Very small control room remodel... less absorption ETC
Old 15th February 2010
  #31
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There's a lot going on here.

I'm still highly in favor of the soffit idea, but I became disallusioned by the 90 degree angles being poo poo'ed. AT 60 degrees, there's no possibility of this working.

Let's assume the angle situation is moot, just to discuss why the modular soffit is insufficient.

Dan you said:

...I expect the sand would do a stellar job of damping speaker cab resonances, plus contain any leaks. A soffit however is not an isolation structure. The principle at large here is similar to a loudspeaker with an infinite baffle. A speaker cone moves back and forward. In order to generate sound we need to lose the back radiation. A speaker box does this. However such a box has issues, modifying the speakers movement due to the springiness of the air inside plus cabinet resonance. Now lets fold that box out into an imaginary 'infinite' baffle. Imagine a huge panel (or wall) large enough to prevent the lowest bass frequencies from sneaking forward, we would have the perfect speaker. Not quite, but that is the idea. A soffit is a very large speaker baffle. That is why it is good to pretty much seal the speaker to it and not allow leaks from behind to come forward. Because the speaker is in the boundary, SBIR effects are zero....
DD


All three structures would be massive. I'll use your qualification of a true soffit, and let's say all faces are constructed of 2 sheets of mdf. Now given that the middle box of the furniture soffit is completely sealed, and placed between to equally massive boxes, how does this not create the effect... even if mostly but not totally? What if the upper and lower boxes had a solid face, but perhaps with perforations to perform as "tuned" traps?

You said: "a soffit is not an isolation structure" but later: "that is why it is good to pretty much seal the speaker to it and not allow leaks from behind to come forward"

This is confusing to me.

The reason I can't build actual walls is the same I can't cut the closet wall. This is a house first and a studio second. Not to mention I don't own it. He's willing to do a lot to get a great studio, but nothing that will lessen the value on his way out.

It seems to me there should be a solution in which these cabinets can behave as a soffit, and perhaps sand is the wrong way to go about it. Even if I build separate frames to this model:

http://www.johnlsayers.com/phpBB2/do...file.php?id=69

and cover all surfaces after they are assembled in the room.
Old 15th February 2010
  #32
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Have at least two books dedicated to Phi. It's way cool how statistics converge on the same number if you look in the right places. The same overall pattern can be seen just about half everywhere if squinting a bit. Neat stuff. This doesn't mean that it's actually Phi. (1+sqrt5)/2 is for calculators. Nature grows in all sorts of ways ever changing ways, it's never precisely at 1,6180339887498948482045868343656. You won't find the best response for your room at that exact point either.

The response at the ear is a product of both speaker and sweetspot placement. Tuning position for modal response only, disregards the opportunity to tweak the modal response with regards to the speaker placements (SBIR). A flatter response will be had if it all works in conjunction. Don't think you should be afraid of going further back, spreading out the triangle. It may help tame the modal issues! In any case, the real modal 38% will be behind the 38% of 9 feet due to the closet.

If it is a problem in the first place..? Is it boomy? Much louder inside than outside?
Old 15th February 2010
  #33
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Partials

Sorry for any confusion, I type quicker than I think!
The perfect soffit would be a hole in a concrete wall with the back of the speaker facing outdoors. Given your considerable construction skills I am sure that you can up with something removeable.
I seem to remember some ancient speaker designs which had simple 'wings' extending the baffle size enormously. Perhaps you should go that direction rather than thinking boxes. Think OTB LOL!
If you had these big soffit walls, probably constructed in sections, fitting snugly into the corners, with no back or side bits at all , it should still be very close to a soffit. Remember that bass wavelengths are enormous. I quite often end up recommending placement of small speakers as close as possible to the wall. Again, almost a soffit.
DD
Old 15th February 2010
  #34
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Quote:
Originally Posted by Lupo View Post
If it is a problem in the first place..? Is it boomy? Much louder inside than outside?
Thanks Lupo for the pointers.

Honestly, the room sounds great. If I weren't to be moving the mixer anyways, I don't know that I would change anything. (I need to move the mixer because it's a real hassle trying to get levels out of the sweet spot, and it will free up some more floor space.) After I get some measurements I may change my tune though. Again, projects made here have so far translated really well in the real world. Surprisingly so.

