Crossover question

[will33]

aha!

so "Xmax" is how far the cone can be thrown and still sound clean, and "Xmech" is where it starts to get physically torn apart. is that the same as "Xlim"?

Yes, xmech and xlim are the same thing, the physical mechanical limit.

Xmax is the distance it can move before it starts to go "non-linear". It doesn't reproduce all the frequencies evenly. At that point it can't make any more bass, mids and highs can still get louder. Audible distortion sets in. If this distortion sounds nice, you call it "cone cry", if it sounds bad, you call it "farting". Both are the result of pushing the speaker past it's limits. Guitar speakers have this designed into them on purpose.

 

[Joe Louvar]

Wow this is great, I’m not sure what the answer to the question (Anthony’s distortion vs. BFM’s clipping - are they both talking about the same thing or something different) is for sure yet and I’m learning a lot so I really like this but is there an easy “yes/no” answer to the question?

 

[billfitzmaurice]

the area under the power curve for a square wave (very hard clipping looks very much like a square wave) is twice that for a sine wave of identical peak amplitude.

True, and that spells death for tweeters and the occasional midrange. But when you take that waveform and send it though an inductor, ie., a woofer voice coil, a goodly percentage of the harmonic content responsible for filling the area under the power curve is filtered out. The proponents of the under-powering myth love to point at a square wave trace on an oscilloscope as evidence in support of their arguments. But in the real world no woofer ever actually sees a true square wave, nor anything even approaching it.

 

[Joe Louvar]

But when you take that waveform and send it though an inductor, ie., a woofer voice coil

Ok, that helped. Now I understand. The coil acts as an inductor rather than a resistor. Cool - and that gives me some ideas to play around with.

But I’m still waiting to read if the distortion and clipping referred to by BFM and Anthony are absolutely one and the same or different? And please remember this in reference to a woofer only and not a tweeter - thanks.

Also, I want to thank everyone for this adult type discussion so this thread doesn’t get closed - thank you.

NOTE: Chef, if a troll jumps in please give them their own room instead of closing this thread - please, thank you.

With that said, I’m on the sidelines ~

 

[agedhorse]

Ok, that helped. Now I understand. The coil acts as an inductor rather than a resistor. Cool - and that gives me some ideas to play around with.[\quote]

This is not entirely true, though it is partly true. Here's why... an inductor is comprised of both a resistive and inductive component, and in the case of a speaker VC, the resistive component in the range of the bandwidth that we are talking about, is generally the dominant factor overall. The contribution for the inductive portion is going to equal the resistive portion beginnning around 1000Hz (will vary with driver electromagnetic circuit). This means that a clipped signal of say 100Hz will have most of it's harmonic energy fall below the point where the inductive portion begins to dominate. This is not a simple concept, nor is it totally black and white.

But I’m still waiting to read if the distortion and clipping referred to by BFM and Anthony are absolutely one and the same or different? And please remember this in reference to a woofer only and not a tweeter - thanks.

IMO, yes it is.

Also, I want to thank everyone for this adult type discussion so this thread doesn’t get closed - thank you.

NOTE: Chef, if a troll jumps in please give them their own room instead of closing this thread - please, thank you.

With that said, I’m on the sidelines ~

I second this request.

 

[agedhorse]

Yes, xmech and xlim are the same thing, the physical mechanical limit.

Xmax is the distance it can move before it starts to go "non-linear". It doesn't reproduce all the frequencies evenly. At that point it can't make any more bass, mids and highs can still get louder. Audible distortion sets in. If this distortion sounds nice, you call it "cone cry", if it sounds bad, you call it "farting". Both are the result of pushing the speaker past it's limits. Guitar speakers have this designed into them on purpose.

Let's discuss this a little further...

Xmax is a number that represents when the speaker has exceeded some threshold of non-linearity. While this seems on the surface to be a clear-cut concept, in fact it's just full of all kinds of subtle gray areas.

The way that a speaker enters this non-linear reigon can be greatly affected by the design of the magnetic field and the shape of the field as it moves away from the edges of the magnetic gap. In fact a lot of effort has been placed in how gracefully this field interacts with the voice coil under high excursion conditions and can improve the real world (mechanical) power handling of a speaker that may be driven beyond what would be considered a classical Xmax threshold. In fact, this is one area where power compression due to a well designed (graceful) magnetic field fringe can be part of a speaker's favorable voicing and add to the "feel" of the amp.

The easy part is designing the linear part of any system's response, be it bass pickups, preamps, power amps or speakers. The harder, and often more significant part ofthe design process is manahing the handoff to the non-linear regions which is where the real world applications often end up on stage.

Just some food for though from somebody who has spent a good part of my career studying and designing around these issues.

 

[will33]

Let's discuss this a little further...

Xmax is a number that represents when the speaker has exceeded some threshold of non-linearity. While this seems on the surface to be a clear-cut concept, in fact it's just full of all kinds of subtle gray areas.

