Glass brick acoustics

[forestcreature]

Hello all, long-time lurker here. This question is about the acoustic properties of glass bricks.

I'm building a project studio like a Newell non-environment. This would feature monitor speakers built into solid walls straddling the corners of the front wall, angled towards the listening position.

These walls would partly cover each end of an existing window, which takes up most of the width of the front wall. I would like to preserve the daylight that the window brings. So I considered building the wall from glass bricks. These are the square cca 200x200x80mm blown glass things with an airspace inside and a lip around the square perimiter for joining with mortar. Such a wall would be plenty heavy (tick), but I'm not sure how to work out if the bricks or air inside them could be excited into any unwanted resonances by anything that happens in the studio.

Any ideas, or does anybody have any practical experience with these bricks?

 

[krivium]

Hi,
I would figure it out by prototyping a small portion of a wall and integrate an 'inwall' loudspeaker.
Then apply a contact microhone to the glass blocks and see how they reacts when exited by freq sweeps played back on the 'inwall'.

I'm sure that even if it happen ( not sure it will and'll probably vary with mortar type used) it coud be tamed using 'moon pad' if happening not too low in freq ( THE tool to chase unwanted resonnance on drums head)..

Anyway if you follow Hidley's or Newell's built principle the loudspeakers should ideally be decoupled from the front wall. And from the floor too. It's done on the mounting of the loudspeaker enclosure for the one i've seen ( there is other ways to do it i've seen but not cheap and or easy to implement). This could already limits concerns relative to resonance.

From an aesthetic point of view i'm sure it could look quite good and if you plan to spend time into your space it is q premium feature.

It's an excellent idea in my view.

Now the questions: how big is your room? I mean 'traditional' implementation of Hidley's design need huge space. I know as i've been refused by them when we asked for a design and the space was already good size but height was an issue ( too low ceiling at ~3meter).

There is way to implement this kind of approach in smaller room though.
I could point you to people who does that and gave enough explanation of how they do it ( as well as measurements of outcome).

If you don't mind an advice take a look at Thomas Jouanjouan's work too if you've not already, it's an evolution ( in the good way imho) of the non environnement principle.

Do you already have a design/model for loudspeakers?

 

[simon7000]

Measuring a small 16" x 60" glass block wall here, there is a slight resonance at 1,700 Hz and a wee bit (-40+) of second harmonic. Impulse was just under 120dBC and the resonance peaked around 80 dB ish. The equivalent reverb time for the sound to decay 60 dB ranges from .1 to .16 seconds depending on which block we tested.

I would not expect this to change the perception of the sound reproduced by a loudspeaker near the wall.

 

[forestcreature]

Thank you krivium and simon7000!

I didn't expect concrete measurements, so I'm really chuffed.

Following on from what krivium said, I'll look at whether there are any suitable mortars with damping properties. Something rubbery.

To answer your questions:
- It is a smallish rectangular room 3.4 x 4.8m and 2.4m high. But I removed the hard floor in the room above, filled joists with rockwool, with an additional 10cm or so slung below them. The flooring material above will probably be something like an open GRP grid, overlaid with woolen carpet---so the main part of the room is something like a 4.8m high room with 40cm thick absorbtion mid-height. The ceiling and short walls of the room above are plasterboard stud wall drilled to be cca 30% open, with the 10cm space filled with rockwool (30cm in the ceiling). Behind the short walls are narrow storage rooms under the angle of the roof, which contribute to bass trapping because of the drilled and stuffed stud walls.

- The non(ish) approach followed from having to use the wall with the window for listening (opposite wall contains two doors). My room dimensions compared favourably to the (useable) mobile trailer studio described and built by Newell, so I thought why not (although hampered by reduced losses to outside).

Phew, sorry I'm trying to keep it brief.

- I've not built a decoupled inner structure. The house is brick/concrete-block cavity wall construction. At the moment, most noise comes from the undamped roof and eaves soffits. I know already that playing drums in the unimproved space was well tolerated by neighbours. Based on the wind direction, aircraft noise IS a problem approx 30% of the time. It's a hobby studio.

