John Sayers' Design Forum

John Sayers' Recording Studio Design Forum

A World of Experience
Click Here for Information on John's Services
It is currently Mon Sep 28, 2020 3:32 pm

All times are UTC + 10 hours




Post new topic Reply to topic  [ 8 posts ] 
Author Message
PostPosted: Sat May 26, 2012 7:32 pm 
Offline
User avatar

Joined: Fri Mar 09, 2012 3:08 pm
Posts: 50
Location: Detroit Area Michigan, USA
Do you guys see any acoustical problems or benefits from this? I am thinking of flush mounting my nearfields into a drywall wall in the front of the control room of course.. But I want the drywall to only extend about 1/2 way to the side walls from the center and then make the rest of the way to the wall just a fabric covering so that I can put a pair of hi-fi tower speakers there. So the near fields would be the pair closer to the center of the room and the hifi towers would be farther out left and right.

So my first question is: would the benefits of flush mounting the nearfields into the drywall stll exist if the drywall does not continue all the way to the side walls? It seems like I would still get a large baffle increase that would be beneficial.

Next question: but first, there one more thing I should mention. The hifi speakers have side firing subwoofers and a cicular vent hole in the back. I am planning on filling the entire cavity behind the flush mount/fabric wall system with insulation. But if I don't directly cover the subs or the vent hole and leave an air pathway out to the front of the fabric wall covering, I'm good right?

Anyone see any any problems with this system or does it sound like a winner?


Report this post
Top
 Profile  
 
PostPosted: Sun May 27, 2012 11:46 am 
Offline
Senior Member
User avatar

Joined: Thu Aug 21, 2008 10:17 am
Posts: 11938
Location: Santiago, Chile
Quote:
would the benefits of flush mounting the nearfields into the drywall stll exist if the drywall does not continue all the way to the side walls?
I guess "somewhat" is the best answer there: it all depends on how you do it, but I'm not convinced that this would be a good thing for either set of speakers.

Possible issues:
If the soffit does not fully cover the front wall, then there is still potential for SBIR problems.
Some of the energy will still be able to wrap around behind the soffit, in the cavity to one side, but the other side will have a full soffit, so there will be a power imbalance across the face of the speaker/soffit, with more energy being projected towards the mix position from one side of the speaker than from the other side, with a transition defined mostly by the width of the soffit (similar to baffle step problems, but lopsided). It's hard to say what that will do to the sound, but I'm thinking that clarity, frequency response and image will suffer.

Quote:
It seems like I would still get a large baffle increase that would be beneficial.
The baffle itself is useful, to the extent that it makes the front of the speaker significantly larger. If you are not using all of the available space (you didn't say how wide the soffit could be full size, or how large it would be cut down to allow for the other speaker), then you are not optimizing the "infinite" part of the "infinite baffle" concept. For example, if you only use half the available width, then you cut the benefit in half, in terms of frequency: you raise by one entire octave the baffle-step frequency.

Quote:
The hifi speakers have side firing subwoofers and a cicular vent hole in the back. I am planning on filling the entire cavity behind the flush mount/fabric wall system with insulation. But if I don't directly cover the subs or the vent hole and leave an air pathway out to the front of the fabric wall covering, I'm good right?
I'm not so sure about that either! Both the side-firing sub and the rear-firing port are there for low frequencies, implying long wavelengths. I'm not a speaker designer, so I can't tell you what effect it would produce to have those very close to surfaces. "Very close" in terms of wavelengths: those walls will just be a tiny fraction of a wave away from the wall. I suspect some type of acoustic loading will happen there. Perhaps you should write to the manufacturer and ask him if you can use those speakers in an enclosed alcove, such as a broom closet with the door open, and see what he says. My guess is that the answer will be negative. Also ask what the minimum recommended distance is from the rear port to the front wall of the room, and from the side-firing sub to the wall nest to it. That information might even be in the speaker manual.

Is there any reason why you can't just put those hi-fi speakers on the floor in front of the full soffit?

- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.


Report this post
Top
 Profile  
 
PostPosted: Sun May 27, 2012 3:54 pm 
Offline
User avatar

Joined: Fri Mar 09, 2012 3:08 pm
Posts: 50
Location: Detroit Area Michigan, USA
Thanks Stuart, enlightening..

What are SBIR problems?

You said you think the image and clarity might suffer, but compared to what? A full soffit mount Im sure you mean? ..but how would it compare to a non soffit mounted speaker? Clearer, better image? I'm wondering if it would still be an improvement over speakers on stands.

