Intermod distortion 2-way vs 3-way

[TJ Cornish]

I'm doing some long range planning of replacing my current system (EAW JFL - 2-way, dual 10" plus horn) with probably some kind of small to medium format line array. One of the biggest sound quality problems that I perceive - or at least think I perceive - with my current 2-way system, is intermod distortion. The symptom is as follows: Simple tracks are crystal clear - solo vocals for example, but when the band backing kicks in, the vocals sound a little distorted. I'm very confident that this is not a damaged speaker issue, and I'm confident that while this phenomenon gets worse with volume, I'm not anywhere close to pushing the system into non-linearity. The system sounds fine in use - this is more noticable in shop testing with well-recorded tracks.

Anyway, assuming I'm correct that I'm hearing intermod distortion , how much of a difference does the third bandpass make? Most of the choices I'm considering (RCF NX-L23A, RCF HDL-20A, Nexo S8/S12, etc.) are all 2-way boxes. Will these have similar intermod issues to my current system? Does something like the RCF TTL33-A (3-way - dual 8" acting as a woofer, single 8" midrange plus tweeters) minimize this since I'm not putting 800Hz on the same cone as 70Hz? Are the intermod issues as significant on the horn - e.g having 4K modulated by 1.2K a significant issue?

Thanks for any help in understanding this better.

 

[Ivan Beaver]

Re: Intermod distortion 2-way vs 3-way

It is real easy to get "hung up" on a single spec in audio.

Rather than thinking that either a 2 or 3 way (or 4 for that matter) is "bettter", you need to consider how well the particular design is implemented.

This involves many factors-such as the actual layout used-the physical spacing of drivers-crossover points-crossover types-and all sorts of "other things" than are needed for a good design.

As always-it is not always the tool (2 or 3 way) but rather how it is used.

And when you talk "distortion" there are all kinds of different ways to measure the same measurement-and different people do it different ways-so it gets real hard to do direct comparisoms.

Just because a particular product may have a "lower number"-does not mean that there is actually less distortion. Only for the particular measurement made.

And getting IM distortion numbers from manufacturers is another thing.

Let's say you get some numbers from manufacturer A. How do y ou know if they are good or bad? As compared to what? Do you have another similar product from another manufacturer that you can compare to?

 

[TJ Cornish]

Re: Intermod distortion 2-way vs 3-way

Thanks for the response Ivan. My question is general in nature, and I've never seen intermod specs on any of the speakers I've looked at. I am trying to understand the mechanism.

I remember a thread that Lee Patzius participated in where he played two tones through a woofer - 500 hz and 20 hz or something like that to see the interaction. I am wondering if generally there is an advantage in a well-designed 3-way speaker compared to a well-designed 2-way speaker where the smaller band passes mean less interaction between frequency extremes, leading to less objectionable distortion. I am aware that there are trade offs such as phase issues due to relative driver placement, etc.

 

[Loren Jones]

Re: Intermod distortion 2-way vs 3-way

Dave Rat - IM distortion in monitor wedges - YouTube

This video with Dave Rat demonstrates what you are talking about with some two way monitor wedges. You can really hear the difference in his voice when he adds the LF tone and talks over it. There is another video of him doing a similar demo with just a single woofer as well. So it seems that the effect you are hearing is real and it would certainly make sense that taking all that diaphragm movement from LF reproduction and giving it to a dedicated LF driver would really add some theoretical advantage in clarity for the mids. But what to I know....

Loren Jones

 

[Ivan Beaver]

Re: Intermod distortion 2-way vs 3-way

Something else to consider. Along the lines of "getting hung up on one spec".

Yes there will be some interaction between differnet freq-WITH ANYTHING! But how big a deal is that-as compared to a good phase response? Or freq extension-or any number of other "specs".

Consider also that doing a 3 way PROPERLY is a lot harder than a 2 way. So theoretically if the 3 way has the "potential" for less IM distortion-is that more important than having a "not so good" alignment between the different passbands to achive a more multiway loudspeaker?

