Question for MadMike

OK Bro, I just got off the phone with Carvin, and the guy (who wasn't in tech support, as they had closed already, but he worked in sales and knew about the PS15's) told me after I related my tale about my amp cutting out that he agreed with your assessment of needing to have ports in the cabinet. He said that the burnt Band-Aid smell was probably from the lacquer that seals the voice coils getting too hot, but that since the speakers continued to work, all hope wasn't lost. He then went on to stress the importance of putting a speaker into a cabinet that it was designed for, and chances are the SA cabinet is too small to handle what the Carvin's need in terms of cabinet volume.

So since you seem to know about these sorts of things, I was wondering if I could ask (or beg) you to calculate what size 2x15 cabinet would work with the Carvins. Here is the link to the specs, and it would be for the PS15's:

http://www.carvinguitars.com/manuals/tsp.html

The SA cabinet has an outside measurement of 36" wide, 18" tall, and 14" deep. The wood is 5/8" thick. I tired to find a program online to calculate it myself, but I couldn't make heads or tails of anything I found. I think this is squarely in your arena of knowledge.

I'm now wondering if the SA cabinet isn't large enough to handle the Carvins. And if I fried them, it becomes my fault for not putting them into the proper size cabinet. I tell you, after almost 30 years of playing, I had NO clue such a thing would be a factor. You learn something new every day.

So MadMike, I concede to your knowledge and opinion, and I now believe that you were spot in in that the amp was simply cutting out to protect itself since it detected the impedance changes in the Carvins as they became too hot. My only concession is that if I do need to pay to replace the Carvins, they are really affordable.

Can you help, Bro?

No problem bro.

It seems to me that most speaker cabinet manufacturers make lower wattage cabinets more available. They are cheaper and most ameture musicians can get away with 200 to 400 watts. Pros go for the lower watts for tone, not needing volume with a great di out and soundman.

I just wanna be loud too, but a mesa powerhouse cabinet is $1200 to $1400. I know ... I can't afford that either.

Ill do 2 designs tomorrow.

A practical solution for ports in your SA 215. (So you can use it for now and not cook your coils)

Designs for a cabinet more along the lines for what you need. That seismic just isn't deep enough (thus the funny numbers I got for calculating the ports). Ill show you how to build it, how I built mine, how I came up with the specs, etc. If you do research and find cheap parts, it could cost under$ 100.

Im just gonna assume you don't want a sunn reflex design ... its huge! So ill start with the same design format I used ... markbass 215.

Lemme go find one ....

yes ... this is a discontinued cab. again ... with the smaller more marketable cabs.

http://217.64.194.186/products.php?lingua=en&cat=2&vedi=28

another angle of it .......



and mine .........



this cabinet has (2) peavey black widows in it. 300W each / 8 ohms each ... for a cab that is 600W @ 4ohms. i believe the carvins you have are close to the specs of the peaveys i got .... so the design will be similar.

the seismic cabinet is the only 2x15 cab i've seen thats smaller. is this too big for you?

chek out the two 4" ports on either side of the speaker (dont tell anyone ... they are trader joe's cardboard coffee cans!) 15" bass speakers have deep voice coils and need to be able to move with minimal resistance thru their range of motion. too much +- pressure, they are restricted ... not enuff ... the cones get floppy and farty (i forget the proper term ... but you get it ... right?). this, and the cabinet frequency is what we're shooting for.

and you said you looked at speaker cabinet design software. i know ... a lot of it is confusing. since we're not re - inventing the wheel here, you'll need this ............

http://www.linearteam.dk/default.aspx?pageid=winisd

i see there are much updated versions (even since last year) but this is the one i use ... so download this one so we're comparing apples with apples and oranges with those other round things. i'll download the new software and learn to use it later ... maybe its better ... maybe it just looks nicer.

i'll send you some calculations and designs tomorrow.

and ooh ... we should do everything on the board here so the info is available to everyone; if you dont object.

And no ... I don't think you fried the carvins. You keep playing them that way you will. I played my ne10's with that burnt bandaid smell for 3 or 4 weeks when I had that crossover problem. Still using them ... sans bandaid smell for 4 or 5 months now.

Let's get you to some solutions ASAP.

Thanks, Bro! I really appreciate the help, and I think the cabinet design you come up with will be perfect.

No, the size of the cabinet isn't too large. Honestly, it was never the size of the SA cabinet that meant that much to me. It was all about the cost. But if I can build one like yours for under $100, that would totally rock! And again, no, I don't mind in the least posting all the information here. Like you said, it would be for the benefit of All, so post away.

was just trying the WIN ISD pro. didnt even get past the "enter your own drivers" part. i think its just too parameter specific and it wont let you save the driver if its not perfect. i understand ... they want their software to work perfect ... but i'm a bassist, not a scientist.

ok, first thing is first.

i recalculated with the data i input for the carvin ps15's, the SA 215 cabinet size, the ply thickness and the Fs.

again ..........

the software recommends, for a vent mach of .13, there needs to be 2 ports, 4" diameter. it doesnt give length so i double cheked on another calculator. make the vents 2" long.

this seems a bit much to me ... just because its a small cabinet. the other calculations i did gave the same results with the much bigger markbass design. with such a big cabinet ... that seems to make sense to me ... but there is no logic of physics why the cabinet size would effect the internal pressure and its response to a bigger or smaller vent. pressure is pressure and the difference between and inch of vent and the volume of a cabinet +- one foot is minuscule if any at all.

but just to not kill your SA cabinet (because once wood is removed, it cant magically be replaced), start with (2) 3" diameter ports with a depth of 2".

