Changing Control Room Ratios (plus a parallel wall question)

[Wes Lachot]

Seamus,

The best length dimension in your case would be 20.425 ft. This is a ratio of 1.9/1 with the height dimension, and a ratio of 1.57/1 with the width dimension.

This is your best bet because 1) it is always best to stay within the octave (2/1) for all three dimensions, all else being equal, and 2) it is the golden ratio between the two largest dimensions, which is pretty hard to beat. (The only two ratios that are as good or better in some cases are 1.26/1, or the square root of the golden ratio, and 1.4/1, the square root of two.)

Incidentally, your ratio of 1.21/1 is also a good one - a minor third. So your room will be an augmented major seventh chord with no third degree. Pretty hip...no perfect intervals...

Wes

Wes Lachot Design || Studio Design and Acoustic Consulting

[jayfrigo]

Agreed with Wes. Remember, there's more than just the ratio to consider. If you have a few that look good, consider other factors and don't blindly clint to a single criterium in a cognitive vacuum. 17" deep is pretty small, so even if that ratio had looked a tiny bit better, you probably would have wanted to pass on it for other reasons.

Where will you sit in the room to avoid problematic nodes and/or antinodes, especially the room's center? What gear do you need to fit? Are the monitors free standing? Do you want to be able to use diffusion in back? Will clients be in attendance? With all these things taken into consideration, you'd probably pass on 17, no matter how good the math looks. Also remember that with enough treatment of the proper kind, any reasonably good ratio can work just fine. It's not like there is one, and only one possibility to the exclusion of all other factors.

[Seamus TM]

Thanks, guys.
I was hoping that 17 feet was not the answer for the reasons that Jay suggested.
Too small.

What about making the new wall not parallel with the back wall?
I feel like it's more trouble than it's worth and could introduce bigger problems than we already have.
Keep in mind that the wall that we are constructing will be the front wall.
Seems like a bad idea.

Thanks, again,
Seamus

[nosebleedaudio]

Originally Posted by Mumblesound

Thanks, guys.
I was hoping that 17 feet was not the answer for the reasons that Jay suggested.
Too small.

What about making the new wall not parallel with the back wall?
I feel like it's more trouble than it's worth and could introduce bigger problems than we already have.
Keep in mind that the wall that we are constructing will be the front wall.
Seems like a bad idea.

Thanks, again,
Seamus

Which direction would you slant?
Could make things worst..
I would not worry about parallel, symmetry is very important as well...
People think that any wall being parallel is the kiss of death...
Treatment is your friend.. but it also depends on other things..
A well designed room requires time and experience, no substitute for either one...

[Seamus TM]

Thanks, everyone.

Sounds like I'll make it 20.425 and parallel to the back wall.

Seamus

[Seamus TM]

One more hair-brained question.

There is a very large room behind the control room that is just storage.
I am able to take the back wall of the control room totally out and it would open up into this room.

My question is, would it be nuts to take that wall down and replace it with 6-10 feet of velocity trapping (705)? In my head, it would be like there was no back wall at all... would that be a good thing?
In reality, the back wall would be about 75 ft away from the front wall.

Thanks,
Seamus

[Ethan Winer]

Originally Posted by Mumblesound

it would be like there was no back wall at all... would that be a good thing?

Probably!

[Glenn Kuras]

My question is, would it be nuts to take that wall down and replace it with 6-10 feet of velocity trapping (705)? In my head, it would be like there was no back wall at all... would that be a good thing?
In reality, the back wall would be about 75 ft away from the front wall.

If you do that use less dense fiberglass. The fluffy stuff would work just fine. BTW that would be ONE THICK BASS TRAP!

[Seamus TM]

So, I wouldn't need to buy 800 cases of 4" 705?
That's a good thing.

If I just used the fluffy, how deep do you think I should go for it to be worth it?