Of course if everything is done "to perfection", THEN and only THEN-can we start to say that one aspect is better than another-in a particular "way" loudspeaker.

But since we live in the real world-and our loudspeakers are far from perfect-there are a lot of other issue that come into play-or at least must also be considered-before a general comment can be made.

I would take a well designed/implemented 2 way over a poorly designed/implemented 3 way anyday.

However-as a general rule- the more bands you can "splitup" the signal into-the better. This is for several reasons. First each device is not trying to cover a wide range of freq-so it can be more optimized for the particular band it is trying to do-there will generally be less heating on each individual component-becuase there is less going to it.

HOWEVER-also consider this. Let's take 2 sources-lets say completely different sources-say 2 trumpets-yes the kind you blow into. Would you agree that they are seperate- and what happens in one should not affect the other?

Now there are all kinds of various freq/notes that can be played (such as like demonstrated with a tone and a voice through a single monitor). When you get "the right" combinations-you will hear all sorts of "beat freq" and "harmonics" and such. NEITHER of which is being played by either instrument.

In fact look at simply tuning a guitar. How do you do it? You get one string right-then you play the same note on another string and listen to the "beats". when you don't hear them-it is in tune. If it is way out of tune- you hear a much faster beat than when you are close.

The strings are seperate-but the SOUNDS are combining to produce the other tones-ie distortion. If you consider distortion something that is not in the origional signal.

As with many things-it is real easy to start going down one path-and it making proper sense-only to realize later that the particular path has "issues" that may not seem real clear at first.

I have chased a lot of "rabbits" in my day-only to come up empty handed.

HOWEVER-if you learn something from chasing those rabbits-THEN the effort has not been wasted.

It is also real easy to get "swayed" from reality-especially in this business.

There are "demos" done all the time that attempt to "pove something". And they can appear to be very effective-but often the thing that is actually "proved" is completely different than what the person conducting the demo is actually saying or what the viewer "wants" proved.

I remember awhile back I did a side by side with an existing system. It was clear that the system I brought in was much better. There was one guy who simply did not want to have my system go in. So he tried-and tried-and tried to adjust hte house eq to get the current system to sound better-or like mine.

At the end of the night he said "well it really wasn't fair-your system sounded a lot better". Somehow I THOUGHT that was the idea.

But he was wanting both systems to "sound the same" yet be able to choose (from some other method that he would probably come up with) which one sounded better? OK I'm confused now.

But he was just grasping for any "excuse" he could come up with.

Our system ended up being installed.

Sorry to rant.

 

[Mark DeArman]

Re: Intermod distortion 2-way vs 3-way

Yes there will be some interaction between differnet freq-WITH ANYTHING! But how big a deal is that-as compared to a good phase response?

Well phase response is a global quantity of a linear measurement. It doesn't really have anything to do with non-linear behavior. I have found that a typical loudspeaker can be broken down into at least 5 mono components in a two way system.

Next Thoughts on the Thread:
Lets say our speaker system is properly built. The source drivers are at distances consistent with their cross-over frequencies. Wont a 3-way, 4-way system suffer the same type distortions, although not identical, to a two-way system?

Other Thoughts on speaker designs:
This brings up another thought I have been having about Coax boxes of late. Is the distortion caused by putting a fixed horn in front of a cone loudspeaker better than the distortion caused by the cone working as the horn/wave-guide? Trade-offs abound in this area of design.

As for the two-way+ cabinet; A simple experiment to be done.... Power one of the drivers and measure the voltage generated by the other drivers in a cabinet. There is no real damping provided beyond resonance so this should be a good indicator of how much pressure is coupling to the other drivers.

Any other thoughts on that? Anyone want to comment on non-linear loudspeaker measurements? I do have a tool I have made recently, never used yet for any speakers, which I will post later. It's not dependent on the input being a frequency response derived by linear methods. In fact the best input would be a linear sweep which would show the difference from linear IF. I'll put the pictures here.