- Speakers are on independent platforms attached to the front wall. I would be building the speaker walls on top of the house concrete slab, so could take steps to decouple them from the house structure. But at some point I suspect it might be overkill. I considered KH310s or something similar, but settled on JPW AP2 bookshelf speakers that I had lying around. With amplifiers in the store room directly overhead, I am already having fun with biamping and saving up for other stuff. They are 2-way sealed vintage hi-fi speakers, with a fairly low crossover frequency. So a mono auratone-like speaker could be hung from the ceiling near the front wall as a comparison speaker to catch anything missed in the midrange. And an active sub somewhere as and when.

- Since you seemed pleased by the aesthetic possibilities, I thought that the window could be used to backlight the display removed from a discarded TV and stuck to the inner glass. I think what I'm looking for is OLED. If it works I'll post a photo.

I wish I could post meaningful measurements as I go, but the studio becomes the workshop and junk store for the rest of the house renovation, so it's hard.

krivium I would gratefully welcome any advice you have! I will check out what you've referred me to already.

I haven't figured out what I'm doing with the long walls and back wall. Since it seemed to me to be so useful to make use (acoustically) of the space above the studio room, I can't make use of some of the limp-mass type tricks I've read about, treating the space like a mostly airtight bag. So I started to think about just filling 30cm along the long walls with rockwool, and as deep as I could bear on the back wall (considering it is a project studio, so should be space to jam, record etc.). And for listening time gobos to screen the back wall door openings).

*Thomas JouanJEAN --- found him!

 

[krivium]

Hi,
Ok thank you explaining the situation and i see no need to keep it brief, it is always usefull to have informations.

So first i don't think a non environement approach is the way to go: you said you'll jam and track within the space.
Non environement control room are very dead space with only floor and front wall being reflective. From the one i've heard it is not a place in which you could track. And to be honest the room was a bit oppressive to me after some hours in it.
That is the main difference T.Jouanjean ( Northward acoustics) bring to the concept by bringing back some 'ambience' through the use of the diffusors on backwall and above listening position.

But it's not a recording space still...

For multipurpose space like yours i would try something different than a box full of rockwooll ( basically this is what a non environnement is, a huge room with many many 'hangers' angled to increase effectiveness, on all inners room boundary).

But i won't try to convince you otherwise if you already made your mind. You'll learn by yourself.

Could you point to the Newell's realisation you take as inspiration please? ( book and edition please, i suspect this is in Focal's press 'recording studio design'?)

Are you member of Gearslutz/Gearspace? If not you should start lurking there and search for posts from member Audiothings. He is member here too but he presented his approach to implementation of non environement in smaller room there. He documented his quest and some measurements were presented with greetings from Newell's son and Thomas Jouanjean, validating results he got.

Worth a read/search about it. And don't be surprised he use something different than rockwool as absorbers...

About mortar, well yes it play a role for sure. Not sure i would look at something rubberish ( i'm not even sure it would be approved technically by rules/regulation in your country), but a research about them and their properties is worth it imho.
Depending how you build it the front wall could became a membrane resonator, a large tuned bass trap...
It' is all in the detail of built.

Bummer you didn't go the box into a box way. I know it is costly, time consuming and can be a nightmare to implement ( i've built/been involved in a number of profesional studios some of them built like that and so i talk from experience) but to be blunt: the noise insulation is what i miss the most from those place.

I mean acoustic treatment and setup inside the room is important but to have zero noise constraint is golden. Lower noise floor, increasing the level of details either during takes or listening... but it is not the way you did so it's too late.

There is nothing overkill when it comes to structure born vibration isolation. I'm serious it is true for millions dollar studios but for yours too.
Above all your space is not decoupled and close to your living space.


