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[Bill Burford]

ahhh.. thats right.
great point.

xmax could change for the exact same mix in other words depending on the box.

earlier-- I hadn't thought of it like that.
that pretty much means my question is a bad one.

it might be a decent question if we were talking about a specific sub-- but i've had enough of the beat down for today.

[Adam Schaible]

Dude, you aren't getting it.

Xmax is a specification of a speaker, and doesn't change.

Excursion will change based upon the mix -- but that should be obvious.  As you mentioned, live sound instruments don't really produce sine waves.  I really haven't seen any synths produce sine waves, but the crest factor is similar.

The reason you're getting the beat down is because you ask a question, someone answers it correctly (re: evan) and then you try and correct him when you have no clue what you're talking about.

Excursion is the lowest at the box tuning.  For an 18" subwoofer in a cabinet tuned around 40hz, you'll see the cone barely move at all at 40hz, less than 1mm.

Kick drums, as has been stated, are impulses.  Often times in a mix the kick is way louder than the bass (10db, maybe more).  The bass kind of sits in the pocket but the kick gets out in front of it.  In that case, it's likely that the kick is going to create more excursion than a bass guitar.  This is subjective, as was stated, it depends on the sub, bass guitar note, kick tuning, relative levels, etc.

Also, as Evan said, as long as the kick isn't bottoming out the subs it's not likely to create issues because since it's an impulse it's not generating heat and heat is going to be the killer.  Crank the bass up until the sub bottoms and you're more likely to have thermal issues.  Trying to look at sine waves and determine how much excursion exists at xyz frequency and xyz input power doesn't tell the whole story.

[Bill Burford]

ha ha.. I have no idea what I'm talking about.

I still haven't said anything that is contradictory to anything anyone else has said.  if you really read into what I said,
I mentioned where in a mix did max excursion occur.

you'd have to stretch to imply that I meant that the mix could be moved from box to box in order to change the meaning of my question.

In other words, you would have to be searching for something wrong with me to bring that up.. because when someone asks ME where in a live-mix does max excursion occur, I would assume that they were asking for a live mix that was using the same box for the entire mix.

now you did bring up a good point when you mentioned it depends on the box.. the max might actually occur at a different location for different boxes.. although, in my humble opinion, it would probably occur at nearly the same mix for just about any commercial box even if the performance of those boxes varied greatly.. maybe for the worst subwoofer vs the best subwoofer.

but for comparable subs, I'd say it occurs in roughly the same spot for the same mix.

Now if you are saying that you are the greatest subwoofer designer in the world and you can think of one box with the exact same driver where the kick creates the most excursion, but you have another box where the tuning causes a "trumpet" to cause max excursion.. well, excuse me for asking you a bad question. (completely joking about the trumpet by the way)

[TJ (Tom) Cornish]

Bill Burford wrote on Tue, 13 April 2010 15:20

ha ha.. I have no idea what I'm talking about. I still haven't said anything that is contradictory to anything anyone else has said.

Bill, the problem is that you contradict yourself.  

For example:

Up a few posts you ask a question.  People try to answer it.  You say they're wrong and that you know the answer.  Then later on you restate and agree that it was an unclear question.  Then you say people were picking on you by putting strange conditions on the circumstances and that your question was perfectly valid in the first place.

On some posts you are talking about one thing, then you either post something else, or edit your original post to change your mind.  Your posts often are confusing to read and hard to figure out what you are saying.  People aren't attacking you personally - and I'm not now either.  They are just trying to answer questions in a way where the truth gets out and bad info quashed.  After this happens a few times, people get frustrated and it comes out in their language.  Slow down in your posting and think a bit more carefully, you'll get better answers to better questions.

BTW, it is completely reasonable for someone to not answer a question in the way a person wants.  If I ask "What's the best vehicle to get to Mars - a pontoon boat or a pickup truck?" The problem is not that someone tells you that actually a rocket is the best tool, but rather the asker doesn't understand as much about Mars as they think they do.

[Bill Burford]

actually, I didn't say ANYONE was wrong.
now I did go back and edit something.  I added

Quote:

(sarcasm) and (more sarcasm)

but I didn't add anything to the question.  the question asked already about recorded music/ synth bass or accoustic bass.  
I asked a question and they said I was wrong.  I never said they were wrong.  not in this thread.  I was responding to a guy who has personally attacked me before on here.
and sure enough, it came right back again.
telling me I should get

Quote:

another hobby

you said:

Quote:

Up a few posts you ask a question. People try to answer it.

let me stop you right there, they didn't try to answer it. they said I was wrong if anything.  but certainly tried to find a problem with the question.

