在英语中，通常字母 p 做音节头时发音时 [ph]，注意，这里[p]右上角的 h 表示这是个送气音; 但是如果 sp 一起出现在音节头，也就是说 p 跟在 s 后面，那么 t 的发音变成 [p], 也就是不送气了。此时在听觉上近似于 /b/，但是声带不振动，所以也可以标记为 [bo].
下面列出一些 [ph] 和 [p] ([bo]) 对比的词供大家练习：
| [ph] | [bo] |
| port | sport |
| pend | spend |
| pi | spy |
| pill | spill |
| pin | spin |
| peak | speak |
| peach | speech |
| pray | spray |
以下是一些含有 /p/做音节头和 /sp/做音节头的词语的句子，供大家练习：
1. Tom will pay $100 to buy a sport bike.
2. Bill sprayed water to put out the fire.
3. The bus speeded up to pass the intersection.
4. Brain spent one day playing in the park.
5. Bill prayed before he gave a speech.
6. The spy is hiding in a bus in the port.