Please provide your impressions and advice on my REW graphs - AVS Forum
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post #1 of 21 Old 03-04-2010, 08:03 AM - Thread Starter
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OK – I’ve spent some time with my Radio Shack SPL meter, Behringer UCA202 external soundcard and REW to generate FR graphs of my subs. The REW online help thread at the 'shack is fantastic for an inexperienced REW user - like me. No way could I have gotten everything set up to measure without it.

I have an eD P7S-650 in the front of the room and two Infinity CSW10 in the back of the room. I measured the P7S separately from the CSW10. I measured the CSW10 together since they are basically co located about 3-4’ apart. There are pics of my room in my build thread, but I can post some here if it will help with analysis of the graphs. Now that I have the graphs, I have some questions and would like some impressions from those that are familiar with these graphs.

Here is a graph of the initial measurement of the P7S


Here is the graph of the P7S-650 with REW’s optimize pk gain and q


Here is the graph of the CSW10 with REW’s optimize pk gain and q


1. What do you think of the FR?

2. These graphs are telling me that I need to add equalization to remove the largest peaks, correct? But, do I need two eqs – one for the P7S and one for the CSW10?

3. I noticed the FR rolled off and then began to climb in both graphs so I extended the X-axis down to 2Hz. Here is the same graph of the initial P7S measurement down to 2Hz. The graph shows 104dB at 2Hz. What have I done wrong? Has this error compromised all of the measurements and do I need to start over?


4. I ran the sweeps with all of my speakers connected. Should I have turned off my L,C,R speakers as I could hear bass coming from them during the test. They are crossed at 80Hz.

5. I ran a measurement with all subs going but didn’t save a jpeg of it. Should I be attempting to measure all subs together or focus on measuring separately for the front and back of the room?

6. What adjustments/corrections should I make to measure everything correctly?

Thanks for the help.

kjlewie

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post #2 of 21 Old 03-04-2010, 09:08 AM - Thread Starter
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I think I may have this thread in the wrong section of the forum. Should this be in the Audio setup section? If so, would a moderator please move it?

Thanks

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post #3 of 21 Old 03-04-2010, 01:29 PM
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Looks like a measurement artifact to me. Don't trust anything below 20 Hz with your gear, and that may be pushing it some.

I doubt a R/S meter could measure anything meaningful at 2 Hz. The electronics simply do not allow it. I don't trust mine below 10 Hz, and I have modified my meter and changed the mic capsule.

The UCA 202 is probably the best usb soundcard under $50 out there for REW measurements, but I know it is not flat to 2 Hz. IIRC, it is not even flat (+/- 0 dB) to 20 Hz. I owned several and have measured them multiple times. I have modified them with larger coupling capacitors to help with the low end. Ultimately, I switched to a better sound card as a result of these efforts.

Don't get me wrong, for $30, the UCA 202 is a phenomenal piece of equipment, and it is a worthy addition to anyone's measurement arsenal if they are in need. It will do fine from ~15 Hz to ~15Khz with minimal correction, and can be flat from 10 Hz to 20 Khz with corrections properly applied.

In all honesty, my USB cards are not flat to 2 Hz, but I do not expect or need them to be.

The UCA 202 has limits, you just found them.
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post #4 of 21 Old 03-04-2010, 04:31 PM
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kjlewie,

If you're crossed over to your mains in those measurements EQing the "peaks" to go along the curve isn't necessary IMO with the P7S subwoofer. In your first measurement you are pretty flat from 50-100Hz, so I wouldn't change anything between those frequencies. If I were you, I'd move the sub around to obtain lower bass depth. Looks like you're down 12dB from about 50 to 30Hz according to the P7S measurement. Room gain and "better" placement should help give you higher output at lower frequencies. Of course, moving the subs isn't always possible, so...

