Home Theater Shack Forums
Epik Subwoofers manufactures world-leading high performance subwoofers for die-hard home theater and music enthusiasts who won't settle for anything less than the best.
PacParts, Inc.: Since 1969, PacParts has been supplying quality replacement parts & accessories from the most recognized manufacturers in the Consumer Electronics Industry.
GIK Acoustics: Home audio acoustics at its best... especially when you have help from the owners right here at the Shack!  Check out their very affordable acoustic panels!
Discount Merchant:  If you need a replacement bulb for your video device... look no further... save big!
ReliableHardware.com: A Reliable Source for Case, Cabinet and Acoustical Hardware!
Fi Audio: Infinitely amazing balanced high end musicality designed drivers!
SVSound: The Sound Authority in speaker and subwoofers as well as the astounding AS EQ1 Subwoofer Equalizer!
Elite Screens offers the finest in affordable projection screens.
Creative Sound Solutions: Loudspeaker kits and components for subwoofers, midwoofers, woofers and full range speakers!
Emotiva is your Home Theater Component Source for Audiophile Quality Home Theater Equipment at Factory Direct Prices
RAM Electronics: Audio, Video, Home Theater and Computer Cables.
Ultimate Home Entertainment: Providing home theater seating and accessories such as popcorn machines and signage... at very affordable prices!
Go Back   Home Theater Systems - Electronics and Forum - HomeTheaterShack > Equalization | Calibration > REW Forum
Room EQ WizardBFD Guide
Forgot Password?
Favorites Home Theater Links Donations Image Gallery

REW Forum

Are comparisons odious?

Discuss Are comparisons odious? in the Equalization | Calibration forum; Are comparisons odious? Hi The purchase of an ECM8000/Xenon 802 today instantly provided a chance to confirm the accuracy of the various testing ...


 Reply     Post New Thread
Views: 722 - Replies: 20  
Thread Tools
Old 04-14-08, 04:37 PM   #1
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Are comparisons odious?


Hi

The purchase of an ECM8000/Xenon 802 today instantly provided a chance to confirm the accuracy of the various testing devices in my possession.

Using the correct REW cal files my Galaxy 140 so closely matches my ECM8000/preamp combo as to make the latter merely desirable luxuries.

You chaps obviously did a superb job on the cal files and these devices do seem very similar from example to example.

The problems start when I try to compare my old/new RS analogue SPL meters with the above two.

There is obviously some disparity here which is quite probably the result of a simple testing error on my part: I had similar problems in matching the RS curves when I first obtained the Galaxy 140. I have tried both C-weighting and disabled. The ECM8000 and Galaxy 140 both had C-weighting disabled for their tests.

Rather than further damaging my few remaining brain cells it is very likely that you can point straight to the problem.

My old and new RS meters have near identical curves despite there being 10 years in age between them. They do not seem to share the same curves with the other two more expensive devices despite careful loading of the correct cal files for each REW test. Close matching of the position of the various mic capsules [on the tripod at the listening position] was achieved with rubber bands.



Thanks.


Forum Rules Reply With Quote
Alt Advertisement
Old 04-15-08, 06:51 AM   #2
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


Retested with all three SPL meters. One old RS , one new RS and Galaxy 140.

I didn't bother with the ECM8000 today because the Galaxy is so close.

C-ticked and not ticked for each meter in turn.

Correct cal.files loaded for each meter after clearing cal.file each time.

I downloaded the latest cal files from the download area.



The two RS meters match well despite the 10-12 year age gap. (Upper green curves)

The Galaxy 140 and ECM8000 match within a hairsbreadth.

Neither pair agrees with the other.

I started out hoping this test would be a useful comparison to save people wasting money upgrading their test equipment unnecessarily.


Forum Rules Reply With Quote
Old 04-15-08, 07:19 AM   #3
Shack Administrator
Platinum Supporter
Alias: brucek
User: #6
Since: Apr 2006
Posts: 7,181
  brucek is offline    
Re: Are comparisons odious?


I tried to come up with a reason why the Radio Shack meters don't compare well to the better Galaxy and ECM, but I don't have any idea.

The C-Weight must be enabled on the meters themselves. The ECM is a flat mic so it has no C-Weight switch.

The C-Weight in REW is only a factor when measuring outside the range of the REW calibration file.

