I finally decided to try out an idea I've had for many years for a straight horn loaded speaker.  What finally prompted me to pull the trigger was the great bass I got from my corner horn when I put a subwoofer speaker in it.  Unfortunately, that frequency response falls off a cliff at 40 hz so I'm going to see if I can do better.

The thought for years was to build a horn out of 4 sheets of plywood.  This would yield a very simple build, an 8' long horn with a 4' x 4' mouth and a 1' x 1' throat.  I already have the 10" Dayton classic sub speaker I will put in a 1' x 1' box that will screw into the horn throat.  I will make the box deep enough to get a volume that looks good on my ProBox software program for that speaker.

Rather than plywood, I decided to go with braced 1/8" hardboard or "Masonite".  I should finish the 4th panel today, the speaker box tomorrow, and assemble it the day after.  As to where its going to go, I'll worry about that later when and if I know it works.  I'm lucky to have my own building with no WAF to worry about.


Dan

Well, it turned out a little bigger than I was expecting.

The speaker box is making all kinds of port noise, even though the ProBox software said the port was big enough to not have any issues.

The horn panels are vibrating like crazy, not enough bracing I suspect.  I am glad I didn't build it out of 3/4" plywood though...I suspect the plywood would be vibrating just as much and it would be so heavy I couldn't move it.

It seems to be getting down to 30hz, but its taking a ton of power.  I plan on taking some sine wave measurements this afternoon to see just how efficient the horn is and how low it goes.  Also thinking of cutting about 2' off the big end to make it more manageable...then maybe it could be set up in a corner.


Dan

I admire your courage, but dam your judgement. I'm not saying that a folded horn would be easier to build, but it would inherently have much more stiffness so that the horn would shake itself to death. I too, have built acoustic boxes, experiments on a note, and found the truth to be harsh.

Dan, I hope I do not speak out of turn if I say: To me your bracing does not look like bracing. I think it is ballast weighting down the panel. At least mostly. I think what is needed to brace the panels is internal cross struts.

I hope that is helpful.

Brian

I think you are right Lin.  But won't internal braces be needed to to get the panels stiff enough to stop that resonance?

Brian

I have built Voice of the Theater A7 cabinets using 1/8" masonite for the horn that was braced with 2x2's and never had any trouble with it.  I also never felt any pressure in the horn.

With this much longer straight horn the pressure inside the horn is VERY noticeable.  Also, there is nothing to tie the horn bracing to...on the Voice of the Theater it was all secured to the cabinet itself, whereas on this straight horn its all "floating".  The two obvious choices would be to run internal braces, or put the thing in a corner and brace it to the walls.

Too much effort to overcome all the issues with something that turned out too big for actual use (unless I use it as an excuse to build a bigger workshop!).  I've scrapped it.

Dan

 More than few times, I have scraped a project due to issues of use or performance. The good thing to know is that you paid for a lesson and that makes up for most of the loss. Besides, not many people will take their thoughts to action, and for that, you should feel good about yourself.

Never let your success or failure be due to a lack of effort.

I would have suggested a layer of dynamat and another layer of masonite on the outside. Standard mod for small horns.  I may be too late for this project, but it might help someone else.