Adam,
The nearfield is the best way to see what the driver is doing, without the effect of the baffle or room. As long as you keep the mic somewhere > x-max of driver and half the cone diameter you can in the near field- no need to get it too close that you might damage your mic or speaker. So as you've discovered, that blip at 600Hz is certainly real. As you've seen it's related to the pole vent, perhaps turbulent air flow. Damping with the tissue paper reduce it, but in real life use keeping the pole vent open may be beneficial for cooling of the voice coil. Of course, another way you can see if the blip was real was through taking a look at a zoomed impedance measurement.
REW's method of the exponential since sweep got an update recently (5.40 beta). Depending on your room, if you take a long sweep eg. 1M samples, or 256K samples x4 repetitions, you reduce the noise floor, thus better revealing the harmonics. Right now your environmental noise seems a bit high, but it's not clear if the SPL is calibrated or approximated.
Often higher order harmonics are really just your microphones noise floor getting in the way; I find it easier on the eyes if you just have a few colors eg. H2-H5. Yes, it's not lost on me the audibility of harmonics, if one has to work extra hard to reveal them. 😢
The nearfield is the best way to see what the driver is doing, without the effect of the baffle or room. As long as you keep the mic somewhere > x-max of driver and half the cone diameter you can in the near field- no need to get it too close that you might damage your mic or speaker. So as you've discovered, that blip at 600Hz is certainly real. As you've seen it's related to the pole vent, perhaps turbulent air flow. Damping with the tissue paper reduce it, but in real life use keeping the pole vent open may be beneficial for cooling of the voice coil. Of course, another way you can see if the blip was real was through taking a look at a zoomed impedance measurement.
REW's method of the exponential since sweep got an update recently (5.40 beta). Depending on your room, if you take a long sweep eg. 1M samples, or 256K samples x4 repetitions, you reduce the noise floor, thus better revealing the harmonics. Right now your environmental noise seems a bit high, but it's not clear if the SPL is calibrated or approximated.
Often higher order harmonics are really just your microphones noise floor getting in the way; I find it easier on the eyes if you just have a few colors eg. H2-H5. Yes, it's not lost on me the audibility of harmonics, if one has to work extra hard to reveal them. 😢
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Hi Thanh!
Yes, I think it is best to allow for air flow through the pole vent. Once I have a closed box, I wonder if the frequency of the resonance will shift, as it looks into a different impedance? I'm not terribly worried about the resonance, but it might be nice to address if possible. Perhaps I will try a few things, damping around the edges of the vent, without blocking it. I expect it is based on the volume inside the vent, and that there is nothing to be done if you wish it to continue moving air.
SPL is not calibrated (getting a calibrator for the holidays, so will have that to play with before long, woo!). I am measuring outside, there is traffic noise, I am in town.
The harmonics in REW fade to white - I am not sure what that means, if REW is indicating they are of low confidence. I see traces below the noise floor, and wonder how REW knows they're there if they are below the noise floor. Probably they have a help page that explains if I find the right place to look. I have just taken it at face value up to now.
Yes, I think it is best to allow for air flow through the pole vent. Once I have a closed box, I wonder if the frequency of the resonance will shift, as it looks into a different impedance? I'm not terribly worried about the resonance, but it might be nice to address if possible. Perhaps I will try a few things, damping around the edges of the vent, without blocking it. I expect it is based on the volume inside the vent, and that there is nothing to be done if you wish it to continue moving air.
SPL is not calibrated (getting a calibrator for the holidays, so will have that to play with before long, woo!). I am measuring outside, there is traffic noise, I am in town.
The harmonics in REW fade to white - I am not sure what that means, if REW is indicating they are of low confidence. I see traces below the noise floor, and wonder how REW knows they're there if they are below the noise floor. Probably they have a help page that explains if I find the right place to look. I have just taken it at face value up to now.
How REW knows is beyond my undergrad math knowledge...
You have to turn off "Mask harmonics below noise floor" - which is in the Controls function...
When there's plenty of background noise (measuring in the garden, carpark, outdoors.. try 4 or 8 repetitions of sweeps at a shorter length eg.)
I've switched to a new thread for the speaker I'm building with this woofer. I sorta figured people who just want to discuss the woofer can do so here (not that many will as it's NLA), and the other thread can be specific to my build.