Most meters and microphones are quite accurate at 80Hz and require little or no compensation, In fact you'll find all the cal files are basically zero at that point. Your comparisons should be normalized to 80Hz.
My RS meter is fairly close to my ECM and so are Sonnies, so I have no answer for you. Wish I did. We have had discussions about RS changing capsule suppliers at various times, so I suppose it makes the RS meters a shoot.

brucek


Forum Rules Reply With Quote
Old 04-15-08, 07:32 AM   #4
Senior Shackster
Alias: Doug
Loc: Juliette, GA
User: #15964
Since: Jan 2008
Posts: 218
  DougMac is offline  
Re: Are comparisons odious?


Your dilema reminds me of an old Chinese saying:

"A man with one watch always knows what time it is. A man with two watches never knows what time it is."

Doug


Forum Rules Reply With Quote
Old 04-15-08, 02:58 PM   #5
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


brucek

Thanks.

I feel this has to be related to the cal files.

Nothing else changes when the next meter is connected.



DougMac

Abandon hope all ye who enter here! (I have a lifetime's interest in clocks)


Forum Rules Reply With Quote
Old 04-16-08, 06:27 AM   #6
Elite Shackster
Alias: Steven
thewire's Avatar
Loc: Midwest
User: #9828
Since: Jun 2007
Posts: 1,218
  thewire is offline  
Re: Are comparisons odious?


My theory is that the differnet mic except the RS meters are running on a different voltage and this is why they read different. Here is an example of with a digital RS meter mic plugged in to my sound card and (green) without. Turning off the mic has a similar result.

Name:  mic and no mic.jpg
Views: 182
Size:  93.9 KB


Forum Rules Reply With Quote
Old 04-16-08, 07:41 AM   #7
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


Quote:
thewire wrote: View Post
My theory is that the differnet mic except the RS meters are running on a different voltage and this is why they read different. Here is an example of with a digital RS meter mic plugged in to my sound card and (green) without. Turning off the mic has a similar result.
I am swapping the same 9 Volt battery between the meters to exclude random variations.

Here's an new REW graph for your entertainment. RS meter V Galaxy 140.

I hope the annotation is easily understandable.

CW and AW refers to meter switch weight settings.

Cal/No Cal refers to REW meter cal file loaded under Mic/Meter. [33-2050.cal]



Forum Rules Reply With Quote
Old 04-16-08, 08:00 AM   #8
Shackster
Alias: Matt
Loc: UK
User: #951
Since: Jun 2006
Posts: 15
  3ll3d00d is offline  
Re: Are comparisons odious?


cross-post from avforums for completeness

it looks to me like that meter needs the RADIOSHACK-33-2055_4050.cal file. This would take off 6dB @ 20Hz, ~13.5dB @ 10Hz and 10dB @ 7Hz which I reckon would make it map reasonably closely to the galaxy curve.

if so then this goes back to the "how do you know which cal file to use?" issue


Forum Rules Reply With Quote
Old 04-16-08, 09:08 AM   #9
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


Quote:
3ll3d00d wrote: View Post
cross-post from avforums for completeness

it looks to me like that meter needs the RADIOSHACK-33-2055_4050.cal file. This would take off 6dB @ 20Hz, ~13.5dB @ 10Hz and 10dB @ 7Hz which I reckon would make it map reasonably closely to the galaxy curve.

if so then this goes back to the "how do you know which cal file to use?" issue
Well done!

I was using the 33-2050 cal file for my new RS meter.

It really needed the old meter cal file. 33-2055-4050

Another senior moment!

I'll post a properly annotated graph later.

ECM8000/Galaxy 140 and New-Old RS SPL meters.

For the moment here's just the Galaxy 140 and RS meters with the correct cal. files and 1M sweep.



Forum Rules Reply With Quote
Old 05-30-08, 11:47 AM   #10
Shackster
Alias: Dent
User: #416
Since: May 2006
Posts: 41
  Dent is offline  
Re: Are comparisons odious?


Chrisbee,

Would you be able to do a sweep from 5 to 20000 Hz with the ECM8000 and the Galaxy CM-140? I'm just curious to see how they compare when you do it. I believe when you hook up the Galaxy to do the sweeps that the C-weighting option in REW should definitely be checked. Someone else can correct me if I am wrong.


Forum Rules Reply With Quote
Old 05-31-08, 05:14 AM   #11
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


Okay.

First graph ECM8000 at listening position head height C-weighting ticked and unticked.



Second graph Galaxy 140 C-weighted ticked and C-weighting unticked.



Third graph ECM8000 and Galaxy 140 together. With and without C-weighting.



All graphs 1/2 octave smoothing.

I need to work on my frequency response!


Forum Rules Reply With Quote
Old 05-31-08, 12:07 PM   #12
Shackster
Alias: Dent
User: #416
Since: May 2006
Posts: 41
  Dent is offline  
Re: Are comparisons odious?