 

[Ivan Beaver]

Re: Intermod distortion 2-way vs 3-way

As for the two-way+ cabinet; A simple experiment to be done.... Power one of the drivers and measure the voltage generated by the other drivers in a cabinet. There is no real damping provided beyond resonance so this should be a good indicator of how much pressure is coupling to the other drivers.

.

That is one of those "experiments that proves NOTHING.

Let's take 2 speakers-one is playing and another (in a seperate cabinet) is not playing and a physical distance away.. Now measure the voltage at the terminals of the one that is not playing. You will be able to read a voltage-assuming the loudspeaker is not hooked to anything.

The other loudspeaker is simply acting like a microphone. The louder the source volume in the room-the more the voltage will be.

I have actually see loudspeakers that have a power meter in them-make the meter light up-even though the speaker was not hooked to anything. When another loudspeaker is playing. The drivers inside the cabinet are simply acting as a mic-and then driving the meter circuitry.

ANd in the REAL world-a driver is not unterminated. It is either hooked up to a crossover or an amplifier-or both.

This will provide a very low impedance load to the driver.

So hook it up the way it would be used in the real world-and see what voltage you read.

And it would not matter if it is a coax or seperate components-the sound from the other driver would still get into other loudspeakers

 

[John Roberts]

Re: Intermod distortion 2-way vs 3-way

In an amusing related story I recall an early Crown class D amp that would literally shut off it's output stage, if there was no audio input. The sensing circuit was so sensitive it could be fooled into thinking there was signal if a loud noise in the room generated a voltage from the speaker.

This was rather unexpected as speakers are generally terminated with a very low impedance from conventional amps. I suspect this was a quirk of how the Crown amp was configured at idle that left the speaker floating or terminated with a high impedance.

JR

 

[Frank Koenig]

Re: Intermod distortion 2-way vs 3-way

Here's a classic paper by Paul Klipsch on the subject. I haven't heard much discussion on the relevance of FM (Doppler) distortion in recent years but interesting reading in any case.

http://www.audioweb.cz/down/modulation-distortion-in-loudspeakers-1-3.pdf

 

[Mark DeArman]

Re: Intermod distortion 2-way vs 3-way

That is one of those "experiments that proves NOTHING.

Haha, man I must have been really drinking when I wrote that. You're completely right. Drivers only vibrate near resonance or high impedance when they are "shorted" ie. connected to an amplifier. The real experiment is to measure the cone motion.

And it would not matter if it is a coax or seperate components-the sound from the other driver would still get into other loudspeakers

Well that wasn't what I was wondering about regarding coaxes. It's not really about sound getting into the other components. It's about whether the cone moving effects the HF more than the horn body effects the LF-MF from the speaker.

More in regards to my tool photos. It is actually pretty neat. If the system is linear you should be able to slide all of the pulses together on the 3d graph with all-pass filters, and when you do that, the system should be minimum phase and linear phase. If you can't slide them together then something else is at play. No FFTs involved although it does agree pretty well with a spectrogram and WVD. It's just not showing Fourier 'frequency' on the y-axis.

 

[Peter Morris]

Re: Intermod distortion 2-way vs 3-way

I'm doing some long range planning of replacing my current system (EAW JFL - 2-way, dual 10" plus horn) with probably some kind of small to medium format line array. One of the biggest sound quality problems that I perceive - or at least think I perceive - with my current 2-way system, is intermod distortion. The symptom is as follows: Simple tracks are crystal clear - solo vocals for example, but when the band backing kicks in, the vocals sound a little distorted. I'm very confident that this is not a damaged speaker issue, and I'm confident that while this phenomenon gets worse with volume, I'm not anywhere close to pushing the system into non-linearity. The system sounds fine in use - this is more noticable in shop testing with well-recorded tracks.

