Basics of RFZ design

dymaxian · Post by **dymaxian** » Wed Dec 10, 2003 2:15 am

Hey guys! If some of you forum-veterans here can point out any older threads that talk about RFZ design guidelines, I'd appreciate it. I ran a search, but aside from one excellent post that discussed creating a horn-loading effect (certainly didn't occur to me before) I couldn't find much more than just the mention of RFZ.

I'll be using free-standing speakers in my design, and I'll probably end up doing the control room/practice room combination.

Thanks for the help!

Kase
www.minemusic.net

giles117 · Post by **giles117** » Wed Dec 10, 2003 5:00 am

The info in detail is by Barefoot in the acoustics forum. that might be the thread you are speaking of. it is an excellent piece of information.

Bryan Giles

knightfly · Post by **knightfly** » Wed Dec 10, 2003 5:06 am

Kase, I've seen people refer to RFZ and heavy absorption as one and the same, but it's really not. If you're going to build angled walls to create an actual RFZ, it would be silly NOT to flush mount your speakers. The difference is large enough to be worth the effort.

In all fairness, I'll once again point out that the majority of my info comes from study, whereas John's is firsthand - still, nothing I've seen from Everest, Newell, Moulton, Storyk or anyone else refutes the advantages of flush mounted monitors.

This can be as simple as a pair of "gobos" with holes in them and speaker stands behind, to full built-in-the-wall (but isolated) construction. The goal is to extend the baffle in every direction enough to defeat the lower frequency "wrap-around" and force the sound to the front only, vastly simplifying the reflection pattern at lower frequencies. This gets rid of phasing problems at lower freqs, which cleans up and tightens the bass response much closer to what you'd hear if your speakers were outside and you only got the direct sound.

Philip Newell is particularly adamant about the necessity of accurate monitoring, to the point that he's written a separate book JUST on that. I've not read that one yet, I'm still wading thru Recording Studio Design, and Project Studios - A More Professional Approach, both of which are excellent. The second one can be had used for around $40, the first runs $80 and so far appears to have some of the same material in it but goes into more depth.

Do you have any floor plans drawn yet? If so, might wanna throw 'em out for grins (we're too polite to actually laugh

) Ignore the last, half-awake attempt at humor... Steve

dymaxian · Post by **dymaxian** » Wed Dec 10, 2003 5:53 am

Hey Steve!

All valid points. The reason I'm close to giving up on soffit mounting my speakers is because they're Mackie HR824s, and no matter how much reading I've done around here, I can't figure out how Giles keeps his from overheating... I have a pair of broadcloth dustcovers on them when not in use, and just leaving those on while playing music makes the speakers overheat. I suppose I could install an exhaust fan system using a couple little PC fans, but we'll see. I suppose I could design the control room adjacent to the mechanical room, with the control room front wall between them and the speaker's backs just venting right back at the furnace... =\ I could set up a air-exchanger there, too...

I didn't know that just building gobos in front of the speakers would have the same effect, tho. I'll look into that more (there's a recent thread with a bunch of info on that...).

I've been trying to keep the design of my new studio as simple as possible- I'd thought soffit mounting the speakers would complicate the design... But it sure eats up floor space to have freestanding speakers, so I'd LOVE to be able to build them into the walls...

As far as plans go (*snicker*) I have an AutoCAD drawing with about 40 different possible designs on it. I'm at the playing stage right now... my new wife and I are still looking for a new home. I'm exploring every option I have right now, that's all.

I can post a couple of the designs I have, tho. There's a couple that have died on the vine, but theres a few that look pretty good to me.

It'd give you a good laugh, tho...

Thanks for the advice!

Kase
www.minemusic.net

giles117 · Post by **giles117** » Wed Dec 10, 2003 6:08 am

Is your room air conditioned? I am assuming they are overheating while freestanding right now correct?

That is baffling, I have had mine since a month after they came out. Very Low Serial #'s and never had overheating prob.s unless I was in an EXTREMELY hot and humid environment.

OR when I was running them at extreme volume levels.

I tend to mix and montior between 70 and 85/86 dbA

Bryan Giles

dymaxian · Post by **dymaxian** » Wed Dec 10, 2003 6:39 am

Yeah, it's odd. That might have been a fluke, but they sure felt awful warm. And the dustcloth wasn't sheepskin or anything...

