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[Evan Kirkendall]

Bill Burford wrote on Tue, 13 April 2010 16:40

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.

Bill,
Since your post is obviously directed toward me, I'd like to set some things straight. First of all, I never once argued with you, or personally attacked you. All of my posts in this thread have been pretty harmless. You have just chosen to take them personally for reasons I do not understand.

And, you've really taken my quote out of context. Here's the original quote:

Evan Kirkendall wrote on Tue, 13 April 2010 15:18

Bill, There's no arguing going on here. Just stating facts. If you can't figure out that a kick drum is an impulse that creates a good amount of cone movement, then you probably should consider a new hobby.

I didn't tell you to get a new hobby, I simply joked about it, as it is something anyone should be able to figure out. The should make it pretty obvious that you can take it with a grain of salt.

These forums are here for people to learn. It's the community's job to make sure that correct information is given to people, and that the incorrect information is corrected. If you're not willing to learn, and admit being wrong, then you really shouldn't post. I know when I'm wrong, and I'm fine with being corrected, because I'm learning. People have to sift through your posts to try and make sense of what you say as is, and it doesn't help when you just repeat yourself over and over.

I don't know what beef you have with me, but it's not helpful to this website, and it's rather childish to keep claiming to be the victim of some non-existant attacks.

Jeff,
I'm sorry this thread is drifting so far off topic. I'm done with this, and hopefully you've figured out what you need to do.



Evan

[Jeff Wheeler]

Evan Kirkendall wrote on Tue, 13 April 2010 18:02

Jeff, I'm sorry this thread is drifting so far off topic. I'm done with this, and hopefully you've figured out what you need to do.

Off-topic discussion is often educational.  As long as no one asks what kick drum mic I am using, I will keep reading the thread.

Art Welter wrote on Tue, 13 April 2010 17:11

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.

I don't understand how I could measure Xmax if it is defined as when the driver begins producing more than 10% distortion vs useful output, except if I measured in a particular cabinet with an analyzer capable of measuring distortion vs program material or generated signal.

Incidentally I did briefly look at the 2269 drivers but it looks like they are over-engineered to take a lot of abuse at the expense of efficiency, which is not what I think I need.

[Bill Burford]

another
joke:

"Bill, if you can't [A], then you should probably not "?

ha ha.. i get it
I should probably not "post" any more?

since you've deemed me wrong or at least failing to admit I was wrong.. and/or deemed that I've failed to learn.

and I'm also childish.

-- this is coming from a guy who posts a picture of an air-conditioning unit mounted in the back window of a van.

I have no beef with you.  I am willing to admit I'm wrong.. and I still tend to think that I there haven't been any significant revelations as far as the technical aspects of what I was talking about are concerned.  I'm reading what these other guys are saying and I'm following it.. its pretty cool.  Definitely learning something.  
Are you learning anything?

[Art Welter]

Jeff Wheeler wrote on Tue, 13 April 2010 17:24

Evan Kirkendall wrote on Tue, 13 April 2010 18:02 Jeff, I'm sorry this thread is drifting so far off topic. I'm done with this, and hopefully you've figured out what you need to do. Off-topic discussion is often educational.  As long as no one asks what kick drum mic I am using, I will keep reading the thread. Art Welter wrote on Tue, 13 April 2010 17:11 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. I don't understand how I could measure Xmax if it is defined as when the driver begins producing more than 10% distortion vs useful output, except if I measured in a particular cabinet with an analyzer capable of measuring distortion vs program material or generated signal. Incidentally I did briefly look at the 2269 drivers but it looks like they are over-engineered to take a lot of abuse at the expense of efficiency, which is not what I think I need.

Jeff,

Distortion testing does not require fancy equipment, though fancy equipment makes it faster.

You can make a real excursion chart , and see what power level is required to exceed Xmax  by using the chart below to measure distortion.

You can also just do it “by ear”, if harmonics are quite noticable, you have exceeded Xmax.

It will require an RTA, and a sine wave source,  which are available as free software. You will need a flat response test microphone able to handle high SPL with low distortion. You will also want to check your amplifier output to see that you do not exceed the power your speaker can safely handle.

You will need to remove the grill to see the cone excursion clearly. A dot of Whiteout or a silver sharpie makes cone movement easy to track because of persistance of vision, holding a ruler next to the dot  will make it easy to measure.  You will be seeing peak to peak motion, Xmax is measured as  half of that.
Wear hearing protection, the test will get loud.

The test should be done outdoors so room rattles and standing waves do not effect the results, but  if the microphone is placed quite close to the center of the cones and port, an indoor test will still give you a reasonable idea.

Below Fb, the box tuning, excursion and distortion will rise dramatically, so it is a good idea to find Fb by rocking the sine wave tone up and down in frequency, the excursion minima will be Fb.
Testing below Fb is interesting,but watch out that Xlim or Xmech is not exceeded, obvious bottoming out of the spider of voice coil, or suspension pushed to the point where the pleats are stretched flat.

You will find that Xmax can be exceeded with very little power below Fb. The excursion test will allow you to set a prudent HP, usually just a few Hz below Fb.

Now advance the level of the  sine wave tone into cabinet, raise level until a harmonic is noted at 10% distortion of the fundamental tone, in other words, if  50 Hz measures 100dB SPL, and 100 Hz (the second harmonic) measures 80 dB SPL, you have reached Xmax.

Well, technically you need a little more math, adding up the contributions of all the harmonics, but usually the second harmonic is far enough above the third and fourth that their contribution is minimal above Fb. However, the odd order harmonics, being not musically related, are more objectionable.

This test will reveal much about the character of the sound of your speaker, and how it changes as level is increased. It may suprise you with how much LF distortion you accept as “not too much”.

Since JBL says the PE is 800 watts for the 2268H, to be safe, do not exceed 80 volts for more than a few seconds at a time. If you do approach that level, don’t apply it for much time, and back off if you start to smell anything funny.

If you want to get a feel for the different distortion levels,(they will go up as the level is increased) for a four ohm load, a 2 volt(1 watt), 6.3 v (10 w), 20 v (100 w), 63.3v (1000 w) and 80v (1600 w) .
For an 8 ohm load, those wattage levels are 2.83 v (1) , 9 v (10), 28.3 v (100), 63.3 v (500), 80v (800).
Probably best to use 60 Hz to set your voltage levels, unless you know your volt meter is accurate at all frequencies.



Sine waves really make it clear what a speaker is capable of, and show distortion quite easily.

Art Welter

[Charlie Tappa]

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[Dave Rickard]

Mike Caldwell wrote on Tue, 13 April 2010 16:24

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

Priceless.