BBC documents

[PaulP]

The BBC did a lot of research into studio acoustics since the 60's and have made numerous reports available on the internet. They're not always easy to locate though, so I figured I'd provide that information here.

The entire list of documents, covering a lot more than just acoustics, can be found at : BBC Complete list.

If you search within the document for things like absorber or diffuser you get many hits.

The documents themselves can be be found at : BBC Reports.

Here is a list of the ones I've found most useful :

RD 1969/16 The measurement of sound diffusion index in small rooms

RD 1971/15 Low-frequency sound absorbers

RD 1978/27 The variation of absorption coefficient of absorber modules with ambient conditions

RD 1980/12 An investigation into the mechanism of sound-energy absorption in a low-frequency modular absorber

RD 1981/8 The effect of fabric coverings on the acoustic performance of modular absorbers

RD 1982/8 The design of a new wideband modular sound absorber

RD 1987/15 Theoretical and practical aspects of the Functional Absorber method of arranging sound absorbing panels

RD 1988/5 The development of prototype sound absorbers with variable characteristics

RD 1990/15 The design and application of modular acoustic diffusing elements

RD 1992/10 The design of a modular sound absorber for very low frequencies

RD 1992/11 A modular wideband sound absorber

RD 1995/1 Modular acoustic diffuser : The development and performance of a modular acoustic diffuser

Happy reading.

Paul P

[Seamus TM]

Holy sticky, Batman.

[DanDan]

That was a useful and nice thing you have done PaulP. Thank you.
DD

[avare]

A great summary Paul. Thanks for posting it.

To others, there is a great wealth information in the BBC RD reports. Paul linked some of them. If you are serious about acoustics, an excellent course in studio acoustics is to study all of the reports relating to acoustics. The ones on Transmision Loss are fantastic. Want to see the construction of a wall with TL greater than 100 dB at most frequencies? It is there. In addtion to the RD reports there is much usefull information in the BBC Engineering publications and the BBC Monographs. For the geek, it includes a paper on the development of the (now known as Coles 4038) BBC rifbbon mic.

Of course there is also THE BEST FREE DOCUMENT ON STUDIO DESIGN, Rose's seminal Guide to Acoustic Practice.

Loving Aunt Beeb,
Andre

[Seamus TM]

The Guide to Acoustic Practice is very cool.

Take a look at "Absorber D2" on page 116.

Looks familiar.
The inside (behind the absorbent and perforated panel) is quite like a Space Coupler.

Interesting.

Thanks to both Paul and Andre for the links.

[PaulP]

Thanks Andre for the link to The Guide to Acoustic Practice. It's great to
have a document that links all the different BBC reports together like that.
I especially liked seeing photos of the standard absorbers installed in
rooms. They look pretty good and I like the flexibility of being able to mix
and match them, as well as easily change them when needed. Especially
for us diy'ers who don't necessarily have a definite idea where we're going
this lets us play around with things until we find a combination we like.

I can see the utility of making some diffusers that fit the system and even
some modules that are simply flat and reflective.

One thing that strikes me in all the BBC documents, except the recent one
for the deep bass absorber, is their use of fairly thin absorption, usually
only 30mm (~1-3/16") with a 6" air gap.

I hadn't seen the A8 and A9 before (the same but for the front cover)
which contain two densities of mineral wool in front of a solid hardboard
panel which is itself in front of the air gap. The air space behind the panel
is then vented through holes in the sides.

Paul P

[avare]

Originally Posted by PaulP

One thing that strikes me in all the BBC documents, except the recent one for the deep bass absorber, is their use of fairly thin absorption, usually
only 30mm (~1-3/16") with a 6" air gap

The BBC RD documents are great.

Your comment about absorbers, quoted above, has me confused. You have been here at Gearslutz long enough to have read many times that the total depth of an absorber and the gas flow resistance of the absorbent material are what is important. Also, BBC has been using solid, as in homogeneous, absorbers for many years. The multiple layer absorbers are obsolete, for reasons detailed in the relevant RD reports.

Smoothly absorbent, and full of it too,
Andre

[PaulP]

Originally Posted by avare

Your comment about absorbers, quoted above, has me confused. You have been here at Gearslutz long enough to have read many times that the total depth of an absorber and the gas flow resistance of the absorbent material are what is important.

You're right. I was just struck by the difference between the 1+ inches
of insulation for the BBC A1-3 compared to the 2"-6" usually recommended
around here. I realize that total depth (insulation + air gap) is what counts.
It's been a while since I read the BBC documents and see now that they
went to thicker insulation even in their broadband absorber, the A11. And
they no longer have air gaps, the boxes are completely filled.

I'd actually intended to point out that readers of these documents should
be aware that the different BBC treatments have gone through changes
over the years and that there is a progression that is worth following.

As can be seen in the following, their latest absorbers use much thicker
insulation :

RD 1992/10 for the A10 low frequency panel absorber (8" loft insulation)
RD 1992/11 for the A11 wideband porous absorber (7" thick mineral wool)

These two are supposed to replace most of what came before.

Question : the BBC recommends that wood and hardboard components should
be fireproofed. I've never heard of fireproofing wood. How is that done ?

Paul P

[avare]

Originally Posted by PaulP

I'd actually intended to point out that readers of these documents should be aware that the different BBC treatments have gone through changes over the years and that there is a progression that is worth following.

+1! A goldmine on acoustic treatment evolution.

Question : the BBC recommends that wood and hardboard components should be fireproofed. I've never heard of fireproofing wood. How is that done ?

Sorry, I have no idea. I had missed that completely

Andre

[mattyRPG]

1995/1...We woked closely with the BBC to bring the ideas to fruition.

fireproof wood with either class 0 base and top laquer or with a ******ing liquid that penetrates the wood.

[cborg]

a ******ing liquid that penetrates the wood.

Oh, you mean booze!

[JVergence]

Does anyone know of a manufacturer that produces a retail version of the A10 absorber as described in the 1992-10 doc???

Thanks.

JV

[DanDan]

JV, I am pretty sure shipping costs would make retail of such devices impossible. These BBC designs were usually tweaked to be easily constructed on site, using commonly available materials. That is one of their big strengths.
Due to this and of course many other ingenious features, the BBC achieved remarkable consistency amongst their many listening rooms.
DD

[Cb Media]

I am also interested in the A10 absorber, just finished reading that and many other BBC documents... i feel i may need to add some of these even after superchunking all corners from top to bottom absorption FTW!

[Sebg]

Personally I am also a fan of the door reports:

http://www.bbc.co.uk/rd/pubs/reports/1994-14.pdf

http://www.bbc.co.uk/rd/pubs/reports/1994-15.pdf