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Author Topic: How cabinets are measured  (Read 2434 times)

Luis_Marquez

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How cabinets are measured
« on: December 24, 2018, 02:18:02 pm »

New to taking measurements.I have some time this week to play around with my passive rig. Currently applying eq off ear and music source  but going to build some presets in the venue 360. My dirt backyard is ok in size. Working with REW software, berrymic, Art dual usbpre into X32rack. Iím having issues with the monitors in that donít like the sound ,unnatural. No manufacture settings available. Goal is to have a fairly smooth passive rig and eq to taste at venue. What is the best cabinet position and mic location for taking measurements for mains, subs, and monitors?

Online search was vague. Got several articles indicating Cab on ground with mic 2m away. Does this apply to all cabs? My mains are three way so on ground in upright position or laying across?

Thanks and Mery Christmasís to all
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Steven A. White

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Re: How cabinets are measured
« Reply #1 on: December 25, 2018, 11:03:20 am »

Hello Luis.  I started a response to this and deleted it twice.  First off, my systems are all active with DSP's, everything including monitors, the DJ systems, even the system in my den that supports the TV.  The only passive stuff I have is my whole house music system and it's bi-amped with subs LOL!

That being said, I do have a bit of experience with system setup and design.  Let's see, I turn 65 in 2 weeks, built my first home speaker system ~50 years ago, got into DJ setups in 1978, pro sound in 1981 - How much do I know now?  Enough to know when to keep my mouth shut.  :)

Your questions cover lots of ground.  A suggestion would be to take it one step at a time - mains then monitors.  Read read read - you're off to a good start by posting here.  I'm fairly new to these forums, joined a year ago and have only put up a few posts.  The guys seem great - this is the real deal in here.

Have a look at this thread:  https://forums.prosoundweb.com/index.php/topic,169371.0.html

Read read read.  There's theory, then there's the application of the theory via knowledge gained using theory.  For any given problem, different engineers may come up with the same solution(s), sometimes not.  Each path may yield a good result, yet subtle differences.

Kinda like practicing medicine or dog training.  The thread I referenced is a good read.
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Brian Jojade

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Re: How cabinets are measured
« Reply #2 on: December 26, 2018, 12:35:31 am »

Using measurement microphones to tune your system means that it will be tuned exactly where the mic was placed.  Different positions will mean different measurement results.  For FOH this can make it very difficult for a measurement mic to provide meaningful results unless you take measurements from several different positions and then come up with a compromise that makes everyone happy.

For monitors, it's a bit easier since you know roughly where the monitor will be compared to where the listener will be. And since there's only one listener, that's the only position that you really care about.

Now, you didn't specify which speakers you are dealing with.  Depending on the accuracy of the speaker, you may or may not be able to get decent sound out of it.  One major issue with speakers is that their response curves change between low and high volume.  If you use an EQ to adjust the level at low volume, then turn it up, your settings are meaningless.  Better speakers tend to have similar frequency response curves at more levels.  It's rare that you'll ever see that in any of the marketing materials though, which makes it pretty tough to know how they might react.

Like all things in audio it's going to come down to compromise.  Do as little as possible to the signal to make it sound as good as possible.  Rarely does the auto EQ's function end up being what you want the system to work like.  It's handy to give you an idea of what's happening, but when you see frequency bands next to each other at 20db discrepancies, that really says there's something either horribly wrong with the speakers (most aren't THAT bad) or the measurement system isn't doing what you need it to.  Learn to adjust by ear. It'll be much easier in the long run than trying to rely on tools that may or may not do the job!
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Mark Wilkinson

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Re: How cabinets are measured
« Reply #3 on: December 26, 2018, 12:37:37 pm »

New to taking measurements.I have some time this week to play around with my passive rig. Currently applying eq off ear and music source  but going to build some presets in the venue 360. My dirt backyard is ok in size. Working with REW software, berrymic, Art dual usbpre into X32rack. Iím having issues with the monitors in that donít like the sound ,unnatural. No manufacture settings available. Goal is to have a fairly smooth passive rig and eq to taste at venue. What is the best cabinet position and mic location for taking measurements for mains, subs, and monitors?

Online search was vague. Got several articles indicating Cab on ground with mic 2m away. Does this apply to all cabs? My mains are three way so on ground in upright position or laying across?

