PLYWOOD 1/2" or 3/4" FOR CABINET

[TequilaCaster]

I build all my 1x and 2x speaker cabinets out of 1/2" Aurauco ply, using simple butt joints and PE (gorilla) glue, no bracing required as the corners are strong, with 1/8" round-over routing on all cabinet edges for a nice finished look. I use corner clamps when gluing to keep things square, adding on one panel at a time. Polyeurethane glue dries quickly, and I remove the clamps after 2 hours, and add the next panel. I build the box first, then cut the speaker holes and jack panel holes. For open back cabinets (which I prefer), I calculate the total area of the openings in the speaker basket(s), and then cut the same size opening (or 5-10% larger) in the back panel. I use a 1/4" router bit and a simple circle router jig, so all the opening are circles, and it is super easy to do because all the surfaces are planes, with no obstructions. For grilles, easiest is an oversized round metal grille (for 10" speakers I use 12", 12" speakers get 15" grilles) screwed to the box.

I like 2 cubic feet minimum for each 12" speaker, 1.5 cubic feet minimum for each 10" speaker. For a 6.5" speaker I would go minimum 1 cubic foot per driver. I would use thicker ply for a 4x cabinet though.

 

[telepraise]

I believe my Fender combos are 5/8" plywood. I would think 1/2" would be fine for your smaller speakers. I like to glue/nail some corner blocking in to make sure speaker vibrations to weaken the joints over time (probably unnecessary).

 

[AriajazzJulio]

I don't know much about speaker cabs, but what I have read is that speaker enclosures should not be too symmetrical. I would compromise at something like 12"x10"x8" for each enclosure. And don't forget to figure the dimensional space the divider and insulation will remove. I think I would lean toward a firm insulation on each side of the divider. Or better yet, two thinner dividers separated by sound insulation material to better isolate the chambers.

One advantage of the 15" width dimension for each speaker is additional separation. You could also investigate not centering the speaker in the chamber but shifting it to the outside to increase separation even more. Perhaps move the speakers closer to the edge and put the ports toward the center.

I do agree with you, as an audio engineer I know about that symmetrical aspect. Listening and studio control rooms are built, as possible, not symmetrical and even with not parallel surfaces facing each other to avoid boosts of frequencies and phase cancelations. This makes me think it applies for speaker cabinets too. I probably will go with 12x10x8 inch idea you suggest. Stereo image and separation is already planned by a 1/3· panel in between speakers and also they are both angled outwards by 5 degree angle.

There are some other design changes in consideration. According to speaker specs (Qts=0.966 which is pretty high) they seem to be better suited for open back cabinets and/or infinite applications. So I'm taking in consideration to built a semi open back cabinet, maybe with an opening of jus a couple of inches to have the best of both worlds, sealed and open back. This could provide a more open sound that is better suited for small venue gigs which is what the amp is intended for.

Still thinking about using some insulation material but in the case of the semi open back I don't know about its benefits. Placing an air chamber in between both speakers is not a bad idea, it is done all the time in studio designing. For a cabinet construction I think it complicates things.

 

[Boreas]

I do agree with you, as an audio engineer I know about that symetrical aspect. Listening and studio control rooms are built, as possible, not symetrical and even with not parallel surfaces facing each other to avoid boosts of frequencies and phase cancelations. This makes me think it applies for speaker cabinets too. I probably will go with 12x10x8 inch idea you suggest. Stereo image and separation is already planned by a 1/3· panel in between speakers and also they are both angled outwards by 5 degree angle.

There are some other design changes in consideration. According to speaker specs (Qts=0.966 which is pretty high) they seem to be better suited for open back cabinets and/or infinite applications. So I'm taking in consideration to built a semi open back cabinet, maybe with an opening of jus a couple of inches to have the best of both worlds, sealed and open back. This could provide a more open sound that is better suited for small venue gigs which is what the amp is intended for.

Still thinking about using some insulation material but in the case of the semi open back I don't know about its benefits. Placing an air chamber in between both speakers is not a bad idea, it is done all the time in studio designing. For a cabinet construction I think it complicates things.

Would there be any benefit of porting it out the sides instead of a semi-open back? Wouldn't opening the back start cancelling your stereo separation?

 

[AriajazzJulio]

Would there be any benefit of porting it out the sides instead of a semi-open back? Wouldn't opening the back start cancelling your stereo separation?

Good question... Acoustics is a complex science, unless you are really an expert you never know what to expect. There are so many variables, even something as simple as cabinet placement in a room makes a big difference, it is almost a try and error thing.

The idea of a semi open back is to have an airy sound and let the speaker breathe a little. Phase cancelation at the back can occur but I do think most of the sound will come from the front of the cabinet and considering the angled factor of the speakers stereo image can be preserve. I forgot to tell that the circuitry of the amp includes a stereo field control (spread) that widens and narrows the stereo image.

 

[Boreas]

Good question... Acoustics is a complex science, unless you are really an expert you never know what to expect. There are so many variables, even something as simple as cabinet placement in a room makes a big difference, it is almost a try and error thing.

The idea of a semi open back is to have an airy sound and let the speaker breathe a little. Phase cancelation at the back can occur but I do think most of the sound will come from the front of the cabinet and considering the angled factor of the speakers stereo image can be preserve. I forgot to tell that the circuitry of the amp includes a stereo field control (spread) that widens and narrows the stereo image.

