Feel free to ask questions. I'll do my best to answer.

Tuesday, November 6, 2012

Sound Audyssey

Since I nursed my bass issue back to health, I decided to have another go round with Audyssey and see where it could lead me.  I did a basic 3 measurement calibration at ear level for each seat on my couch.

My prior bass graphs:
Black Lines are the most recent

So after Audyssey did it's thing, my listening couch graph(s) look like this:

Not bad, but a significant hole centered at 68Hz and audibly a little bass shy.  That's not exactly acceptable to me.  SO I did a little fiddling with it to see what I could come up with using the unit's EQ.  Check it out:
So the hole moved up a few Hz and filled in a bit.  Here's the 1/6octave smoothed (for clarity) overlay:

Oh, I restored the treble back to the speaker's natural response.

The receiver's default setting uses Audyssey's Dynamic Volume.  So I took measurements of it's default setting as well:

Some other Audyssey settings with Dynamic Volume engaged:

The Black lines bypass Audyssey on the left/right channels

You can see that even though the microphone was in a very close position on all 5 measurements (each one had the microphone position marked), the measurements are significantly different above the modal/transition zone(s).  Just more eveidence that there is no ideal "room curve".  So calibrating above the transition zone seems futile.

Monday, November 5, 2012

Bass, The Final Frontier

In my previous bass experiments, Multisub and Fast Bass, I was tried to replicate others experiments using a simplified, Dan "The Man" method with better success using the multisub.  Since that time, my two cheaper and older subs have died so I'm down to three.

Looking at the data from my multisub experiment, the first sub didn't add much to the response, and the fourth and fifth left the response looking nearly the same.

Compared to the nearfield, fast bass subs, the response looked pretty good:

The sound difference matched that graph more than any of the other Time Response views.

So with my three subs, I placed the subs where the second, third, and right in between the fourth and fifth placement.  The response came out similar:
Black lines are with 3 subs placed to approximate the 5 multisubs placement.
The lack of deep bass is due to the cheaper subs actually having a deeper response.


Friday, November 2, 2012

Requested Bass Experiment

Well, a forum member requested a bass experiment where I would keep the mic in exactly the same position and hit the power on my subs one by one and do some CSDs of the results.  I obliged, but I'll just show the extreme cases.  There's nothing else to see really.  It will give you an idea of the changes you can expect.

That's a wrap.

Dry (fast) Bass...

After reading this:  http://mehlau.net/audio/dual_nearfield_sub/ I wanted to try some nearfield subwoofing myself.  In my previous multisub bass experiment, I was able to smooth out my bass response by using five subs in a somewhat random fashion.  Well one of those subs died on me(the fifth one added) during some hardcore Willy Nelson listening.  So I had to change the set up and I came across Mr. Mehlau's experiment.  It was interesting to me that the fourth and fifth sub added were the closest to the listening position--right behind the couch.  It was suggested that I should see what the fifth sub's response was, so in this experiment, I decided to use three subs directly behind my couch.  

I had just purchased a Marantz HT pre that has Audyssey MultEQXT and I wanted to see if I could duplicate Mr. Mehlau's success with it.  Note that he has the upgraded '32' version of Audyssey.

Okay, enough talk.

 Frequency wise, the 5 sub set up was a significant improvement:
The time domain would slightly favor the nearfield subs in general:

Note the absolute level below 50Hz 

Inevitably I'm going to be asked which "sounds better"?  Well, I hate to disappoint, but the frequency graph says it all.  I don't hear any difference in the bass 'speed'. All I hear is less deep bass.  That said, if I could have it all (deep, flat, and dry bass) I would just to make sure I have the best possible.  I think this also shows a good argument for the '32' version of Audyssey.  Maybe I'm wrong however, but all of Mr. Mehlau's responses look better than mine.

Monday, October 22, 2012

Pitfalls of "Room Correction"

Intro:  It’s been demonstrated (and essentially common knowledge in the audio world) that humans suppress early reflection--as continuously evidenced by the fact that we don’t hear echos all day long everywhere we go.  It’s the law of the first wavefront/precedence effect/Haas Effect/etc...  Drs. Toole/Olive have demonstrated a very similar phenomenon with tonality.  Preferred Loudspeaker Measurements  An accomplishable experiment for a musician might be that you’d recognize the sound of your guitar in a living room or a gymnasium even though the acoustics in the gym are essentially awful.  You’d be able to point out it’s location as well.  Neither of those internal ‘filters’ are exactly cut and dry however and Dr. Olive hints at that in the previously liked blog post and Salmi and Kates show here:  AES Paper  In a small room this tonal filter essentially goes haywire around 300Hz:  Hearing Beyond Haas   Dr. Olive's iPod Demo  Dr. Olive's Data  Localization below 80Hz(of course play your sub alone and you’ll hear that it’s spitting out a lot of stuff above 80Hz and some more recent experiments suggest that the cutoff is even deeper for lateral displacement).  When in doubt, go overboard IMO.  Symmetrical placement of a great number of subs isn’t a bad idea either. ;)   This is 1 or 2 deep rabbit holes, but that's the essence of what we hear in a small room.