Quote:

You say they're wrong and that you know the answer. Then later on you restate and agree that it was an unclear question. Then you say people were picking on you by putting strange conditions

no by getting personal and telling me I need a new hobby other than sound-- or other comments designed to discredit me personally in other threads by the same person..
continue...further, I never said they were wrong.  in one spot maybe you could say that, I didn't really say they were wrong but I did say that min impedance is where I thought that max excursion would occur.  and I tend to believe that is closer than the max impedance.  but that was a separate issue not really related to my question.

Quote:

on the circumstances and that your question was perfectly valid in the first place.

whoah whoah whoah.. strange conditions arent my problem.  I could care less.  
my only gripe was that people want to argue or find something wrong with the question rather than to have a discussion.
In that, it is not contradictory at ALL for me to concede that my question was actually not very clear (in an attempt to NOT fight about it)..    

however, it WAS clear to me.  and probably plenty of other people who are ignoring this because its pointless.
I can say the question is not clear and that it is clear.
without saying who it is clear to..
the question was always clear to me.

I can see how some people might not however.  But then, I'm a reasonable guy.  Some people might say it would take an unreasonable guy to say that I am contradicting myself by attempting to be diplomatic like that.  But I'm not personally saying that you are unreasonable.  I'm only saying that I can understand if someone else might.

[Art Welter]

Elliot Thompson wrote on Mon, 12 April 2010 21:46

Art, It seems JBL purposely marketed the JBL 2268H with a high xmax however, never explained it is based on xmax damage. In order for the JBL 2268H to offer a 23 mm xmax, the efficiency would be very low since all of the coil will be sitting outside the magnetic gap. Yet, it offers an no.% of 2.8 The numbers are based directly from the engineer’s specifications. I would imagine this is before marketing got their pretty little hands on it. There is no xmax rating on the engineer’s sheet. However it clearly states, “Xmax, damage 23 mm peak before the spider bottoms on gap sleeve.”  It also states, “Special Notes: JBL 2241H Replacement in Neo Differential Drive line of transducers.” It seems the JBL 2241 offers the mathematical xmax. As we know, manufactures were more conservative on their specifications when the “2241” was classed JBL’s best decades ago. Today, that 7.62 mm measurement would be marketed as 9 mm taking distortion into account. Best Regards,

Elliott,

Your JBL engineering note quote does sound convincing that the 2268H does not have substantially more Xmax than other drivers, in which case the lesser power compression due to double the voice coil surface area (and lighter weight) would be the main advantage.

One correction to a previous post of mine, the 2268H is only 800 watts(PE), the "Ultra Long Excursion" 2269H is 1200 watts (PE).

I found no Xmech figures for JBL differential drive speakers other than on the  VT4880A spec sheet, which states an 89 mm (3.5”) maximum peak to peak excursion, in other words a 44.5 Xmech (or Xlim, whichever flavor you prefer) for the 2269H, which is only rated 19 mm Xmax.

The 2269H  has only a fraction of the efficiency of the 2268H or 2241H, what one would expect from extra long (and heavy) coils that extend well beyond the magnetic gap.

This would correspond to the engineering note you mentioned, I’m inclined to agree the 2268H is basically a differential drive dual coil version of the 2241H.

In which case a pair of decent Xmax drivers like the Eminence Lab 12, the 4018LF or the B&C18TBX100 will certainly walk over a single 2268H.

The Lab 12 has an Xmax of 13 mm, 659 cc Vd.
Vd is the amount of air that can be linearly displaced by the speaker, just like in car engines, the more displacement, the more ultimate power.
The 4018LF has an Xmax of 7.9 mm, 939 cc Vd.
The B&C 18TBX100 has an Xmax of 10 mm, 1188 cc Vd.

The 2268H most likely lies right between the two 18”, if it has the same ratio of Xmax to Xlim as the 2269H, it would have an Xmax of 9.82 mm, about 1167 cc Vd.

