An idea to improve isolation cabinet performance

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kyolic

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As we all know iso cabs tend to sound boxy because of the wave jams going on inside the box. The waves coming out of the speaker hit the wall in front and they are reflected back to the speaker and this is just a neverending cycle which is causing boxiness in the recorded sound. Something like this:

iso.webp

My theory is that with a setup like in the below illustration, it could be possible to trap the sound in a separate area in the iso cab and let it dampen there without being able to hit back to the speaker.


iso2.webp

As you can see above there are two inclined traps in the iso cab. First one has a slight gap at the bottom and the second one has a slight gap at the top. They drive the waves to the dampening area and the waves dampen there without being able to escape back.

I am not saying that no wave would be reflected from the first trap but it would be much less than a standart iso cab reflection.

What do you think? Worth trying? Or it just makes sense in theory but wouldn't work practically?
 
You need to research speaker cabinet design--paying attention to ports--to learn what the effect of your design would be. It isn't quite what you think.
 
You mean there is need for ports to make this work? Then that would not be an iso cab because of the leakage. Wrong?
 
kyolic said:
You mean there is need for ports to make this work? Then that would not be an iso cab because of the leakage. Wrong?
Click to expand...

I think he means that those gaps you have in the interior baffles ARE ports. Just because they're inside doesn't mean they won't affect the sound and will likely be tuning those compartments. So you might help with the standing waves but cause a problem somewhere else.
I'm not saying it's not worth trying but the size and positions of those ports is gonna be a factor in how the cab sounds just as much as the standing waves you're trying to eliminate.
 
Let's think about this on a macro scale, instead of a box you have a room which is the first chamber of your box. The slot at the bottom is a window. If you open a window, do you decrease the standing waves in your room? Yes you do, a little.

Now, remove an entire wall of your room and open it to the outdoors. The standing waves just decreased a LOT.

OK, let's shrink it--go into a closet and close the door. Now open the door to your room just a little bit. Did the response of a closet improve with the door open a little? Yes, a little. Now open the door all the way. Which is better?
 
using that scenario ....... wouldn't you also decrease standing waves by angling one of the walls ?
 
Lt. Bob said:
using that scenario ....... wouldn't you also decrease standing waves by angling one of the walls ?
Click to expand...

Sure, that's what opening the closet door a little does. But isn't it better to open it all the way, or just take it off its hinges?

Whenever you build an iso box, you're really building a speaker design. You have the consider the effect of the box (front and rear) not only on standing waves, but also on the response of the driver. An iso box probably isn't going to sound like an open-back cabinet unless the box is really big.
 
Mshilarious check this:

youtube.com/watch?v=ESOrSKGojtg

I listened to many clips and what he claims is true. He is not bullshitting.

Of course I am not saying they nailed it like I illustrated above but somehow they did it. The box dimensions are 22'' x 20'' x 35'' which SHOULD sound boxy but it doesn't. Actually there is a small hint at 2:30 of the video but not enough to get the whole idea.
 
I agree with what he is saying, but note something about his design: it's vented to the exterior. I didn't look for his drawings, but I imagine he's done a transmission line design (what he calls a labyrinth) or something similar. That's a well-described method of speaker design.

If you don't vent the design you'll improve FR at some frequencies and make it worse at others, which is also the same thing that will happen if you take a wild guess at the TL design.
 
There are important differences in your design vs. his. Yours has about 1/3 of its volume behind the speaker, as a sealed enclosure for the speaker. The problem is as the volume of the iso box becomes smaller in comparison with the volume of the enclosure, you can't treat the iso box as arbitrarily large in terms of the sealed enclosure design.

Next, I think he has devoted the bulk of his available space to his first chamber and taken care to make all surfaces nonparallel and angled out from the speaker until the far wall (the top I think). Your chambers are roughly equal in size, and by your drawing you have at least 3 out of 6 walls in the first chamber parallel/perpendicular (5 out of 6 if you don't flare the sides). He follows up with what seems to be a transmission line/folded horn/whatever you want to call (it's not really either, but is related to both) it running down the back and bottom of the cabinet, and then vented. Google an image of the guts of a transmission line speaker and you'll see something like what he did, and note how that differs from your design.

It wouldn't leak as much sound as you'd think because he also would employ massive amounts of absorption on the way, and the interior walls look to be pretty thick plywood. Put your ear next to a port of a typical speaker; all you hear is muffled bass and that speaker wouldn't employ the same degree of interior absorption. The purpose of the port is to control interior pressure, not so much radiate sound.

The devil is in the details . . .
 
I understand totally Mshilarious. It seems we need the plans for his iso cab. :)
 
not to take to many steps backwards but, I'm real interested in what your talking about. I just got a randall iso cab and I am less then impressed. I'm thinking of making some modifications to it but I want to do it I an informed fashion. I am getting big spikes in db at specific frets/frequencies. I've cracked the lid open about a half inch and this seams to lessen the spike. but I want to eliminate it all together. I wonder if I drilled some 1\4 inch holes in the lid and/or the lower part of the box to let the speaker pull and push some of the room air a bit to allow it to respond more as if it wasn't it a air tight box. I realize it would be a bit louder but I could put it in a closet with some heavy blankets over it to compensate the loss of volume dampening. I think the above mentioned design would help a little but I think the big issue is allowing the speaker to travel as if it were in an open room. also some better quality acoustic foam would greatly reduce the standing waves. IMHO. the randall comes with some cheap foam. would this be something worth trying or are there flaws I have to consider.
 
another thing I just found out. I've been micing my mesa 4x12 cab in the garage and it sounds amazing. just cant be loud inside when its to cold to be outside so I got the randall iso cab cuz it comes with a vin30. same as the mesa cab but, I recently found that celestian makes their vin30 spaeker a bit different for mesa then they do for marshall or other customers like randall. so I'm not getting the same tone as well as the above mentioned issues with an air tight cab. I just want the same tone from the mesa cab out of the randall or at least close. I don't know if that is possible? any help?
 
I guess I could just put one of the mesa cabs speakers in the randall but I'm still left with the boxy tone of the randall cab. I'll try that but still interested in your feedback on the iso cab mod.
 
theres an ongoing discussion on isocabs in the diy section that might be of intrest to you. re grimtraveller
 
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