if you just cut 3" holes for now ... ittl have the same effect. running around, looking for 3" cylinders that are perfect takes some time sometimes. dont not cut the holes and play thru the cab (and kill your speakers or amp) because you dont have the cylinders.

now, this will definitely relieve some pressure off your cones as the voice coils are trying to move. your voice coils will defiantly move more efficiently now.

the way you'll know that 3" diameter ports are too small is that you'll exceed the vent mach. in a perfect world, you'll want a vent mach of .1 ... and you cant always get it. the 4" diameter port readings give a vent mach of .13. the 3" ports give you a vent mach of .19.

how will you know you've exceeded the vent mach?

youll hear the air whistling thru the ports. i've never heard it, because i think i've always gotten close enuff. i've even had cabs with 2 ports and floppy speakers and plugged one of the ports up and not gotten it. i understand those who have say its very annoying ... so i guess you'll know.

if you cut (2) 3" holes in your cabinet, this should relieve the pressure. if your vent mach is too high and you hear whistling ... open them up to 3.5" or 4". then go find the appropriate diameter cylinders, cut them to 2" length and seal them in the openings ... screws, tacks, staples, whatever; as long as they are secure and seal them up with silicone or liquid nails (from the inside).

appropriate (?) tools for the job ........

hole saw - you know ... that doodad that has a drill bit in the center with saw looking circles at different diameters going out. these are expensive for what they are and i dont know if you can get one at 3"

dremel with a rout bit - if a hole saw will only get you to 2 1/4 ... open it the rest of the way by hand with this. those sanding wheels make it end up with a nice finished edge. you could always get the platform and rout it out. (this is what i do).

hand scroll saw or a jigsaw - if you feel like sweating a bit ... i've done it. draw the 3" circle on the spot. drill a big hole to start inside the circle. work your way to the edge and start spinning around like curly. woobwoobwoob.

router - some come with circular jigs. i wouldnt buy one just to cut 2 holes. make a template out of cheap thin ply or plastic. this is the best way to go.

cut the carpet (felt) away where the hole is gonna be. thatll just mess up any cut you try to make.

this shud get you there ... for now. depending on the results will determine whether or not your willing to start cutting 3/4" birch plywood. i'll design it for you either way tho so you can see it.

i'll get to work on that markbass design in the morning. i entered all the specs in win isd already ... i just gotta make you a blueprint.

then we'll start finding you some materials.

Cool deal, Bro. Thanks!

I wish I could afford to have you build me the thing!

No sweat bro. Im figuring out all the hard parts and designing everything so if you measure and cut everything correctly and follow my directions, you'll be suprised how easy it is to put together. It is just a box you know.

Do you have access to the necessary tools? Access to a table saw will make your life a lot easier. Square. Good measuring tools. Router for cutting speaker holes. A good drill / screwgun. Stripped / crimper for fastons.

And the only thing I wasn't able to find for my cab ... extrusions for the edges. I didn't tolex, felt or carpet mine so the bare wood edges needed to be covered. Extrusion, plastic or metal, was expensive ... so I used black rubber recycled into garden hose.

Gotcha, Bro. Yeah, Andy has all of the aforementioned tools, and I think he'd let me borrow his shop. Heck, he'd probably do the entire build for me! And even if it isn't convenient for him, I have access to all of those things at my work.

I'm still hoping that I can make the SA cabinet work, since that would be the easiest thing.

One day, I'm going to go all Marshall!

why i build this stuff. and why i use carvin. built in the usa ... so is mesa. i dont know where marshall is havin their stuff built now.

anyhow ..............

i am definitely not an engineer working for NASA. they would laugh at my blueprint designs. since i have more colors ... and to scale ... i tried to utilize that in my drawings so, as much as possible, i wouldn't have to spec out, explode view and most stuff just be self explanatory.

so it all makes sense in my mind (remember ... its just a box). that doesn't mean my drawings will make sense to you or anyone else. if you embark on this endeavor and you have questions ... please ask them before you start wasting innocent plywood. i will be happy to help you in any way i can. doing this all out of my head and scribbling numbers on my workbench, i only needed to re-cut one piece of ply (again ... its just a box). i hope that everyone will need to re-cut none and have this built in 2 days.

and in order for this to work ... please have the right tools for the job and cut everything square. if its assembled out of whack and gappin ... i guarantee that it will leak air, whistle and buzz.

i recommend all plywood used be 3/4" (actual .71") birch ply.
i used 1" drywall screws with a medium screw pitch to fasten all boards to the 4" reinforcements, 2 each, 2.75" apart.
i used liquid nails to seal every wood to wood seam on the inside of the cabinet.
i also used .5" acoustic block PSA (like a sticker) foam as well as eco household insulation on the inside of the cabinet (theres a lot of space for sound to bounce around in there).
the ports are 4" diameter X 3" length.
this cabinet is tuned to 40Hz. its vol is 22.255 ft3.
the finished cabinet dimensions should be 35"H x 25"W x 22"D (with the speaker baffle @ 18").

here it goes ......................................









lemme know what you think ..............

I think it's awesome, and you've really outdone yourself on doing this design, Bro. Thank you! I've copied all of the information and images, and when I can get some time out of Andy, we will try it out.

Kewl. Glad you like it. It wasn't really outdoing or overdoing it. Its the same basic design I used. I just had to incorporate solutions for the mistakes I made (and im sure you will have a few of your own), recalculate the dimensions to work with your speakers, and draw up the design.

Monday, ill post a list of places to get decent cheap parts you'll need ... grille, corners, casters, etc.