XMAX

[HolmeBass]

Thanks you for allaying my fears, Greenboy and Bill FitzM. And interesting to find out, Bill, that Eminence is using Klippel Analysis for Xmax. I thought that the big deal about the drivers in fEarful design was the nice high Xmax value in a light driver- so also surprised to hear that Xmax is not as crucial for bass speakers as it is for PA subs, but I suppose that makes some sense when you think about it too. Thanks to Arjank for bringing this up, I had missed the earlier threads, and to Seamonkey and other experts for chiming in. So... so we need a thread on harmonic distortion- how much is enough, and are odd-order harmonics really bad? I'll review the FFT document Greenboy introduced first. Fascinating stuff, especially for someone who's only ever done an FFT on oceanic current velocity data, with a Nyquist of 1 sec and low freqs down in, well let's just use the period- periods of up to 5 minutes!

 

[greenboy]

Arjank,

Even some time spent in non-imitative synthesis would shock you. You can also look at a lot of bass guitar waveforms in the http://www.talkbass.com/forum/f15/bass-frequency-waterfall-plots-what-they-mean-rigs-510749/ thread, in both fft and flatscaled, and a few guitar ones in Ralph Novak’s Lecture on Scale Length and Tone.

 

[greenboy]

so also surprised to hear that Xmax is not as crucial for bass speakers as it is for PA subs -

Uh, how is one to interpret that? It's important in a dedicated mid design if you want more SPL per cubic measure. I'm sure not going to choose a 6mm xmax driver if I can find a better 9mm one. It's important in a "full range" bass guitar box too. It's a tradeoff item there though, because there is no midrnage driver to help out. Better not just accept this stuff at face value without putting it in context.

 

[Sundogue]

Thanks you for allaying my fears, Greenboy and Bill FitzM. And interesting to find out, Bill, that Eminence is using Klippel Analysis for Xmax. I thought that the big deal about the drivers in fEarful design was the nice high Xmax value in a light driver- so also surprised to hear that Xmax is not as crucial for bass speakers as it is for PA subs, but I suppose that makes some sense when you think about it too. Thanks to Arjank for bringing this up, I had missed the earlier threads, and to Seamonkey and other experts for chiming in. So... so we need a thread on harmonic distortion- how much is enough, and are odd-order harmonics really bad? I'll review the FFT document Greenboy introduced first. Fascinating stuff, especially for someone who's only ever done an FFT on oceanic current velocity data, with a Nyquist of 1 sec and low freqs down in, well let's just use the period- periods of up to 5 minutes!

Xmax is still crucial for bass speakers, depending on their intended use/design. As BFM explained, most bass speakers' xmax is not above 10mm, but the 3015LF is close at 9.6mm and it's use in the fEARful designs for instance really give one a lot of tonal control where one does not have to sacrifice as much low end as that of a speaker with lower xmax. Most designs will exaggerate the low mids at the expense of low end in order to produce more volume because if a bass speaker has low xmax there is only so much you can do with it and deal with the low end in a bass cab.

Many who use fEARful cabs know they can often run without PA support entirely and still have good low end out front. In a way the 3015LF makes it possible to have bass cabs that act as their own PA. I don't think that would be completely possible without decent xmax in that speaker.

When it comes to xmax, it's kind of like the ol' "Size doesn't matter...it's knowing how to use it." Well, it's even better having more xmax and knowing how to use it. But like everything else, there are more parameters to consider than xmax alone.

 

[Arjank]

For me there is no difference between PA bass or bassguitar. For every application where you want true reproduction you need low harmonic distortion.

My main concern with some loudspeakers is their exponential increase in distortion when the voice coil starts to leave the air gap. Some really start to sound nasty, while some others still sound okay. The thing I noticed is that all the drivers that still sounded okay have shorting rings.

E.g. I have two pairs of 12" philips woofers, one pair is from the mid 70's the other pair from the early 80's. Both have the same voicecoil lenght and poleplate height. The ones from the 70's start to distort once the voice coil starts to leave the airgap partially. The 12's from the 80's stay very clear without much distortion even when pushed far beyond where the voice coil starts to leave the airgap. These 80's models have shorting rings.

 

[seamonkey]

Until you get up to a certain frequency anyway ; } ...Gotta laugh if you think saying "Horns!" and clicking your heels three times transports you to the land of audio perfection. That's why the constant push for better CD devices, truer waveguides less dependent on acoustic coupling efficiency and more interested in directivity control and accuracy and sound quality - and in recent years a lot of interest in HOM control - Higher Order Modes distortion. Google Earl Geddes (who Duke Lejeune has worked with, BTW).

