Bob01464 Posted January 13, 2016 Share Posted January 13, 2016 Hi Guys, I'm new to the forum but have been doing a lot of reading on it the last month or so. I currently have a pair of Chorus 2's that were given to me probably close to 6 years ago (Yup free of charge). Well I recently got them out of storage as they finally have a place to go in my office over the garage I'm building. The problem is one of them is missing the passive radiator all together so I have a 15" hole in the back. Its one hell of a port...LOL. So I'm looking at my options here. I have not been able to track down a stock replacement passive. What are the thoughts of covering the hole in the back and placing two 4" ports in the front as the original Chorus had. Only tuned to a enclosure frequency of around 37Hz (If that's the best recommended freq). Would that give me more flexibility in placement also (Might not be a issue as they will be in the corners). Might the ports be better off higher on the motor board or maybe rear ported. The other option that seems to be readily available is the 15" JBL Passives that are available on Ebay (Expensive though). Of course I have no idea if they would even be a good match and are close mass wise. I do have 4 4" flared port kits sitting in the garage just asking to be used so its tempting as all hell...LOL. I did purchase the Crites (Great Guy) Ti Tweeter drivers and crossover repair kit. I will be installing these once I have decided on which direction to proceed in. Are there any other mods that would be recommended while I have them torn down. Let me just thank you in advance and welcome your thoughts Bob Quote Link to comment Share on other sites More sharing options...
ZEUS121996 Posted January 13, 2016 Share Posted January 13, 2016 You should post a WTB in the garage sale. You want the 15 passive, it's a better speaker IMO than the front ports. There should be someone that has a spare or 20 in their collection Mark Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 13, 2016 Author Share Posted January 13, 2016 Thanks Mark, I took your advice and posted a WTB. Still would love to hear anybody else's thoughts on the subject. Is the PR better then a properly ported configuration. Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 14, 2016 Author Share Posted January 14, 2016 Had some good input over on the Garage Sale board. Going to shift it back to this board. My current thought is to block the PR holes and rear port at the top corners. 2 - 4" flared ports between 8" and 10" Figured the rear porting might give me a boost as these will be in the corners of the room (20' x 22'). Also I won't have to cut into the motor board. I had thought about putting the ports where the PR used to be but they would extend too far into the cabinet due to the woofer magnet occupying that area. So a couple of questions. - Whats the optimum tuning frequency for the enclosure. Was figuring around 37Hz but does going lower have any advantage. I know you don't get something for nothing. - Does flaring the port internal to the box provide any benifit or just take up space. - Would adding any internal bracing say mid cabinet provide any benefit - Any other mods I should be considering. Mid horns might get some new Crites diaphragms (Not the Ti one's at this point). Thanks alot Bob Quote Link to comment Share on other sites More sharing options...
Marvel Posted January 14, 2016 Share Posted January 14, 2016 Are you going to make both of them ported? That would be the best. I would make a plywood disc with ports mounted to simpy replace thepassives until you could replace them both or get a second that matches the one you still have. Bruce 1 Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 14, 2016 Share Posted January 14, 2016 For the port, you could make a circular disc with the port in the middle and then install the whole assembly into the same place as the original passive radiators. This would give you a fully reversible mod should you ever find passives for sale in the future... 2 Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 14, 2016 Author Share Posted January 14, 2016 I'm shying away from that approach due to the port calculations I'm getting. What I'm coming up with is a min port dia of 5.5". A pair of 4" ports puts me at about 8" apiece and a single 6" port would be approx 8". This would run right into the woofers magnet. So my thought was to use 2 4" flared ports on the rear of the cabinet in the upper corners. Hopefully getting at least 1 Dia distance from the surrounding structure. Also my gut feeling and I don't know if any fact supports this, is to put some distance from the woofer to the ports. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted January 14, 2016 Share Posted January 14, 2016 You could just 90 degree the ports away from the woofers. Use PVC and fittings. 1 Quote Link to comment Share on other sites More sharing options...
