The engineers have been up to speed and have created a new woofer that's better than its otherwise pretty amazing predecessor. Read about the exciting design and creative solutions here.
The new and the old. The kinship is obvious when you see the new woofer on the left and the old one on the right. It's evolution at work.
If you think the woofers in these pictures look like something that's in any speaker, let me just say: Hurry, read on! To give you an idea of how special these speaker units from Danish Scan Speak are, listen to this point-by-point comparison. The magnet, i.e. the motor, of a good bass speaker of the same size as ours usually has a diameter of 72-85 mm. Here it is 110 mm. The voice coil, which works in the magnet fork, is usually 25 mm in size. Here it is 38 mm. On a good bass speaker, the diaphragm has a linear travel of +/- 3 mm. Here it is +/- 6.5 mm. Such differences come at a price, of course, and a Scan Speak costs about three times as much as an ordinary good woofer when we're talking about the version a DIYer can buy for his project. It's not just the objective data that's interesting. It's the creative engineering that really gives Scan Speak's level of ambition wings, in my opinion.
Slits act as traps for vibrations
The very conspicuous lines on the membrane are in fact continuous slits that are punched out in the process of casting the membrane. The slits are in an irregular pattern that minimises breakage of the membrane. They are filled with a sticky substance that dampens vibrations and every other slit has different materials injected that damp in different ways. And there are more fun solutions.
Big engine and no brake
The yellow centering disc that holds the voice coil in the magnet's yoke is not wave-shaped as usual. Therefore, it does not stretch and brake the diaphragm when the music has a strong energy discharge and requires large fluctuations of the moving parts. The magnet is the speaker's "motor" and its strength determines its ability to control the movement of the diaphragm. Copper rings (patented principle) in the magnet fork give the speaker less dynamic distortion, and the vent in the pole piece prevents air from compressing behind the diaphragm dust cap. It is therefore safe to say that something has been done to release the music's energy, and some of the built-in brakes normally found in a loudspeaker are much less in a Scan Speak Revelator.
How we improve the best
I'm sure no one will feel slighted when I claim that the Scan Speak 15W Revelator is one of the world's best 5½-inch bass/midrange speakers. When we developed the SA2K in the first place, we didn't end up using a completely rebuilt version. It was a version adapted for the purpose.
The old one. A frequency measurement of the woofer for SA2K, without cabinet and crossover. A wide dip around 1 kHz affects the overall impression. An improvement here will be audible.
A pure Formula 1 racer
When we designed the SA2K, we had the challenge that the speaker could risk playing itself to death. The high movement of the mechanical system and the absence of a braking function could send the diaphragm and voice coil into such wide fluctuations that both parts crumpled and sent the whole thing to the eternal speaker fields. A bit like a Formula 1 racer losing traction. If it goes wrong, it goes wrong. So we had to do something that has always bothered me a little. We had to use a form of aluminium for the voice coil. There's nothing sinister about that, because the material conducts the heat of the flywheel away and that's good. But the aluminium shape also acts like a coil (with one winding) and when it moves in a magnetic field, it will try to counteract the movement the more it moves. Like a brake. That's exactly the effect we were looking for, for the speaker to protect itself. It just sucked to put in a brake when so much had been done to remove them. In addition, the bass speaker for SA2K was the first Danish speaker to use wood fibre as a membrane material. A strong and lightweight material, it consists of five types of wood fibre and a binder. And it sounds great! Still, there was one thing we couldn't get rid of back then. Right around 1 kHz, our otherwise very hefty and fine woofer had a 2 dB dip in frequency response that we would have liked to have avoided.
Therefore, it is quite clear what evolution is all about
Evolution is about improving something that has been proven to work. That's why the new woofer also builds on the original basic design of Scan Speak's 15W Revelator. The engineers' task has been to find a way to eliminate the two blemishes of the previous version, namely the need to slow down the voice coil and the 2 dB dip at 1 kHz. Here, as in the talk of edge reflections, it is the engineering craftsmanship and meticulous approach that drives development.
The engineers got the job done
The first consideration was to identify how deep bass is actually needed. It is beyond doubt that even a small minimisation of the diaphragm's fluctuations could eliminate the need for a braking effect in the loudspeaker. We want to. The lowest E string on a bass guitar is around 41 Hz, which most small speakers are unable to reproduce. Conversely, surely that's exactly what you'd expect from a world-class speaker? The SA2K could do it with little trouble, but the Q113 should do it without grumbling. That's why a 40 Hz lower limit frequency is a goal in itself, and it will help give the soundstage a nice size. Hear how the task was solved.
Simulation of base response. Usable output down to around 40 Hz. That's really good for a speaker with a volume of just 10 litres.
New work distribution in the bass, without brake
The bass response of a bass reflex speaker occurs in an intricate interplay, reviewed in a previous blog post, which you can refresh here. The engineers have done an analysis that shows how much each part contributes to the bass response, for example you can see how much the diaphragm moves at different frequencies and how much air velocity is in the bass reflex port etc. Here the engineers could see that in the SA2K the woofer accounts for a slightly too large part of the total output. The bass reflex port could do a bit more without the air velocity being too high. Therefore, some new Thiele/Small parameters were calculated, based on a slightly stiffer suspension of the woofer cone and a change of the bass reflex tuning compared to SA2K. The Q113 Evolution gets (on paper) a bass reproduction like the SA2K, but it is more the bass reflex port that reproduces the bass. This results in lower distortion. The new woofer is now constructed with a fibreglass voice coil form rather than aluminium. This is an important goal. So it will be very exciting to hear the speaker without brakes!
Now with edge lubrication. The wide dip around 1 kHz appears to originate from the transition between the diaphragm and its suspension. So the new woofer gets a coating and the dip is gone.
The dive came from the edge of the membrane
The idea of fixing the 2 dB dip at 1 kHz is not new. It dates back to the early days of loudspeakers, when mechanical solutions had to be found to smooth out the frequency response of the loudspeaker. It is nevertheless an amazingly simple and effective method. The so-called edge lubrication lies as a bead of viscous material that is placed in the transition between the diaphragm and its suspension. In principle, the edge lubrication can be applied to either the front or the back of the membrane. We have put it on the front. We have kept the wood fibre membrane. Just coloured black.
The new. The edge smearing works and there is a fine and regular progression of the frequency response up to the 2 kHz or so, from where the sound radiation becomes more directive. This is important because we need to control the power response.
The parts for the Q113 Evolution are ready!
Q113 Evolution has come to the point where we have the speaker units ready, we have designed the speaker and we have simulated things working. Now we just need some test cabinets so we can get on with real measurements, part filters and listening tests with the Engineer readers. It's really exciting! Now we just need to make the final technological acquaintances with the restless boy of the class: the Q113 Revolution.
More news coming soon. The engineers are working!