Right - you still need crossovers to mids
Mids can be horns with good dispersion themselves.

 

[knuckle_head]

I know you can get odd overtones on a stringed instruments when you hit it on the "wrong" spot.
But, odd order harmonics produced by a speaker just doesn't sound good.

It doesn't sound good coming from an instrument either - inharmonicity is truly unpleasant.

 

[billfitzmaurice]

Right - you still need crossovers to mids

That's not the question here.
The issue is the creation of harmonics above the driver passband. You hear it all the time with DJs pushing subs hard, so hard that even crossed at 100 Hz or lower they're throwing out all sorts of content two octaves above that. The technical word for that content is harmonic distortion, while the DJs call it 'punch'.
We do the same thing with our woofers, with the distortion taking place in the mids. We call it 'crunch'. Even if you cross a woofer at 1kHz if you push it hard enough it will have plenty of output to 2kHz and higher. If anything long excursion woofers like the 301x LF series have far less crunch, because they take much more power before creating a lot of harmonics, not because they're being crossed over to mid drivers.

 

[greenboy]

It doesn't sound good coming from an instrument either - inharmonicity is truly unpleasant.

Guys,

Inharmonicity is NOT the same as having the full natural overtones series on tap for an instrument. Why is this getting slopped together into one stinky gopher stew along with a bunch of other non-defined glop?

And hey, "inharmonics" are BIG SPICE, for guitar, bass guitar, tuned bar percussion such as vibes, steel drums... pretty much all percussion depends on various balances of the natural overtone series and content that is outside of it.

I think you should study this stuff more, and also quit mixing it up with 2nd order, 3rd order, even order, odd order discussions, which are also being misconstrued here.

 

[HolmeBass]

Unfortunately for us, in the early part of the paper he reveals a disturbing assertion: different speaker manufacturers determine Xmax, possibly our most revered parameter, (...)

With respect to electric bass high xmax isn't problematic, as we don't use very high xmax (over 10mm) drivers anyway. Most are between 4 and 6mm, and don't present a particular problem with respect to harmonic distortion. It's HT and PA subwoofers that can exhibit very high THD, for the reasons explained by Paul Klipsch a half century ago. His cure, the folded horn, remains the way to obtain the highest possible output with the lowest distortion of any speaker alignment.
http://www.readresearch.co.uk/loudspeaker_papers/klipsch_modulation_distortion_article_3.pdf

Xmax is still crucial for bass speakers, depending on their intended use/design. As BFM explained, most bass speakers' xmax is not above 10mm, but the 3015LF is close at 9.6mm and it's use in the fEARful designs for instance really give one a lot of tonal control where one does not have to sacrifice as much low end as that of a speaker with lower xmax. Most designs will exaggerate the low mids at the expense of low end in order to produce more volume because if a bass speaker has low xmax there is only so much you can do with it and deal with the low end in a bass cab.

Many who use fEARful cabs know they can often run without PA support entirely and still have good low end out front. In a way the 3015LF makes it possible to have bass cabs that act as their own PA. I don't think that would be completely possible without decent xmax in that speaker.

When it comes to xmax, it's kind of like the ol' "Size doesn't matter...it's knowing how to use it." Well, it's even better having more xmax and knowing how to use it. But like everything else, there are more parameters to consider than xmax alone.

Well in my first post I obviously noted that Xmax was important, and I understand why. I think all I did was misinterpret BFM's comment about how large THD problems due to high Xmax are more of a concern for PA subs than bass cabinets. I'm all about a 3-way bass enclosure based on a high Xmax driver like the 3015LF or possibly the 12" variant; fEarful, Nearful, Barefaced, not sure which one I'll go with but it's near the top of my GAS list.

 

[Arjank]

The issue is the creation of harmonics above the driver passband. You hear it all the time with DJs pushing subs hard, so hard that even crossed at 100 Hz or lower they're throwing out all sorts of content two octaves above that.

This is the reason why low quality subs even crossed at 80hz can be localized.

Even if you cross a woofer at 1kHz if you push it hard enough it will have plenty of output to 2kHz and higher.

And indeed, a driver with high distortion numbers can generate frequencies that one would think are filtered out by the crossover. A crossover can not filter out harmonics thta are based on frequencies in the passband of that particular driver.