Thanks a lot Chrisbee! This is exactly what I wanted to see. I guess there are variations when measurements are compared with those done on different days. In your graphs at the very beginning of this thread with the Galaxy and ECM8000 they were pretty much spot on from 5 to 200 Hz (which were the limits of your graph at that time). With these latest graphs, the Galaxy and ECM8000 only seem to match from about 19 Hz to 225 Hz except for that "dippy" area at about 175 Hz where it doesn't match. Above 225 Hz the two meters compared to each other are all over the place.

I assume with the middle Galaxy graph that the response that is higher from the 2500 Hz area and up (greenish-blue line) is the C-weighting checked line and the lower (more bluish color line) one is the C-weighting unchecked line.

From "maybe" about 5000 Hz or so to 20000 Hz the Galaxy follows a general trend of the ECM8000 but it is by no means matched. I wonder how Ilkka gets his calibrated mic and Voltcraft/Galaxy meter/mic to match so closely:
Quote:
Ilkka wrote: View Post
Sorry that it took so long, but here are the measurements. It looks pretty good.

Again, Chrisbee, thanks a lot for doing this.


Forum Rules Reply With Quote
Old 05-31-08, 12:26 PM   #13
Shack Administrator
Platinum Supporter
Alias: brucek
User: #6
Since: Apr 2006
Posts: 7,181
  brucek is offline    
Re: Are comparisons odious?


Quote:
C-weighting unchecked line
The ECM8000 is a flat mic. It has a calibration file that covers the entire audio band. The C-Weight checkbox has no effect.

The Galaxy is a C-Weight meter. The calibration file only extends to 200Hz, therefore the C-Weight box must always be checked.

brucek


Forum Rules Reply With Quote
Old 05-31-08, 01:01 PM   #14
Shackster
Alias: Dent
User: #416
Since: May 2006
Posts: 41
  Dent is offline  
Re: Are comparisons odious?


Quote:
brucek wrote: View Post
The ECM8000 is a flat mic. It has a calibration file that covers the entire audio band. The C-Weight checkbox has no effect.

The Galaxy is a C-Weight meter. The calibration file only extends to 200Hz, therefore the C-Weight box must always be checked.

brucek
That is what I figured was correct also.

Was my assumption correct regarding the middle Galaxy graph, i.e. that the response line that is higher (greenish-blue line) from 2500 Hz and up is the measurement with the C-Weighted check box checked in REW?


Forum Rules Reply With Quote
Old 05-31-08, 01:21 PM   #15
Shack Administrator
Platinum Supporter
Alias: brucek
User: #6
Since: Apr 2006
Posts: 7,181
  brucek is offline    
Re: Are comparisons odious?


I assume so, but really, with respect to the measurer, doing graphs with a C-Weight meter with the box unchecked just adds confusion. In fact, comparisons are quite difficult to do between two mics and fraught with all sorts of chances of errors with regard to element positional differences and quckly changing responses.......

The ECM and Galaxy are fairly reliable for home use with the cal files we provide for full range. The Radio Shack meters are not. That's about it.....

brucek


Forum Rules Reply With Quote
Old 05-31-08, 01:25 PM   #16
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


It was all a bit of rush so I rubber banded the two together to ensure coincidence of the microphone capsules. They were then mounted on the tripod together. There were almost insignificant variations of level which I adjusted out in REW. I'm still rather surprised at the variations at different frequencies. It comes down to: Which do you trust?

Thanks brucek. I should have posted the final graph of the ECM8000 sans C-weighting against the Galaxy 140 with C-weighting for a simpler comparison.


Forum Rules Reply With Quote
Old 06-02-08, 12:16 AM   #17
SRR
Shackster
Alias: Tim
User: #20375
Since: May 2008
Posts: 36
  SRR is offline  
Re: Are comparisons odious?


Try a better preamp then the behringer stuff, even a m-audio DMP3 will give better results. I don't think the 802 mixer has an EQ bypass and I would never trust it for measurements.


Forum Rules Reply With Quote
Old 06-02-08, 02:20 AM   #18
Elite Shackster
Alias: Chrisbee
Chrisbee's Avatar
User: #33
Since: Apr 2006
Posts: 1,011
  Chrisbee is offline  
Re: Are comparisons odious?


