iso cab - looking for comments/suggestions

[sprack]

I'm planning on building a 1x12 iso cab for mic'ing at home. The current cabs all bother the wife or wake the kids when I'm trying to reamp. It's essentially a transmission line cab, though I don't know if it should be combined with a band-pass cab. Its 15x21x29 internally, 1 : 1.4 : 1.9 ratio. The speaker baffle wall is tilted 5 degrees on 2 dimensions to avoid parallel walls. The air labyrinth is 3in wide which should make it tuned for around 70hz, B1. It's difficult to find any real info on building a iso cabs though. I'm guesstimating a lot here based on a little studio design for room modes combined with some more fuzzy science on air labyrinths and then again loosely on the Rivera Silent Sister.

Materials are 3/4in birch ply. I'm going to line the mic'd portion with auralex and the back wall with rockwool. The air labyrinth with 1in rockwool on both walls to help dampen bass transmission. My first concern is that it doesn't sound too boxed in like the Randall cab. If it doesn't attenuate the sound enough I'm thinking of a box to put it in.

This first one is the transmission line:


Here's the band pass:


I'd really appreciate any guidance you guys can offer.

[sprack]

Has anyone built an iso cab with good results? Any insight would be appreciated.

[Steve Conner]

I'm no expert, but I think if you're trying to build an isolation cab, then putting a hole in it to let the sound out is a really bad idea. And that's what your air labyrinth is, a hole that sound will escape through.

An iso cab has to be completely sealed, and made of the heaviest, deadest construction materials possible.

I don't think the bass tuning works the way you're expecting, either. The mic'd portion of the cabinet will have "cabin gain" like what you get in car audio. Stating this another way: Even if you coupled a transmission line to the back of the driver, the front is still loaded by a small sealed enclosure.

I notice that some iso cabs use tuned ports that couple from the compartment behind the driver to the mic compartment. This could roll off excessive bass. In your transmission line design, that would equate to hooking the free end of the air labyrinth back into the mic compartment, instead of the open air.

[sprack]

Steve,
Thanks for the feedback. I'm building it out of marine 3/4 inch birch. MDF might be better, but I hate working with the stuff. The reason I'm giving it the vent though is because of prior experience with the Randall ISO cab which is fully sealed. It sounds muffled and boxed in. Whereas all the recordings of the Rivera Silent Sister sound really close to an open room, mic'd cab.

Rivera Silent Sister Vs Demeter by Scott Whyte using Van Halen riffs - YouTube

I agree the first drawing would suffer from "cabin gain". Initially I thought of running separate labyrinths for the front and rear cabins. I've settled on a hybrid of the two that will allow me to close off or open up both areas to see which sounds the least boxed in. I could also try a case where they share the labyrinth. I'm just winging it here. I guess in this way I'm still basing it on the porting at the bottom of the Rivera.

Here's another idea. I realize it's spiraling a little out of control.



Thanks for bearing with me,
Jesse

I'm no expert, but I think if you're trying to build an isolation cab, then putting a hole in it to let the sound out is a really bad idea. And that's what your air labyrinth is, a hole that sound will escape through.

An iso cab has to be completely sealed, and made of the heaviest, deadest construction materials possible.

I don't think the bass tuning works the way you're expecting, either. The mic'd portion of the cabinet will have "cabin gain" like what you get in car audio. Stating this another way: Even if you coupled a transmission line to the back of the driver, the front is still loaded by a small sealed enclosure.

I notice that some iso cabs use tuned ports that couple from the compartment behind the driver to the mic compartment. This could roll off excessive bass. In your transmission line design, that would equate to hooking the free end of the air labyrinth back into the mic compartment, instead of the open air.

[sprack]

Rough fitting shot.

[sprack]

I'm putting in corner angled reflectors. Should I fill the gap behind them or leave it an air gap?

[Sowhat]

I made an iso cab for studio work and playing out. It's a Demeter like design but with a removable hatch. Most times I stand it up on it's closed endwith the hatch off and put the head on top making a mini stack for playing out. With the hatch off it blasts out sound as good as a Marshall 1/2 stack and it only uses a single 12" Eminence Texas Heat Speaker. It has a lot of low end as you would expect but I had to take great pains to dampen out resonances in the guitar range with selective foam padding and internal geometry discontinuities. Closed up for studio use with a nice Heil instrument mic it sounds strong and punchy, no sign of a boxy tone from it.

Here's a few shots of it.

[sprack]

@SoWhat That's a great looking cab, looks great with the head. Great finish work and tolexing job. How much noise reduction are you seeing open vs closed?

I finally finished got mine together this last weekend, paint and tolex left to go. Got a test run in on the 2203KK, I cranked it to about 4. Sounded great through an SM57. About as loud as what what I usually monitor at with it closed. I probably should have put a layer of MLV under the bonded-logic for more dampening, but I'm still happy.

[Sowhat]

Mine is not a ported iso cab but is instead a sealed iso cab. When sealed it cuts down on the SPL a tremendous amount. I sometimes use it in my shop where I repair amplifiers so as not to disturb my neighbors too much. I remember a David Eden Traveler where if I do remember right puts out about 300 watts. I just rebuilt the amplifier section and plugged it in, and started bringing up the volume with a guitar plugged in. I thought something was wrong with my repair because I could barely hear the thing. Then, I realized that I had the hatch closed on the isocab, so I popped it open and literally blew myself away from the high SPL. The difference was shocking.

That's not Tolex... it's Rustoleum truck bed liner rolled on and then colored with plain old Rustoleum satin granite spray paint, a tough durable and easily repairable surface, way better than Tolex and it looks better too, no seams or any of that nonsense. I've had it with scuffed and ripped Tolex, it's way too delicate for road use unless you have some good anvil cases, and even then you need to be careful.

[sprack]

That's a great idea using the bedliner instead of tolex. I wonder if something thick like Rhinoliner would have an additional damping effect? I'll have to look into it. Thanks!

[Sowhat]

One other thing, all surfaces inside of the cabinet are covered with 1" open cell foam sheeting, I think they call it upholstery matting. Thats both chambers, the speaker chamber and the microphone chamber. This dampening is what makes the cabinet work so well, without it the thing rings and resonates. Also the hatch is sealed with closed cell butyl rubber gaskets that fit tight when closed, this makes a big difference as well.
The pictures do not show this detail.

[sprack]

That makes total sense. I went with a cellulose base insulation by bonded logic that had some of the highest NRC values I'd seen. I'd considered also trying a 2" Mineral Wool everywhere, which in retrospect probably would have been easier to apply.

PRODUCT THICKNESS DENSITY MOUNTING 125HZ 250HZ 500HZ 1000HZ 2000HZ 4000HZ NRC
R-13 3.5" (mm) A 0.95 1.30 1.19 1.08 1.02 1.00 1.15

[sprack]

Just thought I'd throw small clips and a vid on.
Roadster into isocab

[J M Fahey]

Ugh !!! It *does* become boxy when closed
Oh, well, what was I expecting?

[sprack]

Are you going by the clip or the video?

[exclamationmark]

Any properly mic'd A/B clips with the lid closed/open? It'd be interesting to see if it has any resonance issues. How does the sound compare to using impulses?

[sprack]

The link right above the vid is a quick take, mic'd. First half is SM57, 2nd half is an Audix i5.