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Tommy_tucker

bookcase design for dampening

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Can I pick your brains.

 

I am having a bookcase built in to my living room (proposed location in blue below).  I find low frequency bass becomes muddy in my room and was hoping I might be able to correct this by putting some material behind the bookcase, or by designing it in some other way to maximise its dampening ability.  If there is no dampening benefit to be gained by putting material behind the bookcase, will the bookcase in itself help my issue?  I have read conflicting advice on the acoustic benefits of books.

 

As the bookcase will be at the opposite end of the room to my speakers (but not facing them), is there still a benefit to be had in this location?  I am assuming anything is better than the existing bare wall (brick).  Layout below:

 

1837096462_livingroom.JPG.38c73c174a3b5cdf76ef7378bb07e5c3.JPG

 

 

Secondly, my toddler's bedroom is next door to the living room, the other side of the planned bookcase.  My next priority (after dampening) is to increase soundproofing.  Again - can someone recommend a material that I can put behind the bookcase to help soundproofing of the room.  My gut feel is soundproofing may be easier to achieve than dampening but keen to learn from others, thanks in advance.

 

 

 

Edited by Tommy_tucker

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I'm not convinced putting anything behind the bookcase will help with dampening especially if the bookcase covers most of the wall can't hurt but I don't think you'll reap much benefit I have seen some people hang decorative rugs on walls for that purpose same principle as carpet on the floor.

 

The actual bookcase should provide a noise buffer for your toddlers room by itself all those books should absorb some of the sound brick wall is a pretty effective sound barrier anyway , thing is you've got a toddler means you can't really turn it up that much realistically.

 

Just on a side note I believe if you could rearrange your setup so the speakers actually sat in front of the book shelf down firing towards the window that would actually improve your acoustics but obviously the TV then becomes a problem or perhaps the speakers and TV could be placed in front of the window hopefully there's some heavy drapes already in place to assist with the potential window rattling and brightness from the sun for viewing TV, subs don't matter where you put them they aren't directional really comes down to what you're allowed to do in the room if it's a shared space, it's not a bad size a lot of guys get shoved into a corner somewhere or under stairs and thats what they have to work with if you could play with the posItioning a bit you might find the sound will improve.

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Soundproofing a room is a big job and difficult to achieve.  Think of a recording studio.  High class studios use a room built within a room to achieve this.  This is not really practical for a living room.  Attenuating the transmission of sound between rooms is a bit easier.  You could install in wall insulation between the two rooms which will provide a significant improvement by attenuating structure borne transmission.  There is lots of information available on the web provided you are prepared to do some reading.

 

With regards to the muddy bass, I would look to introduce some corner bass traps as the first step.  Also speaker position is very important and from the look of your layout, speakers mounted flush with a wall (as opposed to in the wall like a recording studio) can cause all sorts of boundary effects that are detrimental to bass response.  Again lots of info available on the web.  My advice would be not to rush into this but do your research and decide on an appropriate budget using the various techniques for addressing room acoustics.

 

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This bookcase we built with the express purpose of it being(hopefully) a 'natural'  damper. the back frame of the three bookcase pods is 16mm ply screwed into the wall studs , with two sheets of soundcheck gyprock and acoustic insulation behind it(as are the other walls. A very thick acoustic underlay and a very thick pile pure wool carpet complete the picture.

Weak points are the windows on the left.

 

If you could arrange your speakers in front of the proposed bookcase you'd be heading i the right direction.

Obviously I have OB's but I've had box speakers in there as well, both standmounts and small towers. No muddy base issues yet.

Just a couple of pics showing the raw pods as they went up. Nothing too special in the construction of them.

post-117697-0-98680800-1373789072_thumb.jpgpost-117697-0-88207100-1373789198_thumb.jpg

 

1798347968_Roompic1.thumb.jpg.d8370c3d10998bc8ea1efca9759282c5.jpg1299389811_Roompic2.thumb.jpg.116b4da588b1867bf6b15e622930855f.jpg

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Just my 2c regarding...

 

thing is you've got a toddler means you can't really turn it up that much realistically.”

 

I agree that most will take this approach.  My missus and I did the opposite (ages ago now!).  Turn it up.  Bring the noise!  Little kids will sleep through anything if used to it.  If you tiptoe, then that’s all they know, and they’ll wake to a feather hitting the floor.  If you just go about your noisy business, and they have a sleep routine, then sound won’t matter.  

