# Resonace and damping



## needspeed52 (Aug 2, 2008)

Hello to all,
I have a pair of original Athena F2's in good condition. They are big boxy speakers with resonating cabinets, I just removed the drivers and noticed the lack of bracing and cheap carpet pad lining the cab walls. I'm going to try and add some bracing and dampening foam. I was looking at the Madison foam insulation sheets, 1/2 inch thick and fairly inexpensive, what are your thoughts on this material? The cabinet walls are 3/4 inch MDF and front baffle is 1 inch thick. The driver recess cutout is fairly deep I guess to accomodate the plastic ring that screws down over driver basket, my question is can I get rid of this plastic ring and place some adhesive foam around the cutout so as to make the driver more flush with baffle, this will make it possible to better tighten down the driver also, the plastic ring won't be there, or will this cause an adverse reaction? Thanks guys for listening, Im on a strict budget, so I need to make the best of what I have. The xover is for another disscusion...
Best regards...Jeff


----------



## dyohn (Apr 17, 2008)

I can't comment on your plans to modify the loudspeaker system since I'm not familiar with it, but I have used the stick-on foam sound barrier material from PE and it works as advertised.


----------



## lsiberian (Mar 24, 2009)

There are several levels you can take this modification too. 


Easy way:

First step replace the lining with 2" of rockwool(make sure to cover with a burlap or something similar)

Rock wool can be gotten for around 40 bucks for a pack of six panels and has lots of usefulness in this hobby. It's the best stuff for speakers for it's price. 

Second step is to add rib braces. For this I suggest 1" x 4" oak or 1" x 2" oak. 

Ideally you'd add them on every axis at 4" intervals, but there is probably a limit you'd want to add. 

Insane way:
apply peel-n-seal to all the walls. and then use some card board to create a forming structure add some concrete and let it set. Then use steel to brace the interior. 

Line the walls with rockwool as you did before and you have a reference enclosure.

I'm lazy So I'd just add some wool and oak bracing. I might even do them in a shelf style. and apply the wool in between. 

If this is a ported enclosure we will need to take a different approach.


----------



## needspeed52 (Aug 2, 2008)

Where can I get the rock wool, I don't know what a rib brace is and yes the cabinet is single front ported. That insane way surely is insane, I'm crazy but not that!!!! Thanks. Someone suggested I use all thread with nuts and a turnbuckle to apply pressure to side walls. This is getting interesting. What do you think about mounting drivers without that plastic ring?
Thanks again


----------



## dyohn (Apr 17, 2008)

How large is that enclosure? Unless it is very large or the drivers are extremely capable and driven by very large amplifiers, I am from the design school that says there is no real gain to be had from over-bracing and over-damping a system. The point of diminishing returns was likely already considered by the original designer assuming it's from a reputable company.... But hey, the fun of DIY is to give it a go, eh? Do some before and after measurements and see how the performance changes.


----------



## lsiberian (Mar 24, 2009)

A rib brace is single piece of wood that goes from one side of the cabinet to the other. Think of wood as string. A brace is like putting your finger on a string. As you know that raises the frequency. The goal of bracing is to raise the frequency out of the audible range. 

The goal of dampening is to absorb energy. By absorbing energy less is reflected back at the driver to cause distortion in the sound amongst other things. 

I wouldn't mess with a driver. The concrete thing is actually easier than it sounds. And is actually easier than building a wood substructure. But it's not my thing either. 

Make sure you do use some foam tape in between the driver and baffle ring. I wouldn't want you listening to the screws. 

Rockwool(mineral wool) can be gotten at insulation places usually or online at Ata-acoustics. Generally it's cheaper to get a pack from a local place, but if time is not your friend or you are scared of contractor places it's an option.

You can also make bass traps out of the stuff and even improve house insulation. It's not as nasty as fiber so that's why I prefer it. 

for a ported design you will want to only treat the back wall and half the interior surface. I'd do the bottom, left and back.


----------



## lsiberian (Mar 24, 2009)

dyohn said:


> How large is that enclosure? Unless it is very large or the drivers are extremely capable and driven by very large amplifiers, I am from the design school that says there is no real gain to be had from over-bracing and over-damping a system. The point of diminishing returns was likely already considered by the original designer assuming it's from a reputable company.... But hey, the fun of DIY is to give it a go, eh? Do some before and after measurements and see how the performance changes.


I understand you, but mods can be quite fun and do improve performance. I've seen plenty of measurement on the subject to demonstrate that. 

Of course most speakers sound great if they have a good builder/designer. My speakers are barely dampened and unbraced. LOL. But don't let that get around. :R If I had to do it over I'd go overboard. Overboard is fun. :devil:


----------



## dyohn (Apr 17, 2008)

Absolutely "overboard" can be fun, and it is part of the reason for DIY! As long as you know it *IS* going overboard and you're not doing it simply because someone told you you should do it is my only reason for posting my thoughts here. (Not "you" specifically, but "you" in a generic all people sort of way.)


