An Anechoic Chamber for SPCR

and

Test Equipment Upgrades: SPCR 2008

cool! Great to see where reader's money is going and how thoroughly researched and carefully considered the purchases are.

I think all the upgrades are already flowing into the product reviews and they're better for it, thanks!

Nice article.

Its good to see where all the donations have gone.

Great stuff !

Looks like our money has been very well spend.

Keep up the good work.

cool beans

When do the tours start? haha I'm gonna be in Vancouver this winter coming from the East. Let me know Mike

Nice upgrades, the purchases seem to be well thought out, with value for money in mind. Shoud be able to make som killer tests with this setup.

AtW

Hello Guys,
Make sure to Digg Mike's story here...

http://digg.com/hardware/DIY_Anechoic_S ... er_Project

Awesome project!

Nice article!

I wonder if sheets or something similar could be draped or attached over the insulation to keep the dust level down.

As mentioned in the article, it's due mostly to the way the blue fill covers the door. It gets rubbed/moved every time the door is moved. I'm planning to replace the stuff around the door with foam wedges that won't rub against the blue fill. Also, periodically, I leave a good HEPA air purifier running in the chamber overnight. It does a good job of clearing the air.

Mike,

First, thank you for all your hard work - both in creating the space and for documenting it for all of us living vicariously through you (yes, I'm one of them). Your dedication to 'doing the job right' is inspiring.

But, I am afraid I want a little more from you. You have documented the new room and the new equipment; now could you update your Audio Recording Methods Revised article? You and Devin did an excellent job on that article back in 2006, but now that you have the chamber I think it deserves an update.

Chris

It's the nuggets of info like your dust issue and the air purifier use that make this site so much more useful than just a review site. Some sites would hide any issues in an attempt to seem more perfect.

SPCR really is a place to learn and share information and I thank you for hosting our geek party and sharing the bad along with the good.

Yes, I'm aware of that... but it will have to wait for a bit. We're back to tweaking our fan testing scheme yet again.

Hi Mike,

Can you let us know about the "custom built, virtually silent AMD A64X2 system".

Thanks

Congratulations for your new setup. It is really impressive. It was also nice you shared this building project with us.
I've also done some amateur work in this field. It is easy to agree with the decisions you have done. Only the sound calibrator left me wonder if it is up to the quality of other equipment.

There are several things to be taken into account in accurate sound calibration: The quality of calibrator (Hz, dB, THD-%), combined volume of calibrator and mic capsule, atmospheric pressure, temperature and relative humidity. Calibration needs to be checked before and after measurements. It is quite an extra job to be done. A sound calibrator with internal feedback can make it fast, easy and reliable. The very good ones for 1/2" and 1" capsules are B&K 4231 and Norsonic Nor-1251. I've the B&K and it was quite an inexpensive second-hand purchase from eBay. Norsonic is also sold as Microtech Gefell Sound Calibrator 4000, G.R.A.S. Sound Calibrator Type 42AB and NTI Sound Calibrator.

Bottom half of page 3 of the "New Audio Test Gear, SPCR 2008" article: http://www.silentpcreview.com/article875-page3.html

Thanks for your comments.

Did you not see the paragraph about how the calibrator was compared to B&K units at UBC? I quote from the article:

The ND9 was within 0.1 dB of all the others. Prof. Hodgson was quite impressed and excited, as others in his field seek cheaper alternatives to B&K. He immediately forwarded the info about the ND9 to a colleague working abroad who was seeking a bunch for field work.

Do you know how the mic capsule volume, atmospheric pressure, temperature and relative humidity affect the calibrator’s frequency and sound pressure? Your sample of the ND9 can be good in one test now, but only a long term multiple units testing with different microphones and environmental conditions will assure performance. Before such a reputation is build there is more proven solutions available.

Sound calibrators should be calibrated each year. Imagine what it means if the calibrator is too much off. You don't know when problems started and what tests are affected. In practise it means a lot of unnecessary retesting.

My point is that why to take a risk when it is not even a real cost issue?

I appreciate the comments, and it is a goal to acquire another "brand name" calibrator for insurance. The need for annual calibration has been mentioned by others, but it's also exaggerated, imo. The climate in Vancouver is benign. In any case, I meet up with M. Hodgson periodically, so it's no big deal to make quick checks against the many UBC calibrators from time to time. BTW, it's been several years since any of the UBC devices were calibrated and they all read with 0.1 dB of each other, despite some devices using 94db/1khz tones, others 114db/1khz, and the B&K pistonphone using 124db/250Hz.

In the lab, the conditions hardly change. The temp range in the lab -- which is the only place this thing will be used -- is 18~26C. When it's actually being used, it's a much tighter range, probably 19~23C. Humidity I'm not as sure about, don't think it ever gets to 100%, but rarely does it go to 0 either. Atmospheric pressure changes some... how much? not that much, imo. The claimed specs of the device are v. good, tho the question is can you rely on them:

Temperature Coefficient : 0 to 0.01 dB/°C
Altitude Effects : Approx. 0.1dB decrease for each 2000 feet increase in altitude from sea level to 12,000 feet elevation, or comparable atmospheric pressure change (approx. every 50mm of Hg decrease).

I agree with you. It still happens to be the standard practise due to historical reasons. Meters and calibrators didn't use to be before as stabile as they are nowadays. And of course calibration labs need to make their annual revenue.


Idea supported.


