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Where's The 400 HZ "hum"?  
User currently offlineKELPkid From United States of America, joined Nov 2005, 6428 posts, RR: 3
Posted (8 years 10 months 6 hours ago) and read 4182 times:

Hi,

anyone remember the not-so-distant past, where in-flight PA announcements and airliner radio transmissions often featured the familiar 400 Hz "hum" in the background? (presumably from the 400 HZ AC electrical bus...).

Either I'm going deaf at the 400 Hz level, or this once familiar airline aviation sound has disappeared? (presumably due to better electronic filtration...)

Anyone know the answer?

Thanks!


Celebrating the birth of KELPkidJR on August 5, 2009 :-)
9 replies: All unread, jump to last
 
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17166 posts, RR: 66
Reply 1, posted (8 years 10 months 5 hours ago) and read 4170 times:

Quoting KELPkid (Thread starter):
Either I'm going deaf at the 400 Hz level, or this once familiar airline aviation sound has disappeared? (presumably due to better electronic filtration...)

I think you answered your own question there  Wink



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineTimz From United States of America, joined Sep 1999, 6902 posts, RR: 7
Reply 2, posted (8 years 10 months 4 hours ago) and read 4149 times:

I just heard it a couple days ago-- some sort of WN 737 I think it was.

User currently offlinePrebennorholm From Denmark, joined Mar 2000, 6534 posts, RR: 54
Reply 3, posted (8 years 10 months 4 hours ago) and read 4146 times:

If someone has a cure, then please come here and repair SAS's MD'80's.

After 25 years of 400 Hz hum it would be nice to hear what they want to tell us before take-off and landing.

I used to assume that they want to tell roughly the same thing as they tell on their Airbusses.

I always wondered how a plane can be certified for flight with such a lausy PA system. What if there was something important to tell the pax?



Always keep your number of landings equal to your number of take-offs, Preben Norholm
User currently offlineStarlionblue From Greenland, joined Feb 2004, 17166 posts, RR: 66
Reply 4, posted (8 years 10 months 3 hours ago) and read 4118 times:

Quoting Prebennorholm (Reply 3):

I always wondered how a plane can be certified for flight with such a lausy PA system. What if there was something important to tell the pax?

Yell. Incomprehensible but you can try to get your point across with volume.  Wink



"There are no stupid questions, but there are a lot of inquisitive idiots."
User currently offlineBuzz From United States of America, joined Nov 1999, 697 posts, RR: 21
Reply 5, posted (8 years 10 months 2 hours ago) and read 4085 times:

Hi KelpKid, Buzz here. Maybe i'm going deaf also.... i don't hear it so much.
Lst time i really noticed it was when i was wearing a headset and let the dangling cord get close to the External Power cord, it transmitted reasonably well into the headset.
g'nite


User currently offlineSCCutler From United States of America, joined Jan 2000, 5613 posts, RR: 28
Reply 6, posted (8 years 10 months ago) and read 4047 times:

...I always figured that, when I fly in some of the airspace known for being more "hostile" (ORD Approach comes to mind), I could improve the quality of service if I had a tone generator overlaying a slight 400hz on my audio when transmitting.

I could be the first Bonanza with a 400hz AC bus, and CSD!



...three miles from BRONS, clear for the ILS one five approach...
User currently offlineMX757 From United States of America, joined Aug 2005, 628 posts, RR: 12
Reply 7, posted (8 years 9 months 4 weeks 1 day 7 hours ago) and read 3904 times:

Quoting Starlionblue (Reply 1):
Quoting KELPkid (Thread starter):
Either I'm going deaf at the 400 Hz level, or this once familiar airline aviation sound has disappeared? (presumably due to better electronic filtration...)

I think you answered your own question there

He did. Most new aircraft have better filtering (Shielding) then older ones.

Here is something a little off subject. If you take a multi-meter into an E&E bay of an aircraft, powered up of course, and set it on Hz you will pick 400 Hz with the leads hanging in free air. The 757 is the best to do it in.



Is it broke...? Yeah I'll fix it.
User currently offlineCancidas From Poland, joined Jul 2003, 4112 posts, RR: 11
Reply 8, posted (8 years 9 months 4 weeks 1 day ago) and read 3830 times:

when you plug in 400hzand a ground comm headset you're nearly microwaving your brian....


"...cannot the kingdom of salvation take me home."
User currently offlineA/c train From United Kingdom, joined Jun 2001, 501 posts, RR: 4
Reply 9, posted (8 years 9 months 4 weeks 15 hours ago) and read 3783 times:

improved cable screening, radio filters and checking static wicks is what rids radio interference.

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