4645C : beyond Xmax excursion

[shacard]

Hi,

Watching the BR of Batmam :The Dark Knight, i have heard some weird bass on 2 or 3 chapters (french track, UK edition). Nothing frightening but disturbing to my ears.

I've made some tests after the movie on the 152nd minutes (second part of the hospital explosion).
Putting my finger on the external part of the woofer (my only simple way to "analyze" the move of the woofer), it clearly pushes it 10mm away.

Looking at JBL 2242 pdf http://www.jblpro.com/pub/components/2242.pdf , the Xmax is 9mm and the maximum peak to peak excursion before dammage is 50mm.
I believe the 2242 is working between this 2 values on this movie scene. (closer to 10-15mm, not 25mm)

The question is why ?

I use a Crown Xti2000 with Architec 1.9. Here is my setup :




My room is 4.15mx7.35x2.2m. Huge room mode at 25-30Hz.

I have try to change the HP filter from 12db/oct to 48db/oct, to lower the bandpass gain at 0db instead of +3.24db : the woofer was still pushed out around 10mm.
So i don't believe the probleme is coming from very low bass but maybe to the signal around 30-40Hz.

S.

[clmrt]

Do you think the signal in the soundtrack is intentional or not?

If your system plays well with all other media, why chase this?

[shacard]

Do you think the signal in the soundtrack is intentional or not?

I don't know. I will test the other tracks next time.

If your system plays well with all other media, why chase this?

Well, just because it doesn't sound like it should

[jeenie67]

Hi, Just to add some "experienced phenomenon" concerning woofer excursions; I played Pink Floyd "The Wall, Live in Berlin" DVDA though an OPPO DV980H disc player, straight into two Crown XLS 202's bridged, and my Altec Model 14's. I thought that, in certain selections midway through, my woofers were going south for the winter via the grille cloth. The deepest ungodly bass oscillation? Synthesizers? I never heard these speakers go that low. I quickly turned down the volume and backed the disc to the beginning to analyze. It was the instruments and the mix. Scarey!

[Don Mascali]

WAG = Attempting to reproduce a frequency below Box Tuning. The cone will be unloaded. The 2242 woofer can survive this without drama. Many woofers will slap the mass ring or bottom out the cone.

Many dvds have material in the 10hz area. I would try a steeper slope on the sub cut off filter.

[shacard]

Many dvds have material in the 10hz area. I would try a steeper slope on the sub cut off filter.

I have already try with a 48db/oct highpass filter instead of my 12db/oct@20Hz.
The woofer is making the same excursion
This why i don't believe the problem is coming from very very low frequencies.

S.

[pos]

try to put you HP filter at (or just below) the port tuning frequency (ie 25Hz for the 4645c), because the excursion will increase rapidly under it, as with any BR box.

This is the excursion curve for the 2245H in a 226L box tuned to 25Hz (the 2242H should behave similarly) :

As you can see the other excursion peak is around 40Hz, but it should be ok up to many watt!

[shacard]

Thanks, pos. I will try to move the filter at 25Hz.
Watching the 2245H curve excursion, i will try also to drop the EQ filter at 50Hz (+5db...)

S.

[JBL 4645]

WAG = Attempting to reproduce a frequency below Box Tuning. The cone will be unloaded. The 2242 woofer can survive this without drama. Many woofers will slap the mass ring or bottom out the cone.

Many dvds have material in the 10hz area. I would try a steeper slope on the sub cut off filter.

I have to disagree with you Don, as much as I, like film soundtracks (I’d say there is small percentage) that go extend below 30Hz down into the 20Hz register and a few rare ones that go down into the infrasonic range.

Most of what I’ve seen with films dating back to the Dolby era are within (30Hz range 9 times out of 10) few that might be within (30Hz and 20Hz might be around 6 out of 10) (20Hz to 3Hz might be within a narrow window of 4 out of 10) but why settle for my opinion.

