Hi,
I'd like to do some basic frequency response (SPL) measurements on 4 of my old 12" 4Ohms woofers (20+ yrs old, noname, no datasheet).
I have REW and a MiniDSP UMIK-1.
I thought I can do a classic measurement at 1m/2.83V/4Ohms (and then converted into 8 Ohms terminology, final response will be 3dB lower in reality than what I get here).
How do we measure to get not perfect, but acceptable results (no near-field yet) ?
1. signal is 50Hz, set volume pot 'til I measure 2.83V on the terminals unloaded ?
2. same as 1) but with the drivers attached ? (So, with real load).
3. same as 1) but with a dummy load of 4 Ohms resistor and then leave the pot as is, amp is 'calibrated' and finally change the resistor to the driver for the actual measurement ?
Amp is a little cheap $2 Class D module up to the task I think (25W RMS max). If the speaker is attached, speaker terminal voltages fall a bit below 2.83V (compared to unattached) and vice-versa, if I calibrate 2.83V on the amp with the volume pot while driver is attached, unattached the measured voltage is higher on the terminals.
Where's the truth ? (I assume I can do an amp volume pot 'calibration' to nominal value with a dummy resistor just to know the best pot setting for the measurement and then measure the speaker as a real load, but still not sure). Since amps are mostly voltage devices I don't think output voltage shall change at all between loaded and unloaded states but I might be wrong.
I'd like to do some basic frequency response (SPL) measurements on 4 of my old 12" 4Ohms woofers (20+ yrs old, noname, no datasheet).
I have REW and a MiniDSP UMIK-1.
I thought I can do a classic measurement at 1m/2.83V/4Ohms (and then converted into 8 Ohms terminology, final response will be 3dB lower in reality than what I get here).
How do we measure to get not perfect, but acceptable results (no near-field yet) ?
1. signal is 50Hz, set volume pot 'til I measure 2.83V on the terminals unloaded ?
2. same as 1) but with the drivers attached ? (So, with real load).
3. same as 1) but with a dummy load of 4 Ohms resistor and then leave the pot as is, amp is 'calibrated' and finally change the resistor to the driver for the actual measurement ?
Amp is a little cheap $2 Class D module up to the task I think (25W RMS max). If the speaker is attached, speaker terminal voltages fall a bit below 2.83V (compared to unattached) and vice-versa, if I calibrate 2.83V on the amp with the volume pot while driver is attached, unattached the measured voltage is higher on the terminals.
Where's the truth ? (I assume I can do an amp volume pot 'calibration' to nominal value with a dummy resistor just to know the best pot setting for the measurement and then measure the speaker as a real load, but still not sure). Since amps are mostly voltage devices I don't think output voltage shall change at all between loaded and unloaded states but I might be wrong.
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Do (2). You could do (3) but your amp should be constant voltage regardless of load so it doesn’t matter if your woofers are a perfect 4 ohm or not. Don’t do (1) since some Class D amps can break if you run them without a load.
When you’ve set your volume knob to 2.83VAC @ -50Hz at the speaker terminals, double check if your amp puts out 2.83V also at 1kHz (although your DMM/voltmeter may not be fully accurate at 1,000 cycles.
When you’ve set your volume knob to 2.83VAC @ -50Hz at the speaker terminals, double check if your amp puts out 2.83V also at 1kHz (although your DMM/voltmeter may not be fully accurate at 1,000 cycles.
Thank you for the confirmation. I'll check the amp at 1kHz too. I'm going to measure these woofers 'til approx. 1kHz anyway. Class D-s tend to be rather insensitive of load impedance, let's see what these little toys do 🙂
And you don't have to measure at 2.83 volts. Unless you want to measure sensitivity at that voltage. 2V would be the equivalent for 4 ohms.