First graph, and some questions

[affeking]

OK...first of all, I'm not 100% confident with how I have this set up. You can see the post about using the SB24 USB with Vista for details :P

Another setup issue I encountered had to do with calibrating the SPL reading. When I chose to set it with the sub, I get a notably different reading than with the full range. I assume this is probably normal but the online help implied it did not matter which I set it with. I think the first time I set it with the sub, and then I did a full range measurement...the chart was really odd with readings of 135DB when I was only doing about 85. The two calibrations were only off by about 5DB, so that doesn't make sense to me. Anyway, I redid the calibration with the full range pink noise and my subsequent measurement looks more normal.

Let me know if it looks like I set things up correctly based on the above statements and this graph:
http://picasaweb.google.com/jrames/R...07866514340002

Yeah, the graph looks pretty terrible. My speakers aren't really setup quite in their correct places yet (that's what REW is for!) and my wife is making a lot of racket upstairs.

Thanks!
affe

[JohnM]

Measurement looks fine. Try setting your SPL axis to 45 .. 105dB, that way you get a ready comparison with the other plots you'll find posted here.

[brucek]

Post your graphs with a vertical axis of 45dB-105dB to comply with the standard we generally use here. Also note that the horizontal axis should start at 15Hz and extend to your desire..

Note that you should turn on smoothing (~1/3 octave) when plotting for full range measurements, since reflections can cause comb filtering that makes it difficult to see the underlying trend of the response. (It is rarely used for low frequency measurements as it would obscure the true shape of the response and so not allow accurate correction filters to be determined). But, for full range it should be used.

Certainly the levels will change when switching from sub pink noise to full range pink noise for setup. They contain completely different energy levels. You need to recalibrate when you switch between them.

Hopefully you're not using a Radio Shack meter for full range measurements...

brucek

[affeking]

Thanks John. Great product, and I appreciate the help. I realized my graph was in the wrong scale right after I uploaded it I will fix that next time I post.

I'm also struggling with another question. I've heard people on these forums talk about graphs showing issues with the crossover. I assume they must all be people with crossovers built into their sub? I have an SVS PB10, and my LFE management is all handled in my receiver. This means I'm pretty much out of luck as far as testing that component, correct?

I'm not really sure how its working right now - I suppose the speakers just kick in whenever they can and same with the sub. Does this pretty much invalidate all of my low frequency measurements? Any way around this?

Thanks,
Jeff

[JohnM]

Most people use the receiver for bass management, but there are still controls on the subwoofer that affect the behaviour through the crossover region, either a phase adjustment or a phase inversion switch. From your plot there looks to be a sharp dip around 80Hz which suggests your sub phase needs inverting.

[affeking]

brucek wrote:

Hopefully you're not using a Radio Shack meter for full range measurements...

Ummm...yeah I was. My understanding was always that the RS was pretty good for everything but the small dip in the sub range, which is handled by the calibration file. Apparently, I was wrong.

[brucek]

The RS meter should only be used up to about 3KHz. No higher than that.

For full range measurements most people will use an ECM8000 (with a preamp)............

brucek