iso cab - looking for comments/suggestions

[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.

[NateS]

I've been kicking around a 1x12 iso cab idea. The secret to avoiding boxiness seems to be more volume. One idea i had was building a 1x12 inside a stack lookalike. That would get you a load space about 5-7x the volume of the "speaker box". A single baffle slanted down the center gets you a transmission line to nowhere and avoids parallel surfaces. If you need to tame resonances, a tuned resonator cavity inside the box is a cut rather than boost if it were vented to the outside.

I have a MG412 cabinet I bought because it was too cheap to pass up. It's too small for this, but I like the size. (26.375x26.375x14) If I could figure out a way to break it down for transport, I'd be pushing other projects aside for this one.

[sprack]

If you can find technical info on designing a good "listening space" inside a small box let me know. I took what I could from the calculators for a band pass design, adjusted a little for the golden ratio and winged it for the rest. I might try again if I have the time one summer. Most of the boxiness was reasonably EQ'd out in the DI signal by notching at 77Hz before going into the mesa.

[NateS]

I don't know why it didn't occur to me, but yeah, the Rivera Silent Sister, is actually a 4th order bandpass enclosure. I'd think that you'd want to tune it LOW though. Size the acoustic suspension part as you would for a typical speaker cabinet. (1.4-1.6ft^3 for ROTM Celestions), Make the bandpass chamber as big as practical and tune it to 20Hz - that should get you -48db down at 80Hz.

And if you flip the speaker, now your voice coil is at nearly ambient and has a "DC path to ground" thermally speaking. AND I think I might can actually build this inside the MG412 cabinet. Win-Win. Looks cool, fits in the backseat of a sedan, and puts an otherwise sucky cabinet to good use.

[Sowhat]

I have struggled with boxiness for a few years now and have found a method to keep this from happening. First one is to open the hatch if you can stand the volume. The second and more appropriate is to play at the proper volume, too high and it goes boxy because you flatten out the mic. The mic I used has changed, originally I used a Heil only for the fact that Billy Gibbons of ZZ Top uses one with his iso's. I since tried a high quality condenser (big mistake), a ribbon mic (an even bigger mistake) and finally settled on the venerable Shure SM57. That old workhorse dynamic Shure mic does the trick.

I have converted a corner of my repair shop into a recording studio and currently me and the boys are putting together an album.



I call it Busted Junk studios because that's what I repair there, musicians busted junk. Looking the other direction from this photo would reveal an electronics repair shop cluttered with busted junk. I use the rig in the corner which is my iso cab and two 100 watt master volume power amplifiers, one solid state and the other tube. The tube head has both pre and post phase inverter master volumes while the solid state has your typical single master. I do guitar as well as bass with this rig. Those privileged enough to have heard studio cuts of the album so far are stunned by the tonal capabilities of this rig... sounds incredible.

[NateS]

Yours was sealed though, right? Nothing wrong with either, and sealed is probably easier to get more quiet, but boxiness comes down to tuning of the spaces. I think tuning a ported enclosure low and using it LPF all of the speaker signal out is probably more space efficient and the sealed space it would require to eliminate midrange boxiness.

[NateS]

Yours was sealed though, right? Nothing wrong with either, and sealed is probably easier to get more quiet, but boxiness comes down to tuning of the spaces. I think tuning a ported enclosure low and using it to LPF all of the speaker signal out is probably more space efficient than tuning the acoustic suspension chamber to lower Q or move the hump to a less objectionable frequency.

[NateS]

Thinking about this some more... in a sealed box, both sides are acoustic suspension enclosures. I took Warehouse's Green Beret because it's what I'm considering and it has specs. Vb per speaker seems to run from 1.45 in a 1960B to 1.6 in a 1936 2x12. Vb=1.6ft^3 givese a Qtc of 1.25 and fc=144Hz.

I also did some digging into infinite baffle sites, and it would appear that we can consider an enclosure to aproach infinite baffle at 10 * Vas for unstuffed boxes, and 4*Vas for stuffed boxes. (Which, btw - I don't recall seing anyone stuff the resonant space of the box itself - which should help boxiness a lot.)

4Vas for the Green Beret is 4.8ft^3. 3/4 of a 1960B is 4.4ft^3 - so a 4x12 sized 1x12 isolation cabinet is tantalizingly close. The double wall stuff makes it bigger though, and a 1960B is already a tight fit - adding depth to make up the volume lost to double wall construction would make it totally unwieldy.

Enclosing an infinite volume is where we'd like to go, but a bit cumbersome. I'd wager though, that merely getting Qtc of the load side below 1, or even just below Qtc of the suspension side is a good start. My MG412 is a handy size, because it actually fits into a car. Going with slightly thinner layers, I can get close to 1.6 ft^3 per side. I think we can use a much much smaller port diameter, since there is no load at the tuning frequency - so 1.6ft^3 w/ a 1"dia port, 2" long gives us that 4 octave down tuning.

[Sowhat]

Yours was sealed though, right? Nothing wrong with either, and sealed is probably easier to get more quiet, but boxiness comes down to tuning of the spaces. I think tuning a ported enclosure low and using it LPF all of the speaker signal out is probably more space efficient and the sealed space it would require to eliminate midrange boxiness.

You may have not seen my previous posts on this thread but yes, I keep the hatch battened down, at least in the studio for recording. Playing out live I pop the hatch and let it all out. I implied that I did a lot of geometry changes and selective dampening inside the enclosure to move the cabinets resonance frequency outside of my intended operational range. It was during this exercise that I realized how important a rugged high SPL microphone is to the whole equation, that, and using top quality master volume amplifiers to pre limit the sound. Makes all the difference in the world for me.

[NateS]

I was planning to parallel the speaker with a reactive load taking up 3/4 of the power. I guess recording is as much about keeping noises out as keeping the ruckus in, but thrashing the power stage was a driving consideration. I can definitely get the load space to 4Vas if I go with the full stack.

. I'll have to see if I can get a one piece of the MG or 1965 size in the backseat.

[NateS]

I had another revelation about using T-S parameters for figuring BOTH sides of the speaker. The Vas of the speaker certainly has an impact on the loaded side. But the "unloaded" side - we need to shoot for 4x Vas in order to approximate an unloaded airspace. (Obviously more if you can get there, but we'll have trouble getting to 4 as it is in most cases). Here's where the Vas and Qts REALLY matter. About 4x as much as for the "suspension" side. We can trade a little bit of Qts for Vas and end up at the same Qtc.

WGS's Green Beret is one of the lower Vas in the "british" family, but it has a Qts of 0.95. The Reaper has a tiny bit higher Vas, but a lower Qts (0.78), so it can handle the undersized box a little better before getting boxy. Certainly something to consider when picking your speakers. There might be something you like almost as much in a normal cabinet that may tolerate being stuffed into a small box a LOT better.

[NateS]

I finally got a chance to run the numbers. Not only did I like the demo clips for WGS's Invader a lot, it has one of the lowest Vas. In any quad box of any size, it's Qtc will be around 1.4, and you can take the suspension side pretty low while maintaining Qtc = 1.4. Of their entire line, this speaker gives the highest Vb to Vas on the "room" side. In a 1960B size box it can get to 4.5*Vas. It can still get to 3*Vas in the MG size box. I think I smell sawdust this spring.

[NateS]

Is there any conventional wisdom of the mass/stiffness distribution between inner and outer cabinets? Full stack, double wall 3/4 mdf + 1 layervof drywall tips thevscales at 250lbs. When its stationary, mass isbyour friend. Not so much when transporting. My intuition isnt sure how to approach optimizing weighg distribution between the shells.