Pushing a Compression Driver past it's limits? (2414H)

I had a rather alarming experience today with my JBL 590 speakers (which use the 2414H compression driver), where I am now getting "crackling" sounds from the compression drivers at high volume levels (music). Yesterday I finally integrated a miniDSP 2x4 HD into my system, and setup a 60Hz high-pass filter for the 590s. This is because previously I felt like the 8" woofers (580J) were the "bottleneck" of the system. When the 590s are run full range, they just don't have the output necessary to properly reproduce deep bass, and the high-levels of cone excursion had a predictably detrimental effect on all of the higher frequencies that the top 8" woofer is also responsible for (everything below 1.5kHz). The high-pass filter seemed to solve that, and combined with my subs using a matching 60Hz low-pass filter, it seems to have solved the "bottleneck". But today was the first time I was able to test that new arrangement at much higher volumes. The crackling only occurs at high output levels, and is clearly coming from the compression drivers. This is occurring on both speakers at about the same time (obviously dependent on slightly differing volume levels per channel as you would expect while playing stereo content). It does not occur at lower output levels. Have I simply discovered the next "bottleneck"? Am I now pushing the compression drivers past their limits? What exactly does it sound like when you push a compression driver past it's limits? It does seem very surprising to me that I have never encountered this problem before, as it's hardly the first time that I've driven these speakers loudly. Even though the woofers have often been the bottleneck, I'm not always playing content with that much bass where that would be an issue. And certainly this would be an issue during loud movies, which is what many use these speakers for, and where bass redirection to a sub is commonplace.

Maybe ( if you're new to integrating digital devices as part of the playback chain ) it's the miniDSP overloading.

You wouldn't be the first to overload a digital front-end and wonder ( what's up? )

:)

so I don't know what is being overdriven but....as posted above,try taking your DSP out and crank it up!If it's gone then you found it (dsp). If it stays, your amp maybe to blame.Does your amp have any clip indicators?You could overdrive the speakers but I would guess as posted, it's something in your chain being overdriven. The tweeters just make it clear. They may not be what you think is overdriven.I have cranked up my 590s pretty loud with no noise. It's hard to know just how loud you're describing.I'm using a Denon avr3313ci surround to drive my all speakers in passive crossover mode.

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Originally Posted by Earl K

Maybe ( if you're new to integrating digital devices as part of the playback chain ) it's the miniDSP overloading. You wouldn't be the first to overload a digital front-end and wonder ( what's up? ) :)

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Yeah, this does sound increasingly likely. I've been looking up anything I can find about this and apparently the mini DSP has an input limit of 2V and my Yamaha C-80 preamp has 8.5V max output (with others reportedly measuring upwards of 12V at max output during real-world testing). I wasn't at max output but I was at about 2 o'clock on the volume knob so absolutely possible if not very likely that I was clipping the inputs on the mini DSP. I did have some input attenuation on the amp that the 590's are hooked up to, to match up with the other amps, which likely exacerbated the issue. That would certainly be a better reason than one involving the compression driver as a cause, and one that is fairly easily fixable.

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Originally Posted by engineerjoe

so I don't know what is being overdriven but....as posted above,try taking your DSP out and crank it up!

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Yeah, it's certainly not the first time I've run the system loud, which made it seem very confusing that I would never have heard the crackling before. https://www.youtube.com/watch?v=wq8cwl1Fy2o I didn't hear any crackling from the subs but I guess it's just the nature of clipping that it would be much less apparent below 60Hz. It really does seem increasingly likely that it's the mini DSP inputs being overloaded. I appreciate all of the input.

I echo what the other members said about removing the DSP from the system & trying again and about clip indicators. Being an SPL junkie, I won't run an amp unless it has those. Instead of that highpass filter, you could try an Ashly XR4001 to divide the signal path. When I was running my XPL200's, that's what I used to take bass below 50hz away from the XPL's. Downside to one of those is relatively low slew rate and high SNR. I tried using it with my UREI 813C's & B460 clones, but found that when compared to the BX63A, the Ashly added too much noise.

The software for the mini DSP allows me to monitor the levels on the inputs (I was not keeping an eye on this previously) and it does show that it's clipping the inputs, so it seems pretty conclusive at this point. The mini DSP has jumpers to adjust the max input voltage from 2v to 4v so I'm going to change those and go from there.

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Originally Posted by DerekTheGreat

I echo what the other members said about removing the DSP from the system & trying again

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I've already been running these speakers for a while, as I bought them a couple of years ago at this point. I already know that they work without the DSP. I was just initially wondering if I was perhaps pushing them farther than I was before because I had removed the woofers from the equation due to the high-pass filter (the woofers having previously been what limited max output, at full-range). Testing them without the DSP would be testing them full-range and I already know that works.

