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DIY GFRP Sandwich Panel 1x15PR400

#121
Don't know about the hum. That's a straight forward, one-speaker connection. Can try removing the parallel jumpers and see if it helps. It's happened to me before where an amps ground prong snapped off the plug end and was just stuck in the outlet. Stuff was always hooked up at my house and I didn't know it had happened until I went around checking stuff one day trying to track down some annoying microphone shocks.:p

As for the crooked baffle, I'd just make your grillcloth frame to match it. One side deeper than the other, top and bottom a bit wedge shaped, or whatever you need so when you put it on it looks straight. I'd rather do that than go about sanding or filling on the actual baffle.
 
#122
Thanks for the input Will.

As for the baffle problem, I'm using spacers/shims on the deeper side. Should work well because each long side is at a constant depth.

Speaking of, I'm still considering bolting the baffle on, mainly for looks. Otherwise have to cut out areas of the baffle carpet for velcro. With bolting though comes t-nuts at this point, and I had a scare last night trying to put them in for the speaker (non fatal, but did not go well...)

Hmm...
 
#123
Thinking velcro for expediency. Maybe do bolts later if I really want them.

Weight update: 11.0 lbs last night as a tolexed and carpeted box with only feet mounted. Unfortunately, I did not weigh before tolexing, which I'm bummed about because I was curious how much it added. But it couldn't be more than 1.5 lbs from the last weigh in. I was expecting more, so that's good news.
 
#125
Petebass said:
I can't believe I missed this thread. I just read through 7 pages and it seems like you're doing a great job! Subscribed.
Click to expand...

Now I got both godfathers of composite cabs looking on. :hyper: Welcome Pete.

Just finished the tuning. It came out to 35Hz. It's not the worst, just a bit shallower roll off, lower power and lower SPL. For now, I think I'll leave it, but maybe go back and just skip the straight tube, coupling the two port ends directly together. And that will be what it is! (probably +/- 40Hz). Wish there was a way to test volume. I'll add it to the to-do backburner list ;)

For anyone savvy to Matlab, this is my quick and dirty code:

Fs = 1000; %# Samples per second (must be higher than tone freq)
for toneFreq = 30:50; %# Tone frequency, in Hertz
nSeconds = 60; %# Duration of the sound
y = sin(linspace(0, nSeconds*toneFreq*2*pi, round(nSeconds*Fs)));
sound(y, Fs);
toneF %# Prints frequency
end
Click to expand...

And then you just wait till you hear the rice stop rattling.

BTW, 30Hz is nuts. Fun to hear raw frequencies. :D My ears are sore even at VERY low levels. (Sorry neighbors!)

Edit: Just tried this: Went to the PP calculator, inputed my knowns and played with volume until I got 6" for the flared tube length. The calc says my box is effectively 4.3 cf -- that's 1.2 cf larger that my goal volume! Any ideas?
 
#126
On the logic that you can't change it, it wouldn't focus on the internal volume now the cab is built. I would instead be focusing on the port tuning because it not too hard to measure, adjust, repeat as necessary until you end up where you want it.

And FWIW, I've never treated cab volume as anything more complicated than using a tape measure, subtracting for area taken up by ports, speaker etc. Anything more than that is probably just over-thinking it :)

Oh and while I remember, you mentioned several pages back about the possibility of using drywall anchors but can't find any at the correct length. The ones I used were plastic and I was able to easily cut them down to size with one grap of my wire snippers. I may evey have pics somewhere. Let me know if you'd like to dig them up.
 
#127
Cool, thanks for the input Pete. Really appreciate it.

My problem with drywall anchors is there's a lip on them and don't fit flush. I actually found some "plug anchors" yesterday, but testing today (on scrap!) showed they won't grip. These will be for the corners. Hmm, I could also try cutting out a matching circle of tolex, might get it close...

In other news, THE CAB MADE IT TO THE GIG. Sound check shortly. I'm probably crazy having never played through it before, much less with the band. Worst case it's like a random backline. Didn't get the handle or corners on yet, so I'm babying it to the max. It'll be out of the club the minute we're done.

Note to self: order that cover already.

Gig review, pics and the last of the processes/how-to stuff to follow!
 
#129
Come on man! Have some faith! I'll finish it out this weekend and then I'll show proof.

At the show it sounded great! I was really surprised how well it kept up. At sound check all 3 guitars were too hot at first and I had no issue of being washed out. I think some of it has to do with the "slotting" effect of a 50Hz-5kHz response. Off axis wasn't too bad, even compared to the Baer ML's, IMHO. At least I didn't feel like I was missing a whole lot. At the end of the set I could tell I was reaching it's limits, but I think that's just the place to be. Also, the sensitivity is right on par with a pair of the ML's, although the ML's will take more power and at 4 ohms work at the full 500W. That said, I don't think I'd consider upgrading to a 4 ohm Faital unless I had an SVT or the like that wanted it. Otherwise, I think having a pair of these Faital loaded cabs would DESTROY beyond anything I ever need.

