........ once I dreamt of building my own Cremona speakers. To show you how ambitious and lofty the dream... Just look at the finishing, the sexy curves, the elegance of stature and etc etc etc. The techincals are equally impressive;
| System Type: | 3-way, Lute-shaped cabinet |
| Cabinet: | 32 individual layers of solid and laminated maple |
| Woofer: | 2 x7 in. sliced hard paper cone with Symmetric Drive motor |
| Midrange: | 6 in. sliced hard paper cone with Symmetric Drive motor |
| Tweeter: | 1.1 in. high-resolution Ring Radiator with copper cap motor |
| Crossover: | 300Hz / 3khz, non-resonant acoustic first-order, optimized acoustic phase response, highest grade components |
| Frequency Response: | 32Hz - 40kHz |
| Impedance: | 4 ohms, nominal |
| Sensitivity: | 90dB 1W/1m, 2.83V |
| Power: | 50-300W, without clipping |
| Finish: | Maple or Graphite ecologically sensitive medium gloss lacquer |
| Dimensions: | 8.9 x 17 x 42.9 inches (WDH) 225 x 430 x 1090 mm (WDH) |
| Weight: | 159 lbs / pr 72 kg / pr |
After searching through the local (Singapore) DIY forum, it seems making the cabinet myself to be the only choice based on my requirements - i.e. absolute control. This would mean investment in powertools. Most likely I'd be getting a rotary tool and some routing bits to make the holes and steps to be enable flush mounting of the drivers.
Initially, I wanted to treat this as a test or prototype,... but reconsidering the substaintial investment cost, it just don't feel worth it. So it has to be first and final effort. This means a cautious, systematic, detailed and precise approach to both design and execution.
The driver selections are pretty simple, all from ScanSpeak with the famous sliced paper cone. Checking with the local supplier Leda Resources, a simple 2-way system would cost S$1.3K just for the drivers alone. That, without getting the very expensive radiator tweeter ($1.2k/pair) as used in the Cremona!!!
this are the candidates;
Tweeter: D2905/990000 Revelator
Woofer: 18W/8531G00
I chanced upon this fantastic enclosure simulation software, Unibox. It uses the Theil-Small parameters to generate all manner of charts and what not for enclosure design. You can have closed box, vented box, bandpass, passive radiator and with various combination of drivers. You can even save charts for comparison. Surprisingly, it is just an excel worksheet!!
So I started playing with the tool and more or less finalised on my target design (this is specification design rather that form and finish). So how does the response charts look like? Here they are;
Now, that wasn't that hard.... and the result is pretty impressive.
So the next step is the x-over. A lot had been said about how difficult this part is without explaining in greater detail how or what is involved. I decided on the design for a 2nd-order Bessel slope after reading an excellent article from ESP (see article).
It ended up to be a pick and match kinda thing... know your alignment slopes - Butterworth, Linkwitz-Riley and Bessel. A typical 2nd order (12db/oct slope) is shown;
There are formula or calculation required - input a few impedance values and desired x-over frequency and voila - you get your textbook perfect values for your x-over network. Take a look at such a typical site here.
So how do you know the impedance and cut-over freq? All I did was take a look at the manufacturer supplied response graph - check out the impedance, select a relative wide overlapping area where the SPL is flat and take that mid point.
From the ESP page, it was also mentioned to tame the rising impedance of the woofer by means of a zobel network. The difference in driver sensivity is also attentuated by using a L-pad network. As previous, these are std design and their calculation are automated as provided in many similar internet site.
All I had to do now is order the drivers and the components for the x-over. After which is to design the enclosure to house all these at the right internal volume. Of course, the cabinet design would be quite simple even with my rusty mechanical engineering knowledge. No complex and critical calculation required as no human lives involve. :)
The choice of electronic part such as resistor, capacitor and inductor should be given some consideration. Prices varies widely from one make to the other... a good explanation on what makes a diff is outlined here.
So there you have it, the short and simple run down of what were to be a dreamer's hope against all hope. As it turns out, the whole thing is just a lesson in speaker DIY. Good thing I did not succumb to my initial excitement and ran out to buy these stuff. After aquiring more modeling and simulation software, it turns out that a much more thorough and interative effort is required to make this dream a reality.....