 

On the topic, I’m also keen to hear about deadening material for in-wall insulation and sound buffering.  

 

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Thank you for the replies.


batmaqn - Speaker position is non-negotiable with my wife unfortunately.  I have tried, trust me!  Originally I had it set up facing away from the bookcase wall but it is a shared room and I had to compromise.   I have moved the fronts around in their current location and have noticed a significant difference in sound, even with only 15cm adjustments.  Ultimately the bass problem may be exacerbated by my listening position which is close to the back wall.

 

Bilbo - In wall insulation is probably a step too far for me, I am only considering treatment between the planned bookcase and the existing wall.  Equally, corner bass traps would be ideal, but I can only go as far putting something behind the bookcase for aesthetic reasons.  From the responses is sounds like the bookcase and books may reflect most of the sound before it reaches any material placed behind the bookcase.

 

Luc - thanks for the photos, looks like a great room.  So soundcheck gyprock and acoustic insulation behind the bookcase was your choice.  What acoustic insulation did you use?  Was your intention to dampen the room with this or prevent noise escaping the room?  I can imagine your acoustics being good from your photos (carpet especially) - I have wooden floors partly covered by rug.

 

Mat - agree 100%, our child is also good at sleeping through noise, even with the sub vibrating the house 😉.  He is 2 now, wondering whether he start complaining in a few years.

 

 

 

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13 hours ago, Mat-with-one-t said:

Just my 2c regarding...

 

thing is you've got a toddler means you can't really turn it up that much realistically.”

 

I agree that most will take this approach.  My missus and I did the opposite (ages ago now!).  Turn it up.  Bring the noise!  Little kids will sleep through anything if used to it.  If you tiptoe, then that’s all they know, and they’ll wake to a feather hitting the floor.  If you just go about your noisy business, and they have a sleep routine, then sound won’t matter.  

 

On the topic, I’m also keen to hear about deadening material for in-wall insulation and sound buffering.  

 

I'm not a toddler but I can fall asleep with my system pumping through a playlist.

I've woken at 2am to silence and staggered off to bed quite a few times!!!  🕑

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6 hours ago, Tommy_tucker said:

What acoustic insulation did you use?  Was your intention to dampen the room with this or prevent noise escaping the room?

Can't remember the insulation but it's readily available through Bunnings or other hardware stores. The stuff has a rating so you just go by the number. Google will find it for you.

The entire idea was to separate me and my passion from the house as best I could.

 

I've been to a lot of members places and the majority have their systems in the main room of the house and that's shared obviously and limiting to a degree so in my case I had this room which was originally  designed as my library and an area separate from the lounge area. So I'm lucky in that we built and didn't buy which gives you options.

So yes, the idea was to contain the sound, to mute it and it does that admirably as for damping I've never needed to do it to be honest. 

 

Soundcheck gyprock is one way and there are others as well. There a quite a lot of threads on this. Green glue, studwall separation(two frames with an air gap in between).

 

How long is a piece of string? That's the problem you face in regards to both cost and implementation.

If your bookcase is actually filled with books and not just some random books and nic nacs, then it'll do the job of absorption. You'll have so many different faces(book faces, the spines of the books) that they'll do a good job of scattering those soundwaves. We tested the bookcase here when it was empty and then after it was chocka full of books and cd's.

Chalk+ cheese, reflections while empty and none that we could really hear when it was full.

It's very easy to find the sweet spot  and the speakers sound like they aren't actually on which is what you want in a sweet spot isn't it.

 

As you have considerations that I didn't have to worry about I'm probably not helping much but a bookcase full of actual books will certainly make a difference to reflection points that's for sure.

 

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On 08/11/2019 at 5:01 PM, Luc said:

Can't remember the insulation but it's readily available through Bunnings or other hardware stores. The stuff has a rating so you just go by the number. Google will find it for you.

...

As you have considerations that I didn't have to worry about I'm probably not helping much but a bookcase full of actual books will certainly make a difference to reflection points that's for sure.

 

Cool, thanks.  I will put some stuff down the back and see what happens.  Looking forward to testing the room after it is complete. 

I would like to move from bookshelf speakers to floorstanders but I am reluctant to do so while I  have this issue.  Have also wondered whether a more powerful amp might control the bass better but that is a different conversation.