Like I said, didn't have a handle, but being +/- 20 lbs (final weight to come) I loaded it onto and off the stage holding it over my head to show off. Boy did I feel awesome. :hyper:

Oh, and as usual for the places we play, sound guy mic'd my cab. I'm feeling more and more these days that having a full range cab makes a lot of sense for this reason alone. YMMV if you get DI'd everywhere. Funny story: He looked at the cab and was confused as to where the speaker was. I pointed him to the top and he said, "Ah, OK. You know it makes a lot of sense for the designer to have a bigger box for a bass cab." "Oh, really??" says I. :D

One happy camper today.
 
#130
astack said:
Come on man! Have some faith! I'll finish it out this weekend and then I'll show proof.

At the show it sounded great! I was really surprised how well it kept up. At sound check all 3 guitars were too hot at first and I had no issue of being washed out. I think some of it has to do with the "slotting" effect of a 50Hz-5kHz response. Off axis wasn't too bad, even compared to the Baer ML's, IMHO. At least I didn't feel like I was missing a whole lot. At the end of the set I could tell I was reaching it's limits, but I think that's just the place to be. Also, the sensitivity is right on par with a pair of the ML's, although the ML's will take more power and at 4 ohms work at the full 500W. That said, I don't think I'd consider upgrading to a 4 ohm Faital unless I had an SVT or the like that wanted it. Otherwise, I think having a pair of these Faital loaded cabs would DESTROY beyond anything I ever need.

Like I said, didn't have a handle, but being +/- 20 lbs (final weight to come) I loaded it onto and off the stage holding it over my head to show off. Boy did I feel awesome. :hyper:

Oh, and as usual for the places we play, sound guy mic'd my cab. I'm feeling more and more these days that having a full range cab makes a lot of sense for this reason alone. YMMV if you get DI'd everywhere. Funny story: He looked at the cab and was confused as to where the speaker was. I pointed him to the top and he said, "Ah, OK. You know it makes a lot of sense for the designer to have a bigger box for a bass cab." "Oh, really??" says I. :D

One happy camper today.
Click to expand...

LOL- You know I just had to yank Your chain a bit on the pics thing. :)
Very cool Glad You like the cab/ speaker combo. As I have said before, and will say again. IMO-The Faital 15PR400 is one of the best sounding full range 15's I have ever heard.
 
#131
@OP: I've heard of some people using Styrofoam blocks to reduce internal volume. Shouldn't be to difficult to calculate considering its squarish. Just gonna want to secure it VERY well so you don't have to worry about vibrations.
Cant wait to see the cab though, you know how we like pic around here....
 
#134
astack said:
BoxDimsCalc.gif


Gray boxes are inputs, yellow are outputs/important.
Click to expand...
Like this one, Pete? :p

I updated values with the "as-built" dimensions and was still off. The gross volume is smaller even. Starting to think that it might just be that with such a short tube length (basically none) the equation's assumed end corrections break down. Again, 35Hz tuning isn't bad, probably a tad safer.

Another idea for the corners: Go old school Marshall style with rivets?
 
#135
astack said:
Another idea for the corners: Go old school Marshall style with rivets?
Click to expand...

Rivits work, but you'll need to back standard rivets. Either extra glass or fender washers or tinnerman washers. If not I've had them pull through the inside layer of glass. There are special rivets made just for composite construction too. I've been bonding corners in place. Epoxy adhesive on properly prepared surfaces and they will stay put. I've only don't this with plastic corners though.
 
#136
You have plenty of leeway in this system, you can pretty much do it by ear from here on out. You're well within the "safe" range for the driver. Yeah, styrofoam will shrink the box in trade for some low freq. extension with no weight penalty. Whether or not you need all the reach into the bass end is your call. Raising the tuning will put some fullness into the lows if you do shrink it some. Plenty of leeway there too, don't really have to worry about unloading until you get north of 50hz or so. You're so meticulous, you'll do a fine mod job, whatever you decide to do, I'd just let your ears take you in for a nice landing.

Nice work.
 
#140
In the end for bracing I decided to go with just two "fins" on the front and back. I epoxied those in the same way I did the sides of the box. Epoxy/micro/silica and the ends and then filleted the sides. Doing the tap test tells me they're doing something.

Here they are:
DSC01131.gif


And the final round of fairing and sanding (2-3 times):
DSC01133.gif


With that, I was done with fiberglass and epoxy. One last thing before moving on. Last time I was in the fiberglass specialty store, I found these gems for a quarter each:
DSC01132.gif


Turning the bottle into a ketchup bottle made weigh out MUCH easier. Best 50¢ I spent on this project.
 

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