MookieStl Posted January 14, 2016 Share Posted January 14, 2016 I agree with Carl, use a 90(s). Makes it easier to convert back to passive radiator if you so choose and you don't have to drill more holes in your back panel. I have not seen inside the Chorus II but the Chorus I had no bracing for the back and it may react poorly to additional weakening of the structure. IMHO 1 Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 14, 2016 Author Share Posted January 14, 2016 Yea I did consider PVC but 4" Schedule 40 PVC is huge and heavy. I also wanted to utilize a flared port. I think my intention will be to make a panel the complete size of the back thereby covering the existing cutout, strengthening the entire rear structure and my 4" flared ports won't require huge cutouts in the existing cabinet to clear the flares. Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted January 14, 2016 Share Posted January 14, 2016 Schedule 40 PVC Don't use schedule 40 then. Use schedule 35 or that stuff they use in RV's. It's pretty thin. 1 Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 15, 2016 Author Share Posted January 15, 2016 Thanks CECAA850 I hadn't considered that. I'll add it to the option list...LOL Quote Link to comment Share on other sites More sharing options...
DrWho Posted January 15, 2016 Share Posted January 15, 2016 Also my gut feeling and I don't know if any fact supports this, is to put some distance from the woofer to the ports. Distance adds propagation delay, which in turn affects the phase coherency between the port and driver. If you're too far away, then you can actually get a small dip in response just above the tuning frequency. Hornresp actually has a method for calculating this effect. I suppose directly behind the driver motivates higher frequencies to fire straight through the port. Making the ports smaller is beneficial in this regard. You also want to avoid the internal port mouth to be sitting in the middle of an internal standing wave (since this will couple that resonance out of the box). I'd argue there should be damping material inside the cabinet anyway. I've been using the cheap $20 polyfill pillows from walmart with great success. You can easily see it clean up the frequency response, and the pillow casing makes it easy to mount it in the right location. Just knock some staples through the system. Quote Link to comment Share on other sites More sharing options...
wvu80 Posted January 15, 2016 Share Posted January 15, 2016 (edited) I'd argue there should be damping material inside the cabinet anyway. I've been using the cheap $20 polyfill pillows from walmart with great success. You can easily see it clean up the frequency response, and the pillow casing makes it easy to mount it in the right location. Just knock some staples through the system. I was thinking about that as well. The rule of thumb is to use lining for ported, polyfil for sealed. I used a small amount of polyfil in my ported CF-4's and it took out the classic Klipsch "harshness" in the upper frequencies. That means I mixed both the stock foam sheets behind the drivers and probably a pound of polyfil at the bottom near the ports, but not blocking the ports. Edited January 15, 2016 by wvu80 Quote Link to comment Share on other sites More sharing options...
ricktate Posted January 15, 2016 Share Posted January 15, 2016 I have never had Passive speakers. But why couldn't you use a another speaker and just not hook it up? Just wondering. Quote Link to comment Share on other sites More sharing options...
oldred Posted January 15, 2016 Share Posted January 15, 2016 (edited) Do not modify cabinet..... Just buy 15 inch passive from parts express. If you do Crites mods that's good. It is easier and you won't be chopping something up. G.E.M Edited January 15, 2016 by oldred Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 15, 2016 Author Share Posted January 15, 2016 The 15" is no longer available through parts express. Totally agree on the lining and polyfill. Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 15, 2016 Author Share Posted January 15, 2016 If these were some nice oil finished cabinets I would be more hesitant on any mods but they are the black version that have been around the block a few times. Quote Link to comment Share on other sites More sharing options...
wvu80 Posted January 15, 2016 Share Posted January 15, 2016 (edited) I have never had Passive speakers. But why couldn't you use a another speaker and just not hook it up? Just wondering. After doing a nationwide search, there were very few passives available for the C2. OK, there were none. The 12" passive I found on PE was $34 (15"s were not available). The cheapest 15" woofers on PE that even looked like they might be close to the same size were around $100, and who knows if that would even work? Edited January 15, 2016 by wvu80 Quote Link to comment Share on other sites More sharing options...
Bob01464 Posted January 15, 2016 Author Share Posted January 15, 2016 Yea I did take a look at the JBL 15" passive but most were going for 150+. Alot of money for something that might not even be optimum Quote Link to comment Share on other sites More sharing options...
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