements when the speakers blow.
The FE103NV is able to extend to 20khz (starts rolling off about 16khz but still plays up there as its a full-range driver).

I wonder if these kinds of defects or damage to the speaker surround can cause issues when playing extremely high frequencies of 15-20khz since they require more precise fast movement of the cone compared to a bass note.

Thanks.
 
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#2
Pictures?

If you are concerned, perhaps you can do a sine sweep and capture (with a measurement mic) of both drivers? That could tell you whether the defect you see is causing unusual distortion in some bands.

Years back I had a JBL 15" driver from a band-pass pro subwoofer that wasn't reconed properly -- slop in the glue job on the surround. That ended up in a tear where the (paper) cone and surround meet, resulting in another recone job. Wiith LF drivers (drivers with high Xmech), a defect in the surround could be catastrophic. With midrange and HF, it may only cause distortion that's well within specs, and likely below our threshold of hearing.
 

AnalogSteph

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#3
I wouldn't expect the surround to be involved very much at all by 15-20 kHz, which tends to be well into breakup territory, with only the center part of the cone doing much of anything. The art of building a wideband driver is all about controlled breakup. Going by supplied graphs I would say this driver is definitely in non-pistonic territory above 10 kHz.

Given that most of the restoring force tends to come from the spider rather than the surround (and I am assuming the surround is doing its job of keeping things airtight?), I would expect few problems from imperfections like these. It just isn't something you like to see.
 

egellings

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#4
The spider provides most of the restoring force in a cone driver. Surround, not that much.
 
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mononoaware

mononoaware

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Thread Starter #5
Pictures?

If you are concerned, perhaps you can do a sine sweep and capture (with a measurement mic) of both drivers? That could tell you whether the defect you see is causing unusual distortion in some bands.

Years back I had a JBL 15" driver from a band-pass pro subwoofer that wasn't reconed properly -- slop in the glue job on the surround. That ended up in a tear where the (paper) cone and surround meet, resulting in another recone job. Wiith LF drivers (drivers with high Xmech), a defect in the surround could be catastrophic. With midrange and HF, it may only cause distortion that's well within specs, and likely below our threshold of hearing.
Hi goldenpiggy,

I have access to a brand-new Beyerdynamic Fox USB mic would that do the job?

The FE103NV is marketed as a "full-range" driver, but so far observing it's attempts at excursion I would say it is closer to the behaviour of a midrange driver.

And yes upon testing I find it to sound just fine, if I had heard something odd I would have asked for replacements.
 
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mononoaware

mononoaware

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Thread Starter #6
I wouldn't expect the surround to be involved very much at all by 15-20 kHz, which tends to be well into breakup territory, with only the center part of the cone doing much of anything. The art of building a wideband driver is all about controlled breakup. Going by supplied graphs I would say this driver is definitely in non-pistonic territory above 10 kHz.

Given that most of the restoring force tends to come from the spider rather than the surround (and I am assuming the surround is doing its job of keeping things airtight?), I would expect few problems from imperfections like these. It just isn't something you like to see.
Hi AnalogSteph,

I see so when breaking up, the dust cap almost acts as a tweeter dome?
Thanks for your insight into the non-pistonic nature above 10khz.

Yes the surround is perfectly fine/sealed. It is just a small defect, maybe from early in the manufacturing process.

I would expect few problems from imperfections like these. It just isn't something you like to see.
Yes I mean I was fine with how it appears. I am ok with little nicks and imperfections.
The drivers were definitely new and straight from the factory.
They were out-of-stock at supplier, then they happened to receive stock soon after I enquired. They also come boxed in pairs.

I just found it odd that both drivers have 2 defects, and both in random spots.
 
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mononoaware

mononoaware

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Thread Starter #7
The spider provides most of the restoring force in a cone driver. Surround, not that much.
Hi egelllings,

Thanks, I was just concerned about the movement and "damping" effect of the surround.
I just thought even a small defect in the surround could affect its flexible nature.
In this case 2 small defects interrupting a semicircle.
 
