Bonder Posted July 31, 2009 Share Posted July 31, 2009 Hello all, I'm an infrequent poster on the forum (but an avid reader!), I'm hoping someone can point me in the right direction with regards to my issue. I'm building new 1st order crossovers (similiar to a B-1 network) for my new Speaker project: EV Sentry IV bass bins crossed to a Altec 511B / GPA 902 mid driver and then a Beyma CP 25 tweeter. I'm trying to cross the Bass bins as high as possible which in this case looks to be 500 hz as the bass bins are down 8 db at 630 hz, my problem lies with crossing the GPA 902 driver (8 ohn version) at 500 hz, it just doesn't seem to want to reach that low. The Beyma is being crossed above 9- 10,000, I'm just letting the 902 run out as it starts to tail off over 12,000 (Edit, this likely isn't accurate as my meter isn't reliable over 10,000, in any event I'm very happy with the mid to tweet crossover, very smooth and integrated) I've read numerous posts about forum members crossing this driver as low as 400 hz, however it's not clear to me how they're doing this, I've tried a number of capacitor values (8 uf, 10 uf, 14 uf) and even ran them without caps (low levels) and am getting consistent results that say the driver won't go lower than 700 - 800 hz before it takes a dive. Additional background that likely is contributing to my problems: 1. I'm using a rat shack spl meter with a correction table 2. I'm assuming the reflected impedance to the Autotransformer (3636) is approximately 26 ohms (4 X the impedance of the driver) 4. Measurements are being taken 7 feet from speaker at listening positon in my Garage (24 ft x 24 ft), 3. I'm a noob when it comes to electronics Here's a table of my measurements GPA 902 (8 Ohm) - Reflected impedance ~ 26 Ohms (Taps 5/3 on 3636 Autotransfo rmer) DB's HZ 8uf 10 uf 14 uf No Cap 250 54 54 54 54 315 55 57 59 60 400 61 64 67 68 500 60 62 66 66 630 68 68 67 68 800 78 78 78 78 1000 80 80 80 80 Anything in the above surprising? For those running 902's are you getting stronger results at 500 hz? Again I'm not even trying to get to 400 hz, I'd be happy with 500 hz. All suggestions / comments welcome, thanks in advance! Quote Link to comment Share on other sites More sharing options...
IB Slammin Posted July 31, 2009 Share Posted July 31, 2009 Hey Bonder, There has been much discussion of this topic, and the experience's and opinions are all over the place. I ran 511b/GPA 902-16A on a Cornwall (in three way) for a few years, and even crossed at 400hz first order for a while. I had no prob, but some have. As I understand it, those who had probs noticed a buzzing or other distortion when crossed too low. What does your ear tell you? Shoot me an email if you like ibslammin@gmail.com tc Quote Link to comment Share on other sites More sharing options...
Bonder Posted July 31, 2009 Author Share Posted July 31, 2009 Hi Terry, I haven't heard any buzzing or distortion at 90 - 95 db levels while listening to music, I don't want to play it any louder in my garage out of respect for my neighbors. My bigger concern at this time is whether the driver actually goes down to 500 hz, it seems to go down to about 750 hz but then takes a big dive. When you were running 3 way do you recall what size of cap you were running before your autotransformer (and the tap you were running to the mid). Overall it sounds very good, perhaps I'm getting too caught up in the numbers/measurements... occupational hazard being an accountant [] Thanks, Shayne Quote Link to comment Share on other sites More sharing options...
LARRY Posted July 31, 2009 Share Posted July 31, 2009 Bonder, I am also more of a reader than responder.. others are usually more knowledgeable! I am using the GPA 902-8 on either a Tractrix and Altec 511b horns, and my tests with True RTA software and Behringer mic/mixer, etc. have given different results. The 902's are excellent from about 550 hz to 17000 hz where they fall off until about 19000 cycles where they return on both horn lense. I am using ALK 600 hz steep slope crossovers in two way systems (left, right and center chanel-all folded horns). This protects the 902 driver. IMHO 600 hz is the low end of the 902. In reading others input on the GPA 902/Altec 511B combo, my sense was that there was no problem on the top end and that a two way system is as good or better than a three way system. I have pair of Klipsch Belles and Khorns, and the top end is very good, but the GPA 902/Altec 511B or Tractrix is noticeably better. The Klipsch K55V would be a good bet for the 500 Hz crossover, as it is a true 400 Hz driver. Good luck. Larry Quote Link to comment Share on other sites More sharing options...
