Wave interference

[Enzo]

I am sitting in my apartment, and the smoke alarm is going off. A steady scream rather than the pulsed beeping, but still annoying. NO we have not been cooking or otherwise generating smoke. A couple weeks ago it took to beeping for a time then quit. I suspect a battery, but they just replaced those a couple months ago.

We are not allowed to touch them, long story short, this apartment does receive some federal funds and has to play by some extra rules. They are wired into the panel down in the office anyway.

SO after calling it in, we wait for the guy.

So I sit here on the sofa, and I note the standing waves of the tone have a lot of cancellation around my head. If I lean 6 inches to one side I can get cancellation down to almost nothing or the other way a lot louder. Same leaning forward or back. Not a subtle variation, but indeed quite a difference in loudness. I have just discovered on head position - leaning forward, turning to the right a bit - I can exactly cancel, and honest, cannot hear it at all. Then a few inches back and it shrieks.

I remember when touring I would set up the PA system, then walk the house floor to listen to my mix around the place. I found it interesting to hear what I guess would be comb filtering? I could hear the cancellation pattern as I walked across the field of the two stacks.

This just a steady tone - 1kHz maybe? Piercing. My cats were freaking out, but have gotten used to it...sorta.

[Leo_Gnardo]

I remember when touring I would set up the PA system, then walk the house floor to listen to my mix around the place. I found it interesting to hear what I guess would be comb filtering? I could hear the cancellation pattern as I walked across the field of the two stacks.

Eggs ackley! A free flanger for those dancing around in the audience. Psychedelic effects without drugs, what's better than that? The good ol' days were so much fun. Sometimes.

And the cancellation effect you're having in the apartment - I first noticed that sort of thing when I learned to align tape decks in the mid 70's. Depending on the frequency, and where your head is in the room, the sound could drop to nearly nothing. I learned mostly to ignore my ears & watch the meters whilst adjusting tape gear.

[Enzo]

Well color me embarrassed. Turns out it wasn't the smoke detector, which is up on the wall about 9 feet. It was my oxygen concentrator on the opposite wall. The sound was reflecting around to the point it was hard to detect the direction.

The machine sits there whirring and thumpin. If it loses power, it has an alarm. Somehow the power plug had lost contact in the wall outlet, and it sat there screaming. I finally noticed when I went to put on my cannula, and no oxygen was coming out. I went over to check my tubes, and found the machine was not running and the red warning light was on - along with the noise.

Push in the plug and reset the power switch, et voila...oxygen.


And no more noise.


We called the building people and cancelled the service call.

[J M Fahey]

Glad you found it.

Just curious/worried: do you use that thingie while sleeping or just when you do some significant activity needing an extra boost?

As in: what if you are sleeping/napping and obviously don´t hear the alarm?

In any case, can´t you "enhance" the alarm?

I bet you are forbidden to mess with it (Medical Device, Liability, yadda yadda, even if you know 10X what maintenance Techs do) but you might tape an electret or piezo near original alarm beeper and feed/trigger something louder.

I remember old days when you could hook nothing to phone line, specifically a Modem, and were restricted to use the klunky "phone couplers" which relied on soundwaves only, no copper involved.

[Chuck H]

Well color me embarrassed. Turns out it wasn't the smoke detector, which is up on the wall about 9 feet. It was my oxygen concentrator on the opposite wall. The sound was reflecting around to the point it was hard to detect the direction.

The machine sits there whirring and thumpin. If it loses power, it has an alarm. Somehow the power plug had lost contact in the wall outlet, and it sat there screaming. I finally noticed when I went to put on my cannula, and no oxygen was coming out. I went over to check my tubes, and found the machine was not running and the red warning light was on - along with the noise.

Push in the plug and reset the power switch, et voila...oxygen.


And no more noise.


We called the building people and cancelled the service call.

Classic Enzo troubleshooting

Just be glad the service guy didn't show up and find it first! Then you'd be "that" guy and every time you called for service they'd say "Is the device plugged in Mr. Enzo?" Very un befitting a man of your experience.

[Leo_Gnardo]

Wow! Glad you found the real problem. Oxygen is good - keep it flowing. And yes as Chuck said, would have been a whale of an embarrassment... nice to miss out in that!

[nosaj]

Wow! Glad you found the real problem. Oxygen is good - keep it flowing. And yes as Chuck said, would have been a whale of an embarrassment... nice to miss out in that!

Oxygen concentrators = Hookas for the older generation ) just playing

[Chuck H]

Oxygen concentrators = Hookas for the older generation ) just playing

Hookas were the older generation!

More like old school vaping Apple pie scent anyone?

[Enzo]

Oh my, we actually have a couple of hookah lounges here in Lansing.

I always use oxy while sleeping, I tend to breath shallow then. When I am active I don't need it much if at all. Just sitting her at the computer I usually use it just to keep my numbers up.

If it went off in the night, I wouldn't implode, I'd just get a headache. The alarm would likely wake me unless I had my head at a cancellation node.

[g1]

So smoke is pulsed tone, O2 unit is steady tone?
I know the smoke alarms have a lifespan and have run into ones that act up (deliberately I assume) when they are expired. I had thought this was going to be the case here, but I don't think they have a separate tone for 'expiry', maybe a chirp though.

[Enzo]

In retrospect, I have learned a lot about the behaviors of the two systems. But until now I had no idea what various modes the smoke detector had. These things detect smoke, but also monoxide. Of course the O2 thingie has no relation to the alarm system. But I had no history of it having indications. Now I know.

The revealing part was being unable to locate the source of the sound by ear within the apartment.


Yes, the smoke alarm pulses with shrill beeps.

[eschertron]

Clearly you need more tapestries in the apartment to help the reverberant field decay

[doctor]

This is well-known "standing waves" effect caused by reflection from the walls.

[Chuck H]

I get the same effect in the wee morning hours in my yard. I hear coyotes making a lot of noise and because I'm in a sort of cul de sac I need to walk around my yard a bit to get a trajectory for which woods area they're in. It can literally sound like it's coming from opposite directions depending on where you stand or even become almost inaudible if you're standing in just the right spot. Coyotes have actually been a problem in neighborhoods adjacent to their roaming grounds so I try to keep up with where they are so I can warn people (it's a small-ish town). I love all dogs and coyotes are really cool, but they are a problem for house pets around here.

[nosaj]

I get the same effect in the wee morning hours in my yard. I hear coyotes making a lot of noise and because I'm in a sort of cul de sac I need to walk around my yard a bit to get a trajectory for which woods area they're in. It can literally sound like it's coming from opposite directions depending on where you stand or even become almost inaudible if you're standing in just the right spot. Coyotes have actually been a problem in neighborhoods adjacent to their roaming grounds so I try to keep up with where they are so I can warn people (it's a small-ish town). I love all dogs and coyotes are really cool, but they are a problem for house pets around here.

Spatial Hearing Loss probably due to sound checking those massive speaker arrays in your youth.
I have it and it's a real pain in the a$$ to go walking in unknown woods because it messes with my sense of direction, highway noise is not where I percieve it to be, etc.

nosaj