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Suspended wooden floor - do I need to bass trap under it?
Old 2 weeks ago
  #1
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Suspended wooden floor - do I need to bass trap under it?

I've recently been converting a room into a dedicated listening room and have been doing some acoustic treatment on it. I've bass trapped a significant portion of the room (near square unfortunately) with bulk soft fiberglass in bags and am listening in a near-field setup using dipoles. I've recorded the room acoustics and have got an acceptable frequency response with short decay of every frequency above ~100hz (150-200ms). However, I've still have modal ringing from around 60-90 hz (which may be due to the near-square nature) although I'm hoping to improve a little more if I can.

To get to my question, the room I'm using has a suspended wooden floor and sits approximately 1.5ft (30-45cm) above the foundation (ground). The outer wall of the foundation is brick and I'm wondering whether bass could be escaping through the floor and reflecting back up off the ground underneath the house and through the floor again. I'm wondering whether I should try and put bulk traps into this space but given the cramped size and the long/difficult crawl I'd have to subject myself too, I thought I'd ask in case it's unlikely to be necessary.

Does anyone know how readily these sub 100Hz frequencies would penetrate the wooden floor boards? Could some of the room modal issues actually be due to reflection back through the floor or are most reflections due to internal room dimensions itself?

Thoughts would be appreciated
Old 2 weeks ago
  #2
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Jason Foi's Avatar
 

Quote:
Originally Posted by John B View Post
I've recently been converting a room into a dedicated listening room and have been doing some acoustic treatment on it. I've bass trapped a significant portion of the room (near square unfortunately) with bulk soft fiberglass in bags and am listening in a near-field setup using dipoles. I've recorded the room acoustics and have got an acceptable frequency response with short decay of every frequency above ~100hz (150-200ms). However, I've still have modal ringing from around 60-90 hz (which may be due to the near-square nature) although I'm hoping to improve a little more if I can.

To get to my question, the room I'm using has a suspended wooden floor and sits approximately 1.5ft (30-45cm) above the foundation (ground). The outer wall of the foundation is brick and I'm wondering whether bass could be escaping through the floor and reflecting back up off the ground underneath the house and through the floor again. I'm wondering whether I should try and put bulk traps into this space but given the cramped size and the long/difficult crawl I'd have to subject myself too, I thought I'd ask in case it's unlikely to be necessary.

Does anyone know how readily these sub 100Hz frequencies would penetrate the wooden floor boards? Could some of the room modal issues actually be due to reflection back through the floor or are most reflections due to internal room dimensions itself?

Thoughts would be appreciated
Open the bags and fluff up the insulation for better performance. Your wood floor is likely resonating quite a bit and can be stopped/lessened by dampening the vibration. I dont think stuffing the crawl space is the best bet, but it would work. You could also add mass or mass/green glue to dampen the vibration. Its not so much a modal issue as it is resonance. Modes are determined by solid boundaries, so your floor is likely the acoustic boundary. Bass escaping through the floor is only bad in regards to isolation, not acustics.
Old 2 weeks ago
  #3
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Quote:
Open the bags and fluff up the insulation for better performance. Your wood floor is likely resonating quite a bit and can be stopped/lessened by dampening the vibration. I dont think stuffing the crawl space is the best bet, but it would work. You could also add mass or mass/green glue to dampen the vibration. Its not so much a modal issue as it is resonance. Modes are determined by solid boundaries, so your floor is likely the acoustic boundary. Bass escaping through the floor is only bad in regards to isolation, not acustics.
Thank you for your reply, so essentially I'm probably dealing more with floor vibration than reflections.

Do you have any thoughts how I could go about doing the dampening? I had a look at the green glue but am unsure how exactly to approach it given my room's construction. The underfloor space is somewhat similar to this picture from the internet, except instead of polyester insulation I'm got stapled rolls of soft fibreglass insulation.

https://tinyurl.com/y8s4xsfd

In terms of adding mass, I presume I'd have to add weight to the floorboards somehow. Are you able to provide any more insight in to logistically how this could best be done?
Old 2 weeks ago
  #4
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GYMusic's Avatar
Are your speakers on the floor? They shouldn't be.
Old 2 weeks ago
  #5
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The speakers I use (depending on which set is out) are either Magnepan 1.7's (more often) or Kef LS50s. The Kefs sit on Partington super dreadnought stands while the maggies have there stock 'feet'. I've also got a 10 inch sealed subwoofer that is sitting on small rubber legs.

This is an older waterfall recording from the room, I've managed to improve on this slightly however the 60-70 hz region is more or less similar and is the issue I'm trying to work on (if actually possible). That plot was recorded with the maggies so the response looks a bit better with the LS50's due to the maggies quirks.

https://ibb.co/tqD0VCK
Old 2 weeks ago
  #6
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Jason Foi's Avatar
 

Quote:
Originally Posted by John B View Post
Thank you for your reply, so essentially I'm probably dealing more with floor vibration than reflections.

Do you have any thoughts how I could go about doing the dampening? I had a look at the green glue but am unsure how exactly to approach it given my room's construction. The underfloor space is somewhat similar to this picture from the internet, except instead of polyester insulation I'm got stapled rolls of soft fibreglass insulation.

https://tinyurl.com/y8s4xsfd

In terms of adding mass, I presume I'd have to add weight to the floorboards somehow. Are you able to provide any more insight in to logistically how this could best be done?
Hmm... i dont know if your floor is causing problems or not. That seems like a pretty open space, i was picturing more of a giant drum. The insulation stapled to it underneath may be damping the floor sufficiently. Decoupling the sub/speakers from the floor is probably all that you need.
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