Sealing the Ports on a Cab?

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Paisley
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Sealing the Ports on a Cab?

Post by Paisley » 15 Oct 2018, 12:13

I'm looking at sealing up the ports on a 410 Cab. Not actually a permanent seal; more like a rubber insert that I could fit into the ports for certain gigs where the response of a sealed Cab would be preferential.
Does anyone know if there could potentially be any damage done to the Drivers by doing this?

Also, has anyone actually done this before; and how well did it work?
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david1234
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Re: Sealing the Ports on a Cab?

Post by david1234 » 15 Oct 2018, 13:47

Paging PeteBass

From memory, some speakers can't damp their movement properly if sealed, some can't damp properly if ported, and others are okay with what you're proposing. So you'll need to do some research.

Some Trace Elliott cabs in the past used rubber plugs like this to deliberately do what you're aiming for: https://www.talkbass.com/threads/trace- ... -2.301868/
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Petebass
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Re: Sealing the Ports on a Cab?

Post by Petebass » 15 Oct 2018, 14:06

Actually Dave, you covered that pretty well.

At moderate volumes, you'll get the effect you were after. But once the dB levels climb, drivers that aren't designed for a sealed environment will run out of puff very quickly.

The better option is to only block half the ports. What this does is lower the running frequency of the porting. The result is similar to what happens when the cab is sealed, and you will still be introducing excursion issues, only not as badly.

What cab is it?
* 2 Stingray 5's (one heavily modded), Ibanez SR805, Ashbory, + more...
* Carvin B1500, Epifani PS1000, Ashdown Superfly amps.
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narcdor
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Re: Sealing the Ports on a Cab?

Post by narcdor » 15 Oct 2018, 17:42

This guy makes cabs with ports to be plugged up, crazy times!

http://www.audiokinesis.com/hathor-1533.html
Strings: Fender, Custom, Framus, Warwick
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Petebass
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Re: Sealing the Ports on a Cab?

Post by Petebass » 15 Oct 2018, 18:37

narcdor wrote:
15 Oct 2018, 17:42
This guy makes cabs with ports to be plugged up, crazy times!

http://www.audiokinesis.com/hathor-1533.html
The guy behind Audiokinesis knows what he's doing. If he's offering port plugs, you can bet your house he's designed it properly!
* 2 Stingray 5's (one heavily modded), Ibanez SR805, Ashbory, + more...
* Carvin B1500, Epifani PS1000, Ashdown Superfly amps.
* Lots of DIY neo/lightweight cabs including one made from composites http://www.ozbassforum.com/viewtopic.php?f=5&t=2546

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narcdor
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Re: Sealing the Ports on a Cab?

Post by narcdor » 15 Oct 2018, 18:58

Oh it looks like it’s built by a sound technician, just look at it. Probably sounds amazing too. Incredible stuff.
Strings: Fender, Custom, Framus, Warwick
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Paisley
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Re: Sealing the Ports on a Cab?

Post by Paisley » 15 Oct 2018, 19:48

Thanks for the replies guys. :thumbup:
Petebass wrote:
15 Oct 2018, 14:06
What cab is it?
Epifani; depending on the gig it's either a UL1-410 or a UL2-310 (occasionally both).

Actually I'd seen that Audiokinesis gear before, which is what gave me the idea. :yep I'm finding as I do more & more Weddings & Corporate work that I'm often scrunched into a tiny corner space with my Cab smack bang against a hard wall. The Epi Cabs aren't low end monsters (particularly the UL-1), but in certain venues I still end up having issues with the bottom end.
I love the Epi's, but before I got them I usually used sealed Cabs, & I remember them having less (or no) issues in some of the same venues as what I'm having trouble with now.

I've been toying with getting another sealed Cab for this reason, but if I can tame a bit of the Epi's bottom end it'll be a lot easier (& cheaper!).
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maxgroover
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Re: Sealing the Ports on a Cab?

Post by maxgroover » 15 Oct 2018, 20:05

Could you tame the lows with a high pass filter instead in the tricky venues?
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Re: Sealing the Ports on a Cab?

