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This past weekend, having wheeled out a pair of EBS Evolution Pro Line 2000 810 Bass cabinets, going thru the speaker system, initially driving it with 1/3 Oct Pink Noise at 4kHz to check the Tweeter & it’s attenuator, then sweeping downward, manually turning down the SPL level via GK 1001RB bass amp used to drive the cabinet, and finally getting down to 50Hz & 40Hz, I found the cabinet severely rattling. I changed to Sine Wave on the Bruel & Kjaer 1027 generator, and tuned it in the region of 40-50Hz, finding at 44.7Hz, it was shaking itself apart, or so it seemed. The cabinet was literally walking backwards on the concrete floor, at a level of around 115dB SPL Wideband.
I stopped briefly to change to the Fender Bass, after unplugging the generator from the Effects Return jack, and got the same results on low G on the E-String. Put the bass aside, and started looking at the cabinet to see just what is causing this. I plugged the Generator back into the Effects Return jack, and found no obvious way to both install let alone remove the large cell wire-mesh protective grille installed on this cabinet. In the middle vertical centerline of the grille, there are three spacers pushing the grille outward from the left/right gap between the inside cabinet lips to form a very subtle arc, with the grille under tension from that. Very stiff wire mesh, like maybe 12AWG steel, and this grille is captive within the gaps between the top, sides and bottom of the cabinet walls and the baffle. No fasteners found to remove them. And, if you can’t remove the grille, how in the dickens do you remove blown speakers? The speakers are stamped metal frame 10” woofers, each held with flat-head screws into the baffle, front-mounted. The inside cabinet’s front lips all around have carpet covering, with no seams found nor screws to remove them to allow the grille to be removed. The second cabinet I wheeled out, after finding the first one rattling severely, it too did the same as the same pitch range. It's grille near the very top was bent differently than the first one I was working on, as seen on the last photo below.
I did find tweaking the middle screws putting the grille under tension affect the rattling a little bit, but, sounded more like wood joints not well joined. Trying to tighten cabinet screws with this cabinet severely ratting was impossible. Usually on the other cabinets having rattles, you can tighten hardware thru out the cabinet to tame it or cure it. After dropping the drive level substantially, I was finding everything tight, so if all this is from that thick wire mesh, all being pivoted by the center spacers, I'll be surprised. I had hoped to resume the task, only to find the building close up tight this morning, obviously closed for the Christmas holiday....nobody bothered to tell me last week!
The past few weeks, I’ve been going thru Ampeg, Aguilar, GK, Eden, Orange and SWR 810 cabinets, having to reject a lot of speakers and cabinets where I was unable to yet replace the blown woofers with new ones to restore the cabinets to full working status, but this was the first one I’ve come across so severe. Has anyone worked on this particular model before? I haven’t yet contacted EBS, and will be checking in with them and other mfgr’s at this coming NAMM show.
This past week, I added one of my B & K 1/3 Octave Filters which can be switched into circuit with the Pink Noise source, so you can generate 1/3 Octave Pink Noise. At low bass frequencies, the random amplitude signal with Pink Noise has much higher transient amplitude than you get with the Sine-Random noise. Still not as aggressive as what I can produce with the Fender Jazz Bass plugged into the test amp…been using a GK 1001RB for the purpose. The pile of bad woofers has been growing steadily with loads more cabinets yet to go thru. Interesting & fun project, while thinning out what should be taken out of active rental inventory, less a client becomes the one on stage to reject what got rented and delivered!
I stopped briefly to change to the Fender Bass, after unplugging the generator from the Effects Return jack, and got the same results on low G on the E-String. Put the bass aside, and started looking at the cabinet to see just what is causing this. I plugged the Generator back into the Effects Return jack, and found no obvious way to both install let alone remove the large cell wire-mesh protective grille installed on this cabinet. In the middle vertical centerline of the grille, there are three spacers pushing the grille outward from the left/right gap between the inside cabinet lips to form a very subtle arc, with the grille under tension from that. Very stiff wire mesh, like maybe 12AWG steel, and this grille is captive within the gaps between the top, sides and bottom of the cabinet walls and the baffle. No fasteners found to remove them. And, if you can’t remove the grille, how in the dickens do you remove blown speakers? The speakers are stamped metal frame 10” woofers, each held with flat-head screws into the baffle, front-mounted. The inside cabinet’s front lips all around have carpet covering, with no seams found nor screws to remove them to allow the grille to be removed. The second cabinet I wheeled out, after finding the first one rattling severely, it too did the same as the same pitch range. It's grille near the very top was bent differently than the first one I was working on, as seen on the last photo below.
I did find tweaking the middle screws putting the grille under tension affect the rattling a little bit, but, sounded more like wood joints not well joined. Trying to tighten cabinet screws with this cabinet severely ratting was impossible. Usually on the other cabinets having rattles, you can tighten hardware thru out the cabinet to tame it or cure it. After dropping the drive level substantially, I was finding everything tight, so if all this is from that thick wire mesh, all being pivoted by the center spacers, I'll be surprised. I had hoped to resume the task, only to find the building close up tight this morning, obviously closed for the Christmas holiday....nobody bothered to tell me last week!
The past few weeks, I’ve been going thru Ampeg, Aguilar, GK, Eden, Orange and SWR 810 cabinets, having to reject a lot of speakers and cabinets where I was unable to yet replace the blown woofers with new ones to restore the cabinets to full working status, but this was the first one I’ve come across so severe. Has anyone worked on this particular model before? I haven’t yet contacted EBS, and will be checking in with them and other mfgr’s at this coming NAMM show.
This past week, I added one of my B & K 1/3 Octave Filters which can be switched into circuit with the Pink Noise source, so you can generate 1/3 Octave Pink Noise. At low bass frequencies, the random amplitude signal with Pink Noise has much higher transient amplitude than you get with the Sine-Random noise. Still not as aggressive as what I can produce with the Fender Jazz Bass plugged into the test amp…been using a GK 1001RB for the purpose. The pile of bad woofers has been growing steadily with loads more cabinets yet to go thru. Interesting & fun project, while thinning out what should be taken out of active rental inventory, less a client becomes the one on stage to reject what got rented and delivered!
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