How it's possible? (Soffit/Flush mount specs question)

#1

Hi All!
My name is Mattia, i live in Sardinia (the most beautifull island in the planet :lol:

in Italy)

I've read a lot on John's forum, and now in this one.
I really appreciate the work that you all do to disseminate very technical knowledge, and help others.
I'm using my basic english knowledge with some help by google translate (i don't like it, but i need it sometimes).

My questions is "easy" and just one...

How it's possible that the Soffit/Flush mount system, attenuate or eliminate SBIR problems?
I'll explain my self better...

We know that a specific low frequency, like 80Hz have a wavelength around 4.3mt (14.10 ft).
i suppouse that a good material for build a flush mount baffle, is MDF around 4cm (1.57 inch) of thikness.
How can a 4cm baffle, block a reflection of a frequency that have 4.3mt of wavelength???

Of course i'm not considering something :horse:

i Hope that i don't have forgotten nothing before posting :oops:

#2

the soffit mounting (baffle plate really) prevents the wrap around of LF. this prevents the interference from that effect. you will still experience SBIR due to the rest of the room but the main LF issue is removed (in a correctly designed soffit system). however, you are also then limited in what you can do with those speakers once in place or if you want to mount multiple speakers (a number of my clients wanted two or even three "main" speakers mounted - e.g. extra large (dual 15), large (dual 10 or single 12), and surround. needless to say to do that requires some planning on how you would use those speakers :-)

of course after all that it's still all about the NS-10s and cubes on your console lol :-)

#3

Thanks for your answer gullfo!

So, ok it's more clear now...

And just another question:
How many "parts" are there in the sistem?

I thinks something like that:
- Front large Baffle
- Speaker Box/enclosure (decoupled from the speaker)
- below and above bass trap made with Hangers or filled with insulation
- Solid wood structure (and maybe decoupled from floor/ceiling/walls with neoprene or similar? it's a good idea?)
- If we have active monitors, ventilation system
- If we have rear passive radiator or rear bass reflex port, more large speaker box/enclosure, filled with some insulation.

#4

here's a couple of examples:

#5

With the remark that the details to "float" the loudspeaker in the soffit is not visible (present?), and it show cooling vents and ducts for a active loudspeaker to be used in this nice drawing. The soffit is described by Stuart, in the downloads part of the web-site, in how to design (partly) based on the size of the (LF) driver and offset the loudspeaker position in the soffit according to some ruling. The (grey) parts below and above the (brown)soffit panels are used to absorb when they are filled with absorbing material and / or acoustic hangers. If I understand correctly, this approach is "trying to get as close as physically possible to an infinite baffle". One of the added positives is that a soffit lifts the low frequencies up around + 6dB, which is also a pitfall, as not all speakers need that uplift or can be adjusted to balance the low's. Then it can become a negative which calls for EQ'ing. In case the speaker is adjustable in LF roll-off, the uplift by the soffit helps as the driver does have to "work as hard" in the real LF so to speak. (In a nutshell...). Correct me if I'm off Gullfo.

#6

yes this is a "standard baffle plate arrangement". :-)

the extended plywood on the back side ensure the full extension of the baffle plate while helping to reduce reflections off the desk/console. in the speaker box there are a couple of ways i go about it - directly use sorbothane pads, or create a nested box setup and use the pads on that box. the nested approach is good when you are starting with smaller speakers and later want to upgrade - so you make the main boxes large enough for those, and a smaller box to fit in that. and you could put the pads on the speakers or that nested box. the key though is twofold - keep the speaker rock steady in place, and to keep the speaker front from touching the baffle plate without leaving a significant gap. one way is to use highly precise bezels to get to 1/32" (1mm) of the front.

this design is something i acquired from John Sayers and then tweaked to make building it a bit easier. but is essentially his design.

#7

I just wrote a long post about the subject of soffit mounting, on another thread. You might find it interesting for your question too:

All about flush-mounting ("soffit mounting") your speakers

- Stuart -

#8

Soundman2020 wrote:I just wrote a long post about the subject of soffit mounting, on another thread. You might find it interesting for your question too:

All about flush-mounting ("soffit mounting") your speakers

- Stuart -

In that post, you said:

8 ) Make the front baffle of your soffit as wide and tall as you can, within reason. The width should be at least three times the diameter of your low frequency driver. In other words, if you have a speaker with an 8" woofer, then you want the soffit baffle to be at least 24" (60cm) wide. Wider is better. If you have a three-way speaker where the tweeter is in the middle, between two identical woofers, then the "diameter" is the distance from center to center of the woofers.

You've established a minimum. Is there a maximum, or at least a point of diminishing returns where the marginal gains for going any bigger are reduced and/or other problems start being introduced by having a couple giant plates at the front of the room? I don't understand the relationship between the size of the baffle, the diameter of the driver, and the frequencies that will be impacted.

9) Do not put your speaker in the middle of the soffit baffle: Offset in both directions. In other words, the distances from the acoustic center of the speaker to each edge of the baffle should be very different, by at least 20%.

