Quote:
Arkasha wrote:
 Yes my interest is stereo, rather than multi-channel. I did try using REW to figure out the -3dB point, but the results are confusing. It seems the room "contributes"  so much that the actual point is somewhat buried.
Thanks. |
Hi Arkasha,
I believe what you are trying to do is find the -3 dB point of your mains (the Quads) so that you can integrate a sub nicely. Most of us around here don't use REW to determine the frequency response of our mains. This is primarily because the crossover point is generally determined by whatever receiver or processor is being used. So if I set my crossover frequency for my mains to be 60 Hz, it should integrate reasonably well with my sub -- as long as my sub has usable output above 60 Hz, and my mains have usable output below 60 Hz. We want to cross over
before we run out of response on both sides.
So, since the frequency response of your mains is stated to be 35 Hz by the manufacturer, I would probably cross them over at 60 Hz, and I might play around with a 40 Hz crossover point. Again, I do this using the "bass management" of my preamp/processor.
Since you are focusing on 2-channel listening, I'm going to go a step further and guess that you are working with a preamp or integrated amp that doesn't offer bass management -- keeping the signals as pure as possible. And you are using a sub that has a variable crossover point as part of its built-in amp. You want to figure out where to set that crossover point in order to seamlessly integrate your mains with the sub -- and you want to use the full frequency response of your mains, without cutting them off unncessarily or prematurely. I may be wrong about this, but that's kinda what I'm thinking.
Now, you've noticed that the room contributes a lot, especially in the lower frequencies. That's why so many of us are concerned with equalizing our subs using the BFD. Although a sub manufacturer will offer specs and plots, those specs and plots may have nothing to do with real-world frequency response once we get that sub home. So -- how do sub and speaker manufacturers normalize (well, as best they can...) their specs and plots? They take their measurements in anechoic chambers. If you're trying to recreate the manufacturer's specs using an RS SPL meter and REW, you'll have to find a place that doesn't resonate with, and contrary to, the speaker's natural output. Since most of us don't have fancy and expensinve anechoc chambers available to us, we need to find somewhere else that won't reverberate when we start making some noise. A good place is generally outdoors -- someplace where there aren't a lot of surfaces to reflect, absorb and amplify the source material. If you can do that, and if your manufacturer is honest, and your equipment is accurate (did you use the RS SPL meter cal files?), you should be able to get close.
So the question is -- how do I get my mains and sub to integrate nicely using what I have? Here's what I would do. First would equalize my sub's frequency response using the RS SPL meter, REW and the BFD. EQ your sub well above the point where you think you're going to cross it over. I would EQ up to 60 or 80 Hz if I was doing what I think you're doing. Do these measurements with all other speakers off. Second, I'd set levels of each channel individually. You can do this with the pink noise generator of REW and your SPL meter, or you can use your pre/pro/whatever's integrated level-setting system if it has one. This will help get you in the ballpark. Third, continue to do REW sweeps with both the sub and the mains on. If there is a major overlap in which both the sub and the mains are running, you may see a hump in the plots. You can also do a sweep of your mains in their normal position. This will give you an idea of what kind of frequency response to expect from them, on their own, in your room. As you see your mains drop off, you'll want the sub to come in. Start with your crossover point somewhere around the point where the mains drop off. Continue tweaking and doing REW sweeps till you are happy with the frequency response.
Now, if everything turns out right and you get a nice, flat and well-integrated frequency response, you might find it a little thin in the bass. If so, you may be looking for a "house curve", in which the bass is boosted in particular region. You can do this kind of thing with the BFD, and, in your case, you may be able to do it as well with some overlap in the cutoffs of your mains and sub. Wayne A. Pflughaupt (sp?) wrote an excellent discussion on the topic, and you shoud be able to find it here at the HTS with a quick search.
Anyway, that's enough for now. If I'm way off base with my assumptions, let me know. Good luck with your project. I ran a few different sytems the way that I've described above for quite a while with decent results (many years ago, before REW and BFD).