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Sound deadening a Chevy, and some small calculations

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Eric The Viking

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I have a telly in the bathroom*. I like to watch/listen to junk TV in the morning (Pick/Quest), as the ad breaks help me time things like washing my eyes, and make sure I don't linger in the bath too long.

But Pick has just started showing series 8 of Wheeler Dealers. This morning one episode was a really nice 1950s Chevy pickup, lovely straight 6 engine, beautiful restoration, but a really, really noisy cab. Edd China applied a sound-deadening kit. The measured results went from 104 dB(A), down to 93 dB(A) after the kit was fitted.

This is that very Chevy - nice innit?

I'm an ex-professional sound engineer ("Eh, what?"), so I understand decibels. But you're an educated lot too, so I'm sure you already know that a measurement in decibels is defined as 1/10 of the log of the ratio change (of anything - the "A" part defines what the 'anything' actually is). It's 1/10th of the log value (base 10, not log e), a deci-Bel, because a whole Bel (yup, really exists) is too big to be practically useful. That's also why the unit is abbreviated to a small "d" with a big "B".

Never mind the detail though, for most of us wot use decibels, the important thing to remember is that a 3dB change is almost exactly a halving (or doubling) of whatever you're measuring**.

See where we are going here? The Chevy's cab got quieter by almost 16 times. Or, to put it the other way round, the sound in the treated cab was 1/16th what it was originally. That's impressive by any measure! And to prove it, they recorded their usual end of restoration test drive in the cab, and you could tell that voices did not have to be raised (at 104dB(A) plus road noise they would have almost needed sign language).

So sound deadening can work really well if it's done properly.

Obviously it can work for woodworking too. One of the important things Edd China did, which is often neglected when the subject comes up, was to block as many holes in the engine bulkhead and the floor that he could. In audio studio construction, this is also closely attended-to. If you fail to do that, you risk the studio being quite limited in its usefulness, because sound leaks through from the control room monitor speakers, and people digging the road up outside. It's the air movement that matters - stop that and you stop the sound.

You can also head the problem off at source, so to speak.

My machines are not expensive. So the sheet metalwork is probably thinner than it could be (on better machines), and its tendency to behave like a drum skin is increased. What can I do? Answer: dampen the vibration and increase the mass of the resonant panel.

There is a cheap and effective way to do this, using a roofing repair material, known as "Flashband". It's basically just heavy gauge aluminium foil with a bitumen coating on one side, that sticks to pretty much anything (and bloomin' everything when you are trying to use it!). You cut it to shape with a Stanley knife or tin snips, peel off a greaseproof-paper type of backing (now thin plastic - I'm ancient!), and stick it down. For really horrifically good adhesion, apply a hot-air gun and a wallpaper seam roller. You can also hide it by, for example, using it on the inside of saw cabinets, metal cupboards, etc., and it really works: It changes the clang of a tinny panel to a soggy thud - way better if you want as much quiet as possible. I've even put some on the back of my parabolic microphone reflector (for long distance sound recording), which stops it ringing like a bell which is, er, unhelpful***.

For bigger "panels," for example up-and-over garage doors, you can use thermal insulation, such as Celotex. It's not very heavy, and doesn't need to be very thick either. Anything that keeps it in place - glue, wire, whatever - will serve.

There is no point doing this for concrete or brick walls as they don't really vibrate from sound in air hitting them, so they don't transmit sound very well that way. But they do bounce sound back around the workshop, so for a nicer working environment, you could still go ahead and put absorbency on the walls.

In this case Celotex won't help as much as open-wool Rockwool slabs - it's the open "weave" that makes it absorb sound well. Rockwool is a standard tool for professionals doing acoustic treatment, and it has the big advantage that it's very fireproof. Bear in mind though that it will collect airborne dust very enthusiastically (think baby elephants and dust baths), so if you want cleanliness too consider something that lets you hoover it yet still keep it out of the dust bag - you might enclose it in chicken wire for example or an open-weave fabric (that's the normal studio solution).

Generally, for a comfortably quiet life inside the workshop, you want as few sound-reflecting surfaces as possible, so consider floor, ceiling and walls first-off, but don't forget acres of storage cupboards etc. (if you're lucky enough to have them).

Deadening the surfaces inside will also make a difference to what's heard outside, but not as much as most people hope it will. So we're back to that Chevy pickup: look for and block-up unnecessary air passages between the workshop and the outside world. That includes at the roof-line, draughty gaps round and under doors and windows, and ventilators or vent ports of any sort that you don't need. You don't want to kill yourself through asphyxiation, so cabin hooks for doors (and window stays), to hold them open in hot weather, are obviously sensible, but if you have to be really noisy you want to be able to close up for a short time, while you get the job done.

