How To's

Measuring Stuff with Studio Six Digital's Acoustics Analyzer for iPod Touch and iPhone - Pt 2.

I went back to my office and played my Ayre Acoustics pink noise track:  turned on the FFT; I was immediately greeted with a familiar noisy green line frequency response spectral display that was settling nicely as it continuously averaged over last two seconds.  :wings An  FFT analyzer performs a fast fourier transform calculation which very rapidly takes in samples of a continuously varying analog signal and spits out spectral information. In other words, play pink noise (which is a signal with equal amounts of energy in all frequency ranges), and an FFT analyzer will very rapidly show a frequency response curve. In the case of pink noise, the response should be a flat line.
[caption id="attachment_589" align="alignright" width="300" caption="Harbeth HLP3ES-2 Speaker Frequency Response"]Harbeth HLP3ES-2 Speaker Frequency Response[/caption] Let's have a look at one of my Harbeth HLP3ES-2 speakers. As you can see the response of these speakers is fairly flat from 125 hZ to 20 kHz. This is a small two-way speaker, so you don't expect great bass extension, and you can see the fairly rapid loss of lows below 125 Hz, which is 10dB down by the time you get to 63 Hz.
[caption id="attachment_590" align="alignleft" width="300" caption="Ruh roh! Something's wrong with this speaker!"]Ruh roh! Something's wrong with this speaker![/caption] Unfortunately, I've also got a sick speaker --- that's been bugging me since it traveled last --- so I measured it. Yup, sure enough, something's wrong. Odd that it has any highs at all; I was suspecting a blown tweeter but because it still has some highs I thought maybe one of the crossover components lost a connection with all the rattling around during shipments. Regardless, this handy little acoustic analyzer made it very simple to see the something was wrong immediately,  and now before I send it in I can send a snapshot of the problem.
[caption id="attachment_592" align="alignright" width="300" caption="The Boaston Acoustics Duo-i plus sounds pretty darn good."]The Boaston Acoustics Duo-i plus sounds pretty darn good.[/caption] Let's measure some other stuff. How about the Boston Acoustics Duo-i plus iPod dock/clock radio, it sounds pretty darn good and has bass and treble controls that we can play around with. I docked the company iPod and played some pink noise with all the controls set to neutral.
[caption id="attachment_594" align="alignleft" width="300" caption="BA Duo-i plus with all controls set at neutral."]BA Duo-i plus with all controls set at neutral.[/caption] As you can see, this little unit is flat within roughly 6dB from about 80 Hz to 16 kHz, and then it starts to wander a bit.
[caption id="attachment_595" align="alignright" width="300" caption="BA Duo-i plus with bass and treble controls at max."]BA Duo-i plus with bass and treble controls at max.[/caption] I then set the bass and treble controls up to maximum and remeasured. You can easily see the lows are up about 5dB, and the highs are up about 10 dB.
[caption id="attachment_597" align="alignleft" width="300" caption="BA Duo-i plus with bass and treble controls at minimum."]BA Duo-i plus with bass and treble controls at minimum.[/caption] I then turned both tone controls down and remeasured. Now you can see about a 5 dB cut in both the bass and treble.
[caption id="attachment_599" align="alignright" width="300" caption="Duo-i plus up agains a wall with additional gain in lows resulting."]Duo-i plus up agains a wall with additional gain in lows resulting.[/caption] Lastly, I set all controls to neutral and pushed the unit up against a wall. Here you can see the 3dB gain in low frequencies do to reinforcement from the proximity of the wall. Just exactly what you'd expect ... cool, this little gadget works good.  :thumb
[caption id="attachment_602" align="alignleft" width="300" caption="The Skullcandy Pipe ruuns on 4 AA batteries."]The Skullcandy Pipe ruuns on 4 AA batteries.[/caption] What else can we measure? How 'bout the Skullcandy Pipe? You would think it would be abysmal.
[caption id="attachment_603" align="alignright" width="300" caption="The Pipe response is flawed, but what did you expect?"]The Pipe response is flawed, but what did you expect?[/caption] I must say, I was really surprised how good the Pipe sounds for it's size. Sure, it's about as good as my blown Harbeth speaker, but that's not bad considering it's about the size of a rolled up dinner napkin. I just might have to get one of these for my 13 year old daughter this Christmas.
Needless to say, I'm very impressed with the Studio Six Digital "Audio Tools" iPhone app. I went back to the shop to talk a bit more to Jamey, Jorge, and the gang about the iPhone and Audio Tools as an acoustics measurements tool,  and showed them how to use this device when evaluating iPod docks and speakers. We played around for a little while, and were able to see comb filter effects from first reflections of the desk surface with the docks. And the Boston Acoustics i-DS3 plus has a stereo image widening function, and we could observe the steering of the upper mids and lower treble off to the side by moving the analyser from side to side. We had a fun time playing around with this really great little audio tool, and I expect we'll use it quite a bit. At the end of the meeting, Jamey came up to me and mentioned that it wouldn't be too hard to build a little gizmo to measure headphones with using the iTouch. You'll never guess what I did next. :augie On to part 3 ---->

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