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Custom 115 Cab Build [Long!]

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Patman27

Nov 7, 2009
62
0
Guaynabo, Puerto Rico
patman2700.wordpress.com
#1
Hey all,
I'm new to the forum, so this should be a great way for me to warm up. So, after much contemplation, thought, and pondering, I've decided to go ahead and build a custom bass cabinet. Unfortunately, despite all of my specifications, I'm still left with more questions than answers, though. I currently play through an SWR Goliath III Jr. (8 ohm), and want to add more low end to the mix. I almost bought an SWR Son of Bertha a while back, but I think I can do better than that for cheaper.

1 - Materials: OK, so I've decided on 5/8" Cedar ply (from the Depot) for the top, bottom, sides, back, and bracings, but could I use 3/8" ply for the baffle and/or ports? would this be a good idea? If need be I could just stick to 5/8" all around.

2 - DRIVER SELECTION! I'm really lost here. I play a 6-string, so I want the F3 (if possible) to go to at least 30Hz. Again, I use a Goliath jr. for the mids and highs, so I don't need as much of those to go into this one. I'd prefer something with a rolloff around 2-3KHz, at least handling 400w (to match my goliath). I've been using software like WinISD and Bassbox 6 to test some possibilities out. I'd prefer something under or at $120.

3 - Design: I've looked around and checked up on measurements for the Son of Bertha, the Eden 115XLT, RedStar Anvil 115, Ashdown ABM 115 (or whatever it is) and a few others. To fit under my current cab, I'd like a width of 23". Depth can be up to 18", and height can be anywhere up to 25"

4 - Porting: I think I'll stick to slot ports, It seems they're a lot easier to make and tune. I was thinking of having either slot ports on either edge or on the top/bottom.

5 - Joints: I think Butt joints are enough for me for now, considering I'll have the sides resting on top of the bottom board, not next to.

6 - casters: removable/locking/permanent. I'm thinking permanent, yea?

So, having said all this, my basic concerns are:
  • Which driver would be best considering requirements?
  • Slot ports?
  • Is there a basic design I should conform to for this first build?
  • is 30Hz too low to maintain a reasonable SPL? (95-100<)

And, most importantly, How can I keep the price of this build (excluding the basic materials) under $140??

Thanks to everyone who can help me out on this, It's much appreciated!!! :hyper:
 
#2
Patman27 said:
If need be I could just stick to 5/8" all around.
Click to expand...

I want the F3 (if possible) to go to at least 30Hz.
Click to expand...

From my experience, that will be very expensive and it will take a lot of power to match the rest of your system in volume.

I'd prefer something under or at $120.
Click to expand...

This may be unrealistic.


I'lll stick to slot ports, It seems they're a lot easier to make and tune.
Click to expand...

I like commercial round ports because they are easier to tune. You have to cut wood to do it with slots.

  • Which driver would be best considering requirements?
  • is 30Hz too low to maintain a reasonable SPL? (95-100<)
Click to expand...

I don't think you can pick a driver until you decide what F3 you want to pay for.

F3 of 30hz is a subwoofer, and they are usually not very sensitive. I have done it with car audio subwoofers, and as I recall a pair of 12's ended up being 94db or so, and it sucked a lot of power for little benefit.

Your idea of a reasonable SPL is a very good goal. I'd start there and backtrack, and see what drivers fit your price range, and then see what sorts of F3 you can make.
 
#3
Welcome to TalkBass, Patman27!

Check to see how strong the glue is holding the plies together on the plywood you chose. If it's questionable, you may want to use cleats to reinforce the joints. But if the plies are well glued together then don't bother with the cleats as they don't contribute significantly to panel stiffness.

Thin panels are okay as long as they are very well braced. You'll probably want to use T-nuts or hurricane nuts to hold the woofer in place, especially if the baffle is thin.

As Schecter4 pointed out, -3 dB at 30 Hz is unrealistic... and probably unnecessary. Relatively little energy is carried by the low-B fundamental; the first overtone (at 62 Hz) is much more important.

I estimate your maximum internal volume at about 4.5 cubic feet. In order to get a -3 dB point of 30 Hz in that size box, you're looking at efficiencies of around 91 dB/1watt. So, you gotta choose.

If you decide to accept flat response (-0 db) at the first overtone as your target, then I think everything else becomes feasible. My suggestion for a reasonably priced speaker for your application would be the Eminence Delta 15LF.
 
#4
DukeLeJeune said:
As Schecter4 pointed out, -3 dB at 30 Hz is unrealistic... and probably unnecessary.
Click to expand...

Indeedy. Marketing departments of bass enclosure companies may insert fictitiously low numbers like 30 Hz in their specs, but such low extension is impractical with MI woofers in the sizes of enclosures they are typically used in. And Duke is right, it's mainly about the octave overtone for lower notes.
 
#6
Seems like you'd save 8lbs going with a Basslite C2515 or Deltalite 2515. - although the LFA seems to beat it out significantly in some aspects, they both share similar Spl, excursion limited handling, and similar. The LFA does have a huge XLim though which is kind of bizarre - it's enormous.

Neither of the mid-range neos are that expensive (~105 for the basslite, 123 for the deltalite). They do push the edges of your budget, however:)
 
#7
DukeLeJeune said:
As Schecter4 pointed out, -3 dB at 30 Hz is unrealistic... and probably unnecessary. Relatively little energy is carried by the low-B fundamental; the first overtone (at 62 Hz) is much more important.

I estimate your maximum internal volume at about 4.5 cubic feet. In order to get a -3 dB point of 30 Hz in that size box, you're looking at efficiencies of around 91 dB/1watt. So, you gotta choose.

