Mineral wool vs rigid fiberglass

  • Thread starter Thread starter FZfile
  • Start date Start date
FZfile

FZfile

New member
I been digging around suplliers catalogs at my workplace (which is a manufacturing and distribution center) and found some things that apear to be useable for the DYI acoustic projects suggested here and through SAE.

I found that 2'x4' sheets of semiridgid mineral wool are quite a bit cheaper that 2'x4' sheets of ridgid fiberglass.
Like $3 ea. vs $11 ea at 1"thick.

Is mineral wool close in properties to the fiberglass (the lbs/ft density of both is similar)?????
...and is semi-ridgid a pain to work with for panel work and traps verses a ridgid fiberglass?????

Also available from the closest supplier is "Rock Fiber Pipe insulation" for bass traps and is cheaper (than the fiberglass pipe ins.) but only comes up to 8 5/8" ID big.

Is this acoustically comparable?????????????

-mike
 
Both will absorb about the same in the higher frequencies the semi rigid fibreglass will absorb down a bit lower than the mineral wool ie below 500hz

Your wallet will probably dictate which you use :):)

cheers
JOhn
 
Thanks John

I appreciate your responses and inight considering my set up is a pretty modest "bedroom" studio compared with some of the beautiful and elaborate studios you help design and build.

You are correct about budget (minimal) dictating most of my choices.

One additional question.....

My console area will probably consist of a premade, assemble-it-yourself corner computer desk.

I think I found one that should work pretty well...
-open center with 6" raised shelf for the monitor and for cables to go under.
-bookshelf stacks on either side that are 22" wide so I can put some rack rails in there.
- enclsed computer section underneath with door

(fairly typical)

Would it benefit me any to make a "flushmount" pannel for my monitors (which would be on the 2nd shelf...so to speak)??.

I was thiking I could line the shelf "box" with some extra ply, then some neoprene on the bottom (for decoupling) and then some fiberglass or mineral wool around the monitors.

Would this just create a bigger speaker cabinet (without a whole wall to soffit the speakers in) or would this make any improvement?????????????????

I figure this would be pretty darn easy (and cheap) to do.

Thanks,

-Mike
 
Mike - I don't think there would be any advantage in what you intend doing - Flush mounting really works when you can get away from the speakers and listen to them in a full room - if you know what I mean :)

cheers
JOhn
 
John Sayers said:
Mike - I don't think there would be any advantage in what you intend doing - Flush mounting really works when you can get away from the speakers and listen to them in a full room - if you know what I mean :)
Click to expand...
John my wise friend, I disagree with you here.

The typical distance for speaker design and test measurements is 1m. This distance clearly shows the effects of the baffle size, and moving out to 3m or 4m makes little difference in this regard.

One of biggest problems with typical homerec nearfield setups is upper bass/low midrange comb filtering caused by interference between the direct and rear wall reflected sound waves. The larger the baffle dimensions are relative to the distance to the rear wall the better in my opinion - even at nearfield* listening distances.

* near field is a term used in physics with a specific definition. The true near field is where the dimensions of the source (speaker cone diameter) are large compared the distance of the receiver (your ear), such that certain terms in the mathematical equation describing the system become irrelevant. In the case of loudspeakers this is just a few millimeters distance from the woofer cones and less than a millimeter away from the tweeter domes. Only at these distances do the effects of the baffle and room become irrelevant.

barefoot
 
I humbly stand corrected -- thanks barefoot :):)

As you know I'm a great fan of flush mounting speakers as I've heard the effect many times and heard the improvement made to pretty average speakers.

FZFile - do your worst :):)

cheers
John
 
I will certainly try....

I'm guessing that putting a 4'x4'x4"(or 6") absorbant pannel on the wall directly behind the "flushmount boxes" would not be a bad idea either......??

I was actually planning on doing the pannels first and then thought about making the flushmount facing for the shelves (which would have been open backed before the box idea).

This is goin to be fun.


Cheers :)

-mike
 
Hey Barefoot - long time no baffle(take that however you like, :=) - how would you handle flush mounting nearfields that have radiused cabinets, ostensibly to minimise diffraction? would you need to set the front of the baffle flush with the front of the extended baffle and then fill the radiused edge area with caulk, or would it be enough to weatherstrip the cutout and just not have anything projecting forward of the baffle?

