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Old 21st April 2006, 08:41 PM   #1
diyAudio Member
 
Join Date: Jul 2004
Location: Columbus, OH
Default Need some measurement help

Itís a little long, but I could really use the help

I have a pair of line arrays in my basement listening room. Iím using a DCX2496 to handle crossover duties and have it set at a Butterworth 24db/oct at 2.25khz for both the woofers and the tweeter. The sound is incredible. What I did next was purchase the Behringer ECM8000 measurement microphone, an M-Audio Mobile Pre which is an external soundcard for my laptop, and TrueRTA with the 1/24th octave resolution. I then used the Quick Sweep function in TrueRTA on each speaker to get their curve and captured this into TrueRTA. I then used the EQ built into my DCX2496 and got both speakers almost perfectly flat, all the way down to 40hz (they cross to my IB at 60hz). The before and after is absolutely astonishing. I have my wife turn the EQ on and off on the DCX2496 and I canít believe how much better the EQed setting sounds compared to the unEQed. I thought they sounded terrific before I EQed them, but now they sound better than anything Iíve ever heard in my life. Now, my questions:

Iím sure my methods of measuring and EQing my speakers arenít optimal, but the results are absolutely staggering. I did only EQ for my listening position, and I know most people recommend doing a few different spots, but Iím the only one that listens to music and since it is my spot, I figured it would be best to EQ it for that. Iíve also read that an RTA isnít optimal for measuring.

With that, how could I go about measuring the ďright wayĒ? I love the DCX2496 and couldnít imagine taking a step back to passive crossovers, and I know a lot of the measurement packages are for measuring and designing passive circuits. Yes, this is the first pair of speakers Iíve ever built and I jumped right in, built some line arrays, and got the DCX2496 because of the ease of use and all the features.

Also, Iíve read that applying anything more than 3-6db of EQ is a bad thing. Iím at work right now but I know that some of my EQ settings, mainly in the bass region, are for more than 6db. For my ribbon tweeters (Fountek JP-2.0) I didnít need to apply any EQ at all above 4khz, which is pretty nice. I think there was a small 2-3db dip around 3khz that I cleaned up with a small filter.

Well, I had a hard day at work and some of this mess probably doesnít make sense, but if you could digest it and leave me some feedback Iíd really appreciate it.

Thanks!
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Old 24th April 2006, 04:06 PM   #2
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Up for some help.
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Old 24th April 2006, 04:30 PM   #3
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Join Date: May 2004
Location: Dallas, TX
Mazeroth,

You'll get lots of differing opinions, so here's mine :

IMHO, if you are designing a passive crossover then you need to measure in an open field or remove the interactions with the room in some way in order to design a good crossover/eq/notch that will work in alot of different settings. If you are using a DCX the only thing that matters is that it sounds good in YOUR application, in YOUR room, in YOUR listening position..

I'm assuming you already time-alligned your drivers using the DCX's auto-allign function? You may want to invest in a DEQ for your equalisation since it has lot more features than the DCX's parametric EQ...

BTW: What are you using below the founteks?

I'm currently running an open baffle dipole with Fountek JP2.0s, PR170m0 midranges, and El-Pipo lineage bass drivers...

--Chris
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Old 24th April 2006, 04:38 PM   #4
sreten is offline sreten  United Kingdom
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Join Date: Nov 2003
Location: Brighton UK
Hi,

due to baffle step the minimum eq in the bass should be 6dB,
given your 6dB maximum this actually becomes 12dB in the bass.
(i.e. your speakers will drop 6dB between 1kHz and 100Hz)

You should average the EQ over a number of positions, because
you can overcompensate for an effect at one position that doesn't
occur in other positions.

Generally a flat overall room response over a number of positions
will sound more natural that response optimised for one position.
This is because overall room drive is still percieved in room decay
as well as the flatness of the direct sound from the loudspeaker.

Also note that the top end whilst usually measuring flat on axis,
when measured over a number of postions has a smooth roll off.
You should not try to correct this roll-off.

TrueRTA not optimum ? I can't see whats wrong with it, though its
generally agreed 1/3 octave resolution is enough to be effective.

/sreten.
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Old 24th April 2006, 06:31 PM   #5
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Join Date: Jul 2004
Location: Columbus, OH
DIY_newbie,

I knew the DCX had the auto-align function but totally forgot about it. I'm looking at the DCX2496 Remote program that I use to connect the DCX to my PC and nowhere do I see a way to do the auto-align. Does this have to be done on the front of the DCX? I'm at work now and can't fiddle with the DCX, but I do have the program on my work computer to mess around with once in a while. Also, I am still a speaker newb and was wondering what exaclty time-aligning buys you? This just assures that the woofers' output (2.25k and below) and the tweeter's output (2.25k and above) arrive at you at the same time, right? This, technically, does the same thing as when someone slopes the front of a speaker baffle, correct?

I do own a DEQ2496 and initially used it so I could go optical in and so I could utilize the Auto-EQ feature it had. After reading up on the Auto-EQ I found out it wasn't optimal (obviously) so I got a copy of TrueRTA, did my own measurements, and used the EQ built into the DCX instead, because I was a lot more familiar with it and all the EQ features on the DEQ are a little overwhelming to me. Aside from the parametric that both the DCX and DEQ have, which other EQ settings on the DEQ are really worth using? I like being able to visually see what the EQ is doing on my computer screen, then measuring it with TrueRTA and getting a good sense that the change I made did what I wanted. It looks like the DEQ is going to buy me the same exact thing, so why should I use it?

Oh, and below my Founteks I'm using some PE buyouts which were the Vifa JBL 4 7/8" buyouts in 6ohm flavor. 10 per side with a single Fountek. I built both speakers, with wood and finishing supplies for under $400. I can't complain

sreten,

About the overall flat room response. My listening position is generally the only place where music or movies are listened to. I never get up and walk around and listen to music because this is a dedicated room in my basement that's only used for sound. Should I still EQ for more than one position, and if so, how far apart from my listening spot and how many measurements should I make? The room is rather small (11x18) and I sit about 9 feet from the speakers so I could only see the radius of my measurements to be no more than 3-4 feet.

Thanks guys!
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Old 24th April 2006, 07:22 PM   #6
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Join Date: May 2004
Location: Dallas, TX
Mazeroth,

I believe you will need to do the auto-align from the actual DCX. Its in the "setup" menu.. You will need to hook up your microphone to the "C" input of the DCX and then run the auto-align function. It will walk you through the steps and its pretty easy

The DEQ has a realtime 1/6 octave analyzer and has more advanced parametric EQ functions than the DCX. It also has a graphical equalizer which allows you to boost/cut with a resolution of 1/3 octave. It also has a "true response" feature which smooths the graphic equalizer to make it act more like a transfer function than several parametric EQs applied seperatly...

--Chris
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