Problem to solve with speaker and room reflections...

[matt-korban]

Hi all!
I'm building my recording studio, and now i have to build the control room...
I have a "little" problem to solve, with my speaker, the size of my room, and some reflections that i hate...

I have the windows on my left, and the monitor (amphion one18) in front of me.

Unfortunately i can't mount these speakers inside wall (flush mounted) because these monitor have a passive radiator behind, and this create some problem with the 180, and 170 degrees first reflections...

Is there any alternative to flush mounted speaker?
Do i have to respect the 38% rule, or i can change the distance from the wall?
Can i change just a little the angle of the speaker?
Any suggestions?

Some pics to understand what i mean...

Thank's all, and sorry for my english (i'm italian).

[Soundman2020]

Hi. Please read the forum rules for posting (click here). You seem to be missing a couple of things!

, the size of my room,

What IS the size of the room? All three dimensions...

Unfortunately i can't mount these speakers inside wall (flush mounted) because these monitor have a passive radiator behind,

Yes you can soffit.mount them. No problem. Practically any speaker can be soffit mounted, even if it has rear ports or rear passive radiators. The only ones that CANNOT be soffit mounted, are the ones that have active drivers on the sides or top. Anything is is possible, with the right precautions. Take a look here, for example: www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=20471 Those are Eve Audio SC-407's. Those things have huge bass reflex ports on the rear, yet there they are, successfully soffit mounted. Several forum members have successfully soffit-mounted their own rear-ported speakers, including a couple of cases of Mackie HR824, which have rear passive radiators. (Gareth, for example). This is not a problem if done correctly.

and this create some problem with the 180, and 170 degrees first reflections...

At 180° you don't really have specular reflections at all. You do have low frequency issues, yes, but the reflections beyond about 60° or 70° are no longer specular, and have to be dealt with in different ways.

Is there any alternative to flush mounted speaker?

Well, you COULD put them on stands right up right against the front wall, but then you'll have all of the artifacts that arise from having the speakers located inside the room.

Do i have to respect the 38% rule, or i can change the distance from the wall?

The 38% "rule" is related to modal response of the room, not the speaker location. It is not related at all to speaker location (well, OK, to a certain minor extent if your speakers happen to be located in modal nulls...

Can i change just a little the angle of the speaker?

Yes you can. There are limits, but there's no problem with slightly adjusting the speaker toe-in angles if necessary.

What speakers are you using (brand and model)?



- Stuart -

[matt-korban]

Hi Stuart!

What IS the size of the room? All three dimensions...

Sorry! Of course!
W= 400cm
L= 522cm
H= 320cm
(without plasterboard/gypsium angled wall)

The 38% "rule" is related to modal response of the room, not the speaker location. It is not related at all to speaker location (well, OK, to a certain minor extent if your speakers happen to be located in modal nulls...

Shure, but my question was related about the distance of the speaker from the wall... if i can modify the 38% point, than i can modify my speaker position near the front wall moving the modal frequency (I do not know if I have explained myself, see genelec speaker placement guide)

Yes you can. There are limits, but there's no problem with slightly adjusting the speaker toe-in angles if necessary.

What speakers are you using (brand and model)?

Ok, nice! The speaker are the Amphion one18

[Soundman2020]

if i can modify the 38% point, than i can modify my speaker position near the front wall moving the modal frequency

No you cannot. You are confusing two unrelated issues.

I repeat: The 38% rule is NOT related IN ANY WAY to the location of the speakers in the room. It is ONLY related to the modal response of the room itself, which is fixed by the dimensions of the room and nothing else. It does not matter where you put the speakers in the room, the modal response will ALWAYS be exactly the same, since it is a function of room dimensions, not speakers. Modes are related to the hard, solid, massive boundary surfaces of the room, not to the speakers. In fact, the modal response would still be exactly the same if there were no speakers at all in the room! You could stand in the room and shout loudly, and the modal response would be the same. You could even clap your hands, fire a gun, or pop a balloon, and the modal response would be identical to what it would be with speakers. Or any musical instrument.

I repeat: modes are ONLY related to the room itself, not the speakers.