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egellings

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#8
The surround does help damp non-pistonic vibrations in the cone. 'Pistonic' means like a piston, that is, all points on the cone move through the same distance at the same time-the cone shape does not distort on loud passages or certain frequencies. It's solid, like a piston in a car engine.
 

hardisj

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#9
I believe Vance Dickason wrote in Loudspeaker Cookbook that the surround is responsible for about 20% and the spider is the other 80% of the total suspension of a drive unit (generally speaking). The surround is what helps hold the suspension in place (especially at the extremes) and keeps from the driver having asymmetry as it moves through its excursion range. So, if it is damaged, then it's a problem.
 
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mononoaware

mononoaware

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Thread Starter #10
Just had a go at taking a photo, I took 10 photos of 1 driver, but I simply could not get the defects to show well in the photos, even with flash activated. From the photos they almost appear non-existent.

And having a second look at both drivers mounted in the enclosures, it seems like the defects have reduced in size, maybe it was just under better light when I could hold and inspect the driver's in my hand.

Initially each defect looked like a 3mm wide 'gentle' bubble on the inverted surround.
Having looked just now all the defects seem less obvious, almost as if they have conformed to the shape of the rest of the inverted surround.

Whether it is actually less of a bubble or it is just the light, I guess I feel slightly better thinking they are extremely minor defects.
 

restorer-john

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#11
I believe Vance Dickason wrote in Loudspeaker Cookbook that the surround is responsible for about 20% and the spider is the other 80% of the total suspension of a drive unit (generally speaking).
That makes a lot of sense.

You can easily operate woofer without a surround, inverted and at low excursions, whereas I wouldn't want to try it the other way. :)
 
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mononoaware

mononoaware

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Thread Starter #12
Update. (related to original topic of speaker surround)

Thanks to my clumsiness, I dropped one of the drivers a 2-3 inches onto a hard surface.

After putting it back and listening, I swear the one I dropped was missing high frequencies (somewhere between 13-15khz and above) and sharp edged sounds were much duller than before.
I first brushed it off to the speaker + head positioning, but over a few days it became obvious there was something wrong.
After listening for the amplifier's self noise by putting my ear up to the driver, the dropped driver definitely had a muffled hiss.

After going back and forth inspecting both driver's, on the dropped one the left and right of the surround is pulled tighter than the top and bottom.
Oddly, the top and bottom of the surround is still an inverted curve as it should be.
I did inspect the spider after I had dropped it and pressed the cone in and out to test the voice coil (no scraping or odd sounds from the voice coil) so I thought it was fine.
But just checking again now with drivers in resting position, the dropped driver sticks out slightly more by around 1mm.

The maximum excursion of the FE103En 0.6mm so assuming the FE103NV is the same, my guess is this "slight" change (damage) to the voice coil/cone's position has affected the speaker's performance.
I am thinking since Maximum excursion is 0.6mm and I can visibly see that the driver is sticking out by around that much, it is pretty much stuck close to maximum excursion and is a serious problem.

I guess speaker's are more fragile than I thought they were... you would think they survive that kind of rough handling in their factory packaging...

Probably need to order a new driver...
 
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mononoaware

mononoaware

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Thread Starter #13
Brand new driver installed today. Problem solved.

Getting proper stereo sound again.

This is my first time handling and experimenting with "full-range" drivers, maybe they are more fragile than your average "mid-woofer".

I had another look at the old "good" driver, and can see the inverted surround is starting to flatten out at 3 a clock like the dropped driver (which was flattening at 9 and 3 a clock).
Probably caused by my "testing" of pressing on the cone. :)

During testing of the old dropped driver and confirming NO voice coil rub when the cone was moving straight in and out, I noticed a light touch to the 1-2 a clock area caused the voice coil to rub, when the same light touch applied opposite at 7-8 a clock there was no voice coil rubbing.
I became curious and did the same thing to the old "good" driver just to see if it had the same issue, which it didn't (but I may have done some damage here).
When looking at the resting position of the old "good" driver it looks identical to the brand new driver.

Now I am thinking that full-range Fostex drivers are on the fragile side of speakers.
Maybe more delicate components or tighter tolerances are required for a driver playing from 100hz to 18khz.
(the cone is paper, thin light and small, so also a thinner more easily damaged voice coil?)

For the moment I am not too fussy about it so both speakers are considered "functional" for now.
Compared to most, I am listening at mouse-whisper levels near-field so I'm sure no damage can be done that way.
Maybe it was the low cost of the drivers which helped in the careless handling.

From now on I will be very careful when handling these fragile little drivers.
 
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