Springbok10,
Let me chime in here to clarify some things. First of all… thanks
Duke for your input! Duke is a very knowledgeable guy and he’s pretty right on about the placement issue and all. Before I get very deep into the subject (you’ll learn to be more careful next time – as the rest of the guys can testify to
), let me just say that as Duke pointed out, our Revelations or any of our speakers are probably one of the least sensitive designs available with regards to room placement. In other words, if you don’t have an ideal placement situation, you REALLY ought to consider our stuff above a lot of the rest.
In your situation, two of the WORST designs that you would definitely want to avoid would be either an omni (as in say…mbl) or a dipole (planer electrostatic) or even an open baffle design. There’s really only one design that would stand a decent chance of sounding good and that would be your standard “monopolar” speaker. Now, if you could find one of those that also offered some directivity control, then you’d have a real good chance of achieving quality sound. Hey…whaddaya know… that’s just what our designs offer!!!
OK, down to some math. Our Revelations are 15.75-inches deep and 12.5-inches wide. Divide the width by 2, add the depth and then add the 12-inches you say that you are able to pull the speaker away from the back wall. By my math that adds up to 34-inches. Divide 13,618 (the speed of sound in inches per second) by 2 x 34 to get the frequency that is equivalent to a 68-inch wavelength. That works out to almost exactly 200Hz.
So…we find that we have a reflection path length of ½ wavelength at 100Hz from the front-center of the enclosure to the wall behind the speaker. Now, if 100% of the reflected energy were to return to the point of origin (the woofers), the system would exhibit a perfect null (a complete loss of SPL) at 100Hz. But… we must remember that the wave front is expanding as it leaves the woofers as well as the entire time it is traveling to the back wall and then reflecting back to the woofer again. That means that far less than 100% of the reflected energy will likely return to the drivers. If we assume that as much as 50% were to return (somewhat unlikely) then our system would exhibit a 6dB reduction of SPL at 100 Hz. A more likely amount of 25% would yield a 3dB reduction of output.
This all adds up to the fact that the odds are a pair of Revelations placed 1-foot from the wall behind them would exhibit a dip of only about 3 to 6dB at 100Hz. This is a worst-case scenario, as any phase nulling will decrease in magnitude as the frequency being reproduced is lowered from 100Hz. As the frequency is raised from 100Hz the radiation field will change from 4pi (omni-directional) to 2pi (hemispherical) as a result of baffle width and then on to less than 2pi as a result of waveguide control. We might get a bump in output at 200Hz as well, but again it's magnitude shouldn't be much more than about 3dB or so.
To be sure, the Revs would benefit by being pulled out further from the wall, as this would push the first reflection null down to a lower frequency. Although...and this is something a lot of you guys probably haven't thought of... pulling the speakers out away from the wall will lower the first reflection null frequency - it is also likely to make it WORSE!
This is because more of the reflected energy is likely to converge with the speakers if they are farther out in the room. Try using an SPL meter and some test tones if you don't believe me.
Regardless, in your situation Springbok10, (specifically BECAUSE the speakers will be closer to the wall behind them) the magnitude of any null will likely be relatively mild and well within the frequency “averaging” nature of human hearing. 100Hz is also at the very bottom of the midrange and therefore our hearing is also far less sensitive to any frequency variations in that range. Actually, a small dip there might be a good thing as a lot of rooms often have a peak there anyway.
The other consideration is the consequence of early reflections affecting/contaminating the time-dependant spatial (imaging) information in the recordings being reproduced. This is always a concern to some degree, but it is important to note that it has been found that human hearing has a very great ability to separate and identify the first arrival signal from those generated by reflections. This is how we are able to locate the origin of a sound source in a darkened room. Were it not for this ability, we would be at a total loss in trying to identify the location of a friend’s voice in a crowded, noisy space. Again, due to the directivity control afforded by the waveguide in our designs, they will exhibit far less sensitivity to this problem than virtually any other speaker design.
The upshot is that the worst artifact to result from such placement would be a boost of the frequency range below the 100Hz null – i.e., the bass range (100Hz on down). Well… that’s pretty easy to compensate for. In fact, I can easily design and build a passive network to place in line with your power amps (that would be a passive, line-level equalizing network). Beyond that, if I can find out a few specifications regarding the output impedance of your amps, I can run some simulations in SPICE (circuit modeling software) to find whatever compensation networks would be needed for you amp. Be it impedance compensation for the speakers or frequency response correction for first reflection boundary gain – we can fix it - piece of cake.
The bottom line is… don’t let either the amp or room situation scare you. We can tweak the Revs to as close to perfection as any speaker could ever be.
Now… will somebody please give me a REAL challenge! Nevermind. Already got one. It’s called MAKING MONEY!!!
-Bob