----------



## needspeed52 (Aug 2, 2008)

dyohn said:


> How large is that enclosure? Unless it is very large or the drivers are extremely capable and driven by very large amplifiers, I am from the design school that says there is no real gain to be had from over-bracing and over-damping a system. The point of diminishing returns was likely already considered by the original designer assuming it's from a reputable company.... But hey, the fun of DIY is to give it a go, eh? Do some before and after measurements and see how the performance changes.


The enclosure dimensions are H=41" x W=10" x D=15", (specified specs.) two 8" injection molded polypropylene woofers, one 1" silk dome tweeter, 93dB effecient, freq. response 35Hz-20KHz +or-3dB, power handling: 25 to 250 watts, two way design. They are driven with 125 watts of clean power, they actually sound good with deep bass extension but at certain registers a tad boomy, I'm attributing this to lack of bottom cabinet bracing and dampening, there is adequate bracing in the top half of cabinet, this may be the point of diminishing returns. That is why I started this thread to see if it would be worth while to add an additional brace and some dampening to improve SQ, I just wanted to get some feedback and insight before I did something stupid, since I am not so inclined as to loudspeaker design and principles, but then again I would not have entertained the idea of removing drivers and xover's a week ago, I'm just getting my feet wet and I enjoy the conversations here at the Shack. Isiberian, I will put the foam around baskets to start and open for more interesting talk. Thanks guys. PS..I'm thinking about rewiring internally.
Best regards...Jeffrey


----------



## dyohn (Apr 17, 2008)

Just remember the more bracing you add the smaller the effective enclosure size becomes, and if it sounds boomy now that is usually an indication of too small enclosure size to start with. I suggest beginning by using silicone sealant on all internal seams and then adding about 16 ounces of polyfill in the woofer chamber (keeping it away from the port opening.) Line the bottom, top and rear baffles with damping material if you choose. Remount the drivers using gasket tape as suggested earlier and see if it performs any better. Then you can decide if you need to go further.


----------



## needspeed52 (Aug 2, 2008)

dyohn said:


> Just remember the more bracing you add the smaller the effective enclosure size becomes, and if it sounds boomy now that is usually an indication of too small enclosure size to start with. I suggest beginning by using silicone sealant on all internal seams and then adding about 16 ounces of polyfill in the woofer chamber (keeping it away from the port opening.) Line the bottom, top and rear baffles with damping material if you choose. Remount the drivers using gasket tape as suggested earlier and see if it performs any better. Then you can decide if you need to go further.


Thanks dyohn, I will seal the internal seams, about the polyfill, where do I get this and do I just put it loose on bottom of cabinet or put it in some type of mesh sack or bag? You refer to damping rear, bottom and top baffles, I guess this means the top, bottom and rear cab walls? Any preference for that material? Thanks so much for your help.
Jeff


----------



## dyohn (Apr 17, 2008)

Yes, sorry, baffle means enclosure sides. We were talking about using the acoustic foam from Parts express, yes? Polyfill can be purchased from any craft or fabric store, they call it polyester fill for pillows or quilts and it comes in plastic bags. Or you can order a product called acoustastuff from Parts Express, which some people claim works a little better. It can just be put into the enclosure loosely.


----------



## lsiberian (Mar 24, 2009)

dyohn said:


> Just remember the more bracing you add the smaller the effective enclosure size becomes, and if it sounds boomy now that is usually an indication of too small enclosure size to start with. I suggest beginning by using silicone sealant on all internal seams and then adding about 16 ounces of polyfill in the woofer chamber (keeping it away from the port opening.) Line the bottom, top and rear baffles with damping material if you choose. Remount the drivers using gasket tape as suggested earlier and see if it performs any better. Then you can decide if you need to go further.


That's a terrific idea. You can get poly fill from almost any crafts store or even a walmart.


----------



## needspeed52 (Aug 2, 2008)

Thanks guys for all your help.
Happy and Blessed holiday
Jeff


----------



## lsiberian (Mar 24, 2009)

You aren't off the hook. We want pictures!

Make sure you document this for yourself and our pleasure.


----------



## needspeed52 (Aug 2, 2008)

lsiberian said:


> You aren't off the hook. We want pictures!
> 
> Make sure you document this for yourself and our pleasure.


Thanks Isiberian, that was nice of you to say for our pleasure, really makes me feel welcome. I know you from AH, read a lot of your posts along with Chris's, wish I could be that insanely sane. Yeah I still got the hook in my mouth, I will order what I need to work on the speaks and keep you posted. I ordered an Emo amp today, the baby UPA-2 to drive the F2's in my HT setup, take a little load off the receiver. So until then my friend, Merry Christmas and God Bless.
Jeffrey...


----------