The way that a speaker enters this non-linear reigon can be greatly affected by the design of the magnetic field and the shape of the field as it moves away from the edges of the magnetic gap. In fact a lot of effort has been placed in how gracefully this field interacts with the voice coil under high excursion conditions and can improve the real world (mechanical) power handling of a speaker that may be driven beyond what would be considered a classical Xmax threshold. In fact, this is one area where power compression due to a well designed (graceful) magnetic field fringe can be part of a speaker's favorable voicing and add to the "feel" of the amp.

The easy part is designing the linear part of any system's response, be it bass pickups, preamps, power amps or speakers. The harder, and often more significant part ofthe design process is manahing the handoff to the non-linear regions which is where the real world applications often end up on stage.

Just some food for though from somebody who has spent a good part of my career studying and designing around these issues.

Thanks.

I partly understand the grey area/transition and you certainly can hear it when pushing the speaker further and further, it's not a "now it's there/now it's not" kinda thing at all. I can only imagine the headaches designing for that knowing your product is going to get pushed past this point on a routine basis.


@ JoeLouvar- I think some of us may be getting confused in the technical vocabulary. An engineer can correct any of this if it's wrong but--

To the engineer, distortion is anything coming out the back of the amp that isn't the same as what's going in the front. The musician says distortion to describe something other than clean tone.

To the engineer, clipping has to do with looking at the wave form on a scope. A clean waveform looks like camel humps. When the amp gets pushed beyond that point, the tops and bottom of those humps get clipped off..."clipping". The musician says clipping when the little red light on the amp flashes or when they hear a "distorted" sound that isn't pleasing to the ear.

The engineering prowess comes in managing all this stuff, making it sound nice and keeping the gear reliable and not letting it burn itself up.


Wwaaayyy oversimplified I know. Just that when we say distortion or clipping and when an engineer uses those terms, we may not be talking about the same thing.

 

[will33]

Just to add a little to agedhorses point on xmax. When you hear musicians say a cab is "power hungry", or you have to turn it up to the "sweet spot", or if you send it X amount of power and it really "opens up" or has "character". What they're doing is finding the nice sounding spot in that non-linear grey area that was designed in there.

Just trying to correlate some abstract musician type terms here to the hard number/design end of things.

 

[Windreaper]

The way that a speaker enters this non-linear reigon can be greatly affected by the design of the magnetic field and the shape of the field as it moves away from the edges of the magnetic gap. In fact a lot of effort has been placed in how gracefully this field interacts with the voice coil under high excursion conditions and can improve the real world (mechanical) power handling of a speaker that may be driven beyond what would be considered a classical Xmax threshold. In fact, this is one area where power compression due to a well designed (graceful) magnetic field fringe can be part of a speaker's favorable voicing and add to the "feel" of the amp.

Now this is actually interesting. Not directly related but I have been toying around with some ribbon designs as it recently dawned to me that you can actually build one with decent sensitivity (probably in the 90dB+ range if done right) using neodymium magnets (would be kind of cool to make a small 2-way bass/instrument cab using the 8" B&C 8BG51 into a DIY corrugated ribbon, probably giving it a try next year). I have only done simulations so far but it is kind of interesting how suitable air gaps and ferrous materials can influence the field and in best cases make it a little smoother. I guess this is about hundred times more difficult with regular piston drivers as you have the VC moving violently inside the gap. I am actually interested in how engineers manage the magnetic field distortion. Is there a resource you can recommend?

@will33

I know, have to be careful with using layman terms when discussing with engineer types like Bill and agedhorse, lots of room for misunderstandings .

 

[Joe Louvar]

Thank you Bill and agedhorse.

Will - I understand that however IMHO I believe the distortion and clipping referred to in this discussion by both Anthony and Bill are the same - and thank you Will. Anyway, this thread has cleared up something’s for me so I’m back on the sideline - reading and learning.

 

[Windreaper]

Just to add a little to agedhorses point on xmax. When you hear musicians say a cab is "power hungry", or you have to turn it up to the "sweet spot", or if you send it X amount of power and it really "opens up" or has "character". What they're doing is finding the nice sounding spot in that non-linear grey area that was designed in there.

Just trying to correlate some abstract musician type terms here to the hard number/design end of things.

Let us not forget cone materials, correct me if I'm wrong here. Paper (made of unpressed pulp) is relatively acoustically inert (or well damped) and exhibits mostly low order (especially 2nd order which is considered kind of musical) distortion in the low/mid range without nasty high Q spikes. In other words should sound pretty nice.

Some people like aluminium cones which tend to be stiffer and less damped resulting in increased amounts of high order distortion, often in the high mid range which can be perceived as harshness or detail depending on the listener. Why people like rigid cones in midbass drivers beats me. I see them a lot in car subs which is ok I suppose as the resonances can be filtered out easier.

 

[will33]

Let us not forget cone materials, correct me if I'm wrong here. Paper (made of unpressed pulp) is relatively acoustically inert (or well damped) and exhibits mostly low order (especially 2nd order which is considered kind of musical) distortion in the low/mid range without nasty high Q spikes. In other words should sound pretty nice.

