You know which boat this is, and where it's located. Worth clicking through to get a better view of all those cables and ropes, none of which are called "cables" or "ropes" by Real Sailors, but then. I'm not a Real Sailor.
Friday, 21 March 2025
Tuesday, 18 March 2025
Charlton House
Most of it is open to the public, but sadly there's no historic furniture, art or decoration there. It's a ten-minute walk up the hill from Charlton station, and worth an amble around the park, a cup of coffee and slice of Victoria cake in the cafe.
Friday, 14 March 2025
Negative Space, London Bridge Station
All the Kool Photographers talk about using "negative space", but I always thought it meant they exposed those part of the picture incorrectly. But this one seems to work.
Tuesday, 11 March 2025
Bleak Mid-Winter Suburbia
It's not enough to get out for a daily walk. The walk needs to be pleasant, or at least neutral, to look at. Hedges on country lanes, with an occasional glimpse across a valley, or perhaps a path across a flat moor, or maybe even along a canal. Not round the outside of an industrial estate. But we make do and carry on.
Friday, 7 March 2025
One Wall of the Walled Garden, Golders Hill Park
Golders Hill Park is a couple of stops up the hill from the station. It's well worth the visit.
Tuesday, 4 March 2025
Room Resonances
Room resonances are a real thing, but... a) the wavelength has to match the room dimension almost exactly.
While it looks as though there are "as many notes as we want", in Western music there are only 88 notes. But not really. There are actually 12 fundamental notes - starting with A0 at 27.5 Hz and ending at A♭1 at 51.91 Hz. Double those frequencies to get the next octave; double again to get the next; and so on until reaching C8 at 4186 Hz.
So a room that supports a standing wave (resonance) at, say, C2 65.41 Hz, will support standing waves at all the other C's as well. The sound will be quieter with each jump up or down of an octave. However, people only worry about bass resonances. That's because notes below a limit that varies with the room, are non-directional, appearing, as it were, at once everywhere in the room. (Above that limit, the notes become directional, which is how you ears tell you that the drums are right in the middle of your speakers.) Think of the bass notes as being produced in the middle of the room and going in all directions. If one of the dimensions of the room fits the note, and if there isn't soft furniture in the way, up pops a resonance.
If you're really unlucky you might get three different resonances: floor-to-ceiling, side-to-side, front-to-back. Highly unlikely, but possible. Chances are you will get one. There won't be others, unless your room changes dimension somewhere (sloping walls or ceiling?). Most people will get one. And that's it.
My listening room is 2.5m high, so a slightly out of tune C♯3 / D♭3 of 138.6 Hz will cause a stomach-churning resonance. Here's the thing: the 3-octave is used for effect, not for carrying the tune. That's usually done an octave higher where resonances don't happen. Bass players famously "play the root note" (unless they are Jaco Pastorius or Jack Bruce), and C♯3 / D♭3 (or C♯2 / D♭2) are not the most frequent root notes. Also, the instrument would need to be slightly out of tune to make my room react. That's why it happens so infrequently.
That doesn't mean I don't get quieter and louder patches if I move the subwoofer around. Very much so: interference isn't resonance. Its current position was chosen because it produced the most uniform level throughout the room. It's very un-nerving moving from one chair to another and suddenly hearing more bass.
Anyway, here's a list of the notes most likely to cause resonances, along with the wavelength. Measure the room (wall-to-wall, ceiling to floor. You can ignore diagonals because corners create bass boost, but do not create standing waves) and if any of those three numbers are within 0.02m (20mm) or so (depends on how reflective the material is), you will likely get resonances
D♭3 2.47m
While it looks as though there are "as many notes as we want", in Western music there are only 88 notes. But not really. There are actually 12 fundamental notes - starting with A0 at 27.5 Hz and ending at A♭1 at 51.91 Hz. Double those frequencies to get the next octave; double again to get the next; and so on until reaching C8 at 4186 Hz.
So a room that supports a standing wave (resonance) at, say, C2 65.41 Hz, will support standing waves at all the other C's as well. The sound will be quieter with each jump up or down of an octave. However, people only worry about bass resonances. That's because notes below a limit that varies with the room, are non-directional, appearing, as it were, at once everywhere in the room. (Above that limit, the notes become directional, which is how you ears tell you that the drums are right in the middle of your speakers.) Think of the bass notes as being produced in the middle of the room and going in all directions. If one of the dimensions of the room fits the note, and if there isn't soft furniture in the way, up pops a resonance.
If you're really unlucky you might get three different resonances: floor-to-ceiling, side-to-side, front-to-back. Highly unlikely, but possible. Chances are you will get one. There won't be others, unless your room changes dimension somewhere (sloping walls or ceiling?). Most people will get one. And that's it.