What's the theory/purpose behind this? I looked around and couldn't find an explanation. I'm doing a surround/atmos room and was planning on soffit-mounting the front LCR. The horizontal asymmetry for the L and R is easy enough, but due to some quirks in the geometry of the room, having the C being placed off-center of the baffle could be a little tricky, and also require a bit more work in making the aesthetics visually symmetrical. If the purpose is to control resonances within the baffle (and make one side not resonate at the same frequency as another), could this also be accomplished with asymmetric bracing behind the baffle?

10) Make the baffle as massively heavy as you can, and as immensely rigid as you can.

How "massively heavy" are we talking here? I have a lot of leftover drywall and a bunch of salvaged MLV, so I can get pretty ridiculous if it's warranted.

-Dan.

#9

couple (or a few) thoughts:

for a surround room - stereo mains in the soffits and separate surrounds (which is probably 98% of rooms i design when they want both).

theory - the "infinite" baffle allows the LF energy to seamlessly extend onto the walls, floor and ceiling. and the +6db bump - you can carve off with EQ if you're speakers don't have settings for it. and if you have a digital parametric EQ to better shape the response, you can do things you cannot do with a simple speaker switch. in some cases, smaller speakers will benefit from the bump up esp if you're not using subs.

in practice, you have stuff. that stuff is likely in the way of perfect. so we can get away (generally speaking) w/ 3-4x the LF driver diameter(s) (so if you have 10" LF drivers, then 30" on the sides of the speaker is about right -- however -- in practice, your mains (let's say ATC 110s) will be minimally 36" (more like 44") off the floor to clear your surround speakers and other stuff) and you'll want some lower side of the baffle absorption -- to solve it - in the baffle assembly is the backing plywood panel which extends below the main plate and provide the support and leaves space for absorption materials + an opening for trapping on the bottom and the vent opening.

massiveness - minimally i would recommend 1" of MDF, but if you can 2" of MDF or equiv (or more) density. so layering in drywall between two sheet of plywood could be useful. using adhesive to create a single solid panel.

of course you need to consider your speakers and any sub speakers (which would go into the lower section below the mains) and since you're not likely to have vertical spacing, creating the necessary baffle for those would be a good idea.

#10

gullfo wrote:Source of the post couple (or a few) thoughts:

for a surround room - stereo mains in the soffits and separate surrounds (which is probably 98% of rooms i design when they want both).

That would be nice, but I don't think I can justify something quite that fancy. Current plan is one set of speakers, with the front LCR being 3-ways in the $2500-3500/ea range, so something like Neumann KH310's, Adam S3V, Dynaudio Core59, etc. with smaller matching models for the surrounds and heights. If I have an extra stereo pair, it'll be a consumer Aurotone/NS-10 kind of thing.

theory - the "infinite" baffle allows the LF energy to seamlessly extend onto the walls, floor and ceiling. and the +6db bump - you can carve off with EQ if you're speakers don't have settings for it. and if you have a digital parametric EQ to better shape the response, you can do things you cannot do with a simple speaker switch. in some cases, smaller speakers will benefit from the bump up esp if you're not using subs.

in practice, you have stuff. that stuff is likely in the way of perfect. so we can get away (generally speaking) w/ 3-4x the LF driver diameter(s) (so if you have 10" LF drivers, then 30" on the sides of the speaker is about right -- however -- in practice, your mains (let's say ATC 110s) will be minimally 36" (more like 44") off the floor to clear your surround speakers and other stuff) and you'll want some lower side of the baffle absorption -- to solve it - in the baffle assembly is the backing plywood panel which extends below the main plate and provide the support and leaves space for absorption materials + an opening for trapping on the bottom and the vent opening.

That makes sense.

Out of curiosity, why does the size of the original driver matter? I really have little to no idea of what the theory looks like.

massiveness - minimally i would recommend 1" of MDF, but if you can 2" of MDF or equiv (or more) density. so layering in drywall between two sheet of plywood could be useful. using adhesive to create a single solid panel.

Oh, I have more than enough for that.

As a practical matter - what strategies do people have for accessing active speakers once the baffles are built and installed? For a passive speaker where everything is accessible from the front, that's fairly easy. But with an active speaker with controls on the back and a baffle that's north of 100 lb, that could get a bit dicey. Or does this not really come up in practice?

#11

the diameter "math" is a "rule of thumb" for minimum sizing. really it should be based on the LF response of the speaker and room sizing, and a whole bunch of other considerations (such as surround speakers reflecting off the baffle plates in the front of the room and related timing issues causing additional comb filtering effects and so on).

access in the speaker after installation - several strategies - one is to remove the electronics to another place so the speaker is effectively "passive" in its mounting - some companies support this out of the box, other begrudgingly support it, and some revoke the warranties. next up, use a bezel to marry the speaker to the baffle plate so you can remove it and slide the speaker out. and another is provide an access panel to allow access to the speaker - like a window plug to let you reach in and alter it.

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