Cornwalled Posted September 11, 2006 Share Posted September 11, 2006 Hey Guys, Apparently from 25 years of pumpin away, my Cornwall cabinets have had it! Over the last month or so, I've noticed a gradually increasing resonance coming from the right side whenever I play music that is relatively heavy in bass. Today, playing Crystal Method, it is absolutely unbearable. So, I go behind the right Cornwall and check it out, and it's the back of the cabinet! All screws are tight, and it's coming from right in the middle of the back panel. In order to keep it quiet, I have to push the back in pretty hard. And this is at moderate levels, i.e. below 80db, way too low for Crystal Method. So, question is, what are my options? These cabs already look like they were dropped off a truck (maybe more than once!). However, I don't have woodworking ability at all, and don't really have the money to buy another set of cabs. Is there anything I can do to reinforce these guys? In the meantime, I'll have to take them out of service, cause they sound worse than me farting! Thanks, Jon EDIT: I went into the receiver and set speaker size to small, which rolls off everything below 80 HZ and they still do it! Surprised by that! Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted September 11, 2006 Share Posted September 11, 2006 remove the back, get some angle iron or angle aluminum (easier to cut) and screw a couple of lengths of that diagonally across the back. Squeeze some paneling adhesive between them first, just so nothing vibrates. Tools needed, Hacksaw, drill, screwdriver, caulk gun. If the screw holes holding the back onto the cabinet are loose, you can insert a couple of toothpicks in the holes and snap them off before reinstalling the back, the extra wood will tighten the hole up. Michael Quote Link to comment Share on other sites More sharing options...
Good2BHome Posted September 11, 2006 Share Posted September 11, 2006 Jon, 1) Be very careful NOT to put any screws that penetrate the back near the Mid-range!! 2) Some have screwed and glued another piece of 3/4 inch (slightly smaller in dimension than the original) to the backs, with good results. 3) Quick and dirty for those with minimum wood skills: The Mid-range is intended to touch the the back of the inside of the speaker, inorder to stiffen the back. Add 1/8" to 3/16" sheet rubber from a good hardware store, to the inside back of the speaker right where it touches the Mid-range AND be sure you can tighten down the screws. The toothpicks in each of the crew holes is a good way to do this. Mike Quote Link to comment Share on other sites More sharing options...
PrestonTom Posted September 11, 2006 Share Posted September 11, 2006 .... The Mid-range is intended to touch the the back of the inside of the speaker, inorder to stiffen the back. ........ Are you sure about this? It seems like a rather suspect design, if it was done intentionally. Personally, I would do as little as possible in terms of altering the cabinet, especially if the mods are visible. BTW, what is meant by a "resonance"? Does this mean something was rattling around? If this is the case, then there is a more direct solution.... -Tom Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted September 11, 2006 Author Share Posted September 11, 2006 Hey Guys, As far as the "resonance", what I'm hearing is a rattling of the back panel during bass hits. Most noticeable with electronic music, or deep kick drums, or moving electric bass, etc. I didn't remember if the midrange touched the back or not. I know there is old damping material on the back panel. I believe the damping material touched the midrange. However, it's the woofer that's really creating the vibration. Maybe the damping material has worn out and the midrange is rattling more directly against the panel? I don't think that would be possible though. I think without the damping material, there would be a slight gap between the midrange and the back panel. -Jon Quote Link to comment Share on other sites More sharing options...
BEC Posted September 11, 2006 Share Posted September 11, 2006 The midrange drivers on my Cornwalls do compress the damping material. Let me give you one other suggestion though. Make sure the midrange horn screws are very tight. I had that problem once. I heard it when the woofer was producing lots of bass below 100 hz. Tightening the mid horn screws fixed it. Bob Crites Quote Link to comment Share on other sites More sharing options...