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11 hours ago, Tommy_tucker said:

Cool, thanks.  I will put some stuff down the back and see what happens.  Looking forward to testing the room after it is complete. 

I would like to move from bookshelf speakers to floorstanders but I am reluctant to do so while I  have this issue.  Have also wondered whether a more powerful amp might control the bass better but that is a different conversation.

Be careful you don't mistake the presentation of an amplifier for problems with room acoustics.

I have seen some friends burn serious amounts of money on new gear thinking it will fix the fundamental problems with the room.  It never does in reality.

There are various implementations of DSP that can help with room issues but some basic room acoustic treatment will be the best bang for buck in my experience.

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it's a brick wall that the bookcase is going on?? and this is the wall you'd like to increase isolation?

 

The brick wall will likely have very good isolation already - elevated noise in the baby's room will likely be from "flanking" noise - not through the brick wall, but through the ceiling/floor/hallway/windows etc etc

 

It's very hard to change soundproofing/isolation without room re-construction.

 

The concept of using furniture as room treatments to improve "in room" sound (as opposed to isolation/sound proofing) is something that interests me greatly - I've often thought about designing furniture that improves the "in room" sound...

 

With a book case across an entire wall I would consider:

  • using absorption at the top/bottom/sides the entire the depth of the book case
  • limp mass at the front of the absorption on some "cells" of the book case - requiring some design based on your room's bass issues

Your large sofa will already be soaking up bass, but if you can get away with it, put some cheap poly batts underneath - fill the space if you can get away with it.

 

Given you have an internal wall that's brick, I'm assuming you have other brick walls in that room also?

Rigid walls are a really big challenge for achieving good "in room" bass - brick veneer with Gyprock on studs with fluffy behind is not too hard to manage - double brick or besser is an acoustic nightmare for managing bass "in room".

 

Absorption needs to be large/wide/deep to absorb lower frequencies, and simply gets too big and takes up too much real estate to be effective at lower frequencies...that said, in your current layout, simple fluffy insulation under the entire couch area would have an impact on the "in room" sound

 

The treatment approaches for "rigid" rooms are different to "lossy" rooms. below 150Hz or so.

 

"Lossy" rooms can get away with using only absorption treatment and some EQ for <150 Hz or so.

 

"Rigid" rooms need the same absorption treatment as "lossy" rooms" plus specialist "bass trap" treatment working <150Hz, with EQ applied over the top.

 

cheers

Mike

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Along the wall you have marked in blue, would there be a hassle in slapping a layer of 18mm Fyrecheck plasterboards up against it with some Green Glue on it? That's yer basic interior soundproof wall and you end up with a wall that looks identical to what you have, just 20mm further into the room. The plasterboard sealer for the joins is the Bunnings sealer rated "acoustic" or buy the green glue sister product "joint sealant". Noise is like water, it will creep through the gaps, so seal them all. Hence audiophile obsession with air vents, power points, joins. Then build your bookcases against it, as Luc says.

 

If you want to go further (and it looks like this is the path I will take because I have some plasterboard and two tubes of Green Glue left over) I'll put some plasterboard inserts into the roof space between the beams to stop any noise creeping around the edges. Not that it's happening into the room next door, it's more to stop the Rottweiler next door barking at 1.00am.

 

By the way, the wall in our room that our speakers are against is a brick feature wall. It helps the sound generally and is recommended but as said above, isn't helpful if you wish to retard bass. A friend moved from an apartment with concrete block walls to a unit with studs, plasterboard and insulation, and reckons he's lost about $3k in sound accuracy and attack, from lower midrange to the topmost audible notes.

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almikel / thirddrawerdown,

 

Thanks for your replies.  The priority is control of bass in the room.  Sound isolation is a secondary concern.

 

The room is double brick on all four walls (with exception of the large window on the left).

 

almikel - I am assuming these design recommendations are at the front of the bookcase?:

  • using absorption at the top/bottom/sides the entire the depth of the book case
  • limp mass at the front of the absorption on some "cells" of the book case - requiring some design based on your room's bass issues

I was hoping something behind the bookcase would provide some benefit as I am limited with how I can change it aesthetically.

 

'cheap poly batts' - I looked at the bunnings website, should I go for something in particular - ie. higher R number or lower?