Ok, i know it is totally off context but i think it will give some insight about some things ( overkill no,no,...): here is Noisia's project studios. Take a closer look at how the room are decoupled from the outside structure and how the loudspeakers are then decoupled from the room shell. Spot the diffusers too. It is a nice example of what T.Jouanjean design. Notice he use ATC monitors and there is a reason about it ( their directivity behavior is known and relatively constant over a wide range, it help to design the room's shape to reduce early reflections).

 

[forestcreature]

Thank you, I appreciate that you're sharing your knowledge despite my not entirely forum-friendly efforts.

I had some primitive thoughts about deadness, e.g. a hard reflective side to the repositionable gobos. I was also comforted by this non notion that the hard front wall solves what's missing psychoacoustically (which, evidently, has been improved upon since!). But more importantly there is the light and pleasant room upstairs with scope for mixed absorption and diffusion and a partial floor cutaway to a sleeping platform above and the angle of the roof.

To give you an idea where I am with reading: I read about the acoustic basics, then Recording Studio Design (?2nd ed). I am not married to the non concept. What happened is that a hard front wall answered a concrete question in the space that I had, then I just accepted the rest of the premises that came with it. I've seen project studios on GS with mixed treatments and philosophies, tuned elements &c.---but I didn't have an overall understanding of how to design with them, except for treating for calculated and measured responses. Reading a Thomas JJ interview last night suggests that things have moved on in psychoacoustics and design especially.

(Incidentally GS is becoming very heavy to load; and, recently I couldn't even sign in with sensible browser privacy settings.)

Audiothings on GS rings a bell. I can still browse there with the appropriate breathing exercises, so I promise I'll do my homework!

When you say it's too late for a decoupled inner room, do you mean in the sense that the fabric of the house is already built? Otherwise sorry if it sounded like I was set against building it within the existing structure. But I see the limiting factor being the 2.4m height before hitting floor joists. I (living near to a major airport) agree that an isolated starting point would be ideal. This does cause me an amount of concern. Contact mic measurements might be the thing. What do you think though? Including the space between the joists in ceiling treatment also seemed like a win with the flavour of a logical necessity. I dunno. With my arms above my head I easily touch the joists as is.

I agree with the rationale for using v predictable speakers. I'm only interested in studio design for its interestingness, and to complete these personal spaces, but not for its own sake. So it was the same with tweaking the two-ways and learning the basics of sound reproduction. It has been fun, and seemed my best chance for getting a good result that I could exert conscious control over, with my current budget.

p.s. The best thing, studio-wise, would be to sell this house and include a principled build from scratch as part of a move. I do this thought experiment too...

 

[krivium]

I appreciate your attitude too and in my view you are very forum friendly.

It's just that in this kind of project you really need to have some clearly defined targets as there is some contradictory requirement in a multipurpose space.
Dedicated room for a given task are in a way easier in that there is less trade off to be made.

So you have to define what is going to be the use for the room and the percentage of time for each use.

Eg: drum practice: 10%, mixing/mastering/composing 50%, tracking/recording 20%, rehearsal 20%.

From there some choice could be made: in the exemple it is 50/50 between the two main use: monitoring and acoustic instrument playing/recording.
Compromise to be made will be on the highish side ( as it'll have to satisfy both usage).

If you have Recording Studio Design read the introduction of both recording room and control room as Newell list the requirements of each kind of rooms.

As a big shortcut:
_ a recording space need some ambiance for acoustic instruments to sound good. And it needs to be 'balanced' regarding acoustic treatments ( 33% absorbent, 33%reflective, 33% diffusive). A must could be a variable acoustic space ( Olympic studio example in R.S.D.).
_a control room need an Reflection Free Zone (for Early Reflection control) and a low ( and balanced) Reverberation Time. Ideally the room own 'imprint' should not colour the reproduced signal.

From there i can tell Non environement won't satisfy first requirement. And you have a need for a reflective front wall. As well as inwall monitoring...
I would impose another rule: everything have to be modular: furniture, acoustic treatments,... this way you could 'taylor' the space to a specific need.
Gobos are a way to get this but the acoustic treatments could be 'standardized' on their size and way to hang them...