Some people like aluminium cones which tend to be stiffer and less damped resulting in increased amounts of high order distortion, often in the high mid range which can be perceived as harshness or detail depending on the listener. Why people like rigid cones in midbass drivers beats me. I see them a lot in car subs which is ok I suppose as the resonances can be filtered out easier.

There's that and more than likely a few other things going on there that are above my paygrade.

 

[Joe Louvar]

NOTE: I just sent a message to Anthony inviting him to join us here.

EDIT:
UPDATE - I was just told it’s against Eminence’s policy for employees to post on forums, oh well I tried.

 

[Joe Louvar]

Let us not forget cone materials, correct me if I'm wrong here. Paper (made of unpressed pulp) is relatively acoustically inert (or well damped) and exhibits mostly low order (especially 2nd order which is considered kind of musical) distortion in the low/mid range without nasty high Q spikes. In other words should sound pretty nice.

Some people like aluminium cones which tend to be stiffer and less damped resulting in increased amounts of high order distortion, often in the high mid range which can be perceived as harshness or detail depending on the listener. Why people like rigid cones in midbass drivers beats me. I see them a lot in car subs which is ok I suppose as the resonances can be filtered out easier.

This is on Eminence website about cones.

Cone and Surround Materials
The cone is usually the most important contributor to the sound of a particular speaker and Eminence Speaker’s engineers may have more experience with cone responses than anyone else on earth. We currently stock over 300 different cones. Cone and surround materials are available in a wide variety and are ever changing.
Speaker Components | Eminence Speaker

 

[Windreaper]

There's that and more than likely a few other things going on there that are above my paygrade.

Yup and there is even more to that such as cone geometry, rigidity and the like which are kind of hard to understand (I don't know much either). For example hifi drivers tend to have softer cones while guitar drivers tend to have pretty stiff cones. As they are meant to be loud, I suppose. This can result in some prett wild breakup modes. On the other hand some guitar speakers behave pretty well in the upper midrange which would probably be a combination of cone material and shape (and maybe magnet field design but I am a total layman in that field, agedhorse will probably be around to explain that).

 

[Joe Louvar]

Yup and there is even more to that such as cone geometry, rigidity and the like which are kind of hard to understand (I don't know much either). For example hifi drivers tend to have softer cones while guitar drivers tend to have pretty stiff cones. As they are meant to be loud, I suppose. This can result in some prett wild breakup modes. On the other hand some guitar speakers behave pretty well in the upper midrange which would probably be a combination of cone material and shape (and maybe magnet field design but I am a total layman in that field, agedhorse will probably be around to explain that).

This made me think about hemp fiber cones, lol.
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Anyway hopefully BFM will address your questions.

This thread was good - thanks again everyone, and with that I’m out of here for a while.

 

[Windreaper]

And to reiterate my previous statement. You would of course want as light and stiff (rigid) cone as possible (there's a reason why they are cones in first place, for stiffness) but without the resonances that come with most materials with good stiffness to weight ratio (aluminium, titanium, beryllium, carbon fiber, kevlar and composites involving these and other materials). You can buy good composite cone drivers (made by Seas and others) but they tend to cost money and are hard to use properly. But I digress. Paper is good .

 

[agedhorse]

Every parameter has it's pros and cons. When it comes to designing speakers, there is plenty of art involved in managing the science.

 

[fingerbun]

Just to add a little to agedhorses point on xmax. When you hear musicians say a cab is "power hungry", or you have to turn it up to the "sweet spot", or if you send it X amount of power and it really "opens up" or has "character". What they're doing is finding the nice sounding spot in that non-linear grey area that was designed in there.

Just trying to correlate some abstract musician type terms here to the hard number/design end of things.

THANK YOU for saying that.

My ears tell me lots of amps and speakers have sweet spots, yet the prevailing wisdom seems to be "have such massive headroom that nothing is ever working too hard". My current journey is a quest to find the best of both worlds, and after people looking at me like I'm mad, your post makes me feel like I'm not a moron. I shall now bask, however shortlived it may be, in the glory of my delusions of adequacy!

 

[will33]

THANK YOU for saying that.

My ears tell me lots of amps and speakers have sweet spots, yet the prevailing wisdom seems to be "have such massive headroom that nothing is ever working too hard". My current journey is a quest to find the best of both worlds, and after people looking at me like I'm mad, your post makes me feel like I'm not a moron. I shall now bask, however shortlived it may be, in the glory of my delusions of adequacy!

You're not a moron, your ears work fine. That approach can sound good but it comes with it's drawbacks like anything else, mainly in volume/output. You are walking a little bit of a fine line between tone and damage although there is some wiggle room. If that sweet spot is too loud for some situation, you can turn down but you lose some of the tone along with it. If it's not loud enough, you can only crank it so much before damage. You get around it by having a couple different size rigs, say a 100 watt tube amp and a 410, and a 300 watt tube amp and an 810. There's then enough mixing and matching you can do to match the sweet spot with the volume requirements.