bassboy
Ex Member
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Here's my two cents. I didn't bother to look at any of your pictures or graphs because it's not really necessary. (And I have a dial up connection) The design of this subwoofer is solid. As far as I can tell it appears to be in the area of a 35-38 hertz horn with a flare inspired by the tractrix contour. I have done a lot of research and this is a great design. I am assuming that you did a good job building it. I am assuming it is absolutely airtight where it should be. Assuming these things there are only three varibles left - the driver, the hole in the front and room position.
The hole in the front of the driver is NOT NECESSARY. If it is doing what it is supposed to do, great, by all means it improves on the overall design. If not, and it obviously isn't helping you, cover it up. It won't hurt anything and you can rest assured that is how it is usually done anyway.
I would try a smaller driver, or one with a smaller vas. Or restore the chamber to original size. It's not going to hurt anything and you really don't need to try to max out this box, trust me.
That leaves the room position. Consider this - I spent about 20 hours making my Imperial from the 1956 plans. I spent about 5 hours modifying it to make it a front loaded design, similar to yours, and many other horn plans available on the internet. (Without the slot, of course, simple as possible works well for me.) I have spent over 60 hours listening to this thing and adjusting it's position. It's still not perfect, but here is what I found.
My garage has no treatments and it is about 30x30 with a 12 foot ceiling. Backed into the corner it sounded great but low frequency extension was painfully inadequate. I found, as you did earlier that it was a whole lot louder when facing into the corner. Better lf extention as well, but at about three feet out the response was very jagged. At high power levels (100 watts) the fluorescent lighting, the garage door and garage door opener, the electric panel and anything leaning on any wall would vibrate almost as loud as the bass. You could even feel the concrete floor vibrating.
Moving it closer to the corner helped a lot but even a couple of inches in any direction made a huge difference in frequency response and lf extension. Still not happy with this arrangement, I remembered the Big Fun Horn project and how much I was fascinated that in this design, the box itself actually cuts the corner in half. So I turned the box so the SIDE was facing into the corner, tight to the walls. Huge improvement, with less power it was louder and lower. Angling it in even further helped, until the mouth was only about a foot from the wall on one side, tight to the wall on the other. Placing a 100 lb slab of door on top, closing it off to the ceiling and further preserving directionality seemed to help too. It looks oddly like the corner horn design, also on this website, but with a mouth on only one side.
This placement yeilded highest SPL, even frequency response, and oddly enough, the least room vibration noise. In fact, leaning on the drywall near the mouth listening to a 20 hz note at 10 watts feels like a vibrating bed and makes it difficult to breathe.
That being said, the response is still pretty erratic as you move through the room, but if it's a listening room, you only have to pick one good spot anyway. Room treatments would probably do miracles as well. But don't try to get flat response below about 40, mine drops off pretty fast below that. I have 2 10's in an infinite baffle situation, using the full box size available in there. You guys can question this if you like but I think the horn flare, not the sealed chamber OR the driver is going to determine your low cutoff. Of course they will have some effect on the overall outcome but I don't think you will get much lower than 40 flat unless you use room placement and room characteristics to effectively extend the horn or at least preserve directionality as long as possible, which I suppose is kind of the same thing.
But probably the easiest thing to try is actually turning it down. Try going from 0 to 10 slowly and this is what I found. Up to about 3 watts total peak, everything sounds great, and you can actually FEEL the SPL like an invisible vice around your head. At about five watts it sounds louder but a lot sloppier and the pressurization effect is gone. Some of the extra noise is the room rattling and most of the power is used shaking the hell out of the drywall. Unless you are in a big nightclub, you really don't need more than 10 watts to lose your hearing.
By the way, if you want to take a meaningful measurement, do it right in front of the horn mouth, before the room gets ahold of it. That's the only way to tell what's truly there before room effects add and subract.
Good luck
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Imperial SO has problems, need help (Read 59638 times)