I see an approach which could satisfy this requirement in a better way ( given this is a dedicated space i consider you could do whatever you want for it):

http://downloads.bbc.co.uk/rd/pubs/reports/1995-04.pdf

The other acoustic treatments needed ( than the room shape which is 90% of acoustic treatment in CID approach) could be the one Bob Walker refer too ( availlable through the bbc archive using the search function and year of publication) which were the 'standard' treatments used in BBC room.

You will have a reflective wall to locate drums for recording (if you do rock it can be nice) and a 'real' room sound to rec.

Another thing, it is easier ( and cheaper) to render a space dead rather than trying to reintroduce diffusion to make a dead space 'live again'.

This is not a miracle however and there will be a set of constraints anyway whatever you do....

I will answer other point later this day.

 

[krivium]

When you say it's too late for a decoupled inner room, do you mean in the sense that the fabric of the house is already built? Otherwise sorry if it sounded like I was set against building it within the existing structure. But I see the limiting factor being the 2.4m height before hitting floor joists. I (living near to a major airport) agree that an isolated starting point would be ideal. This does cause me an amount of concern. Contact mic measurements might be the thing. What do you think though? Including the space between the joists in ceiling treatment also seemed like a win with the flavour of a logical necessity. I dunno. With my arms above my head I easily touch the joists as is.

If i understood correctly you already have some work done, and in that case you won't destroy everything to start away from scratch?!
Maybe could you post a drawing of floor and elevation plan as well as some pictures?
I must confess i eyeballed the descriptions you gave ( and i'm lazy to translate some of the built words you used i'm not sure what they describe exactly... i'll do my homeworks too! ).
It would be easier with a plan.

Let's be clear about sound insulation: it is a must, but the cost to be engaged are high ( a dual leaf build means everything is at minimum doubled so cost increase signifanctly and not nescessarly proportionally if you want to implement 'top notch' results), it can be tricky to built into an existing space ( renovation). And by tricky read a REAL P.I.T.A.

That said once done... you want to make a cover of Slayers 'Reign in blood' at 3am with baby sleeping nearby, it is possible.

I agree with the rationale for using v predictable speakers. I'm only interested in studio design for its interestingness, and to complete these personal spaces, but not for its own sake. So it was the same with tweaking the two-ways and learning the basics of sound reproduction. It has been fun, and seemed my best chance for getting a good result that I could exert conscious control over, with my current budget.

p.s. The best thing, studio-wise, would be to sell this house and include a principled build from scratch as part of a move. I do this thought experiment too...

My comment about loudspeaker was a bit sneaky i confess: ATC design philosophy is to have low Directivity Index loudspeakers but over most of their reproduced range. In practice when inwall mounted they have a nearly constant hemispheric radiation pattern and so 'spread' wide.

It means ER management requirements is transfered to the room acoustics treatments ( i.o.w. need for absorbers). And why they are used by M.Jouanjean in his design ( and they have great quality otherwise too, even if not my own preference).

Loudspeakers does not help in this case. But if you choose another kind of loudspeakers with same constant directivity behavior (constant) but restricted to a lower coverage angle ( higher DI thanks to... waveguide) into a CID design you could have a very effective rfz...

 

[forestcreature]

Okay cool, there are a lot of things discussed in parallel here. I will need to do some reading before responding to many points

It is handy that a lot of our assumptions are the same. For example the requirement for modularity. Everything on wheels, &c.

Firstly, I am glad that you gave me a kick up the butt on sound isolation (?you call it insulation). I restarted my thinking from the beginning.

I also asked my partner, who will say she doesn't know anything about audio and follow this with some accurate and pragmatic insight. The idea of a sort-of live room in the room above a sort-of control room is out. We will have one multi-use downstairs studio room, with an isolating shell. The acoustically transparent floor between the top and bottom room is out. If it can be achieved, the idea of balancing aircraft take-off directions with time of day, current introversion levels at home &c. is out. Slayer at 3am is pencilled in.

