Diy 2x15 cabinet build (the real deal)

Hey guys quick update

been busy partying ......so dont get to upset....
found strange bruises all over my body.... ooops lol

But been working too, on the 2x15 box and also wrapping up a 1x15 car sub for a friend. Not sure if anybody is interested in the sub box. I might do a thread on that. Used 2 slot ports for that, and guess what program i used to determine the port length:scowl:...but good news is it was only 5hz lower than i wanted.

Anyways update on the 2x15 i have cut the ports 2 times already. And also added more bracing to the front baffle rear baffle and side walls.

Let me tell yah it is a real pain in the ### to cut the port tubes already mounted. had to use remove a hack saw blade from the handle and just cut by hand.

first cut was at 6" raised the Fb from 29 to 32 hz

second cut was at 3.5" raised Fb from 32 to 35 hz

I would be happy with 40 to 44 hz...but
with damping its gonna get lowered 2 to 3hz

so i want to bring it up to at least 46 to 47hz
and then filled it should be at 44 to 45hz.

these things are going to end up being really short.
( to bad the resonant frequency of the 3015 is so high
if i was using k-140's or legend 158's in this thing it would be done with already
those both have a Fs around 30hz)

so hang in there been working on it, just dont have any fancy pictures or anything.

 

The difference between 2.4 and 3.2 cubic feet is a little more bass extension.

average fill is just a lined cabinet, im going a little more extreme
with the poly fill.



nothing wrong with 3/4 and yes you should brace it, at least the back wall
1/2 construction is to reduce weight, but yes even if there is no audible rattling and the cabinet does not shake
and move around with the extended amount of bracing you need. , Yes you can brace it and have no audible rattles and it wont dance across the floor, but is does for sure effect the Q of the cabinet, and there is still going to be 1 to 3dB of loses as ThisBass pointed out, pretty much non audible difference...but but it still would be 0ne louder.

I can tell there is losses with lightweight construction
hearing and feeling it right here in front of me
have a 1/2 lightweight box made of plywood, and a 3/4 mdf subwoofer box, with large amounts of braces, and a double layer 3/4 inch baffle, keep in mind MDF is very dense and heavy one sheet is almost 120 pounds.

i have done sweep tests with both of them, both are fine and do not rattle and dont have any nasty resonance.
but doing a sweep test with the sub box it has a very different sound and feeling the box with your hand its very very firm.
with the 1/2 box you can hear a difference and feel very slight cabinet resonance with just your hand. even the 3/4 mdf has a slight vibration
but you can definitely tell the difference. it has a very firm tight sound.

so 3/4 plywood will definitely give you a better box technically, and adding bracing will definitely improve cabinet Q but 1/2 construction saves so much weight. and the audible difference is very shallow. Keep in mind the example is for a proper braced 1/2 cabinet with no resonance or walking from vibration. im not going to argue such a box it is still a professional usable equipment. but 3/4 construction is still going to have way better cabinet Q, and again differences are hard to test and pretty much non audible.

I dont even have the back panel nailed or glued onto this thing and there is still no resonance or rattles
so all buttoned up 1/2 construction still works when braced well enough.

 

pretty much for the most part, i tack it in place with temp nails and then seal the outside and inside with tape.

will mentioned sealing it with something and i forgot to say i was already doing it.

cabinet Q was always a concern i have to say the whole thing is actually really embarrassing. makes it seem like the cab has inadequacy issue.

god forbid if a male gets inadequacy issue.

but thats the thing i could dial this thing in at 44hz and once I glue and seal the back everything is going to change or not.
50/50 chance right? little bit of Schrödinger's cat...lol

good thing is like i said earlier even without glue and just hanging there, there is no resonance or rattles. so its a pretty sturdy deal. i second guessed it and tested it before and after adding braces, and the Fb never changed.

 

yes i did, just to make sure they were all working.

and of course they were, i just second guessed it again because when i checked the numbers against win-isd it was behaving like there was only 2 ports not 4

when i plugged each one of them at a time it would change tune. plugging them would lower the tuning
and of course also confirmed they were all working. i figured they did there was no obstruction, it is all just errors from the program

 

Ok so a little update I have shortened the ports once again
to 1.5" or 38mm.

Fb was 40hz.

Re attached screen covers over ports and should have more impressive photos in a few hours.
Also installed some T nuts for attaching speaker



I cannot really shorten them anymore because of the way i mounted the port tubes, So 40hz it is.
(this cab wants to fight me, but secretly its saying...hey butt wipe you need to buy some K-140's because 40hz is just perfect for them)

I am sure Will and a few other might remember when we did some calculations of an old Acoustic Control 215. It did not have any port tubes it simply had 2 holes drilled in the baffle.