Also, I have 5 KRK K-ROK's, 3 with mag shielding, for the step to 5.1 surround, with a 200W Hafler 10" sub. Would I need to build a continuous baffle with two wings at 30 degrees, with the center channel spkr in its own separate plane and the L + R each in their own baffle? Would this be practical with the speakers about 4 feet from the listening position? What about the rears, would they need the same baffling? These spkrs will be crossed over to the sub at approx. 80 hZ, so how large a baffle would be necessary? I calc the wavelength of 80 hZ as 84.6", would a baffle that extended for 1/2 wavelength be enough?

Someone mentioned a link to some ideas for this stuff you had, but I saw nothing there to click on - could you point me in the right direction?

I know this is a bunch of questions, but it's a bunch of info to absorb and the more I learn the more I feel like a moron - any help you can give will help me get stupid even faster, now who wouldn't appreciate that... Steve
 
Barefoot - I have a speaker question I have been meaning to ask for a while if you don't mind...

I am currently building a small home studio (2 rooms plus a control room) and would like to flush mount *some* speakers in front of the mix position. Being on a tight buget at the moment, I have a pair of NS10's that I would like to leave as near fields but I also a couple of Acoustic Research AR2's with speakers that are completely trashed... maybe I should do the same to the cabinets but... like I said, I am on a budget.

The AR2's have a rock solid cabinet, are a three way speaker with an adjustable crossover, (10" woofer 5" mid and 1 or 2" tweeter) and I am wondering if it would make sense to replace the drivers on these and use them for this application.

I guess this is kind of an open ended question but in your experience, does restoring older speakers make sense dollar wise?

Thanks
Kevin.
 
Sorry for taking so long to reply. I was in New York last week and just couldn't get my damned internet service to work.

Steve,

The face of the baffle extension should always be flush with the face of the speaker baffle.

Ideally, when mounting a radiused edge cabinet, in order to minimize the gap you would cut the inner opening of the baffle extension small then rout a cove on the inner side to accommodate the cabinet edge. A Cove or Round Nose router bit with about a 1/8" larger radius than the cabinet radius would work.
Code: 
***********   *********** 
        *   *
       *   *
********   *
           *
           *
But this isn't a must. A simpler flush mounting still improves the situation dramatically with respect to edge diffraction since the 1/2" or 3/4" at most radius used on speaker cabinets is not large enough relative to the respective wavelengths to significantly reduce the first couple instances of diffraction induced frequency response ripple.


Turning to your 5.1 setup, one potential problem I can imagine is due to this 4' listening position. The closer the listen position is, the narrower the center baffle must be. So you run the risk that the angled front baffles will create a significant horn loading effect on the front monitors. If you can, I'd strongly recommend moving your listening position back. Don't worry about using "near field" monitors further away. This whole near field distinction is for any practical purpose a myth. 1m or 2m is not the near field in any respect in an average size room.

Yes, if it's not too much extra expense I'd recommend flush mounting the rear channels too.

Actually the wavelength at 80Hz is 167.3", twice what you calculated. In this frequency region the entire room comes into play, rather than the dimensions of any single partition – unless you have a large room. So don't worry too much about this. Make the baffles as large as is practical.

Sub crossovers are a tricky business and should really be custom designed to fit the particular set of speakers. Simply inserting an 80Hz crossover will not result in a flat response unless the subs and satellites have over 2 octaves of response overlap – certainly not the case with your K-RoK's. Sharp slopes help a little, but they have their own issues.

I did post some ideas regarding flush mounting, but I think the links to all the diagrams disappeared when I changed web sites. When I get the time soon, I'll repost this all in one thread – hopefully this week.



Kevin,

Wow, AR-2's, now that's vintage.:eek: :) Are they the AR-2a model with the dome tweeter?

Either way, I'd say they're just too long in the tooth to be of any value as monitors these days. I'm not even sure you can find direct replacement drivers for these anymore. So you'd have to redesign the crossovers as well. No, these are vintage audio enthusiast speakers, not studio monitors. Though, I might describe NS10's the same way.;)

barefoot
 
You must log in or register to reply here.
Back
Top