But that 11 dB of improvement proves it's easily possible, which ought to be an encouragement.

E.

*in the attic next door, behind glass let into the wall - perfectly safe.
** "Er, not always!" I hear the electronics guys shout in unison. That's true but not relevant. Move along folks, nothing to see here...
*** Flippin' annoying actually.
 

sunnybob

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There is no point doing this for concrete or brick walls as they don't really vibrate from sound in air hitting them, so they don't transmit sound very well that way. But they do bounce sound back around the workshop, so for a nicer working environment, you could still go ahead and put absorbency on the walls.


An anecdote on that subject;
In the late 80's I was heavily involved with the building of an indoor shooting range (decibels? we got tons of 'em!)
The inner side walls were made of breeze block . 25 metres long x 3 metres high.

When the range was commissioned and in use, a committee meeting was held to discuss the building work. It was decided that one man would paint the place to make it look better. He painted those walls with a thick white emulsion.
Looked much brighter, but when the range was next used,,,,,,,,

Oh boy, Ed China in reverse!!! The extra noise created by filling up all the holes in those walls was unbelievable! Of course, we were stuck with it. Luckily every one who went in had to wear ear protection anyway.
 

Eric The Viking

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sunnybob":ebihbo7v said:
The extra noise created by filling up all the holes in those walls was unbelievable! Of course, we were stuck with it. Luckily every one who went in had to wear ear protection anyway.
[Takes ready-lit briar pipe from tweed pocket. Inserts into notch in teeth.]

"Ach Zo. Zet vill be a vunderful example of ze creation of ze phase coherent reflection."

[clears throat in preparedness. Audience remembers that Really Important Thing it had to do... and walks off hurredly, leaving one small, scruffy boy.]

"Rubbish mister, it was the blooming guns!"
 

thetyreman

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MLV (mass loaded vinyl) is good stuff, Tecsound S100 is what I'd use, if you sandwich it between layers of MDF you'll get amazing isolation performance down to very low frequencies, it's very expensive though but for good reason, rockwool does not block or stop low frequencies below about 150Hz, and personally I do not think it's safe regardless of what the industry tells people, I would rather use organic sheeps wool even though it's more expensive, in fact I am currently planning on building some diaphramatic bass traps that will use MLV and sheepswool for my own studio.

That's a nice looking Chevy by the way :D
 

Droogs

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Bet you could get a 100dB reduction with an electric motor conversion :p
 

Eric The Viking

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thetyreman":3a5g8udj said:
MLV (mass loaded vinyl) is good stuff, Tecsound S100 is what I'd use, if you sandwich it between layers of MDF you'll get amazing isolation performance down to very low frequencies, it's very expensive though but for good reason, rockwool does not block or stop low frequencies below about 150Hz, and personally I do not think it's safe regardless of what the industry tells people, I would rather use organic sheeps wool even though it's more expensive, in fact I am currently planning on building some diaphramatic bass traps that will use MLV and sheepswool for my own studio.

That's a nice looking Chevy by the way :D
I think it's one of the best vehicles they've done (dons flameproof suit), expensive but sympathetic resto/upgrade (added a carb to the straight 6 block that originally only had one). To be fair though they bought it part-restored, and the previous owner had done good things.

Nothing really controls bass below 150Hz, apart from Helmholz resonators (their original purpose, IIRC), but you need a huge volume of unused space to put them in and some very careful design if they are to be any good. For me, it's far easier to just roll off the mic response as necessary and beware of room eigentones. About the only time I would worry about good acoustic response down that far for a _distant_ mic would've been either orchestral recordings or organ music, and in both cases you have some leeway in mic positioning for the stereo pairs. For most other jobs, such as jazz or string quartets, etc, you're usually either too close for it to be a problem or in a good acoustic to start with (usual for classical stuff). It's much more of a nuisance dealing with the sound of small rooms than big ones, usually.

Buildings can be jolly deceptive though. The weirdest acoustic I was involved with for a short while was All Saints Clifton*. It's an odd post war rebuild after bomb damage, I think. Leaving aside the spring that rises through the flagstones around the font at the back when it rains (great for buried cabling!), all that beautiful "stained glass" is also unusual, because a lot of it is actually fibreglass. It doesn't behave as you would expect glass to do, and the acoustic is rather poor for speech, because the windows are acoustically transparent/absorbent in wanted bands. And the concrete coffered ceiling (think 1960s multi-storey car parks) also interferes with natural reflections. It is visually stunning, but something of a PA system graveyard.

E.

* https://bristolopendoors.org.uk/events/ ... s-clifton/ (there are a few pics in a slideshow at the top of the page).
 

RogerS

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Fascinating thread, E, and of great interest at the moment as LOML has been dropping hints that I might like to consider sound insulating what will become my study/listening room.

