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Author Topic: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?  (Read 2782 times)

Brian Jojade

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #60 on: October 05, 2017, 03:54:53 pm »

Within the last year I've moved to in ears for monitoring as well, and it's been fantastic. But in a live band situation I still need to feel some air moving from my rig in order to be comfortable and play my best. I suspect that the ultimate solution for me is to get a shaker platform like the Tecamp Bass Board.

Studio playing seems to be completely different from my perspective. I've done the vast majority of recording with just headphones, but I'm not directly adjacent to a loud drummer and guitarist like I am in a live situation. For me it boils down to whether I can 'feel' what I'm playing over what other's are playing.

Keep us posted on how the amp works out. I've moved to micro amps nowadays but for almost 20 years my live rig was a Demeter tube preamp and a Crown Macrotech 2402. ~1500watts bridged into 4 - 12" cabs. Headroom is a beautiful thing.



Your tube amp mounted crooked in that amp is making me angry.
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Brian Jojade

Patrick Cognitore

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #61 on: October 06, 2017, 12:36:45 am »

Your tube amp mounted crooked in that amp is making me angry.
Haha. Yeah, that preamp was annoying. Apparently Demeter made an entire batch of that model using the same rack ear on both sides (making one side "upside down"), so utilizing all four bolt holes meant mounting it into the rack crooked. I did drill an extra hole in the "wrong" rack ear but that meant I could only utilize three holes to mount it, which I sometimes did.
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Frank Koenig

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #62 on: October 06, 2017, 03:10:45 am »

DC has frequyency of 0Hz  ;)

This is correct. Furthermore, for real (not complex) signals, as we usually encounter here, the response to negative frequencies is the complex conjugate of that to positive frequencies, mirrored around zero frequency. For example, a low-pass filter has a symmetrical magnitude response centered on zero frequency. My point is that we can't really talk about frequency rigorously without accepting the idea of negative (and zero) frequency.

If we want the response to negative frequencies to be zero we require an analytic signal, which has the property that its real and imaginary parts are related by a Hilbert transform. In any case, it's complex, not real, and as such needs to by represented by two real signals.

--Frank

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Yes, it is a giant stereo system!

David Sturzenbecher

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #63 on: October 06, 2017, 08:58:41 am »

Haha. Yeah, that preamp was annoying. Apparently Demeter made an entire batch of that model using the same rack ear on both sides (making one side "upside down"), so utilizing all four bolt holes meant mounting it into the rack crooked. I did drill an extra hole in the "wrong" rack ear but that meant I could only utilize three holes to mount it, which I sometimes did.

Interesting that they won't fix their mistake.
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Jeff Schoonover1

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #64 on: October 11, 2017, 04:56:20 am »

So, I built the box and it sounds great.  I would like to tune a bit lower as it has more than enough volume capability already.
Doing so requires extending my ports by 8 inches. I'll still have about 4 inches or so of clearance to the back. The clearance area from the rear of the ports will still have a larger area than the cross-section of the ports themselves by a good margin (about 200 sq. in. vs. 185 sq. in.).

Question, is that enough room to avoid audible artifacts like "chuffing"?  My WinISD program seems to indicate no appreciable difference in rear port turbulence.
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David Morison

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #65 on: October 12, 2017, 08:52:41 am »

So, I built the box and it sounds great.  I would like to tune a bit lower as it has more than enough volume capability already.
Doing so requires extending my ports by 8 inches. I'll still have about 4 inches or so of clearance to the back. The clearance area from the rear of the ports will still have a larger area than the cross-section of the ports themselves by a good margin (about 200 sq. in. vs. 185 sq. in.).

Question, is that enough room to avoid audible artifacts like "chuffing"?  My WinISD program seems to indicate no appreciable difference in rear port turbulence.

WinISD's calculations for port length and air velocity assume you will keep the back end of the vent at least one diameter away from the back wall of the box.
That means the back of your 185 sq in port needs to be at least 15(& a little bit)" away from the box rear wall otherwise you can't necessarily trust the predicted tunings and airspeeds will be correct.
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Jeff Schoonover1

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #66 on: October 12, 2017, 10:02:46 am »

Before it was 12" from the rear, with driver mechanical noise being louder than any chuff I heard, and that was below Fb anyway. The box is already deeper (30") than I'd like, so extending that wasn't an option.  Adding elbows seemed to have its own set of issues with turbulence from what I read.  Flares weren't really an option either unless I wanted to go with circles, which would require a much larger box to get the same port area.

I added the port lengths yesterday, now I have 3.5 inches of clearance X2 ports.  The area of clearance is now 172 Sq. in.  I guess we'll see what happens and how it sounds, where the Fb is, etc. today.  Some chuff with a sine near the X-max doesn't concern me, it's a question of whether the noise will audibly effect my real-world conditions.  Right now the trade-off for ideal port performance vs. being able to hit a low 'B' (31 Hz) cleanly, and within 3dB is acceptable.  I can always pry 'em off and go shorter.
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TJ (Tom) Cornish

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #67 on: October 12, 2017, 10:16:57 am »

Haha. Yeah, that preamp was annoying. Apparently Demeter made an entire batch of that model using the same rack ear on both sides (making one side "upside down"), so utilizing all four bolt holes meant mounting it into the rack crooked. I did drill an extra hole in the "wrong" rack ear but that meant I could only utilize three holes to mount it, which I sometimes did.
Every set of rack rails I have worked with is symmetrical - there is no "left" and "right" set.  A 1U chunk of normal rack rail has a high, low, and middle hole.  Cutting rack rail is done between the upper hole of the lower "U" and the lower hole of the upper "U", and then any piece is interchangeable.

What your rack manufacturer did was to either cut the rail wrong, or mount it wrong.
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Mike Caldwell

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #68 on: October 12, 2017, 03:12:13 pm »

Haha. Yeah, that preamp was annoying. Apparently Demeter made an entire batch of that model using the same rack ear on both sides (making one side "upside down"), so utilizing all four bolt holes meant mounting it into the rack crooked. I did drill an extra hole in the "wrong" rack ear but that meant I could only utilize three holes to mount it, which I sometimes did.

Maybe it's just the angle of the picture but to me the pre amp does not look to be a standard rack space sized unit, with the amp as a reference the pre amp look like it may be something like a space and a half tall.

Jeff Schoonover1

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Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #69 on: October 12, 2017, 10:11:14 pm »

WinISD's calculations for port length and air velocity assume you will keep the back end of the vent at least one diameter away from the back wall of the box.
That means the back of your 185 sq in port needs to be at least 15(& a little bit)" away from the box rear wall otherwise you can't necessarily trust the predicted tunings and airspeeds will be correct.
So, with the new port extensions, it RAISED my Fb! (???) I was at about 38-39, now at about 43?  Subjectively it sounds smoother and less 'peak-y.'  Seems to be 'deeper.'  There is LESS chuff or mechanical noise than before.  IOW, it sounds better.  I'm at a total loss to explain why the Fb went up instead of to 32 Hz.  All I can guess is that maybe 30 Hz needs much more excursion than 40 Hz and that makes up for Fb (???)  Maybe my sweep isn't linear? 
It still gets floppy below 30Hz but seems to stand up otherwise.  My low 'b' is strong...
I'm very confused.

Setting the Qp in the advanced box tab of WinISD at any value doesn't duplicate this.  Even a one (default is 100) doesn't produce this result. 
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