Thanks and Mery Christmasís to all

Hi Luis, I continue to struggle with the questions you ask....but I guess i've come to the conclusion that getting rid of reflections is the 'name of the speaker measurement game'.

Subs are the easiest IMO,.... sub on ground, mic on ground. 
I like the 10m / higher voltage method, but will go as close as 2m if trying to measure distortion and keep noise floor low.
Otherwise 4m is the minimum.

Mains?  I think the same technique....speaker on ground, mic on ground.  I like 10m here too, but will drop to 3-4m if need be. 
I think going closer than 3m creates too much triangulation distance/differences to align HF/VHF overlap well. 
Sometimes I lay the boxes on their side, sometimes stand them up...but either way I tilt them towards perpendicular to the mic.

Never done any monitors... that might be the one time I'd be happy with box on the ground and the mic up in the air where the talent's ear is..

I hope more folks will chime in with their techniques....
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Luis_Marquez

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Re: How cabinets are measured
« Reply #4 on: December 26, 2018, 04:13:45 pm »

Thanks for your replies.
Steve. The cabs to be measured are MI grade Carvin trx12nís, trx 153nís, and trx subs. Local bands, and church festival. Coming back after being several years out. Working on building the mix and want to get comfortable with what I have. Step up down the road. Will probably end up going powered as this has been the trend.
      I will continue read,read, read and thanks for the link. I did read it when it was first posted. Will go over it serveral time to digest. Btw wish you many more birthday cakes

Brian- That is something I did notice in walking the horizontal coverage. The response did change closer to the outer coverage. So will take multiple measurements and find a compromise.

Mark- Looks like you use 10m mic distance as reference for mains /subs. In the sm80 thread, Mr Ivan Beaver also mentioned subs on ground with mic at 10m. I remember reading somewhere that cabs were raised 12ft from the ground and measured at that height. I guess only possible If you have equipment to raise the cabs safely.
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Steven A. White

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Re: How cabinets are measured
« Reply #5 on: December 30, 2018, 02:06:40 pm »

Thanks for your replies.
Steve. The cabs to be measured are MI grade Carvin trx12nís, trx 153nís, and trx subs. Local bands, and church festival. Coming back after being several years out. Working on building the mix and want to get comfortable with what I have. Step up down the road. Will probably end up going powered as this has been the trend.
      I will continue read,read, read and thanks for the link. I did read it when it was first posted. Will go over it serveral time to digest. Btw wish you many more birthday cakes

Brian- That is something I did notice in walking the horizontal coverage. The response did change closer to the outer coverage. So will take multiple measurements and find a compromise.

Mark- Looks like you use 10m mic distance as reference for mains /subs. In the sm80 thread, Mr Ivan Beaver also mentioned subs on ground with mic at 10m. I remember reading somewhere that cabs were raised 12ft from the ground and measured at that height. I guess only possible If you have equipment to raise the cabs safely.

Ok, I kind of have a feel for what you are doing now, what you are working with.  I've been out for a while myself, and returning to pro audio.  The tools today, compared to what was out there 25-30 years ago are amazing.  I can remember going into the Troubadour on showcase night as the 2nd or 3rd band and quickly dialing in the old analog mixer that was upstairs in a cage sitting directly across from a JBL 4560/2350 horn hanging down stage center.  :)

As I stated, I now use DSP's (dbx DriveRacks & Ashly Protea's) on everything.  I got my first DriveRack ~10 years ago, set it up in my den music system, tri-amped and never looked back.

I'm currently working with an old DJ pal out in California that I built systems for back in the 80's.  He's gone from full on custom pro stuff to basic over-the-counter music store gear, which is similar to what you have in terms of setup.  Plug and play stuff.  Not knocking anything here.  Just bringing his stuff up to date and giving him some consistency and bit of "pro custom" back into his system.

