Sunday, June 5, 2016

What HiFi doesn't talk much about - The Room Response

One of the big differences between the world of HiFi and Pro Studio Sound, is the mount of science applied to understand what is going on.

The sound of the room, and how to modify  bass absorption, standing waves and early reflections is a taken in setting up a studio or mastering room.  Your speakers may be flat to within +/- 3dB  over a useful frequency range, but your room isn't without treatment.  Without any treatment there will be standing waves of +/- 10+ dB  at frequencies determined by the size of the room. All simple physics, and way more significant than the sound of the speaker or power cables.

There are some devices that will measure the room and attempt to compensate the speaker response to fix the room. An ex-bosses company, DEQx has such a device, but there are others.  Some companies like Genelec even build it in to some of their speaker system.
But when there is a physical null due to a standing wave, no amount of power at the frequency will remove the null, even if the peaks can be handled with this intelligent and analysis and then applied EQ.

And the real interesting thing is that the technology to build Basstraps and early reflection treatments is the very low tech rigid fiberglass, closed cell foam and similar materials.  Things that look out of place in the high fashion world of Hi Fi.

Addition June 18 2016

Well well. Just seen the MAY 2016 HIFINEWS magazine, and see this born out again.  Page 119 has the question titled "Whats a regular size room?" 

A guy has amazing PMC speakers, says they are "boomy" and asks about replacing them with B&W 802 D2 speakers instead, and mentions his room size, but then nothing else about the finishing of the room.  The answer from the magazine displays a lack of the science of acoustics I talked about above.
The guy may have a concrete walled and tiled floor room, or  lush carpet and drapes that are completely inappropriate for his listening room, and this would have been involved with the real answer to his question, but wasn't.

"Boomy" bass indicates narrow peaks in the low end room response.  Changing the position of speakers and listening position will have an impact of where the nulls and peaks are. The pro audio solution is to add absorption at those frequencies.  In practice adding Bass-trapping will reduce "boom."   Changing this level of  speakers will make no significant difference....

Friday, June 3, 2016

GainClone Amplifier Revised, the Chinese Electrolytics..

We have been using the GainClone Amp in our little studio since December 2014 and opened up to put in a larger 160VA  toroid transformer, instead of the 2 traditional units I had on hand at the time I first put it together.  Also going to replace the speaker terminals for ones  that can take banana plugs.

The Amp has been working great.   But upon opening it up, we see that would not have continued for much longer.

One of the 4 10,000uF 50V electrolytic capacitors in the power supply would soon expire.  It has expanded and will rupture.

The bulging capacitor  before it was removed.

So we caught this in time before any damage was caused. Only real issue for me was I expected to get it up and running again in a few hours, but I will have to order  new supply caps online for delivery next week, around $25, as the local shop doesn't carry 10,000uF 50V PCB electrolytics anymore. Then again, 10,000uF at least on a channel is completely usable, until the new one arrives.

If one is near dead, they are all suspect and replacing them is the safest thing to do.   That cost is as much as the PSU and Amplifier modules cost in the first place. Stuff from China on eBay is just incredibly cheap, not always the highest quality but it isn't as if this is much of a problem. Now the capacitor is actually a Japanese Rubycon, and should be a quality part, but it may be forgery or a reject part.... who knows.

In the mean time I can use it fine with only 3 capacitors....

Some time later...

We ended up getting nichicon 10,000uF 50V capacitors from RS Components. .. mostly as it is free postage here, and no minimum order.