John Sayers' Recording Studio Design Forum Archive

Hello,

1. What dimensions and density to I need for DIY FOAM BASS TRAPS?
2. How do I keep my Genelec tweeters from popping?
3. My Hammond organ is playing three-and-a-half steps flat!

I have recently relocated my studio from Washington DC to Lusaka, Zambia (Africa). My wife works for USAID and we are trying to help combat the rampant AIDS epidemic here. I am maintaining my client base while working on my second album. If you want to, you can see my credits here:
http://allmusic.com/cg/amg.dll?p=amg&sq ... qlgldse~T4

I have a terrific room it is 24.5’ long, 16.5’ wide and 9.5’ high, concrete block construction with tile floors. I am monitoring on Genelec 1031As with a 1092A sub (but I can hardly bear to turn them on due to a 70Hz rumble and the power issue described in question 2), Yamaha NS10s and Sony SRS-58PCs (desktop computer speakers – I love them). Photos below.

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1. What dimensions and density to I need for DIY FOAM BASS TRAPS?

I’d build super chunks but I have not been able to find any type of rock wool, mineral wool, or fiberglass insulation. The temperature rarely drops below 70 degrees here and insulation of that type does not seem to exist in Zambia. Anytime I ask construction people about fiberglass, I get referred to a boat repairman or a roofing tile manufacturer. If I ask about rock wool I just get a blank stare.

I was able to find a foam manufacturer! He makes seat cushions and mattresses but he’s taken an interest in my cause and is willing to cut corner style foam bass traps. He has medium, high and extra-high density foam. When I asked him what the density per cubic centimeter of each was, he paused for a moment and then reiterated that he had medium, high, and extra-high.

What dimensions do I need?
What density do I need and how do I translate it to my manufacturer?

(I sent these questions via email to Auralex and, understandably, got a very quick and kind response saying that they won’t tell me anything about density or dimensions. They directed me to their sales affiliate in South Africa).


I know these next two questions don't fit into the Acoustics forum but since I can only get online about once a week here, I'm trying to get everything done in one post - if this breaks too many rules than please disregard questions 2 and 3.

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2. Popping tweeters - Power-conditioning question.

Zambian power is 220 Volt 50 Hz. I have everything plugged into a 5000 watt step-down transformer / regulator. The computers, hard drives and computer monitors are plugged into a 1500 watt APC UPS. So far, everything is running fine except for when Zambian power dips (it’s at its worst between 10am and 1pm), the relays switch in my transformer / regulator and I get a heart-palpitating pop out of my Genelec tweeters. I’ve tried plugging them into the APC UPS and it lessens the pop but not by much.

I have not yet tried switching them to 220V and plugging them directly into the wall because that idea really scares me.

How do I stop the popping?

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3. The Problem With My Organ.

My Hammond M3 is playing three-and-a-half steps flat! I didn’t think that was possible but the organ was designed to run on 120v at 60Hz and it’s getting 120v at 50Hz. Is that my problem and if so;

How do I make up the missing 10Hz?

Thanks for a terrific resource!
Andrew

I really don't have good news for you with regard to a 60Hz power source. My company (at my real job) had a similar issue when we were doing some clothes washing machine work for an OEM. We sent the machine to our parent company in Europe, and they had exactly the same problem. The way they found around it was to purchase a generator designed to output at 60Hz.

There are solutions for it, but they aren't exactly easy on the wallet.

Regarding the foam: It may or may not work, depending on what TYPE of foam it is. You'll have to find out if it is "open cell" or "closed cell". What you want is open-cell: Closed cell is pretty useless for acoustical purposes. Of course, this refers to the structure of the foam at the microscopic level, and only the manufacturer can tell you for sure what type it is.

Regarding the popping tweeters: Your UPS is probably not a true on-line, double-conversion UPS, which is what you need. "Double conversion" means that the incoming mains power just charges the batteries, and the batteries just run the inverter, which is always on, always producing clean sine-wave power. You need to look for one that does that. Another possibility is a good power conditioner with built-in filtering, but I'd till prefer a UPS. In the meantime, until you get one, I'd suggest that you NOT connect your Genelecs!

Regarding the 50/60 Hz issue: Bob is absolutely right: Your problem can be solved, but cheap it ain't! Since you need a proper UPS anyway, that MIGHT be one possibility: I seem to recall reading somewhere that there are a very few UPSs that will take in 50Hz power and produce 60Hz, but I don't recall who makes them. However, cost will probably be an issue: it might be cheaper to just buy a new organ! (especially if you have to import the UPS from somewhere overseas...)


my 0.02


- Stuart -

Hello Bob and Stuart,

Thank you for the replies,

Hammond Organ:
I’ve been able to do some more Hammond organ research and yes, I do have a frequency problem. The instrument will only play in tune with a 60hz power source. There is a company called TrekII (http://www.trekii.com/) that makes replacement parts as well as all sorts of modification kits for Hammonds and Leslies. Their 50hz to 60hz converter (SC-60D-2) goes for $411. Not an option for me.

Power:
The Online UPS is terrific information, thanks Stuart! I’ve done some research and an Eaton Powerware 9130 is what I need. It is both an Online UPS and it can function as a frequency converter! I could fix 2 problems with one unit! Unfortunately they start at $450, but since I’ll probably be overseas for some time it will be a worthwhile investment. I’ll be able to get it here without any problem, if I had to pay for international shipping, it might be out of the question. Eaton also has a lot of downloadable PDF files full of everything that you need to know about power regulation and UPSs. http://powerquality.eaton.com They build units that you can run a hospital on.

DIY Bass Traps:
I spoke with my foam manufacturer again, he was very confused when I asked him if he had open cell or closed cell foam. He first asked me how open I wanted it, and then said that you could blow into it. So I do think we’re dealing with open cell.

Do density and dimensions correlate to each other? Are density and dimensions important or am I over thinking things? Do I just get as much of the most dense material that I can afford and stack it in all of my corners?

Thanks,
Andrew

I spoke with my foam manufacturer again, he was very confused when I asked him if he had open cell or closed cell foam.

If the MANUFACTURER doesn't even know what kind of foam he is making, or even what the density is, then I'd sure as hell switch to another one, who does! Or if you can't find another one, then just go with plain old fluffy pink fiberglass insulation, or plain old mineral wool insulation. Surely there must be SOMEONE in the country that makes it or uses it? What about cold storage rooms, air conditioned trailers, and suchlike? The folks who make those must use come kind of insulation that might be useful to you. Maybe people don't need insulation in your country to keep the heat in during winter, but I'm betting that they do need to keep the heat OUT during summer!

- Stuart -

"cold storage rooms, air conditioned trailers, "

A thermal environment like cold storage and time sensitive transportation trailers make use of styrofoam which is known to be of no use in an acoustical environment.