 

[knuckle_head]

Guys,

Inharmonicity is NOT the same as having the full natural overtones series on tap for an instrument. Why is this getting slopped together into one stinky gopher stew along with a bunch of other non-defined glop?

And hey, "inharmonics" are BIG SPICE, for guitar, bass guitar, tuned bar percussion such as vibes, steel drums... pretty much all percussion depends on various balances of the natural overtone series and content that is outside of it.

I think you should study this stuff more, and also quit mixing it up with 2nd order, 3rd order, even order, odd order discussions, which are also being misconstrued here.

'kay

 

[billfitzmaurice]

I think all I did was misinterpret BFM's comment about how large THD problems due to high Xmax are more of a concern for PA subs than bass cabinets.

Distortion is proportional to excursion, so if you've got a subwoofer that's running at 30mm peak to peak it will have much higher distortion than one running at 5mm peak to peak, assuming that the power applied is only that required to reach those excursions. If you want it pristine clean more low excursion drivers get the job done better than one longer excursion driver. But that's PA.
With instruments we don't care so much about being pristine clean, so we routinely push more power than required to reach xmax. When you do that distortion rises dramatically. Just right sounds sweet, too much and you fart out. That makes using long excursion drivers a trade off, as they're less likely to fart out but also not as sweet, so choose your weapon carefully.
Guitar takes it to the opposite extreme, using very short xmax drivers so that they'll get a really sweet tone with minimal power. But then idiot guitar'd players use four or eight twelves and then they can't get that sweet tone without cranking the bejesus out of their amps anyway.

 

[Arjank]

Arjank,

Even some time spent in non-imitative synthesis would shock you. You can also look at a lot of bass guitar waveforms in the http://www.talkbass.com/forum/f15/bass-frequency-waterfall-plots-what-they-mean-rigs-510749/ thread, in both fft and flatscaled, and a few guitar ones in Ralph Novak’s Lecture on Scale Length and Tone.

Interesting read, Novak's lecture is pretty clear on all the harmonic stuff on strings. I also see that the 2nd harmonic (which is sort of the 3rd order distortion with speakers) leaves a pretty big mark on the total radiated sound.
It's pretty sure this gives the "clang" to the instruments sound. With loudspeakers lots of 3rd order distortion will sound kinda "harsh".

 

[Arjank]

If you want it pristine clean more low excursion drivers get the job done better than one longer excursion driver.

I totally agree

But of course there are examples of high excursion drivers that do have low distortion even when pushed hard. But in general I totally agree.

 

[knuckle_head]

Interesting read, Novak's lecture is pretty clear on all the harmonic stuff on strings. I also see that the 2nd harmonic (which is sort of the 3rd order distortion with speakers) leaves a pretty big mark on the total radiated sound.
It's pretty sure this gives the "clang" to the instruments sound. .

Clang lives higher in the spectrum than the second or third harmonic . . .

 

[will33]

Okay.....most of this stuff is above my paygrade but I am saving links and will settle in for a good read when time allows. Will it make my stuff sound different/better than it does now? Probably not. But it will help me understand why it sounds like it does. Stuff like this is so much more useful than the typical "what's the best this for my that?" stuff. Thanks.

 

[GrowlerBox]

Okay.....most of this stuff is above my paygrade but I am saving links and will settle in for a good read when time allows. Will it make my stuff sound different/better than it does now? Probably not. But it will help me understand why it sounds like it does. Stuff like this is so much more useful than the typical "what's the best this for my that?" stuff. Thanks.

I'm with you on that, although as far as paygrade goes, I think I'm in the mailroom to your middle management. Nevertheless, it's threads like this that almost allow me to justify the time I spend on this forum. Almost.

 

[will33]

I'm with you on that, although as far as paygrade goes, I think I'm in the mailroom to your middle management.

I wouldn't be too sure about that. I know what I know from reading posts and following links posted by those who really do know.

Edit: I should add that the more you learn, the more you know how much you really don't know.

 

[fdeck]

This is a nice little description of distortion and harmonics:

Audio Amplifiers

If the distortion effect is symmetrical, then you get a series of odd harmonics. If asymmetrical, then you get a mixture of even and odd harmonics. If the clipping mechanism imposes a hard limit, then you get more higher-order harmonics.

A voice coil suspended in the pole gap is likely to be fairly symmetrical, thus it is likely to produce an odd harmonic series. It doesn't seem particularly useful to make the coil asymmetrical just to tailor the harmonic series, since this would make the driver less efficient.

'less I'm missing something.