Going back to Beeb days, my mate worked for SPID and installed a new studio at Maida Vale that was separated entirely from its surroundings . Sat on huge blocks of Sorbo rubber or similar..so that the noise of tube trains running under couldn't be heard. He took me there one evening before it had been handed over to Operations and it coincided with a trial Surround Sound broadcast ...four channels IIRC being broadcast simultaneously on Radio 3 and 4 (two on each). We didn't have to mess around with tuners etc ..simply plugged into the jackfield. We sat in the optimum position...best possible quality. That dagger whizzing past my ear was a shocker :shock:
 

Eric The Viking

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It's more that you want to use the acoustic sympathetically in big rooms (concert halls, cathedrals, etc.) - it's part of the performance. In small rooms, usually, you want only the source of the sound, for example a voice reading or speaking or possibly singing, and to abstract it from the environment. Unless it's a drama scene, small acoustics tend to distract and intrude.

The above is for radio,podcasting, etc. though. For telly (dubbing), apart from commentaries, you want to match whatever's on the sync tracks as well as possible. When we got our first digital reverb, a Lexicon 224, in Bristol's dubbing theatre it was wonderful, as it let you dial-in the room dimensions, as a pretty close starting point. What wasn't so wonderful in high summer was standing next to the fan intake on the rack part of it with a can of freezer spray, to keep it from breaking down. That was American. The Brits had AMS (later AMS/Calrec), which sounded nicer for music (longer reverbs), but which was a lot harder to control when you wanted to match acoustics. Oh the joys of early digital equipment!

<geek-only>
Regarding quad, As a youngster I was taken to the BBC 50th anniversary technical exhibition by my dad, I think in the Langham in 1972 or 73. They had a quad demo running there (coming off a J37 4-track, I think), using four LS 3/5a to replay. It was quite impressive. Later, once I'd grown up and actually joined the Beeb, we got to play with the AMS/Calrec Soundfield mics, which are still made, which have the capsules in a tetrahedron. You output through a matrix to get stereo, but the system lets you point a virtual stereo pair in any direction after the recording has been made, in all three axes. It's a weird thing to play with - you can, for example, take a symphony orchestra recording and "turn round" to the audience shuffling, squeaking their seats, rustling sweet packets (really? at a classical concert?) and coughing of course. I was told (Evesham) that for the maths to work out correctly and get a virtual point in space, the capsules must have a polar response of 2 - cos theta (rather than 1 - cos theta for a conventional cardioid mic). I have no idea how they got that, because it's not a standard hypercardioid (with a back lobe), more a cardioid superimposed on a small omni.
</geek-only>

Regarding building isolation, the middle part of London Broadcasting House was intended to be isolated. [edit: this following is urban myth - see below]It too was built on springs - the part including the Concert Hall (now the Radio Theatre), and the big basement studios. Apparently "the tower" the inner part of BH, was simply constructed very heavily, with the intention to decouple it from the outer parts of the building as much as possible. But the inner construction was too heavy and it sagged on the springs and never really worked properly.[/edit] See Roger Beckwith's site for the details.

I have worked on/in a few studios where isolation has been done, and it can work very well, but it is hugely expensive. And the little things tend to get you - you still need cables to bridge the divide, and poor designs of studio window can also upset things - the good BBC studios had a third pane of glass in the middle set "squiffy" (angled both horizontally and vertically), and I think all three pieces were different thicknesses too. I find laminated glass is particularly useful, as it damps itself. It's also very often the case that there is insufficient air gap, so if there are only two panes they act like the two skins of a snare drum.
 

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Eric The Viking":2tocrloz said:
.... I was told (Evesham) ....
Was that Talbot-Smith who taught that part of the course ? Or Kevin Oliver ?
What vintage were you ? TA (TO?) or A/B/C generation ?
Happy Days ! :D
 

Eric The Viking

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RogerS":3gsxrj7v said:
Eric The Viking":3gsxrj7v said:
.... I was told (Evesham) ....
Was that Talbot-Smith who taught that part of the course ? Or Kevin Oliver ?
What vintage were you ? TA (TO?) or A/B/C generation ?
Happy Days ! :D
A56, IIRC. I was taught at various times by both MTS and Kevern Oliver (odd spelling, which I think is correct). The Soundfield stuff was MTS on a later course, which also included an introduction to digits, IIRC, but by then we were already struggling with an AMS Audiofile in Bristol (yup, software bugs are not a new concept!), so a friend and I contributed a fair bit about operational issues - much of the course wasn't based on practical experience. I did my film training at Ealing, Lime Grove and TC on a long attachment - at the time Wood Norton didn't have any film facilities (apart from one TK machine I think). I vaguely remember that they got some of our equipment from Bristol when we refurbished, as dubbing kit was extremely expensive.
 