My listening room is 2.5m high, so a slightly out of tune C♯3 / D♭3 of 138.6 Hz will cause a stomach-churning resonance. Here's the thing: the 3-octave is used for effect, not for carrying the tune. That's usually done an octave higher where resonances don't happen. Bass players famously "play the root note" (unless they are Jaco Pastorius or Jack Bruce), and C♯3 / D♭3 (or C♯2 / D♭2) are not the most frequent root notes. Also, the instrument would need to be slightly out of tune to make my room react. That's why it happens so infrequently.
That doesn't mean I don't get quieter and louder patches if I move the subwoofer around. Very much so: interference isn't resonance. Its current position was chosen because it produced the most uniform level throughout the room. It's very un-nerving moving from one chair to another and suddenly hearing more bass.
Anyway, here's a list of the notes most likely to cause resonances, along with the wavelength. Measure the room (wall-to-wall, ceiling to floor. You can ignore diagonals because corners create bass boost, but do not create standing waves) and if any of those three numbers are within 0.02m (20mm) or so (depends on how reflective the material is), you will likely get resonances
D♭3 2.47m
C3 2.62m / 130Hz
B2 2.78m
B♭2 2.94m
A2 3.12m / 110Hz
A♭2 3.30m
G2 3.5m
F♯2 3.71m
F2 3.93m
E2 4.16m
E♭2 4.41m
D2 4.67m
D♭2 4.94m
C2 5.24m
B1 5.56m
B♭1 5.88m
A1 6.24m 55Hz
A♭1 6.6m
G1 7.0m
F♯1 7.42m
F1 7.86m
E1 8.32m
E♭1 8.82m
D1 9.34
D♭1 9.9m
C1 10.48m
B0 11.12m
B♭0 11.76m
A0 12.48m 27.5Hz
How do you stop a resonance? Only big, obtrusive, and expensive bass traps made of materials sourced in an Ardennes forest and hand-assembled by elves in a workshop outside Dusseldorf will do the trick... it says here on the PR handout.
Resonances result from room dimensions. So change the dimensions of the room. No builders needed. Nice full shelves full of absorbent things: paperbacks are always good, just don't line them up precisely. LP's or big art hardbacks may not be a good idea if the resonances are at higher frequencies. This will work for side-to-side or back-to-front resonances, but floor-to-ceiling you are pretty much stuck with. Unless you put nice thick carpet in everywhere, which will damp it a little.
How do you stop a resonance? Only big, obtrusive, and expensive bass traps made of materials sourced in an Ardennes forest and hand-assembled by elves in a workshop outside Dusseldorf will do the trick... it says here on the PR handout.
Resonances result from room dimensions. So change the dimensions of the room. No builders needed. Nice full shelves full of absorbent things: paperbacks are always good, just don't line them up precisely. LP's or big art hardbacks may not be a good idea if the resonances are at higher frequencies. This will work for side-to-side or back-to-front resonances, but floor-to-ceiling you are pretty much stuck with. Unless you put nice thick carpet in everywhere, which will damp it a little.
Friday, 28 February 2025
Hi-Fi Lessons (2): Useful Numbers
You will wind up learning a bunch of numbers by heart:
The sensitivity of your speakers in dB / m at 1 watt
343 m/s = speed of sound (roughly) at sea level
The sensitivity of your speakers in dB / m at 1 watt
The diameter of your speakers' woofer and tweeter
Twice the power = 3dB volume increase
10 times the power = 10dB increase = "twice as loud"
30dB = what you think is silence - but actually isn't
30dB = what you think is silence - but actually isn't
40dB = when no-one is talking on a new train
50dB = it's not quite loud enough
60-70dB = about the loudness of a normal voice. Or my acoustic guitar.
80dB = the volume audio reviewers say they listen at - until their partners yell "TURN THAT DOWN" 95dB = the volume of the taped announcements on London Underground trains
343 m/s = speed of sound (roughly) at sea level
Frequency = 343 / wavelength in metres; wavelength in metres = 343 / frequency;
27.5 Hz = frequency of lowest note on the piano, and known to music (outside stunt instruments)
27.5 Hz = frequency of lowest note on the piano, and known to music (outside stunt instruments)
41 Hz = lowest note on double bass
261 Hz = middle C - literally the middle of the piano keyboard, and the note between the treble and bass clefs in the Grand Clef
440 Hz = note the oboe plays for everyone else to tune to, otherwise known as "A440"
4,186 Hz = frequency of highest note on the piano, and known to music (outside stunt instruments)
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