hello community!
i'm having serious issues with vibration in a closed-PR subwoofer enclosure i built without cutting any corners in design and manufacturing...
Description:
-x1 12" scanpeak Subwoofer (peerless XXLS copy)
-x1 12" scanspeak matching passive radiator
-front baffle mounted with EPDM rings
-65 Liters internal Volume
-Baffle: 38mm. MDF
-Body: varying thickness from 38mm.-to-45mm. All edges filleted.
-shape: like an 8 with a depth of approx. 65cm.
-Bracing: 38mm MDF board in the center (parallel to the baffle) with 90% of its area opened with holes of various diameters.
-internal double layering with 2mm car sound deadener (rubber-leadSheet-rubber sandwich)
-mounted on rubber feet with wheels underneath
-amplification: Behringer NU6000DSP
this is an over-engineered subwoofer and measured results are:
Incredible frequency response (23Hz-200Hz @103dB SPL with +-2dB max dev. in open space and 10Hz-200Hz @ 4pi)
BUT! the freakin cabin still resonates in frequencies above 120Hz! Especially the Baffle. (Sadly i do not have an accelerometer to measure it exactly)
If anyone please, has any experience on these, give me any input on how i could stop the enclosure from vibrating at levels above 90dB.
Would it work if i used another 12" sub in PP and still keep the Passive Radiator? I've never tried a PP and all measurements show better 2ndHD suppressed. Maybe this way i could actively lower or extinguish the enclosure resonances?
With Respect to all and this amazing forum,
George K.
i'm having serious issues with vibration in a closed-PR subwoofer enclosure i built without cutting any corners in design and manufacturing...
Description:
-x1 12" scanpeak Subwoofer (peerless XXLS copy)
-x1 12" scanspeak matching passive radiator
-front baffle mounted with EPDM rings
-65 Liters internal Volume
-Baffle: 38mm. MDF
-Body: varying thickness from 38mm.-to-45mm. All edges filleted.
-shape: like an 8 with a depth of approx. 65cm.
-Bracing: 38mm MDF board in the center (parallel to the baffle) with 90% of its area opened with holes of various diameters.
-internal double layering with 2mm car sound deadener (rubber-leadSheet-rubber sandwich)
-mounted on rubber feet with wheels underneath
-amplification: Behringer NU6000DSP
this is an over-engineered subwoofer and measured results are:
Incredible frequency response (23Hz-200Hz @103dB SPL with +-2dB max dev. in open space and 10Hz-200Hz @ 4pi)
BUT! the freakin cabin still resonates in frequencies above 120Hz! Especially the Baffle. (Sadly i do not have an accelerometer to measure it exactly)
If anyone please, has any experience on these, give me any input on how i could stop the enclosure from vibrating at levels above 90dB.
Would it work if i used another 12" sub in PP and still keep the Passive Radiator? I've never tried a PP and all measurements show better 2ndHD suppressed. Maybe this way i could actively lower or extinguish the enclosure resonances?
With Respect to all and this amazing forum,
George K.
Last edited:
Hi, I presume the vibration at that frequency doesn't cause it to walk? From your measurements it doesn't cause much deviation in frequency response?
Hello Scott.
Indeed no waking or any deviation on FR.
the FR is incredibly flat for a subwoofer and even runs up to 550Hz with no more than 3dB dev.
Indeed no waking or any deviation on FR.
the FR is incredibly flat for a subwoofer and even runs up to 550Hz with no more than 3dB dev.
It seems to be non resonance vibration and if this is the case it's not a problem Issues in speaker design - 2 If it is a resonance it will show as a peak in the response and you should be able to determine it's frequency by tapping on the cabinet
Thanks scott for the valuable input. In your experience, such an irregularity would be measured accurately on a close-up measurement? 2cm from the dust cap of the woofer?
Hi George,
A couple of thoughts
- First up, I'd recommend doubling up the passive radiators. Your PR does most of its work at a lower frequency than the main driver, so they usually need around 2x the volume displacement of the main driver. If you're not running at high volumes, it's likely to be fine, though.