This thread was started to offer SAC an opportunity at a real world model of a small space, as he had asked for an opportunity in the shroeder frequency thread. It's kinda taken on a life of it's own despite the fact he hasn't spoke here.

Dan, the mixer is essential. I don't want to get into the whole tape machine debate, so I'll leave it at that.
Old 15th February 2010
  #35
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Quote:
Originally Posted by DanDan View Post
If you had these big soffit walls, probably constructed in sections, fitting snugly into the corners, with no back or side bits at all , it should still be very close to a soffit.
DD
can you clarify the bolded portion?

Here's a quick view of 60 degree soffits and the triangle it would create:

As Lupo stated, I could probably back up a bit because of closet volume
Attached Thumbnails
Very small control room remodel... less absorption ETC-sofitri.jpg  
Old 15th February 2010
  #36
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Sure thing

I am talking about heavy MDF panels. Obviously you will need some sort of frame to keep them upright, and they may be in two halves. However I see no real need for them to have sides or backs. Construction may determine that sides or backs are the easiest way to keep them standing up but in that case I see no need for them to be massive.
I am thinking like a wall in a film set here. We only need the front bit.
If your speakers have good horizontal dispersion, that plan looks fine to me. Both myself and a ME friend use our ADAM S3A's like that. Too close theoretically, like big headphones. Works for us. Just in case anyone follows this suggestion, the ADAMs need to be vertical. I have secret information.........
Measurements will focus the mind very quickly on varied listening positions. Let's not forget the back 38% can be just as good or better than the front one.
DD
Old 15th February 2010
  #37
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Dan,

wouldn't having a back and sides allow me to achieve the effect, without having to scribe the panel to the side walls, not to mention remove base, shoe, and crown molding?
Old 15th February 2010
  #38
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Quote:
Originally Posted by DanDan View Post
Let's not forget the back 38% can be just as good or better than the front one.
DD
Not realistic in this room. If I sit at the back 38, not only am I so close to the back wall's reflections, but there's no room for anyone else. Oh, and that tape machine is hot and noisy.

I am considering having a second set of monitors at standing height, orientated to the back 38% for the band
Old 15th February 2010
  #39
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Sure

Yes of course a fully sealed triangular box will work. I was trying to make life easier. The front panel with just enough to keep it upright is all we actually need IMHO. I don't think there would be much difference between a huge panel (wall) with a relatively small gap around it and one perfectly sealed/scribed to the existing walls. That gap is surely tiny compared to bass wavelengths. I wish I could find a picture of one of the old bass bins with fold out wings.
= a thousand words.

DD
Old 15th February 2010
  #40
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Quote:
Originally Posted by DanDan View Post
I wish I could find a picture of one of the old bass bins with fold out wings.
= a thousand words.

DD
No, I get it. But I thought we were trying to keep the waves from the back of the speaker box from coming from behind the panel. That's why I wanted a sealed box.
Old 15th February 2010
  #41
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If guys haven't guessed yet, I just like to draw

How bout some slanted side wall slot absorbers?
Attached Thumbnails
Very small control room remodel... less absorption ETC-slots.jpg  
Old 15th February 2010
  #42
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Ok, I'm done now.
Attached Thumbnails
Very small control room remodel... less absorption ETC-2mix.jpg  
Old 15th February 2010
  #43
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Quote:
Originally Posted by dykstraster@gmai View Post
Ok, I'm done now.
I like it. I'm not sure it'll work though. Did I mention your room is awfully small ?

[sorry]

I'd trace some rays from the monitors on a flat drawing and see where they bounce.

Having an extra set of monitors seems kind of extreme just for the guy standing behind you.
Can't he and anybody else just bring in a few folding chairs or something ?

I won't say anything about the tape machine.

Paul P
Old 15th February 2010
  #44
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Quote:
Originally Posted by PaulP View Post
Having an extra set of monitors seems kind of extreme just for the guy standing behind you.
Paul P
Just wasting time. Sorry I wasted yours too!
Old 15th February 2010
  #45
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Quote:
Originally Posted by PaulP View Post
I'd trace some rays from the monitors on a flat drawing and see where they bounce.
Most certainly. Remember, I don't even know the exact room dimensions yet

If this ever gets off the ground, I will be starting from scratch, and build drawings from the frame up. I'm just bouncing ideas around right now.

