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-   -   Measuring speakers in-room. Practical considerations. (http://www.diyaudio.com/forums/markaudio/195647-measuring-speakers-room-practical-considerations.html)

chuyler1 29th August 2011 08:01 PM

Measuring speakers in-room. Practical considerations.
 
Just a quick update on the room placement suggestions people made.

https://lh5.googleusercontent.com/-r...0/P1040492.JPG

I ran some sweeps to check the frequency response. When located in the corners as seen above, I get significant gain from 40Hz to 80Hz but a major dip from 100Hz to 200Hz. This is the bass heavy sound I've been hearing. When watching movies, you get tons of thud and hip-hop bass...but it seems to come out of nowhere.

The rest of the response was very good except a sharp hump at 7K followed by a gradual roll off. Removing the tow-in on the speakers so you listen slightly off-axis removes the hump, but you sacrifice top end extension with the roll off occurring at 10k instead of 15k. There is definitely a sweet spot where you get just the right amount of treble without it jumping out.

Moving the speakers directly in front of my bookshelves and about 2 ft from the wall creates a much smoother curve in the bass dept. The low end gain is reduced but I get back the 100-200Hz region.

I also experimented with placing them on either side of the TV but it ruins the imaging. The center vocals become about as wide as the TV, rather than focused at the center.

So basically, the optimum spot is a no-go. I think I will likely leave them in the corners for daily use and bring them in front of the shelves for serious listening.

I also experimented with a 2.5w MiniWatt tube amp, a 10w chip amp, and my 50w receiver. All three produced relatively equal output on the RTA. I detected a bit of graininess from the receiver at loud volumes that wasn't there with the 10w chip amp, but it did a better job with the bass. The tube amp sounded great at low levels and had the lowest noise floor, but couldn't play loud enough. I wish there was a quick way for me to switch between them. I had to keep getting up and switching cables around so it was tough to really dig into what I was hearing.

silverhairbp 30th August 2011 04:03 AM

Interesting observations. Did you try any listening positions far out into the room, maybe even along the room's center-line? Was the 7K hump related to room position or was it an on-axis / off-axis problem? Was that 7K hump an issue listening to either instrumental music or vocals?

chuyler1 30th August 2011 04:30 PM

The hump is consistent with the reported frequency response. I get the appropriate on-axis rise, but it does not extend to 20Hz like the graph below when measured 1-2 meters from the speaker.

http://www.madisoundspeakerstore.com...g2-imp-opt.png

When listening on-axis it adds a slightly abrasive sound to trumpets and puts them sort of in your face. Switching to off-axis ~10 degrees removes the abrasiveness but sacrifices cymbals which don't cut through like they should and are slightly muted. Of the two options, off axis is definitely more enjoyable and you likely won't miss much...but it makes me curious to see what a super tweeter would do to the sound.

buzzforb 30th August 2011 06:02 PM

I would say this agrees with my listenings of the 10.2. I have some 7.3's on the way, hoping to get, more soundstage depth (width on 10.2 was fine), and more extended top end while maitaining tonal balance (less directivity). Runnning the 10.2's on tube amps seems to improve the dpeth issue, but this makes sense in keeping with tubes ability to make individual instruments bloom/standout somewhat in their place in the soundstage.

chuyler1 30th August 2011 06:38 PM

I will take some more measurements and post my findings...if it helps. I use a Behringer ECM8000 with TrueRTA.

FWIW, I did enjoy the sound when powered off my 2.5w tube amp. I just wanted more volume out of it. I couldn't tell you if the increased clarity was due to it's construction or simply lower volume. I didn't try it until late in my session and my ears were already tuned into a louder volume. On my next session, I will level match using the max volume of the MiniWatt tube amp so i do a better job analyzing the differences. However, I probably won't make the MiniWatt my primary amp simply because it won't be loud enough for watching movies.

buzzforb 30th August 2011 09:07 PM

I am going to try a F4 driven by grounded grid tube pre. Biased with ccs instead of resistors, it can swing the 20V for the F4 and is an easy build. Maybe I can get the best of both worlds.

markaudio 30th August 2011 11:41 PM

Quote:

Originally Posted by chuyler1 (Post 2691568)
I will take some more measurements and post my findings...if it helps. I use a Behringer ECM8000 with TrueRTA.

