Concrete floated soffit...

reader · Post by **reader** » Thu Jun 17, 2004 8:49 am

Thomas or anyone with experience....

I went too far !

When building our studio, being very paranoid about isolation, I badly designed a floated concret slab to soffit some big main monitors.
The 25 cm slab suspended on 5 springs isn't stable with the speaker on it. If you push the speaker, it'll move back and come back to its standing position.
The isolation is overkill, but am I loosing in bass tigthness because of this floating slab ?
Would removing the full float thing help ?
The room is fine (Hidley approach with added reflexion after) with huge bass absorbtion. The system is based around an actif Quested 2 X 15"
I tried some Brystons on the lows, which helped a lot in tightness, but I haven't got the budget to upgrade yet.
any clues ?

regards

Chris

PS nothing to do with this problem :
Just for the info for all those out there thinking dsp crossovers can help...forget it ! I had some very good ones, but after many months of tweeking, I still found the mids not right... Got some good old analogue crossovers...and yes it was perfect after the first setup. I was thinking that with the digitals and all their functions, I was gonna be able to fine tune the monitoring... No way ! Speaker and room design is the secret.

barefoot · Post by **barefoot** » Fri Jun 18, 2004 1:14 am

So, if I understand you correctly, you basically made a concrete table with springs as legs, right? Yeah, that is overkill!

I think the main issue is that you don't have any damping in the system. You could try putting some squares of highly absorptive foam like Sorbothane between the spring coils.

Thomas

reader · Post by **reader** » Sat Jun 19, 2004 5:10 pm

Thanks Thomas for your reply.

The problem is I only have access to the front springs... So it's either, I remove everything and sit the cabinets on something hard and firm or leave it like it is ?
Isolation isn't the issue anymore and since the control room is floated (floor and walls), having the speakers sitting on the main building floor will still keep them decoupled from the control room.

My main objective is gaining tightness in the bass.

Now don't think that if I play a very loud bass drum the cabinet starts rocking back and forward...
I spoke to a speaker designer telling me it was happening at a micro scale, I was then loosing in definition.

Could you confirm this ?

regards

Chris

barefoot · Post by **barefoot** » Sun Jun 20, 2004 12:24 am

The ratio of cabinet mass to cone mass is typically so high that this idea of the cabinet moving back and forth and robbing the bass is really a non-issue. However, in your current situation, it's certainly not out of the question that you might excite resonances in your "mass on a spring" platform, generating amplitudes large to cause problems. So, I would definitely modify it. Maybe you can do something like shove a bunch of fiberglass insulation under the platform with a stick?

In general the more realistic concerns with respect to bass coloration are: flexing of the speaker cabinet walls; exciting resonances in floor and wall panels of the room; and, of course, acoustic standing waves and reflection interference.

Thomas

reader · Post by **reader** » Sun Jun 20, 2004 7:26 pm

Thanks Thomas.

You just gave me the idea of spraying polyurethane foam in the right amount under the slabs around the springs. This would reduce the float with something firmer.
I'll think about both options...

regards

Chris

barefoot · Post by **barefoot** » Mon Jun 21, 2004 3:20 pm

Yeah, foam could work. The only thing I might worry about is its lack of control. If the platforms are unstable, then any uneven expansion of the foam might throw them out of level. Of course, you could just clamp the slabs in place unit the foam sets.

Let us know how it goes!

Thomas