Help? Loud rattle in Sunn 215BH with Eminence Kappa 15LFAs with CGCG tuned bass

[bovine mind]

My Sunn 215BH has a loud rattle that I hear on certain notes on my fretboard with my CGCG tuned Gibson Ripper bass. The rattle is worse if I use bass heavy effects like my Moog low pass filter or boost the bass and low mid eq on my SVT-II [300w all tube] amp. My apologies if some of this info has been posted in other threads but I'm hoping a dedicated thread might help solve this problem.

I upgraded the speakers with Eminence Kappa 15LFA's and use the cab with an Ampeg 410HLF stacked vertically. I had my tech go through the entire Sunn cab and repair all air leaks inside. Besides this rattle, which I can't hear while my band is playing but can be heard when solo'ed, the trio sounds amazing and the deep sub bass from it is huge and satisfying, I only have to turn my amp up to 4/10 to get the entire room shaking and really FEEL the bass, so I'd like to keep the rig.

Once I got to his shop with my bass we still heard the rattle. We were able to reduce the rattle somewhat significantly by having him press fairly hard on the back of the cabinet with his hands while I played the problematic notes. He mentioned that some guys use a sheet of wood attached to the back of their cabs to damped notes that rattle as such and suggested that we could try this. Has anyone heard of this working, or can anyone suggest any ways to fix this? I have a few sheets of thick foam, would lining the interior help and if so exactly where should I add it?

I've read in a thread here that some of the old Sunn cabinets were not tuned low enough to take the lower tuning of modern speakers and lower tunings. I'm not sure how to find out how low my cab is tuned.

Here is the best photo I have of the cab and the speakers specs on the Eminence Kappa 15LFAs.



speaker specs:

Nominal Basket Diameter 15" / 381mm

Impedance 8 ohms
RMS Power Rating 600 Watts
Program Power Handling 1,200 Watts
Frequency Response 38Hz - 2.7kHz
Sensitivity (1W/1m) 99dB
Voice Coil Diameter 3" / 76.2mm
Max. Crossover Frequency 2.7kHz
MOUNTING INFORMATION

Overall Diameter 15.16" / 384.9mm
Bolt Circle Diameter 14.562" / 369.9mm
Baffle Cutout Diameter
13.77" / 349.6
No. Of Mounting Holes 8
Mounting Hole Diameter 0.275" / 7mm
Overall Depth 6.375" / 162mm
Magnet Weight
95 oz.
Shipping Weight 22.3 lbs. / 10.1 kg.
THIELE-SMALL PARAMETERS

Resonant Frequency (fs) 39 Hz
Impedance (Re) 5.4 ohms
Coil Inductance (Le) 1.27mH
Electromagnetic Q (Qes) .41
Mechanical Q (Qms) 6.08
Total Q (Qts) .38
Compliance Equivalent Vol. (Vas) 159 Liters/5.6cu. ft.
Voice Coil Overhang (Xmax) 5.5mm
Surface Area of Cone (Sd) .08563 m2

response curve:



Any thoughts?

[D.M.N.]

Is the cabinet front loaded, so that the back is sealed? I had some rattles with my 2000s cab at higher volumes, but that was solved by putting more screws into the back panel. So if there are screws in the back, it may be a good idea to put more in to help tighten things up.

[Mr. Foxen]

There is a way of figuring port tuning if you have a means of producing a sweepable sine wave, putting the cab on its back and putting some rice or salt on the cone. You sweep the frequency about to the point the cone moves in a certain way, either it peaks or in dips in movement for same volume level, would guess it dips at the port resonance as the port is producing sound and a corresponding resistance, but I'm not sure.

Edit:Found where I read it, I was about right: http://basschat.co.uk/index.php?show...dpost&p=786768

[billfitzmaurice]

Originally Posted by bovine mind

We were able to reduce the rattle somewhat significantly by having him press fairly hard on the back of the cabinet with his hands while I played the problematic notes.

That indicates insufficient, or non-existent, panel to panel bracing.

I have a few sheets of thick foam, would lining the interior help

It will do nothing to stop panel flex, but the cab should be fully lined with an inch or two to damp internal midrange reflections.

I've read in a thread here that some of the old Sunn cabinets were not tuned low enough to take the lower tuning of modern speakers and lower tunings. I'm not sure how to find out how low my cab is tuned.

It's best determined with an impedance sweep. Whether or not changing the tuning is warranted requires reverse engineering the box in modeling software.

[bovine mind]

Originally Posted by billfitzmaurice

That indicates insufficient, or non-existent, panel to panel bracing. It will do nothing to stop panel flex, but the cab should be fully lined with an inch or two to damp internal midrange reflections.

It's best determined with an impedance sweep. Whether or not changing the tuning is warranted requires reverse engineering the box in modeling software.

What method do you recommend to brace the back panel more securely? Would adding a wood plank help this as suggested?

I'll address the foam soon, thank you.

How do I do an impedance sweep? Any links in laymen's terms that explain this? I'm not familair with a lot of this vocaublary.

[bovine mind]

Originally Posted by D.M.N.

Is the cabinet front loaded, so that the back is sealed? I had some rattles with my 2000s cab at higher volumes, but that was solved by putting more screws into the back panel. So if there are screws in the back, it may be a good idea to put more in to help tighten things up.

Yup, font loading, looks like we have a similar problem. Thanks for the suggestion!

[billfitzmaurice]

Originally Posted by bovine mind

What method do you recommend to brace the back panel more securely? Would adding a wood plank help this as suggested?

The back and baffle should be connected with braces.

How do I do an impedance sweep?

Testing gear that you don't have, and probably don't want to spend $100 to get, is required.

[bovine mind]

Update:

Last night my drummer and I installed a plywood board of these dimensions on the back of the cabinet:

38 x 23 x 7/16

the cab dimensions are about:

46 x 27 x 21

The board successfully dampened back panel vibrations and I didn't hear the rattle nearly as bad as I did before. Unfortunately our measurements didn't account for the 1/4" input panel, and the board is buckled a bit where this is. we are going to cut a section out of the board to account for this and re-install. I think it should work.

I asked my tech about the idea to connect the back and baffle with braces, he said it should work but it would change the resonant frquency of the cab and I'd probably lose some of the really deep sub frequencies that I love so much.

[billfitzmaurice]

Originally Posted by bovine mind

he said it should work but it would change the resonant frquency of the cab

No, it won't. And a single 1x1 inch brace running from the middle of the back to the middle of the front of an unbraced cab is more effective in controlling vibration than doubling the thickness of both the baffle and back. A few braces, even better.

[faceinbass]

bump!

I just got one of these cabs in a trade.
Can anyone recommend a modern speaker to replace the 160w at 4ohm speakers? LOL1

300w at 8ohms or 4ohms is fine.

Anyone?