Feature requests for loudspeaker design

dcibel

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Of course...REW is for room EQ, it is not purpose built for loudspeaker design. However, it has many features beyond EQ functions, and only a few more features to be fully there in my mind.

1. Full 2-channel measurement. Currently REW supports a semi-dual channel measurement where one channel is used as a timing reference. With that in mind, it should not be much of an addition to provide a complete 2-channel measurement. Record both inputs fully, and normalize the measurement input to the reference. This allows for a self-calibrated measurement, where all non-linearity of equipment upstream of the reference input is compensated for. This allows for compensation of nonlinear amplifiers, addition of filters and protection capacitors with very minimal impact on the measured frequency response. Addition of this feature would provide REW the same measurement functionality of loudspeaker design software like ARTA or SoundEasy.

The next 2 requests are available by simply exporting all REW measured data to VituixCAD, but I'm sure a lot of people would find the features built-in to REW a great benefit.
2. Polar response graphs. For each measurement, assign an angle, allowing for generation of a polar heat map type of plot.
3. "Spinorama". Using the same set of polar data, allow for generation of CTA-2034-A chart with in-room response and power response.
 

John Mulcahy

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Using a reference channel does not compensate for non-linearities, it can only handle linear effects. The loopback calibration does the same thing but has the advantage of being based on the channel being used for measurement rather than a different channel. Polar maps are on the todo list, but quite a long way down the list.
 

dcibel

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What I meant by nonlinearities is "linear distortion". If you have any meaningful difference between left and right channels on your audio equipment, that equipment should not be used for measuring, listening or recording. Loopback calibration as it is written in the REW documentation is only calibrating for the response of the audio interface, missing the amp, any filters you place in the loop (for example a protection capacitor that I mentioned above), the long leads running across the room...True loopback calibration would be completed at the speaker terminal, of course it can be done with just a couple resistors to feed back speaker level signal to line level input.

The Full dual channel configuration provides a lot of benefits, not only for loudspeaker measuring but for circuit analysis as well, it is essentially a differential measurement.
 

jschwender

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My AV System  
Front Speakers
Nubert digital pro
Other Speakers or Equipment
Philipd dss940
Please, can you explain what you mean by protection capacitor?
 

John Mulcahy

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You can include anything you want in the loopback measurement. Using another channel as the loopback response reference introduces errors due to channel differences, such as the effects of component tolerances.
 

dcibel

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Please, can you explain what you mean by protection capacitor?
A capacitor in series with the driver, providing a basic 1st order filter so you don't sent bass frequencies to a delicate ribbon tweeter for example.
 

dcibel

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You can include anything you want in the loopback measurement. Using another channel as the loopback response reference introduces errors due to channel differences, such as the effects of component tolerances.
The error is of absolute level only, which can easily be calibrated, and most irrelevant for a loudspeaker measurement. As a simple calibration process, I have individual input gain knobs on my USB interface, so I can run realtime measurement with both inputs and adjust the gain to match if I really need that sort of comparison. An automated calibration process already exists in REW for impedance measurement for example, where both inputs are utilized precisely as I suggest. I am only suggesting to be able to use both inputs in the same manner for acoustic measurement. Resistor tolerance is really out of the question for matching with individual gain on each input.
 
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John Mulcahy

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Not using the other channel as the response reference was a design decision made in 2011 to improve accuracy. Before that (REW versions 3 and 4) the loopback channel was used as the response reference but it was limited by the channel matching, which is often poor at very low frequencies due to the tolerances of coupling caps. ARTA is excellent software though, it has many features REW lacks.
 

dcibel

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People just need to stop using UCA202 thinking it is competent measurement gear.. ;)

Thanks for your consideration, I had always wondered why REW would not complete a full 2 channel measurement so it’s nice to have some context. Unfortunately I am likely to keep using ARTA for most of my measurement needs. REW has a nicer view for distortion analysis, and of course all the EQ functions so it still has its use cases for me.
 
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