I emailed the guys at Mackie and asked them about soffit mtg them, too; their response was pretty much the same as Barefoot's... you're better off not doing it. Between the rear porting and the overheating problem, it's too risky. There was a plan around here somewhere for a soffit-mount with an air passage behind the speaker, but I can't imagine that enough air would get thru it without a fan helping out.

Maybe that's not such a big deal...

So I'm just trying to find a good spot to stand them. I havent had too much trouble getting a room shape to push reflections past the sweet spot instead of into it, but they sometimes get pretty complex.

I dunno. In the room I'm in now, they're almost flat against the wall, and they sound just fine.

Maybe I should just put them on a shelf, right against the front wall, and put 4" of rigid fiber-board behind them. *shrug*

I'll put up one of my designs for free-standing speaker RFZ later on, Steve. That'll make you laugh plenty.

Kase
www.minemusic.net

knightfly · Post by **knightfly** » Wed Dec 10, 2003 6:55 am

"Maybe I should just put them on a shelf, right against the front wall, and put 4" of rigid fiber-board behind them." -

Yeah, that's definitely one option - have you downloaded Barefoot's Wall bounce calc on the Acoustics forum? Eye-opening... Steve

giles117 · Post by **giles117** » Wed Dec 10, 2003 7:01 am

Well for me that is the soffit plan I built. So your units actually shut down? I'd have to finger point at Mackie. Genelecs don't over heat and the only diff between them and the 824 is the passive radiator.

Perhaps the soffit with the vent hole and a small cpu fan to cirulate air past the heat sink?

Just really odd to me. Convection cooled amplifiers usually are made to wrok in some of the worst situations. AB amps live for instance on a hot Nevada day don;t go down. Your transistors might not be properly mounted on the heat sink. Which again would be a mckie problem or they didn't use enough heat transfer gunk when mounting the trannies.....

Having built amps back in the day (205wpc mosfet deals) you learned to proplery mount the trans on the heat sinks or you;d get hot spots and overheating would occurr.

Bryan Giles

How long have you had your mackies? I f they are Overheating in the free field you have a warranty issue.

dymaxian · Post by **dymaxian** » Wed Dec 10, 2003 8:13 am

Anyway, assuming that I'm using free-standing monitors, what precisely is the idea behind creating a reflection free zone? Is it to keep 1st-generation reflections from one monitor from reaching the opposite ear? This seems like the primary goal, but there's probably more to it. If I was gutsy enough, I'm sure that I could create a wall design that keeps almost all the wall reflections from BOTH speakers from reaching the listening position from the front half of the room. The term 'reflection free' is ambiguous here...

If I was too worried about reflections off the walls, I'd just mix on headphones and be done with it... but that's not where I'm headed.

Thanks!

Kase
www.minemusic.net

Post by **John Sayers** » Wed Dec 10, 2003 8:37 am

Kase - the RFZ is primarily for soffit mount speakers systems as Steve mentioned. If you are going to free stand your speakers then the front wall should be treated differently - i.e. Dead. Here you are trying to reduce the low frequencies that are radiating 360 degrees from your speakers - as opposed to the high end which is directional. When the low end reflects off the front wall it comes back to the listening position and combines with the direct signals causing phase cancellations/additions, thus muddying the low end response.

Thus instead of soffit mounts you should build bass traps across the front walls and in the corners to solve this problem. The splayed side walls are relevent to both situations.

cheers
john

dymaxian · Post by **dymaxian** » Wed Dec 10, 2003 9:04 am

Hey John! Thanks for the advice! I suppose it'd be a lot easier to build that way... just need to allot enough space there. I think this will make the overall room sound better- one of the design ideas I'm going with now is to make the tracking room big enough to also be a practice room, rather than dedicating a second live room to my band's rehearsal. With the 'mixing' end of the room highs-reflective and bass-absorptive, it won't make the room overall sound too dead.

Kase
www.minemusic.net

knightfly · Post by **knightfly** » Wed Dec 10, 2003 1:33 pm

Good plan Kase - if you can possibly spare the space, bigger is always better acoustically. Even with the exact same room RATIOS, if the actual dimensions are bigger, all modes will move down in frequency, so the point where modal response smooths out will be lower in frequency and the room will have a flatter response within the music passband... Steve

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