Last edited by johndykstra; 15th February 2010 at 10:43 PM.. Reason: paul edited his
Old 15th February 2010
  #46
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Ooops

Jeez John you are definitely showing up my slipshod fast answers here :-O
I was trying to get the picture in my head across, this flat film set panel. Unfortunately I referred to various things which I can see now are confusing and poorly or not explained by me. If you really want to know how these things work, I suggest johnlsayers and studiotips or textbooks.
To clarify my analogies and lite explanations I will add a a few points to illustrate differences and similarites.

An infinite baffle's purpose is to prevent positive and negative pressures meeting.
That baffle could be folded into a box, even a triangular one. This would stop back radiation right? However such a box will prevent the speaker cone from moving so much or so easily. This raises the lower LF limit that such boxes can produce. This is quite high, 50Hz I seem to remember in some sealed box designs e.g. by ATC.
Now if such a box is integrated into a large and massive boundary, or very near one, the sound power is now flowing into half the space. This doubles the SPL in that half space. I would have to look it up for a coherent reason why. but I am sure you know that this doubling is confined to LF. From memory the bass is increased by 6dB per octave as you go downward, within other practical limits of course.
The small sealed baffle speaker has exemplary transient resonse. The bass is fast, for perhaps obvious reasons. It is I believe very well suited to the organic extension downwards of it's LF limit and doubling of output. I would chose such a non ported speaker to begin with. The presence of a half space compensating filter is a priority though. Those sources earlier should have plenty more detail if you need it.
The only thing I am not fully sure of here is whether that gap around the edge would diminish the system. If it does, I reckon it would be minimal, but I can't confirm that.

One last illustrative puzzler. If you built large corner shaped, airtight boxes, with your speaker nicely sealed in the middle. Isn't that simply a very large speaker box with a unnecessary smaller box within it?

DD
Old 15th February 2010
  #47
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Quote:
Originally Posted by DanDan View Post
Jeez John you are definitely showing up my slipshod fast answers here :-O

...words...

One last illustrative puzzler. If you built large corner shaped, airtight boxes, with your speaker nicely sealed in the middle. Isn't that simply a very large speaker box with a unnecessary smaller box within it?

DD
I'm glad to see we are on the same page now.

I have switched the design over to my Event 20/20's. They are ported, but on the front. I would remove the amp from the back of the speaker and re-mount that to the outside of the soffit, extending the speaker leads of course. This allows me to completely seal the speaker within the soffit, no need for cooling. A concept illustrated over at John Sayers, where I should point out, he fully endorses the idea of using Events for soffits.

Regarding your puzzler, how is that any different than a true soffit?
Old 15th February 2010
  #48
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Sorry, that was a bad question, and poorly phrased, I had to leave work.

Let me refer back to my original idea.

Three boxes, stacked on top of each other. The middle box contains the speaker. It is entirely sealed, and filled with sand. This in an attempt to prevent the speaker from radiating to the sides and rear. The top and bottom boxes are there to fill the space, but are super chunks. Helping to not only tame low frequencies in the room, but also to further dampen speaker vibrations.

All in all, I'd say not just larger boxes around smaller speakers.
Old 16th February 2010
  #49
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Here is a detail of the speaker portion of the soffit. The top two layers of 3/4" mdf removed to reveal the amount of cavity to be filled with sand.

You'll notice a tiny hole to allow the speaker leads to penetrate the speaker housing and connect to the amp, which is now external.

The back plate with the amp that was on the speaker would be replaced with a new wood plug, and I'm thinking I will add some blocks of wood to the inside of that plug to compensate for the volume the amp used to occupy inside the speaker. Again, these speakers have no rear vent. They are ported to the front. (Event 20/20s)

The surfaces of the "soffit" that make contact with the monitor are colored grey in the model, to represent a soft seal layer. Possibly mass loaded vinyl, or the thin foam type stuff you find on the bottom of Radial d.i. boxes.

