Low freq. from small drivers? Is it possible

The specs of small drivers can have a low cutoff - my bedroom speakers have a pair of 5.25" mid-bass drivers and are flat in-room through 30Hz.

In practice it doesn't work.

SPL is purely a function of displacement and frequency. Displacement requirements quadruple for each octave you drop in frequency, meaning excursion increases 4-fold in a sealed system when you don't change the diameter.

Play with www.linkwitzlab.com/spl_max1.xls if you want.

This has a couple of problems
1. Physics prevent reaching reasonable SPL levels with small drivers outside a car or closet environment where you have up to 12dB of cabin gain below the fundamental resonance .

2. Excursion increases 4-fold with each octave lower if you don't change diameter. Distortion is a function of excursion. My 5.25" midranges (about equal to a 6.5" driver - they have more area, but will have less excursion) double at low frequencies - the harmonics are loud enough that you hear the higher tone. IM distortion (why old transistor amps sound bad) also increases. I never got good midrange performance from drivers <= 6.5" when bass notes were also present. Adding a sub-woofer with a 80Hz cross-over always cleaned up bass and midrange in music with a bassline. I now use an 8.5" midrange, 2 10" long-throw subwoofers per side for bass below 120Hz, and add a 14.5" subwoofer for theatrical tracks where the bass is really out of hand.

If you want small speakers use subwoofers too. You can have small boxes for WAF, small baffles for minimal difraction, place the midrange+highs for their best performance, and the sub-woofers for the flattest response at your listening position.

Many people find the best integration when crossing over an octave above ported speakers' F3 point (LR4 order electrical high and lowpass) or at sealed speaker's F3 point (2nd order butterworth high-pass, LR4 low-pass).

If you don't want sub-woofers and do want full-range music (symphonic, rock, jazz with an upright bass, etc.) you need 3-way speakers with a large bass driver.

>Here is the frequency response of the Ultimate Monitor from >Karl Schuemann

The specs don't tell you enough to be useful.

1. They don't tell you about distortion. The mid-ranges used in my speakers are good for .3% THD @ 96dB/1 meter in their operating range with an increase to 1% at the tweeter cross over frequency where they're 6dB down and distortion should be less. Run at lower frequencies they'll have horrible distortion at much lower output levels - maybe 10% at 70dB one you reach 30Hz. This is especially bad at low frequencies where tight spacing of the equal loudness curves makes the harmonics sound louder than the fundamentals. IM distortion is even more of a problem.

2. They don't tell you what the maximum output level is at those frequencies. Using a pair of 6.5" scan speak mid-bass units (Sd = 145 cm^2, xmax = 5mm) in a sealed box the linear limits are about

88dB @ 35Hz
94dB @ 50Hz
100dB @ 71Hz

3. They don't tell you what the off-axis response looks like. At reasonable listening distances you're picking up more sound from the reverberant field than direct sound. The shape of the off-axis curves has a _huge_ effect on what you hear.

4. The don't quantify thermal compression. This is especially important where you start equalizing. The BOMB is a Linkwitz Transform which allows you to change the F3 point and Q of a speaker thus getting you lower bass extension and less group delay at higher frequencies. Low group delay means "fast bass." The problem is that your power requirements go up. The extra power increases voice coil heating and therefore resistance. That means more thermal compression and changes in the cross-over response with output level than you'd have in a speaker without equalization.

I'm sure the Ultimate Monitors are exceptional speakers although they can't break the laws of physics. If you want natural sounding bass at realistic output levels you need a 3-way or sub-woofers, the later being better because high and low frequency transducers interact with the room differently and therefore work best with different placement.