From the beginning: the 3.4(w) x 4.8(l) x 2.4(h)m room is in an existing masonry construction house built in the 70s (not by me) on a residential street. I am interested in composing, recording, and mixing DIY-pop, rock music including drums. Soon I will be less young, my guitar playing less bad, and I will want to record more lovely things and write the score for a well-loved independent film. Rehearsals are better to do in studios in town. I prefer less aggressive processing.

Commercial music or studio operations are out (my friend does this and I helped wire their studio, and it's fun and interesting but not for me). Non-fatal traces of technical limits and room character are welcome in the music. And there is no need for interoperability with other work flows, or for any client to be impressed by anything.

I will need to sketch a replacement for the CAD plans lost to a coffee incident. Front wall makes sense. Back wall has two doorways, one right in the corner. Will need some thought. I haven't made that much mischief yet, just the floor that I pulled up. Honestly, replacing with a fairly conventional floor upstairs is a relief compared to the original plan of (expensive) GRP grid etc. The other issue I think is the limited space for ceiling treatment. I had a thought about it but will hold it back until I've caught up on the materials you recommended. I think that the double-wall masonry construction is a bonus in providing a starting degree of isolation. Really most noise is air-borne, from aircraft, or mid-to high frequency fox hullaballoo. I sleep on a futon, so my ear tells me there is not a lot of ground-borne (traffic type) noise, although some impact noise from car and house doors &c.

On speakers, I thought that the two-ways I'm using (i.e. dome tweeters without waveguides, flat front face, flush mounting) would usefully approach that hemispheric source behaviour that you described, except in the vertical distance between woofer and tweeter.

Okay I'll try to have something concrete to show in a follow-up.

P.s. by non-forum friendly efforts I meant that it is most useful for respondents and readers when somebody starts with the resources to plan, build, measure, and report, and when they're single-minded. My time and resources are split, so I might get excited about a notion on a forum and actually carry it out a few years later, for example.

 

[krivium]

Hi,
Well i don't know if i kicked you in the... but, you have to carefully plan your needs and do a list of priority.

As i've been active at the era where big commercial studio was still the norm and at dawn of the kinda space you want to built, i've got point of view about what is needed for ergonomic. Modularity, enough lighting, a dedicated electrical circuit...

I would say first make a place you want to be in, that keep you inspired. Daylight play a role definitely. As fresh air ( yes, you'll have to think about this too as if you make a 'shell' for it to be effective in sound isolation ( not insulation... apologize my aproximate english... you know, i'm French! ) it'll need to be sealed. So if you don't want to suffocate...

If the main culprit are airborne noise then it should be easier to treat and you might not need double leaf.
Study Newell's book, i think he list the degree of isolation of different techniques single leaf, dual,... with the attenuation you can expect by freq range.
From there use an spl meter to record bakground noise and offending sounds to define what you need within your space.

If there isn't this much structural born sources it's fine as they are the harder to manage... if the slab is common to the space and your living one then you'll need to decouple sound source within your room: loudspeakers, drums, amplifiers... Auralex had some stand which were ok for amp and loudspeakers ( but you can do better for loudspeakers imho) and a 'stand' for drums, like a big plate with foam feet. It works. Not a 0,2hz decoupled system but it gaves acceptable results when i used it).

Yeah your ceiling is low. And it could be a real issue for sound isolation.
I suppose there is technical answer but like all specific need it might not be cheap. Or maybe it'll be as simple as letting a plenum( space) of 5cm between existing ceiling and inner shell's one.

About the loudspeakers one last thing: more than for anything else i'm convinced loudspeaker and room works together. It's a couple.
If you take this into account from the start then there is chance you'll have a positive outcome. Otherwise...

Yes your two way could probably have an hemispherical directivity behavior like ATC but... does your room is big enough to allow to create an RFZ with a loudspeaker spreading that 'wide'? Have you the width to angle the side walls to redirect ER outside sweetspot? Does you have enough width in the room to accept the 40cm deep absorbers ( minimum) located on each walls?

