Home Brew FRFR

[Cagey]

I'm not a drummer so forgive my ignorance, but for monitoring purposes, do you really need to reproduce the drums exactly, like a hifi or PA system would? Since theoretically, you're the only one hearing them and the need for that is to provide aural/tactical feedback onstage to keep you honest, it seems like you could forgo the very low end. That would perhaps allow you to build something a bit smaller.

 

[swarfrat]

I have a 32" marching bass drum, tuned WELL above lowest possible pitch that is tuned to an honest 30Hz fundamental. And it shakes your innerds.  I LOVE the solid THWOMP it has.  I think 45Hz is more reasonable limit. In this case  the combination of cost, box size, and excursion limits just happened to work out that low for a flat box/driver response, loud enough to match up with the single Beta8CX, in a not too big box. If i can trade that bottom octave for another 6db headroom, 3db size or 3db cost, I probably would.

Picking numbers out of thin air free of other constraints, I think max spl 126db, -3db @ 40Hz is a better target. Mostly that loud because drums are extremely transient.  150db is easy with real drums. We don't need to play as loud, but I think I'd want at least 10db headroom over average, cause average is basically meaningless for drums.  And if your guitarist is playing at 105db avg 3 meters away, thats probably about where you need to be at 1m.

 

[mayfly]

I got through about 3 pages of that without figuring out what it was other than the fact that it was some huge contraption  that didn't seem particularly suited to sound reinforcement because of its uniqueness and non-packable shape.

I dunno - the plans for the 8" driver don't seem to be too much larger than my little box.  Given the measured bass performance at low excursion limits it seems like it could be a winner.

But it has reignited my search for a good FRFR monitor (design)  that CAN do justice to drums.

But that is the most important thing!  ccasion14:

 

[mayfly]

Update:  I've been using the little box for rehearsals as a PA speaker and guitar speaker and it's working out well.  I like it.
But!  I'm building another cabinet.  This is as bad as guitar building!

I ordered up a flatpack of a Bill Fitzmaurice designed box, which Leland Crooks of speaker hardware made up for me.  It's the 'simplex 10', which uses the 10" version of the Beta 8CX I used in the little box.  It's supposed to be the easiest of the Fitz designs to make.  Let's see if that's right.

The flatpack arrived today and it looks like very high quality stuff.  Leland is great to work with and at first blush the quality of materials and workmanship seems first rate.

 

[mayfly]

Not bad for a nights work.  But this cabinet is HUGE!!!

 

[Logrinn]

I ordered up a flatpack of a Bill Fitzmaurice designed box, which Leland Crooks of speaker hardware made up for me.

So, a "flatpack" is like an ordinary IKEA package?

 

[mayfly]

I ordered up a flatpack of a Bill Fitzmaurice designed box, which Leland Crooks of speaker hardware made up for me.

So, a "flatpack" is like an ordinary IKEA package?

You bet!  Almost as easy to assemble too!

 

[mayfly]

Update:  The Bill-Fitz Simplex 10 cabinet is done and loaded with a Beta 10CX (see below).

The speaker has the same motor and magnet as the 8CX, and uses the same crossover and compression driver.  The box is about double the volume of the one I made for the 8CX and was actually designed by someone who knows what they are doing (instead of copying the Eminence suggested design).  The result?  well - it sounds better    Deeper bass and a much more natural sound in the lower mids and bass.  It sounds pretty great actually.  A pair could easily be a good PA for medium sized shows - assuming the bass player ran their own rig and there was a HPF on the bass drum.  But it's big.  just BIG.

BTW, I can easily recommend the flatpack from speaker hardware.  The material quality was excellent and the cuts were perfect.  The box (including the 45Deg ports and the tricky internal bracing) went together with no issues at all.  It was a pleasure to build.  Now I just have to finish it.

I can put up more pics of the inside of the box if anyone is curious.

 

[swarfrat]

Couple questions:
1) Is the 10" the Volt extended Xmax version or the regular 10CX version?
2) If you don't mind - what were your box volume and tuning parameters for the 8 and the 10?

 

[mayfly]

Couple questions:
1) Is the 10" the Volt extended Xmax version or the regular 10CX version?

It's the regular version

2) If you don't mind - what were your box volume and tuning parameters for the 8 and the 10?

I'll have to get that to you later tonight.  My drawings are at home for the one I designed, and I'd have to measure the Fitzmaurice one.

 

[mayfly]

Here we go:

The "Trev" 8CX: 

H: 13.5", W: 9", D: 9".  Cab vol: 1093.5 cubic inches (internal)
Port dia: 3".  Port area = Pi r^2 = 7.06 "^2
Port depth: 4.352"
Total port vol: 30.76 cubic inches

The Simplex 10:
H: 15.5", W: 17", D: 12".  Cab vol: 3162 cubic inches (internal)
Ports:  4 x right angle triangles, 2.625" on a side.  Port area (each): 3.44"^2
Port depth: 8.5"
total port vol: 3.44 x 8.5 x 4: 117.14 cubic inches.

