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[Joseph Metoyer]

I'm new to this board.
I have a question.

I built a PA cab consisting of (2) Beyma 18LX60's & (2) Eminence Kappa-15LFA's wired in parallel to 2 ohms.
I'm powering it with a QSC PL2.4MB

Upon testing this configuration I have only been able to reach a max SPL of 105db.

According to WINISD I should be able to hit 130db+

Can anyone offer an explanation?

Thanks!

[Caleb Dick]

Sounds like the drivers are 'fighting' with each other.  Why not build a cab with 4 matching drivers?  

Caleb

[Ivan Beaver]

Joseph Metoyer wrote on Wed, 14 April 2010 23:36

I'm new to this board. I have a question. I built a PA cab consisting of (2) Beyma 18LX60's & (2) Eminence Kappa-15LFA's wired in parallel to 2 ohms. I'm powering it with a QSC PL2.4MB Upon testing this configuration I have only been able to reach a max SPL of 105db. According to WINISD I should be able to hit 130db+ Can anyone offer an explanation? Thanks!

You might have a problem with your wiring and they are not working together.

Are those drivers is seperate chambers?  If not they should be-as they are different drivers.

Or you could have a problem with the way you are measuring it.  Is your meter calibrated?  

Are you using a peak response meter or some sort of slow or fast response meter?  

Do you have any weighting on the meter?

What is your test signal?

Lots of variables.

And remember you are using a prediction program-there could be variance there-especially with different drivers.

[Scott Shaw]

Joseph, since I don't know you or how much experience you have, please let me ask a dumb question. Are you measuring the spl from 1 meter away and using a frequency within the speaker's range?

Scott, Everyone has a duh moment,Shaw

Edit: sig fix

[John Halliburton]

Also, the meter used in testing is probably "Weighted", with an "A" or "B" rating, and the difference being a roll off in the lower frequencies is introduced.  Since this looks like a bass rig to me, you might be having inaccuracies in measurements too.

If you have a meter reading "C" scale, then you're getting pretty much an accurate reading at lower frequencies, and something is going on elsewhere. As others have suggested, perhaps the wiring of all four drivers is out of polarity somewhere, causing cancellations in output between the speakers.

Best regards,

John

[Joseph Metoyer]

Thanks for the responses. Really appreciate it.

I have been testing the box with a few free iphone SPL applications. The apps have Fast and Slow sampling, "C" and "Zero" weighting, as well as a Peak reading. I stand roughly a meter away and play cd's, adjusting the volume on the mixer until the amp is approaching clipping.

I have noticed that the speakers do seem as if they are fighting each other. However, I am not sure if that is really the case and I don't know what to do about it. I am interested in hearing about how building separate chambers will reduce cancellation.

The wiring appears to be accurate. All the positives together, all the negatives together, connected to two poles on a NL4MPR jack.

I am a noise artist. I built this cabinet to fit in the backseat of my car. Lugging one big box with wheels is easier than carrying four separate boxes. The box is LOUD but I was surprised to see that it is only reaching 105db.

Thanks again!

[Art Welter]

The Iphone mic preamp clips around 105 dB, get a real meter if you want to test loud.



Separate chambers will keep the cones from modulating each other, which will clean things up and allow proper tuning for the different speakers.
Car amps often don’t deliver rated power even if you have a huge battery bank and alternator.
Make sure the voltage at the amp is not dropping below 12.6 volts or so.

Art Welter

[Bob Henley]

Joseph Metoyer wrote on Thu, 15 April 2010 11:19

I have been testing the box with a few free iphone SPL applications. The apps have Fast and Slow sampling, "C" and "Zero" weighting, as well as a Peak reading. I stand roughly a meter away and play cd's, adjusting the volume on the mixer until the amp is approaching clipping.

This might be the problem. I've heard (but can't reference, so don't take my word for it) that the iPhone mic isn't any good above 105 dB. You might be maxing out the iPhone mic and not realizing it.

I have a friend who does the noise thing. I can imagine it's pretty demanding on gear!