Welcome! Need support, you got it. Or share your ideas and experiences.
Return to Planar Speaker Asylum
69.65.69.236
In Reply to: RE: Are my ears really that sensitive? posted by Davy on September 13, 2014 at 10:06:18
[my wife's got me shopping...or rather she shops and I sit on a aisle bench and pray...lol! This is me wriritng on phone while hooked to my PC via remote VPN. i have copied and pasted an earlier relevant post. ]
--start snip
...I mentioned that in recent times the availability of calibrated microphones has increased while the prices have come down. I have tested several units and they fare well vs my more expensive ones, at least for all practical purposes. In fact, the Dayton Audio iMM-6 Calibrated Measurement Microphone is less than $20 and works well with REW on PC/Mac (though it was originally designed for iPhones & Android). Look it up at Dayton (link below).
I wish I could offer a proper basic "how-to" but I am a bit short on time these days. ...count also on others who have similar experience to pitch in. You may also want to roam REW's forum on HometheaterShack.com
I do plan to place more emphasis on some practical examples of what can be achieved with REW or similar packages. Folks tend to become more motivated to learn when they see the usefulness.
Once they see how easy and practical it has become to measure, the real challenge is to remind them that some discipline helps achieve the best results.
---end snip
Follow Ups:
Thanks a lot for the info. Sounds very interesting. I can get that microphone you linked from Amazon UK ( double the price though!) . So I assume you just get an extension lead and plug it into the pc's (or soundcard's) mic input?
I will have to read up thanks for the advice I'll take a look at the Hometheatreshack site.
Is measuring FR and measuring distortion levels the most useful thing to use it for?
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.
Thanks for very much info and graphs. Looks like a really useful tool indeed. I haven't had time yet to read the hometheatreshack guides but will do soon and also use what you've written here.
Just a quick question for now though. How does it measure the room noise floor?
The room & ambient noise floor can be done in at least 2 ways:
- In RTA mode while playing nothing, the mic is just listening to the background noise. In the case shown earlier, above, I asked the program to average 16 continuous samples (about as many seconds, I think). When compared to the pink noise reads in the RTA, there's good SPL correlation if using the same input gain settings. I may repeat this up to 3 times when I suspect there's too active an external environment. Approaching thunderstorms, hot days (A/C) and delivery trucks are the worst offenders. A nearby soccer park contributes with crowd and whistle noises during weekends and some evenings.
- In "sweeps mode" I let REW try taking a sweep but I turn off the power amps. The program records the noise anyway. Right now I am on coffee break. So, I just took the one below remotely while my wife watches TV (the mic is in place). The sound is from the small speakers on the TV, not the surround system. She reports that the program is "The Chew"...they are cooking some delicious stuff...and I can only have a miserable tasteless snack, LOL!
Sorry didn't see this earlier. Thanks a lot again for the info. Will bear all that in mind when I eventually use this great program.
Post a Followup:
FAQ |
Post a Message! |
Forgot Password? |
|
||||||||||||||
|
This post is made possible by the generous support of people like you and our sponsors: