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Creating a false ceiling as a huge bass trap?!?

Customising, building or repairing your own gear? Need help with acoustic treatment or soundproofing? Ask away…

Re: Creating a false ceiling as a huge bass trap?!?

Postby Siejen » Tue Nov 30, 2004 2:05 pm

Hi all,
well, progress update time: I'm half way through. Would have been finished if I'd started before 6pm on saturday, but there you go.
The ceiling is held with a perimiter frame of timber, with joists crossing left to right above the listening position. The fore / aft joists are only for holding the muslin which is the 'visual' ceiling. I've put the rockwool in at facing (rather than side) walls, but have cut down a little on how much is up there. I bought 30mm thick panels and was going to double them up all round, but my joists (2x2) started looking a bit saggy, so discretion being the better part of valour...
The rockwool is 60mm thick and has a 150mm airgap behind it, but is not continuous. Tonight I'm going to offset space the top panels so its continuous, but only 30mm thick in places. And do the centre of the room as suggested, thicker towards the walls, spaced in the middle. It's heavy when there's that much of it!
I've also got permission for two horizontal traps by spending silly amounts of money (to me) on heavily embroidered facing cloth so they appear as wall hangings. These can be 60mm thick and 0.6 * 1.35M long (one and a half panels).
As for early reflections, I've a new set of velvet curtains on one side and a large panel of pu foam for the other; again fabric covered, but this time much lighter material. There's nothing I can do about the back wall apart from the sofabed, so that will have to do.
As an aside, I measured the room response at the listening position with my old setup, and can fully understand why I couldn't judge the amount of bass required. 20dB dips!!! between 50 - 160Hz, room nowhere close to flat until 300Hz. Even above that there was a dip between 1-2KHz of about 8dB(IIRC).
I'm now choosing some furniture to go with my properly designed acoustic room. My Mackie HR 824s were previously on floor stands, but with the big office style desk I fancy thats no longer possible. Are these REALLY going to be OK if I wall mount them?? (Strong brackets and foam isolation pads notwithstanding)? Anyone?

Right, back to work.
Iain
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Re: Creating a false ceiling as a huge bass trap?!?

Postby Scott R. Foster » Tue Nov 30, 2004 2:11 pm

James:

I think its great that you are confident that your can trade DIY skills for cash in hand by building absorptive devices and expect as a result to come in under budget enough on this part of your project to have a few bucks left over for to spend on a bit of "more expensive stuff".

My $0.02 is that if you set out to start building absorption devices, there is no need start balancing the benefits of "store bought" versus "home made". The store bought stuff [when properly selected] can "get-r-done" and relieve you of the need to go into DIY mode altogether, but if you are going to start building stuff I can see no reason to mix the approaches... there is nothing you can buy in the field of manufactured absorptive devices that you can't build as good or better once you dive into the matter. Mineral fiber is just so easy to cut and fit [even the scraps can be re-used], and once you get a cloth covering method down, this basic method should be able to handle whatever you are up against.

That being the case, I'd suggest you go whole hog on DIY treatment [in for a penny...] and use the budget excess on a nice vocal mic / mic pre or some other spiff piece of kit as Paul suggests.

Also, I think it is smart of you to get a treatment plan for the whole room [and the whole frequency band] put together before you start... if you do some basic calculating to assure yourself that your treatment plan has handled your transmission loss / isolation needs, LF and Mid-Band absorption, and then come up with a approach to control early reflections, then, with these three basic tasks addressed you'll be well on your way to satisfaction given that these three issues cause 90% of folks failures in DIY small room acoustic treatment. IMO, focusing your attentions here, from the outset, will greatly lessen the likelihood of making gross errors, and is bound to save time/money in the long run.

In anticipation of your work on this element I would suggest you take a look at using this software to model the room modes [all of em - not just axials]:

http://www.acoustics-noise.com/RoomModesCalculator.shtml

Also a model of the room's overall absorptive qualities /residual resonance field [post treatment] would be helpful in vetting your absorption element treatment plan. Even though such models suffer from vast uncertainty, having a gross thumbnail sketch of what the treatment plan will yield as far as overall results can be helpful in determining you are on the right track.

Finally use the "mirror trick to assure yourself that your early reflection controls are hitting the right spots on the front wall [one way to avoid this concern is to treat the entire front wall / corners / ceiling with broadband devices].

Good Luck

PS: What is the proposed use for "Nidaplast" in the project, and what does it cost?
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Re: Creating a false ceiling as a huge bass trap?!?

Postby Scott R. Foster » Tue Nov 30, 2004 2:22 pm

Lain:

Can you provisionally locate the monitors before you go to the trouble / expense of permanent installation?

I had a set of these speakers wall mounted on steel swing arms, and the sound OK, but I hated the required additional height [I was always craning my neck to look up and get my ears in the same horizontal plane as the stereo field].

I ended up build stands that stood at the back corner of my desk. A sketch of what you are up against as far as dimensions and available space would help folks think about this question.
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Re: Creating a false ceiling as a huge bass trap?!?

Postby Siejen » Tue Nov 30, 2004 3:00 pm

Hi Foz,
and thanks for your interest, although this could probably be a thread on its own...
The room is 3m x 3.1m. The listening position is on a blank 3m solid wall with (soon to be installed) corner traps at each end. The other corners have a boiler and a door. I have to keep enough space for a sofabed to be pulled out, which takes up most of the room. At the moment I have a desk that is 700mm deep and this is about as far out as I can go without fouling the bed (so to speak). For symmetry I want a central listening position (left and right of me are the heavily curtained window and acoustic panel mentioned earlier), behind me the sofa. Central as opposed to corner based, as I'll never get that symmetrical.
The speakers are currently on floor stands, but this spaces them about 2m apart either side of the desk, firing into a very flat triangle, not equilateral at all.
So, I want to bring them closer together for a more even listening position, which means shelf, table or wall mounting. My worries were that
a) they are heavy
b) they are big.
Big implies they could do with a bit of free space behind them to work, and that compounds worry (a).

Iain
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Re: Creating a false ceiling as a huge bass trap?!?

Postby new sonic arts » Tue Nov 30, 2004 3:06 pm

hi foz

dont get me wrong i dont plan to mix diy and pre-made stuff from studio suppliers (just a pre made bass trap would screw my budget...!) what i meant was maybe i might need other materials on top of the rockwool? the 'nidaplast acoustic' is apparently some honeycomb material, costs about £12 for 4x4ft, 10mm thick. im waiting to hear receive some specs and details about it from a supplier (just a regular fibreglass supplier, nothing pro-audio...) but if it happened to be a good absorber that is lightweight and rigid, it might make for quick and easy wall panels, and might save the need for covering the rockwool (which i presume is fairly messy like fibreglass?). so something like that might be useful as remember i want to keep this installation relatively mobile.

if i get some nidaplast specs i will of course post some details here. its probably nothing special however, as you guys would have already heard about it...!

cheers

james
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Re: Creating a false ceiling as a huge bass trap?!?

Postby Paul Woodlock » Tue Nov 30, 2004 5:34 pm

Hugh Robjohns wrote:Great contributions Paul. I'm sure everyone here will find your suggestions useful. However, can I gently suggest a little more moderation when it comes to some of the other comments:

Paul Woodlock wrote: And now he can hear how bad the 824's really are in a well treated room, he's going to uprade them ASAP too ;)

I know there's a smiley face there, but this is hardly a constructive or objective comment, and is likely to cause an unwarranted degree of unrest in several quarters.

If you happen not to like the performance of the HR824s, that's fine. If your budget allows you (or your friends) to purchase far more accurate (and more expensive) monitors, that's fine too.

However, I think most would agree that for the money the HR824s offer a very respectable performance compared to the immediate competition. Sure, if compared to serious high-end three-way active systems the 824s exhibit deficiencies. But it's all a matter of perspective and budgetry restrictions -- compared to lower budget monitors the Mackie HR824s represent a significant boost in quality, and since people tend to upgrade in stages over time, this is a far more relevant point.

I'm not a Mackie user and I'm not trying to wave a banner in favour of Mackie. These comments could apply equally to many other monitors. However, I don't think it fair to castigate a product in this way without making it clear that it is a personal and subjective opinion, and in an appropriate context.

hugh

Greetings Hugh :)


Sorry, I tend to take for granted that forum comments are always the poster's own opinion.

Yes, my 824 comments are PURELY MY OWN OPINION. I had a pair on appro for some weeks once, and listening to the pair at Mark's place confirmed my distaste for them. But again my OWN opinion.

....and is likely to cause an unwarranted degree of unrest in several quarters.

........and similarly if I'd said the 824's were the BEST Monitors in the WORLD :)

Anyway, I think it's important that individuals CAN have a voice for their own opinions here, but you're right, it's also important to stress that the opinion IS a personal one.

So rather than take that for granted, I will make a point of providing an 'IMO disclaimer' the next time I say something bad ( Or good ) about a product.

Cheers :)


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Re: Creating a false ceiling as a huge bass trap?!?

Postby Hugh Robjohns » Tue Nov 30, 2004 8:03 pm

Paul Woodlock wrote: Anyway, I think it's important that individuals CAN have a voice for their own opinions here, but you're right, it's also important to stress that the opinion IS a personal one.

So rather than take that for granted, I will make a point of providing an 'IMO disclaimer' the next time I say something bad ( Or good ) about a product.

Thanks Paul. Sorry to be heavy, but after posting so much good authorative advice about room treatment, the Mackie comment might have been taken in the same authorative way, which I know wasn't what you had intended.

Hugh
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Re: Creating a false ceiling as a huge bass trap?!?

Postby Scott R. Foster » Tue Nov 30, 2004 10:44 pm

Lain:

Can you mount your mixing desk on casters and pull it off the wall far enough to make your triangle equilateral when working, and roll it back when you need to take a nap in the pull out bed?

:headbang:
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Re: Creating a false ceiling as a huge bass trap?!?

Postby Paul Woodlock » Wed Dec 01, 2004 4:30 am

Foz wrote:Hugh:

Ya Paul's a snob!

;)




ROFL!! Now that is funny. Extremely funny actally :lol: :lol: :lol: :lol: :lol:

I know you had your tongue in someone's cheek when ya said it, but I'm the FURTHEST from being a snob as anyone could get. I have a beat up car, and fart loudly in supermarkets for starters.

Cheers though! I've been smiling about that comment all day ;)


Of course if Paul would like to send me his monitors for an extended season of destructive testing, I am ready to be proved wrong.


I rest my case :lol: :lol:


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Re: Creating a false ceiling as a huge bass trap?!?

Postby Scott R. Foster » Wed Dec 01, 2004 1:52 pm

Paul Woodlock wrote:I rest my case :lol: :lol:

PFFFFFAAAAAHHHHHHHHHHHRRRT!


:beamup:
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Re: Creating a false ceiling as a huge bass trap?!?

Postby MarkEdmonds » Tue Dec 07, 2004 2:19 pm

Hugh Robjohns wrote:
Thanks Paul. Sorry to be heavy, but after posting so much good authorative advice about room treatment, the Mackie comment might have been taken in the same authorative way, which I know wasn't what you had intended.

Hugh

Hugh - I generally share Paul's views on the HR824s (strictly IMO of course!). However, I would add that they can sound surprisingly good in a treated room and as my studio room has been balanced round the characteristics of the 824s, I would challenge anyone to get them sounding better!

The real message and moral is though: build your foundations first - get the treatment done and then you can justify looking at top level monitoring solutions.

Mark (probably guilty of stating the obvious).
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