 

Would you describe my room as rigid?  the measurements below are from my anthem mrx AVR. 

measurements.JPG.2172bece21482ba59ca2ef9b0ec74d89.JPG

 

When I turn on ARC it cleans up the bass but it sounds like I lose the lowest frequencies.

Edited by Tommy_tucker

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On 18/11/2019 at 10:00 AM, Tommy_tucker said:

The room is double brick on all four walls (with exception of the large window on the left).

 

On 18/11/2019 at 10:00 AM, Tommy_tucker said:

Would you describe my room as rigid?

your walls are rigid - is the floor a concrete slab? if so then the only non rigid boundary is maybe the ceiling (hopefully? otherwise it's a concrete bunker)

 

On 18/11/2019 at 10:00 AM, Tommy_tucker said:

The priority is control of bass in the room

You will struggle to manage bass in your room especially with the constraint of...

On 18/11/2019 at 10:00 AM, Tommy_tucker said:

I was hoping something behind the bookcase would provide some benefit as I am limited with how I can change it aesthetically.

Bass absorption requires width and depth, and EQ can only help so much and is very position dependant - ie applying EQ may help in one listening position, but negatively affect the sound in a different listening position - like the next seat on the couch...

With rigid walls, the bass remains in the room, just bouncing around (ringing) at the room's resonant frequencies...you need compliance in the room boundaries to absorb bass

 

On 18/11/2019 at 10:00 AM, Tommy_tucker said:

I am assuming these design recommendations are at the front of the bookcase?:

yes - front of bookcase...some limp mass membranes at the front of the bookcase at the top/bottom sides...appropriately designed to absorb the problem frequencies could help...

 

...that said, if you wanted to add some compliance behind the bookshelf (and increased isolation is not a concern), then attaching furring channel or studs to the brick with normal gyprock over the top with fluffy insulation behind will give that wall some compliance/bass absorption...but that's construction work...

...and that's only a single wall you've added compliance to - which will help - but you still have mostly rigid boundaries bouncing low bass around - IME lightly constructed rooms are much easier to manage low bass, as it leaks out everywhere so it doesn't remain in the room bouncing around causing ringing.

 

Typically rigid rooms will require specialist treatments (eg limp mass, membrane traps, pressure traps) targeted at specific problem frequencies and combined with EQ to achieve good "in room" bass.

 

On 18/11/2019 at 10:00 AM, Tommy_tucker said:

'cheap poly batts' - I looked at the bunnings website, should I go for something in particular - ie. higher R number or lower?

Search for Greenstuf Batts - my Bunnings only stocks fiberglass - you want polyester - Greenstuf is an Autex brand, but any polyester batt is fine - in the fluffy stuff the R number relates to depth - higher R is larger depth - work on R2 or above - it doesn't really matter - volume/$ is all that counts

 

Mike

 

 

 

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On 07/11/2019 at 3:21 PM, Tommy_tucker said:

Can I pick your brains.

 

I am having a bookcase built in to my living room (proposed location in blue below).  I find low frequency bass becomes muddy in my room and was hoping I might be able to correct this by putting some material behind the bookcase, or by designing it in some other way to maximise its dampening ability.  If there is no dampening benefit to be gained by putting material behind the bookcase, will the bookcase in itself help my issue?  I have read conflicting advice on the acoustic benefits of books.

 

As the bookcase will be at the opposite end of the room to my speakers (but not facing them), is there still a benefit to be had in this location?  I am assuming anything is better than the existing bare wall (brick).  Layout below:

 

1837096462_livingroom.JPG.38c73c174a3b5cdf76ef7378bb07e5c3.JPG

 

 

Secondly, my toddler's bedroom is next door to the living room, the other side of the planned bookcase.  My next priority (after dampening) is to increase soundproofing.  Again - can someone recommend a material that I can put behind the bookcase to help soundproofing of the room.  My gut feel is soundproofing may be easier to achieve than dampening but keen to learn from others, thanks in advance.

 

 

 

Hi,  I have a built in bookcase in my room which was part of the acoustic treatment design.  The rear wall includes corner bass traps with a  bookcase made from tiers to act as a diffuser.  The size and angle of the tiers are based on the room length.  
 