What he's doing is picking up a couple of more amps and 2 Driverack PA's.  Going from a Crown XTi 4000 on his subs to an XTi 6002 as they were a bit underpowered.  He has some McCauley tops I built for him in 1989 that he's going to put back in service just to see what they will do with a DSP on them in lieu of the 18db/octave analog Ashly crossover.  1 Driverack PA2 in a rack with 3 amps (low mids, high mids, highs), setup for tops on the McCauley's.  They have a 12, 1" horn lens with JBL2425 driver, and a JBL 2404 HF driver.  The second amp rack will have it's own Driverack PA2 and a Crown XTi6002.  The top Driverack will be setup near field for the McCauley's and left alone.  The Driverack in the sub rack with the XTi6002 will be programmed and tuned for his whole system - 2 subs or 4 subs.  Then further tuned to work with various top end configurations:  The McCauley's or some powered EV 15" & EV 12" tops he has.  The only way for him to know if he likes the old rack setup or his powered tops is to use both and decide.  I'm thinking the McCauley's will win in the end as they are full active and sound better than the EV's - but he's been informed of the GIGO constant.  Garbage in = Garbage out - so, we compare using CD quality audio, not the thrashed-out MP3 crap downloaded from Youtube.

Long winded I know.  The point here is methodology.  I always setup a baseline on systems doing near field (1-2m) measurements on individual components with the DSP's and tweak all the crossover parameters and touch-up with the output channel parametric eq's, set limiters, etc.  Then, once I have a baseline on tops and subs separately, I set the system up as it will be used - tops up on tripods or stacked - however it will be used.  Then take readings @ 3-5m with the whole system setup together and work time alignment, sub crossover point and that stuff to again get a general baseline for the system.

When setup at a show, the tuning is usually pretty close and not too much correction needed, and I will use the graphic eq in the input side of the Driveracks.  For the mains anyway, then comes the monitors.  Not going to get into that right now.

Not a dbx salesman here.  As I told my pal, a used Driverack PA2 can be had for just over $250 and they are really a nice timesaver and will offer lots of cool features.  Might be worth consideration.

Establishing a consistent & solid baseline and tuning with a building block approach is the point here.  Rather than starting from scratch each time you setup.  Too easy to get completely lost, especially on a re-entry trajectory you are on.
« Last Edit: December 30, 2018, 02:12:53 pm by Steven A. White »
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Luke Geis

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Re: How cabinets are measured
« Reply #6 on: December 30, 2018, 06:13:32 pm »

Not knowing exactly how you have your system setup, I will give a few words of advice.

1. Try to measure the system as it would be as you normally set it up.

2. Measure 1 half ( or 1/3rd if going with subs on aux ) of the system at a time.

3. Keep in mind that going for a totally flat/linear response is often an effort in futility, so just focus on areas of the response that have problems. Note that large holes in the response, or commonly recurring dips and peaks may be comb filtering or reflections and cannot be fixed with EQ.

4. With monitors, I find that less is more. They are meant to be loud, not sound good. Placing the measurement mic about where the performer will be is what I do. And then I ONLY get rid of stuff that is peaking or standing out. I typically roll the lows off somewhere between 140-200hz, going for what sounds natural and NOT TOO FULL OR BOOMY. I try and not do any real corrective EQ until a problem actually arises. There is often only 1-2 frequencies that will feedback and once those are stabilized trying to go any louder is often not possible. Just because the fader is going up does not mean it is actually louder.

5. A good rule of thumb for any part of the system is that if you are using more than 6 bands of EQ, you need to stop, re-assess and see what you can do to reduce the # of cuts to keep it under 6. Once you start cutting beyond about 6 bands, you are going backward, not forwards.

I am not a huge fan of the whole baseline or pre-set EQ idea myself. Every venue and setup is just a little bit different and a linear PA in space #1 will not be linear in space #2. If there are inherent characteristics of the PA that are easily able to be heard and measured, yeah sure, nail those down, but to me measuring a PA is something done at the job site and handled on the spot. Obviously, if the PA always has a large hump around 250hz or something, that should be addressed.

The Carvin TRX stuff isn't bad by any means, but it does require proper DSP and setup to work right. My trick has been to find what works well in the system and build on that. It may not sound great, but instead of trying to make a PA something it's not, it pays to work with the strengths and build around that.
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Frank Koenig

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Re: How cabinets are measured
« Reply #7 on: December 31, 2018, 01:41:10 pm »

This is a big subject that we hammer on here periodically but I'll try to "Powerpointize" my ideas on it for reference and discussion.

