Diphthong · ou / ow Same start as /aɪ/ — low and front — but with unrounded lips. Rounding is what happens in the second half on the way to /ʊ/. Round at the start and it sounds like /ɔ/.
Three steps to /aʊ/
Open first, round later.
Low front start, spread lips
The jaw drops and the tongue is low and front, almost the same as the /aɪ/ start. The lips are the key: neutral, even slightly spread.
Glide to /ʊ/, rounding on the way
In the second half the lips round and the tongue back rises. Rounding is a process, not a starting state.
Self-check: watch the first third
Say now. In the first half the lips are open and the teeth visible; only the second half rounds. Round from the start and you are saying /ɔ/.
Articulation (side view)
One speaker, one instant: tongue position and lip shape only. The amber circle marks what to look at; the caption says how it differs from the sound it is usually confused with.
Spelling: ou and ow, roughly half each
Both spell /aʊ/, and ow also spells /oʊ/ — that is the trap.
house, loud, mouth, round, sound. Many exceptions (soul /soʊl/, you /juː/, could /kʊd/) — per word.
★ The reverse of know / show / low, which are /oʊ/. A weak cue: ow before n, d or l is often /aʊ/ (down, town, sound, howl). A cue, not a rule.
bough /baʊ/, plough /plaʊ/. ough is the least consistent digraph in English; this page mentions only this reading.
Why learners replace /aʊ/
The nearest L1 diphthong already starts rounded.
Rounded from the start — /ɔ/
now → /nɔ/, how → /hɔ/. If your L1 has an «ao»-like diphthong, its start is already rounded and the habit transfers whole.
The test is a mirror: in the first third the teeth must be visible.
Glide dropped
house → /has/, down → /dan/. The same flattening as on the /aɪ/ page.
A hand under the chin: the jaw must drop and then rise.
ow read as /oʊ/ everywhere
After know and show, now becomes /noʊ/.
Per word: now, how, down, town, loud, mouth, flower are /aʊ/.
Word list
27 words grouped by where the sound sits in the word. Click a word to hear it. These are recorded as separate words, not cut out of the sentences above — a word cut from a sentence carries its neighbours' transitions and always sounds muddier. All three groups use the same speaker, so what changes between them is position, not voice.
Word-initial9
Word-medial9
Word-final9
Three groups of nine. The initial group (out, owl, ounce, our, hour, outside, outlet, outline, outfit) is sparse — learn each one.
Corpus and acoustic measurements
Click any word in a sentence to play from that word. The pale band over the waveform marks the measured boundary of the target word.
Per-token data
Every number below is measured directly from the audio, not hand-annotated.
| Token | Accent | Sex | Target | Word length | aʊ duration | F0 | Pitch range | HNR |
|---|
Where the numbers come from
Every figure on this page can be recomputed from the description below.
Corpus: 12 English sentences synthesised with four American voices (two male, two female), each containing one target word, covering initial, medial and final positions. Audio is 22.05 kHz mono 64 kbps; each clip runs from 1.2 s before to 1.5 s after the target word.
Word boundaries: taken from the engine's word-level timestamps (WordBoundary) and corrected for the fixed offset between the engine timeline and the audio start (estimated per item). The target word is shaded in the waveform.
Phoneme boundaries: measured by forced alignment with the MMS_FA acoustic model. Each character's aligned frame range is kept, then a dynamic program maps the character sequence onto the phoneme sequence (th→θ, ng→ŋ, ck→k). Boundaries fall in the middle of the transition between characters; within-word coverage is 100%. Time precision is the model frame length, 20 ms, and boundaries are taken at midpoints, so effective resolution is about 10 ms.
Pitch: Praat's autocorrelation (to_pitch), 10 ms frame step, search range narrowed to the speaker's estimated range, octave errors removed. «Pitch range» is max minus min F0 within the word.
Why there are no paired differences here: this is a single-phoneme page. Eight other pages are contrast pages (θ/ð, l/r/n, vowel length) where the numbers come from paired words read by one speaker. A single-phoneme page has nothing to compare against — pairing it with a neighbour would measure that neighbour, which belongs to a different page.