You mentioned acoustic loading.. But remember, I would have this whole cavity, minus the airflow paths, filled with insulation.. So wouldn't that dampen any negative effects of being close to a wall? Just to help you understand how much that is, my control room is 12' wide, 7' ceilings, and I would be using 30 degree angles on each wall.

Part of the reason for soffit mounting is to prevent sound coming from the speaker box itself, not the speaker, from entering into the listening space right? In regards to the nearfields, it would seem that the soffit panels combined with the insulation in between the speaker and the outside (around the side, through insulation and cloth front) of the cavity would prevent the unwanted sound from the speaker box from entering the listening space.

ONE more question!! What if I soffit mount the entire space, and cut openings for the nearfields AND the midrange/tweaters of the hifi towers??? If I did this, I would also cut holes near the bottom of the soffit on each side where the air from the woofers could travel out. How bout that idea?? Ever soffit mounted hifi towers?! Ok, that was like 3 questions.


Report this post
Top
 Profile  
 
PostPosted: Sun May 27, 2012 4:50 pm 
Offline
User avatar

Joined: Fri Mar 09, 2012 3:08 pm
Posts: 50
Location: Detroit Area Michigan, USA
:shock: Ok, I'm cuckoo now.. Stuart, slap me. For the hifi towers, what if I just remove the woofer/midrange drivers/tweaters from the cabinets and mount them to DIY baffles and cut holes in the soffit where I want them to go? Of course the electronics would have to come out too.. And of course I would have to mount them so that they were decoupled from the soffit. And don't worry, I like these speakers but they aren't worth enough to stop me from trying this if I don't get great results from the traditional methods.


Report this post
Top
 Profile  
 
PostPosted: Mon May 28, 2012 10:38 am 
Offline
Senior Member
User avatar

Joined: Thu Aug 21, 2008 10:17 am
Posts: 11938
Location: Santiago, Chile
Quote:
What are SBIR problems?
Speaker-Boundary Interference Response. It refers to the way the speaker and the walls interact with each other, acoustically. It is what soffits eliminate to a large extent, if done properly.

Quote:
You said you think the image and clarity might suffer, but compared to what?
Compared to anything! If you don't have good stereo imaging, then you'll find it very hard to produce a mix that sounds well balanced in other locations (car, house, iPod, radio, etc.) In other words, your mixes wont translate well. They might sound fantastic on your room, but you'll always wonder why they sound lousy elsewhere: the answer is because all the other "elsewheres" wont suffer from the distorted image in your room, which you have compensated for in your mixes.

Will it be a big problem or a small problem? Hard to say!

Quote:
You mentioned acoustic loading.. But remember, I would have this whole cavity, minus the airflow paths, filled with insulation.. So wouldn't that dampen any negative effects of being close to a wall?
A bass guitar can produce notes in the 35 Hz range, easily. The wavelength of a 35 Hz note is about 32 feet. The quarter wave is about 8 feet: Can you get 8 feet of clearance between your side-firing sub-woofer and the closest side face of the soffit? If so, you are fine. If not... :)

As you can imagine, a couple of inches of insulation on the side of the soffit is not going to make a lot of difference to a wave that is about two hundred times longer...

Quote:
my control room is 12' wide, 7' ceilings, and I would be using 30 degree angles on each wall.
So it's a very small room to start with, with very low ceiling. Do the math: if you have 12 feet of width, your speakers will be set about 2 feet to the left and right of the center line, maybe a bit more, and your soffits could be maybe 4 feet wide, if you did them correctly. A 4 foot wide soffit has a baffle step transition at about 95 Hz, which is probably in or close to the bass roll-off area for your speaker anyway, and in reality would be even lower, due to the horn-loading effect of the rest of the room. Not worth worrying about. But assuming that you cut the soffit down to two feet (leaving less than 2 feet for the "hi-fi" speaker), the baffle step transition rises to about 190 Hz, which is certainly well into the normal range of your speaker, and therefor you will also need to build a baffle step correction circuit tuned to 190 Hz, or get a good phase-linear parametric equalizer or cross-over to fix that.

In addition, assuming that your speaker cabinets are about a foot wide, that gives you only 6 inches of soffit baffle on each side! (As compared with about 18 inches on each side, if you build it correctly).

Quote:
Part of the reason for soffit mounting is to prevent sound coming from the speaker box itself, not the speaker, from entering into the listening space right?
Not really. The main purpose of soffit mounting is to eliminate all interaction between the speaker and the front wall, including things like reflections, comb filtering, phasing, interference patterns, and other nasties. A secondary purpose is to eliminate the need for the baffle step compensation that is built into the speaker circuitry, since the lows are also forced to radiate into half space, instead of full space, thus correcting the power imbalance between woofer and tweeter. Sound coming from the speaker box itself is not very high on the list of priorities, in terms of overall problems with small speakers.

