Paul350Z

iTrader: (1)

Recently I purchased TrueRTA (real time analyser) which is a small computer program that turns a laptop into an acoustic analyser. The program is free for a ten octave analyser which really can't be used for much but it does allow you to test your machine prior to purchase. I bought the $99.00 1/24th octave analyser.



www.trueaudio.com

I also bought a Behringer EMC800 omni-directional measurement microphone for $50. This microphone has a very linear response and there are calibration files available for it too.

I calibrated TrueRTA to remove any colorations from my laptop sound card. I installed the microphone calibration file. Then I use my Radio Shack dB meter to calibrate the microphone's response to the dB meter.

The basic hook-up is to run the microphone to a phantom power supply which feeds 24 DVC to the condenser microphone. The output of the phantom supply feeds the microphone input of the laptop.

I used the Avia Home Theater calibration to produce a wide-band audio signal (pink noise). This signal has an equal amount of energy in each octave of music. Fed through a perfect speaker it will produce a flat response on the RTA. The Avia DVD is a great disk for setting up THX sound systems and home theater displays of all types. The video portion of the disk has test signals that allow you to make adjustments and measurements. The disk walks you through step-by-step in plain language what each adjustment does and how to read the test signal to do it.



My Pioneer AVIC N2 doesn't have an equalizer connected but does have three parametric equalizers for adjusting low, mid, and high bands. A parametric equalizer lets you set the amplitude, frequency, and Q - the width of the filter. Parametric equalizers allow you to take care of rough problem areas unlike an octave equalizer which really lets you zoom in on individual problem frequencies. Any equalizer should be used with some moderation as excessive equalization will cause phase distortions and can cause amplifier overloads.

Here's my first measurement which shows an un-wanted cut right at 35 Hz with two large peaks on either side of it. The marker frequency is white and sitting at 9123 Hz which seems to be the frequency of my garage's freezer. The sound pressure level is 104 dB. There's pretty good response down all the way to 20 Hz but it starts to drop off at 25 Hz - that's gut wrenching deep levels at hight amplitudes. You can see the rise from 80 Hz down to 25 Hz - this is the area that the subwoofer is working at - and the gain of the amplifier needs about 7 to 10 dB of reduction.



Here's a second picture taken after a bit of tweaking. I found that 1/6th octave resolution made seeing the overall pattern of the response easier. I've lowered the subwoofer down a few dB and need to go further down before I'm level. This is a pretty reasonable response with 1/6th octave resolution - if I drop this down to 1/3 or lower resolution the response appears even more flat.



Now I have to debate wedging an equalizer into the system.

"Z"orilla

iTrader: (1)

Now here's a guy who is serious about his sound quality!

gt3

iTrader: (10)

Thanks for posting the info. How and where did you mount the mic? Also, how did the music sound after the adjustment? Would appreciate your comments.

bjr

Wow Paul, what a deal! Did I read that right that you spent about $150 total? The Spectra plus software I tried out for 30 days was about $700 to buy and I did not know what kind of repsonse a laptop input is capable of so I did not try a microphone to test real world sound. What I did was compared the HU to my expensive home CD player. I was trying to get my stock HU to sound right and was doing line level measurements.

So with your setup, you are using a good microphone and then you calibrate it to take out all the effects of things like not knowing what accuracy your laptop's sound card has, any microphone non-linearities etc? I would probably buy something like that if I could get it that cheap.

Paul350Z

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I stuffed the microphone into the gap between the headrest and the seat just about where your ears would be. After adjustments the music still sounded good - I lowered the bass a bit toward the more honest end but left it above that line as I'm a bass head.

Paul350Z

iTrader: (1)

The procedure for the sound card is simple - you run the line-level out to the line level input. The software produces a linear pink noise signal which should show up as linear response in the input. You click one menu setting and the system calibrates itself.

For the microphone the lab mic is pretty flat right out of the box. There is a calibration file available to smooth out the manufacture's limitations. If you're really serious you can mail your microphone in and have a custom calibration file produced ... normally this is only done by professionals who are designing speakers and the like. Without the custom file I would expect +/- 0.5 dB of response which is inaudible.

eat rice z33

iTrader: (11)

so how did you run the power to the mic? and what interface from the mic to your laptop? im really interested. thanks again

JimRHIT

iTrader: (6)

Paul, EQ'ing out all the peaks and valleys there is unlikely to do much for you SQ wise. Living in the curve-world here, I can tell you that a flat system will sound, well, flat to you ... lacking any sort of sonic character that most listeners prefer. It is cool to see this though.

I'll see if I can dig up my old LMS files of my Z with my Klipsch horns and RSW subwoofers. Prolly the flattest response I've seen of any car setup ever .... however, I ended up tuning away from flatness to get the sound I pereferred.

Jim

james840a

iTrader: (7)

Dont forget about me

PaulZ, nice find on the software. I was looking at the laptop option and thats when i found the PAII3 unit Sam Ash music online had. How do you like the sound now that you did some tweeking? Its nice to have a EQ, 31band is awesome, i have to say i love the PXA-H710 unit. I can adjust everything right from the head unit. Ill have to post some pictures of my RTA after i replace one of my tweeters.

Paul350Z

iTrader: (1)

The black box sitting next to the laptop is a phantom power supply which sents DC down the signal cord of the condenser microphone. There are two types of microphones - dynamic which don't require power, and condenser microphones which do. Condenser microphones can be designed to be more sensitive and have higher freqency at a budget price but require the phantom power supply.

The phantom supply sits in the signal line from the microphone into the laptop with XLR connectors coming and going. I use a short lead from the phantom supply to the microphone input to my laptop.

Paul350Z

iTrader: (1)

Yeah it's your fault I got this thing!

I looked at getting the PAA2 (without the PAA3's reverb measurement or USB ports) for $300 but then just figured it was just as easy to use one of the laptops I have laying around. I've got a little tiny 9" screen ultra-light laptop that I want to try to get this working on next. On my 2.6 Ghz laptop it uses just 5% of the processor so it might work on my antique Pentium 120 Mhz machine.

After I cut my Uncle Sam a check for $5600 in extra taxes I wasn't planning on I'll have to recover next month and look for an EQ to mount behind the seats some where. The Cadence MEQ30, Eclipse EQ2102, Zapco EQ30-SL, or the Pioneer DEQ-P9 (which matches my head end) appeal to me at this point.

I'd blow away my head-end's cross-over and go with something like the Volenhag ZX-7577 or other 2-way crossover if the EQ didn't provide a sub-woof output like the Eclipse does.

I figure I'll wait until it's 120 degrees in my garage again before doing the work this year.