43E6841A-C7C1-4D8E-95CE-CEF57291AD74.jpeg

264F6F59-F89A-47E4-8599-FE69210D671A.jpeg

8D71168C-9A8A-4349-AB1D-3B0B98D483C4.jpeg

982D6CD0-A91B-4CEE-B37E-611749DAD2AA.jpeg

4C2D4D69-DF43-489D-B0B8-B879A6AD59B7.jpeg

Edited by Gav67
Added more photos

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On 20/11/2019 at 12:12 AM, almikel said:

your walls are rigid - is the floor a concrete slab? if so then the only non rigid boundary is maybe the ceiling (hopefully? otherwise it's a concrete bunker)

Thanks again for taking the time to respond.  Yes, wooden floors and panel type of ceiling (its old, so not really gyprock but similar).

 

Quote

Search for Greenstuf Batts - my Bunnings only stocks fiberglass - you want polyester - Greenstuf is an Autex brand, but any polyester batt is fine - in the fluffy stuff the R number relates to depth - higher R is larger depth - work on R2 or above - it doesn't really matter - volume/$ is all that counts

I will look into this then as a first step.  Sounds like more drastic treatment is needed but will take it one step at a time.

 

Ultimately Im still pleased with the sound I have at the moment but the bass issues have certainly stopped me from chasing after bigger speakers for the moment.  Both a blessing and curse.

Edited by Tommy_tucker

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On 20/11/2019 at 6:45 AM, Gav67 said:

Hi,  I have a built in bookcase in my room which was part of the acoustic treatment design.  The rear wall includes corner bass traps with a  bookcase made from tiers to act as a diffuser.  The size and angle of the tiers are based on the room length.  
 

43E6841A-C7C1-4D8E-95CE-CEF57291AD74.jpeg

264F6F59-F89A-47E4-8599-FE69210D671A.jpeg

8D71168C-9A8A-4349-AB1D-3B0B98D483C4.jpeg

982D6CD0-A91B-4CEE-B37E-611749DAD2AA.jpeg

4C2D4D69-DF43-489D-B0B8-B879A6AD59B7.jpeg

 

Your bookshelf and room design looks really fantastic, thank you for sharing.  I can only imagine how much better a room like this must sound.  The bookshelf design has given me a few things to think about.   

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8 hours ago, Tommy_tucker said:

 

Your bookshelf and room design looks really fantastic, thank you for sharing.  I can only imagine how much better a room like this must sound.  The bookshelf design has given me a few things to think about.   

Thanks.  While the sound improvement was the overall driver, I wanted the treatments to look part of the room.  Not something added as an after thought. Hence the top of the bookcase integration into a plaster wall and concise. Lots of weekend hours over 12 plus months  building and installing all the treatments.  Good fun in the end. Photo of the ceiling diffuser and front corner bass trap.  Good luck with your room.
 

 

F8B18135-AF08-4C8E-93D8-2E21C4FDD1D7.jpeg

DCDEA9A9-B3AC-4E3B-AB7A-B6F0C8465AAB.jpeg

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On 07/11/2019 at 4:21 PM, Tommy_tucker said:

I am having a bookcase built in to my living room (proposed location in blue below).  I find low frequency bass becomes muddy in my room and was hoping I might be able to correct this by putting some material behind the bookcase, or by designing it in some other way to maximise its dampening ability.

Yes, it is likely something can be done of benefit..... but the best thing you can do is know roughly what frequencies are problematic.   (ie. what do you mean by "low bass").    20Hz? 50Hz?  100Hz?  150Hz?    Which one is it really?    20Hz is 5 times the size of 100Hz ..... and so what affects/improves it can be totally different.

 

 

On 07/11/2019 at 4:21 PM, Tommy_tucker said:

Secondly, my toddler's bedroom is next door to the living room, the other side of the planned bookcase.  My next priority (after dampening) is to increase soundproofing.  Again - can someone recommend a material that I can put behind the bookcase to help soundproofing of the room.  My gut feel is soundproofing may be easier to achieve than dampening but keen to learn from others, thanks in advance.

There is plaster products that you could put over your existing plaster before you erect the book case.

 

Then adding a layer of absorbing material behind the bookcase could also help tame the bass.... but it will need to be very thick.  10cm is not really thick enough.    30cm will do something.

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Some excellent ideas in this thread. Have you had the room analysed before you start hurling money at it? Your actions might end up creating new issues or shifting the problem. If you have a budget of say $3k then it might be that a minidsp or behringer device will achieve what you want, without plaster dust and mess.