Thanks,
Seamus

[Seamus TM]

So, I can only really do a 6' x 8.5' section of the entire 13' x 10.75' back wall with the massive bass trap idea.
It's right in the middle of the wall.

That would leave a 2.5' border of actual wall up the sides and along the top.

Still worth trying?

Thanks,
Seamus

[Wes Lachot]

Originally Posted by Mumblesound

My question is, would it be nuts to take that wall down and replace it with 6-10 feet of velocity trapping (705)? In my head, it would be like there was no back wall at all... would that be a good thing?
In reality, the back wall would be about 75 ft away from the front wall.

Thanks,
Seamus

Seamus,

No, it would not be better to do that. If you need proof that massive basstraps many feet thick are not the answer for the back of a control room, just take a trip to Nashville where you can hear plenty of rooms built along those lines. Typically, when you sit on the couch in these rooms, a kick drum sounds like it has the EQ of a pencil on a shoebox. Not the way a kick drum should sound, and quite misleading to the listener.

If you play your cards right, 12-16" of velocity trapping will keep your head close enough to the rear wall to actually hear some bottom end. And anyway, why would you want to take those nice ratios I turned you on to and just toss them aside? Maybe I didn't charge you enough...

--Wes

[jayfrigo]

Originally Posted by Wes Lachot

No, it would not be better to do that. If you need proof that massive basstraps many feet thick are not the answer for the back of a control room, just take a trip to Nashville where you can hear plenty of rooms built along those lines. Typically, when you sit on the couch in these rooms, a kick drum sounds like it has the EQ of a pencil on a shoebox. Not the way a kick drum should sound, and quite misleading to the listener.

Agreed that a massive trap as described is not the best answer here, but that doesn't mean some manner of sizable trapping in the rear of a control room isn't a valid and very workable approach in the right application. Using some of that space for trapping may be appropriate if designed right, but as always, it needs to be part of the whole room plan, and you can't simply open up a huge amount of space, moving the structural boundary back (essentially moving the wall), and maintain the ratio's predicted effects.

Re: the low end response in the rear of the room, I hate how the couch in the back of most control rooms is a boomy mess with unrealistic bass reinforcement. You don't need a wall behind you to hear big bass from a kick drum in a good room with good monitors. If the pressure wave passes you before getting trapped behind you (as much as is possible from a few feet of fiberglass), you will hear it, variables such as proximity to nodes/antinodes (areas of constructive and destructive interference due to boundary effect) and monitoring issues not withstanding of course.

I suppose what I'm saying is that there is some middle ground. The primary seating area for the engineer is most important, but the client often listens on the couch, so it shouldn't be ignored, whether too bassy or too dry. One or two of those Nashville rooms sound OK too, BTW. The good ones don't put the couch in the middle of a nasty node due to the depth of the trap in relation to the actual structural depth of the room. There are good and bad examples to be found of many techniques.

[Seamus TM]

Wes:

OK, OK! Uncle!
After thinking some more about it, I could see how the idea might be useful if I needed to fire down the width of the room, as opposed to the length... maybe..I guess... right? (don't hurt me, I'll give you my milk money).
Since my room is pretty narrow, it would probably cause more problems than it helped.
On a side note, I just noticed how many posts you have. You are a very welcome addition to this forum. Thanks for being here.


Jay:
Understood, agreed and thank you.

Seamus

[Weasel9992]

Originally Posted by Wes Lachot

Seamus,

The best length dimension in your case would be 20.425 ft. This is a ratio of 1.9/1 with the height dimension, and a ratio of 1.57/1 with the width dimension.

This is your best bet because 1) it is always best to stay within the octave (2/1) for all three dimensions, all else being equal, and 2) it is the golden ratio between the two largest dimensions, which is pretty hard to beat. (The only two ratios that are as good or better in some cases are 1.26/1, or the square root of the golden ratio, and 1.4/1, the square root of two.)

Incidentally, your ratio of 1.21/1 is also a good one - a minor third. So your room will be an augmented major seventh chord with no third degree. Pretty hip...no perfect intervals...

