# Using REW with PA Sound System



## andyhingston (Nov 30, 2010)

Hi,

I have been involved with the installation of a sound system for our local pub, which will be used for live performances.

The system comprises HZ speaker enclosures, powered by Nexus power amps and encorporates a Behringer crossover and Ultracurve. (see attached connectivity diagram)

Speaker specifiaction is as follows:

*HZ SB600 Sub*

The SB600 uses a unique hybrid band pass design, to maximise the performance
from a small enclosure, enabling this unit to produce the kick drum and low frequency digital audio of today's music. It features a custom-made dual voice 18" driver, for use in stereo or mono drive.

Technical Data

Frequency Response 30Hz - 250Hz
Connections 4 x Speakon sockets
Sensitivity @ 1w 1m 103dB 
Power RMS Dual Drive 300w per channel
Power RMS Mono 4ohm 400W
Average SPL 125dB - Nominal


*HZ Z500 Full Range Speakers*

This range of enclosures is a complete departure from the standard speaker and horn configuration found in most plastic-moulded boxes. The Z500 features a 3-way system with techniques not generally seen in this type of system. A high power 6.5" mid-range driver is used with a specially designed high-power 12" force cooled light-weight bass speaker and 2 Niobium soft dome high frequency tweeters to give the top end a real 'zing'. A 3-way crossover network is employed to manage these components. The Z500 features our 3-way active Bass Saturation Limiter to improve clarity and reduce loudspeaker fatigue at high power power.

Technical Data
Frequency Response: 40Hz - 250kHz 
Connections: 2 x 'Speakon' 
Dispersion: 90° x 90° 
Sensitivity: @ 1w 1m: 101dB 
Power Handling RMS: 500w 
Peak power: 1500w 
Nominal Impedance: 8 ohm 
Average SPL: 125dB 
Peak SPL: 131dB

With the basic system, just crossover and no EQ, there did not appear to be a good spread of frequencies at the low end. With the DQ2496 I have been able to use the RTA and flatten off the frequencies but still the low ends just appear to blend into each other, which makes me think that it could be room accoustics or the positioning of the sub's. I will draw out the room configuration.

I would like to use REW to get a better understanding of the room accoustics and as Wayne has pointed out that it is more for Home Theatre setup I was wondering if I can use for my application?

I have a USB audio interface which is connected through the mixing desk, so I can easily pick up a signal from the ECM8000 to a laptop.

Do I need to use an SPL meter as it is only a stereo signal?

Also, I have a signal generator on my ipod, but should I be using a test cd, if so does anybody have a recommendation?

Thanks

Andy


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## Wayne A. Pflughaupt (Apr 13, 2006)

Hi Andy,

REW can be used for any kind of room measurement, not just home theater. Without a professionally calibrated mic, the only thing REW will get you that the Ultracurve won’t is greater resolution (1/48-octave, vs. 1/3-octave for the EQ). However, I’ve never had problems setting up a PA system with a 1/3-octave RTA. If the bass sounds bad, perhaps your sub placement could be better, or you just need to turn them up. That diagram you mentioned would be good to see. 

One potential issue I can see with the Ultracurve: A good RTA will come with what they call a “calibrated mic.” That’s actually a misnomer, because you can’t really do any calibration to the mic itself. What’s calibrated is the RTA. Most measurement mics are fairly cheap, which means they don’t have perfectly flat response. In addition, there is no guarantee that every mic sample will be perfectly identical. To compensate for this, the manufacturer of a RTA will tweak each unit to address the inadequacies of the particular mic it comes with, to guarantee that measurements are truly accurate. This per-unit, hands-on calibration is why good hardware RTA’s aren’t cheap.

As far as I know, the Ultracurve does not come with a “calibrated” mic. Naturally, Behringer recommends using their ECM8000, but you can see from this chart reflecting the measured response of dozens of samples that you can’t be assured of accurate results just by using an off-the-shelf ECM8000.










That said, you can see that the ECM’s worse deviations are in the high frequencies, so you should be able to get reasonably good results for the low frequencies using the ECM with the Ultracurve. We also have a generic calibration file (e.g an average compensation of all samples we measured) for the ECM8000 that you can use with REW for improved low frequency accuracy.

However, you have to keep in mind that with a PA system, good sound quality is as much about how well the soundman EQ’s each individual channel as it is the quality of the system itself. In other words, a bad soundman can easily trash even the best sound system.




> Do I need to use an SPL meter as it is only a stereo signal?


One has nothing to do with the other. The SPL meter is for measuring the system’s volume levels.