Before laying out the big cash for 2268H speakers, rather than the others,  I’d be doing a quick and simple Xmax check to verify what is real, and what is a print mistake.

Art Welter

[Jeff Wheeler]

My experience emailing JBL for spec help has been mixed, but I will try that and see what they say.

[Art Welter]

Jeff Wheeler wrote on Tue, 13 April 2010 16:04

My experience emailing JBL for spec help has been mixed, but I will try that and see what they say.

Contacting JBL would be interesting, but I was suggesting you check the excursion yourself, since you have the cabinet, amp, etc. needed to do the test.

[Mike Caldwell]

During the course of this thread I could have cranked out pair of double 18's and been listening to them!

[Elliot Thompson]

Art Welter wrote on Tue, 13 April 2010 22:49

Elliot Thompson wrote on Mon, 12 April 2010 21:46 Art, It seems JBL purposely marketed the JBL 2268H with a high xmax however, never explained it is based on xmax damage. In order for the JBL 2268H to offer a 23 mm xmax, the efficiency would be very low since all of the coil will be sitting outside the magnetic gap. Yet, it offers an no.% of 2.8 The numbers are based directly from the engineer’s specifications. I would imagine this is before marketing got their pretty little hands on it. There is no xmax rating on the engineer’s sheet. However it clearly states, “Xmax, damage 23 mm peak before the spider bottoms on gap sleeve.”  It also states, “Special Notes: JBL 2241H Replacement in Neo Differential Drive line of transducers.” It seems the JBL 2241 offers the mathematical xmax. As we know, manufactures were more conservative on their specifications when the “2241” was classed JBL’s best decades ago. Today, that 7.62 mm measurement would be marketed as 9 mm taking distortion into account. Best Regards, Elliott, Your JBL engineering note quote does sound convincing that the 2268H does not have substantially more Xmax than other drivers, in which case the lesser power compression due to double the voice coil surface area (and lighter weight) would be the main advantage. One correction to a previous post of mine, the 2268H is only 800 watts(PE), the "Ultra Long Excursion" 2269H is 1200 watts (PE). I found no Xmech figures for JBL differential drive speakers other than on the  VT4880A spec sheet, which states an 89 mm (3.5”) maximum peak to peak excursion, in other words a 44.5 Xmech (or Xlim, whichever flavor you prefer) for the 2269H, which is only rated 19 mm Xmax. The 2269H  has only a fraction of the efficiency of the 2268H or 2241H, what one would expect from extra long (and heavy) coils that extend well beyond the magnetic gap. This would correspond to the engineering note you mentioned, I’m inclined to agree the 2268H is basically a differential drive dual coil version of the 2241H. In which case a pair of decent Xmax drivers like the Eminence Lab 12, the 4018LF or the B&C18TBX100 will certainly walk over a single 2268H. The Lab 12 has an Xmax of 13 mm, 659 cc Vd. Vd is the amount of air that can be linearly displaced by the speaker, just like in car engines, the more displacement, the more ultimate power. The 4018LF has an Xmax of 7.9 mm, 939 cc Vd. The B&C 18TBX100 has an Xmax of 10 mm, 1188 cc Vd. The 2268H most likely lies right between the two 18”, if it has the same ratio of Xmax to Xlim as the 2269H, it would have an Xmax of 9.82 mm, about 1167 cc Vd. Before laying out the big cash for 2268H speakers, rather than the others,  I’d be doing a quick and simple Xmax check to verify what is real, and what is a print mistake. Art Welter

Exactly!

If we examine the B&C 18 TBX 100, it offers an xmax of +/-9 mm with an Xvar of +/-11 mm. “Xvar” may be B&C’s terminology of xmax with, if I remember correctly, 10% distortion for, it falls within the voice coil’s winding depth of 25 mm. Half of 25 is 12.5 which seems to be the true xmax. Although, B&C being very conservative, markets the xmax rating at +/- 9 mm to ensure very low distortion when driven within those parameters.

Of course this is pure speculation based on calculating a few TS Parameter figures. However, it may not be not too far from the truth.

Personally, I never focus heavily on xmax for manufacturers have their own methods on measuring xmax. I’ve learned that many years ago comparing an EV EVX 180 B to an RCF 18 LP 300. For me, it is a matter of examining various prospects using Eminence Designer and, choosing which driver suits my requirements.


Best Regards,