Wes

Wes Lachot Design || Studio Design and Acoustic Consulting

Great post. Welcome aboard Wes!

Frank

[Seamus TM]

This is not sucking up.
I just checked out your web site, Wes, and all I can say are words like "wow" and "inspiring".

Thanks,
Seamus

[Wes Lachot]

Seamus,

Thank you very much.

By the way, your 20+ ft. deep room will be nice for monitoring. I've found that if you monitor a couple of feet forward of the midpoint of a 20 ft. deep room, the 12 ft. distance from the back wall puts you in the 1/4 wavelength null point of 24 Hz or so, a very acceptable frequency for a null since it's all but inauduble anyway. The biggest thing you have to worry about then in terms of rear wall reflections is the 3/4 wavelength null (72 Hz). We use tuned traps to combat these type of nulls.

Rooms that are much less deep move the 1/4 wavelength null up unto the 30s and 40s where it really hurts the bottom end. That's fine for certain production tasks, but for critical mixing, a 20 ft. deep room is pretty deluxe.

--Wes

[Seamus TM]

A-ha.
That's great info.

I suppose that rooms that are deeper than the 20 ft would be fine at the 1/4 wave but the 3/4 wave would start to move down, as well, making it more difficult to treat... right?

So, would that be based on the speakers being pretty close to the front wall?
I noticed that you use a lot of soffit designs in the studios that you work on.

Thanks again, Wes.

[Wes Lachot]

Seamus,

Yes, that's right. When you get away from the soffit thing, it gets real complicated fast, because now you are hearing strong reflections from the front wall, and they're louder than h-e-double-hockey-sticks because they're so close to your face. So you get this big huge dip at a fixed frequency (unlike the dip from the back wall whose frequency varies with listener position). The frequency of that response dip is dependent upon the distance of the speaker from the front wall.

The problem with a fixed frequency dip is that it won't go away no matter where you stand (as long as you are between the speakers and the rear wall), so you really start believing it as the real frequency response of the speaker, and hence the mix. So to counteract this response inaccuracy you tend to add back a lot of bass, so that when you take the mix and play it back in a car system, it sounds like mud.

So the upshot of all of this is that I'm a true believer in wall-mount speakers.

--Wes

[Seamus TM]

Originally Posted by Wes Lachot

So the upshot of all of this is that I'm a true believer in wall-mount speakers.

--Wes

That's the upshot?
Yikes.

Well, as much as I'd like to, we can't do soffit mounted speakers in our current location... and/or budget, most likely.

I guess that we'll do the old "measure response-move the speakers-measure response-move the speakers" and so on and so forth.

I'm guessing that since the speakers would be relatively close to the front wall, (in my case- somewhere between 0 feet and 8 feet) that the null would be kind of high in the bass range, no?

Thanks again,
Seamus

[Wes Lachot]

Originally Posted by Mumblesound

That's the upshot?
Yikes.

Well, as much as I'd like to, we can't do soffit mounted speakers in our current location... and/or budget, most likely.

I guess that we'll do the old "measure response-move the speakers-measure response-move the speakers" and so on and so forth.

I'm guessing that since the speakers would be relatively close to the front wall, (in my case- somewhere between 0 feet and 8 feet) that the null would be kind of high in the bass range, no?

Thanks again,
Seamus

Seamus,

The frequency of the front wall null is computed by taking the speed of sound (1130 ft/sec.) and dividing by 4, then dividing that quotient by the distance between the speaker and the wall. So if the speaker is 7 ft. from the front wall, the null frequency would be 40 Hz, since 1130/4 = 282.5, and 282.5/7 = 40.4.

--Wes

[Seamus TM]

Right-o.
This is where I start to chase my tail.

Would that 40Hz null be "at" the speaker, or "at" the mix position?


By the way, one of my partners is going to Electric Lady, today.
I told him to check out your work.

Thanks,
Seamus

[G. E.]

