thoppa Posted February 28, 2007 Share Posted February 28, 2007 Hi, Anyone have any experience of this ? The nice fellas at Pi speakers say this happens everytime a lone cap is connected before a tweeter. The example they gave was a horn-loaded tweeter with a crossover at 1.6Khz and this had resonant peaks at 2.2khz (0.5dB), 1.1Khz (1dB), and 400Hz (4dB). So it seems the protection cap for bi-amping will cause this too ? Cheers, Tom Quote Link to comment Share on other sites More sharing options...
djk Posted March 1, 2007 Share Posted March 1, 2007 No, the protection cap is larger than a crossover cap. Quote Link to comment Share on other sites More sharing options...
thoppa Posted March 1, 2007 Author Share Posted March 1, 2007 Hi, So your protection cap has a value that is two octaves below the crossover ? i.e. for a 12 ohm tweeter, crossover 4khz, your cap is 15uF or more ? Do you use an L-pad or any attenuator ? Cheers, Tom Quote Link to comment Share on other sites More sharing options...
DrWho Posted March 3, 2007 Share Posted March 3, 2007 What is this pi speaker thing to which you refer? Is it just the fact that the impedance response isn't perfectly flat? What's the point of an L-pad or attenuator when you have a volume control on the amplifier? Quote Link to comment Share on other sites More sharing options...
thoppa Posted March 4, 2007 Author Share Posted March 4, 2007 Hi, Open the speaker crossover document listed on Pi's website : http://www.pispeakers.com/contents.html and scroll through to page 27. It says a single capacitor in line with a tweeter (common in bi-amping) will resonate and cause peaks in the response. It also says an L-pad will damp this resonance - the L-pad is to attenuate a tweeter to the level of efficiency of the woofer of course. With an active line level xo you can obviously just adjust the gain so an L-pad is not necessary. As always, I like making life difficult in an effort to integrate/minimise the component count. I decided not to use the cap in line with my tweeter only for protection but, as it is yet another high pass filter, make it work as part of the crossover. I can do this as I'm using a pllxo not allxo; so it is just one less cap in the pllxo. My tweeter is about (!) 2.9dB more efficient than the pair of woofers together so I am using an L-pad (Mills resistors...) to knock it back 2 dB and avoid peaking - trusting in Pi's data. I'm also using the gain on the amp input to fine tune the final .9dB or so to my taste. I was wondering if anyone has any experience of this and could confirm or otherwise the date from the guys at Pi. Incidentally, I also tried bypassing the rather crappy resistor used to attenuate in the original crossover. I used an L-pad instead to maintain the 12 ohm impedance and reduce output by 2.5dB. It was quite surprising to find that beyond anything else, this crappy little resistor worth less than 30 cents was THE limiting factor of my $540 speakers. For less than US$10 my speakers sounded MUCH more open and detailed with more extended response and the slightly brighter output so characteristic of Klipsch. It was this discovery that made me realise you were so right to tell me not to copy the Klipsch crossover. I'm now trying to learn to use the software to do sweep tests and 'start again', again. What a great hobby this is !! I love it. Cheers, Tom. PS I hope everything is all right with your countrymen down there in the South - it got a bit blowy by all accounts ? Quote Link to comment Share on other sites More sharing options...
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