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Any rules about how high to mount a woofer on a baffle? The woofers are going to xover to the mids somewhere between 70 and 100 hz. I was planning on mounting the two woofers vertically as close to the floor as possible to get the tweeter/mids array at the proper listening height.Thanks!
I fooled around with some tower speakers for almost ten years trying out different box volumes and woofer arrangements. I have finally settled on a 4 ft high tower with 2 10-in woofers occupying the lower 2/3rds of the tower. One mounted near the floor and one near the 'top' of the lower 2/3rds. This arrangement provides very smooth bass down to 25 Hz, response in-room, no dropouts or peaks with proper placement because the drivers are at various different distances from the walls/floor/ceiling. In my experience, this is more important than an anechoic-measured flat frequency response. The tonal and timberal accuracy of the bass in my system are remarkable. (If I do say so myself!) And of course the power handling goes way up and the distortion goes way down because of multiple drivers.At low xover frequencies, you have plenty of distance between drivers to work with, but I have found some extra overlap between mid and bass drivers to be helpful many times. Maybe something to do with current vrs. voltage, the energy storage of the xover, textbook vrs. computer analysis, etc.
My only concern about what you have done is the possibility of comb filtering due to the distance between drivers.
...different distances to boundries? No, because the room is being pressurized from 4 different places. That is why one 18" (for example) stand-alone subwoofer is not as effective in a normal room as two smaller (12" for example) subs. <- from Velodyne spokesman no less.
Before you start cutting wood, you might want to have a look at some back issuses of Speaker Builder. You also have to (should) take into consideration the distance between drives and xover fq. That is where SB can help. bobwire
Sort of a mixed bag what to do. On the one hand the closer to the floor, the more of a boost you get because of being closer to a room boundery. But this boost may not be were you want it. Also closer to the floor will cause floor bounce which will cause cancelations at a certain frequency. If you are using two woofers, I would put one on top and one on the bottom. Worry more about getting the tweeter at listening height. That is what is important.Clayton
Mounting the woofers vertically will create a "wavy" output out of the two woofers. This will depend on their total height off of the floor. Having two woofers mounted at different heights will create different pressure zones. This will alter each drivers frequency response even though your using two of the same drivers.Depending on room acoustics and the drivers normal frequency response curve, this can either be a bad thing or a good thing. Most of the time, it is a bad thing as the DIY'er typically does not have enough test equipment or experience to balance the direct radiation with the reflected reinforcement / cancellation of specific frequencies.
You might want to try keeping BOTH woofers down at floor level. To do this, you would have to mount them on different sides of the box. Since bass at those frequencies is considered "non-directional", you can play around a little bit with what sides you use. While i do prefer direct radiation, there are gains to be had from mounting the woofers on the sides of the cabinets also. This is especially true since they wouldn't be reproducing any upper bass range at all. Side mounting would allow a narrower baffle for better imaging from the built in "satellite's" up above.
I will be working on a project similar to this in the near future. I'll be using two 12's mounted on opposing sides and a slightly off-center MTM array up above. These will be used in conjunction with two subs, a center and two surrounds for a friends' HT system.
Keep in mind that side mounting CAN make placement a little tougher in small rooms. You can take advantage of or be hurt by corner placement and / or back wall reinforcement. Like any other design, you'll have to put them in the specific listening area and play around with them a bit. Sean
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Sean, you are correct that unless you have the equipment to measure what you have done, that it is more of a hit and miss situation. Sometimes you can get lucky. This is why everyone sould build test boxes first. As to side firing woofers, yes, they help to keep baffle width down, but IMHO, the tradeoff is that you do not have enough distance from the back of the woofer to let some of the backwave disapate before it arrives at a boundery. Also side walls are the most resonant part of a cabinet. It is not quite as bad having the woofers down lower because there is more reinforcment at the bottom. But side walls are tough to make solid especially as the deep of a cabinet gets deeper. Tkes lots of bracing which takes up space, which makes for a larger box. If doing vented which I hope you are not ;), the braces can really be a headache.Clayton
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