Concerning the Infinity subs, you don't want to measure all of them separately IMO. The way I was taught was to measure the subwoofer nearest the mains first, then add in the other subs one at a time, re-measuring after adding each. Even if the Infinity's are close, you still might have phase issues between the two (depends on the crossover and the wavelength), and you may also have phase issues between them and the eD sub. Can you take a measurement each time you add one of the infinity subs into the mix? In other words, re-measure just the eD, then add one Inifinity and measure, and finally add the second Infinity and measure. Post all three graphs for us to see.

If you do need to EQ, you will probably need to add EQ separately to each subwoofer, just pulling down the peaks. You'd need a PEQ like one of the Behringers or SMS' to do that. If you already own one, setting phase and delay can help (if your model supports it).

Don't pay attention to anything below 15-20Hz or so. As was mentioned, its probably an artifact of something else (such as the room). There is no way your getting 104dB at 2Hz. Just stick with the standard 15-200Hz graph parameters.

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post #5 of 21 Old 03-05-2010, 09:16 AM - Thread Starter
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Nuance,

Thanks for the helpful response. I'll try to reposition the p7s and remeasure. I need to find my furniture sliders because they weigh a ton. I'll also layer in each sub and remeasure. I posted this question in another forum, but I'll ask here. When I add the additional subs (individually) to the measurement, what SPL do I want on the RS meter - 75dB? Or, something higher as I add subs to the mix?

I figured the 104dB at 2Hz was an oddity of some sort. But, I wonder what it would "feel" like?

Thanks for the advice. I'll post results this weekend.

EDIT: Forgot to post these. Here are the graphs I made last night.
Here is the p7s without the mains.


Here are the csw10 without the mains.




Here is all subs without the mains

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post #6 of 21 Old 03-05-2010, 11:26 AM
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Things look pretty good with all the subs and no mains, but I'd like to see a measurement of all three subs together with the mains. This will show if the crossover has phase issues and will pretty much make the bass above the crossover a moot point, because the mains will be handling that. Speaking of which, what is the crossover point?

As for the decibel level of the subwoofers, when you're done EQing you can use REW or a level meter to set them. However, I would start around 75B for all subwoofers (individually set them by measuring each at the listening position) before you apply EQ, then re-adjust when you have applied the EQ filters.

If it were me, I'd set the target level to 72 and start by pulling down the peak at 48Hz on the P7s sub. Then add in the first csw10 and do the same thing (set target to 72 and pull down any peaks. Lastly, perform the same thing after adding in the second csw10 (the third sub). It is imperative you do them one at a time, for what its worth.

What are you using to apply the parametric EQ? Do you see how the two Infinity subwoofer measure differently even though they are close in proximity to each other? Due to this you may want an EQ that allows individual phases and delays. Just a thought.

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post #7 of 21 Old 03-06-2010, 11:12 AM - Thread Starter
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I have my mains crossed at 80 and my surrounds at 120.

I haven't added an eq yet. I'm hoping the REW analysis leads to a recommendation for which eq units I should consider. Each of the REW graphs shows the software suggestion, not any actual eq.

I'll do some testing and post results when we get back.

Thanks

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post #8 of 21 Old 03-06-2010, 11:19 AM
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Sounds good man.

Concerning EQ's, like I've mentioned already I highly recommend one that has individual delay and phase controls. But hey, you gotta do what you gotta do. Its your money.

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post #9 of 21 Old 03-08-2010, 09:24 AM - Thread Starter
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Last night I added in the mains and measured again.



Its not entirely clear to me why the level is higher than the target level of 75db?

But, the FR is somewhat flat, yes?

Based on feedback I will try to increase the 20hz response by moving the subs around a bit. I'm pretty sure I'll need to stretch out and warm up before tackling the P7S.

I do have a couple of places I can move the subs to try to lift the 20hz FR. Is it really all about trial and error, or are there some likely places the subs may yield better results based on my room (pic below)? In this pic:
Yellow = current position of the 2 CSW 10
Red = current position of the P7S
Green = proposed position of the CSW10 (stacked)
Orange = proposed position of the P7S (stacked)


If I can lift the 20hz response through repositioning and keep everything relatively flat (likely wishful thinking), then perhaps no need for an external EQ? I hope this is the case, but I'm expecting (not sure why) a tradeoff in flatness for the lifting at 20hz.

