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SOUND
 

SOUND & ACOUSTICS

 



TERMS

The Decibel, see Specifications ? page

A 1 db increase would just be audible.

A 10dB increase will be judged to be twice as loud, (ten fold increase in power).

Acoustic power must not be confused with electrical power, the power forms must be converted by something like a loudspeaker, but a standard cone/coil loudspeaker can be as inefficient as 3%, so as an example a 100W amplifier at full output would only give approximately 3W acoustic power.

1 acoustic Watt measured at 0.282m, (A sphere radius 0.282m has a surface area of 1m), (4 * pi * r^2) gives:

                                                  Acoustic power = 1W
Power level = 120 dB-SPL
Acoustic intensity = 1W/m sq
Acoustic pressure = 20 Pa or 20ubar

TYPICAL LOUDNESS LEVELS

(with Safety time limits where appropriate, from OSHA (Occupational Safety & Health Act))

                Level Time Description Acoustic power
1dB-SPL Threshold of audibility
15dB-SPL Quiet whisper
20dB-SPL Studio noise level
30dB-SPL Quiet room in house, suburban street
40dB-SPL Noise in large office
50dB-SPL Quiet speech, close proximity
60dB-SPL Noise in restaurant
65dB-SPL Conversation, close proximity
75dB-SPL Factory noise
90dB-SPL 8 hours Grand piano
95dB-SPL 4 hours Noise in underground train
100dB-SPL 2 hours Symphony orchestra
105dB-SPL 1 hour
110dB-SPL 30 minutes
115dB-SPL 15 minutes
120dB-SPL 7 minutes Threshold of feeling
130dB-SPL None Threshold of pain

 

EFFECTS OF EQUALIZATION ( GOOD // BAD )

Below 40Hz Few systems (and instruments) can produce these frequencies, boosting can loose vital headroom and damage bass drivers (ie. Be careful).

GENERAL        Freq Sound Too much EQ??
40 - 80 Bass drum, Sense of power Muddy sound
80 - 250 Bass drum, Toms, Bass guitar Boomy, hollow
250 - 500 Percussion, Strings Honky, Horn like
500 - 1k Percussion, Strings Horn like, Telephony
1k - 4k Strings, Vocals, Brass,Presence Tinny, LISTENING FATIGUE.
1k - 8k Clarity and Definition
4k - 8k Accentuation, Percussion, Strings, Snare
5k up Reduction of this makes the sound
more distant & transparent
8k up Cymbals,overall brightness Sibilance
VOCALS
100 - 1k5Hz Fundamentals
50 - 150 Power in bass singers
100 - 250 Power fundamentals
250 - 500 Quality importance
500 - 1k Warmth, Naturalness Telephone quality
1k - 4k Clarity, Presence,intelligibility LISTENING FATIGUE
masks 'm, b, & v sounds
3k - 3k5 Highlighting Sibilance
4k - 7k Clarity, Accentuation Sibilance
7k up
BASS
(guitar & drum)
30 - 300Hz. Fundamentals
50 - 100 Deep bass Muddy
800 - 2k Definition, Percussive attack Horn like
SNARE DRUM
80 - 2kHz. Fundamentals
500 - 800 Warmth, Fatter sound Tom & bass pickup
1k - 2k Presence, Definition
2k - 4k Crispiness
CYMBALS
2k - 5k Dominant frequencies
10k up Sibilance, Tinny, Paper thin

 

How can I stop the noise from outside getting inside

It depends on the type and level of noise concerned as to how involved the soundproofing would be. Firstly a distinction must be made between 'soundproofing' and 'internal acoustic treatments' which only treat internal reflections so reducing reverberation, echo and general colouration of the sound, these treatments generally consist of soft coverings, padding, furnishings etc. and in some special cases acoustic traps or chambers. These internal treatments will reduce higher frequency transmissions but little else.

For soundproofing there are two different areas to look at, the first is higher frequency noise, this is usually airborne and can be stopped by simply blocking out gaps around doors, windows etc or removing direct uninsulated routes though vents etc (it is not advisable to produce an airtight room). The second are lower frequencies which are usually transmitted though the structure of a building either indirectly (sound hitting wall) or directly (lorry noise through road to wall) and can only be reduced by either mass (weight) and/or isolation. Due to the power of these they are difficult to reduce significantly without large structures; for example doubling the wall thickness and/or introducing isolated internal structures to absorb them, although again these are large and not really suitable for a home.

 

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