Quote:
In regards to the nearfields, it would seem that the soffit panels combined with the insulation in between the speaker and the outside (around the side, through insulation and cloth front) of the cavity would prevent the unwanted sound from the speaker box from entering the listening space.
From that, it sounds like you don't plan to put a face on the side of the soffit that you cut off?! :shock: If you did that, the the entire purpose and effect of the soffit is gone. OK, so maybe not the "entire" purpose, but most of it. If the soffit is open on the sides, then you have not fixed the baffle step issue: part of the sound radiated from the front will still wrap around to the back, and your power balance will be mangled again. Except that now it will be mangled in unknown and hard-to-predict ways, that you'll find it pretty complicated to fix. Insulation does practically nothing to stop sound: it is not meant to be an isolator. In order to isolate, you need mass, so you'd need a side panel on the soffit.

Quote:
For the hifi towers, what if I just remove the woofer/midrange drivers/tweaters from the cabinets and mount them to DIY baffles and cut holes in the soffit where I want them to go?
Well, I guess you COULD do that, but I have no idea how you'd go about designing your DIY baffles. That would be something like an open-baflle design (dipole) but closed on three sides. That's pretty complex. I'm also not sure how you would design the baffle step compensation circuit for that. Speaker design is a huge filed of acoustics, all by itself, and a bit beyond me. I understand the basics, but the details of such a design would require the expertise of someone like Eric Best or Barefoot. I guess you could try contacting them by PM.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.


Report this post
Top
 Profile  
 
PostPosted: Wed May 30, 2012 5:17 am 
Offline
Senior Member
User avatar

Joined: Fri Feb 14, 2003 1:51 am
Posts: 311
Location: Lansing, MI USA
I don't know how I got promoted to "expert" by Stuart, not even close, but here are my 2 cents.

Quote:
Part of the reason for soffit mounting is to prevent sound coming from the speaker box itself, not the speaker, from entering into the listening space right?


The main purpose to flush mount speakers is to support bass response and to reduce edge diffraction on the speaker. A speaker designed for flushmounting would be 6dB more efficient. That is from the speaker designer perspective. From the studio designer perspective, all of the things that Stuart mentioned.

Read this thread starting here http://www.johnlsayers.com/phpBB2/viewtopic.php?f=12&t=718&start=15#p117941

If you put your nearfields in an extended baffle (partial soffit), all you would do is create a 6dB low-mid bump that would start at the frequency determined by the width of the original speaker and would fall off 6dB where the baffle stopped. For example, if your nearfield has an original baffle width of 7" and you mounted it in a 36" wall. You would have a 6dB increase that would start at 650Hz and start falling off by 6dB at 129Hz. That would be mixing hell!

As far as pulling the drivers out of the other cabinets, you would have to completely re-design the crossover. If you like those speakers, don't mess with them. Leave them in your living room and check your mixes on them there.

I really have to finish my control room so I can test my designs of inexpensive DIY flush mount speakers. The problem is, I like designing so much more that I like building!

_________________
"It don't get no better than this"


Report this post
Top
 Profile  
 
PostPosted: Wed May 30, 2012 11:01 am 
Offline
Senior Member
User avatar

Joined: Thu Aug 21, 2008 10:17 am
Posts: 11938
Location: Santiago, Chile
Quote:
don't know how I got promoted to "expert" by Stuart, not even close, but here are my 2 cents.
Aww come on... Credit where it's due! You know speakers and speaker design pretty darn good: Certainly better than I do!

:)


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.


Report this post
Top
 Profile  
 
PostPosted: Thu May 31, 2012 6:36 pm 
Offline
User avatar

Joined: Fri Mar 09, 2012 3:08 pm
Posts: 50
Location: Detroit Area Michigan, USA
Great thread you recommended Eric. Well, it sounds like I can pretty much scrap the idea of using the hifi towers if I'm going to soffit mount the HR824's. So I am back to square one I think. I know that the consensus you two are going to give me is that I should soffit mount the HR824's. Remember, they have a passive radiator.. So from other research it sounds like I should disconnect it. BUT, I am using a subwoofer with them so the signal going to the HR824's would be hi passed, so maybe I won't need to. Still need to figure that one out.

So the thing is, I still want to have a hifi speaker in the control room as a reference, as well as a pair of yamaha ns10s soon. What would you guys do?? Remember, my control room is 12' wide, 7' tall, 20' deep, and I don't want my mix position to be more than 6.5' from the front wall. I'm stuck!


Report this post
Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 

All times are UTC + 10 hours


Who is online

Users browsing this forum: Google [Bot] and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group