If you happen to set up a speaker in a modal null, then that specific mode will probably not be triggered, but all the others will, just the same.

see genelec speaker placement guid)

The Genelec speaker placement guide does NOT deal with modal response! It deals with phase cancellation, or SBIR, which is something entirely different, and not related in any way to the 38% "rule".

You seem to be confusing SBIR with modal response: they are not related. Two totally different acoustic issues. Modal response does not depend on speaker position. SBIR DOES depend on speaker position. SBIR is simple phase cancellation, and does not "ring". Modes can be either peaks or nulls at different points in the room, and they do "ring" (yes, nulls can "ring" too...)

Also, the 38% rule is not a rule: it's just a guideline, a useful first approximation. A starting point. You can certainly move to a different spot, if you need to. In fact, most of the studios I design have the mix position a little forward of the 38% location, for many reasons.

Sorry! Of course!
W= 400cm
L= 522cm
H= 320cm
(without plasterboard/gypsium angled wall)

That's no use, unfortunately. Modal response (and indeed, the entire acoustic response of the room) is related to the FINAL inner-dimensions of the room. Measured from the hard, solid, massive, boundary surfaces of the room. In other words, the size of the room after it is completely built, but before you start putting any acoustic treatment inside it.

Also, PLEASE read the forum rules for posting (click here). You are still missing something!

- Stuart -

[matt-korban]

Ok sorry about all... Yes, i miss something... i added the location.
Any suggestion for soffit mounting my Amphion One18?

Stuart, is there any difference between soffit mount or flush mount metod?

On google, if i search soffit mounting, appear similar to flush mounting...

[Soundman2020]

Yes, i miss something... i added the location

Any suggestion for soffit mounting my Amphion One18?

It would not be too difficult. The cabinet is rectangular, so it would be easy to mount and easy to cut the soffit baffle (front panel) for a close fit. You would just need to leave plenty of space at the back, behind the passive radiator, with sufficient damping material.

Stuart, is there any difference between soffit mount or flush mount metod?

It's the same thing. The correct term is actually "flush mount", but for some unknown reason, the studio industry seems to want to call it "soffit mount". Correctly, it isn't a "soffit" at all! BUt people still call it that. A real soffit is a horizontal panel up high, for example under the edge of a roof on the outside of a building, or maybe a protrusion around a duct on the ceiling: that's really what the word "soffit" means.... but at some point in time, somebody decided that it would be nice to use that wrong word to describe how we mount speakers "flush" inside angled walls at the front of a room...

Here's an example of a control room that is currently under construction, almost completed, where the speakers are "soffit mounted" or flush mounted: http://www.johnlsayers.com/phpBB2/viewt ... =2&t=21368 You can see how that is done, in general, although the details are not very visible.


- Stuart -

[matt-korban]

It would not be too difficult. The cabinet is rectangular, so it would be easy to mount and easy to cut the soffit baffle (front panel) for a close fit. You would just need to leave plenty of space at the back, behind the passive radiator, with sufficient damping material.

Nice! How can i calculate how much space i need with sufficient damping material behind the radiator?
I have to build a massive box, closed in all sides except front, or except front and back?

If the box is completely closed (except front) the insulation damping material must be inside of the box, behind the speaker?

I'm reading the post that you've linked!!!
Fantastic great Job!

I love when you speak about insulation thickness relatively to 1/4 of lambda! haha!
I think i'll build a superchunk absorber on rear wall, maybe something like 25cm of thickness, with an air gap of 5cm, with a 2x1mt QRD diffusor (skyline) on the centre of the wall.

What do you think about?

I've write at Amphion italy customer Service, for have some info about flush mount these speakers... i'll inform you about their answer!

[matt-korban]

Hey Stuart!
The Italian Amphion's technical manager has confirmed that these speaker can succesfully mount on soft soffit mount!
Great! Now i'm design my RFZ zone.

[Soundman2020]

The Italian Amphion's technical manager has confirmed that these speaker can succesfully mount on soft soffit mount!

Excellent news! I didn't doubt it myself, but it's always good to get the manufacturer's OK.

- Stuart -