You've sealed the driver in there and the bass is shaking the snot out of the cab - decouple it from the floor first - put foam under it - that should help - also, don't put it in a corner, it'll be like a subwoofer there! Other than that you will need to add more density/decoupling materials if its still loud.

what would YOU do? should i drill a hole between the back of the speaker and the fron of the speaker so air can flow back and forth?? i was thinking of putting plywood all over the MDF two make double the exterior layers. so it would be, Plywood 1/4'', Mdf 5/8'' 2 layers of 1.5'' SONOpan (1 layer=3'' Roxul Safe N' Sound)

thanks

i made a move all by myself lolll, i took off all the SONOpan (insulation) and decided to put a layer of 5/8'' plywood over the mdf (by the inside) and replace the insulation on the plywood, i'll make test and tell you how it sounds !

after some testing, it's still really bassy. but i came to the conclusion that all of the bass is coming from the back of the speaker cuz when i put my hand in the front part, i can barely feel the cab shaking. if i put it on the back part, it shakes like hell. and i found taht bass is coming from the bottom so i think that i'll either fill the holes that i drilled to let the air circulate OR add a plywood to the exterior of the mdf + some sonopan between the mdf and plywood

To isolate sound inside a box you need the box to be airtight, have plenty of mass, and be mechanically isolated from the surrounding structure. So no holes in the walls. You could have holes between the cavities in front of and behind the speaker (though I don't know what effect that would have on the sound inside the cabinet) but no holes to the outside.

actually, the only hole that i have is for the XLR connectors and the Speakon one. PLUS two 1/4'' on the bottom to let the air flow out so i have a positive pressure and won'T damage anything.

Vince:
First off, check out the Rivera amps' website (Rivera.com). Click on the "Silent Sister" and scroll down so that you can play back clips by Louis Muldanaro. They offer clips that are recorded both inside the box and outside of the box. See how that compares with your box. You will notice that the "outside" is a lot bassier. This is to be expected, as the attenuation of any of these iso-cabs will mainly be the mids and highs. Judge for yourself how well yours is working against that one.
One of the main reasons for the bass build-up in ANY of these iso-cabs is called "standing waves", and parallel walls in a box that small will really aggravate that. One of the first rules of acoustics I learned about recording studios is that you never have 2 parallel walls - you'll get horrible bass build-up every time. Adding more density or absorption will really not do much to dissipate this. In any case, you might want to watch the vid clip of Paul Rivera discussing this, and other issues of designing an iso box. Very good info, check it out.

I'm not so convinced that standing waves are as big a problem as moonbaby thinks. You can use a [[url=http://[/URL]="http://www.marktaw…"]room mode calculator[/]="http://www.marktaw…"]room mode calculator[/] to find the frequencies for your cabinet. For a small box, even the lowest are in the low mid range rather than the bass. If you have built a cube or a square cross section you could have a pretty uneven response when you record, but I wouldn't think it would have a huge effect on transmission outside of the cab. As anyone who has lived in an apartment knows, bass transmits better than mids or highs. I still think the only way to reduce transmission is to make it heavier (drywall?) and more air tight.

Did you watch those videos? I'm sure that the "bassiness" is in large part due to the attenuation of the mid's and high's. But the airtightness of the box has its' drawbacks - the cooling of the motor assembly in the speaker, and how the moving cone works in proportion to the mic's element.

yeah, i checked the videos. actually the air can go out of the box by a ''false bottom'' that i created. i wanted to know, if i drill a hole from the back of the speaker to the ''false bottom'' which is vented, would it be good or wouldn't change a thing

Just curious: How does your cab compare to what's in the video?

I checked out the Rivera videos. Much of what he says is interesting and the design of the cabinet seems clever, but from what I understand the part about eliminating standing waves is incorrect. Every enclosed space has standing waves or resonant modes. Nonparallel walls don't "break them up" in a cabinet any more than they do in a saxophone. (Nonparallel walls reduce flutter echo - a different problem.) The labyrinth design would change the modes and make for longer modes (like bends in the tube of a wind instrument).

Having seen the videos, I like my solution even better: a 50' speaker cable. Put the cabinet in the next room and shut the door. Nice environment for the cabinet and pretty good isolation. Next step is to make a better door, but I'm not really picking up any guitar on the drum and vocal mics now. Admittedly this solves my isolation problem, but there are a lot of other reasons to use an iso cab.

I wholeheartedly agree with you, Bob, the right room IS the best ! ! ! ! Personally, I have an affinity for large tiled bathrooms, but...:)
I am curious if Vince's tonal issues outside of the cab are outside of the norm for an iso box, though. I have used a Randall isolation box with a 50-watt plexi-style boutique head and it was not enough reduction (due to the bass range) to use in my condo. I have had to settle for a V-Twin preamp to simulate the cranked-Marshall-on-11 sound. Sigh.

actually the volume is quite well reduce. i made some modifications. i added plywood EVERYWHERE in the inside even the back part. added SONOpan( sound insulation) on the bottom of the back part (back of the speaker) which was laking in my first version. i then drilled two holes from the back part to the 'false bottom'' which is vented so all the ''pressured air'' can go out. it does let the sound out a little bit. the bassyness is still there but less ''present''. i can't do anything more now, except building concrete walls loll. i'm quite satisfied now but i need to put my mesa boggie single rectifier at low volume (like 2) or the sound is coming out. And trust me, if i would've had the choice, i'd use my Mesa 4x12 but since i live in an apartement with no spare bedroom, it was the only choice i had. And by the way, i do have a Line 6 POD Xt Pro and EVERY guitar plugin/emulation/cabinet impulses on the market and it was REALLY lacking tube sound. the great thing is that it doesn't sound really boxy due to my venting.

The problem is always the same problem.

You need mass, and you are distorting the mass in the assumption that you can construct a typical wall assembly type configuration that will mitigate the low frequency issue.

You can't.

MASS MASS MASS....BUT you never mentioned how big the case was, never mentioned the room and how it might or might not bring issues.

Agreed that decoupling the box from the floor will help in some respects. 703 corning 1 inch or 2 inch would be a better fit, but I still think that maybe the Moon is right, with so little information to work with, that the room, after the sound leaves the box...which it should not leave the box in the first place, which is why it is referred to as an isolation box, may be the issue.

On a side note, insulation reduces the mid/high frequencies...so your want to add it in, is actually taking away from the natural sound, basically stripping the mids an highs off of the sonic landscape, and leaving you with the low frequency.

Get rid of the sonopan and just use hard heavy material.