Quote:
SRR wrote: View Post
Try a better preamp then the behringer stuff, even a m-audio DMP3 will give better results. I don't think the 802 mixer has an EQ bypass and I would never trust it for measurements.
One of our members has checked the Xenyx802 FR in loop with REW: It doesn't look too bad at all provided we all avoid the area below 4Hz. The M-Audio model is 4 times the price and will only ever be used for REW testing. Moving the microphone 4" in my room would make a far bigger difference in FR than changing the preamp.

http://www.hometheatershack.com/foru...x802-loop.html


Forum Rules Reply With Quote
Old 06-02-08, 07:30 AM   #19
Shack Administrator
Platinum Supporter
Alias: brucek
User: #6
Since: Apr 2006
Posts: 7,181
  brucek is offline    
Re: Are comparisons odious?


Quote:
Try a better preamp then the behringer stuff, even a m-audio DMP3 will give better results. I don't think the 802 mixer has an EQ bypass and I would never trust it for measurements.
I'll have to disagree. The 802 is actually quite a good preamp, and bypass isn't necessary since you can calibrate out any response anomolies to zero by including the preamp in the REW soundcard calibration file. It's quite simple to do. This then removes its response from the measurements and renders it flat.

But, if didn't want to include the preamp in the cal file it has a completely acceptable response.

Here's a graph of the 802 with the EQ in detent, using standard REW vertical graph axis, from 5Hz to 20KHz. The response is completely adequate.

Name:  EURO ub802loop_response.jpg
Views: 101
Size:  71.4 KB

brucek


Forum Rules Reply With Quote
Old 06-02-08, 12:59 PM   #20
SRR
Shackster
Alias: Tim
User: #20375
Since: May 2008
Posts: 36
  SRR is offline  
Re: Are comparisons odious?


Just wondering but are you taking into account the impedance of the microphone plus phantom power into the mic VS the input impedance of the board, to come to the conclusions that the lowest priced mixer in existence is good enough? Please ask your local pro shop what's the return rate on them happens to be. V.S. a very respected for the price DPM3 happens to be?; QC is not in Behringers natural language, I would never trust a behringer mic pre in my studio. Volume control for my monitors was a stretch, other then that a tracking headphone amp, patchbay, and now a 1124P for my subs....no further I say, but watch I turn around and buy a XXXXXX Behringer cause I just can't afford proper stuff. I am not trying to be confrontational just if you are going to do it, I guess do it right or go home?


Forum Rules Reply With Quote
Old 06-02-08, 02:15 PM   #21
Shack Administrator
Platinum Supporter
Alias: brucek
User: #6
Since: Apr 2006
Posts: 7,181
  brucek is offline    
Re: Are comparisons odious?


Quote:
if you are going to do it, I guess do it right or go home?
I guess that's correct since most people on this forum do use this mixer only for the home. After a lifetime in engineering, I've come to know that it's all about compromise. The 802 is a perfect example.

The 802 mixer is being used to measure subwoofer response for home use, where the slightest microphone element positional difference can result in a response change of several dB. Do you really think I care about the impedance spread between the mic and line-in inputs? This mixer is completely adequate for home use and anything more would be somewhat wasteful. The money would be better spent elsewhere.

Quote:
Please ask your local pro shop what's the return rate on them happens to be
Why would I care? Mine has been working for years. We've not had anyone here complaining about the 802's reliability. If it breaks, take it back and they'll give you another one.

brucek


Forum Rules Reply With Quote
 Reply     Post New Thread

« Home Theater Shack > Equalization | Calibration > REW Forum »

« Previous Thread   Next Thread »

Bookmarks
Thread Tools

Posting Rules
You may not post new threads... You may not post replies... You may not post attachments... You may not edit your posts

BB code is On... Smilies are On... [IMG] code is On... HTML is not allowed!




Parts Express: The #1 Internet source for all your DIY and electronics needs!

Ultimate Home Entertainment

This site is best viewed with a screen resolution of 1280 x 1024 or higher!

All times are GMT -5. The time now is 02:07 AM.



Powered by vBulletin
Copyright ©2000 - 2009, Jelsoft Enterprises Ltd.
Vendor Tools vBulletin Plugins by Drive Thru Online, Inc.

Copyright ©2006 - 2009, Home Theater Shack, LLC.
John Mulcahy and Sonnie Parker - ALL RIGHTS RESERVED!



Projector Screens   AV Carts   Lectern   WhiteBoards   Audio Video   HDMI Cables   Multimedia   AV Blog
Massage Chairs   Wall Fountains   Bath Vanities   Electric Fireplaces   Bunk Beds
Dish Network     Dish Network deals




Sponsor/Vendor Ad Rates

Search Engine Friendly URLs by vBSEO 3.3.0

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331