Jump to content

Do the Vandertones REALLY require an RS33-2050?


Recommended Posts

Or, you'd think that a simple measurement microphone (there's lots out there for pretty cheap) could be used with a suitable app for a phone or similar device.  The software should not have any problem emulating the performance of the Radio Shack meter, if programmed suitably.  Some may already do this already.  Dunno.   Perhaps REW is capable of this measurement using a laptop.

I no longer own a RS meter, so I don't have a way to test this idea.  Just kibitzing...

https://asa.scitation.org/doi/full/10.1121/1.4964639

http://www.sandv.com/downloads/1507kard.pdf

Link to comment
Share on other sites

Agreed. A snazzy iPhone app could not only walk you through the process, but suggest adjustments taking into consideration the Q of each pot.

 

However, I'd be happy just to clicky-click @ Amazon and order a functional, reliable digital SPL meter and verify my setup.

Link to comment
Share on other sites

My RS meter must be at least 25 years old and is also getting a bit flaky.

It should be possible to create warble tones for a measurement mic with a more flat frequency response.

Instead of using test tones and an SPL meter, you could use a measurement microphone and an RTA (Real Time Analysis) tool, like the one in REW.  But you'd have to adapt Richard's calibration method to that.

It's a lot easier to do in the digital domain.  

 

Link to comment
Share on other sites

This is a complicated answer so I will give it a shot.  Measuring frequency response in a room is not easy.  First if the speaker is flat to 20Hz the measurement must compensate for room gain which is part of every recording.  The Radio Shack designer had the presence of mind to know idiots like me would be trying to measure speaker response  in a room.  This is why the meter is rolled off in the lower frequencies so that the user can work with flat response when it should be rising as the frequency goes lower.  The need to use an analog meter on fast is because a human watching the needle can visually eliminate the random noise (even in a quiet room) taking the reading that persists.  Anything digital must take several samples and average the result which is not accurate as the noise pumps up the average.  I have found the correction must only be about 60% because the brain cannot be fooled into thinking the room problems have been fixed but we can carefully minimize the negative effects.  My experience with all of the digital room correction disciplines I have tried (many) the result  differs even if nothing has been changed.  The result in the bass can be good but the midrange and high frequencies are not as open and clear.  After years I find using the old analog meter (easy to find) with correction in the analog domain within the subwoofer amplifier the most transparent with best imaging .  The whole process does not add one extra component or circuitry in the sacred main signal path we pay so much to keep clean.  I know the Radio Shack meter will become hard to find and Vandersteen will need to produce one.  It will have a rechargeable lithium battery, power switch, no range switch (fixed at 70db), no "A" or "C" weighting switch and an analog meter!  Simple, so it will be difficult for me to make a mistake at all the shows we do every year.  Having said all that "hearing is in the ears of the beholder".  However one decides to set up their Vandersteen's for satisfaction is fine with me!

RV

Link to comment
Share on other sites

20 minutes ago, Richard Vandersteen said:

  This is why the meter is rolled off in the lower frequencies so that the user can work with flat response when it should be rising as the frequency goes lower. 

I always wondered about this.  So the inverse of the frequency response of the RS meter is being used as a sort of "house curve".  The Harman house curve also rises below 100 Hz.

 

spacer.png

Link to comment
Share on other sites

I found a surprisingly useful and informative manual for the Radio Shack SPL meter:

https://pages.uoregon.edu/baker/tools/toollibrary/RS (Sound Level Meter).pdf

It even has a schematic.  My, how times do change.

Anyway, I also found this app:

https://www.cdc.gov/niosh/topics/noise/app.html

It looks to me that the app can be set up to give similar time constants to that found in the RS meter, as well as similar frequency response or weighting curves, even if the names don't match.

So, if any of you guys out there have a Radio Shack SPL meter, it would be interesting to see how this app performs in comparison when using the Vandertones.  OK, I'd find it interesting; perhaps you wouldn't.  The app is free, too.

