How to make quasi-anechoic speaker measurements/spinoramas with REW and VituixCAD

[mwmkravchenko]

Yes I do. I'm just starting with the off axis measurments and I was almost sure that nearfield measurments will not work here. I was just curious if the ground plane would be better or in the open space

Ground plane measurement is the best in many respects. Remember that you need to have 2 metres groundplane to equal one metre 2 pi simulation. Also having done many many ground plane measurements, the odd smallish structure in the area will not make that much difference. If you orient your loudspeaker properly it will make zero difference. I am interested in how deep a null you get in the response between the front and rear driver. There will be some point where this happens.

Mark

 

[BURNART]

Ground plane measurement is the best in many respects. Remember that you need to have 2 metres groundplane to equal one metre 2 pi simulation. Also having done many many ground plane measurements, the odd smallish structure in the area will not make that much difference. If you orient your loudspeaker properly it will make zero difference. I am interested in how deep a null you get in the response between the front and rear driver. There will be some point where this happens.

Mark

I'm also expecting nulls. There's not any spinorama of this kind of speaker that I know.
The next thing that bothers me now is that woofers should be in some angle that depends of the distance between woofer and the microphone. Then if I'm rotating the woofer to measure off axis should I keep the angle? Because when I will reach 180 degrees I would have woofer that is angled slighly up not down if that makes sense.

 

[mwmkravchenko]

I'm also expecting nulls. There's not any spinorama of this kind of speaker that I know.
The next thing that bothers me now is that woofers should be in some angle that depends of the distance between woofer and the microphone. Then if I'm rotating the woofer to measure off axis should I keep the angle? Because when I will reach 180 degrees I would have woofer that is angled slighly up not down if that makes sense.

The angle of the woofer is tiny in comparison to the wavelength of the operation bandwidth of this loudspeaker. Even if you use it to 250 hertz the wavelength i is a little more than 1.3 metres. Close to the driver air behaves more like a fluid than a gas, as you get farther away the pressure dissipates and is more difficult to influence by the angle of the driver.

If you want to compare, you can test the loudspeaker as it would sit in your room, and on it's side and measure to determine if there is a large difference in the polar pattern from either set of measurements.

When I do polar measurements I use a thin sheet of plywood and lay it on the ground as a smooth surface. I live in the countryside, so no pavement for me!

Mark

 

[BURNART]

The angle of the woofer is tiny in comparison to the wavelength of the operation bandwidth of this loudspeaker. Even if you use it to 250 hertz the wavelength i is a little more than 1.3 metres. Close to the driver air behaves more like a fluid than a gas, as you get farther away the pressure dissipates and is more difficult to influence by the angle of the driver.

If you want to compare, you can test the loudspeaker as it would sit in your room, and on it's side and measure to determine if there is a large difference in the polar pattern from either set of measurements.

When I do polar measurements I use a thin sheet of plywood and lay it on the ground as a smooth surface. I live in the countryside, so no pavement for me!

Mark

So it is okay if it would look like this?

 

[fluid]

So it is okay if it would look like this?

Just leave it flat. You have two woofers at different angles in the cabinet so the advice of tilting the cabinet down won't work anyway. That method is assuming you have a woofer on a flat baffle and are trying to make the measurement valid to a higher frequency.

 

[mwmkravchenko]

So it is okay if it would look like this?
View attachment 356419

When you look at some of the directions for doing a groundplane plane measurement you do have instruction to angle the device under test forward about 10 degrees.

 

[BURNART]

When you look at some of the directions for doing a groundplane plane measurement you do have instruction to angle the device under test forward about 10 degrees.

Sure, that is what I'm aware of, but when you look at my terrible drawing then it will not work for this kind if woofer I think.
Either or I will leave it flat all the time or I should at 0 angle measurement make it 10 degrees forward then at 90 make it flat then at 180 make it 10 degrees backward to make it symmetrical.

 

[bigjacko]

So it is okay if it would look like this?
View attachment 356419

When speaker is on the ground baffle will become twice as long. Raise the speaker up in the air is better if it is convenient for you. But then you will really need to point into mic at that point.

 

[mwmkravchenko]

When speaker is on the ground baffle will become twice as long. Raise the speaker up in the air is better if it is convenient for you. But then you will really need to point into mic at that point.

If you do this you need to incorporate a correction for floor bounce. Your measurements are no longer anechoic.

 

[bigjacko]

If you do this you need to incorporate a correction for floor bounce. Your measurements are no longer anechoic.

That is a defect for doing this way. For low frequency it is not a huge issue. Too much compromise in life....

 

[Ageve]

Thank you for the excellent guide. I know it's less accurate when the speaker is placed close to walls or other speakers, but these results are still quite good. My Revel C426Be stays within +/- 2dB up to 16 kHz. Sorry for the funny looking rugs. I used them to dampen the floor bounce.

I'm using REW V5.30.5 (mac) and a calibrated UMIK-2.

Receiver: Denon AVR-X5200W (multi ch stereo with front/surround power amps off).
Amplifier: Audiophonics MPA-M400ET (Purifi)
Source: AppleTV 4K (sweep generated in REW, 0-20000Hz 256k 5.5s mono).

No EQ or room correction used when measuring.

Compared to measurement by Audioholics:

edit: Another measurement, at 30cm (+/- 1.8 dB from 200 Hz to 16 kHz). Not much difference, but the small dip at 2.6 kHz is gone (caused by the room).

Revel PerformaBe F226Be Tower & C426Be Center Loudspeakers Review

We reviewed the Revel Performa F226Be, a three-way floor-standing speaker, and the C426Be, a monster three-way center speaker using four 6.5" bass drivers to see if they live up to the brand reputation.

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