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PostPosted: Tue Jul 28, 2015 7:20 am 
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Hi!

After moths of being just the reader of this forum I decided to ask some questions. I'm trying to figure out the best way for flush mounting my monitors and prepare as best as I can before building process. I've found the formula below posted few years ago by Eric Best.

Eric Best wrote:

f3 = 4650/x where x is the baffle width in inches.

So for the 7" baffle we used you have 4650/7=651.43hz.


I understand that 7" and 18" width baffles with single driver flushed in that baffles are just examples and showing how frequency roll off can vary. If we change values to let's say 50" width (similiar in size to real baffle), the roll off frequency will start from 93Hz, which means (if I understand correctly) that all below 93Hz would be boosted +6db when flush mounted. Or maybe I've messed all this?!

1. If monitor have low shelf control starting from 300/400Hz wouldn't it make a huge frequency drop between 93 and 300/400hz?

2. What about the height of the baffle, or the surface size in m2? Isn't it required?

3. What is the meaning of 4560 number?

4. If my understanding is correct, should I build crossover starting the shelfing from 93Hz down instead of monitors build in low shelf?

I hope I've put it clear as my english is very poor. It would be great to hear from you guys, and Eric.


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PostPosted: Wed Aug 26, 2015 11:41 am 
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Quote:
which means (if I understand correctly) that all below 93Hz would be boosted +6db when flush mounted. Or maybe I've messed all this?!
It won't all be rolled off: it's not a sudden drop in response, but a gradual change, over a couple of octaves. Also, the equation gives you the center point of the roll-off: the point where it is -3dB. So there's a couple of octaves below that point, and a couple above it.

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What about the height of the baffle, or the surface size in m2? Isn't it required?
No. because the baffle step is all about the smallest dimension of the baffle, and with most speakers, that is the width. If you have a speaker that is wider than it is high, then you would use the height for your calculation, not the width. Whichever dimension is smaller.

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What is the meaning of 4560 number?
It's a constant. It is 4560 if you are measuring in inches, 380 if you are measuring in feet, and 115 if you are measuring in meters.

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If my understanding is correct, should I build crossover starting the shelfing from 93Hz down instead of monitors build in low shelf?
If the equation gives you 93Hz, that's the center point of the curve: the point where the roll-off is already 3 dB. The roll-off would start 2 octaves higher, at about 372 Hz, and it would end 2 octaves lower, at about 23 Hz. so your shelving filter would be designed for those parameters: start the roll-off at 372 Hz, -3dB at 93 Hz, and -6 dB at 25 Hz. Note (the 2 octave things is just a very rough estimate: there are more accurate ways of calculating the end points.)


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PostPosted: Sat Jun 25, 2016 11:09 am 
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Location: San Antonio, Texas USA
The more I read, the more questions I have, and I was hoping you could clarify some things for me.

1. Why does John's soffit design require the monitor to be placed inside a box, and Thomas's does not? Are there drawbacks or advantages to either?

2. I see no provisions for ventilation using Thomas's design. Does filling the cavity with loose fluffy pink stuff allow enough ventilation as is? Or should an airway be provided?

3. Should the bezel be as large as possible both horizontally and vertically? Ie. Floor to ceiling/wall to wall using Thomas's design? Or could a rigid backed broadband absorber be placed above and below the bezel? If so, how tall vertically would the bezel need to be before adding a little absorption?

4. I've read that the monitor should be centered in the bezel and I have also read that it should not. Which is correct, or is that dependant on the flush mounting design implemented? If an offset is preferred, how great or little of an offset is ideal?

5. For example, if I created a bezel that was 48" wide and 24" tall, would the center frequency be approx 93 or approx 227?


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PostPosted: Sat Jun 25, 2016 1:03 pm 
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Quote:
1. Why does John's soffit design require the monitor to be placed inside a box, and Thomas's does not? Are there drawbacks or advantages to either?
John's design holds the speaker very rigidly in place, since the speaker is attached to the baffle via the box. John's design is massive and rigid all around, keeping things very firmly in place. Thomas's design still keeps the front baffle very rigidly mounted, but doesn't need to be as tight on the speaker, since they are independent with his concept.

Quote:
2. I see no provisions for ventilation using Thomas's design. Does filling the cavity with loose fluffy pink stuff allow enough ventilation as is? Or should an airway be provided?
You still need ventilation. I think Thomas does not show that for clarity, but you do still need it. You can't enclose a speaker that is generating hundreds of watts of heat in a small area with no ventilation and expect it to keep on working.