Next up, if you push gently on the main driver's cone, does it move smoothly?
Are all the screws tight?
All internals joined together properly (bracing to cabinet walls, for example)?
Are the internal cables secure?
Are the wheels rattling?
Is it possible something else nearby is resonating at that frequency?
Try and narrow down the frequency that's causing the problem. Then, play a low-level tone at that frequency (so you can hear the rattle) and then start hunting.
Chris
A couple of thoughts
- First up, I'd recommend doubling up the passive radiators. Your PR does most of its work at a lower frequency than the main driver, so they usually need around 2x the volume displacement of the main driver. If you're not running at high volumes, it's likely to be fine, though.
Next up, if you push gently on the main driver's cone, does it move smoothly?
Are all the screws tight?
All internals joined together properly (bracing to cabinet walls, for example)?
Are the internal cables secure?
Are the wheels rattling?
Is it possible something else nearby is resonating at that frequency?
Try and narrow down the frequency that's causing the problem. Then, play a low-level tone at that frequency (so you can hear the rattle) and then start hunting.
Chris
Hi Chris,
i was thinking of using two PRs or more but they are too expensive.. So i started with one and left the option open for adding up to two more on the rear of the enclosure. This raises a question though. If i were to install the two extra PRs on the back, would there be any type of destructive cancellation since they will be opposed to the one in the front baffle?
Also these scanspeak 12" matching PRs have a feature that doesn't allow for tuning them by subtracting mass in order to resonate higher. They are tuned by the factory @ 14Hz and have a relatively wide Q so the bell reaches up to 30Hz but it is not enough. So there is a small dip in the response from 23 to 16Hz. They only have the option of tuning them even lower!
And as for your suggestions, the only thing that agrees is that i have not stabilized the cable running from the back to the woofer's terminals. But in reality it is suspended in the air inside the cabinet..
But i will give it a try to clamp it.
Thanks.
i was thinking of using two PRs or more but they are too expensive.. So i started with one and left the option open for adding up to two more on the rear of the enclosure. This raises a question though. If i were to install the two extra PRs on the back, would there be any type of destructive cancellation since they will be opposed to the one in the front baffle?
Also these scanspeak 12" matching PRs have a feature that doesn't allow for tuning them by subtracting mass in order to resonate higher. They are tuned by the factory @ 14Hz and have a relatively wide Q so the bell reaches up to 30Hz but it is not enough. So there is a small dip in the response from 23 to 16Hz. They only have the option of tuning them even lower!
And as for your suggestions, the only thing that agrees is that i have not stabilized the cable running from the back to the woofer's terminals. But in reality it is suspended in the air inside the cabinet..
But i will give it a try to clamp it.
Thanks.
You're welcome. No, it would be swamped by the woofer's output, I'd measure from the listening position, are you feeling the vibration with your fingers and is it at a certain frequency?
Yes Scott, it is a very noticeable feeling when you touch the baffle and the curved sidewall. But i haven't run a step by step manual sweep to investigate the triggering frequencies yet. I will!
One more question,
if i were to add another baffle layer in front of the current one made out of 22mm plywood in order to make her heavier and stiffer, would it reduce significantly the vibration? Or tiny returns?
Apologies for the bad english (not my native language)
Thanks a lot.
One more question,
if i were to add another baffle layer in front of the current one made out of 22mm plywood in order to make her heavier and stiffer, would it reduce significantly the vibration? Or tiny returns?
Apologies for the bad english (not my native language)
Thanks a lot.
There are two main ways to deal with vibration: 1) stiffness, which will increase the resonant frequency, this can also be achieved by dividing up the panel into smaller areas by bracing.
2) damping, to absorb the vibration, this can include decoupling the driver from the baffle.
Were you able to make sense of the information on the Linkwitz Lab site, I linked to?
Are you using a low pass filter on the sub? 200Hz is really no longer sub territory
2) damping, to absorb the vibration, this can include decoupling the driver from the baffle.
Were you able to make sense of the information on the Linkwitz Lab site, I linked to?
Are you using a low pass filter on the sub? 200Hz is really no longer sub territory
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