What are the smallest speakers that are clean and flat down to 20hz?

How clean and at what SPL?  

Very few speakers of any size (that I know of) maintain clean output (call it 10% THD) at 20hz at 90 db.  If you really want that kind of performance from a small speaker, you'll almost certainly need a subwoofer.  

Some people might argue that 30%+ THD is clean enough at 20hz (where hearing is very insensitive).   That may be true, but it means that any answer to your question will be awfully subjective (and you'll still probably need a subwoofer).

Hi Mapman,

Clean and flat = big driver. Best I've had is a 15" Hsu which was flat to 16 Hz after acoustic treatments and EQ.

However, it's really important to understand, below 400 Hz or so, your room becomes a very important part of "clean and flat" so much so that getting to the lowest octave is a completely different ballgame. The lower you try to go the bigger the dragons. This is why smaller 2 way speakers are often preferred to full-range.

It can be done and it's glorious, but it's not trivial. If you aren't willing to spend the time or hire qualified help, you are often much better off with limited output speakers.

Best,


Erik

FYI, there’s a rule of thumb, that for any given driver, going down an octave causes 10x the linear cone travel. So, if you attempt 20 Hz with a 6" driver you’ll need it to move a foot back and forth or something ridiculous like that. :)

This is why larger is better. Those who argue they are slow or not musical have not been able to integrate them properly which has nothing to do with the quality of the driver but not managing the room acoustics and EQ properly.

You may also find this resource helpful:

http://bass-db.gforge.inria.fr/BASS-dB/

Also look for Room EQ Wizard where you fill find many bass geeks to discuss things with you.

Having adequate drivers for a subwoofer is very important, but to my ears, the quality of the EQ matters much much more. So, JL to me is one of the best off-the-shelf subwoofer makers. Of course they use a high quality sub driver, but their auto-EQ is perfect.

Personally, I do my own EQ, so I’m quite happy with Hsu VTF-15H MK II for $1,300 (including EQ). If I had all sorts of money and no time, I’d go with JL.

Best,


Erik

Clearly larger active or powered speakers or speakers with integrated powered subwoofers are best able to do it but I’m wondering more about purely passive speakers even if only in a smaller room.  I realize room acoustics play a big part.   I'm also wondering more about low end extension and  distortion levels assuming other external factors will need adjustment for truly flat response.