Anyway, assuming I'm correct that I'm hearing intermod distortion , how much of a difference does the third bandpass make? Most of the choices I'm considering (RCF NX-L23A, RCF HDL-20A, Nexo S8/S12, etc.) are all 2-way boxes. Will these have similar intermod issues to my current system? Does something like the RCF TTL33-A (3-way - dual 8" acting as a woofer, single 8" midrange plus tweeters) minimize this since I'm not putting 800Hz on the same cone as 70Hz? Are the intermod issues as significant on the horn - e.g having 4K modulated by 1.2K a significant issue?

Thanks for any help in understanding this better.

I don’t think your problem is intermod distortion. There is nothing in the design of the JFL210’s that would make it any worse than any other speaker in its class….and there are plenty of boxes that sound great.

The JFL 210 sounds Ok with normal processing but sounds very good on a UX8800. What processing are you using?

If sound quality is your only issue, I don’t think you would notice much of an improvement with any of the boxes you listed compared to a Gunness Focused JFL 210, in fact, I would expect some of them to be worse.

The TT33a is a very good box and sounds better than the NX-L23a, but won’t pole mount like the NX. I have not heard the HDL-20A, but from what I’m told it’s ordinary, very “rock-n-roll” type of sound quality.

If you want to step up to “real” mid size line array I would check out some of the newer boxes that have been release in the last couple of years – the “new generation” of boxes sounds noticeably better that some of the older boxes.

I had a very quick listen to the new d&b V series, it sounds fantastic, throws very well and makes a lot of SPL as does Turbosound Flex (3-way with lake processing). FWIW, I have not been that impressed the Kara, but I may have heard it on bad day.

If you don’t need to satisfy a rider and want a good ROI, check out db Technologies T12, you will be amassed! If you want something smaller check out JBls new 4886, sounds great and has a huge output for a tiny box.

 

[TJ Cornish]

Re: Intermod distortion 2-way vs 3-way

Thanks for the reply Peter. I do use a UX8800 in focus mode. I'm generally happy with the performance of the JFL system, but the scope of my potential gigs has expanded. I originally bought the JFLs to do up to 600 people indoors - and that of moderate volume corporate stuff. I've expanded into somewhat louder youth conferences that have the potential to be 750+. I'm already borrowing subs to do these larger shows, and am hoping to make a sub purchase decision with a new main system in mind so they will work together.

What's attractive about the NX-L23A is that it's basically what I have with variable angle capability, and therefore some scale, without giving up the portability I'm used to. I'm struggling with the abominable software and less than awesome technical info I've been able to get out of RCF, though I'm encouraged by the reports of the several folks on the forum that have them - particularly David and Hal who moved up from the same JFLs that I'm using to the NX-L23's.

I think I've eliminated the HDL-20 as I've heard several reports of "not really better than the NX-L23 and some coloration you have to work around", not to mention the lack of pole mounting.

The DB Tech T12 is definitely in the running, as any show that would have a real rider would be out of my league and/or would come with a budget to rent the box du jour.

I'm in the classic situation where I need a little bit of scale, but also don't want to get something so big that it's too cumbersome to take out for the majority of my shows which are sub 500 people. The T12 is on the line for that since there's no pole mounting option, and Genies are out of the question for cargo van gigs. I'm told that the T4 pole mount physically connects to the T12, and can be used in a questionable fashion with some kind of strap to hold the back of the box down, but that's a little sketchy.

I'm still interested in the 4886s, as they have the brand name and the support behind them, but they lack the "new generation-ness" in that they require external power. Also, they're shorter than the T12s so it takes more of them to get the same line length and the benefits of pattern control. Pole mounting the 4886 is easy, and that coupled with the 36lb weight is a big plus.

My closest partner in the city is a Nexo shop so cross-renting opportunities abound, but the S8 is a little small for me, and the S12 is more expensive and pretty heavy.

I thnk d&b and Turbosound are out of my price range, and I really do need to be careful if at all possible to keep the boxes sized for 250 - 1000 people, rather than larger stuff that's too big for most of my work.

