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Crossover confusion

Hi All, 
  While I'm not a technical expert with stereo electronics and software, I do understand a lot of it. My problem is clipping on my woofers when playing the Stereophile test CD track 31 (20Hz 1/3 octave at -20db ). 
It would probably be best that I list my equipment from source to sound.
1.) Cambridge CXC transport
2.) Nad M51 DAC ( via fiber optic)
3.) Audio Research LS3B preamp ( all other interconnects are Kimber PBJ's ) 
4.) Bryston 10B Hi Lo crossover. ( Settings are 80 Hz for the low pass. 70 Hz for the high pass. High pass db is 0.)
5.) Low pass frequencies go to a pair of Audio Fathom F-113's which are active subwoofers
6.) Hi pass frequencies go to a Krell FPB 300 power amp
7.) Kimber T12 cables connect to PNB B741 speakers ( with two additional midranges) that have been fitted into a 
    pair of Dunlavy SC-IV's. The cables are Bi-wire that are common at the amp. The smaller conductors feed the midranges and tweeter. The larger conductors feed the woofers.
  My thoughts are that none of this 20Hz signal should  even be going to the Krell amp.  While I haven't heard any clipping when listening to music I am concerned. I was researching passive crossovers and came across Marchand Electronic's website. They make both active and passive crossover's. One of the diagrams show a hybrid setup that uses an active crossover with the hi pass going directly to the midranges and tweeter and the lo pass going to a passive crossover and then to the woofer. Before talking to Marchand Electronics I thought it would be a good idea to come here first since I've gotten a lot or good info here. If I have to use a hybrid setup, it would also be useful to know what the crossover Hz should be. The PNB B741 woofers bottom out at 25 Hz. Hope this is enough info for those that can help.
  Thanks to all concerned

















 
evelyn1
12 responses Add your response
evelyn1 OP
51 posts
 
Me again,
  Screwed that part about the Marchand diagram. It actually showed the woofers getting a signal directly from the active crossover and the midrange and tweeter having a passive crossover between the active crossover and them. For me the low pass would be for the sub's and the hi pass for the rest. 
swampwalker's avatar
swampwalker
5,138 posts
 
Are you saying that the "clipping" (not sure if that is the right term) is heard on the JLs or the PBNs?
evelyn1 OP
51 posts
 
Hi,
  On the PBN's. I thought clipping was the correct term but it was a clicking sound coming from  what I thought were the woofers on the PBNs. I don't want to run the test CD again for fear of permanent damage. That was the lowest frequency on the test CD and all the other frequencies were ok. I don't think that the PBN crossover for the associated woofers have a shunt for frequencies lower than it can handle.
Please correct me if I'm wrong about the term clipping. I make an effort  to correct my ignorance. It could possibly be that my Bryston crossover isn't functioning properly. I don't have the test equipment to check it out. Having it tested and repaired if needed would have been my next step. I was thinking about just going with a passive crossover to separate the subwoofers from the PBNs. The Marchand Electronics passive crossovers only have a left and right channel in and a left and right channel out. That would serve to eliminate lower frequencies to the Krell amp. So I'm wondering why Marchand's passive crossover only has a single pair in and single out and why their hybrid schematic needs a passive and active crossover. Thanks for your reply.
erik_squires
16,056 posts
 
Crossovers are not absolute brick wall devices. they have a roll-off or slope, expressed in db/Octave. A 12dB/octave at 80 Hz would be down 12 dB at 40Hz , and 24 dB at 20 Hz.
ivan_nosnibor's avatar
ivan_nosnibor
1,047 posts
 
Hi, first I’d like to know what slopes on the Bryston you’re using. The frequency choices of 70/hipass and 80/lopass should make for a rather wampy response overall, but I understand the limited selection choices with your equipment. A new standalone passive crossover will not necessarily help you any if you currently have to ’guess’ at what the frequency selections should be. It would likely be much better in this regard for you if you had a unit with much more flexibility of control in order for You to experiment enough to discover what settings will work best.