 

Please note that this is really a separate discussion from whether analog processing in the audio playback system is better or worse than using DSP.  (I have yet to hear a DSP-based equalization system that sounds "right" to me.  I can't explain why that might be, so I won't even try.)

 

Here's some more information that might be helpful:

https://www.nti-audio.com/en/support/know-how/frequency-weightings-for-sound-level-measurements

https://www.nti-audio.com/en/support/know-how/fast-slow-impulse-time-weighting-what-do-they-mean

  • Like 1
Link to comment
Share on other sites

Thanks as always BK.  I have never pulled the switch on the RS meter.  I need to probably think about getting one though as I have to move my speakers about 8" closer than they were before I changed my cabling.  I assume that's going to throw off the bass as Rutan had them almost touching the side walls.  

 

Link to comment
Share on other sites

I had a lot of downtime during the pandemic, so I wrote my own real time spectrum analyzer for calibrating my Quatros (see screenshots). 

Disclaimers: I did not consult with anyone when doing this, let alone anyone at Vandersteen. The design is based on my own guesswork and was written for my own entertainment.
(I have no associations with any commercial audio entity; I work for a medical device company doing data analysis.)  Also, I have no academic training in digital signal processing, so my understanding of it is imperfect, to say the least.

I stopped working on it after moving to digital EQ, but this discussion prompted me to dust it off and put the code up on github.

https://github.com/daverz/vndcal

How it works: a repeating frequency sweep is played back by the app.  The microphone input is then displayed as a 1/4-octave spectrum (to match the frequencies of the Vandertones).   The app then takes you through the calibration steps for each speaker using the rules from the Vandersteen manual. 

The first step is adjusting the system volume so that bands 8, 9 and 10 average to 70 dB (first screenshot). 

In the second step an EQ target is computed using Richard's 60% rule and displayed on the graph (red line in second screenshot).  Once you've adjusted the 11 EQ pots for the best fit to the target, the same steps are carried out for the right speaker.

I'm not sure how to code the "Soular Energy" step as a computer algorithm, so the best I could think of was playing the frequency sweep on both speakers but shifting it up an octave so that it straddled 120 Hz.  You can then adjust the levels to smooth out the overall frequency response between the bass and mid-bass octaves.   I've always left the contour control at 1, so didn't code that step.

If there is interest, I can write some documentation, clean it up a bit to make it more generally useful.  and create binaries for Windows and Mac.  I'm not very good at UI design, though (I'm a data guy).

 

  

 

 

 

 

volume_adj.png

target.png

  • Like 1
Link to comment
Share on other sites

2 hours ago, TomicTime said:

what mic did you use ? i think that’s the crux...and of course, how does it sound ?

cool

I have two omni measurement mics to test with, a miniDSP Umik-1 USB mic (comes with an individual calibration file), and an Audix TR-40 analog mic (no longer made, and I don't have a calibration file).  If you use an analog mic, you'll need an SPL meter to calibrate dB levels (that feature is not currently working in the code, but could be added back in.)  And, of course, I have the analog Radio Shack meter, which has an RCA output, so it can be used just like the other mics.

The code, as is, is set up for a Umik-1.

Yes, the question is, can the standard Vandersteen/Radio Shack procedure be replicated with this one so that you can you get the same sound?  There's a lot of flexibility in the method, so that I think it should be possible.  

Link to comment
Share on other sites

  • 1 month later...

I found an analog Radio Shack sound level meter.  (Actually my wife did - long story.)

First, remember my suggestion to try the iPad/iPhone app?  I compared the two approaches.  Forget the app.  It's really pretty good above 60 Hz compared to the RS meter, but below that it was way off.  Keep looking for a RS meter if you don't already have one.

I'd originally set up the Quatros using an RS analog meter a few years ago, but then the meter disappeared.  (see above)  Since we'd recently put granite bases under the Quatros with Vandershoes between, and some of the non-audio objects in the room had changed some, it made sense to realign the subwoofer.  So, I started from scratch per the instructions.

A couple observations:

It's not nearly as hard to get the various equalizer controls set to within +/- a dB or two as people seem to suggest.  I imagine that if you wanted to get within a quarter dB it might be painful, but that's not the goal.  Or, it shouldn't be.  As clearly stated in the manual...

One of the goals is to get the two subwoofers aligned closely between channels.  Here's the problem - most preamp volume controls don't track that well.  Yeah, if you have an Ayre preamp with a switched volume control, that's not an issue.  But, even the best Alps continually variable potentiometers are only within a dB or two, and the mismatch often changes at different volume settings.  So, be sure you know where you stand with this.  An AC  voltmeter reading is a good confirmation.

Just to be sure that the low frequency level controls were set properly, I also made a couple tracks from ~360 Hz warble tones at -9 dB RMS amplitude.  One for the left and one for the right channel.  That's similar to the Vandertone levels.   I then measured those tones in comparison to the Vandertones.  Pretty close.  Of course, you might want more bass or less, but I just wanted to be sure that I wasn't way off.

Finally, playing with the meter reminded of something.  90 dB sound peaks are friggin loud.  When you consider that the sensitivity of Quatros is around 87 dB for 2.83 volts at 1 meter, that suggests that 800 watt amplifiers may not really be what's needed here.  Yes, I get that the peak to average power ratio of a music waveform can be substantial and that the sound meter doesn't really catch the absolute peaks, but it still is something to think about.  There's often reasons other than the peak output power to consider with regard to an amplifier (too much for discussing here), but lower powered amplifiers might be fine for any listener based on her or his preferences.  As usual, listen before you buy!

 

Link to comment
Share on other sites

Great stuff BK. Thanks for that.  I have to set my speakers up from scratch again as I did hte granite and other stuff has changed in the room also.  Pizza's on me if you ever want to come over, lol.   I just need to make the time (new puppy since Mother's Day hasn't let me listen nearly as much as I need to) to do some basic set up.  I am not happy with the tilt just yet.  Close but no cigar as I was trying to do it on my own and it's impossible for me to be able to do it, lol.  

Link to comment
Share on other sites

Get yourself an iMM-6 calibrated microphone from Dayton Audio.  Each microphone is specifically calibrated and you download the equalization file for your specific microphone from their site.  It plugs into your phone's rca jack.  Then get the "Audio Tool" app for Android or Apple.  Then drop kick that Radio Shack nonsense into the nearest lake.

Link to comment
Share on other sites

 

On 4/23/2021 at 8:59 PM, Richard Vandersteen said:

This is a complicated answer so I will give it a shot.  Measuring frequency response in a room is not easy.  First if the speaker is flat to 20Hz the measurement must compensate for room gain which is part of every recording.  The Radio Shack designer had the presence of mind to know idiots like me would be trying to measure speaker response  in a room.  This is why the meter is rolled off in the lower frequencies so that the user can work with flat response when it should be rising as the frequency goes lower.  The need to use an analog meter on fast is because a human watching the needle can visually eliminate the random noise (even in a quiet room) taking the reading that persists.  Anything digital must take several samples and average the result which is not accurate as the noise pumps up the average.  I have found the correction must only be about 60% because the brain cannot be fooled into thinking the room problems have been fixed but we can carefully minimize the negative effects.  My experience with all of the digital room correction disciplines I have tried (many) the result  differs even if nothing has been changed.  The result in the bass can be good but the midrange and high frequencies are not as open and clear.  After years I find using the old analog meter (easy to find) with correction in the analog domain within the subwoofer amplifier the most transparent with best imaging .  The whole process does not add one extra component or circuitry in the sacred main signal path we pay so much to keep clean.  I know the Radio Shack meter will become hard to find and Vandersteen will need to produce one.  It will have a rechargeable lithium battery, power switch, no range switch (fixed at 70db), no "A" or "C" weighting switch and an analog meter!  Simple, so it will be difficult for me to make a mistake at all the shows we do every year.  Having said all that "hearing is in the ears of the beholder".  However one decides to set up their Vandersteen's for satisfaction is fine with me!

RV

Bill, this is why the RS meter works.   Richard may want to weight in again, but others have mentioned other meters etc and they won't work properly.  

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...