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Eric The Viking":3nafkjeq said:
RogerS":3nafkjeq said:
Eric The Viking":3nafkjeq said:
.... I was told (Evesham) ....
Was that Talbot-Smith who taught that part of the course ? Or Kevin Oliver ?
What vintage were you ? TA (TO?) or A/B/C generation ?
Happy Days ! :D
A56, IIRC.
LOL...I wondered if you might have been on the A/B/C system. A56 ..must have been around 1975 or so ? Remember that wee book you had with questions in ? That were written by me :D
Eric The Viking":3nafkjeq said:
I was taught at various times by both MTS and Kevern Oliver (odd spelling, which I think is correct). ......
You are right with the spelling. It's what I initially put in but thought 'That can't be right'. So two of us can't be wrong!
 

Eric The Viking

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Crikey! If you mean the blue covered "Technical Training Book", a sort of mini ring-binder thing, almost flash-card sized, it's on the shelf next to my right knee as I type!

I am definitely not worthy, etc...

Can I blag some of the answers from you? Won't tell anyone.

Seriously though, the A course was really thorough, complex numbers 'n' all. I never quite got my head around colour signal timings though...
 

RogerS

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Eric The Viking":2z3klhj0 said:
Crikey! If you mean the blue covered "Technical Training Book", a sort of mini ring-binder thing, almost flash-card sized, it's on the shelf next to my right knee as I type!....
Yup...that's the one. :D God, that was such a long time ago. :(
 

Steve Maskery

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Am I the only one who feels like he's walked into a fifth dimension when he thought he was just opening the fridge for a pint of milk?
:)
S
 

Eric The Viking

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:oops: :oops: :oops:

Sorry!

E. :)

But I am smug, coz I've just come back in from flying one of my Flexfoil kites on the Downs today, for probably the first time in ten years, and the Peregrines even contemplated stooping on it (all three flew in circles right overhead - brilliant!).
 

Mark Hancock

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No apology needed. I've found this thread to be the the most interesting one in ages and I don't understand a word of it! :)
 

RogerS

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Bit of history to help fill in the gaps.

For many years, the BBC ran many different departments.

Research Department - still going and does a lot of innovative work in video and audio codecs and digital transmission.

Designs Department - who, as the name suggests, designed a lot of the equipment that the BBC used

Equipment Department - who built the stuff that Designs Department designed

SCPD - Studio Capital Projects Department - who put the stuff that Equipment Department made into studios, Outside Broadcast (OB) vehicles (known as 'scanners' since the early ones were (a) green and (b) looked like wartime mobile radar vans).

Then you had Television Centre in London (then split up into specific areas such as studios, videotape (VT), telecine (TK) ..playing films, News etc.

And Outside Broadcasts.

And ETD (Engineering Training Department) based at Woodnorton, Evesham and where the BBC 'lived' and broadcast from especially during WW II. Although called 'Engineering', Woodnorton also ran courses for Technical Operators (TO's...we loved our acronyms) and other more specialist courses, for example, Studio Managers (based in radio) of which elite group EtV was one such. In a lot of ways, ETD pioneered approaches to learning with, for example, feedback classrooms where stuff was taught using 35mm slides and multiple-choice questions (A>E). Each student position had a bank of five pushbuttons (A>E) and a red and a green light. Instant feedback if they'd got the answer correct and the lecturer could see from his master panel how the topic was going down. We're talking mid-1960's here.

There were a whole host of other courses, for example...the C course which was mandatory for an engineer to pass and progress. And one week specialist courses...effectively a one-week extra paid holiday as no exams at the end !

Thing is that all these departments needed people. Some came in via Direct Entry (having gone to Uni) but most went through a basic course at Woodnorton - TA course (Technical Assistant) for the engineering stream (of which I were one) and TO course. Trouble was that by the early '70's, broadcasting was expanding with more and more commercial stations - whose pay and conditions were much better than the BBC - which resulted in the BBC haemorrhaging staff as quickly as they could train them.

So the TA/TO course was abandoned and in its place the A/B/C courses referred to earlier in the thread. There were so many being run that ETD offered secondments as an Assistant Lecturer (I were one of them as well and wrote the book mentioned earlier).

Here endeth the lesson. As you were :D
 

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Couple of years ago we went to do a job on a college refurb. They'd massively over ordered sound proofing insulation, so I gave the site agent £100 for all of it - 3 transit vans FULL of 100mm thick heavy density Rockwool slabs. I have 2 layers in the loft of my house (which halved the winter energy bill) and there was enough left over for a single layer in the roof of the garage - it made a big difference to the amount of noise that escaped the workshop.
 
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