Before you do your own simulation of the bass response in a virtual Q113, say hello to Neville Thiele and Richard Small. They are two of the speaker industry's greatest pioneers and without them, speaker building would be a circus.
Without the so-called Thiele/Small parameters, part of the development of a loudspeaker would be extremely slow, based on pure guesswork and any progress would be more luck than sense. Part of the story is that Thiele published a scientific paper on loudspeaker calculation as early as 1961. No one bothered to look at it. It wasn't until 1972, when it was reprinted through AES (Audio Engineering Society), that anything started to happen. A few months after the publication of the article, loudspeaker manufacturers started advertising their Butterworth, Chebyshev and other bass reflex principles, all of which stand on the shoulders of Thiele/Small's groundwork. Consumers of the time could have no idea what had happened! People don't read AES papers, but fortunately the speaker manufacturers did. What had Thiele and Small created?
Example of an equivalent diagram of a woofer, in this case a Scan Speak 15WU.
They made a mathematical equivalent of the speaker
Thiele and Small's contribution to the art of loudspeakers consists in a kind of translation, where the electrical and mechanical properties of the loudspeaker are rewritten in mathematics. A transfer function, in other words. With three basic Thiele/Small parameters, you can calculate how a given woofer behaves in a given cabinet. The method is even predictable because speaker manufacturers now disclose the Thiele/Small parameters under the technical specifications of their speaker units. Today it is difficult to imagine a speaker world without Thiele/Small, because although sound must be experienced with the ears, it is important to have precise knowledge and some reliable tools to reduce the amount of black magic. Good news is that four Danes have expanded the Thiele/Small model, with some new advanced parameters.
Danes have expanded Thiele / Small
An AES article from June, 2010 is interesting for us with speaker glasses on, because here four Danes publish an article highlighting the need for a better Thiele/Small model. One is Claus Futtrup, who is development manager at Scan Speak A/S. He says: "The Thiele/Small model ignores some not unimportant effects around the speaker unit, namely frequency-dependent damping and coil induction. At the same time, it has compensated by over-simplifying the situation around the cabinet calculation. It is all "boiled down" to a T/S model, where you have to do certain things in the cabinet simulation (QL = 7), to compensate for the simplifications. Advanced parameters separate the device and the cabinet, so that the effects appear separately. This is more accurate, it gives better simulations and the model allows you to "extrapolate" better from free air to in-box and you can better explore more varying amounts of damping material", Claus Futtrup concludes. For a project like Loudspeaker Q113, it is obvious to use the best methods, especially when the readers can also participate.
Calculate yourself. Download Scan Speak's free advanced data simulation tool and make your own calculation on Q113.
Calculate Q113 yourself with the new advanced model
With a handful of extra data in hand, you can no longer use the usual calculators, so Scan Speak has created their own, which can be downloaded for free. Find it here. Above you can see the data used to simulate the 15WU woofer in an 8.3 litre woofer reflex cabinet. This is the first attempt at a cabinet match for the Q113 in the Revolution edition. Try entering the same data and see what frequency response, impedance, diaphragm excursion, bass reflex port air velocity and group delay the program calculates for you. Afterwards you can experiment with making the cabinet bigger or smaller, changing to closed cabinet, changing the port diameter and many other things. I hope you will play along. It is quite interesting.
Here is Scan Speaks 15WU. The bass speaker that is designed to sit in one version of the Speaker Q113.
Tell me if you make a discovery
If you make a discovery that could benefit the Q113 or any other speaker project, please post it in the comments section of the blog. It could be something about the amount of damping material, the port diameter, the tuning frequency, the DC resistance of the crossover components, the cabinet width or a whole sixth thing. It's impossible for me to calculate all the hundreds of possible adjustments one can make. And there's one more reason. One discovery might also be of benefit to others building speakers. Nobody can know what a new discovery is, so better write about one observation too much, than one too little.
Now a very spartan Q113 has been built
In fact, a couple of very simple test cabinets have just been built by Speaker Q113. They're not going to win any design awards, because they're built for a single purpose. We'll see if we can generate our own specs on the Scan Speaks 15WU woofer. More on that next time, when we unleash the LEAP 5 program, the loudspeaker industry's best and most advanced computer program. Hope to see you on the blog for a chat about simulations on the woofer 15 WU with Scan Speaks online program.
