44605
From: Wim, [91.86.111.172]
Subject: newbie questions
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Hey all I'm new to subwoofer building and stumbled on this site when i wanted to convert my old car subwoofer to a living room subwoofer Is there a site or page that explains it all from the very beginning? I must confess i'm a bit lost. I calculated the T/S parameters and came up with a very high Qts, did i calculate wrong or is it just an unuseable driver ? anyway, here are my calculations Driver lanzar 12" Source Voltage Vs 1,955 Volts Source Resistance Rs 6,000 Ohms Speaker DC resistance Re 4,300 Ohms Voltage across R 1,139 Volts Source current (DC) Is 0,190 Amps Voltage across R at resonance Vm 0,280 Volts Current flow at resonance Im 0,047 Amps Resonance frequency Fs 26,300 Hertz Speaker impedance at resonance (Rm) Rm 35,893 Ohms -3dB current Ir 0,094 Amps r0 r0 4,067 -3dB voltage Vr 0,565 Volts Fh 28,650 Hertz Fl 23,900 Hertz Fs check 26,167 Hertz Cubic Feet of test box Vb 3,000 Cu. Ft. Resonance of driver in test box Fb 35,000 Hertz Vas 2,313 Cu. Ft. Qms 11,166 Qes 1,520 Qts 1,338 If the driver isn't all that bad as i think it is, Vb should i pick ? Thanks in advance |
44606
From: andrewt, [host86-149-46-27.range86-149.btcentralplus.com]
Subject: Re: newbie questions
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Hi, look at the design for an infinite baffle speaker. This loading suits higher Q drivers although your one may just be a bit too high. Infinite baffle benefits from lots of cone area and lots of baffle area to minimise the amount of EQ required to bring up the low end response. |
44617
From: wim, [91.86.117.8]
Subject: Re: newbie questions
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So i redid the entire test again 5 times with diffrent voltages and resistor values to see if i had a constant test result. I also brought some better measuring equipment from work ( a fluke 187 multimeter and a fluke 199 scope meter) They all came with similar results Fs 26,300 Fh 35,50 Fl 18,80 Vb 1,35 Fb 55,80 Vas 4,68 Qms 8,92 Qes 0,12 Qts 0,11 This is totally diffrent from what I got with a cheap multimeter and I'm assuming I have correct values now. Altho the QTS seems very small now, or am I mistaken ? |
44626
From: andrewt, [host81-129-79-3.range81-129.btcentralplus.com]
Subject: Re: newbie questions
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Hi, different results is putting it rather mildly. You have to decide if either can be believed. You to identify WHY the different equipment and/or method give different results. What effect test error for each parameter measured has on the accuracy of the results. Only when you understand why the results are different can you make an informed decision on which may be more accurate or both may be nonsense. BTW, I recently found that test temperature makes an enormous difference to Fs and all the other frequencies used to calculate the Qs. |
Responses:
[44640]
44640
From: wim, [91.86.113.54]
Subject: Re: newbie questions
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in aother thread of me I posted that i think the problem is with the amp dropping his voltage at low frequencies, it doesn't stay constant. I'm looking at a new amp now http://www.velleman.be/be/en/product/view/?id=9193 I hope this would be a nice amp to drive the unit. In the meantime, i'm looking for a diffrent amp i can borrow to mease the driver again. BTW the tools I used were FLUKE 187 multimeter and Fluke 199 digital osscilloscope that I borrowed from work. The metering should be accurate. As far as my performing the test correct, I do have basic electric/electronic knowledge. The first series of test i performed with a cheap noname multimeter I had lying around. So my best bet is getting my hands on a better amp first. |
Responses:
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