ESL Bias Supply Polarity

[bolserst]

Just curious if anybody has noticed there being some sonic benefits to using a positive vs negative HV bias supply for charging the diaphragm of an ESL.

I have tried both and don't measure any change in sensitivity or notice in change in sound quality. But, I own just one set of ears.

I seem to remember reading once that Sound Lab found that a negatively charged diaphragm collected dust less quickly. But, I can't seem to find the quote now. My own 2 week test did not seem to show any appreciable difference in dust collecting abilities.

Perhaps there are other technical or practical reasons to choose one over the other...

Any comments or thoughts are welcome.

Steve

[david yost]

I think the Acoustat supplies were +5000V and they seem to do better than most at staying clean, and they do not use dust covers as Quad does.

[oshifis]

Charged dust particles are floating around in the air. I remember once so-called air ionizators were common, they allegedly are good for the health, keep you awake while driving etc. I can't remember whether they produced positive or negative ions. Anyway, if the dust particles are charged let's say mostly positive, then a positive polarized diphragm would distract them (at least in theory).

I built a similar ionizer (voltage multiplier, several kilovolts) a while ago, and after a few days of operation I noticed that dust was collected on the wall, so I stopped using it.

[bolserst]

Originally posted by oshifis
Charged dust particles are floating around in the air. I remember once so-called air ionizators were common, they allegedly are good for the health, keep you awake while driving etc. I can't remember whether they produced positive or negative ions. Anyway, if the dust particles are charged let's say mostly positive, then a positive polarized diphragm would distract them (at least in theory).

I built a similar ionizer (voltage multiplier, several kilovolts) a while ago, and after a few days of operation I noticed that dust was collected on the wall, so I stopped using it.

Your mentioning of charged dust collecting on walls triggered my memory and I finally recalled where I read the quote from Roger West of Sound Lab concerning using negative bias to reduce dust collection…

It was from his patent 3,935,397…on the last page. Here is an excerpt:

“…The electrostatic dust shield effect assumes that the dust in the air is negatively ionized, which is usually the case. Most actual dust accumulation occurs when the speaker is not reproducing sound --- that is when the DC supply is on but no AC signal is applied. Therefore the DC bias supply is preferably made negative so that dust will be repelled…”

[Capaciti]

Hi,

long ago i read about the advantage of a negative charged membran. The Advantage would be less corrosion of the high voltage contact to the membran when charged negative.

If true i dont know


Capaciti

[MJ Dijkstra]

Hi,

It is true that a negative voltage will protect metals (anodic protection) as it prevents the reaction M -> M+ + electron.
The opposite is true for the positive side.
Whether this is a significant factor I don't know. But as replacing HV connections can be pretty clumsy or impossible without tearing apart the whole ESL I used a negative voltage.

Cigarette smoke is supposed to have a positive charge so a positive voltage may be good for repelling this particles. Do not know if this is significant as well.

I have not noticed any change in sound while using + or - voltage.

[moray james]

for the majority of the year air is normally positively charged. That's why Acoustat used a pos diaphragm charge so dust and smoke will be repelled.

[bolserst]

Originally posted by moray james
for the majority of the year air is normally positively charged. That's why Acoustat used a pos diaphragm charge so dust and smoke will be repelled.

What determines the polarity of airborne dust & smoke?
Your comment implied to me that part of the year it tends to be negative and part positive...

[oshifis]

I found this on the web (Google for ionizer + health, 3rd hit):

"Negative ions are found after a rainstorm (falling water creates negative ions) or after a lightning strike. Every home has its own built in negative ionizer- your shower. The smell in the air generated after a rainfall is actually the odor of negatively charged ions in the air."

"Positive ions are found in high concentrations before a storm when it is windy and in areas that have high outdoor air pollution. Sitting in traffic on a busy highway or freeway is a great place to get a dose of positive ions."

[bacon665]

As for the corrosion factor alot of airplanes (military) have current applied to their bodies and antennas to keep them from corroding in the air