If you are planning to run these through some modeling software, I'm very curious to see the result!

 

[swarfrat]

Here's what I ran through WinISD Pro (free btw). Of course there are lots of possible alignments which have various tradeoffs. I went for more or less maximal flat but before it starts to hint at the extended bass shelf (a large box / low tuning that can work for some things, but it trades off a LOT of maximum SPL, and will distort sooner because excursion isn't controlled as tightly).

I elected to keep the box size the same in all cases, as it was close and it's much easier to change tuning than box size (build new box).  Tuning them a bit higher (shortening ports) actually increases the bass response a bit, flattens out the curve, and gains you a fair bit more volume before distortion.

 

[swarfrat]

Not to drag your thread further off topic, but I spent several nights crunching drivers. Trying to find the optimum bang for the buck and bang for the box. I'd almost resolved myself into needing a $200 traditional high power high performance woofer, when I found this Pyle. Yeah, I know, but it's only gotta do 35-200 Hz.

Anyway - http://www.parts-express.com/pyle-pdw15125-15-high-power-subwoofer--292-2522
It'll  do 118 db, -3db @ 35 Hz in a 6.5 ft^3 box tuned to 33 Hz, excursion limit is very close to the thermal limit (yay! No wasted specs), and it happens to match up nicely with the Beta 8CX - which, as I said earlier, will do about 120db if you cross over at 200 Hz or above. And it only cost $100 in singles. Yowza.

The Pyle @ 260 Watts crossed over at 200 Hz, the Beta 8CX @ 200W, dovetail perfectly @ 118db in a box that'll honestly do 35Hz and is actually sorta compact. Arena no, but I'd be happy playing @ 100db avg with that much headroom and solid whomp.  The sensitivity difference requires biamping though.  I think I now know what my next project is. Thanks Trevor! (And if you're looking for something that'll handle low/modest volume PA for the whole band - it sounds promising)

And oh yea, since it's based on the Beta8CX, if you don't crossover, and leave the sub at home, you still have a -3db @ 82 Hz, 113 db guitar monitor that's TINY.

 

[mayfly]

Very cool.  Please fill me in on the design of that sub when you get things going.

 

[swarfrat]

I left off the port changes - On that 8CX box you listed, shortening the 3" dia port to 2.75" will raise the tuning to 78 Hz, flatten the bass out to flat to 100 Hz, -3db @ 73 Hz, and get you about 2.5 db more headroom before farting out.

 

[mayfly]

I'm going to try that tomorrow.

 

[mayfly]

Update - Hey that made quite an improvement!  Comparing the two back to back they now have similar sounds in the low end!  The 8CX is quieter, but then again the driver is about 3db less efficient than the 10 incher.  That's the most noticeable difference.

I like it!

 

[swarfrat]

Similar improvements can be had on the 10, but I wasn't sure if your triangular ports were easily trimmed.

 

[mayfly]

Similar improvements can be had on the 10, but I wasn't sure if your triangular ports were easily trimmed.

Sadly they are not - not at all.  They are glued down with construction adhesive.  However - it's just a cab.  It can be made again.

 

[swarfrat]

In WinISD Pro, once you have your driver parameters entered, you can create a box, and drag the slider around to change box size and tuning on the fly.  As i mentioned previously, there are  ton of various alignments, many of which I don't pretend to understand the full implications of. Generally I shoot for maximal flatness without any hint of the extended bass shelf (because of the tradeoff in excursion - for hifi speakers at home where we won't be peeling paint off the walls, I might consider an EBS -but they tend to be big).

I have played around with in WinISD but not built some boxes where I allowed a significant bass hump in order to get the tuning up to increase the excursion limit. With the DSP models of iNUKEs, you can build equalization into the amp.

At any rate, a maximally flat but still convex (no EBS starting to happen) box for the 10CX that looks good in WinISD is:
2776 in^3, tuned to 60 Hz. (3" dia port, 2.9" long, or 4 triangular ports 2x2 and 2" long. This gives a -3db @ 60 Hz, the excursion limit for the 10CX is actually lower than the 8CX even though the xmax is higher, mainly because it goes a lot lower. It reaches the excursion limit at 112db @ 85 Hz with only 35W input power.

On the 10CX you can squeeze 6db more before the excursion limit to hit 118db, in a 2110 in^3 box tuned to 85 Hz (4 triangular 3x3 ports 3" long) but you'll have a 4.5db hump at 110 Hz. You can almost completely flatten that out with a parametric -4.5db @ 83 Hz and Q=0.5. That yields a box that's -3db @ 88 Hz (-5.5db @ 80 Hz), but with the aforementioned extra 6db volume before distortion.  It only takes about 60w to get there too. But as I've said - I've not built or tinkered with any such xmax optimized boxes.