SilverSport Posted September 11, 2006 Share Posted September 11, 2006 ...y'know Bob, if you weren't so nice you could probably parlay that into a set of new crossovers...that Bob always helpin' ...[] (just teasin' Bob...very happy BEC customer who was once helped when I thought I blew the mid out on my Heresys) Thanks, Bill Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted September 12, 2006 Share Posted September 12, 2006 There are sometimes only 4 wood screws holding the woofer in place. It's possible that you've shaken one loose. Check for tightness, add toothpicks to holes and reinstall screws. You could mark positions for the other four screws, remove woofer, drill out screw holes (being careful NOT to puncture through the front baffle board), then reinstall woofers using 8 screws to reinforce it. I suppose it's possible that the back could be vibrating and striking the mid driver, tightening the driver, adding material or stiffening the back could all be solutions to that dilemma. BTW, I was speaking of putting the stiffening ribs INSIDE the back panel. I think those who use a double panel for the back add the extra thickness to the outside of the cabinet so as not to subtract from the internal volume of the cabinet. (you also wouldn't have to cut hole for mid driver) Let us know how it works out. Quote Link to comment Share on other sites More sharing options...
ZAKO Posted September 12, 2006 Share Posted September 12, 2006 Yes upgrade the structure....But also consider the woofer cone surround plus spider may need replacing as they get tired & floppy after many many a years of use. (30yrs) Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted September 12, 2006 Author Share Posted September 12, 2006 Hey Guys, Thanks for the suggestions. I'm leaving for Colorado tomorrow to attend the CEDIA conference, but I'll try some of these out when I get back. As far as the woofer getting floppy, this is a replacement driver, only about 1-2 years old, so Ithat shouldn't be a problem. Thanks, Jon Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted October 23, 2006 Author Share Posted October 23, 2006 Hey Guys, My Dad is building some speakers of his own right now, with BG Ribbon drivers. Once they're done, we're going to take apart the Cornwalls. I ordered some Solen caps for the crossovers from Parts Express. Figured while we're at it, I'll recap the crossovers. -Jon Quote Link to comment Share on other sites More sharing options...
mark1101 Posted October 23, 2006 Share Posted October 23, 2006 Cornwalled, One thing that no one mentioned, is that the back of the cornwall resonating when you drive them hard (vibrating like mad)......is pretty much normal. You won't get it to stop. But...by tightening everything up on the midhorn, woofer, and rear access panel you will be able to make the cabinet noise go away. My cabinets are silent but the backs vibrate like heck. Everything is tight. Without making a change to the back it's not going to go away. They still sound fantastic. I don't even worry about it. They are old and that was inherent in the design. I think if I replaced the rear access panel with a brand new unfatigued piece of plywood.....it would still do the same thing. It vibrates way too much to think it would simply stop altogether. Maybe you could minimize it some. Quote Link to comment Share on other sites More sharing options...
IB Slammin Posted October 25, 2006 Share Posted October 25, 2006 The 3/4" plywood sheet on the back, screwed & glued, (outside) and 1-1/2X1-1/2" angle iron across the motor board (inside) works for me. The side panels of the production CW's are too small to have much, if any, deflection. This kind of bracing allows the "back-side" of the bass reflex woofer to punch through the ports with more acoustic energy. Again, this is only me. Others could / will disagree. Regards, tc Quote Link to comment Share on other sites More sharing options...
mark1101 Posted October 25, 2006 Share Posted October 25, 2006 You glued them shut? Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted October 26, 2006 Share Posted October 26, 2006 I think he means he doubled the thickness of the back panel by attaching a second sheet to the exterior of the cabinet. (placing it inside seriously affects cabinet volume.) Quote Link to comment Share on other sites More sharing options...
Cornwalled Posted October 26, 2006 Author Share Posted October 26, 2006 Hey Guys, Thanks for the ideas. Hopefully my Dad will be done "working" with his speakers relatively soon and we can work on these. Of course, they'll probably end up sitting in his garage for 2 months, just like his current ones have. -Jon Quote Link to comment Share on other sites More sharing options...
IB Slammin Posted October 26, 2006 Share Posted October 26, 2006 You glued them shut? Mark, Oh no. As a matter of fact, I should install zippers on the back! tc Quote Link to comment Share on other sites More sharing options...
colterphoto1 Posted October 26, 2006 Share Posted October 26, 2006 I wonder if Indycar 'camlocks' would work? Quote Link to comment Share on other sites More sharing options...
D-MAN Posted October 26, 2006 Share Posted October 26, 2006 Vibrating back panels represents a loss of acoustic energy that would normally come out as "music" had it not been "sidetracked". I would definitely strengthen and reinforce the back panel to prevent it from vibrating as much as possible. Look what Altec did with the a7/828 cabinet in the end... 2-2x4's! DM 828cabin.pdf Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.