I thought it would be great for a diy cab to not even use port tubes and simply just have a simple opening.
I had no intention of incorporating that into this design but it looks like 4 x3" round ports in 3.2 cubic feet will actually yield a tune or Fb of 45hz, if you simply cut 4 x 3" (76mm) round openings symmetrical around the driver, and the actual depth
of the baffle will provide the correct tune. No tubes needed

So resonant frequency or (Fs) of most 15" pro audio drivers being 30hz to 45hz, It is completely possible for this design
to suit any of those drivers and be able to provide a BB4 alignment or close to a BB4.
Mainly just a simple enclosure providing 3.0 to 3.3 cubic feet of volume for good bass response
and small enough for good power handling, and matching Fb at Fs of driver or simply 3 to 5 hz above or below Fs

for 30 to 35hz, port length will range from 6.5"(165mm) to 3.5" (88mm)
well known drivers in this range are JBL K-140/ E-140/ 2226H
Legend CB158, , Celestion FTR15-4080F and Faital Pro 15PR400

for 40 to 45hz, port length will range from 2" (50mm) to .5" (12mm)
well known drivers in this range are Electro Voice EVM15L/B, Eminence 3015/3015LF , Celestion FTR15-3070C / TF1530
Peavey Black Widow 1502/1505

many others should squeeze in there, just wait for me to confirm this after a button this thing up and fully seal the back. Also should work out a possible correction factor for Win Isd. By plugging each port and recording data, then compare to modeled data.

 

Ok some more blah blah about damping material, and some modeled responses I have done for a single cavity in this enclosure.

Mainly the Effects of cone excursion, spl and impedance curves
of a unlined and lined and filled enclosure. Just for fun

Qa is the Q-value due to enclosure damping material.
unlined box will have a value of 100 to 80
moderate lined box 50 to 30
moderate filled box 20 to 15
and a heavy filled box 10 to 5

lower number showing more absorption

So I just changed Qa in winisd for my enclosure and since win-isd does not compensate Fb for Qa values, I simply slightly
lowered Fb for each model, which has been proved already in real world tests.

from what I read damping seems to improve midrange and tighten up the lowend, over filling will still tighten up lowend but can reduce overall presence of bass or simply just reduce it.

I was more interested on its effect of cone excursion, because when i did sweep test with a filled box, I noticed it was more difficult to detect Fb, it seems cone movement was increased around resonance, and frequencies above Fb seem to be less and very well controlled. Wanted to model this, to see if it matched my observation's from sweep tests of a lined and filled cabinet.

Lets take a look a cone excursion with unlined (100) to fully filled (5) Qa values with 200 watts of power being applied in all graphs



Effect might be more clear at both extremes shown only



So a medium to heavy fill will reduce cone excursion above Fb and will actually increase excursion at Fb, just as i observed with the sweep tests. I was interested to see the effect of Maximum Power handling also



^ seems to be a overall improvement on a med to heavy fill, at the most extreme almost 100 watts of power handling can be gained.
a more realistic number is closer to 30 to 40watts, which can compensate for my method of tuning so close to Fb which can lose 30 to 40 watts
I dont believe in gross amounts of high tune to gain power handling, the effect on the actual instrument reproduction is more important
and more clarity and accuracy will come from lower tuning, or simply using a driver with lower resonate frequency or (Fs)


V Now after reading a few threads about various peoples descriptions of the effects of bass response with a heavy to overfilled box. I had a
feeling all various descriptions could simply be summed up as.......Bass response can be reduced.
and that is really all it is....Lets take a look at the effects on Sound pressure level or SPL below 200hz



So with the age old concern of error factors of modelers, and the age old believe of 20% to 40% of additional " Virtual Volume"
that is believed to be gained by med to heavy fill of damping material. And also settling on my estimated Qa value of around 15 with roughly 20% of error compensation, which can be model error ...or virtual volume whatever you chose...I simply go for model error...that is easily proved from my resent experiences.
I have included a green bar showing most likely the effect on bass response.



you can agree or disagree with my compensation, but if you look at the extreme effects in the model on the impedance curve for a Qa of 5. I seriously doubt it will effect or flatten out the impedance curve that much. So most likely SPL losses shown for a Qa of 5 are unrealistic, and my 20% compensation green bar is a somewhat provable by a more realistic impedance curve shown in the model. Again win isd does not compensate for effects on Fb so i have included that correction as well. Which is just a basic drop of Fb by 2 to 3 Hz as measured in the real world with my basic test.



so you can now see some trade offs and benefits of a med to heavy filled reflex box, opposed to lined. Benefits including more cone control and power handling below 200hz , and of course mid range clarity
and the reduced effect of standing waves on midrange and upper harmonics above 200hz



and course last but not least, more mumbo jumbo about reducing distortion and inaccuracy of ports with non symmetrical waveforms by adding damping at the end of the port to reduce out of phase material exiting and standing waves from non symmetrical cycles. This model wont prove it but does shows reduced port velocity at Fb and at frequencies when cone movement starts to be restricted. Increasing my faith that damping material at the end of the port will reduce said distortion. And only slightly effect Qp which would only result in a impedance curve shift, effect on Fb is no different than typical Qa values which is lowering of Fb and impedance curve shift. Most likely also part of the reason losses in bass response from low Qa values or high damping it simple reduces port velocity, but the extra absorption will decrease standing waves and distortion found in the port

 

nothing exciting just wanted to seal the inside with paint, might help with moisture and what not. Seen this plastic dip rubber stuff in a can it was the same price as normal paint. so heck why not seal it up with that.




first coat, battery in camera went dead after second
but you get the point