Working with REW

[cassb]

OK cool... I'll mess around with speaker placement then. I don't have an EQ other than the bass and treble controls on the receiver.

Bryan

[cassb]

Here is a graph of 25 to 5000Hz with the subwoofer included, crossover is set to 80Hz in the receiver. On the plate amp, the phase switch is set to "normal," frequency is 180Hz and gain is set to the middle of its range.

What's that dip at 100Hz? Or is that a peak at 50Hz and 120Hz? When I change the receiver to crossover at 100Hz, the graph looks the same.

[brucek]

Take separate measures of the sub and then the mains to get a better idea.

[cassb]

OK, here we go. Mains first, then sub. Wow... look at that dip in BOTH of them at 100Hz! Something's wrong here, but what?

Thanks!
Bryan

[fouiz]

Try to invert the sub phase. I had a similar problem.
Got rid of that dip with inverted phase or changing crossover freq.

[brucek]

Something's wrong here, but what?

Nothings wrong. Your room is creating that dip. Move the listening position where you're measuring and/or move the speaker positioning and it should change.

brucek

[cassb]

Ah, OK... thanks, I'm new to this type of tweaking.

Fouiz -- I did try the phase switch and it did not affect this 100Hz dip. I also tried setting the crossover to 100Hz, but that didn't help either.

Thanks guys!
Bryan

[fouiz]

cassb wrote:

Ah, OK... thanks, I'm new to this type of tweaking.

Fouiz -- I did try the phase switch and it did not affect this 100Hz dip. I also tried setting the crossover to 100Hz, but that didn't help either.

Thanks guys!
Bryan

So, as Bruce said, you have to move your sub and check the impacts. Maybe your furniture is disturbing too. Good luck !

[cassb]

fouiz wrote:

So, as Bruce said, you have to move your sub and check the impacts. Maybe your furniture is disturbing too. Good luck !

This is actually pretty fun...

So I did another experiment. I held the SPF Meter about 6" from a main speaker and did the sweep (unplugged the sub), then held it about 6" from the sub and did the same sweep (with mains on). There's no dip at 100Hz at all, so you are correct -- this seems to be room acoustics I'm dealing with. It's amazing how the room can really change what your speakers "sound like."

[brucek]

Yeah, doing a near-field will usually reveal the speakers response rather well, particularily if you move it away from any boundary. Of course, outside would be best, but simply measuring close can reveal that the room was at fault.

Sometimes moving the speakers or listening position a few feet can help a lot. The REW RTA feature is very useful for this determination.

Remember to limit your upper range to 3K, because after that I would not trust what I was reading with a Radio Shack meter (note the peak at 5KHz)..............

brucek

[cassb]

brucek wrote:

Yeah, doing a near-field will usually reveal the speakers response rather well, particularily if you move it away from any boundary. Of course, outside would be best, but simply measuring close can reveal that the room was at fault.

Sometimes moving the speakers or listening position a few feet can help a lot. The REW RTA feature is very useful for this determination.

Remember to limit your upper range to 3K, because after that I would not trust what I was reading with a Radio Shack meter (note the peak at 5KHz)..............

brucek

Aha! I didn't know REW had a Real Time Analyzer! This just gets better and better... thanks!

[brucek]

I didn't know REW had a Real Time Analyzer!

Select SPECTRUM tab.

Select mode of RTA 1/24th octave.

Select FFT length 645536.

Select any Averaging. (2 to start out with).

Select Rectangular Windowing.

Select Signal Generator and select Periodic Pink Noise.

Press the RED BUTTON. (ensure clipping warning is not on)

The display will also show any frequency response you've just taken for comparison.

brucek

[cassb]

Cool -- that actually looks pretty flat from 30-3000Hz.

[JohnM]

cassb wrote:

Cool -- that actually looks pretty flat from 30-3000Hz.

Try setting the vertical scale to span 60dB like the usual subwoofer plot scaling, it's a little bumpier than you think.

[brucek]

that actually looks pretty flat

hehe, yeah like John says.......... you're being kind to yourself here.

The normal swing we use for response measurement graphs is from 45dB to 105dB. This is an appropriate swing of +/- 30dB around the 75dB target level.

So, if you see your RTA rests around 40dB, you would want to use a vertical scale of ~10dB-70dB.

brucek

[Blaser]

brucek wrote:

You can certainly use it, but I would limit the upper range to a few 1000Hz. After that it's a crap shoot....

brucek

Hi Brucek! Long time...

Do you have any idea what the range of inaccuracy might be? Is it also true for the digital RSmeter?

[brucek]

Do you have any idea what the range of inaccuracy might be? Is it also true for the digital RSmeter?

Read about the Radio Shack Meters here.

brucek

[cassb]

brucek wrote:

hehe, yeah like John says.......... you're being kind to yourself here.

The normal swing we use for response measurement graphs is from 45dB to 105dB. This is an appropriate swing of +/- 30dB around the 75dB target level.

So, if you see your RTA rests around 40dB, you would want to use a vertical scale of ~10dB-70dB.

brucek

Are you saying it could be even flatter than that somehow? It's in a 20db range, so I figured that was good. How do you flatten all that out then -- solely placement would do it? That's hard to believe.

[brucek]

Are you saying it could be even flatter than that somehow? It's in a 20db range, so I figured that was good

I'm saying to use a scale that is +/-30dB around the average reading.

20dB variation isn't that good.

How do you flatten all that out then

That's the tough part. Treatment, EQ, traps, positioning, etc, etc. It's an entire science.

brucek

[cassb]

OK. I guess I was just happy that the plot was somewhat horizontal. I've got a lot to learn.

Although, this is a home office that I'm working on, not a home theater. So the room is never really going to be acoustically perfect. I guess I just want it to sound as good as possible with minimal room changes. If I have bumpy bits in my plot, then I supposed I'll have to live with that -- I really don't know what my goal should be with REW and my system.

[cassb]

Believe it or not, I am just now finally playing music through my new speakers and sub that I built a couple months ago. I have not had all the pieces to my system together yet until my Pioneer DV-400V-K arrived yesterday. It was a deal on eBay for only $20.50 -- I just had to take it apart and bend and resolder the USB port back into place, but other than that it's working fine.

So playing familiar music for the first time, the DIY speakers sounded like there was too much mids, in the 500-1000Hz range. But I think they just need to be broken in since the drivers are new. Plus I probably should move them farther than 12" from the back wall. Other than that, I'm really happy with the sound and power from this system.

Now I need to figure out a way to play movies in this DVD player and output the video to my computer monitor... hmmm...