Linn Tukan loudspeaker
Bass extension works against good sound quality in small rooms or rooms with poor dimensional ratios. Any volume of air in an enclosed space will reinforce certain frequencies when that air is excited (such as by a woofer cone moving back and forth). This reinforcement is called resonance, and the frequencies at which the resonances occur are the room's resonance modes. The frequency of a resonance mode is determined by the distances between the room's walls. The greater the distance, the lower the resonance frequency (footnote 1).
When you blow into a bottle, you are not producing the pitch you hear; the bottle's resonant modes are. You are simply exciting the air in the enclosed space nearly randomly; the bottle reinforces certain frequencies that you hear as a pitch. Similarly, a loudspeaker exciting the air in a listening room causes the room to reinforce certain frequencies. The result is smeared and boomy bass (footnote 2).
The larger the room, the lower the room's fundamental resonance and thus the more closely spaced and dense the resonance modes. Closely spaced resonance modes are a good thing; if the resonances approximate a continuum, individual resonances are less likely to be audible. Conversely, a small room's resonance modes are spread out more widely over the band. With large gaps between resonant frequencies, those resonant frequencies are rendered much more audible. That's one reason why it's hard to get good-sounding bass in a small room.
The solution, then, is to choose a loudspeaker that will minimally excite the small room's resonance modes. The modes exist only when the air in a room is driven by a sound source. The less hard you drive the air—such as with a small loudspeaker—the less you'll hear the room's resonant signature.
Choosing a small speaker for a small room has musical as well as acoustical advantages. It's far easier to overlook a lack of bass extension than it is to try to ignore persistent boom and bloat. If we hear harmonics of the missing fundamentals, the brain tends to fill in what should be present. Conversely, boomy bass is a constant reminder that we're listening to a mechanical facsimile of the music.
When I moved into a small listening room temporarily, I was faced with choosing loudspeakers that would work well in a room measuring only 11' by 15'. These dimensions could spell disaster for many loudspeakers. I therefore acquired review samples of two loudspeakers that I thought held promise for my room's size, and also fit my current mandate only to review budget equipment. Those loudspeakers, the $1800/pair Aerial 5 and $799/pair Linn Tukan, have played tag-team in my system for the past five months. Here's how they performed under critical scrutiny.
The $799/pair Tukan is Linn's entry-level loudspeaker, and a replacement for the original Kan. The Tukan is significantly smaller than the Aerial 5. In fact, the Tukan is the smallest loudspeaker I've reviewed. Unlike many budget loudspeakers of the same size, however, lifting the Tukan gives the impression of solidity and mass.
The Tukan is beautifully finished in real-wood veneer. The grillecloth is a black fabric sock that stretches over the front baffle and seats in a channel machined into the cabinet. This design eliminates diffraction from a grille frame. Both drivers are mounted flush with the baffle, and the driver mounting bolts are recessed to further reduce diffraction. The rear panel has two pairs of recessed banana jacks for bi-wiring or bi-amping, and a small port.
Footnote 1: The fundamental resonance is supported between two walls at a frequency whose half wavelength equals the distance between the two walls. Another resonance mode occurs at one wavelength, one and a half wavelengths, and so on at every multiple of half a wavelength.
The formula for calculating the fundamental resonance mode is 1130/2D, where 2D is twice the distance between two walls and the speed of sound in air at "room temperature" is 1130ft/s. A 20' room thus has a fundamental resonance at 28.25Hz (1130/40), with further modes at 56.5Hz, 84.75, 113Hz, and so on.
Each pair of room surfaces (length, width, height) will exhibit its own set of modes. A room with suboptimal dimensional ratios causes the modes from different pairs of walls to occur at the same frequency, reinforcing that mode. A room with good dimensional ratios spreads the modes out evenly.
Footnote 2: At the recent CES in Las Vegas, every demonstration room at the Alexis Park Hotel was plagued by a nearly identical midbass bloat.