Post by noplanb » 15 Oct 2018, 20:23

^ I like the above idea, and have been toying with it in my mind on and off. It could likely be an op-amp design with a high rate of roll-off (-20dB per decade or more), but with more than one frequency roll-off point (-3dB); maybe selected via a switch. That way R's and C's in the filter may be switched at the same time. Over to someone with Spice for a design. My suggestions for -3dB points would be: 40Hz, 80Hz, then maybe 120 or 160Hz(?).
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NotTheFish
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Re: Sealing the Ports on a Cab?

Post by NotTheFish » 15 Oct 2018, 21:18

Another suggestion is to use something like the Empress ParaEq. You can notch out a very small band that is causing the problem without effecting the tone. You just sweep through the low end while boosting until the problem freq jumps out at you and then simply turn the boost to cut.

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Paisley
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Re: Sealing the Ports on a Cab?

Post by Paisley » 15 Oct 2018, 21:24

Actually that's not a bad idea at all! I wonder how well the Cave Tight Arse would work for something like this?
:hmm
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Re: Sealing the Ports on a Cab?

Post by NotTheFish » 15 Oct 2018, 21:39

The tight Arse is a different beast. It is a low pass filter. Without looking it up I would guess it has a steep rolloff of say 12bd per octave below 30hz. The ParaEq is a parametric Eq with 3 different Frequency widths (Q settings). The narrowest is very narrow which is great for the purpose of hitting a booming note on the head. Lets say you play a Bb and it really booms. Looking up a table I see that is 233hz. You adjust the ParaEq bass control to that freq and cut it with a narrow Q and that boom is gone. That is my understand anyways..

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Bill Fitzmaurice
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Re: Sealing the Ports on a Cab?

Post by Bill Fitzmaurice » 15 Oct 2018, 21:54

Sealing a ported cab makes sense if you change the drivers from low Q to high Q. If you know what Q is you know why this is the case. If you don't then you shouldn't be thinking about messing with your cab. As for sealing ports, also not the best idea. Doing so does more than lowering cab tuning, it also changes system Q (there's that term again), and more important, reduces port area, which results in port chuffing noise. Worst of all it lowers the frequency where cone excursion is at a minimum, which can result in blown drivers. As for emulating the response of a sealed cab with a ported cab, as already pointed out that's a rather simple affair: turn the bass EQ down. That's why amp designers go to the trouble of putting those knobs and sliders on there.

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Paisley
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Re: Sealing the Ports on a Cab?

Post by Paisley » 16 Oct 2018, 00:24

NotTheFish wrote:
15 Oct 2018, 21:39
The tight Arse is a different beast. It is a low pass filter. Without looking it up I would guess it has a steep rolloff of say 12bd per octave below 30hz. The ParaEq is a parametric Eq with 3 different Frequency widths (Q settings). The narrowest is very narrow which is great for the purpose of hitting a booming note on the head. Lets say you play a Bb and it really booms. Looking up a table I see that is 233hz. You adjust the ParaEq bass control to that freq and cut it with a narrow Q and that boom is gone. That is my understand anyways..
That's interesting; for what it does, I would have thought of the TIght Arse as more of a HPF. There's a few threads on it on OzBass; I'll go through them tomorrow.

You're right though; a parametric with a variable Q should do the trick. I've actually got a three band semi-parametric on my Amp (Eden WT-550), but even with the low band of the EQ, I was unable to tame the offending frequencies without killing the bottom end altogether. If I could have narrowed the Q on the low band it might have worked a lot better.
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Re: Sealing the Ports on a Cab?

Post by Bill Fitzmaurice » 16 Oct 2018, 01:03

Paisley wrote:
16 Oct 2018, 00:24
even with the low band of the EQ, I was unable to tame the offending frequencies without killing the bottom end altogether.
When the problem is boom don't assume that it's sourced in the first octave. Chances are it's in the second octave, so rather than pulling down at, say, 50Hz, trying pulling down at 100Hz.

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