Clearly, there's a weak spot in the isolation. That being the back left corner in this shot... it's the thinnest area to the outside of the box. I'm wondering if I shouldn't just make a channel around the speaker enclosure of this same thickness and fill it with sand... or do the thicker areas provide benefit in spite of the weak link?
Attached Thumbnails
Very small control room remodel... less absorption ETC-iso-detail.jpg  
Old 16th February 2010
  #50
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And with the super chunks re-rendered and an integrated rack on lower right
Attached Thumbnails
Very small control room remodel... less absorption ETC-superchunks.jpg  
Old 16th February 2010
  #51
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Sketchup

I reckon I understand your plan. Unfortunately IMHO it is not going to deliver, and in fact may be extremely troublesome. If you would just measure the response of any speaker in a corner or right next to a SSC, you will immediately appreciate why you never see speakers in corners.
The 'soffit' part is I believe way too small to do anything.
What you have there is a slightly extended speaker in a corner. Also while it can do no harm and would probably have a small benefit, the sand seems a bit overkill.
It is most likely that the Events has sturdy braced cabinets, designed not to vibrate and radiate sound.
Sorry, the ideas are intriguing, look great, but I can't find a reason why they might work.
Very much the opposite I am afraid.
DD
Old 16th February 2010
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Very nice, at least visually. I have a couple of comments.

First, the sides may prove to be too reflective though that depends on what's
on the rear wall (are the sides supposed to be slot resonators ?).

Second, you may end up with a funny dispersion shape from the monitors
because you're missing one side of the infinite baffles. There's bound to be
some diffraction happening at the edges of the empty space between them.
And it also looks like the sound from the monitors is hitting the sides of the
mixer ?

Paul P
Old 16th February 2010
  #53
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Hey guys.

Dan, I'm not arguing in regards to the corner speaker placement... though I don't really see this as in a corner. The problem I am going to run into, is: furniture or not, this is where the monitors are going to have to live. Again, unless I raise them , narrow the triangle, and tilt them downward. This will have them living over the mixer, and I fear the resonance that will come with basically a shelf over the meter bridge.

While I don't doubt that the Events are plenty sturdy, they still have to radiate sound 360 degrees. Why don't they build them with extra mass surrounds? Because they would be a lot heavier and bigger, and cost more money. I'm under no allusion that these iso structures will eliminate unfocused radiation, rather reduce them. After all, if stock Events didn't radiate behind the baffle, they'd be far more recommended.

I was planning to build a little insulation fort and test the performance of an un-surrounded speaker, and repeat the test with the modified version. I suspect the sound will be more focused, but along with that, I imagine there will be a difference in frequency response. A perfect job for a speaker performance eq correction, as it is a source correction, not a room correction.

Paul, those side wall renderings are as slot absorbers. My "plan" for these, is again modular. The current drawing is quick so detail is lost. THe "point" where they meet the back of the side wall would need to be truncated, to allow it to be separately constructed. Where the soffit and side walls meet, I plan to make the dead space rectangle at the corner of the room a separate structure, simply a large rectangle frame filled with pink fluffy. The side walls would be roughly 2' tall sections... and where they are not visible to the room (front edge and toward the wall, they are a panel-less frame, covered in fabric. This will allow bass to radiate through to the front corners of the room, as well as through to the room's side wall. Being that these devices are constructed of roughly 2' tall modules, I could for example, build the ones at ear level to simply be fabric covered... and put slats only higher, or lower, or nowhere... if that's what the room dictates.

In regards to the speakers pointing at the mixer. The woofer is currently a few inches higher than even the knobs, so a bit more still to the top face of the mixer. Is it a concern? Of course. I had planned to make a "mixer pillow" to lay on the surface of the mixer during critical mixes. The mixer is solely a front end device, all mixes are done ITB after tracking.


You guys may have noticed that neither the side walls or the corner modules currently go the entire height of the room. I was imagining cloud panels, constructed in halves, and assembled after being placed above the wall treatments. A sort of fort. This allows me to not do a ton of hangers in the ceiling. As a safety precaution, the soffits and side walls would be strapped to the walls, to make sure my fort doesn't collapse on anyone.

Another HUGE benefit of this plan, as a whole, is that it allow me to construct these devices at my leisure, all the while the studio can remain fully operational. After all, even the monitors to be used aren't even in the studio currently.

I fully plan to stew on these details for a good amount of time, and get as much input from as many people as I can find to take the time. As Andre says "90% planning and 10% construction".