Bonder Posted July 31, 2009 Author Share Posted July 31, 2009 Thanks for your input Larry, I certainly need better testing equipment to validate what I'm seeing, perhaps the rat shack meter is off and I'm actually at or around 500 hz before it dives. I agree 600 hz is a preferred low end, just can't get my bass bins to reach that high. Good to hear your happy with a two way set up, I've tried this with my Cornwalls and with some music I thought I was missing some sparkle, I'm bringing the Beyma's in high and they do seem to integrate well to the point I'm very happy with the mid and top end. I have a K51 from my Cornwalls I could try to validate my readings at 500 hz, good suggestion, it's worth a try, thanks again. Quote Link to comment Share on other sites More sharing options...
IB Slammin Posted July 31, 2009 Share Posted July 31, 2009 Bonder & Larry, "tests with True RTA software and Behringer mic/mixer, etc. have given different results." That is the reason that I hesitated to reply to this post, and the reason that I said "all over the place". I have curves that show the 511b/902 to be solid as a rock crossed at 400hz, others that show a significant role off at 750hz and some that show a HUGE crater from +/- 500hz to 1,200. ??? There is the 902A, 902B, and 902T and perhaps more. There are the original Altec diaphragms, some after market heavy diaphragms, and the lite ones. Some have phase plugs that limit diaphragm excursions and provide protection at higher wattage, SPL, and lower cross point. I like the 902 (in three way) over the K55V for a reason. The 902 was designed for two way application. Because of the designed HF extention, the upper mids best the K55V by a mile, even in three way IMHO. No dis to the K55's, they are cost efective and bulletproof. But for the conservitive and faint of heart,...... Larry, I agree that the ALK ESN 600 is an outstanding choice for that horn and driver. Sounded great when I used them. Running one of the wooden Trax horns with the 902-16A for ear test now. They are very nice and open. tc Quote Link to comment Share on other sites More sharing options...
IB Slammin Posted July 31, 2009 Share Posted July 31, 2009 Thanks for your input Larry, I certainly need better testing equipment to validate what I'm seeing, perhaps the rat shack meter is off and I'm actually at or around 500 hz before it dives. I agree 600 hz is a preferred low end, just can't get my bass bins to reach that high. Good to hear your happy with a two way set up, I've tried this with my Cornwalls and with some music I thought I was missing some sparkle, I'm bringing the Beyma's in high and they do seem to integrate well to the point I'm very happy with the mid and top end. I have a K51 from my Cornwalls I could try to validate my readings at 500 hz, good suggestion, it's worth a try, thanks again. " I've tried this with my Cornwalls and with some music I thought I was missing some sparkle," That is EXACTLY what I thought as well.......... tc Quote Link to comment Share on other sites More sharing options...
sheltie dave Posted August 1, 2009 Share Posted August 1, 2009 I have been over to Carl's house many times in the two years he has had the GPA new 902/511 or Trachorn combo set up in his system. Bill told Carl the drivers would be replaced if he had any trouble with them crossed at 500 hz. Carl has been spanking the sheeeiitttout of them since the day he bought them, and they haven't even burped once. Based on my experience hearing Carl's setup, I would get the GPA 902s with Trachorns, and run the Khorns as a straight two way...it doesn't get much better. You can spend more money and get the JBL pro drivers, or the TAD drivers, but the seriously good seems to start at the 902s. Quote Link to comment Share on other sites More sharing options...
seti Posted August 1, 2009 Share Posted August 1, 2009 I have been real curious as to the difference between GPA altec and the various 902's. The two sets of curves are puzzling. Some are golden from 500-19 while others 1khz - 22khz. What surprises me is how glat they are out to 20khz. If you have curves of your drivers without crossover I'd love to see them with a description of exactly which driver your using. The 902s sound great no matter which one you have. They really took me by surprise. I'm saving for TAD2001's. The TADs seem a better investment than the market lately. LOL. Quote Link to comment Share on other sites More sharing options...
Bonder Posted August 1, 2009 Author Share Posted August 1, 2009 Seti, The rat shack SPL meter is pretty unreliable over 10,000 so my curves wouldn't be useful, I'm pretty sure I'll need to get a RTA to figure this out. Overall I'm happy with the 902, it's a great driver for it's price point. If I can't get it to get down to 500 hz then I'll just leave it and enjoy the music. Quote Link to comment Share on other sites More sharing options...
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