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2 hours ago, ThirdDrawerDown said:

Some excellent ideas in this thread. Have you had the room analysed before you start hurling money at it? Your actions might end up creating new issues or shifting the problem. If you have a budget of say $3k then it might be that a minidsp or behringer device will achieve what you want, without plaster dust and mess.

Ha, no I try to avoid hurling money around when possible.

I have taken room measurements using ARC on my anthem mrx avr and posted them above. Is there more to it than that?

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Quote

> I have taken room measurements using ARC on my anthem mrx avr and posted them above. Is there more to it than that?

Hopefully the room measurement experts will chime in. Others know far more on this.

 

Also, I was speed-reading and didn't register your post. I apologise.

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On 18/11/2019 at 11:00 AM, Tommy_tucker said:

I was hoping something behind the bookcase would provide some benefit as I am limited with how I can change it aesthetically.

Yes as long as there is some way for the sound to partially reach through the bookcase to get to the absorption material .....   but we are talking a lot of material to make a difference.    If you put a 20cm void behind the bookcase, and filled it with soft insulation (like you'd find inside a wall) then it would help.

I have oversimplified things here a bit... and you do need to be careful what you build, so it will work effectively (don't close off the insulation too much)....  but this should give you a rough idea for now.

 

Quote

'cheap poly batts' - I looked at the bunnings website, should I go for something in particular - ie. higher R number or lower?

The flow resistance is the important bit (eg. if you tried to blow air through it) ....  something about 40kg/m3

 

On 18/11/2019 at 11:00 AM, Tommy_tucker said:

When I turn on ARC it cleans up the bass but it sounds like I lose the lowest frequencies.

You can see that when you turn on ARC it is reducing the 30-100 (and 50-100) quite significantly .... I would say this is what you are noticing.

 

Do you also run a subwoofer.   Do you have a measure on that? .... and a chart of the whole total response?

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2 hours ago, davewantsmoore said:

The flow resistance is the important bit (eg. if you tried to blow air through it) ....  something about 40kg/m3

Dave's correct - the flow resistance is the important bit, but almost never quoted, nor is the density typically quoted in standard consumer thermal insulation (ie kg/cubic metre).

The standard consumer thermal insulation you would expect to buy from say Bunnings - usually only quotes the R number - this is what many call "fluffy" insulation. and the R number describes the depth eg this product:

PRICEWISEINSULATION.COM.AU

We sell R2.5 wall insulation at discounted prices to builders and DIY installers. Order Greenstuf® Polyester Wall Insulation online today!

 

Unfortunately insulation companies don't typically quote density until you reach up in cost to "acoustic" grade insulation, and they never quote flow resistance (the technical term is Gas Flow Resistivity)

 

Standard cheap "fluffy" poly batts are around 14kg/m3 - much less dense than the 40kg/m3 Dave suggested.

 

As soon as you want insulation denser than fluffy (standard domestic thermal batts), in the domestic market most products will be labelled as "acoustic" insulation - and the "acoustic" tag carries a heavy cost premium.

 

The construction industry, and especially the air conditioning industry, uses lots of "medium density fiberglass" boards/panels in 48kg/m3 - which is about the sweet spot for acoustic density - and if you cover the fiberglass in close weave fabric the fibres won't leak out.

This would be the least expensive option for denser batts than "standard consumer fluffy batts".

 

Poly is more expensive than fiberglass, so the building industry is unlikely to swap from fiberglass to poly anytime soon - so sourcing poly batt products in higher densities than fluffy will likely require venturing into "acoustic" grade insulation, like this

WWW.SOUNDPROOFINGPRODUCTS.COM.AU

Acoustic Batts - Find out which are the best Acoustic Batts in Australia. Find out How to Choose the Best Acoustic Solutions for Your Project. Buy On Line!

 

I swapped out all my fiberglass treatment for poly treatment several years ago - and managed to buy "acoustic" grade insulation at a reasonable price - Tontine Acoustisorb3 - around 48kg/m3.

I just prefer not to deal with fiberglass, and the smell from the fiberglass binder stayed in the room from installation to removal (I did have 40 bags of fiberglass in the room).

 

I agree with Dave that with limited space you probably should go denser to around the 40 - 48kg/m3 with at least 200mm deep behind the bookcase (with ability for the sound to get through the bookcase to be absorbed behind) to get much effect down low.

