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Author Topic: JBL's New SRX800 Series Subs - How do they compare?  (Read 38577 times)

Steve Garris

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #30 on: September 28, 2015, 04:56:23 pm »

I am finding it very interesting that there are a number of posts on various threads here at PSW that refer to  'manipulating' DSP and configuration in order to get higher SPL on the SRX818 and 828. Surely we shouldn't have to do any of this - isn't one the main reasons for choosing powered boxes so that we don't have to overthink things and we can just plug and play (for the most part) ?
Before these SRX threads, I hadn't heard of using compression make-up gain or using both channel inputs in order to get more gain from the system. Does this seem odd to anyone else that we should even have to go there?
My understanding in the past has been that in order to balance the lows to the highs, we would simply use the level pots on the back of the units till balanced. Why is this not sufficient anymore?

For me, it is because I would have to turn my tops down to the point of having to run my board fairly deep into the red in order to get the same output. That 3db of volume I got from using both inputs made a huge difference.
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Debbie Dunkley

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #31 on: September 28, 2015, 05:18:06 pm »

For me, it is because I would have to turn my tops down to the point of having to run my board fairly deep into the red in order to get the same output. That 3db of volume I got from using both inputs made a huge difference.

I had never heard of this practice before now Steve and would never have thought of doing such a thing till I read about it here. Do you not get the levels you want from simply reducing the gain slightly on the subs to match the tops instead?
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Jamin Lynch

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #32 on: September 28, 2015, 05:45:55 pm »

For me, it is because I would have to turn my tops down to the point of having to run my board fairly deep into the red in order to get the same output. That 3db of volume I got from using both inputs made a huge difference.

So you have to turn down the tops, run the mixer in the red and squeak out every extra dB you can get from the subs so they will keep up?  :o
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Steve Garris

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #33 on: September 29, 2015, 12:05:28 am »

So you have to turn down the tops, run the mixer in the red and squeak out every extra dB you can get from the subs so they will keep up?  :o

Yes. The volume on the subs is all the way up. My tops are at their usual setting of 12 o'clock. By plugging into both inputs on the subs, I feel the system is now balanced. First gig with them is next weekend.  I'll report back here after that.
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Luke Geis

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #34 on: September 30, 2015, 01:27:50 am »

It doesn't sound like it makes sense until you use them and go " ok where is all that SPL at "?

Should we be able to get the level needed without DSP manipulation? The answer is yes you can and will, but you have to run the mixer pretty hot. Here is my findings as to why.

1. The input metering is the dbfs representation of the analog signal sent to the speaker.

2. The metered input when scaled against the output metering on the speaker is almost identical. I.E. what goes in is about what comes out. I am referring to available headroom on the input vs. the output.

3. In order to get the SPL that is indicative of a rock show, you have to be sending signal that is around -10dbfs or less of clipping. This is above unity gain on most mixers. The issue isn't so much the need to run the mixer hotter, but that the peaks can sometimes creep very close if not all the way to clipping on the speakers inputs and it's output section, as well as the mixer. 

It has something to do with the speakers input sensitivity. It is different from most powered speakers and amps. It is almost like they scaled it so that the output always matches the input in terms of headroom. This makes sense as you can look at the input metering and know how close you are to limiting and clipping. Most powered speakers simply show a clip light and produce whatever level of volume they produce. The input level knob is simply for attenuation. With the SRX you can adjust the DSP sections output level from ∞ to +12db. It has a unity gain.

So where is the breakdown? The input of the speaker shows a level from ∞ to +12db as well. So when you set the input and the master output level both to unity or 0db, there is a 12db deficiency in potential level from the speakers input. There is also a potential 12db of gain that you could add back with the output. I think this was done so you could maximize the gain structure with just about any mixer.

What most are not understanding of is that the speakers SPL output is pretty relative to its metered input and of course its metered output. So you have to be running pretty close to +16dbu if you want rock show SPL levels. This means that many mixers will be between unity and clipping and likely closer to clipping if you plan on getting close to the speakers potential output.
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Tim McCulloch

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #35 on: September 30, 2015, 08:32:06 pm »

THERE IS NO SUCH THING AS "UNITY" AS AN OPERATING LEVEL.  Kindly purge the word, as used in this context, from your vocabulary.
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Luke Geis

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #36 on: October 01, 2015, 12:35:41 am »

As an operating level no, but as a reference level yes....... The point I was making above was not that I ( or anyone else ) want to set it up so the mixer, speakers and everything else are OPERATING at their respective " UNITY " gains, but more that you will be running the mixer hotter than you're used to and it may be rather close to clipping. Unity is not the problem ( and in digital doesn't technically exist at all ), it's the lack of available headroom in the mixer once SPL is achieved.

The tricks as prescribed in other threads simply allow you to get a little more, while running both the mixer and the speaker at a safer metered level; I.E. not close to clipping.........
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David Sturzenbecher

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #37 on: October 01, 2015, 10:34:13 am »

There is one other place to adjust gain inside this SRX828SP.   It is the processing output fader.  This fader does not appear on any of the stock control panels JBL gives you.   If you create a new custom panel, then find CH1 and CH2 processing output, the first parameter listed will be the "fader" control.  It appears to allow for an additional 12 dB of gain. Just grab those parameters and drag them to your custom panel, and then launch.  The common output fader as seen in my screenshot tracks the fader on the stock panel.

Also note, there are about 500 other parameters in this "venue explorer" list that can be placed on custom panels and monitored or adjusted. Use this at your own risk...it's not my fault if you change the limiter settings and blow your stuff up.

