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PostPosted: Sat Feb 03, 2018 11:38 am 
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Ok, that clairifies things a bit. Thank you, Stuart. It seems a resilient system would be much more involved than I anticipated. I think my best bet would be decoupling the monitor tray from the baffle framing.


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PostPosted: Sat Feb 03, 2018 2:20 pm 
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I think my best bet would be decoupling the monitor tray from the baffle framing.
The exact same principles apply... :)

The only thing easier about that, is that you have the additional mass (weight) of the tray and speaker enclosure box, which is useful for compressing (deflecting) the Sorbothane correctly...

But it still has to "float": decoupling ALWAYS implies that it has to be done at the right frequency, no matter where you do it: at the speaker, or at the tray, or even the entire soffit! You still need to get that resonant frequency down low enough.


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PostPosted: Sat Feb 03, 2018 2:37 pm 
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I dont see where thomas used a speaker enclosure box in his design. It looks like the monitor just sits on a tray that has zero contact with the baffle or baffle frame. I dont even see how an enclosure box would be possible with the sc208's. The manufacturer states that there should be a minimum of 2mm gap on the sides and top of the monitors to allow for proper function of the bass port. How would i rigidly mount a monitor and leave a gap?


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PostPosted: Sat Feb 03, 2018 4:24 pm 
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JasonFoi wrote:
I dont see where thomas used a speaker enclosure box in his design. It looks like the monitor just sits on a tray that has zero contact with the baffle or baffle frame. I dont even see how an enclosure box would be possible with the sc208's. The manufacturer states that there should be a minimum of 2mm gap on the sides and top of the monitors to allow for proper function of the bass port. How would i rigidly mount a monitor and leave a gap?


It's 2cm, not 2mm.

From the manual: "EVE Audio monitors can also be flush-mounted in a wall, in which case there should be enough air flow. This is important to keep the electronic components cool but also to allow for the best performance of the bass reflex port. We recommend to keep at least 2 cm to the sides and top."

Which is why I do not mount speakers tightly in a rigid box! I mount them loosely in a rigid box, with separation on all sides (including underneath). There is air flow all around, on all sides, plus correct compensation for the bass reflex port. I'm not sure if you have seen the Studio Three Productions thread ( www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=20471 )? Those are the "big brothers" of your speakers: Eve Audio SC-407's, and they are soffit mounted using my system. You can see the results. When I did that, I spoke to the chief engineer at Eve Audio, I explained what I intended to do and why, including mounting them vertical instead of horizontally. He agreed, and gave it his blessing, with a couple of tips. Great people at Eve, by the way. Very helpful.

Those speakers are mounted inside large, rigid, heavy, massive enclosure boxes, but with an air gap all around, and provisions for both the rather large bass reflex port on the rear, and also for cooling air flow up past the rear. They are resiliently mounted on Sorbothane pads, and the resonant frequency is a little below 13 Hz. They are hooked up with a couple of subs, and there is a cross-over in there, set a little above 90 Hz. So the resonant frequency is roughly three octaves below the cross-over point, and as you can see, they are fully floated and working fine. The cross-over is fourth-order (24 db/octave). There's very little energy coming out of them below about 35 Hz, which is the low end spec for those guys (35 Hz, -3dB), and no discernible vibration in the soffit structure. I doubt that I could have got that performance with any other mounting method.

You don't need to be too daunted by the task: it can be done, with a little patience, careful design, and a few calculations...

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PostPosted: Sat Feb 03, 2018 4:50 pm 
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I see. I sent the folks at eve an email earlier today. Hopefully they can point me in the right direction. I know the baffle frame and 1.5" thick baffle will be extremely rigid. So basically, youd advise making a massive speaker enclosure about an inch too big on all sides and then place multiple sorbothane pads evenly inside on all sides of the box to have the monitors "float"? Would i leave a 2cm gap between the baffle and monitor as well or shrink it down to 3mm?


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PostPosted: Sun Feb 04, 2018 1:07 am 
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So basically, youd advise making a massive speaker enclosure about an inch too big on all sides and then place multiple sorbothane pads evenly inside on all sides of the box to have the monitors "float"?
That's the basic idea, yes, but the pads are not spaced even around the speaker: they are spaced where needed, and sized accordingly. For example, the pads underneath the speaker will have the full weight of the speaker on them, plus the pressure applied by the ones on top, but the ones on top will only have the pressure applied by the "lid" of the box. So you need to adjust the dimensions of the pads to account for that. And the ones on the sides have no weight at all on them, but they do have the pressure applied by the side walls of the enclosure box. so you need to adjust the dimensions of the box to get that pressure correct, and adjust the sizes and placement of the pads for that pressure. You will probably also need to adjust the locations of the pads under the speaker, to keep it on an even keel, since speakers often have uneven weight distribution inside. That leads to some pads being more compressed than others, so you need to nudge their locations around to compensate, such that the speaker sits level with just the pads under it (no pads on sides or top yet).

