sbhattac@rnd.gba.nyu.edu (Shankar Bhattacharyya) (09/18/90)
Here are numbers for closed box alignments for a few drivers which look like good candidates for home made woofers. Separately, I will also post the numbers on a bunch of drivers which looked decent at first glance, but did not look so good when I worked them through. The numbers were generated by a C program of about 20 lines of code, the guts being in about 5 lines. Since there may well be errors in my code, I suggest that you check numbers out before you believe them completely. I posted formulae earlier. If anyone finds errors, please let me know. I should track down bugs in my code. Perhaps some woofer sophisticates would check some numbers? I would appreciate that, as, I am sure would anyone who might use these numbers. Some of the Q's were entered to 3 sig. figures, incidentally. I looked at every woofer in the Madisound and Audio Concepts catalogues, chossing those which looked like they had acceptable EBP (not too far from 50). Those are the only current ones I have. There are obviously other drivers out there. I tried to stick to drivers with polymer cones (much more rugged, and possibly better able to work as a rigid piston). With one or two exceptions, I have tried to avoid vastly expensive drivers. Dynaudio and Eton drivers are very highly regarded, so I have included some of those, including a couple which cost over $200 just by themselves. Finally, I have tried to restrict myself to drivers which are capable of producing serious amounts of bass in a closed box alignment. So I have stayed away from 6" drivers and other such things. Most of these drivers are 10" or 12" units. There are a couple of smaller ones. This article has the drivers which show promise. The Audio Concepts AC-10 and AC-12 look far better than anything else I have seen from either the Audio Concepts or Madisound catalogues. All frequencies are in hertz, volumes in liters. For convenience: 1 liter = 61 cu in 1 cu ft = 28.3 liters Dynaudio 24W100 $ 110 looks good, but expensive, for a small system Qts = 0.35, Vas = 132.00, Fs = 23.0, Qes = 0.45, EBP = 51.11 qtc alpha Vb Fc F3 (hz) (hz) 0.50 1.04 126.82 32.86 51.05 0.60 1.94 68.08 39.43 47.67 0.70 3.00 44.00 46.00 46.47 0.80 4.22 31.25 52.57 47.16 0.90 5.61 23.52 59.14 49.06 1.00 7.16 18.43 65.71 51.66 1.10 8.88 14.87 72.29 54.70 1.20 10.76 12.27 78.86 58.02 1.30 12.80 10.32 85.43 61.54 Dynaudio 30W54 $ 150 works very well with some bass boost Xmax is less than I would like, but may be Expensive, but conservatively stated. My 30W54 based possible within woofer makes quite enough noise for me. a budget of $200 Rolls Royce grade construction, excellent rise time. Qts = 0.36, Vas = 254.00, Fs = 22.0, Qes = 0.42, EBP = 52.38 qtc alpha Vb Fc F3 (hz) (hz) 0.50 0.96 264.15 30.81 47.88 0.60 1.82 139.20 36.97 44.71 0.70 2.84 89.29 43.14 43.58 0.80 4.02 63.16 49.30 44.23 0.90 5.36 47.43 55.46 46.00 1.00 6.85 37.10 61.62 48.45 1.10 8.49 29.90 67.79 51.30 1.20 10.30 24.66 73.95 54.41 1.30 12.26 20.72 80.11 57.71 Dynaudio 30W100 $ 240 looks quite promising; if you can accept a Qtc of 1.2, with its attendant 2 db respone hump Included because in the midbass, this is a hell of a driver. people are inte- Rolls Royce grade construction, huge voice