Hiss from HVAC system

[polyphonic]

I have noticed a lot of high frequency hiss from the HVAC system tunnel. From researching the issue it seems that every EV out there has some complaints about high frequency noise. It sounds a bit like an old CRT TV. The noise is around the 10-15 kHz range.

High frequencies like this are relatively easy to control. I would like to add some dampening near the top of the HVAC tunnels, and perhaps something more under the hood to absorb sound from the motor and inverter.

I would love to hear thoughts and suggestions for going about this. Especially if anyone has experience adding sound dampening to the F56.

https://www.secondskinaudio.com/acoustics/hushvac
https://www.secondskinaudio.com/acoustics/ecoverb

 

[Carsten Haase]

I went nuts and ripped out the entire interior (dash and all) from my Miata in a hunt for rattles and an attempt to make it less deafening. From that experience, I think it's going to be very difficult to find the source of the noises and to effectively block all of the potential paths to your ears (unless you block the noise at the receiver... aka earplugs lol).

I have also noticed the high pitch noises and some mechanical clicks. The clicks seem to happen immediately after hard acceleration but I haven't found any pattern to reproduce the high pitch tones.

I think its very likely that the noises are all actually coming from the electronics in the engine bay and what you are hearing is the little amount that gets through the firewall and HVAC ducting.

A good example of how much noise the motor/inverters can make is the stripped Unplugged Performance Model S for pikes peak

Start at 2:50

 

[polyphonic]

Yep, I think you're totally right regarding the source of the noise. The HVAC seems to be piping it into the cabin. I'll start by covering the openings with some of that acoustic cotton which I already have.

I've noticed the mechanical clicks too, FWIW, but they don't bother me. Kinda curious about them..

There's a little bit of soft dampening material attached to the hood and around the motor already. There's also room for plenty more

 

[polyphonic]

This thread should really be titled "reducing motor and inverter noise."

I did some more digging and found that the SE already has soft materials for absorbing high frequencies covering the motor, inverter, on the firewall, on the underside of the hood, and even under the vehicle where noise would reflect off of the ground. I think it just needs a lot more for my taste.

The Mercedes EQC uses giant pieces of lightweight acoustic cotton insulation to absorb these sounds. My thinking is the entire engine bay would need to be filled in. It might be possible to make a single giant insert that would fit like a puzzle piece, filling in all of the gaps.

 

[Carsten Haase]

Whatever material you use, definitely make sure it's fire retardant and non-absorbent! I guess the other thing I'd be concerned about is heat. I think the inverter is probably liquid cooled but some of the other electronics are probably just air cooled and may not be too happy wearing a blanket.

BMW and other manufacturers use giant cast blocks of acoustic foam over the engine in their ICE cars, it would be possible to make something similar for the SE if you could figure out what material they use:

 

[Luis Hoffer]

I haven't really focused in on any high pitched noises. The pedestrian warning tone washes out everything under 25 mph and above that speed tire and wind noise create a new noise floor.

 

[polyphonic]

Whatever material you use, definitely make sure it's fire retardant and non-absorbent! I guess the other thing I'd be concerned about is heat. I think the inverter is probably liquid cooled but some of the other electronics are probably just air cooled and may not be too happy wearing a blanket.

BMW and other manufacturers use giant cast blocks of acoustic foam over the engine in their ICE cars, it would be possible to make something similar for the SE if you could figure out what material they use:

View attachment 12662

That's just what I'm looking for! Of course there are a lot of unknowns with heat and airflow like you mentioned.

I haven't really focused in on any high pitched noises. The pedestrian warning tone washes out everything under 25 mph and above that speed tire and wind noise create a new noise floor.

Exactly, the noise floor buries it pretty quickly. The car is objectively quieter than the gasoline version. Admittedly I have pretty sensitive hearing and am easily bothered by sounds.

 

[Toi]

Years of engines, turbines, rotor wash, and jet fuel have made me immune to hearing things in this frequency range. (and many other things... sadly) - perhaps my HK system in mine is wasted? I wish you all the best in combating your unwanted noise.