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3. Should the bezel be as large as possible both horizontally and vertically? Ie. Floor to ceiling/wall to wall using Thomas's design? Or could a rigid backed broadband absorber be placed above and below the bezel? If so, how tall vertically would the bezel need to be before adding a little absorption?
That's a little tougher to answer!

The basic concept of flush mounting id to create an "infinite baffle" for the speaker. One that appears infinitely large acoustically. In other words, much lager than the longest wavelength that the speaker can produce. Obviously, in the real world that is impossible, since we are talking about waves that are dozens of feet long. So next best is just "as big as possible". But even that isn't strictly necessary, as you can see from the baffle-step equation. The real purpose of the baffle is just to prevent the wave from "wrapping around" behind the speaker (technically, it prevents it from radiating into full space and forces it to radiate into half-space), so as long as your baffle does that, you are fine. So if your baffle extends out to the side wall and front wall, you are fine horizontally, and if it extend up to the ceiling and down to the floor, you are fine vertically.

But even that isn't necessary: There's another issue involved here: the further away you go along the face of the baffle, the smaller the effect is, and the lower the problematic frequency is, so it gets to the point where level is low enough and the frequency is low enough that it doesn't really matter too much any more.

That's why John can do exactly what you suggest: set up a hard-backed absorber below the speaker to deal with reflections from the back of the desk. You could, in fact, do that on all four sides, starting a a decent distance from the speaker center. The further you get away from the speaker cone, the deeper the absorption can be.

The above applies to all soffit designs, not just John's or Barefoot's

With my soffit designs, I follow John's concepts for the part below the speaker, then I take the baffle up almost to the ceiling, but I do generally leave a gap of many inches, and I use that area for bass trapping. There's a "lid" on top of the area where the speaker is, of course, and on top of that lid I put a lot of absorption, then a fabric front on it. For high-end rooms, I borrow form both John and Barefoot to create a rigid box around the speaker but with suitably designed resilient pads all around, so that there is no contact at all between the speaker and the enclosing box: the speaker "floats" inside the box. I tune the mounting system to a low enough frequency such that resonance will not be an issue.


Quote:
4. I've read that the monitor should be centered in the bezel and I have also read that it should not. Which is correct, or is that dependant on the flush mounting design implemented? If an offset is preferred, how great or little of an offset is ideal?
If you center it in the baffle, then there will be symmetrical focused lobing patterns forming for some frequencies. If you offset it from the center, that effect is reduced. A good rule of thumb is to center it about 2/5 of the width of the baffle, but that's also not written in stone. I used to think that centering it was ideal, but in reality it isn't, so you might still find some of my older posts from many years back, that say it should be centered. Ignore that! :oops:

Quote:
5. For example, if I created a bezel that was 48" wide and 24" tall, would the center frequency be approx 93 or approx 227?
I think you mean baffle, not bezel, and a baffle that was much wider than it is high would be unusual anyway! But the baffle step response is always related to the SMALLEST dimension of the baffle, so it will be the higher frequency.

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PostPosted: Sat Jun 25, 2016 1:16 pm 
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Thank you, Stuart. I appreciate your generosity with your time and knowledge. It helps a great deal.


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PostPosted: Thu Jun 30, 2016 4:59 pm 
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:thu:


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PostPosted: Wed Jun 21, 2017 3:34 pm 
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Informative thread for me.

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PostPosted: Thu Jun 22, 2017 3:09 am 
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viktorokiro wrote:
Informative thread for me.


Yup! Very true... you informed us that you are a signature-spaming low-life twerp, so that information got you blocked, banned, and deleted... informatively!

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PostPosted: Sun Jul 30, 2017 5:41 am 
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I have low end studio monitors that are back ported. Will flush mounting work with speakers that are not front ported. :?:


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PostPosted: Sun Jul 30, 2017 8:03 am 
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Dirkg wrote:
I have low end studio monitors that are back ported. Will flush mounting work with speakers that are not front ported. :?:
Absolutely yes! The majority of rear-ported speakers can, in fact, be flush mounted, as long as the flush mount system is designed correctly. Here's an example: viewtopic.php?f=2&t=20471 The speakers in that studio are Eve SC-407s, which have rather large ports on the rear. As you can see, they were flush mounted very successfully, and
the performance is outstanding.

So very likely your speakers can also be flush mounted. What speakers do you have? (make and model). Unless they are very unusual in some sense you should be OK.

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