Folded bass horn
Well, there I am looking tired and pleased that this project has reached completion. I began this project when my brother, who is the drummer in his Christian rock band, proposed that I design and fabricate a bass horn for his band's PA system. Needless to say, I jumped at the opportunity.
It began with Hornresp, which led to a simple bi-conical horn with a throat adapter.
I tweaked the software to get the smoothest SPL curve, a strong impulse response, great extension, and still be reasonably easy to fabricate. Even though the SPL graph depicts the low end roll off at 35hz (3 db down), I think the horn, when corner loaded, is capable of far greater extension. I fired it up with a mere 125 watts and played a test CD used for car subwoofer testing. I heard all the synthesizer bass notes; nothing seemed weak, or absent. Another bonus came in the form of "punch" -- this baby slammed so hard that the entire warehouse space, and the interior offices as well, came alive with concert level bass, and it did so with 125 watts.
I also managed to achieve a strong impulse response.
Then came the task of converting/crunching Hornresp's schematic data and drawing the prints to build this bad boy. It takes about three and a half sheets of plywood to complete the fabrication process, and lots of PL polyurethane caulking and Tightbond glue.
There's enough information in these drawing for a determined individual to build one of these horns for themselves should they desire a copy. As I mentioned on my home page, I sell these prints for $25.00 as a complete set -- there's more information and the drawings are larger.
I've heard mentioned that my horn resembles a LAB-12 unit, but a cursory glance at these drawings should dispel that notion. My horn's throat is (relatively) much smaller, and my horn's net width is 24" rather than the LAB-12's 20". There's quite a few more cuts to make with my horn, so it's not for the impatient/restless at heart.
Best of all, this baby sings -- I mean, I've never heard a horn that loves the lower octaves to this degree. When my brother's bass guitarist moved to the lower strings, the bass just grew louder, and it wasn't just EQ, I experienced the same powerful bottom end when I fired her up in the shop; a very happy experience to say the least.
One last thought: this horn requires massive internal bracing -- shown in the drawing, below. If you don't brace the panels, the horn will resonate, and it won't sound pretty... ask me how I know. ;^)
There's enough information in these drawing for a determined individual to build one of these horns for themselves should they desire a copy. As I mentioned on my home page, I sell these prints for $25.00 as a complete set -- there's more information and the drawings are larger.
I've heard mentioned that my horn resembles a LAB-12 unit, but a cursory glance at these drawings should dispel that notion. My horn's throat is (relatively) much smaller, and my horn's net width is 24" rather than the LAB-12's 20". There's quite a few more cuts to make with my horn, so it's not for the impatient/restless at heart.
Best of all, this baby sings -- I mean, I've never heard a horn that loves the lower octaves to this degree. When my brother's bass guitarist moved to the lower strings, the bass just grew louder, and it wasn't just EQ, I experienced the same powerful bottom end when I fired her up in the shop; a very happy experience to say the least.
One last thought: this horn requires massive internal bracing -- shown in the drawing, below. If you don't brace the panels, the horn will resonate, and it won't sound pretty... ask me how I know. ;^)
Not mentioned in the drawing is the side panel's over all height and width (relative to the drawing, below). Both dimensions are 45". My brother's van just happens to be a shade over 45" wide, and the horn width chosen seemed the perfect solution for his transportation.
I purchased 3/4" plywood and began the layout. Notice the clamps? I stacked the side panels directly on top of one another and drilled holes through both sheets where screws would eventually secure the inner baffles that create the horn's flare.
Being a prototype, I didn't want to spend a great deal of energy routing dadoes, and with a decent bed of polyurethane caulking (I favor PL) the panels wouldn't even consider breaking loose.
Side note: Home Depot used to have a PL caulking display board. On it, there were aluminum strips glued on edge to the display board with a bead of PL. The display's information tagline suggested that I pull on the aluminum strips (which I did with gusto) and attempt to rip the caulking bead. I failed, kept bending, and failed, twisted repeatedly, and failed... I've been a believer in PL products ever since.
Being a prototype, I didn't want to spend a great deal of energy routing dadoes, and with a decent bed of polyurethane caulking (I favor PL) the panels wouldn't even consider breaking loose.
Side note: Home Depot used to have a PL caulking display board. On it, there were aluminum strips glued on edge to the display board with a bead of PL. The display's information tagline suggested that I pull on the aluminum strips (which I did with gusto) and attempt to rip the caulking bead. I failed, kept bending, and failed, twisted repeatedly, and failed... I've been a believer in PL products ever since.
After installing all the panels, the horn is taking shape.
After several attempts with pencil, I finally decided on the speaker access panel cutout. You can see one of the two Lab-12 drivers in the compression chamber.
I filled the the screw holes with bondo, sanded like crazy, routed the edges, stained the cabinet "mahogany red", then sprayed a dozen coats of shellac.
All things considered, this has been an excellent adventure. Unfortunately, I began fabrication in an unheated shop in the middle of winter. It was the thought of hearing this little monster that kept me from noticing my cold hands and feet.
A slightly wider folded bass horn profile:
I fabricated another version of this horn for a customer, and made the horn slightly wider. The result is that I don't have to fold the driver's mounting baffle plate. This greatly simplifies the construction process. In essence, make the horn 3/4" wider.