coil, rested in Dynaudio excellent rise time. Too expensive for a budget woofer. Qts = 0.62, Vas = 269.00, Fs = 24.0, Qes = 0.80, EBP = 30.00 qtc alpha Vb Fc F3 (hz) (hz) 0.50 requires non-positive box volume -- not feasible 0.60 requires non-positive box volume -- not feasible 0.70 0.28 964.73 27.14 27.42 0.80 0.67 401.30 31.02 27.83 0.90 1.11 241.47 34.89 28.94 1.00 1.61 167.09 38.77 30.48 1.10 2.16 124.66 42.65 32.27 1.20 2.76 97.53 46.53 34.24 1.30 3.41 78.87 50.40 36.31 Audio Concepts AC-10 $ 50 Looks very good. One of only a few drivers of reasonable cost which will produce Xmax = +/- 7mm F3 below 40 hz in a closed box without bass boost. Excellent excursion. Among 10" woofers, this would probably be my choice. Qts = 0.44, Vas = 138.00, Fs = 23.0, Qes = 0.50, EBP = 46.00 qtc alpha Vb Fc F3 (hz) (hz) 0.50 0.29 473.70 26.14 40.61 0.60 0.86 160.56 31.36 37.92 0.70 1.53 90.14 36.59 36.97 0.80 2.31 59.85 41.82 37.52 0.90 3.18 43.34 47.05 39.02 1.00 4.17 33.13 52.27 41.09 1.10 5.25 26.29 57.50 43.51 1.20 6.44 21.44 62.73 46.16 1.30 7.73 17.85 67.95 48.95 Audio Concepts AC-12 $ 60 This looks stunningly promising. If I were building a woofer today, this is what Xmax = +/- 8 mm I would use. 30 hz, at respectable excursion, without bass boost. The numbers look much better than for the Dynaudios. Qts = 0.43, Vas = 240.00, Fs = 18.0, Qes = 0.49, EBP = 36.73 qtc alpha Vb Fc F3 (hz) (hz) 0.50 0.35 681.66 20.93 32.52 0.60 0.95 253.43 25.12 30.37 0.70 1.65 145.45 29.30 29.60 0.80 2.46 97.51 33.49 30.04 0.90 3.38 70.99 37.67 31.25 1.00 4.41 54.44 41.86 32.91 1.10 5.54 43.29 46.05 34.85 1.20 6.79 35.36 50.23 36.96 1.30 8.14 29.48 54.42 39.20 Madisound 1252DVC (dual voice coil) $ 40 Looks quite promising, but I have no idea how I should deal with the dual voice coil design. My numbers for this may be entirely wrong. But not as promising as the AC-12, or even the AC-10. Note the size required for Qtc=0.7. I would shoot for Qtc=0.8 with this driver. The Qts looks more suited for a vented box, but I think the box would be quite large. If you can live with that, this would produce very deep bass (guestimate; I haven't run the numbers. Qts = 0.36, Vas = 318.00, Fs = 19.0, Qes = 0.39, EBP = 48.72 qtc alpha Vb Fc F3 (hz) (hz) 0.50 0.93 342.30 26.39 41.00 0.60 1.78 178.88 31.67 38.29 0.70 2.78 114.35 36.94 37.32 0.80 3.94 80.75 42.22 37.88 0.90 5.25 60.57 47.50 39.40 1.00 6.72 47.35 52.78 41.49 1.10 8.34 38.15 58.06 43.93 1.20 10.11 31.45 63.33 46.60 1.30 12.04 26.41 68.61 49.42 Eclipse W1238R $ 50 Not bad, but I would prefer the AC-12. As with the Madisound driver, the Qts suggests a vented box, although the EBP, as with the Madisound, looks rather low for a vented box. Qts = 0.33, Vas = 280.00, Fs = 19.0, Qes = 0.37, EBP = 51.35 qtc alpha Vb Fc F3 (hz) (hz) 0.50 1.30 216.10 28.79 44.73 0.60 2.31 121.43 34.55 41.77 0.70 3.50 80.01 40.30 40.72 0.80 4.88 57.41 46.06 41.32 0.90 6.44 43.49 51.82 42.98 1.00 8.18 34.22 57.58 45.26 1.10 10.11 27.69 63.33 47.93 1.20 12.22 22.91 69.09 50.84 1.30 14.52 19.29 74.85 53.92 ---------------------------------------------------------------------- Shankar Bhattacharyya, Information Systems, New York University sbhattac@rnd.gba.nyu.edu ----------------------------------------------------------------------