Measuring speaker with rear firing passive radiator

[lowerFE]

Hi,

 

I want to drag my speaker outside to measure bass performance of the speaker. How would I properly measure a speaker that has rear firing passive radiators?

 

Thanks

[Contrasseur]

Measure at 1m and 10m groundplane facing the driver. The longer distance will ensure you're getting a good sum of the two at low frequencies. The PR will only have significant output at the bottom of the bandwith. At these frequencies your enclosure is acoustically small and therefore omnidirectional. Measuring facing the driver will ensure you accurately capture higher frequencies where the system is acoustically large (ish), and baffle step and diffraction could come into play.

[Ricci]

Measure at 1m and 10m groundplane facing the driver. The longer distance will ensure you're getting a good sum of the two at low frequencies. The PR will only have significant output at the bottom of the bandwith. At these frequencies your enclosure is acoustically small and therefore omnidirectional. Measuring facing the driver will ensure you accurately capture higher frequencies where the system is acoustically large (ish), and baffle step and diffraction could come into play.

 

Pretty much.

 

If the driver is aimed at the mic the error will mostly be in the deep bass where the PR contribution is a little bit under represented. If the sub is turned where the driver and PR fire sideways the low end will be close in shape (down a bit in SPL) but the upper bass range will be rolled off a bit and will get increasingly worse as frequency increases.

 

Also try to make sure that any large surfaces or buildings are as far away from the speaker and the microphone as possible.

The 10m measurement will more accurately represent the total blended output of the system on the low end. However 10m measurements require large open distances and the SNR is usually very bad. Try to use an output level that is high but not so much as to drive the speaker into compression or heavy distortion. If the system is passive 20v or 28.3v are good input levels usually. Make multiple back to back measurements and average them and apply a bit of 1/12th or maybe 1/6th smoothing if needed. The 1m measurement will not require smoothing. Use the same output level as the 10m measurement. Those 2 measurements can be used to develop a correction file for the 1m measurement. If 10m has too much noise you can try 5m or 4m.

[lowerFE]

Thank you very much Contrasseur and Josh. 

 

I was able to do measurements at an empty parking lot where I was at least 100 feet away from any reflective surfaces. Unfortunately the speaker does not have enough headroom to do a 10 meter measurement at an acceptable SNR. I just did a measurement with the woofer facing the mic 1 meter away. I ran out of time to try making a correction file, and I'll try that next time.

[Contrasseur]

One good measurement is better than none. Extrapolating from Ricci's measurements of the LMSR-12 Dual 15" VMP, your 10m f3 will probably be lower than the 1m f3.