ImajournWhispering galleries
Under some domes, a whisper spoken close to the wall can be heard clearly on the far side. The sound clings to the curved wall, glancing off it again and again instead of spreading out across the space. Lord Rayleigh explained it around 1878, studying the Whispering Gallery of St Paul's Cathedral in London. Other famous examples are the Gol Gumbaz in Vijayapura, India, and the Echo Wall of the Temple of Heaven in Beijing.
Choose the circle in Shape and touch the water right at its rim. The waves run round the wall, and Imajourn notes the discovery: "Waves hug a curved wall, the way whispers travel round St Paul's dome."
Focal points: the ellipse
An ellipse has two special points, its foci. Sound leaving one reflects off the curved wall and arrives at the other, every path taking the same time. That's why, under some vaults, a whisper at one spot can be heard clearly at another.
Choose the ellipse and touch one focus, on the long axis about a tenth of the way in from an end. Every wave gathers at the other focus.
Domes, curved walls and soft surfaces
Curved surfaces act like mirrors for sound. A concave wall or dome gathers sound towards a focus, which can make some spots loud and others weak, while a convex surface spreads it out. Soft materials do the opposite of stone: they soak sound up.
In Water, open Touch and choose Wall to draw a wall of any shape, and watch a curve gather the ripples or scatter them. Choose Sponge to draw soft edges that drink the waves, much as curtains and acoustic panels do.
Echoes and reverberation
Clap in a stone church and the sound comes back from every wall, again and again, until the echoes blur into one long ring that slowly fades. That ring is reverberation. It's part of why slow chant and organ music suit large stone churches, and why speech can be hard to follow in them.
Open Room, choose Waves in Touch, and tap to clap. Watch the sound leave, reflect off the walls and fill the space.
Room modes and standing waves
At certain notes, a room's reflections build on each other into standing waves, called room modes. They leave some places loud and others nearly silent, which is why the bass can boom in one seat and fade in the next. A cube is the classic problem: its three equal sides share the same resonances, so acousticians avoid cube-shaped rooms.
In Room's figures PRO, each note rings a sphere, a cube or a cylinder at one of its resonances, and points of light gather on the surfaces where the pressure never changes. With live waves, the Energy view shows where a standing wave is loud and where it's still.
Your own building, in 3D
Import a 3D model of a hall, a chapel, a temple or a room you've scanned, as a USDZ, OBJ, STL or PLY file (USDZ works best). Then clap, or place up to four singing sources, and watch the waves travel and reflect inside it. The model is drawn shaded with its near side as glass, so you can see the waves within. Room and model import are part of Imajourn Pro.
Ancient sound: archaeoacoustics
Archaeoacoustics studies how ancient places sound: the long echoes of stone chambers, rooms that seem to answer a voice at one low note, and the staircase of the pyramid at Chichén Itzá, which returns a handclap as a chirp. Every enclosed shape has notes where it resonates. Draw a chamber's floor plan as your shape in Imajourn, then choose Tones in Sound and sweep the pitch strip to find the notes where that outline rings, in two dimensions.
Vibration you can see
The same physics shapes how floors, panels and plates vibrate. Chladni's figures are what engineers call mode shapes, the patterns they look for when a floor bounces or a panel hums, and violin and guitar makers have long used them to tune their instruments' plates. In Imajourn's Plate, see how the figure changes with the note and with the shape of the plate.
What Imajourn is, and isn't. It's for seeing and understanding how sound behaves: it simulates waves for wonder and teaching. It doesn't measure real rooms, and it isn't a substitute for acoustic engineering software or an acoustician.
Questions
What is a whispering gallery?
A curved wall or dome that carries sound along its surface, so a whisper close to the wall can be heard far round it, as in St Paul's Cathedral in London and the Gol Gumbaz in Vijayapura, India. In Imajourn, touch the water right at the rim of the circle to see it.
Can architects and students use Imajourn?
As a visual sketchbook, yes: for building intuition, and for explaining reflection, focusing, reverberation and standing waves to clients and classes. It shows how sound moves; it doesn't measure it.
Which 3D files can I import?
USDZ (best), OBJ, STL and PLY, from the Files app. Large scans take a few seconds to prepare. Room and model import are part of Imajourn Pro.
Why do acousticians avoid cube-shaped rooms?
A cube's three equal sides resonate at the same notes, so those notes pile up and boom while others stay weak. Rooms with unequal proportions spread their resonances more evenly. In Imajourn's Room, compare the cube's figures with the sphere's and the cylinder's.
See sound move
Imajourn is free to download and play on iPhone and iPad. Room comes with Imajourn Pro, one purchase, never a subscription.