Wes,

could you please elaborate on the measurement of the "distance between the speaker and the wall"? Is that the distance from the rear of the speaker or from the driver or the way sound has to pass around the speaker or...?

Many thanks, Gernot

[Ethan Winer]

Originally Posted by G. E.

could you please elaborate on the measurement of the "distance between the speaker and the wall"? Is that the distance from the rear of the speaker or from the driver or the way sound has to pass around the speaker or...?

These may help too:

Frequency-Distance Calculator

Front Wall Absorption

--Ethan

[Wes Lachot]

Seamus,

That fixed-frequency null will be present anywhere along the axis between the speaker and the listening position. That's what makes front wall nulls different from rear wall nulls, which change frequency as you move around the room. Front wall nulls, on the other hand, stay fixed in frequency as long as the listener is positioned so that the speaker is between the listener and the front wall.

Gernot,

Good question. I always use the voice coil position for my calculations. There's always a bit of rounding involved, but for bass freqencies, this amount of rounding is inconsequential.

--Wes

[G. E.]

Ethan,

don't you think that the directivity mentioned in the article is related to the speaker cabinets themselves (as opposed to the whole speaker) and sound waves from the speaker cabinets start bending around the speaker enclosure above a certain frequency? From my experience sound treatment (mid to high frequencies) of the front wall can make a huge difference -- personally I like putting up large diffusors (closed design) on the wall behind the speakers for those of us who have to stick with a non suffit-mount setup... Greets, Gernot

[jayfrigo]

Originally Posted by G. E.

personally I like putting up large diffusors (closed design) on the wall behind the speakers for those of us who have to stick with a non suffit-mount setup... Greets, Gernot

To get diffusion in the low frequency bands in question you'd need a sizable diffractal or a very deep 2D, neither of which is very plausible behind the speakers in a typical room; not to mention that you'd need to get quite a distance from it for it to truly be effective.

I tend to use a combination of trapping and broadband absorption behind the speakers when not soffiting. Even though infinite baffle (soffiting) solves some problems and looks great on paper, often free-standing monitors end up sounding better. They're certainly easier to fine tune after the room is built. Notice that in the vast majority of high-end mastering rooms the monitors are free-standing. Clearly both approaches can work well.

[davew]

i'm sure many of you will think this post is pure bull-turd! but a buddy of mine actually has 'part of a car,' with audio system in a room of his studio. no wheels, but indeed an enclosed car body with sound! sure saves time! thinking about doing the same!

[G. E.]

Originally Posted by jayfrigo

To get diffusion in the low frequency bands in question you'd need a sizable diffractal or a very deep 2D, neither of which is very plausible behind the speakers in a typical room; not to mention that you'd need to get quite a distance from it for it to truly be effective...

Let me be more specific about upper mids/highs and front wall diffusor placement. For example setting up this diffusor (sorry, no better image available -- theoretical bandwith 1900Hz-2500Hz) instantly made THE most audible improvement ever for me (depth of the soundstage), I clearly preferred it over using absorbption. Btw: speakers have 3ft distance to the front wall, diffusor is a only few inches away from the front wall. Any explanations?

As for the low freq. response I really appreciate Wes' findings: some "problems" follow the speaker position only others depend on both speaker and listening position...

[Seamus TM]

Originally Posted by Wes Lachot

Seamus,

That fixed-frequency null will be present anywhere along the axis between the speaker and the listening position. That's what makes front wall nulls different from rear wall nulls, which change frequency as you move around the room. Front wall nulls, on the other hand, stay fixed in frequency as long as the listener is positioned so that the speaker is between the listener and the front wall.


--Wes

Crazy.
So, after I build the wall to change my length to 20.425, I would probably want to position the speakers in a place that makes that null higher in the frequency spectrum so that I could hit it with broadband absoption. Otherwise, if it's too low, I'd have to build some tuned traps...

does that even make sense...?

Thanks,
Seamus