Cone travel one way more than the other

Augusts

Member
2014-12-11 10:33 pm
Hello

The device under test is Eminence Lab12c. It has been recoiled.

When I test the speaker on free air feeding it a sine wave signal at 30hz, everything is as should be - the cone moves an even distance both ways and starts to scream for help when movement reaches 13mm one way as this is the xmax.

But when I feed it a mastered track that has a rhythm and a bassline the cone moves one way a whole lot more than the other (about 13mm inward vs 5 outward). I tried cutting off the lower frequencies, I went until a bandpass region of 55-100hz. The amp is not clipping.

Why do I have this question is because, the speaker was in a TL enclosure and the sub freqencies sounded nice and could hold the power they are supposed to but at 60Hz up where the kick bass starts to play the speaker started to rattle. So I took it out for a test and this is what I saw.
 

Xoc1

Member
2008-11-08 8:25 pm
Devon UK
When the speaker is in free air the resistance to movement will be minimal. When the speaker is in the cabinet the loading on the driver will be greater. You stated that the driver has been rewound.
Are you sure the driver coil has been fitted at the correct height?
 
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Compliance at the zero point is quite large. Its is like a teetertoter when the moving system is undergoing large oscillations; i.e., the zero point will shift due to any small directional difference in suspension elasticity. Any DC offset in the driving signal will also influence this behavior as well. WHG

See Attached Article. WHG
 

Attachments

  • DC displacement.pdf
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Sometimes I have noticed the same, cone is moving more inwards at some frequencies (especially in ported enclosures and some tapped horns etc). This sympton may actually lead to spider/suspension sagging.

Any good solutions for that "port rectification"? could not find any documents..
 
Speaker manufacturer here, agree with Xoc1, suspect poorly reconed speaker.

Only other possibility is program wave assymmetry, but reversing connections dispels that possibility.

Never heard of port rectification, assume effect if present would not explain such a gross difference, BUT you can mount speaker the other way (even if it requires mounting it from the outside) to test that possibility.
 
Hard spider probably help. Low Vas driver. Servo driver do not insure cone is centered. It doesn't track center position. It's only AC feedback. I suspect BCspeakers ipal pressure sensor feedback each side of the cone to limit better than accelerometer DC offset by tracking pressure difference mean of each side on the cone. Pressure can be tracked to DC contrary to Acceleration. So it should gives more headroom.
 
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Hard spider probably help. Low Vas driver. Servo driver do not insure cone is centered. It doesn't track center position. It's only AC feedback. I suspect BCspeakers ipal pressure sensor feedback each side of the cone to limit better than accelerometer DC offset by tracking pressure difference mean of each side on the cone. Pressure can be tracked to DC contrary to Acceleration. So it should gives more headroom.

I did not specify sensor type that is placed in the feedback loop to implement servo control. As you point out there are superior implementation methods. WHG
 

freddi

Member
Paid Member
2005-08-16 4:21 pm
re:"port rectification" - I've seen offset which think "may" be described as such. Its when the port flow stops having a symmetrical back and forth behavior and to a way of thinking, the cone is offset like a DC component has been introduced.

Jon Risch has a patent for asymmetric flow vents to cool speaker motors and IIRC, help with asymmetries.

I've seen it called "vent rectification" somewhere in the past.

Its mentioned here:

Maximizing Performance from Loudspeaker Ports.pdf - Google Drive


9Y37hVD.png
 
Sometimes I have noticed the same, cone is moving more inwards at some frequencies (especially in ported enclosures and some tapped horns etc). This sympton may actually lead to spider/suspension sagging.

Any good solutions for that "port rectification"? could not find any documents..

While about it, do you know any other type of sensor that can somewhat track, even indirectly, DC position ?

While I have not undertaken design of this particular type of loudspeaker control system, I suspect that the offset can be corrected by evaluation of the difference signal. WHG