Naturally my biggest concern for this project is the unpredictiblity of the end results.
Old 16th February 2010
  #54
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Paul, in regards to the inner portion of the baffle missing, I hear you. I'm thinking of altering the 60 degree ratio to be a bit wider, allowing me to push the speakers out just a bit further... in an effort to retain a bit more of the inner portion of the baffle. This would also allow for more mass at that troublesome back corner of the iso box.
Old 16th February 2010
  #55
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Fundamental

Hi John, I kinda suspected that there must be some basic premise on which we have very different views and thankfully it has revealed itself at last.
Speaker boxes are generally designed to be as rigid as possible. (There are a couple of 'lossy' designs where the cabinet is designed to radiate. e.g. the vintage Spendor BC1)
Thus there will be relatively little energy radiated backwards by the Event box.
However, the energy coming out of the cone, a large amount relative to cabinet losses, will simply flow around the box. There is nothing to stop it. This is diffraction in action.
Diffraction of Sound
Speakers are nearly omni at LF, due to their size relative to LF wavelengths. The key here is size. The speaker is tiny relative to these LF wavelengths, so it is essential a point source, with consequent omni radiation.
Conversely at HF the speaker baffle size is significant and even large relative to HF wavelengths. It is large enough to stop HF finding its way to the back.

Your test would of course have revealed this, but I hope I have saved you the trouble.
DD
Old 17th February 2010
  #56
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Thank you Dan, a true a ha moment. I guess I was confused, because in the John Sayer's forum, the soffit thread showed the bottom portion of the soffit as an absorber. It was explained as an effect to cure the bounce back from the back of the console. I extrapolated that to a room cure solution, and figured the same could be done above the speaker as well... not realizing, I suppose, the actual purpose of the soffit... thus ignoring my complete disregard for the baffle to extend more to the sides... to the boundary. It is clear now. SO sand is out... pointless. At the very least the top absorber is out, all of this assuming that a greater angle will allow me to create a true baffle. A lot to chew on. Thank you for the clarification.

One clarification though. Let's say the baffle were to extend to say 2" from the boundary... allowing me to still treat these as furniture, is the effect lost? I guess we may be back to the "sub with wings" vision of set walls...

- John
Old 17th February 2010
  #57
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^^ cool. "Infinite baffle" says a lot.

Some small things:

Dont' fix angles etc unless you know for certain they'll work in your room. Better to leave the option open to tune these as the room demands, unless you know exactly what you're doing.

Speakers usually have an acoustic centerpoint around midway between woof and tweet. Looks like the tweet is beaming at the ears in the pics you've posted, but it may be a distortion in the rendering due to the viewing angle.

The baffle walls will eat some of the precious cubic volume in your already small room. Have you heard that your room is SMALL? :P Are you sure it's better than leaving the room open? Have no clue myself..
Old 17th February 2010
  #58
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Quote:
Originally Posted by Lupo View Post
Dont' fix angles etc unless you know for certain they'll work in your room. Better to leave the option open to tune these as the room demands, unless you know exactly what you're doing.
I was just thinking the same thing on my ride in today. Safe to say I'm not at the point I can start building walls and know what the outcome will be. On top of that, soffits would dictate may speaker choice indefinately. I don't really want to be married to the Yamahas or the Events.

Quote:
Originally Posted by Lupo View Post
Speakers usually have an acoustic centerpoint around midway between woof and tweet. Looks like the tweet is beaming at the ears in the pics you've posted, but it may be a distortion in the rendering due to the viewing angle.
No they are currently rendered with the tweeter at ear level. I had read that the tweeter could be viewed as the acoustic center of a speaker, so I rolled with it. This is good new though, as it will allow me to bump the height up a tad and hopefully reduce console interaction a bit.

Quote:
Originally Posted by Lupo View Post
The baffle walls will eat some of the precious cubic volume in your already small room. Have you heard that your room is SMALL? :P Are you sure it's better than leaving the room open? Have no clue myself..
I'm not sure. And I think that's why I'm going to ditch that route. Probably not a whole lot of real world examples of designers putting soffits in a room this small. Perhaps it's because designers don't waste their time with such a space, but more than likely it's because the end result doesn't justify it.

Ah well, sure did look pretty.
Old 17th February 2010
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So lonely in here

back to the drawing board : (

Who am I kidding, this is my favorite part.
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Very small control room remodel... less absorption ETC-bare.jpg  
Old 17th February 2010
  #60
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Gentlemen,

Attached are two views of the same scenario. Side and top.

Is it a problem to have such a downward angle?

I would build stands kinda like this
Attached Thumbnails
Very small control room remodel... less absorption ETC-tilt-side.jpg   Very small control room remodel... less absorption ETC-tilt-top.jpg   Very small control room remodel... less absorption ETC-rough-stand.jpg  
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