That field control should help take care of any mud behind the cabinet. As you know, keeping it off the floor should help as well.

Let us know how it turns out - and we always like in-progress pix!!

 

[AriajazzJulio]

Sure, project is still in plans but I'll be taking and posting pictures of the construction progress

 

[AriajazzJulio]

Hi again guys. I attach a preliminary plan for the front of the amp (not finished yet, some details pendant for minor changes). Still don't know if I'm going to port the cab, probably not.

 

[LightningPhil]

Small speakers in little cabinets sounds fun. Have tinkered with this approach too and even had some custom drivers from Eminence when I considered taking it to production.

The resonance and dampening are both a bit high with your chosen drivers, and squishing them into a smaller box than suggested will raise both. The net result will likely be a peak in output a little over 100 Hz. This could make G or A on the low string seem much louder than E.

To counter this, the stiff paper souround can be carefully cut off and replaced with foam. Very likely this would drop the free air resonance down below 60 Hz. It also increases the VAS. But, still, in any given enclosure, the resonance would be lower and electrical dampening improved (Qes). Dampening and evveciency can also be improved marginally by sticking a backing magnet on the motor. Done right, this can give a pleasing and progressive response.

More to come, need coffee.

 

[telemnemonics]

3/4" is only standard for Fender solid pine cabs.
All the Marshall stacks 4x12 cabs are 9/16" plywood.
For a little cab like this I'd choose 1/4" or 5/16" for the baffle, and if using baltic birch even the 1/2" sides is massive.
Stiff baffle tone is stiff, flexible is warmer.
Something like the Tweed Bassman baffle was I believe 1/4" for 4x10 speakers.
All the BF amps up to the Twin reverb had 1/2" baffle boards, of weak particle board.

 

[LightningPhil]

Coffee achieved.

Suggest downloading a copy of UniBox and experimenting with box volumes to see what the response may look like (you'll need to enter Qts as 13 as that's missing from the driver spec).

UniBox - Unified Box Model for Loudspeaker Design

audio.claub.net

You'll soon see that venting, or porting it will result in a significant (probably 6 to 8 dB) hump in bass response with your chosen enclosure volume of 800 cubic inches. Note the spreadsheet is in metric. With a sealed enclosure with moderate filling, the resonance hump would be reduced to 3 dB. Much better, so would lean that way.

Increasing the box size for a sealed enclosure doesn't seem to have an overly wonderous effect in lowering output until the box would be unmanageably huge.

Here's a plot of the driver's expected response in an 800 ci enclosure. Stock driver in sealed case (purple), stock driver with ported case with port tuned to 100 Hz (red), and prediction of meddled with driver (black).

Regarding wood. Yeah, 1/2 inch, which seems to be 11 mm here, would be great for the whole build. Accurate cuts, building up the interior of the joints with triangular or square section bits of wood and use of good wood glue would make a nice job of it. And if the interior bracing is done well (as in pretty much a complete internal frame), the corners can be rounded over without weakening the joints much.

Would suggest a progressive approach, building the enclosure with a removable back. That way you can try open vs closed. Easier to wire and add fluff too. Suggest avoiding insulation material as the glass or rock fibres can upset speakers and be atomised by their movement. Wool or polyester is good. At a pinch, the stuffing from a medium-density pillow would work very well.

Then, if you feel like meddling with the drivers, first slap on a backing magnet to improve dampening, pulling down the hum slightly and increasing the higher end sensitivity also slightly. Before getting carried away (probably don't do this) and replacing the paper surround with foam to lower the resonance and thus overall response curve.

Another option is to use a Linkwitz circuit to emulate any bass response (without blowing the drivers) that you desire. It would be an additional inline equalizer before a power amp stage and after all other equalisation and distortion:

\"Linkwitz Circuit\" Equalizes a Closed B | Maxim Integrated

By introducing zeroes to compensate the poles of a low-frequency loudspeaker, this circuit creates a non-peaked, 2nd-order highpass response as specified by the designer. The resulting low-frequency boost is about 15dB.

www.maximintegrated.com

 

[AriajazzJulio]

Ok guys the thread continues. The information from LightningPhil is very detailed and expertised and adds some more tips to the project. I don't think I'm going to go with the surgery of the stiff paper and/or the magnet addition since it complicates more the developement of the project, which is already complex. I will stick with the original design of the driver. As seen in the chart you provided, foam and magnet technique flattens out the bottom end around 150 - 250 Hz. That boost in original design of the diver is probably why LightningPhill says small drivers sound "fun", I really have to experiment and test, any way, unpleasant tones can be corrected with EQ.

About the wood used is in fact 15 mm thick plywood, wkich is a little bit less than 5/8". I also decided after reading a lot to go for an hybrid design (suggested by LightningPhil too) of a open/closed back with a removable back. In this case it will be a dettachable panel of a 1/3 of the back surface of the cab, as seen in many proven open back amps in the market. This makes it a semi-open back cab.

I definitely will download and use Unibox for tuning up the enclosure dimensions. It come to my mind that I could record and shape a nice guitar tone in my DAW, look at its freq curve with an spectrum analizer and approach it with the cab size adjustment.

Thank you very much to all you guys. This is a great forum with great and serious people. I'll be posting more plans and pix of the project developement.

 

[AriajazzJulio]

Enclosure in progress...