Question about speaker specifications

[Hobbit]

I am trying to understand what bass extension actually means?

If you notice in the B&W curves above the bass frequencies start rolling off at about 100hz. At low frequencies a small room will reflect these waves and augment them. IOW, a small room will confine and add the low freq. waves rather than reflect and absorb them. It has to do with the wavelength vs. room dimensions.

The blue line below is from the room gain.

 

[Seth=L]

I am trying to understand what bass extension actually means.From my limited understanding/knowledge here is what i am thinking.
lets say for example ,I have a 6" driver and the driver has a -3db cutoff freq of 60 Hz, meaning the 6" cone will not move much for freqecies below 60 Hz. how can we have a extented bass response if the cone movement is not producing any noticiable SPL ?

Any speaker system has its limits. In such a scenario where a speaker has a -3dB point at 60Hz that would ideally mean the speaker has had a relatively flat response until that point and begins a process of roll-off (meaning a reduction in output)*. So that same speaker subsequently may have a -10dB point at 55Hz which is a sharper decline in output than -3dB. The cone is still moving but its interaction with the cabinet and room is losing its effectiveness based on its physical limitations.

A good example of examining this in a normal listening situation would be if you where watching the opening battle sequence in Lord of the Rings: Fellowship of the Ring. When Sauron implodes there is a loud bass tone that starts high and smoothly goes lower over the course of about 2-3 seconds. At a considerable volume you can observe the woofer at the beginning of this sweeping bass tone moving shallow and fast at first and then moving deeper and slower as the tone goes lower. You will likely notice the speaker still moving with very little bass coming from the speaker. This all assumes you're not using a subwoofer in this system. If you are then I'll discuss that more down below.

So the speaker still receives the bass signal and tries to produce it despite not being able to produce audible sound. So once you've established roughly where the speaker fails to produce sound you can then decide whether that satisfies your requirements or whether you need to add a subwoofer to satisfy your desired bass response.

*generally a -6dB is considered be a half of perceived output. In a film soundtrack or music in most cases a frequency producted -10dB below the speaker's average output over it's typical audible spectrum would be nearly inaudible.

 

[Swerd]

I am trying to understand what bass extension actually means.From my limited understanding/knowledge here is what i am thinking.
lets say for example ,I have a 6" driver and the driver has a -3db cutoff freq of 60 Hz, meaning the 6" cone will not move much for freqecies below 60 Hz. how can we have a extented bass response if the cone movement is not producing any noticiable SPL ?

Bass extension is a lot of syllables for just what you said, the frequency at which the response has dropped by 3 dB below that of higher frequencies. It's also known as F3.

Sometimes standing waves and the resulting cancellations caused by unfortunate room reflections can increase the apparent F3 frequency of a speaker.

Sometimes locating a speaker near a wall or in a corner can reinforce low bass response making F3 to appear at a lower frequency.