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Would i leave a 2cm gap between the baffle and monitor as well or shrink it down to 3mm?
Thin gap between the baffle and the speaker. 3mm is fine. Don't go too thin on that gap, or you run the risk of the speaker vibrations when played at very high levels causing the speaker to touch and vibrate against the baffle. Some people like to seal that gap with a bead of very flexible caulk or rubber, but I'm not to keen on that. But don't get confused here: even though you have that thin gap around the speaker to the edges of the baffle, you still have a larger gap (maybe 1cm or so) between the rear face of the baffle, and the front edge of the enclosure box around the speaker. Once again, that's for air circulation. And because of all that, the speaker is sticking out well beyond the enclosure box: you say you plan on having a 1.5" baffle, plus another half or so for the gap I just mentioned (enclosure box to baffle rear face), so the speaker is "cantilevered" about 2" beyond the point where it is supported by the sorbothane pads. In other words, it is slightly over-balanced forwards, with more weight on the front pads than the rear ones. That's another reason why you need to nudge those pads around to get the speaker to sit flat inside the box, before you put the side and top pads in.

Lots of stuff to think of when soffit-mounting! :)

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PostPosted: Sun Feb 04, 2018 2:55 am 
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Ok, that seems doable. I can only imagine how difficult its going to be to slide the speaker in that box full of slightly compressed no skid pads. :shock:

Thanks, Stuart. You've been extremely kind, and i truly appreciate your input.


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PostPosted: Sun Feb 04, 2018 3:02 am 
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I can only imagine how difficult its going to be to slide the speaker in that box full of slightly compressed no skid pads.
Hint> Don't do it that way! You'll never get it in. Instead, build the box around it... Start with the base, then glue the pads to the side panels and attach those to the base/back. Then put the top pads on, adjust locations for even pressure, and screw those down too. When it all works properly, take apart, glue, and re-assemble.


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PostPosted: Sun Feb 04, 2018 3:30 am 
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Makes sense. Thanks again


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PostPosted: Sun Feb 11, 2018 3:36 pm 
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Can you think of a reason why this wouldnt work?

If i used the sorbothane hemispheres under the speaker ( and they were positioned as to support the speaker in a level position independently), and then used the sorbothane bumpers for the sides and top, I would be able to insert and remove the speaker as well as make pressure adjustments after the speaker box was built.

Bumpers below..
https://www.isolateit.com/sorbothane-vi ... -1498.html

Constructed as pictured below. Ive seen tensioners built the same way. The nuts on either side of the speaker box securing the bolt would hold extremely rigid.

Image

Id love to hear your thoughts on this approach..


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PostPosted: Sun Feb 18, 2018 1:48 am 
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Can you think of a reason why this wouldnt work?
It's an interesting idea! Looks like it should work.

Give it a try, and let us know. Test it OUTSIDE the soffit, with your speaker and enclosure box set up on a stack of bricks in your back yard, or some place like that, where you can get a good clean test, without interference from the room.

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PostPosted: Fri Feb 23, 2018 9:18 pm 
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Hi,

Ive asked this here rather than the "Soffit Mounting?" thread (which seemed more apt for this particular question), as there doesnt seem to have been much activity there in recent times. Apologies if its in the wrong place!

Nonetheless:

I have a question with regard to using a stand to mount the speaker on within the soffit, rather than an inner frame.

If one were to do this, as Barefoot states is acceptable at the start of this thread, but also incorporate his design for a speaker mount, would it be necessary to partition the spaces above and below the speaker (as per John's design)? While a partition above is easily doable, one below seems a bit more uncertain due to the speaker column running up through the middle of the soffit cavity.

One could of course partition around the column (leaving enough of a gap that the two dont touch), but would that compromise any acoustic properties of the soffit?

Also, while Barefoot's speaker mounting method does not incorporate a box around the speaker (unless im missing something here?!?!), how would one deal with the insulation surrounding it? Just stuff it in and close the thing up? Use chicken wire? Partition it off? Actually build a surrounding box/frame?

Im nearly at the stage where these questions need to be put into practice and am thinking of going down the speaker stand route (build from 2x4" and bolted to the ground).

Thanks

Chris


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