 

A well respected member here on SNA ( @svenr ) did some analysis on "bang for buck" insulation for acoustics a while ago, and his result was (and I'm applying my own interpretation/paraphrasing here) that cheap fluffy can be just as effective (as denser insulation), but takes up more real estate - which you don't have :(

 

You can muck around yourself with absorption calculators like this

WWW.ACOUSTICMODELLING.COM

but you need  the Flow Resitivity for the product you're using...

Normal "fluffy" poly batts are around 5000

High density poly (around 48kg/m3) like Polymax XHD is around 12000 (a very popular "acoustic" grade poly insulation product)

The air gap assumes you place the insulation gapped from the wall (better for bass absorption) - if you fill the gap between bookcase and wall then you have zero air gap.

I don't check the Random incidence box  (at bass frequencies in normal small rooms it's not random incidence - you need large rooms/auditoriums for this) 

 

Here's 200mm of fluffy vs Polymax XHD

Blue is the denser XHD with better performance below 150Hz or so, but the fluffy (green) is better above 150Hz or so:

1620743141_200mmXHDvsfluffy.JPG.c585229635fa7c4bb1b44e5a859bc61a.JPG

 

Modelling tools have their limitations - don't take this as gospel...

...but it does show how ineffective absorption is at lower frequencies - esp below 100Hz.

 

cheers

Mike

 

 

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18 hours ago, almikel said:

Unfortunately insulation companies don't typically quote density until you reach up in cost to "acoustic" grade insulation

It just means you have to do the math (weight of pack vs total volume)  

 

18 hours ago, almikel said:

but you need  the Flow Resitivity for the product you're using...

You need it to do any calculations .... but the reason I mentioned the flow resistance, and the density..... Is that assuming they're going with some sort of "standard insulation product" that they don't go for anything with an extremely high flow resistance.

 

You can see with a 30cm absorber, that above 60Hz the higher flow (Eg. 5000) has a much better performance than something with a lower flow (eg. 12000).

 

18 hours ago, almikel said:

The air gap assumes you place the insulation gapped from the wall (better for bass absorption) - if you fill the gap between bookcase and wall then you have zero air gap.

(You probably already understand this.... but for people reading along)

 

People are easily confused by this when building the sort of absorber proposed in this thread  (filing the space behind a bookshelf).

 

If you have 100mm of absorber (for example) .... it will work better the further you move it away from the wall.

 

.... but.   Filling in the space between the absorber and the wall (with more absorber), doesn't hurt the performance.   ie. "getting rid of the air gap" doesn't hurt the performance....   but you will notice that filling that space in (with more absorber) doesn't improve the performance either.    That's because the absorption that is directly against the wall works so poorly.

 

You can see that in this link.   300mm absorber vs 100mm absorber with 200mm gap.

http://www.acousticmodelling.com/mlink.php?im=1&s13=2&d13=100&v13=10000&s14=1&d14=200&s24=2&d24=300&v24=10000

The have practically the same performance.

 

What does that mean for this build?

  • The space behind the bookshelf is important (more is better)   (eg.  300mm performs dramatically better than 100mm)
  • If you had 30cm space behind the bookshelf....  You could just put 100mm thick absorber in there (and have a 200mm air gap between absorber and wall) ..... BUT, if you just filled the whole 300mm depth with absorption, that won't hurt either  (ie. not having the air gap, won't be detrimental)
18 hours ago, almikel said:

Here's 200mm of fluffy vs Polymax XHD

Blue is the denser XHD with better performance below 150Hz or so, but the fluffy (green) is better above 150Hz or so:

Yes, but the performance difference (0.2 vs 0.3 for example) isn't super big...... especially considering the $.

 

What makes much MORE difference.... is using a thicker absorber (or as discussed above, the same with a bigger air gap).

 

In short.  Size and depth matter dramatically more.... than the type of absorber.     So if like most people and working to a limited budget.... just buy as much fluffy stuff as you can, and build a huge thing.   :) 

18 hours ago, almikel said:

...but it does show how ineffective absorption is at lower frequencies - esp below 100Hz.

Exactly.   Go big.

 

This is why I (well, I think it was this thread) asked the OP if it was "really the low bass" that's the issue.    It's a world of difference whether it's 20hz or 100hz

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