Another Cab

[Alien]

Inspired by all the rave reviews of BFM cabs, I decided to build a mini version.

First up was a Omni-type cab loaded with a single 8, pics can be seen [url="http://basschat.co.uk/index.php?s=&showtopic=380&view=findpost&p=44659"]here[/url]

My current project is a folded bass horn to sit under it. Originally, I intended to build a 2/3 size Titan-alike folded horn, but I decided on a simpler (and slightly smaller) design. Overall size of this cab will be about 330 x 330 x 550mm. As with the first cab, it's a sealed design, loaded with a 50 Watt 8" driver. Again, this cab is made from 9mm ply, with the exception of the baffle and the front of the resonating chamber, which will be 12mm. I'm a bit narked that I actually had to [i]buy[/i] plywood for this build, as there wasn't enough salvaged timber left to make a cab!

Anyway, here's the first couple of photos:

[attachment=2018:PICT0220.JPG][attachment=2017:PICT0221.JPG]

I'll post more as I get it done.

Andy

[alexclaber]

Very daring of you to try a guesswork based horn cab! Curious to see how it turns out, suspect it'll prove surprisingly effective...

Alex

[Alien]

[quote name='alexclaber' post='53176' date='Aug 31 2007, 10:06 AM']Very daring of you to try a guesswork based horn cab! Curious to see how it turns out, suspect it'll prove surprisingly effective...[/quote]

Not entirely guesswork, although educated guesstimates is about where it stands!

The difference between the pistonic area of the cone and the horn throat gives a compression ratio of about 2:1, and the shape of the horn is roughly exponential (allowing for parallel sides and straight lines). The sealed box is a little larger than in the short horn loaded cab, which should lower the rolloff frequency a bit. I'm not expecting flat response to 40Hz, but reasonably flat between 50 and 200Hz should be perfectly attainable.

Couple more photos now. I took a view of the horn before I put the side panel on, which looked OK on the little 1.5" screen on the camera, but turned out to be a big blurry mess when viewed full size. Looks like you'll have to make do with exterior shots, as I'm not taking the side off again now it's glued and pinned!

[attachment=2026:PICT0222.JPG][attachment=2027:PICT0224.JPG]

Just the bottom brace and the front of the resonating chamber to go now, then I can get it wired up and tested.

Andy

[Alien]

OK, it's update time. Got the last bit of bracing done and sorted the front of the resonating chamber. Stuffed a load of acoustic foam and wadding in the enclosure, fitted the driver (with a foam sealing strip around it), closed the cab up (more foam strip) and we're ready to go.

[attachment=2147:227.JPG]

I plugged my Crate Powerblock through my SX21 crossover (nearly blew the bloody thing up plugging the input and output together, but that's a different story ) and gave it a test run.

WHOA! This thing kicks ass! Good solid bass all the way down to low G, and it sounds pretty good all the way down to the low B on my 6-string. Running full-range, it sounds pretty good too, with a lot more high end than I'd expected (actually midrange is probably closer to the truth) but certainly a very 'old school' bass sound.

[attachment=2146:226.JPG]

Running bi-amped with the top cab, the whole thing sounds great. It's got a similar range to my 2x10, and very nearly as much volume, despite only running 100 (ish) watts as compared to 400 for the 2x10. It also weighs less than half what the 2x10 weighs, even including the Crate and the crossover! I reckon this setup could easily handle a small gig, providing the drummer wasn't a total nutter.

OK, so the next step is to get it painted, so time to strip it all down again. I'll post finished pics when I'm done.

Andy

[alexclaber]

Cool! What's the path length? Have you considered using floor, wall or corner loading to improve the apparent mouth size?

Alex

[Alien]

It's quite a short horn, around 950mm or so. The cross-sectional area increases by about 15 times in that length, ending with a mouth just over 300mm square.

I've not tried corner loading it yet, but that would be the way to go for big bottom, pointing the bass horn into the corner with the mid-top horn facing outwards.

Andy

[TPJ]

Nice job there.

[Bill Fitzmaurice]

[quote name='Alien' post='57245' date='Sep 7 2007, 06:36 PM']It's quite a short horn, around 950mm or so.[/quote]The last thing I would do is discourage experimentation, but I would be remiss not to point some things out. While it undoubtably works very well compared to commercial cabs, the path length is half that of a T39, which means the cutoff is a full octave higher. That takes it out of the realm of being a subwoofer and makes it just a woofer. Nothing wrong with that, it's still better than a 4x10, but if you're going to build a folded horn with such a high cutoff do so with a geometry that allows the woofer to work all the way up to 2.5kHz or so. Then a separate top cab wouldn't be necessary. In other words, a DR250 or DR280.