Hi Chuyler, Guys,
Please qualify your posts by letting guys know what measuring equipment you're using when making measurements. Post No. 141 should have included more information on how the measurements were taken and the equipments used. Many members don't know the limitations of low spec measuring equipment and issues on non-anechoic conditions. They become confused between the anechoic measured output of drivers and the effects of in-room measurement limitations, box design and room environmental factors. I get bogged down with emails following up from posts like No.141 (Chuyler) asking me why the driver performance and in-room measurements differ. Please help by making posts more comprehensive and qualified, as this benefits everyone.

Using a US$50 ECM8000 mic has limitations measuring the complete bandwidth of Full-Range drivers. Behringer's info sheet for this mic excludes the "actual" sensitivity of the device. Its useful range will be in in the regions of 50Hz to 15-kHz.

For more reliable measurement, I recommend Earthworks mics. Their M30 is a unit suitable for measuring reliably in the 20Hz to 20-kHz range. This Mic retails around US$650. We use Earthworks M50 as our primary and Linear's M53 as secondary, both these mics will give us reliable data readouts to +30-kHz anechoic. I can't speak for their performance in non-anechoic (room) environments but expect they would be better than cheaper mics.

In-room measurements can be useful to help you adjust your system set-up but they won't give you accurate data on your speakers themselves. For that, you'll need to isolate your speakers by getting them into an anechoic isolated environment.

Cheers
Mark.

planet10 31st August 2011 12:03 AM

Quote:

Originally Posted by markaudio (Post 2691883)
Using a US$50 ECM8000 mic has limitations measuring the complete bandwidth of Full-Range drivers. Behringer's info sheet for this mic excludes the "actual" sensitivity of the device. Its useful range will be in in the regions of 50Hz to 15-kHz.

That range is good for a calibrated ECM8000. From the graphs of my 4 calibrated ones i would say that the safe zone for an unclaibrated one is more like 100-7k

dave

silverhairbp 31st August 2011 12:21 AM

I cannot agree more strongly with Mark regarding recommended testing equipment. A serious hobbyist needs the benefit of good test equipment as much as a professional designer. As we strive for the best sound we can get, regardless of whether we're professional designers or amateurs, we should use test equipment that is at least as good as the results we expect. Using lesser equipment just makes the job of tuning that much longer and can lead to non-repeatable test results (read: "frustration").

But this is probably best addressed in a different thread, eh?

markaudio 31st August 2011 12:48 AM

Quote:

Originally Posted by planet10 (Post 2691900)
That range is good for a calibrated ECM8000. From the graphs of my 4 calibrated ones i would say that the safe zone for an unclaibrated one is more like 100-7k
dave

Correct, we don't know if Chuyler has calibrated his equipment, or the reliability of any calibration. My worry is Chuyler (and many other guys) assume the ECM8000 is capable of measuring reliably beyond 15-kHz.

I'm not trying to criticise Chuyler's efforts. He's making a very nice project build and commend his efforts. I'm letting guys know that its important for those who embark on measuring their systems in non-isolated environments with low spec equipment to understand the data generated will have limitations that could be mis-read.

Evan us pro's can slip up. Evan and me came close to radically changing the design of the Gen. 1 Alp10 because we kept getting weird test data in the upper mid-range from the sweep tests in the isolation chamber. Turned out to interference from the side walls of a thick baffle plate rather than the driver. Knowing what factors affect measurements is a major task in its own right. We spend many hours setting up for sweep test to isolate as many variables as possible.

Thanks
Mark.


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