[JBL 4645]

I’ve adopted my own approach first looking at the SPL db level with LCRS playing and the level with SPL db metre placed at the back of the room behind the sofa, with crossover on DCX2496 set at (80Hz LCR Bessel -12db) produced a 102dbc just as the whole hospital building collapsed into smoky debris of rubble.

Also I could feel this amount of action with JBL Control 5 along with the six JBL Control 1 sidewall surrounds in standard surround mode. Centre back was turned off.

Adding a little sub bass extension for LCRS with smaller sub produced wicked DEEPER in my face 109dbc.

Let me explain I have the low pass for LCRS and LFE.1 feed directly to an audio mixer 6 channel so I can fade or increases any of the (left and right front summed) (centre) (left and right surround summed) and (LFE.1) to any desirable favourer to suit the film. I don’t want to overwhelm the soundtrack and mask the rest of the action too much.

With sub bass extension muted LCRS with LFE.1 around 106dbc I can still feel the sofa vibrating and low end under my feet, now I could have turned this up higher or turned it way down.

Sub bass extension and LFE.1 have there own parametric EQ Behringer BFQ2496 (channel A LFE.1, channel B sub bass extension).

The Lamborghini crash was 109dbc same level so the hospital explosion is slightly under as the crash is so fast and sudden, the hospital is slow sequence for different ranges of explosions.

I’d have to run a few tests of the waterfalls and see where the slam is on the frequency response.


Wtf! Just checked the temperature for my region -3° tonight and I can’t think to clearly, damn its cold.

[JBL 4645]

Shotgun blast peaks higher then building destruction now that doesn’t make sense in real life. Yeah that’s the same actor from (Heat 1995 William Fichtner) Roger Van Zant who played shifty dodgy guy dabbling in money.

104dbc on his last final shot before realizing the shotgun is empty.
102dbc building destruction!

And yes I’m playing at lower realistic level can’t be asked for 126dbc peaks tonight.

[shacard]

Compared to other action movies waterfalls, is this TDK sound track a sub killer ?
The intensity seems huge

Have you watch the excursion of your JBL ?

S.

[Doc Mark]

Compared to other action movies waterfalls, is this TDK sound track a sub killer ?
The intensity seems huge

Have you watch the excursion of your JBL ?

S.

Hello, Shacard,

I was wondering what SPL (sound pressure level) you experienced when your 4645C made those "odd" sounds? Do you think that the sounds you heard might be related to amplifier clipping, rather than a problem with your sub? Just a thought..... Best of luck in tracking this down. I'm considering a sub similar to yours, using the same 2242H 18" woofer. I would love to hear what you find out, and what conclusions you draw, once you decide what really happened in your listening. Take care, and God Bless!

Every Good Wish,
Doc

[JBL 4645]

Compared to other action movies waterfalls, is this TDK sound track a sub killer ?
The intensity seems huge

Have you watch the excursion of your JBL ?

S.

If I, saw excessive movement then I’d back it down (its last 11 years with trilling fun and I’m not prepared to do anything as careless with it now). Must have watched hundreds films laterally over the years. I’ve had it up to 126dbc in the past with little film called (Final Approach 1991) and those SR-71 blackbird afterburner effects where cool even for VHS PAL Dolby stereo.

I think (The Dark Knight 2008) has great soundtrack to serve the stories needs. There are plenty of more out there that can curse possible excursion or bottoming out if played carelessly. I play new films at a lower level and once I’m confident that I can take it higher within reasonable db level then I’ll make the necessary adjustments.

Try (Superman Returns 2006) if, action comic heroes is your thing. It’s got a busting loud mix of lows that SLAM KICK and RUMMBLE with gut wrenching DEPTH!

[jeenie67]

I wish I had the time to study acoustical engineering or electrical. It would be nice and gratifying to be able to analyze, from a technical platform, the subtleties, mass saturation, and crescendomics of sound waves and second partied vibrations produced in music reproduction. I could study the intricate graphics displayed, compare them to practiced theorems, and critically formulate a hypotenuse of what I believe is a more perfect association to the live performance........or I might just set the notched attenuators at five and drop the needle.