Expected Noise Transmission Level Increase from Semi-Coupling Subwoofer Enclosure to Concrete Walls

[STill]

I am intending to build a ported subwoofer whose enclosure is constructed as a floating sideboard (3 × 0.5 × 0.2 m) .
The sideboard is mounted into the corner of two load-bearing and exterior concrete walls which have a strength of 26 cm.
The floor at the corner is also load-bearing and transitioning into a ceiling of cellar rooms.

My concern are the neighbors in the house, particularly the one living over the room's ceiling.

The coupling would only happen at the bolting points (~0.5 m apart), with a ~10 mm air gap to the wall between the mounting points, which I guess still allows some energy absorption by the enclosure.

I wonder how significant the increase of low-frequency noise from the semi-coupled enclosure will be compared to a usual standing enclosure plus the resonance from the output.

Obviously, it is a tricky subject and only a simulation/experiment would give clear answers. The research papers I have tried to dive into have not provided clear answers so far.
But some informed estimates would greatly boost my confidence in finishing the project, or perhaps prevent a disaster.

Thanks in advance!

 

[anotherhobby]

I'm building a "sound proof" audio room in my basement right now. The double walls are decoupled from the house with brackets with rubber bushings. When you whack the interior wall, very little if any nose/vibration transmits to the house framing and the rubber bushings are incredibly effective. However, as a test I drilled 1 single screw thru just one stud so that it created a small but solid connection to a wall that's part of the house. If you whack any stud in the room after the screw is connecting the walls, it transmits quite a bit of noise/vibration into the house framing. The point is, it doesn't matter if it's only 1 small part that's coupled, if the coupling is SOLID, then transmits dramatically more vibration.

 

[EERecordist]

From your description are you mounting your subwoofer to the wall, with space under it, using bolts?

You might consider a steel bracket bolted to the wall, a steel bracket attached to your subwoofer cabinet, and an elastomeric connection between the brackets. If you are concerned about room sound coupling to the resident below, you might consider a layer of jute carpet padding, a layer of mass-loaded vinyl or other mass-loaded acoustic treatment, another layer of jute padding, then your carpet. The problem is that it takes a lot of mass to absorb low frequencies.

You could also put legs on the sideboard and decouple it with elastomeric pads on the floor.

I have not measured it or looked it up, but sand is a good acoustic decoupler. A studio I worked at had a large construction budget. The control rooms had their own foundations decoupled from the building set on sand. Friends building out studios have used a floating floor with elastomeric supports, I don't know the brand.

Other neighbor-friendly approaches are shaker transducers to seating and shaker backpacks, like the Subpac or other brands, even with headphones.

Report back, and for extra credit, get a calibrated microphone and the free Room EQ Wizard software and measure the result!

 

[anotherhobby]

If you want to use isolation brackets as suggested above, I used the RSIC-DC04 clips extensively in my build and they work great:

https://www.pac-intl.com/decoupled.htm

They are quite flexible for usage and can be mounted at almost any angle. Here is one decoupling a wall (horizontal isolation):

And one helping suspend a 200 pound HVAC muffler that I built (vertical isolation):

 

[DVDdoug]

Usually the big problem is soundwaves vibrating the ceiling/floors/and walls, or the soundwaves passing-through.



...I read Jeff Emerick's book . He was the engineer for most of The Beatles recordings and he later built the studio in Apple Records basement. The book is about his life with The Beatles, not about soundproofing or studio building. But he tells a story when he was finishing up the studio and there was a terrorist bombing a couple of doors down. He didn't hear anything and when he came out later he was surprised to the police & firefighters, and they were surprised to see him come walking casually out. I think he was rather proud of his soundproofing!

 

[STill]

From your description are you mounting your subwoofer to the wall, with space under it, using bolts?

Yeah with ~0.5 m space below - and it will be down-firing as there fortunately only are cellars downstairs, allowing a clean top of the sideboard and hiding the woofer.

You might consider a steel bracket bolted to the wall, a steel bracket attached to your subwoofer cabinet, and an elastomeric connection between the brackets. If you are concerned about room sound coupling to the resident below, you might consider a layer of jute carpet padding, a layer of mass-loaded vinyl or other mass-loaded acoustic treatment, another layer of jute padding, then your carpet. The problem is that it takes a lot of mass to absorb low frequencies.

You could also put legs on the sideboard and decouple it with elastomeric pads on the floor.

I have not measured it or looked it up, but sand is a good acoustic decoupler. A studio I worked at had a large construction budget. The control rooms had their own foundations decoupled from the building set on sand. Friends building out studios have used a floating floor with elastomeric supports, I don't know the brand.

Other neighbor-friendly approaches are shaker transducers to seating and shaker backpacks, like the Subpac or other brands, even with headphones.

Report back, and for extra credit, get a calibrated microphone and the free Room EQ Wizard software and measure the result!

Right, I have already considered to use elastomer decoupling elements in the mounting points of the enclosure.
It will complicate the construction of course, particularly because it is important to me that the mounting is floating/invisible.

I will do measurements, comparing the enclosure standing to mounted.
Lucky me has a Klippel engineer as a neighbor in the house, so maybe I can connect based on this project. I live a 5 minute bike ride away from their company headquarter here in Dresden.

 

[EERecordist]

I don't know if anyone has said, welcome to ASR!

Lucky me has a Klippel engineer as a neighbor

You got this. There may be a chapter of the Audio Engineering Society near you and there are acoustics professional groups with chapters. Klippel would know. Carry on and mind the (acoustic) gap!

 

[STill]

I don't know if anyone has said, welcome to ASR!


You got this. There may be a chapter of the Audio Engineering Society near you and there are acoustics professional groups with chapters. Klippel would know. Carry on and mind the (acoustic) gap!

Thanks! I highly appreciate the insights provided here, which defy the alchemical noise in this field.

 

[TheLastGerman]

I faced more or less the same problem, although my subwoofer is somewhat more modest in size and its position relative to the listening position is probably different. The wall supporting my subwoofer is extremely vibrational in the relevant frequency range, but with the simplest possible mounting method I managed to avoid any excitation. Perhaps this will help you with your considerations.