Strange sub issue

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rickryan.com

rickryan.com

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Dec 9, 2009
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This past weekend, we had a photo+DJ gig. The DJ was using my speakers (he had one blow out last week). Alto TS215s subs with QSC K10 tops (in ext sub mode). This was a new venue and I ended up setting up a top over each sub with a full-range signal going to each stack. The stacks were about 12-15 feet apart and about 6 feet behind the DJ table (this was on a porch of a historic mansion). Problem was, the bass was practically non-existent. I didn't have time to help troubleshoot but he adjusted and we got thru the gig. I did look at the subs and did see signal and that they were up on volume.

I know it's just conjecture at this point but do you think it's possible/probably that it was cancellation going on? Each stack was backed up against a brick wall, so I would've thought bass would project well in that setting. I'll be using that rig at another venue this weekend, so just trying to think thru it ahead of time.
 
Did someone inadvertently press the phase/polarity switch on one of them? That would tend to have them cancel each other out ...
 
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rickryan.com said:
I run a full-range signal to the sub first, then pass-thru to the tops. The tops are put in "ext sub" mode, so they work in conjunction with the subs.
Click to expand...
I misunderstood I didn't know altos has a built in crossover and the ext sub stood for external sub, I thought it meant extended sub
 
tunes4046 said:
I misunderstood I didn't know altos has a built in crossover and the ext sub stood for external sub, I thought it meant extended sub
Click to expand...

My understanding, you pass a full-range signal to the Altos (I did the same with my Yorkies). The sub has an internal crossover which only hands the proper band to its amplifier. The output on the sub passes another full-range signal to the tops. Putting the K10s in ext sub tells those cabinets to only reproduce material above 100hz. I could do the same thing with my Driverack (or any other external crossover) but this just seems to be clean and easy and normally works very well. Steve may have nailed it and I might have bumped the reverse phase button on one of the subs. My main question was wondering if natural cancellation could have been happening because of the 12-15 foot spacing between the subs.
 
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You said another DJ had hooked into your system. Did he bring his own laptop?

Could it be that the quality of the MP3s he was playing impacted the bass response?

I notice a HUGE difference in Bass when playing through Subs when I play 128KB MP3s compared to 192 or 320K MP3 files. Also, I have played songs off of Laptop, then switch to a CD, and the Bass is much more Full. Sometimes it seems that there is as much as 80% less BASS when playing a lower quality MP3 File compared to playing the same song off of a CD.

That could be the issue. Hook up a CD Player, and play a Hip Hop Song like Yeah by Usher via CD, then play the song via MP3, and see if you notice a bass response difference in your sound system. I notice the biggest differences in Hip Hop songs.
 
DJ Ricky B said:
You said another DJ had hooked into your system. Did he bring his own laptop?

Could it be that the quality of the MP3s he was playing impacted the bass response?

I notice a HUGE difference in Bass when playing through Subs when I play 128KB MP3s compared to 192 or 320K MP3 files. Also, I have played songs off of Laptop, then switch to a CD, and the Bass is much more Full. Sometimes it seems that there is as much as 80% less BASS when playing a lower quality MP3 File compared to playing the same song off of a CD.

That could be the issue. Hook up a CD Player, and play a Hip Hop Song like Yeah by Usher via CD, then play the song via MP3, and see if you notice a bass response difference in your sound system. I notice the biggest differences in Hip Hop songs.
Click to expand...

It's possible, but I'm doubtful. He used his entire front-end; laptop/mixer. I just handed him a pair of XLR cables to plug into his mixer. The bottom end wasn't just reduced, it was just gone. It was like the subs weren't even turned on at all. Very weird and under the circumstances, I didn't have time to play with it and neither did he.
 
That seems very strange. So they were not outputting any sound at all?

Did he accidentally have his bass turned all the way down on the mixer? If the signal light on the subs was on, and the signal was going through to the speakers, I don't know how the subs were not outputting anything.
 
DJ Ricky B said:
That seems very strange. So they were not outputting any sound at all?

Did he accidentally have his bass turned all the way down on the mixer? If the signal light on the subs was on, and the signal was going through to the speakers, I don't know how the subs were not outputting anything.
Click to expand...

That's pretty much it. He had a peavey 15" full range, that he'd used for ceremony. Plugged it into the mixer and suddenly there was bottom end. Since it was a fairly small party, and already in progress, we just left it like that and got thru the gig.
 
rickryan.com said:
That's pretty much it. He had a peavey 15" full range, that he'd used for ceremony. Plugged it into the mixer and suddenly there was bottom end. Since it was a fairly small party, and already in progress, we just left it like that and got thru the gig.
Click to expand...