*Anechoic measurements are the most useful for most purposes. They can be achieved three ways:

   1. Use a good, sufficiently large-for-the-wavelength, anechoic chamber. Few of us have this luxury.

   2. Suspend both speaker and mic in the air and window the impulse response (IR) to remove reflections (pseudo free-field).
      The frequency resolution that can be achieved this way is limited by how far away from reflecting surfaces (the ground)
      we can get.

   3. Place both speaker and mic on the ground and window the IR to remove all reflections other than that from the
      ground (ground-plane). This allows greater frequency resolution, needed at low frequencies, but fails to give accurate
      results at high frequencies where the source size becomes comparable to the wavelength (typically around 400 Hz).
     This transition frequency can be determined by comparing the pseudo free-field and ground-plane measurements
      in the vicinity of the transition.

*A frequency resolution of at least 1/6 octave is necessary for most purposes. More is better -- we can always smooth.

*All measurements must be substantially in the far field of the source. As a rough guide, 3m is good for mains, 10 m is good for individual subs (not huge sub arrays).

*It is useful to statistically combine (average, for example) measurements across angles for any source that is directional. The angular spatial sampling rate needs to be considered. 5 deg is typically sufficient for mains. Subs, that are more-or-less omnidirectional, can be measured on-axis alone with good results. If settings are being developed for a set of speakers it is prudent to combine measurements across individual units. This represents a lot of work. Statistically combining multiple phase measurements is non-trivial when the variability in measurement distance becomes comparable to the wavelength.

*It may be useful to consider the total acoustic power, integrated over all angles (as we would measure in a reverberation chamber with an RTA), in addition to the sound pressure at a set of points. As most speakers have highly variable directivity at higher frequencies, this curve will look different from the within-pattern SPL response. Without a reverberation chamber (integrating sphere) it is difficult to measure but can be approximated from multiple SPL measurements. The voicing that sounds good subjectively in a reverberant space might be a compromise between SPL and total power. I think most of us start with a flat-average SPL response as our "setting" and compensate for the rest by ear using low-Q filters.

*Once you have a good setting for a system, don't let anyone, including yourself, mess with it. This is your reference or baseline. The idiosyncrasies of different rooms should be compensated by ear (or Caterpillar). This is likely somewhat controversial and perhaps not applicable to complex fixed installations. But then we're getting into the realm of room-acoustic rather than speaker measurement.

*For portable systems in the field, measurement is useful for system health check and sub alignment, and probably not much else. Sub alignment can be done with a tape measure if you know the reference delay for the system.

Personal note: Once I started using monitors that were actually dialed more-or-less flat, "ringing out" (wringing out ;) ) for GBF pretty much became a thing of the past. Never need it outdoors and very rarely indoors.

--Frank
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Chris Grimshaw

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Re: How cabinets are measured
« Reply #8 on: January 02, 2019, 06:16:38 am »


4. With monitors, I find that less is more. They are meant to be loud, not sound good.

I find good-sounding monitors mean they don't need to be that loud for the artist to hear what they need. Clarity and volume are correlated, sure, but other factors are at play.


To the OP,
Measuring speakers can be a tricky business - that's why the people that are good at it can make money out of it!

Anyway. The key is practice, and figuring out which bit of the measurement is an artifact of the environment, and which are the products of the speaker itself. After that, you'll need to learn what to do now you understand the graphs.

I'd recommend learning the basics (and testing the measurement setup) indoors where you're not pushed for time or worried about weather or annoying the locals.
Take a speaker that you don't mind abusing a little, and do some measurements. Try these:

- Close to the cone
- Around 1' away, on and off axis
- Around 10' away, on and off axis again.

Note how each measurement has an amount of "fuzz", and that "fuzziness" generally increases as you move the mic away from the speaker. That's from reflections creeping into the measurement.

Next, EQ the low-frequency response so that, when the mic's close to the cone, it measures flat (NB - best done with sealed speakers). You might need 20dB of boost, which is fine for playing around at home but should be avoided when setting up the PA system.

Now the LF response is nice and flat, take the mic out into the room again. Measure in a few different positions in the room. Note how the once-flat low-frequency response is now anything but. Also note how the response changes according to location.

It's stuff like that which we can't really EQ out. Everyone's getting a different response, so "fixing" one might make the others worse.