I've also loosely researched the following EQs:

1. elemental designs eQ.2
2. Behringer DSP1124P
3. Anti Mode 8033b

So far, it seems owners familiar with both view the Anti Mode as quite easy to use to achieve similar results to the Behringer (which requires significant more effort). The eD unit seems to be effective if you only have 1-2 peaks.

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post #10 of 21 Old 03-08-2010, 10:16 AM
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Your FR looks pretty flat yes, but the output of the subwoofers needs to be boosted. Whether you do that by finding better placement or just increase the subwoofer level is up to you. Personally, I'd try finding better placement first.

I recommend starting with one subwoofer in the corner near the mains (perhaps the one that extends the lowest, which I assume is the eD sub). Then place the other two subs along the walls opposite the corner that the eD subwoofer is in. To find the best spot along those walls, place the subwoofer at the listening position in a chair. Then crawl around on the ground with an SPL meter and find where the output is the loudest, using your ears to listen for smoothness. This sounds silly, but it really does work. However, if its not your forte, just take measurements of the sub in various places along the wall, leaving it where it measures the best, and then repeating the same process with the next sub(s) until you've found the ideal spot for each. Just be sure one subwoofer is in a corner, preferably near the mains (doesn't have to be, but it will help with phase).

The nice thing about multiple subwoofers is you can use them to naturally flatten your response and reduce ringing and phase issues. If you put the time and effort in you'll be rewarded with a fairly flat FR and amazing in-room bass response, all without needing a PEQ.

Each room is very different, but if I were you I'd try the eD in the corner you proposed in the model (the orange mark), I'd put one Infinity along the opposite wall, measuring and listening to find the best spot, and maybe the other Infinity on the back wall somewhere (again, measuring and listening). Experiment with various locations. The idea is to use the other two subwoofers to fill in the nulls and help flatten the peaks.

Do keep us posted.

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post #11 of 21 Old 03-09-2010, 09:27 PM - Thread Starter
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After toting subs around my room and taking many measurements, its time to post an update. Instead of posting to report significant progress, I feel less certain about everything.

On Monday night, I moved and stacked the P7S to the front right corner (next to the mains) and I moved one of the CSW 10 to the bump out next to the first row of seating while leaving the other one behind the 2nd row.

Here is the FR of the P7S stacked in the front corner


Here is the CSW10 next to the 1st row


Here is the other CSW10 behind the 2nd row


Here are all of the subs in the new positions without the mains


Here are all of the subs in the new positions with the mains


Here is the waterfall


Below 25hz was already lacking and then it dropped off even more. The higher frequencies did not trace the blue line as I'd expected. I began to wonder if I shouldn't have left the very heavy P7S boxes in place and instead moved the relatively light CSW10 boxes around first. I was too tired and decided I was done for the night.

Tonight, I decided to put the P7S boxes back in position flanking the center channel about 12 from the front wall with the drivers facing the front wall (its easier to reach the controls and all subs are sealed). I left the CSW10 in their new positions next to the 1st row and behind the 2nd row.

Here is a FR graph of the P7S back near its original position


Here is a graph of the P7S and the 1st row sub


Here are both CSW10 without the P7S


Here is a waterfall of all subs with mains


Here is a waterfall of all subs with mains (blue) with just the P7S back to its original position as an overlay (purple)


I'm not sure what to do next, but I'll try something tomorrow night. I have to be mindful of our desire not to see the subs as I crawl around looking for the sweet spots. I appreciate any thoughts and comments on the attached graphs.

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post #12 of 21 Old 03-09-2010, 11:36 PM
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Wayne beat me to it over at HT Shack. After seeing the new graphs, and you having tried different locations, I say take the infinity subs out of the mix and stick with the eD's. Any time the Infinity's are thrown into the mix you lose low end extension.