(I’m assuming that you have bypassed the active crossover in the Fathoms in order to use them with the Bryston).

Give serious consideration to holding off buying a Marchand (or other crossover, whether passive, active or hybrid), or sending the Bryston in for repair, until the true nature of the audible problem becomes verifiably clear for you.

Audible "clicking" through the woofers might be digital distortion, correct me if I’m wrong here...caused by audible dropouts in volume...not usually considered harmful unless perhaps at very loud levels. That might be a digital input level issue somewhere, if that applies to your situ. If it is actually your woofers bottoming out, then this is indeed dangerous, of course. If you haven’t already, of course, double and triple check your Bryston to see why low frequencies are apparently being passed...change slopes to see if it has any audible effect or none at all. If it has no effect, then I ’might’ begin to suspect a faulty Bryston. Change other Bryston parameters too and see if the problem remains constant.

Check back in with your findings.
ivan_nosnibor's avatar
ivan_nosnibor
1,047 posts
 
I would add that if you experience the woofer clicking again with the same test you ran as before - even at low volume - that the original problem is not really power-related and is actually signal-related...and might be another finger pointing to the Bryston, perhaps.
evelyn1 OP
51 posts
 
Thank you guys for your replies. Seeing the reply that crossovers aren't absolute brick wall devices is an eye opener for me. I failed to mention the db / octave settings on the Bryston. The low and hi passes each have a setting choice of 6,12, and 18. I have them both set at 6. There is also an adjusting knob for the hi pass db level that ranges from -5 to +5. That's set at 0 so my db setting is 6. So my guess is to try incrementing the db's if my problem is a dropout in volume. The Bryston was purchased used so I don't really know it's history. If this doesn't solve the problem then I could have the crossover tested by EBC electronics. They're only 80 miles from where I live in NJ and did a great job repairing my Krell amp. Hopefully nothing gets damaged in my testing process with the Bryston. The subs that get their signal via the lo pass haven't any issues. It might be a couple of days before I can run this test but I'll let you know how it went. Hopefully it will work and save the expense of having equipment tested and purchasing additional components. 
ivan_nosnibor's avatar
ivan_nosnibor
1,047 posts
 
Yes, erik is quite right, they're not brickwall devices. At this point, I would venture to guess that you're now on the right track and that it's just a matter of experimenting and tracking down the right settings, on the digital side of things most likely. Hopefully no need for testing.

Good luck and let us know if the problem doesn't get worked out.

erik_squires
16,056 posts
 
For a high pass, I would suggest experimenting with the 12 or 18 dB/octave settings.

Correctly configuring a crossover is much easier with testing equipment. I use OmniMic, but Room EQ Wizard is free and has an active discussion group you can turn to for help.

Best,


Erik
evelyn1 OP
51 posts
 
Wow! That worked out great! Listening to the test CD again made realize that the 25Hz and31Hz signal were also having problems with dropout. They didn't click like the 20Hz signal but they weren't smooth like they are now. After warming up the equipment I went directly to the 12db setting and played the CD from the 1KHz tract on down. Thank you very much guys for solving my problem. I did a search on OmniMic and Room EQ Wizard and have decided that OmniMic might be the better choice for me. Parts Express is selling it for $298.00 and another bundled with DAT V2 speaker measurement for $348.00. I think I'll opt for the bundled version and let the real fun begin. You both have saved me the expense of testing my crossover and buying another crossover. I now can afford to buy the software and dial in everything correctly.
                Thanks again,
                                        Frank
erik_squires
16,056 posts
 
Not sure if you need DATS though. :) It is for impedance and Thiele-Small parameter measurements.

I have one, but I make my own loudspeakers. Otherwise only useful if you are hacking internal crossovers and want to measure parts precisely.

Best,


E
evelyn1 OP
51 posts
 
Thanks again Erik. You just me saved an additional $50.00. I'm sure I'll have questions in future about OmniMic.
                      Cheers,
                                F    
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