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drew gandy

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #38 on: October 12, 2015, 12:16:41 pm »

As an operating level no, but as a reference level yes....... The point I was making above was not that I ( or anyone else ) want to set it up so the mixer, speakers and everything else are OPERATING at their respective " UNITY " gains, but more that you will be running the mixer hotter than you're used to and it may be rather close to clipping. Unity is not the problem ( and in digital doesn't technically exist at all ), it's the lack of available headroom in the mixer once SPL is achieved.

Luke I think you've got this figured out but you have an issue with terminology.  And it's partly the fault of manufacturers.  Unity, as it pertains to audio equipment, means that the device doesn't amplify or attenuate the signal at all.   The level that goes in is the level that comes out.  Unity tells us about how much 'gain' that particular stage or piece of equipment is applying to the signal.  With an audio device like a mixing console or distribution amplifier, if you set all the level controls to unity then you should be able to completely bypass the device (cable right around it) and the sound level won't change. 

+4dBu on the other hand is a reference level.  It represents approximately 1.23v RMS of signal level.  Some powered speakers may be calibrated to achieve "maximum output" with this input signal level (allowing something like 12dB or more of "headroom" on your mixer output) but other speakers may be calibrated to something else like full output at -10dBV or perhaps even +20dBu!

If we look at a power amplifier by itself (no speaker) then we can analyze the amount of gain offered.  Most pro amps are on the order of 30dB of voltage gain with their input controls turned all the way up.  It's fairly simple.  Unfortunately, a powered speaker is somewhat of a black box.  We have input circuitry, a crossover and EQ section, an amplifier and then speakers.  Very few manufacturers give us information about what is going on in these various stages.  And if they do, it's usually marketing oriented (intended to impress) and it is moistly meaningless because it's just one tiny cog in the greater machine.  The only way to really analyze the gain of this black box is to look at the amount of electrical signal going in and compare that to the SPL coming out. This can give us useful information for designing a sound system but very few manufacturers give this info.  So, to use this kind of info for comparison means we would likely have to measure every speaker we want to compare. 

Some manufacturers put some kind of scale on their powered speaker level controls that make us think that they are referenced to some kind of standard.  In my experience, this is generally not the case.  It's entirely up to the manufacturer and it seems that many err on the side of more gain rather than less. 

I'll say it out loud.  One of the main advantages (to manufacturers) of the powered speaker is that it puts the magic back in the product.  Since it's a system of itself, many parameters are obscured and it makes comparing the product based on the spec sheets alone, difficult.  Comparing from spec sheet has always been risky, especially with speakers, but with powered boxes we are removed at least another step from where we were with separates. 

The other useful parameter is how loud the black box can get before it reaches it's limit (or sounds bad).  Many manufacturers publish a number that is supposed to reflect this parameter but of course, it's a simple answer to a complex question.  Very often it is a useless column on the spec sheet.  As is always recommended, we need to measure and listen (in context if possible) to really make a comparison.  Even then we are likely to be fooled by some aspect of the system. 

Looking at the spec sheet for the JBL SRX828SP I see a spec for "Line Input Gain".  This is listed as 21dB.  I have no way to be sure about how this relates to the system as a whole but it sounds like it's supposed to be telling me the total electrical gain in the system.  21dB sounds pretty low to me, especially for what is supposed to be a haystack subwoofer.  If we look at the math...  The maximum input level is 20 dBu (7.75v).  If that is then amplified by 21dB in the amplifier circuitry we have 87v RMS.  Into an 8 ohm load we get almost 950 watts. This implies that we need about 19dBu of input to saturate the (750w) amplifier.  David's suggestion that you can possibly apply 12dB more gain buried in the dsp might be a good way to make it match up with other products!  Of course, I'm reading between the lines here. 
 
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Luke Geis

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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #39 on: October 13, 2015, 03:57:32 am »

I don't even think it's a terminology thing..................  I never really brought up unity and when I did, it was more for reference, not an operational standard. I only mention that the SRX-800 has a unity gain setting. The metering is in dbfs however and unity for digital technically doesn't exist.

The only point I am trying to make is that the SRX series will likely have most users wanting to find more SPL sooner so it matches their current operational standards. There is nothing wrong with the SRX powered line at all. The way it works is simple:

The max input before clipping is 21dbu, at which point the output of the amp will be clipping as well.

The level metering is different than most all are used to. It is in dbfs ( digital scale ) and has no relation to analog metering levels.

The SPL produced by the speaker is pretty linear to its input. The ratio of input to output makes sense, but is not akin to the way other equipment seems to work. Many are used to having the SPL needed by about the time unity gain is hit on the mixers output buss. These speakers will not start producing that same relative level until you are producing right around 16dbu. This leaves about 5-6dbu of headroom in the speaker. Many lower end mixers will be nearly out of headroom by then. In essence the output of the mixer will be close to clipping right about the time the speaker is.

The +12db available at the speakers master output is the quick and easy way to get you more SPL quicker ( by +12db of course ), but is only giving you exactly what it says. The little cheat dubbed the " make up gain technique " allow you to acquire +14-16db of gain before clipping at the same point as simply turning up the master level to +12. More for less; no more, no less.......

Forget that I ever mentioned unity. I know what it is. It is not relevant to the way these speakers operate other than for reference.





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Re: JBL's New SRX800 Series Subs - How do they compare?
« Reply #39 on: October 13, 2015, 03:57:32 am »


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