> Also, I have a signal generator on my ipod, but should I be using a test cd, if so does anybody have a recommendation?


I don’t see a need for the ipod or a test CD. REW, if you use it, has its own signal generators, as does the Ultracurve.

Regards,
Wayne


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## andyhingston (Nov 30, 2010)

Hi Wayne,

Many thanks for your reply.

You are correct, the Ultracurve did not come with a mic, we purchased the ECM8000 at the same time, which as you say will not be calibrated for the system.

I guess I wanted to use REW because I felt that the room accoustics are causing us a problem and as far as I understand, REW can help to understand the behaviour of the frequencies, especially the Waterfall graph?

I believe that the room is approximately 6m wide by 10m long, windows either side and doors at the end. The Full Range cabs are mounted on a pole from each Sub and these are positioned approximately 6" from the side wall and 6' from the back wall. Our speaker supplier and designer suggested the sub's to be positioned in the centre, but of course that is not practical.

Last time I spent some time on the system I ran with one sub and this appeared to improve things and based on your comment " you just need to turn them up" I too am wondering if we are driving the subs hard enough! Maybe we would be better with some 15" subs.

I will have a go with REW this weekend and maybe post some graphs of my findings, assuming I can get everything hooked up correctly!

With regard the test cd, I guess what I wanted to do was use a single track that had a broad spectrum range so that we could easily do a comparison, ensuring that we are using most of the frequencies. At the moment we are just choosing random songs, so if anybody knows of a good peice of music for this purpose, it would be useful.

Thanks again

Andy


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## Wayne A. Pflughaupt (Apr 13, 2006)

> I believe that the room is approximately 6m wide by 10m long, windows either side and doors at the end. The Full Range cabs are mounted on a pole from each Sub and these are positioned approximately 6" from the side wall and 6' from the back wall. Our speaker supplier and designer suggested the sub's to be positioned in the centre, but of course that is not practical.


That’s a pretty small room, small enough that a house curve would matter. You should have more than enough bass from those subs from a room that size.

I expect that you’re making the common mistake of EQing for flat response. That’s fine for something like a large civic auditorium, but it’s going to deliver anemic bass in a room that small. I’d suggest reading the house curve article you’ll find linked in my signature before you start your weekend system tuning. 




> With regard the test cd, I guess what I wanted to do was use a single track that had a broad spectrum range so that we could easily do a comparison, ensuring that we are using most of the frequencies. At the moment we are just choosing random songs, so if anybody knows of a good peice of music for this purpose, it would be useful.


Not sure I get it. Doesn’t the Ultracurve generate a pink noise signal? That’s what you want to use for EQing the system. Music tracks are only for verifying that you’ve done the job right.

Regards,
Wayne


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## andyhingston (Nov 30, 2010)

Hi Wayne,

Thanks again for such a rapid response to my post.

Yes you are right I am making the mistake of trying to get a flat response, so I have just printed your House Curve articles and will take time to digest.

Sure the Ultracurve has it's own Pink Noise generator, but yes I was looking for a good example music track to use as a "reference" to verify the changes.

I will let you know how I get on and many thanks for your assistance.

Regards

Andy


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## cast55 (Dec 30, 2010)

I use the following house curve on my PA:

20 - 50 Hz, -1.5 dB/octave
50 - 200 Hz, -3 dB/octave
200 - 2000 Hz, flat
2000 - 20000 Hz, -1.5 dB/octave

Of course, my PA doesn't extend down to 20, so I don't bother trying to boost that band. Using a DEQ2496 for this, I set the auto-EQ to allow the maximum possible correction (+/- 15 dB), but if any of the bands ends up being pinned to +/- 15 (due to natural system roll-off) after AEQ, I remove it from AEQ consideration and do it again until I get AEQ determined corrections that are less than the maximum everywhere. For a PA you might expect 1-4 bands on the low end and 0-2 on the high end to pin - depends on the system and the listening space. I am fortunate with my installation - I am only excluding the 20 Hz correction, and my maximum correction on any single band after AEQ is +11 dB.

A sample REW house curve text file for this target response would contain the following text:

20 8
50 6
200 0
2000 0
20000 -5

In my case, I'm not worried about 20 Hz so mine has a slight modification:

25 7.5
50 6
200 0
2000 0
20000 -5

-Sean


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## cast55 (Dec 30, 2010)

I should just add that I use the above target curve for high-energy music. For classical, jazz or other genres which require a more accurate presentation, I use a similar curve with the same high end rolloff but with slightly reduced bass boost - the knee points stay the same, but I use -1 dB/octave from 20 - 50, and -2 dB/octave from 50 - 200.


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