If you decide to accept flat response (-0 db) at the first overtone as your target, then I think everything else becomes feasible. My suggestion for a reasonably priced speaker for your application would be the Eminence Delta 15LF.
Click to expand...

Eminence's Beta, Gamma, and Delta (both 15LF and Delta 15) are some of my primary choices, especially because of price range and sensitivity.

So, with the measurements I put out, (excluding the slot ports) I think my volume was around 6 cubic feet. I could bring this down to 4.5 though.

To get my low freqs out there, with the low B included, what's the lowest F3 I should strive to hit?
I'd prefer a nice balance of SPL/F3, more leaning to the SPL side to match my 210.
 
#10
Patman27 said:
So, with the measurements I put out, (excluding the slot ports) I think my volume was around 6 cubic feet. I could bring this down to 4.5 though.
Click to expand...

Patman27, here's my math:

External dimensions of 25x23x18 inches [your dimensions] with 5/8" plywood = maximum internal dimensions of 23.75x21.75x16.75 inches = 8652 cubic inches = 5 cubic feet. Less 10% for woofer displacement, bracing & ports = 4.5 cubic feet.
 
#12
Well, 4.5 cubic feet looked like the maximum available, and when I modelled the Delta 15LFA it looked good. I did not model power handling, but the excursion is pretty good (4.8 mm). As rpsands pointed out, for a few bucks more you can save about seven pounds.

You asked previously about the -3 dB point to shoot for. In my opinon that's a reasonable approach when designing a speaker that will get an enormous variety of bass signals, like a home stereo speaker (which is what my day job is), but when the lowest note system will be asked to do is well known (low-B in this case), you can design for that note. Get that note right and avoid any major screwups higher up and you should be okay.

My paradigm is that the major concern at the fundamental is avoiding over-excursion, NOT reproducing it loudly (although Andy over at Acme would disagree with me there). So I'd want to use a low enough tuning to avoid fartout on the fundamental, but high enough to avoid fartout on the first overtone. That balancing act puts our desired tuning frequency somewhere around the mid 40's.

So the next thing to look at is a woofer that will give us good, strong output at the first overtone of low-B (62 Hz) in an acceptable box size. Maybe you end up choosing between two woofers, one with a lower -3 dB point but its output is a bit less at 62 Hz. In my opinon the one with more output at 62 Hz is the better choice as long as it doesn't do something else nasty higher up. Like, the Delta 15LFA has a roughly 1.5 dB bump betwen 70 and 140 Hz, and that might be undesirable - but you said you wanted to add more low end to the mix so I figured it was okay.

Anyway the Delta 15LFA is by no means the only game in town, but based on your application and budget that was my suggestion.
 
#14
What amplifier are you working with, Pat?

For my money, I do not like the midbass hump that the LFA exhibits. Some people do, however. I would strive for something a little flatter down there, that you could boost if needed. But that depends on your amplifier and your sound goals. If you want to add some perceived bottom that might be a good way to go.
 
#15
rpsands said:
What amplifier are you working with, Pat?
Click to expand...

I'm currently playing through a Carvin BX600. It gives 400w @4Ohms, which is what I'd be using it at (parallell my Goliath Jr with this 115)

Again, because its not going to be working on its own, I don't need it to cover as many higher frequencies. Mostly, I'd prefer a bit of midrange punch and lower 'oomf'.
 
#16
Patman27 said:
DukeLeJeune, what program did you use to model it?
Click to expand...

For quick-n-dirty simulations, like I did in this case, I use an inexpensive program you can purchase here:

[Invalid or Expired Link Removed]

It only does round ports, and don't trust it to calculate port lengths if you're using multiple ports.

For more in-depth evalutaion and design work I use other programs that require more input data and take longer to run.
 
#18
I think you might wind up happiest if you go with a few extra dollars and get the Kappalite 3015 in a ~3 cubic foot box - it'll be smaller, lighter, louder, and smooth both on the bottom and up top.

The BX600 has excellent eq and should have no problem dialing in midbass boom if you want it, and will dial out the small peaks of the 3015 in the upper mids easily if you desire - whereas the Basslite's monstrous upper mid peak (and the delta 15LFA too) are both uglier up top and bumpier down low...and need a bigger box to perform their best.

I predict if you go that route you will find yourself wanting to run just the 3015 though, most of the time, and have a much lighter rig. The 3015 is an extremely flexible speaker with great response to eq, and will give you more options.

Just my 2 pence. With an amp as powerfully eq'd as the Bx600 I wouldn't design my cabinet with pre-built eq like the 15LFA gives.
 
#19
walterw said:
is a single 15" even the right box for the job?

might not a second 2x10 cab work better if done right?
Click to expand...

Well, I thought about that quite a bit before deciding, but I'm still open to change. Hell, maybe 2 12s might get the job done.
The thing is, the Goliath Jr. really does take nice care of the mids and highs, (IMHO) so I want something to really make the bass felt, not just heard. To achieve this, I imagine a 115 would do nicely, no?

Plus, a 212/210 can be my next build if I get this 1st one done well! :D
 
#20
rpsands said:
I think you might wind up happiest if you go with a few extra dollars and get the Kappalite 3015 in a ~3 cubic foot box - it'll be smaller, lighter, louder, and smooth both on the bottom and up top.
Click to expand...

OK, so I can bring the Dimensions down a tad, make it smaller. Great news!

What about porting? Should I trust numbers calculated with something like BassBox to determine length? I was originally thinking of making a slot port (or two) like Eden and SWR's 115. Perhaps round ports would be better?
Recommendations?
 

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