BillFitzmaurice.info

This was my son's first DJ gig, a snowflake dance at his high school. We used a pair of 3012LF loaded T-39s v-plated and wall loaded. The tops were a pair of OT-12s with the melded array. The speakers were driven with a pair of Peavey IPR 1600s plus a Behringer DEQ2496 and DCX2496 for the EQ and Crossover/Limiter. Overall the sound quality was great, far stronger bass than I was expecting. I measured the sound level at around 110 dBC running pretty much flat out. This was also the first time for the lights. Sorry about my poor video work, but I think you can get an idea of the sound clarity and bass.

Sounds and looks awesome! Applause!

That's identical to my rig except I run T30's. Usually two but four when needed.

Good review

Something sounds amiss though. Perhaps the C weighting accounts for that.
2 x 3012lf loaded T39's wall loaded (yours look to be over 20" wide) should be capable of well over 130dB flat out.
I only say this because I have 4 x 20" BP 102 loaded cabs (ie much the same total output as your pair), and outdoors (no wall loading of course, but V plated) I cruise at around 115dB, with the master faders on about -7dB. Also with a DCX DEQ combo, but different amps.

Was it noticed if the DCX limiter lights were engaging at all?
And the DDT lights on the IPR's?

You can use the DEQ to monitor SPL with a reference mike. You can also turn off weighting IIRC so you know what true SPL is..

Grant Bunter wrote: Something sounds amiss though. Perhaps the C weighting accounts for that.
2 x 3012lf loaded T39's wall loaded (yours look to be over 20" wide) should be capable of well over 130dB flat out.

I noticed that also. I use C weighting and get around 110 dB on the dance floor and the rig is not working too hard...maybe up to about 30-35 volts on songs with the deepest bass. Only a handful of times I've ever been in the +40 volt range. I'd consider full out 45-49 volts for my rig and I don't think I've ever actually sent that to the subs, but of course the amp and DCX have seen it during setup. Do you know if the limiter was engaging and if so, what voltage did limiting start?

Thanks for your feedback. You're right, the T39s are 20". I may need to re-check the DCX limiter settings but I initially set the low pass limiter to 50V for the T39s and the high pass at 35V for the OT12s. It was occasionally hitting the low limiter and I even saw one of the high limiters come once. The DDT lights were not coming on. I have measured the DDT threshold at about 54-55V unloaded on these amps.

I was measuring the sound level with an old Radio Shack SPL meter in about the middle of the room. I had forgotten about the ability to use the reference mic with the DEQ to measure the SPL. I will need to give that a try next time. I also have the little Dayton Audio calibrated mic for my phone. I could also give that a try.

Regardless of the measurement, it did sound loud enough. Since he was playing a lot of club and hip hop music, I was concerned that the 2 T39s might not be enough. But it really was plenty of bass even for this style of music. The only adjustment I made for the room was to increase the level to the OTs by about 3dB. Honestly, I was delighted with how good it sounded.

Where the measurement is made is probably the big difference. Middle of the dance floor vs. 1m from the speakers.

Sounds pretty decent to me from what the video can deliver.

If the DDT lights weren't coming on, something's wrong. A 3012 loaded T39 should be able to take everything the IPR has to offer.

Reset your limiters with the amps unloaded.

BrentEvans wrote:If the DDT lights weren't coming on, something's wrong. A 3012 loaded T39 should be able to take everything the IPR has to offer.

Reset your limiters with the amps unloaded.

If going by the DDT, you might as well delete the limiter from the picture altogether.

It's probably safe to rely on DDT. But I felt like it would be a bit safer to have the external limiter. The AbleTronics test of if the IPR 1600 showed that the DDT/clipping voltage with an 8 Ohm load was under 53V. http://www.abeltronics.co.uk/amptesting ... y_IPR-1600 see slide 17. Since these amps are both the DSP version, I could probably use the built-in crossover and eliminate the DCX altogether.

kkip wrote:It's probably safe to rely on DDT. But I felt like it would be a bit safer to have the external limiter.

That depends on the limiter. The limiters in the DCX square off the signal, which means that if you're really pushing into them, RMS power rises but volume doesn't. The DDT circuit doesn't work that way... in addition to a peak limiter, it also limits RMS current by compressing the signal.

If you have the DSP versions, you very well could go without the DCX, and your sound will probably improve.

My curiosity was definitely peaked. Fortunately the equipment is all in the basement so it was easy enough to make a few measurements. What I found is that the limiters are setup okay. I also measured the amp when DDT was just engaging. To my surprise, at least with my amp unloaded, the DDT waveform looks a whole lot like clipping. Maybe in a more dynamic situation with a load DDT would work more smoothly.

The low tests were at 63Hz and high test was at 400Hz. The DCX worked great. The waveform remained nice and smooth even when driven well into limiting. Below are a few pictures:

Thanks for those photos!

Fantastic to see screen shots of the scope and what they are showing!
Thanks for taking the time to do that for the forum

Apologies for any distraction from your review.

We all know that music is not as absolute as sine waves when it comes to output.
Still, I think perhaps you need to quantify at what frequency (assuming that your meter will measure the loudest frequency or band of frequencies) that your measurement was obtained.

Obviously, with C weighting affecting lower frequencies more than higher ones, it would certainly help to see if it was a lower frequency, but that in no way accounts for around 20db in lost output compared to theoretical maximum. You might understand if the scale was A weighting for that sort of reduction.
20dB is 4 times louder!

Of course, the main reason I have any concern is that decreased output can be symptoms of leaks or panel flex in these designs...

again, he was measuring in the middle of the dancefloor. even if he was only 4 meters away (12 feet) thats 12 db down in output.

sine143 wrote:again, he was measuring in the middle of the dancefloor. even if he was only 4 meters away (12 feet) thats 12 db down in output.

Yep, and that's still in the ballpark of 10dB down from expectation when running flat out.