Lambda is usually the wavelength, do you mean wavelength?

Wavelength and frequency relate through speed of sound. Here is harmonic series in frequency for box walls that are 30cm apart, a typical size for bookshelf speaker. If it is a two way bookshelf speaker, there are four modes within pass band of woofer if crossover is around 2.5kHz, and this is for one dimension only. If box is 15cm wide and 20cm deep there is more.

- 1. 571 Hz
- 2. 1143 Hz
- 3. 1715 Hz
- 4. 2286 Hz
- 5. 2858 Hz
- 6. 3430 Hz
- 7. 4001 Hz
- 8. 4573 Hz

It's easy to approximate whether a sound wave fits inside: speed of sound is roughly 340m/s for easy math, so 100Hz = 3.4m, 1000Hz = 34cm, 10000cm = 3.4cm in wavelength, or in size if you will.

Basically, if one want's no standing waves to fit inside a box, the box needs to be smaller than wavelength at low pass. Actually twice as small because the first mode is half wave. So if there is two way speaker with 2.5kHz xo, that's about 13cm in wavelength. Thus, longest dimension of woofer box must be less than 6.5cm in order no standing waves within pass band fit in. What about the tweeter? It plays up to 20kHz, so it must have smaller cavity behind the dome than ~9mm, or there is a standing wave inside the tweeter, basically standing wave fits within typical tweeter dome ( diameter ~25mm ) so there will always be one or more even with tweeters assuming the back is closed.

With this simple thought experiment and recalling any hifi speaker is larger than 6cm, it basically means all hifi speakers would fit standing wave(s) inside the box except those that do not have a box. Basically only subwoofers make it without modes inside: if low pass is around 80Hz, the box could be 2m long and still no standing wave fits in because 80Hz is over 4m long in wavelength. However, the room is about 2m tall for example, so modes exist now in the room instead.

Sound wavelength is all one needs to figure this stuff out, quite simple calculus. There are more modes than these simple between two walls, but longest dimension of a box x 2 is the most problematic one always as far as I can imagine.