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RE: Are my ears really that sensitive?

Posted by JBen (A) on September 14, 2014 at 23:35:42

In Reply to: RE: Are my ears really that sensitive? posted by Davy on September 13, 2014 at 16:40:20:

Davy, for this particular microphone to work on PC, laptop or sound cards you are going to need an adapter like what I link to at the bottom here. The mic has a thin male connector format like what iThings & Android phones use. The adapter separates the stereo mic and speaker feeds. You may also want to get a pair of long cables so you can use the mic anywhere in the room and also send a REW reference output to your audio gear. At the preamp (or power amp) end of this one, a set of male RCA terminations (adapters), can go to the AUX inputs, for example.

As to what REW is most useful for, it may depend on your needs at different points in time. For a long while, FR, group delay, phase and impulse measurements come in handy most of the time; but waterfalls not too often. Lately, since REW's harmonic distortion & IM distortion measurements have become more reliable in the past 2 years, I often find them very useful while testing the more radical tweaks.

I do many quick FR takes with the RTA, feeding or playing pink noise at the source. However, I can switch to the more informative sweeps very easily. This graph below shows a "quick and dirty" RTA from a few days ago. The PLLXO bi-amp here is set to run both drivers in "same polarity" (see that slight center dip?) which I prefer. (Incidentally, flat enough as it looks, I have actually "de-tuned" the settings. This is not exactly how I really listen but that's another story. )

One thing that I like very much about recent versions of REW is having up to 30 sweeps per file. It makes it easier to compare results. For example, back in 2012 someone had asked me what kind of difference could the line-level bi-amping be making. I found enough of the old original xover parts to restore them in the left MMG. This allowed me to tell a portion of the story with measurements; many actually, all in one file. And not just the a whole MMG but also of its separate drivers. (BTW, knowing individual driver behaviors can be pure gold when tweaking the Maggies.) This image below is an example.

The many sweeps in one file has another huge benefit for me. I can repeat the same sweep a few times when I have concerns about ambient noise intruding into a more critical set of reads. I live in hot South Florida, where A/C compressors' noise easily intrudes into measurements. I schedule most of the critical acoustical measurements for verification in the cooler months. In the warmer months...I sweep and re-sweep, LOL! The group delay comparison of the two settings shown before (old parts vs PLXXO) was repeated. That hot June summer, they still did overlap in 2 out of 3 sweeps. However, look what a starting compressor did at the bottom of the PLLXO (orange) in this one. At this low a frequency it may not seem to matter for the MMGs. Yet, it would, had this been real and not noise-induced like it really was. (There can normally be very faint but real acoutical output down to 32hz in mine and other tweaked MMG systems).

The other thing I like about REW it the ample space to add details about each sweep. I chose this slide below to demonstrate it for 3 reasons. One reason is that it shows the various facilities and options in the program. The 2nd reason is that you can see the space to add comments about an individual sweep. I tend to cram in a lot of details in each here when conducting tests with a long-term intent. One forgets key details easily...and almost everything is really "key"...

The 3rd reason is to show how important it is to consider the room's noise floor in many cases. The first sweeps that I showed at the top display a minor bass peak at right under 40hz from both MMGs. However, THAT ain't really by the MMGs. You will actually find it in the noise floor as recorded below. In fact, it is this same kind of noise peak that distorted the group delay sweep (PLLXO, orange) shown above, back in 2012.

Lastly, there are some of these same sweeps and tests that can be conducted at the line level instead of acoustically. One usually hooks up the output of the sound card to the input (loopback) and adjust signal levels. There are other tests that require a more elaborate hookup setup. Of all these, at least testing the soundcard with a loopback the first time around may be a wise thing to do. Most newer sound cards are good enough by default but one never knows...and it is not hard to make sure that they meet specs.

• 3.5mm TRRS Adapter for PC   (Open in New Window)

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