ProSoundWeb Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: 1 ... 6 7 [8]   Go Down

Author Topic: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?  (Read 2783 times)

David Morison

  • SR Forums
  • Sr. Member
  • *
  • Offline Offline
  • Posts: 445
  • Aberdeen, Scotland
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #70 on: October 13, 2017, 08:39:20 am »

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.

Well, it's got to be some kind of artifact of the port end being close to the back wall of the box, but I don't know an exact mechanism to explain how.
If you like the result though, and it's not introducing any worse port noise etc than the previous version, then just enjoy it ;-)
Logged

Jeff Schoonover1

  • Newbie
  • *
  • Offline Offline
  • Posts: 32
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #71 on: October 13, 2017, 09:45:36 am »

Well, it's got to be some kind of artifact of the port end being close to the back wall of the box, but I don't know an exact mechanism to explain how.
If you like the result though, and it's not introducing any worse port noise etc than the previous version, then just enjoy it ;-)
Part of me agrees, and part of me wants to know why it seems to defy the laws of physics.  Is there a different way to determine resonance than watching a dot on the cone? 
Maybe my test is fouled somehow...  I can't imagine how something with such oversized ports like this which still has 4 inches of clearance behind them can do this.
Logged

Josh Millward

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 704
  • Meridian, MS
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #72 on: October 13, 2017, 10:00:59 am »

Part of me agrees, and part of me wants to know why it seems to defy the laws of physics.

I highly doubt that it is defying the laws of physics. However, it may well be defying your understanding of the laws of physics.

Is there a different way to determine resonance than watching a dot on the cone?

I like to measure the impedance curve of a loudspeaker driver and the driver in the cabinet. You could also measure the impedance curve with and without your port extensions in place to see the difference they are actually making.

Maybe my test is fouled somehow...  I can't imagine how something with such oversized ports like this which still has 4 inches of clearance behind them can do this.

It has already been mentioned, more than once, that the distance between the port and the back of the cabinet should be at MINIMUM the diameter of the port plus a little more. In fact, it should be more than this distance. If your port is larger than 4" and the back of the port is approximately 4" from the back of the cabinet, you are already too close for optimum operation. This is the truth, regardless what you think is right.
Logged
Josh Millward
Danley Sound Labs

Mark Wilkinson

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 491
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #73 on: October 13, 2017, 10:23:15 am »

FWIW, and it's probably just because I didn't learn WinISD well enough, but I couldn't get WinISD to model ported boxes with the same results as Hornresp or Jeff Bagby's spreadsheet.
Those two gave similar results, so I went with them ...and measurements ended up matching the sims..
I had the same concern about box depth vs port length.

Logged

Jeff Schoonover1

  • Newbie
  • *
  • Offline Offline
  • Posts: 32
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #74 on: October 13, 2017, 10:29:35 am »

I highly doubt that it is defying the laws of physics. However, it may well be defying your understanding of the laws of physics.
Key word = 'seems' but I hear what you're saying.
I like to measure the impedance curve of a loudspeaker driver and the driver in the cabinet. You could also measure the impedance curve with and without your port extensions in place to see the difference they are actually making.
Do I need special tools, or can this be done with my multimeter?
It has already been mentioned, more than once, that the distance between the port and the back of the cabinet should be at MINIMUM the diameter of the port plus a little more. In fact, it should be more than this distance. If your port is larger than 4" and the back of the port is approximately 4" from the back of the cabinet, you are already too close for optimum operation. This is the truth, regardless what you think is right.
  I will need to either break/pry the extensions off completely or maybe get a saw in there and cut a couple inches off.  Does it have something to do with how the air enters and leaves rather than velocity?
Logged

Jeff Schoonover1

  • Newbie
  • *
  • Offline Offline
  • Posts: 32
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #75 on: October 13, 2017, 10:40:49 am »

Key word = 'seems' but I hear what you're saying.Do I need special tools, or can this be done with my multimeter?  I will need to either break/pry the extensions off completely or maybe get a saw in there and cut a couple inches off.  Does it have something to do with how the air enters and leaves rather than velocity?
Interesting.  Would you want to input the specs on my design and see what you come up with?  Obviously, it won't matter in the real world with the ports I've just added, because I can see the results for myself.  At this point, I'm just trying to figure out how to tune as low as possible with what I have available in this box.
Logged

Josh Millward

  • Hero Member
  • *****
  • Offline Offline
  • Posts: 704
  • Meridian, MS
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #76 on: October 13, 2017, 12:06:37 pm »

Do I need special tools, or can this be done with my multimeter? 

Most dual channel audio measurement platforms offer this feature. I feel it is generally underutilized by many folks as it is extremely useful.
Audio Tools with the iAudioInterface can do it on the iOS platform
The Terrasonde Audio Toolbox is fully capable as well
Smaart with a dual channel interface plus impedance box on a PC or Mac platform
TEF can do it for sure, though I'm not sure of the particulars
I would expect that SIM and EASERA can do it too, but I'm not as familiar with them.

If you are looking for a low cost way to get it done and you are an avid DIY loudspeaker guy, you really should have one of these Parts Express DATS interfaces. These things are great for measuring drivers and assembled loudspeakers.

I will need to either break/pry the extensions off completely or maybe get a saw in there and cut a couple inches off.  Does it have something to do with how the air enters and leaves rather than velocity?

I'm not totally certain, but I assume it has everything to do with how the pressure waves of the sound enter and leave the pipe, or how the air velocity in the pipe terminates at the ends of the pipe. I have never studied this in any kind of detail, I have always just made absolutely certain that there is at least the diameter of the port plus some between the end of the pipe and the back wall of the cabinet.
Logged
Josh Millward
Danley Sound Labs

Jeff Schoonover1

  • Newbie
  • *
  • Offline Offline
  • Posts: 32
Re: Crown XTi 6002 - 6,000 Watts - but only at 1KHz?
« Reply #77 on: October 13, 2017, 12:12:24 pm »

Jeff Schoonover1 = SUPER genius.
Be sure both the Hi-Pass portion of the crossover and the Hi-Pass filters are disengaged before running resonance tests.   I'm just that smart  :)

Anyhow, now it works like the Win ISD model predicts.  Fb is easy to see right at 29-30 Hz. The cones noticeably un-couple at anything significantly lower.  I haven't gotten really loud yet, but there is no port noise at all so far.

So, now the big question.  My EQ HP filter was set for 20Hz with a pretty sharp Q.  I also had set the HP of the X-Over to BW 48 @ 27 Hz.  I tried using both and separately when I was setting them up before.  Yet, as I've just seen, these still interfered a lot with the response from my sub.
I know there's a curve above the set frequency, but I tried to minimize this as much as possible, by going a bit lower.  Still, it had undesired effects.
I must protect from frequencies below resonance.  I do a lot of thumb-popping, which will send a DC square wave at them if I'm not very careful. Even with lots of care, the thumb thing really abuses woofers.
 
Is it that the EQ and X-Over in the Crown XTi series is less than great?  Should I set them lower?  I need 31Hz, but need to protect from 20 Hz.
« Last Edit: October 13, 2017, 12:14:29 pm by Jeff Schoonover1 »
Logged
Pages: 1 ... 6 7 [8]   Go Up
 


Page created in 0.1 seconds with 16 queries.