Monday, April 11, 2011

Getting the Oppo Music up and Fan Noise down

The weekend started out with a continuation of experiments as to how to lower the audible significance of the fan noise of the Oppo BDP-95.  Using my Genrad 1933 SPL meter (which badly needs recalibration), I measured the noise level before modifications at around 25dB (at 250Hz) at a convenient position (ottoman) about 1meter from the 2meter listening position.  I liked making 250Hz octave band measurements at first because they clearly show the fan turning on and off.  Turned off, the noise level drops to 18dB.  (This is assuming A/C and kitchen refrigerator are not running, both of those together raise room noise level to 30dB or so.)  You can also see that for the first minute or so of operation, the Oppo fan is not running.  The actual drive mechanism is virtually silent.  But after a minute or so of playing, the 250Hz rises from 18dB to 25dB.  The fan stays running even when there has been no disc playing in hours, but shuts off quickly after the unit is turned off.

I figured I could reduce this noise by putting 6" thick Sonex pyamid panel (2 ft square) behind the stack of equipment that Oppo is in.  I also lowered Oppo from the top position to the middle position of the stack, so the noise that it originates is more likely to be blocked by other equipment or the Sonex in back.  With those two changes, noise level at 250Hz lowered from 25dB to 22.5dB.  Then I noticed the A weighted noise level is also around 22.5dB, and drops to 20dB when the Oppo is turned off.

Then I found an additional tweek which seemed to have more subjective effect than measured effect.  I cut a felt cloth into 2 inch wide strips and folded them back on themselves and inserted between the Oppo player and equipment above it and below it in the stack.  Subjectively, this seemed to make it impossible to locate the Oppo in space based on sound.  Fearing that the felt might be blocking air inlets on the bottom of the player, I eventually removed all felt from the bottom, but kept it around the front and two sides of the top.  There are no air inlets on the top of the Oppo.  Most players (which lack fans) tend to get rather warm on top anyway.  The Oppo did not seem to get excessively warm on top, even with felt around 3 sides.

It would be nice to have felt block material for this purpose.  It does seem like the gaps between equipment in a stack provides channels for sound to exchange from front to back and resonate with everything in between.  Though the Oppo player feels pretty solid, nothing is perfectly solid.

Trying to get the Oppo fan noise down, I began paying attention to all the other noises.  I discovered that I could reduce my A/C and water heater noise significantly by putting a folded director's chair across the corner where the A/C return vent is.  I did this in such a way to maximize noise reduction but minimize effect on airflow.  That corner should eventually get a full acoustic treatment.

The fan sound is distinctly measureable at 250Hz, but may actually be greater at 60Hz or so, it's just hard to measure there because the self-noise of my 1933 SPL meter begins to interfere.  It is interesting how well the sound level at 250Hz tracks the A weighted noise level, while the level at 60Hz is actually much higher, maybe 35dB or so.  But probably the higher frequency components of the noise are the most noticeable and distracting.  That's why little tweaks like putting felt dams between pieces of equipment seemed to help.  Those tweaks probably have relatively little effect at lower frequencies, but may interfere with higher frequencies.

Mind you I wouldn't be going to all this trouble if it weren't worth the effort.  The Oppo is the most amazing audio source I have ever had.  Listening to some classic RCA living stereo recordings on SACD, such as HiFi Pops conducted by Arthur Fiedler, it is astonishing to hear so much detail and life.

(Hifi pops also has some serious subsonics, not sure if they were intended.  Some of these are a bit too much.  The balanced connection seemed to give better control of the subsonics, making them actually musical.)

I'm now seriously planning to get a second BDP-95, for actually playing blu ray discs.  I need a second one of these amazing machines just for audio discs in my main audio system.

To get the most out of the Oppo, I reconnected it to the Lavry AD10 ADC with a new 1 foot balanced wire (Belden 1800F) from Blue Jeans Cable.  I moved the Lavry on top of the new equipment stack, and connected it to the Tact digital preamp with a new 5 foot 1800F AES/EBU cable.

As expected, this raised level by 6dB without adding any noise, making the Oppo performances even more magical.

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