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Originally Posted by DerekTheGreat

and about clip indicators. Being an SPL junkie, I won't run an amp unless it has those.

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I'm pretty sure that clipping indicators on a downstream amplifier aren't going to indicate clipping when it occurs on the inputs of an upstream DSP. The amp was nowhere near it's limits; on the contrary, with the high-pass filter implemented, power requirements for those speakers would have been reduced considerably.

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Originally Posted by DerekTheGreat

Instead of that highpass filter, you could try an Ashly XR4001 to divide the signal path.

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Maybe, but having already played around with several passive-filter options, I was ready to go with something more advanced. My lower-volume testing left me very impressed with the mini DSP and what can be accomplished with Digital Signal Processing. My main goal with the mini DSP was actually to get a proper low-pass filter for my passive sealed subs as well as extend their low-frequency response. Being able to also implement a proper high-pass filter on the 590s was kind of a bonus. Every passive low-pass filter I had previously tried with the subs still let through way too much higher-frequency content to the extent that you could still hear vocals, etc, coming through the subs (at a lower volume obviously, but still). With the mini DSP, I've finally reached the point where basically nothing significantly above the low-pass filter point is coming out of the subs anymore, and there is still so much left to explore.

Harmonic distortion products are by definition an octave or more ( often much more ) than the signal that has been distorted. You thus hear them coming from the high end components of your speakers. You're clipping something, likely your power amp. If you have a subwoofer then high passing your full range speakers at the frequency the subwoofers are low passed will reduce the power required from the amp for the full range speakers but if you still run out of gas you need a bigger amp or more power capable speakers. Running the amp at clipping will end the life of your speaker drivers pretty effectively.

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Originally Posted by Chris Brown

The software for the mini DSP allows me to monitor the levels on the inputs (I was not keeping an eye on this previously) and it does show that it's clipping the inputs, so it seems pretty conclusive at this point. The mini DSP has jumpers to adjust the max input voltage from 2v to 4v so I'm going to change those and go from there. …and there is still so much left to explore.

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Sounds like you nailed it. As soon as you start adding processing you need to be aware of your gain structure. This is true with analog gear as well as digital. I imagine once you bump up the max input voltage to 4V you’ll be able to master this thing.

Keep exploring!


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Originally Posted by Riley Casey

Harmonic distortion products are by definition an octave or more ( often much more ) than the signal that has been distorted. You thus hear them coming from the high end components of your speakers. You're clipping something, likely your power amp. If you have a subwoofer then high passing your full range speakers at the frequency the subwoofers are low passed will reduce the power required from the amp for the full range speakers but if you still run out of gas you need a bigger amp or more power capable speakers. Running the amp at clipping will end the life of your speaker drivers pretty effectively.

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The amp powering the 590s is a Yamaha P2200, good for approx 350wpc into 6 ohms (the 590s are 6 ohm speakers). Pretty much zero chance that I was pushing the amp into clipping, especially after implementing the high-pass filter. Either way, it's pretty conclusive at this point that the preamp was clipping the inputs of the DSP and causing the issue, I'm just waiting for the chance to test them again at higher volumes after adjusting the inputs on the DSP from 2V to 4V. My 590s are the first speakers with compression drivers that I've ever owned. Being crossed over at 1.5kHz, they are functioning in many ways as not just a tweeter but a midrange also, being tasked with handling quite a bit of the frequency spectrum. My initial research indicated that these 2414H compression drivers only have a power rating of 35wpc, so it seemed plausible that they might have been getting pushed too hard. I don't think that's the problem anymore, but it's why I was suspicious at first.

After adjusting the jumper on the inputs of the miniDSP to 4V the problem seems to be solved. I pushed the speakers very hard tonight and never came close to clipping the inputs of the DSP. It's also pretty clear to me now that whatever the limit of the 2414H is, it's probably a limit that will never be a problem for me. With the high-pass filter enabled, the 590 does seem to retain more midrange and midbass clarity at higher output levels. Of course, this comes at the expense of adding an extra ADC and DAC into the mix. I'll have to dwell on the pros and cons of that but for now I'd say it's probably worth it.

Thanks muchos for the update!

Much Appreciated!

:)

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Originally Posted by Chris Brown

Of course, this comes at the expense of adding an extra ADC and DAC into the mix. I'll have to dwell on the pros and cons of that but for now I'd say it's probably worth it.

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I wouldn’t worry about it.

High quality DACs and ADCs will have zero audible impact on the sound. I recently compared two recordings. One was a redbook quality file and the other was the same recording that had been run through a DAC and ADC chain 8 times. Listening as carefully as I could on my very high quality system and through headphones I could not tell which recording was the version that had been run through the DAC and ADC chain.


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