JohnA Posted March 6, 2005 Share Posted March 6, 2005 All, Some time ago I posted a picture of a pair of Peavey FH1 bass horns with Altec 511Bs on top. http://forums.klipsch.com/idealbb/view.asp?topicID=49045&forumID=71&catID=19&search=1&searchstring=&sessionID={263506F5-97FE-48FE-8A28-39ADC1C139D6} I used the FH1s at church once on a Saturday. The neighbors got HOT and we were only using a 45 wpc amp. Ive tried a couple of crossover designs and found them lacking. The 511B/902-8Bs will not tolerate a 1st order crossover like the old 802s will. So, to help I bought a copy of X-Over Pro from Parts Express. Using the published curves for the FH1 and response curves and impedance curves from Shawn Fogg and Al Klappenberger, I designed the attached crossover to mate the two. Conventional Butterworth and Linkwitz-Reilly would not sum flat at my chosen crossover point. Everything I did either gave a 5 to 7 dB dip at the crossover point or a peak and a dip. Dissatisfied, I began to experiment and ended here by trial and error. The tweeter section is so odd-ball I asked Al to model it to see it was really doing what I thought it did. Thanks, Al! Well, after stewing about it for some time, I built the networks this weekend. This afternoon, my sons and I moved the Peav-tecs out into the driveway and hooked them up to a cheap receiver and portable CD player. Not the best electronics, but these things are for sound reinforcement, not Opera. Well, the Deputies did not come, but the wife thought they would. These things can ROCK! We listened to the Yes 3-CD 35th Anniversary set while roasting weenies. Not much better than that! They sound pretty darned good, too! Have a look and tell me what you think. Serious listening to come. Quote Link to comment Share on other sites More sharing options...
djk Posted March 7, 2005 Share Posted March 7, 2005 I would drop the resistor in parallel with the polyswitch to 15R/25W. With 100R there the impedance will drop real low at 562hz if the switch opens, could damage the amplifier. Quote Link to comment Share on other sites More sharing options...
JohnA Posted March 7, 2005 Author Share Posted March 7, 2005 Thanks djk, How do I check that? I'm guessing the 108 ohms causes a resonance at 562 Hz. If I drop the resistor to 15 ohms, it looks like that will attenuate the HF horn 9 dB. Is that enough? Quote Link to comment Share on other sites More sharing options...
sfogg Posted March 7, 2005 Share Posted March 7, 2005 John, Looks good. How deep are those Peavey horns? Just compared to the 511 they are obviously wider then LaScalas. "If I drop the resistor to 15 ohms, it looks like that will attenuate the HF horn 9 dB. Is that enough?" That is a pretty large lowering of the power going to the 902 when that opens. That should be very obvious if/when it occurs. Do your 902s still have the loading caps in them? Shawn Quote Link to comment Share on other sites More sharing options...
JohnA Posted March 7, 2005 Author Share Posted March 7, 2005 Shawn, Yes, it appears at least one of them has the acoustical loading cap. You'll notice I was able to get rid of the 500 to 2k Hz hump and thus leave out the L-Pad. That and the response bounce of the FH1 between 1k and 2k was what took me so long to patch together. Quote Link to comment Share on other sites More sharing options...
sfogg Posted March 7, 2005 Share Posted March 7, 2005 John, If you take off the back cover off the 902 and see the aluminum diaphragm you don't have loading caps in it. If you take off the back cover and see a black plastic cover sealing the back of the diaphragm you have loading caps in them. Shawn Quote Link to comment Share on other sites More sharing options...
TBrennan Posted March 7, 2005 Share Posted March 7, 2005 Shawn---Ever run compression drivers with the rear covers off? I got the idea from Don at the Lansing site who said that early WE drivers just had a screen over the back and thought drivers sounded good without rear covers. Interesting thought, kind of a dipole but with the rear wave down several db. I tried it with some old 802s but didn't hear much, if any, difference. Interesting idea though. Quote Link to comment Share on other sites More sharing options...
sfogg Posted March 7, 2005 Share Posted March 7, 2005 Tom, "Ever run compression drivers with the rear covers off?" Nope, never tried it. I don't think it would make much of a difference in my setup. The 511s are in the top half of the LaScala's cabinets and those are pushed up against the front wall. There would be much room for the back wave to get out into the room and my front wall is heavily treated for absorption anyway. Somewhere on the net I saw some wacky idea someone had of horn loading both sides of a compression driver to try to increase its bass response but I don't think I have that bookmarked. The back wave was into a longer folder horn then the front wave. What do you think... back to back 511Bs with a 902 in the middle would fit in many rooms? Dipolar horns... what will they think of next. Shawn Quote Link to comment Share on other sites More sharing options...
fini Posted March 8, 2005 Share Posted March 8, 2005 Good work, John! Any time you can get neighbors PO'd at the curch you must be doing something right! Seriously, I am in awe (and a little jealous) of your abilities (that goes for you other guys, too). Quote Link to comment Share on other sites More sharing options...
hwatkins Posted March 8, 2005 Share Posted March 8, 2005 good work John - I will be adding you to my list of folks to help me finish my current crossover delimma on a JBL build (trust me - it took AL a full two days to get irritated with my elementary school questions). OK, just for grins - since you folks have your pencil neck geek hats on today - Since you are talking about taking the back cover off a compression driver I am a bit interested in what happens to that tiny little back wave when the cover is on. I assume it has the same sort of affect of a sealed box cone. I would think that the back wave is too small to be of significant consequence, however the thought of taking the back of the driver to the drill press and putting in tiny little ports is intriguing. Quote Link to comment Share on other sites More sharing options...
sfogg Posted March 8, 2005 Share Posted March 8, 2005 Henry, " I assume it has the same sort of affect of a sealed box cone." That is what the loading cap is for. It basically makes the rear enclosure on the diaphragm smaller in an attempt to limit the diaphragms excursion on material below its cutoff point. Altec put the loading caps on some of the drivers but not all of them. Since I use Al's extreme slope networks (initially around 150 db/octave) with my drivers they get very little material below 600hz so I pulled the loading caps out. Didn't really notice much of a difference either way, though some say it makes the top end slight more natural sounding. When I was running the 902s with Al's original first order Type A crossover I left the loading caps in them. Shawn Quote Link to comment Share on other sites More sharing options...
JohnA Posted March 8, 2005 Author Share Posted March 8, 2005 Yes, one of mine has a black plastic piece screwed over where I thought the diaphragm would be. The FH1s are roughly 31"w x 25"h x 24"d. Quote Link to comment Share on other sites More sharing options...
IndyKlipschFan Posted March 8, 2005 Share Posted March 8, 2005 I have often wondered what a Peavey Fh-1 Mark III bottom paired with the La Scala top end would sound like? (Assuming the La Scala x over is used or through todays magic building a new one like you did too John?) Quote Link to comment Share on other sites More sharing options...
JohnA Posted March 8, 2005 Author Share Posted March 8, 2005 It will sound pretty much the same as a La Scala, but why cross it at 400 Hz? I wanted to buy a pair of LSI bottoms, but they were sold every time I found an ad. The LSI bottom is smaller. Quote Link to comment Share on other sites More sharing options...
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