Maybe somehow, the connector cable in the Subs came loose from the amps to the Woofer? SO the amps were registering the signal, and passing the signal along to the speakers, but the subs themselves were not producing sound. That seems very, very unlikely though...especially on both subs.
 
rickryan.com said:
My understanding, you pass a full-range signal to the Altos (I did the same with my Yorkies). The sub has an internal crossover which only hands the proper band to its amplifier. The output on the sub passes another full-range signal to the tops. Putting the K10s in ext sub tells those cabinets to only reproduce material above 100hz. I could do the same thing with my Driverack (or any other external crossover) but this just seems to be clean and easy and normally works very well. Steve may have nailed it and I might have bumped the reverse phase button on one of the subs. My main question was wondering if natural cancellation could have been happening because of the 12-15 foot spacing between the subs.
Click to expand...

I would have left the K10's in normal mode, not ext sub mode. You were already using the Alto's internal crossover and assuming you did not push in the Output Full-Range button on the Altos. Using competing crossovers simultaneously will negatively affect the sound, but I don't think that was the reason you experienced no bass.

Having subwoofers on the Left and Right side depending on your listening area can create natural cancellations called a Power Alley, but since it sounds like you did not hear any bass, I don't think a Power Alley issue was the primary reason for that.
The “Power Alley” - Discussion & Solutions To The Troubling Interaction Of Subwoofers - ProSoundWeb
 
DJ Ricky B said:
You said another DJ had hooked into your system. Did he bring his own laptop?

Could it be that the quality of the MP3s he was playing impacted the bass response?

I notice a HUGE difference in Bass when playing through Subs when I play 128KB MP3s compared to 192 or 320K MP3 files. Also, I have played songs off of Laptop, then switch to a CD, and the Bass is much more Full. Sometimes it seems that there is as much as 80% less BASS when playing a lower quality MP3 File compared to playing the same song off of a CD.

That could be the issue. Hook up a CD Player, and play a Hip Hop Song like Yeah by Usher via CD, then play the song via MP3, and see if you notice a bass response difference in your sound system. I notice the biggest differences in Hip Hop songs.
Click to expand...

I think the biggest contributing factor you are hearing a loss of bass through a PA system when comparing a 320 kbps properly ripped mp3 song playing from a computer vs. playing the same song from a CD player is the connection used when connecting the computer to the mixer. I have a pet peeve about DJs that connect their computers to their mixer using the built in analog headphone output of their computer. You are not going to get the full dynamic frequency sound spectrum doing this. This headphone output was designed for casual headphone usage and not designed to be use for a Full PA system. They use the cheapest quality digital to analog converters, worse than a standard CD player's digital to analog converters. The best way to connect a computer to a mixer is with a direct digital connection. If you have to connect them with an anaolg connection, the next best way is to use a quality external sound card.
 
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Freddie said:
I would have left the K10's in normal mode, not ext sub mode. You were already using the Alto's internal crossover and assuming you did not push in the Output Full-Range button on the Altos. Using competing crossovers simultaneously will negatively affect the sound, but I don't think that was the reason you experienced no bass.

Having subwoofers on the Left and Right side depending on your listening area can create natural cancellations called a Power Alley, but since it sounds like you did not hear any bass, I don't think a Power Alley issue was the primary reason for that.
The “Power Alley” - Discussion & Solutions To The Troubling Interaction Of Subwoofers - ProSoundWeb
Click to expand...

If I'm not mistaken, isn't the output from the sub running a full-range signal?
 
You said you gave him XLR cables to connect to his mixer? Exactly HOW did he connect the XLRs to his system?

Did he come from balanced XLR outputs or from other auxiliary 1/4" outputs?
 
rickryan.com said:
I stand corrected. The user manual states that the frequencies above the subwoofer's crossover frequency get sent to the output. Thank you.
Click to expand...

That's how it should be. (Some systems have a switch to change that.)

These were two different systems being used together (Alt0 & QSC.) It sounds like these systems have radically different efficiency. I would expect that for any given input the QSC would overwhelm the ALTO and need to be severely trimmed.

It's also possible that the connection to his mixer was at fault, with one of the signals out of phase, both unbalanced, etc. There are a variety of things that can go wrong at the interface and cable level where the bass is the first casualty.
 
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