Speaker Class (type) vs Room Size

[jomor]

In a previous thread there is a discussion about if a 3-way is proper for a 4x4 m listening room. I always wanted to clear this out, what's the rules that have to be followed when choosing speaker class (number of ways, number of woofers, size of woofers) for a specific room size ? How many woofers and of which size can play in a 15m² and in a 25m² for example?
How "low" can we get (the lowest frequency) in a specific size of room, lets say 15m² and how low on a 25m² ?

thanks in advance

[mike.e]

Things to consider.

How live or treated the room is. The intended SPL at listening position,how compressed your music is.

A small room will have more room gain,well it starts at a higher frequency.

A cone radiates omnidirectionally when the wavelength being produced is relatively long,and then beams like a torch when it approaches the cones circumference/diameter.

A larger cone driver with a horn to match the directivity at the crossoverpoint makes sense. (pispeakers/gedlee)

[poptart]

Is there really a limit to how low you can go in a small room? I saw that in the other thread too. Was this referring to the lowest room mode having a higher frequency in a small room? For a thought experiment, what does it sound like inside the subwoofer box? That's a very small room and I'm thinking it sounds loud and low.

[rcw]

For rooms up to about 50m^3, the level in the room is equal to the level at one meter, and the standard for hi fi is that the system should be able to produce an average of 90dbm. with 20db. headroom.
Most speaker amplifier combinations can do this, the difficulty comes at the lower frequencies and this is where different speaker sizes really start to matter.
Depending upon construction method and sealing a room will have practically non to quite a lot of pressurisation gain, the later being true of tropical buildings in general.
In these you have to assume anechoic conditions and you need bigger speakers and more power to get the same level as you can in very solidly constructed well sealed buildings.
Also for the highest quality reproduction the system should be capable of 120db. peaks, and when you start to consider this type of level that the discussion about efficiency and multi amping etc. start to matter with regard to the mid and upper frequencies.

[Svante]

Originally posted by jomor
How "low" can we get (the lowest frequency) in a specific size of room, lets say 15m² and how low on a 25m² ?

Infinitely low...

If a room is perfectly closed, ie no leaks, there will be a tilt of -12 dB/octave below the lowest room mode. That is a bass boost. This can be pretty handy if you use closed boxes since they have a rolloff of 12 dB/octave below the resonance frequency. The problem with small rooms is the room resonances. They will amplify some frequencies selectively. In small rooms, the modes appear at quite high frequencies, and therefore they will be more disturbing. But there is no lower limit for how low frequencies that can be reproduced, on the contrary.

The experiment with the sound inside a box is quite interesting. In fact the response of a loudspeaker at low frequencies can be measured inside the box if the response is tilted by 12 dB/oct. No need for a large anechoic room, nice! But, beware, the sound pressure level insida a typical box can easily reach 140-160 dB, so don't put your head there.

[Salas]

We all have been in loud cars right? If small was a problem they wouldnt thunder away in the lows. To the contrary then.

[Hans L]

Originally posted by jomor
In a previous thread there is a discussion about if a 3-way is proper for a 4x4 m listening room. I always wanted to clear this out, what's the rules that have to be followed when choosing speaker class (number of ways, number of woofers, size of woofers) for a specific room size ?

In truth, there are no such rules combining room size and speaker size, let alone number of drivers or how many ways. There is only a vague relation between speakersize and bass extension. A rule based on that relationship would not work in many cases. It's all about bass alignment. Even a 5" woofer in a bassreflex box can be made to play flat down to <30Hz, abeit at very modest SPL's. This can sound boomy whereas a so called large 3-way with a closed box woofer mat have a more shallow bass extension that starts to fall off relatively high (100Hz).

Roomgain (the 12dB bass lift) usually starts at around 50Hz. Only when the room becomes quite small (say 10x10 feet) this frequency rises to as high as approx 80Hz. With 'normal' rooms it start at 35-40Hz and as the room becomes larger (>40x40 feet) this freq does not change a lot.

The other 'problem' is roommodes, or standing waves. These depend on room sizes, but more so on the speaker placement and listening position.