Building a 2x12 cabinet that sounds even across the sound spectrum...

[Slobrain]

Well I have a Marshall 2x12 model 1936 that's loaded with the 75 watters and then I have my old home built 2x12 cab that is similar to the bandmaster 2x12 small cabs that sounds different. I have already replaced the back panel on the home built cab with a 1/2 inch MDF board to reduce the boominess and added the brace from the front panel to the back panel like Marshall does on their 2x12s and 4x12 but this home made cab still has a slight boominess that I cant dial out. after looking at the older fender cabinets and the Marshall 2x12 I own I notice the front and back panels are made with MDF.

The Marshall 2x12 top, bottom and sides are plywood and the home made 2x12 I built is made out of solid pine for the top, bottom and sides, the front is 3/4 cabinet grade ply. I now wonder if I should replace the front panel with MDF and see if that changes the low and on the home made cab to make it more like the Marshall?

I've heard others complain on the Avatar 2x12 cabs having some boominess to them. I even stuffed my homebrew 2x12 with insulation but that still didn't change the low end very much... So I have to ask is there something missing in building a good 2x12 that will have a smooth sound all around?

I sure hate to have to rebuild a new cab but I wonder if this home made one can ever be made to sound as good as the Marshall 2x12 I own? Both Marshall and my home made cab use the celestion 75 watters.

[Chuck H]

You could try detuning it with a port. There are a lot of calculators on line. The vent would basically change the resonance of the cabinet. When some resonant frequency is correspondent between the cabinet and speaker you can get woofy notes. A tuned port is designed to even out the LF for a given cabinet and speaker pairing.

[Slobrain]

You could try detuning it with a port. There are a lot of calculators on line. The vent would basically change the resonance of the cabinet. When some resonant frequency is correspondent between the cabinet and speaker you can get woofy notes. A tuned port is designed to even out the LF for a given cabinet and speaker pairing.

Thanks for the info Chuck, That may work. I'm still debating on trying to replace the baffle with MDF first to see if that will deaden down the resonant lows. I think Fender had to do that in their cabs as I have seen the old fender cabs with pine top, bottom and sides but MDF for front and back. I assume that they would have used plywood for the front and back but that was probably too boomy maybe???

I had thought about getting a Avatar 2x12 but I have read in a few places that their cabs are a bit boomy too. The Marshall model 1936 I have doesn't have that issue. Its a nice sounding cab.

Slo

[Chuck H]

I assumed this was a closed back cabinet. And I'm still getting that impression. If so you could try pulling the screws and just open the back a crack to see if that makes any difference you would consider improvement. If it does you could slice and peel back any covering material in an area and take a hole saw to the rear baffle. Then paint the hole edge the right color and try to re-lam the covering around and inside the hole.

[Slobrain]

Hey Chuck,

It was originally a closed back, then I took the back panel and cut a 3 inch port across the back and made it a open back. I didn't like the sound of the open back so I made a new 1/2 inch MDF back panel and added the front panel to back panel brace like Marshall does. For the most part it sounds a lot better but I think either because the top, bottom and sides are pine that's why this cab has the low with a bit off boominess, maybe too because the front panel is 3/4 furniture grade ply.
My Marshall 2x12 has MDF front and back panels with a internal brace between the two. It has a much better evenness to all the sound.

[defaced]

I'm far from a speaker cab builder, but I noticed something about a cab I recently bought that may help you. I have had alot of probelms with boomy cabs. I'd always assumed it was the speaker, but I recently bought a used VHT (now Fryette Amps) Fatbottom cab, and this cab is very tight. One thing I noted is that the front baffle has a slight angle to it. It tilts back at the top by about 2" on a 4x12 cab. It appears to me that this might have been done to keep the front and back panels from sympathetically vibrating at low frequencies. The back panel is MDF, sides are birch plywood, not sure about the face, and it is a completely sealed cab.

[Chuck H]

When de-tuning, port size and depth are critical to even out the resonant frequencies. I did find an on line calculator that I liked but I can't remember which one it was. It was a while ago and I don't have the site saved. I remember there were parameters for enclosure depth/height, speaker resonant peak, etc. It's typically a car audio thing but that doesn't matter. The point is still to even out the LF. I'm a closed back kind of guy myself but I've been super impressed by some of the port tuned 1x12's I've tried.

[GregS]

Boominess is caused by the cabinet flexing and resonating with standing waves to my knowledge. The more solidly built the cabinet is the less this should be an issue. The solid pine you used may be more prone to flexing than plywood. Also, you didn't mention the thickness of the pine. If it is too thin and not sufficiently re-inforced with internal bracing that might be a problem.

I've built numerous guitar cabinets both open and closed back and bass cabinets and have never had this problem. I use 3/4" plywood for all the panels and 2 x 2 bracing for corner re-inforcement and for attaching the front and rear panels. This is probably overkill but makes the panels extremely rigid.

So as long as the cabinet is large enough for the speakers and is built solidly enough there shouldn't be a problem with the sound. Maybe if you were to re-inforce your top, bottom and side panels with some bracing it might fix the problem.

Hope this helps,
Greg

[eschertron]

+1 to what both Greg S and to Chuck H said. The volumetric space will have a resonant frequency, and porting can change that peak. The elastic motion of the enclosure adds it's own sympathetic resonance, and making the enclosure more rigid will affect that. I'm not sure how much the two modalities overlap, so treating one may not have much impact on a resonance generated by the other.

If the cab under discussion is 'pretty close' in size to an existing cab, the latter (flexing) might be more responsible for the artifacts. IMHO I'd be tempted to try bracing as a first response, because there's less math involved and I simply don't have the engineering knowledge to say whether porting will interact with the flexing. It may not do as much as predicted if the modalities don't overlap very much, and can't hurt... anything other than your back!

[NateS]

Boominess probably has more to do with Qtc - your speaker is going to need a beeeger box. I know that guitar cabinets have goals that differ vastly from HiFi, but the same physics still govern them. I'm perpetually amazed that guitar players will stuff speakers with wildly different Vas in the same box, then declare speaker XYZ sucks and PQR rocks. XYZ might have just needed an undersized cabinet for some midbass boost, or maybe it was in too small a cabinet.

[booj]

I'm working with about a 64 Bandmaster cab. The (replaced) mounting board is 1/2" plywood. The original middle partition has been replaced by a 1 x 6 going side to side in the middle and a 2 x 2 pole piece against the center of the mounting board and the edge of the 1 x 6. I've made two port holes in the mounting board which are 2" holes about centered between the edge of the speaker and the right corner or middle. It's loaded with a JBL D120F and an Altec Lansing 417 12", both 8 ohms. Whew.....
The cab sounds good down to low E for my Precision bass. It has a good usable volume level. I Use a Modified Bandmaster amp, wired like a Blonde Bassman, but with 85 watts. that's a different project but the pair go together very well. Anyway
Yes it's boomy sounding, so I'm having the same problem you are having. the porting supplied the low end and in this case the pole piece made a big difference in how tight the sound was. I'm thinking of some batting material but don't want to use fiberglass because of the ports. What are you using for batting material?