The Finnish Northnuance Spiro is an unusual single-driver loudspeaker in two ways. One, it's so designed that free-field and room responses are not a result of a haphazard process but fully under control, and second, more than other widebanders I know it is willing to compromise in bass in order to get the HF content right.
The Spiro sports an aluminium cone 70mm OEM driver in a 1m long transmission line cabinet. The Fs of the unit is 93 Hz, and the TL is tuned to the same frequency. The combination provides a bass response that extends flat down to approximately 80 Hz, and then decreases slowly. In practice, the response begins to fall an octave higher.
There are well-thought reasons for the chosen bass response. First, the speaker's controlled bass reponse is designed for small acoustically challenging 10 - 20m2 living rooms with walls made of stone, where the design helps in attacking adverse room modes by not waking them up in the first place, and by offering the possibility for curbing the upper bass by adding lambswool to the TL tube.
It is noteworthy that already 80 years ago speaker manufacturers knew how to make elements that would cover 80Hz to 8000Hz. The dream was to have an element that would have assisted them to build speakers that go from 50Hz to 15000Hz, and in contrast to the Spiro, the lower limit was considered to be a more urgent challenge and a true condition for the good sound.
The Spiro's bass response is said to go down to 40Hz in a suitable environment but for the real mid and upper bass the company offers Spiro-adjusted bass speaker called Sub-Spiro (1395 euro each).
One of the great features of the Spiro is that even without the Sub-spiro, and without a slavish reproduction of the low/mid bass, and with a certain light-weight character of the overall tone, the sound is fabulously in balance with itself; it feels correct and smooth, and not at all sounding pronouncedly thin.
The other reason for the design is that with a small widebandwidth driver with top notch "distortion and vibration characteristics" (no whizzer cone) the head-designer Mikko Hyppölä has been able to obtain the sort of treble performance he's been searching for.
The goal hasn't been so much to achieve with a single unit a treble extending up to 20kHz than to have in every way a linear and seamless HF response, where transient attacks are reproduced accurately and the highs are not "unbroken".
In this regard too, the Spiro is quite a successful speaker. On the one hand, the violin's highest harmonic overtones come out clean and sharply. On the other hand, cymbals and other instruments with non-harmonic overtones are being reproduced with no artificial hiss. The treble is less "dry" and less uninformative than what can be found of in some larger widebandwidth units, although not entirely free from certain "treble generosity" endemic to all WB drivers, I guess.
The ingenious part of the Spiro is its specialty called "absorption waveguide", the purpose of which is to control the speaker's directivity characteristics by suitably acoustically EQ'ing the response. It's not entirely rare to see horns and waveguides and even Hemholtz resonators built into single-driver widebandwidth loudspeakers, but the sort of device that covers the unit in the Spiro I don't remember having seen before.
The absorption waveguide has a layered structure with three different dampening material: foam, pulped volcanic rock wool and lambswool. The density and amount of each has been carefully chosen in order to affect the Spiro's free-field and room responses.
As a result, the sound is more immune to the room's peculiarities than without the waveguide; it's more predictable when taken from one room to another; it's more unified; and it retains its character in a wide listening area; and so on. In other words, many good things ensue from the waveguide.
From above we see that the one who designed the Northnuance Spiro (Mikko) is not an impractical daydreamer. The speaker features many technical solutions that are really planned to be beneficial to the sound, including the decision to use a single driver.
Many single-driver speakers on the market are high sensitivity (>90dB) designs, not so the Spiro: with 1W it can produce only 83dB SPL, and therefore cannot be run with a small power SET amp. (It's not by accident that the world's most famous widebandwidth units are 7-8 inchers. The effective cone area of such a unit is nine times bigger than that of the one in the Spiro.)
According to the manufacturer, Spiro can do 97dB SPL with very little distortion. That means plenty of pure sound, for most mortals more than enough. No matter, it's clear that the speaker is not primarily designed for the wildest house parties, instead it's at its best when used for calm and quiet listening.
It doesn't follow, however, that the Spiro's direct and open and naturally detailed sound would be limited to a narrow branch of music. Not at all. Perhaps those who are into the heaviest heavy metal could not live with the Spiro's bass and lack of disruptive energy and burning brightness, but otherwise the speaker is surprisingly fairly omnivorous.
Spiro is a risk averter, and for a good reasons so. It is designed to please a wider audience (including women) with an easy and optimistic and immediately likable sound. Strictly from a hi-fi point of view I'd wished a tad more precisely defined presentation and a sound that would not grow with volume and that would more often have stayed on its own territory. But these ar minor remarks in relation to those aspects of the sound in which the speaker is good.
Over the years, I've heard many different types of single-driver speakers with a 3-5 inch (70-120mm) unit: in a baffle, with a rear horn, with a spiral horn, transmission lines, bass-reflex cabs, velocity porting cabs etc. Most of these have not dared to step into the market with such a small and therefore bass-shy cabinet as Northnuance with the Spiro.
On the other hand Spiro has a lot to offer over the frequency range where multiway speakers usually add a tweeter, and where other widebandwidth spekers must rely solely on what the chosen driver is or is not able to do. The time spent with the Spiro proved that the approach Northnuance has opted for with the Spiro has solid grounds.
Given all the effort (hundreds of simulations and prototypes) and expertice that has gone into designing and building the Spiro, I find it almost embarrasing that a pair of Spiro cost only 995 euros! The speaker may not be for everybody (no speaker is) but its price/quality ratio certainly is very good. And there are various color combinations from which to choose.