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Originally Posted by TheSuzie OK I'll bite with a few questions - Hope I am coherent - I have not slept yet
1. Have you devised a methodology to check how well your general calculatons about the lower end response match the cab you have built.? Hard to do in a real room, a good enough reference mic is fairly cheap at least.... I'll also be one to contend that a noise spectrum probably has as much or more real use than a swept sine for this purpose. Both have their place.
2. Without a way to measure actual mechanical displacement versus time, anything to do with response in the time domain - step or impulse response - will be somewhat speculative. Some lab somewhere has this gear but I bet they are designing drivers and not cabs. I think I am in agreement - unless a cab designer goes very far astray, audible transient response issues will not crop up within the intended range of operating frequencies as long as the drivers are being applied to their intended use.
3. Have you A/B tested your single driver cab versus a cab with a tweeter? If so what were your subjective impressions? Have you measured the top end output from the Deltalite?
4. Are you willing to share dimensional/construction details of your current prototype cab with any of us potential home builders either publically or privately?
I gotta get some sleep...
Peace,
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I am glad my article is good bedtime reading.
1. I don't have an anechoic chamber, so I have to be very careful about what conclusions I draw from my data. At the same time, I
assume that the basic electromechanical model is accurate. This assumption lets me draw broader conclusions from measured data, but of course leaves me incapable of actually testing the validity of the model.
I measure the response curve of the driver in near-field using a cheap electret mic element, and then compute the overall response curve of the ported system. That gives me a relative curve, to which I apply an absolute sensitivity scale by comparing with the model curve. My program generates a mixture of frequencies, then takes a FFT and reports the amplitude at those frequencies.
2. It is true that my step response curve is speculative, but again, I am treating the model as a given and drawing some conclusions directly from it without testing.
3. I first plan to try a cone midrange... any day now I will get around to ordering it. The top end of the Deltalite seems to agree qualitatively with the datasheet, with the proviso that I don't entirely trust a near-field measurement above a few hundred Hz.
4. Yes...
Internal dimensions = 14 x 16 x 9.75 inches
External dimensions = 15 x 17 x 12
Port = 8.375 x 1.375 x 10 deep
If you draw a cross section, you note that the shelf port goes almost all the way to the back. A challenge with small boxes is finding space for a port of large enough frontal area to avoid "chuffing." I expected to treat this as a port going around a corner, but misjudged the end effect a bit, so the tuning is around 37 Hz instead of whatever I had originally hoped for. The lesson is: Either make the port adjustable, or test it carefully before gluing everything together. The other thing to notice from the dimensions is that I am condemned to rebuilding the box anyway if I decide that I want the midrange.
Plywood is garden variety birch veneered stuff from Home Depot, 1/2". Judging from the edges, the material seems reasonably void free. I just butt-jointed it with wood glue, then glued in cleats around all the joints to reinforce them. Then I glued in some rather minimal bracing. I am not too worried about bracing since it is such a small box.
The whole thing is slathered in a few coats of poly. Note that the 2512-ii driver came with a rear gasket already installed, so I don't have to install gasketing. Also, I know that I have to get some padding onto the inner walls of the cab... soon.