My dream box would be the size of the T12, great sound quality, built-in amplification and DSP, but pole mountable, and with a sticker that either says Nexo or JBL on it, for the price of the Vertec 4886, and with software that actually gives believable results.

I have some time before I need to pull the trigger and in the meantime am trying to fill in a few of the MANY holes in my acoustical knowledge, so I'm sure I'll have more questions.

Thanks for all the info so far. Any and all thoughts are appreciated, including any names of the nearest therapists that specialize in my flavor of insanity.

 

[TJ Cornish]

Re: Intermod distortion 2-way vs 3-way

One other question on the T12. In the software, virtually any configuration I put into the system leaves the array flat, except for possibly the last box, which is either tilted down all the way, or is flat like the rest of the array. Is this a limitation of the software, or is it really best to run the T12s flat? I've spent a number of hours in various other calculators I've played with, and in all cases, coverage is improved with splaying.

Also, the software indicates pretty incredible pattern control for the T12s all the way down to 125Hz for a 5 box hang. This seems improbable. Playing with 4887s in the JBL calc which are approximately the same height give a lot more off axis lobing, and it takes like 18 boxes of 4889 to make the graph look like the T12 plot. Is it magic, or crappy software?

 

[Peter Morris]

Re: Intermod distortion 2-way vs 3-way

One other question on the T12. In the software, virtually any configuration I put into the system leaves the array flat, except for possibly the last box, which is either tilted down all the way, or is flat like the rest of the array. Is this a limitation of the software, or is it really best to run the T12s flat? I've spent a number of hours in various other calculators I've played with, and in all cases, coverage is improved with splaying.

Also, the software indicates pretty incredible pattern control for the T12s all the way down to 125Hz for a 5 box hang. This seems improbable. Playing with 4887s in the JBL calc which are approximately the same height give a lot more off axis lobing, and it takes like 18 boxes of 4889 to make the graph look like the T12 plot. Is it magic, or crappy software?

The JFL210 / UX8800 I think will sound better than a T4, but the T4 is much more flexible and scalable.

The T12 sounds much better, especially at high SPLs than a T4. I would suggest as a rough guide 1 x T12 = 2 perhaps almost 3 x T4’s in output.

For our non-rider stuff I have both T4s and T12s. I use the T12s much more often than T4s. The customers always comment on the sound quality of the T12s.

Like you I could not get the db Technologies array software to work correctly – I think there is an error in the latest release … BUT you can also use Ease Focus 2 and it will work perfectly provided you do not want to combine T12s & T4s. I would suggest you try Ease Focus 2 (excellent and accurate software) and compare the results to a few other boxes. … you will be surprised.

FWIW I have build heavy duty stands for 2 a side T12s … it works fine, but more often than not, I just put the subs on the stage with 2 or 3 x T12s on top. For large shows we use a winch up tower or a 4 meter high Penn fly frame…

 

[TJ Cornish]

Re: Intermod distortion 2-way vs 3-way

I'd love to have a copy of Ease Focus, but the $5K price tag puts it out of consideration. The crappy software of the 2nd tier manufacturers really is offputting, and that alone might force me to stick to the usual suspects. Do you have a picture of your stand setup for the T12s? I'd be curious to see that.

 

[Peter Morris]

Re: Intermod distortion 2-way vs 3-way

I'd love to have a copy of Ease Focus, but the $5K price tag puts it out of consideration. The crappy software of the 2nd tier manufacturers really is offputting, and that alone might force me to stick to the usual suspects. Do you have a picture of your stand setup for the T12s? I'd be curious to see that.

Ease Focus 2 is free ... Downloads - EASE Focus - Generic Aiming and Acoustic Modeling Software
and the GLL file is here :

dB TECHNOLOGIES: Active Speakers DVA DVA T12 Software

Here is a couple of T4 and T12 photos and ease focus plots (one at 12K5 and another at 1K to about 300ft) .... I will try to take a picture of the other frames tomorrow if I have time.