Now here’s the Audyssey (and/or ‘room correction’) issue:

It may be less intuitive to a musician or Joe Sixpack audio nut than an audio engineer that 2 noises with identical frequency content but different time content would sound different.  Just make a frequency graph swept sine wave and a white noise signal through REW(or your favorite acoustics software) for proof.  How does the graph then look the same when they sound so completely different?  Well, this is very useful question for anyone who wants to make approximately psychoacoustically correct measurements to understand.  Welcome to the (Fast) Fourier Transform or FFT and its progeny the Time Domain and the Frequency Domain. The FFT allows you to look at sound in either.  When doing this conversion, the number of viewable data points in the frequency domain is related to the amount of time used in the data display.  So in a room, the collected data will contain a higher amount of reflections as the microphone gets further from the sound source.  If you later try to gate(narrow the time window) of the displayed measurement so you can look at the direct sound (and get a more psychoacoustically correct spectral response above the modal region) you will end up with very poor resolution.  The resolution will be too poor to properly EQed.  You won't know what the speaker is really doing.  If you move the mic too close to a multi driver speaker, you’ll introduce errors related to driver integration.  IOW, there is no great way to to correct the ‘room’ above the fuzzy 300Hz mark.  There's no substitute for good loudspeakers designed to measure well in anechoic conditions.  

It's not the end of the story though.  There are things you can do to improve your situation: Gating Loudspeaker Measurements  Then EQ the full listening position frequency measurement below 300Hz.

Friday, October 5, 2012

My Multi Sub Attempt

I have five subwoofers and a desire to test Dr. Geddes's approach to bass.  So I placed the subwoofers where they would fit into my room well completely unconcerned with acoustics.  Yea, not really his approach, but a have subs to burn.  Anyway, I graphed the effect of just the stereo speakers in five spots across my couch, then repeated the measurements adding one subwoofer at a time with all of them low passed at 80Hz, but no high pass on the mains.  No EQ is being used--currently I don't even own one.  Here's the results:

stereo speakers
stereo speakers with one sub

The difference between the stereo speakers and the stereo speakers with one sub added:



That should say "-9dB".  Jimi's prophecy came true after all!


"Well what about the time domain?"

Let's look at the center position without any subs verses all five subs in use:

I'll zoom in on the are of concern and make the graphs line up a little better.

Now here's a look at the time domain:

Doesn't look bad at all.  Looks like the only loss is in the financial domain. ;)

Thursday, August 9, 2012


Factors to consider when buying headphones:

Essentially there are 4 types: Over the ear(open and closed back), on ear, ear buds, and canal phones.
Then there is isolation, portability, amplifier compatibility, comfort, and imaging effects on the recordings you'll likely play.

  As far as portability and isolation are concerned, nothing will beat canal phones.  Unfortunately many of them have 2 low of an impedance to mate well with home stereo headphone amplifiers.  A couple buck the trend--Etymotic Kids and their ER-4S and 4B with 300ohm and 100ohm rating.  They will work with pretty much every amplifier and they'll have better isolation than pretty much any headphone available.  Due to the high isolation they will also have the most inside the head sound with most recordings and perhaps have the most tonal issues b/c they'll bypass you head, shoulders, and pinna.  The tonal issues are not necessarily the case as we'll see later.  Since most all commercial recording are EQed using stereo speakers, manufacturers of canal phones with have to take this into account.  Since no 2 people are the same, no universal curve will work.  Having something shoved in your ear canal can be a little disturbing and even painful and insertion depth will have an impact on the sound.  Rin Choi on insertion depth

  Ear buds have a number of issues as well--all the same ones as the canal phones, but also don't isolate as well and have more trouble staying in your ear.  In general they won't have very good fidelity and will be bass deficient because they won't seal, but they're probably safer to run with than the canal type because you can still hear the outside world (cars, bicycles, skateboards, rabid children, etc...) and are just as portable.

  On ear headphones are fairly portable and offer even less isolation than ear buds/canal phones.  They do allow some of the listener's pinna to come into play and could have better tonal accuracy than the ear bud/canal types if as well designed.

  Over the ear can be broke down into the closed back and open back types.  The both allow for the listeners pinna to shape the sound more naturally.  The closed back will of course offer better isolation and have a tendency to image inside the head more than the open back.  If you want to monitor your own recording however, this has it's advantages.  The impedance with 'cans' tend to work better with home stereo equipment as well.

A couple great sites to get you started:
Golden Ears
Head Room
Inner Fidelity
Headphone Info
Let me know if you have some other ones.
Doctor Head

The currently accepted ideal headphone frequency response is more than somewhat debatable.  Generally the diffuse field EQ is applied in order to subjectively sound the most flat.  When measured at the eardrum, the curve should look like one of the below:

taken from: Rin Choi

taken from: Rin Choi

taken from: Rin Choi

taken from: Rin Choi

Diffuse vs. Free Field EQ from B and K via Golden Ears
taken from: Rin Choi

Those graphs are prior to the reverse EQ is applied to make the graph appear flat.

Further reading:
still not finished here... will update more soon.

A couple headphone measurements I just took with my prototype dummy head:

Etymotic ER4B
 Insertion depth definitely makes a big difference with these.

Shure SRH840

The Bass performance is certainly due to the poor seal(well none at all) on my dummy.
Here's the Headroom graph of the same headphone:

Strangely, the graph from Golden Ears looks radically different.  Both have different compensation curves applied to them that really don't account for the measured differences.  There's likely something else at work/play here.

Another highly regarded headphone from German Maestro:

German Maestro GMP8.300D

The bass performance on this is actually outstanding in real life, but again the dummy head seal is really bad and it's hard to say how much that seal issue is corrupting the rest of the response.  It definitely doesn't seem as smooth as the Shure SRH840.

Moving this one around just to see what it will graph like in different positions led to this:

So headphone positioning can alter the sound significantly.  Makes me question how useful these graphs found around the web are.  The sites I've found all have significant differences in their graphs.

Here's what HiFi Headphones from the UK got:
Which seems to resemble what they sound like to me.

Now a Beyerdynamic DT770M with a diffuse field EQ as reported by the manufacturer built in:

Looks a lot like the first German Maestro, but with less bass.

Making a frequency response graph of the JBL LSR 2325 beside the dummy head is also interesting:

This speaker measures pretty flat in a quasi-anechoic fashion:

Much to learn yet...