Quote:
brucek wrote:
 So with a ported design, where does someone correctly take a nearfield measurement to ensure optimum assist from the port effect while eliminating as much effect as possible from the room?
Your graph shows exactly what I would expect.
Right at the cone, we see the pure speaker output without the port effect (more like sealed I suppose).
Then right at the port output, we see the port assist.
Where do they combine to produce the pure speakers total output before the room wrecks it?
My limited knowledge of speaker design is showing.... Steve? Ilkka? Sonnie?
brucek |
Unfortunately it's impossible to take an accurate near field measurement with a ported subwoofer. One needs to place the mic at least 2 meters away from the subwoofer in order to get a good summation of the driver and port output. Of course at that distance room does its thing and it can't be considered as a NF measurement anymore. So an anechoic or GP environment is your only chance. REW's averaging function shouldn't be used to predict the combined response, it's nowhere near accurate method.
It's not useful to try to measure only the port's output either. Port's output will be attenuated heavily around 1/2 octave below and 1/2 octave above the tuning frequency (already around 5 dB down). Anywhere else driver's output will be much higher. Around an octave above the tuning the port doesn't contribute to the combined frequency response at all (more than 10 dB down). So in order to get an accurate measurement of port's output, one would need to mute the driver. And we all know what happens then...or should I say, what doesn't happen.
In-room NF measurement is pretty tricky thing with sealed subs too. Almost every time some amount of room interaction is still being present and can be seen in the measured frequency response. One should understand that it's not easy to measure waves having wavelengths of several meters in small enclosed spaces.