Sidenote - I'm quite lucky at the moment - the living room gives a peak at around 45Hz pretty consistently. Knocking that down a bit benefits pretty much every seat. Other peaks and dips do occur and I have to live with that. There's another one at 15Hz, which is useful - means my sub runs flat to 15Hz without needing loads of power to get there.


Okay, so I'll assume you've got to the point where you've measured everything you can with a small speaker indoors. You've EQ'd it, can spot reflections vs speaker effects, etc.

Lets get the PA system out.

I'm gonna run through setting up a tri-amped system (2-way mid-high, plus sub(s)). Some of this will apply, some of it won't.

LF/MF crossover is fairly easy: the cabinets are basically omnidirectional, and there's limited scope to damage anything so long as you're sensible.
Pick a crossover point that's suitable for the cabinets in play (ie, you might run a 15" down to 70Hz to meet a 15" sub that's only reinforcing a bit, or you might run that 15" down to 120Hz if it has a couple of 18"s to do the heavy lifting).
100Hz is usually a safe bet for most cabinets, but it's something you get a feel for.

Throw an LR24 crossover at it, and see what you get. LR24 crossovers are useful in a few ways (they sum flat, offer plenty of driver protection).
Next, invert either the LF or MF band, and run the sweep again. By tweaking the delays, you'll be able to get a nice deep and symmetrical notch. Set cabinets back to normal polarity and you should get a seemless blend between the cabinets.


MF/HF crossover is more tricky.
This time, you've got to consider how much stick the compression driver/horn combo can take, as well as off-axis response.
Things to consider:
- As the wavelength approaches that of the diameter of the cone, the cone speaker will start to show narrowing directivity.
- We want the off-axis response to be smooth.
- As you go higher in frequency, cone drivers will start to have a fairly rough response. Some drivers are smoother at the top end than others.
- You don't want to drive the compression driver/horn lower than the manufacturer says is safe, unless you're doing something odd. Example - I'm running a 1" driver down to 1.6kHz, but it's only keeping up with a 6" midbass. ie, it's not gonna go that loud. If you tried to run a 1" driver down to 1.6kHz and keep up with 2x15"s, you're gonna be replacing diaphragms most gigs.
- As you move the mic around, you'll be closer to one driver and further from another. Your phase curves will move accordingly.

So, a 15" 2-way cabinet with a 60-degree horn might have a higher crossover point than the same with a 90-degree horn.

Armed with that information, you might look online and find the HF unit is fine down to 1kHz, the horn loads down to 700Hz, and the midbass driver starts getting rough at 2kHz.
That means you'll have a band of 1kHz up to a little under 2kHz to get things lined up in terms of matching the directivity of the cone and horn. Matching them up nicely will get you a nice smooth off-axis response, which is a Good Thing. Have you ever listened to a 15" 2-way box with a tiny 1" HF driver? - Even if it sounds good directly in front of the cabinet, moving a couple of steps to the side will yield a very different sound.


When it comes to EQing things, here are some general guidelines: (some are more set in stone than others - it's up to you to decide which ones are more flexible in your case)

- Avoid boosting below the port tuning frequency.
- Every 3dB of boost means the driver is receiving 2x the power in that area. 6dB = 4x power, 10dB = 10x power.
- A narrow notch in the response is rarely worth the power required to boost it to flat, and usually only occurs in one mic position anyway (see note above about making sure the EQ is beneficial in more than just one seat)
- Narrow peaks sound worse than narrow notches. If some seats get a peak and others don't, it's often best to bring the peak down and give some people a notch in the response.
- Don't worry much about >15kHz. Your HF driver may roll off at 16kHz, and be 10dB down at 20kHz. At live music volumes, nobody will notice. EQing 20kHz back to flat isn't going to be noticed, but will mean the HF driver gets that bit warmer.


Apologies for the long post. I hope some of it comes in handy.

Chris

PS - +1 on everything Frank said above. Good info there.
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Jerome Malsack

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Re: How cabinets are measured
« Reply #9 on: January 10, 2019, 10:22:18 pm »

http://carvinimages.com/manuals/76-15300b-trx2_new_11.11.2008.pdf

The 153 has a 60 degree x 40 degree horn  so the highs are very tight in the center.   mids and bass will be well spread unless your getting a power alley.

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Re: How cabinets are measured
¬ę Reply #9 on: January 10, 2019, 10:22:18 pm ¬Ľ


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