I think in your case the pressure and mic cavity volume makes the biggest difference. If you validate all your mics with the ND9 then different mic cavity volumes are not more an issue. Sea balances humidity year around.


This translates to pressure coefficient of 0.015 dB/kPa. It is quite good value if true. For B&K 4231 it is 0.0008. Where I live the min-max pressure difference during last 2 weeks has been 2.9 kPa. This would have created a 0.04 dB variation. Not bad at all, but it is still a variable to be considered when the period is longer. You should check your local conditions.

Here's where we differ.

In reality, a +,- 1 dB level of accuracy would be good enough for what we're trying to do. As I've repeated here umpteen times, the absolute SPL level is not that important; sound quality aspects take precedence over SPL almost all the time. Typically, a +3 dB component that has a smoother quality is preferred by most people over an alternative that measures 3 dB lower but has a rougher sound quality. This is especially true when both items are close to inaudible. The one that fades into the background of awareness more easily is perceived as quieter.

All the new gear is good, but let's not forget why SPCR is measuring -- to understand and explain what we hear. Not the other way around (most of the time). The chamber and the new gear help us do this better... but I'm not prepared to worry about possible inaccuracies of less than 1 dB.

Great job Mike! My "ultra-quiet" PC might sound like a jet plane in there!

Right on Mike!


1. How about putting some wedges on in the space between the window and chamber? I bet it would absorb a fair amount of outside noise prior to entering the chamber.

2. With such sensitive hearing, how do you sleep? I live near hwy 101 and there used to be a large mound of dirt between me and the noise. The earth berm was recently removed and now the noise is unbearable! I could be using a tornado for a HS and wouldn't hear it now.

Rock on! keep up the great work!

1. ?? The space you're talking about is stuffed with blue fill. Photos show that. Not much gain in soundproffing that wall any more. It's the wall to the kitchen lab that's more a problem. There's a large window in the kitchen (opposite side of the house from the already blocked window in the chamber) which transmits a lot of external noise. That window I am thinking of blocking as well -- it's already blocked with a shelf full of components anyway.

2. My hearing is not that sensitive. Tho it's true I sleep best when it's quiet... but don't most people? It's more that I pay more attention to what I hear than most people do. But when someone is listening closely as I am, especially a younger person, they can often hear more in the high freqs than I do, and they may have better sensitivity to low amplitude sounds as well. There's decades of decibels in my ears!

Awesomeness! Very detailed description.

Next step: Wrap house in bluefill, or get the sleeping beauty to grow a few rose bushes

1.I'm refering to the space between the chamber and the window. that should keep some more noise outside.
http://www.silentpcreview.com/files/ima ... 8lab04.jpg

2. since my new noise level...(worse at 5-6 am when everyone get on the freeway)...Iv'e been experimenting with adding noise with a white noise generator. Just what i need after figuring out how to silence my PC.

3. did the neighbors ask about the construction project?

This really is truly remarkable dedication to bettering the website, thank you Mike.

I have to say I feel for you on the plane issue. I'm very close the the landing path into Heathrow, which is no pleasure. Planes, and Boeing 747s especially, really do produce the most horrendous racket.

1. Ah! OK, I see. That's a maybe. It's not a well insulated window, and the issue of moisture is serious, so I'm not sure if it's wise to put anything organic there -- mold grows on just about anything, tho I know the blue fill is treated, it might still be a risk. Might give it a try -- after I deal with the window in the kitchen.

2. That's sometimes the only solution. Also try an air purifier. If you get one with smooth sounding fans, it can help you breathe better so have a double benefit for sleep. My sis in San Fran lives up on a hill overlooking a freeway, and it sounds a bit like noisy surf at the beach when the windows are open. They installed new double pane, better sealed windows a year ago. Dramatically lowered the ambient noise -- when the windows are closed anyway.

3. Actually, no. It wasn't that loud -- compared to all the other noises of summer: lawn mowers, construction of renos and houses in the neighborhood, the planes over Richmond, music with open windows, kids playing outside, etc. It was not visible except from the sides and back of the house. All the people across the alley are virtually mum to the people on this side, the alley is like a border between uneasy countries. I have the worst excuses for human beings on one side, they'd just watch if someone was having a heart attack on their sidewalk. On the other side, the family was away on holiday through most of it so didn't see any of the big mess in the back. They left only their nearly 90 yrs grands upstairs. Friendly & nice but limited English, live in their own very finite space. The cable guy had to come fix the internet connection... and his eyes were like saucers taking it all in. I invited him to come back for a visit when the chamber is done, but he hasn't taken up the offer yet.

Well, the improvements seem necessary if the site is going to keep on.


Actually, I should be feeling for you, as I'm still kms away from the commercial flight paths. We can commiserate, but it's a major issue for large segments of the population in every big urban center in the world. I shudder to think of the folks close to the airport in Richmond.

1. maybe the expense on foam in the window would be worth it if it kept the mold down and was removable/washable...?
(I still owe you a contribution, so maybe I can help with the odds and ends...)
2. thanks for the tip on the air purifier. I've had ok luck with leaving my PC on with the fan turned all the way up to 1200rpm, but the suburban cowboys and their super turbo diesel 4x4's getting on the freeway every morning still over power it.

Make sure if you come down to visit your sis you leave a day to visit the cal academy of science in SF, its amazing. I bet you would enjoy all the green building techniques used. The living roof is so cool. ( the big problem is the acoustics are terrible inside! Very loud. I can't imagine what the reverb would measure there.)