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post #13 of 21 Old 03-10-2010, 08:41 AM - Thread Starter
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Yeah - Wayne's analysis and suggestions made a lot of sense. I'm going to take the advice and measure the P7S in its original position with the mains. I suspect the result will indicate I need to EQ that peak at 49Hz but at least I should have my extension back. I'll post an update tonight. For those following along that would like to see more detail on Wayne's reply, it is here:

Read more: Please provide your impressions and advice on my REW graphs - Page 2 - Home Theater Forum - Home Theater Systems - HomeTheaterShack.com http://www.hometheatershack.com/foru...#ixzz0hnBSrqT9

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post #14 of 21 Old 03-10-2010, 08:55 AM
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Yeah - if you're getting enough bass output throughout the room using just the eD's, definitely take the Infinity's out of the mix. After you EQ the large peak at 49Hz you'll be flat to 20Hz.

So did you take those measurements from the primary listening position? Once you've got everything said and done, take some measurements from all the listening positions in that room, then go to the averaging tab in REW and average all the responses together into one. This will give you an idea of what the entire in-room response is (at least concerning the seating positions). Many people EQ for only one listening position, which is fine, but if its a theater trying to get a smooth response abroad is the way to go.

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post #15 of 21 Old 03-10-2010, 09:07 AM - Thread Starter
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All measurements are from the front row center seat. Thanks for the tip. I'm quite curious what the back row measurements look like as the seats are on a 12" riser and 2' from the rear wall. To my ears, the bass sounds a bit stronger back there. Once I dial in my primary listening position, I'll take walk back there and open up that can of worms.

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post #16 of 21 Old 03-10-2010, 10:20 AM
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Haha, sounds good.

The reason the bass is more prominent in the back row is because those seats are near a room boundary (the back wall). Heavily treating the back wall will help reduce bass ringing, for what its worth.

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post #17 of 21 Old 03-10-2010, 08:53 PM - Thread Starter
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Tonight, as advised, I turned off my Infinity subs and ran a couple of measurements with the P7S back in its original position. First, just the P7S then with the mains added to the mix.

As a reminder, here is the graph of the P7S. I'll have to double check the crossover on the P7S as the 90-100hz range isn't quite like it was in post #5:


Here is the P7S with the mains added in:


The 20hz stuff is back but what is the graph telling us about 55hz and higher?

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post #18 of 21 Old 03-10-2010, 09:25 PM
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See the response at HT Shack.

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post #19 of 21 Old 03-17-2010, 08:27 AM - Thread Starter
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With my SPL meter, REW and my laptop I've measured the subs in dozens of positions. After repositioning and measuring the P7S in every combination I could think of behind the proscenium, REW showed that my first position was the best.

REW also indicated that the infinity subs (rated down to about 25hz or so) were hurting the FR below 20hz. So, I removed them. The 49hz peak was still there, of course. So, I ordered the Anti Mode 8033 to EQ it. I played around with it last night and got this:


I readjusted the overall level of the mains in the AVR. I'm going to listen for awhile to see how things sound overtime. But, as of now, the sound is so much better, more impactful without booming. I'm very pleasantly surprised at the different bass notes of explosions I've heard many times that used to just go boom - time to rewatch some of the library. This is what I expected the P7S to sound like when I built it.

If I decide to move things around again, I'll give the position next to the 1st row a go.

Kind of funny that, after all of that repositioning, the subs ended back near their original position.

Thanks to all who provided advice and feedback. A big thanks to the guys at the 'shack, including those responsible for REW - a very useful tool.

Measuring, finding a good spot, EQing the peak and matching the volume with the mains has made a huge improvement in bass quality. Time to research house curves and wider area equalization or just watch movies.

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post #20 of 21 Old 03-17-2010, 02:23 PM
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Wow, that looks real good now. I am curious to see what a measurement from 15 to 500Hz looks like (with 1/3 octave smoothing). Enjoy man!

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post #21 of 21 Old 03-17-2010, 08:23 PM - Thread Starter
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Thanks Nuance. As requested here is a FR graph out to 500hz with 1/3 octave smoothing.


Here is the waterfall of the same measurement.

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