That is why i said loudspeakers doesn't help in T.Jouanjean's design. But it doesn't matter as he can make a wide dead room without constraint.

I think a loudspeaker taylored to your space could be an immense help. No need to be fancy, gold plated thingy... A two way based on some compression driver/waveguide +1 or 2 woofer would do the job ( you'll have better management of directivity= less Early Reflections=less need for treatments). And you don't fear a multiamp/dsp approach so it is not impossible to achieve in my view...

But it's a pov...

 

[forestcreature]

Cool!

Well a little disequilibrium can be great for settling into a better plan of action. Although I read Newell carefully the first time around, I was surprised at how the basic priorities could still be cleared up. E.g. letting go of the idea of rehearsing a whole band in there, which feels like a relief, actually.

Lighting circuit, dedicated studio circuit, and air supply are available.

Yes, I had that section of Newell in mind regarding the different levels of attenuation on offer from isolating structures. I think there are some factors reducing the isolation burden, but I'll check it all out with the SPL meter when I get it.

In terms of CID, this was a revelation. When I saw it in studio designs and photos, I thought that I was seeing diffusive strategies to mitigate room modes. I didn't realise the purpose of the reflection. The BBC paper is a very clear explanation.

So there's an empirical route to beginning a design, which is exciting. I also have your recommendations for documented concrete small studio builds to work though.

I think I understand now, regarding the speakers! Yes designing something to fit the space shouldn't be a problem.

 

[krivium]

Yes Robert Walker paper is great, in the legacy of BBC's R&D. So sad they stopped all R&D activity.

C.I.D. is all about creating an RFZ from 1khz and up using room shape (reflective surface) to redirect ER outside the listening spot.

It's not new approach to try to create an RFZ but it differ in that it doesn't require absorbing material for this purpose and require a reflective front wall.

In fact it require the first 1/3 of room to be reflective with angled panels of 1m ( the minimum size to be effective from 1khz and up (~3x 1wave length at freq of interest- there is same requirement for diffusor: they need to be located at a distance ~3x the wl of lowest freq of interest)).

And it is a principle which support inwall. In fact it is even easier to built an inwall room as shape is less complex than for standmount ( there is less reflections as there is no backwave).

The BBC's Bush transcription multitrack room in Bush House is a nice example ( plan page 19). Compare the results they got in this room to the initial target ( ER @ 15ms and -15db). Impressive results they got. That doesn't mean you'll have same results but it's encouraging imo.

In wall relief most issues related to cabinet diffraction , it gives a free +6db boost of low end from approximately 200hz ( in case of a sealed/closed box it mean you can extend the low end freqency extension by half an octave ( through a Linkwitz Transform/DSP): no need of more amplifier power, no increasing distortion or cone mechanical displacement...). It's not bulky and free space to locate drums in front of reflective wall for recording... and looks great.

Really keep inwall high in your priority list imho.

Loudspeakers... ok you got my point. I suggest you take a look at what the 'econowave' loudspeaker's school of thoughts is all about.
A little googling should bring Zach's ( RIP) threads on forums over the web.

Then to study this paper:
http://www.gedlee.com/Papers/directivity.pdf
And this paper:
http://www.gedlee.com/Papers/Philosophy.pdf
Then this one too:
https://www.pispeakers.com/Pi_Speakers_Info.pdf

You should identify things in common ( and differences!) between those approach as well as C.I.D. base principle...

Newell book i've read maybe 10 times and there is still things i discover or didn't get in previous efforts... it is dense and sometime a bit confuse. But it's all in there...

Thank a lot @simon7000 for the measurements of glass bricks. 1700hz is high enough for this to be effective in damping the issue if needed:
https://rtom.com/moongel-damper-pad/

So glass bricks seems definitely a great idea to me.

 

[forestcreature]

This is like christmas! I've been excited all day imagining how to approach the design.

Thank you again. And to return to the opening topic, a few years ago my partner said it would be really cool to build something out of glass bricks...

 

[Arthur Jackson]

Wow! Calculating for the echo inside a glass brick. You guys are obsessed!