 

[Phil Graham]

Re: Intermod distortion 2-way vs 3-way

I'm doing some long range planning of replacing my current system (EAW JFL - 2-way, dual 10" plus horn) with probably some kind of small to medium format line array. One of the biggest sound quality problems that I perceive - or at least think I perceive - with my current 2-way system, is intermod distortion. The symptom is as follows: Simple tracks are crystal clear - solo vocals for example, but when the band backing kicks in, the vocals sound a little distorted. I'm very confident that this is not a damaged speaker issue, and I'm confident that while this phenomenon gets worse with volume, I'm not anywhere close to pushing the system into non-linearity. The system sounds fine in use - this is more noticable in shop testing with well-recorded tracks.

TJ,

My guess is that what you are hearing is inherent in the tracks. Once you learn to listen to the distinctives of IM distortion that are generated from studio limiting, it will drive you crazy.

Some of what you are hearing is the difference in power response of the loudspeaker in the vocal range vs. the wider bandwidth of the overall track. The low and low mid energy is interacting more directly with the listening environment. Further, your ears experience noise masking effects (at the foundation of all perceptual coding) on the wider bandwidth track.

There is also Doppler distortion, but it is not the same as IM. A three way design can improve Doppler distortion, as the excursion of the midrange driver is lower.

IM specifically, could be lower with a three way design, but moving to a three way is no guarantee that the overall IM will be reduced. One thing that will change in a three way design is the range of frequencies where you can see IM products from each transducer.

 

[Mark DeArman]

Re: Intermod distortion 2-way vs 3-way

There is also Doppler distortion, but it is not the same as IM. A three way design can improve Doppler distortion, as the excursion of the midrange driver is lower.

Isn't this an over-classification of IF and Amplitude variation? This is why I have wondered about alternative methods. I have not spent enough time working with it, but I'm wondering if my local program as apposed to global Fourier based methods might lend some insights. Wouldn't the ideal loudspeaker produce a linear T-IF curve if presented with a linear T-IF stimulus? There is no guaranteeing that a perfect speaker produce a perfect Fourier Frequency vs, Amplitude/phase curve?

 

[Darren Scaresbrook]

Re: Intermod distortion 2-way vs 3-way

The DB Tech T12 is definitely in the running, as any show that would have a real rider would be out of my league and/or would come with a budget to rent the box du jour.

I'm in the classic situation where I need a little bit of scale, but also don't want to get something so big that it's too cumbersome to take out for the majority of my shows which are sub 500 people. The T12 is on the line for that since there's no pole mounting option, and Genies are out of the question for cargo van gigs. I'm told that the T4 pole mount physically connects to the T12, and can be used in a questionable fashion with some kind of strap to hold the back of the box down, but that's a little sketchy.


My dream box would be the size of the T12, great sound quality, built-in amplification and DSP, but pole mountable, and with a sticker that either says Nexo or JBL on it, for the price of the Vertec 4886, and with software that actually gives believable results.

Hi TJ,

The T12's should go on the pole mounts just as the T4's do. No "strap" of any kind should be required.

Easefocus 2 is a free download and can model T4's, T12's and arrays combining both elements in the same hang/stack. The db software is, I think, a work in progress. Easefocus 2 is definitely the way to go. db have the .gll files for download on the website.

Two T12's on a double 18" is a potent little van sized rig! As much as it's difficult for some people to admit, they really are up with the best in terms of sound quality.

Darren

 

[Peter Morris]

Re: Intermod distortion 2-way vs 3-way

Hi TJ,

FWIW here are some comparison plots that show IMD in 2, 3 and 4 way systems.
Intermodulation Distortion

Here is a picture of the stands I made for 2 x T12s or 4 x T4s – it’s basically a stronger version of db’s pole mount system with 3 additional legs to reduce the load on the bass speaker's pole mount.

@ Darren - thanks, after reading your post I checked db’s website for updates and there is a new GLL file that combines both T12s & t4s in the same array. ~~:smile: