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Perth - Whats a sub box actually cost to build?


Troyus_

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@Troyus_  I've got the T/S Parameters for these subs if you want (I used DATS) so PM myself, jamiebosco also on here has them now or email/call Peter from DeepHZ as I emailed the specs to him April 2015 after I received mine.

 

Regards,

Brett

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1 hour ago, bjc said:

@Troyus_  I've got the T/S Parameters for these subs if you want (I used DATS) so PM myself, jamiebosco also on here has them now or email/call Peter from DeepHZ as I emailed the specs to him April 2015 after I received mine.

 

Regards,

Brett

well done!

 

@Troyus_ download one of the free speaker design tools like WinISD and you can design your box.

WinISD can be a bit tricky loading the specs for a driver that's not already in the database - which you will likely need to do (WinISD has internal sanity checks on the driver specs that can test the sanity of the user).  Others here on SNA that have used it lots will be able to advise.

 

I remember another great free speaker design tool that @scumbag linked to ages ago but I can't find it.

 

For really simple modelling of a driver in a sealed box, my go to tool is a spreadsheet available on Rod Elliot's website:

http://sound.whsites.net/project71.htm

Just read down the article to find "The Linkwitz Transform spreadsheet can be downloaded here" and download it (requires Microsoft Excel, or OpenOffice etc).

You don't need to bother with the Linkwitz Transform bits (but very useful to get an idea of how much EQ you may need to hit SPL targets) - just go to the "box" tab and enter 3 values that Brett will provide - Fs, Qts and Vas (enter Vas as a negative if litres), and enter a box size for Vb (again negative if entering litres).

You'll see a graph of the frequency response, and take note of the calculated value of Qtc below in row 10.

A Qtc of 0.707 is a reasonable goal, so is lower (bigger box) down to say 0.5.

Smaller boxes will increase Qtc and create a hump before the high pass roll-off - you don't want this - especially if you don't have EQ to smooth it out (think boomy bass).

This spreadsheet is only designed for a single driver in a sealed box, but the same response curve would be achieved with 2 drivers on the same baffle with double the box volume.

 

If you're interested I can guide you through the "Linkwitz Transform Calculator" tab - I use it to give me an idea of how much EQ boost I'll need to achieve a flat response pushing the driver lower than its natural  response in a particular sized sealed box.

A Qtc of 0.707 provides the lowest and flattest response for a driver in a sealed box, but a larger box (lower Qtc) has a slower roll off down low, and less EQ is needed to push it lower.

 

cheers

Mike

 

 

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Thanks for that reply. The sub box design is a little tricky. Its going to be a dual opposed design the same as https://www.powersoundaudio.com/pages/xs30

so I need the software to handle that. If none can then Im back to trying to match the specs of the sub in that link there as close as I can.

 

Thanks

 

(NFI why that silly line/link is there.)

Edited by Troyus_
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That's all the info Troy. I realised Power and xmax were missing. From my research and talking with the US PSA lads that this specific driver has a 380w power handling and xmax they say is 25mm which I don't doubt but I've kept it at 22mm in my sim which you can change. It will effect xmech (no biggy) and Vd (piston displacement at xmax).
Anyway, hope that helps and if any advanced people could chime in for sim advice that would be great....
I'd like a low freq tapped horn myself with these drivers but don't understand the horn software very well! Bassbox is easier.... 1d95409470dd6a1142b46a0f063db4c7.jpg

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10 minutes ago, Troyus_ said:

Thanks for that reply. The sub box design is a little tricky. Its going to be a dual opposed design the same as https://www.powersoundaudio.com/pages/xs30

so I need the software to handle that. If none can then Im back to trying to match the specs of the sub in that link there as cloase as i can.

 

Thanks

 

(NFI why that silly line/link is there.)

Of course it's completely your call how you want to design your own sub!!

 

Checking out that link you provided, it's using DSP and a box <169 litres (based on external dimensions including the feet) with 2 drivers.

Obviously I haven't modelled the drivers in their box, but I suspect the Qtc of the commercial speaker is fairly high and  they've EQ'd the response, or possibly implemented an Isobaric design.

 

If this is your first sub build I would definitely recommend keeping it simple!

 

I respect @bjc's choice to send the T/S parameters to you privately...

 

... @bjc do you see any issue with you or the OP posting the Fs, Qts and Vas of these drivers in this thread?

You measured the specs yourself hence the specs you measured aren't proprietary, now public domain - your call.

 

It would make things way easier to assist the OP in his speaker design, and no commercial benefit would likely be gained (not from me anyway).

 

@Troyus_ (bizarre with such a user name there are 2 of you, and you have the "_" at the end)...sorry :offtopic:

1 hour ago, Troyus_ said:

The sub box design is a little tricky. Its going to be a dual opposed design the same as

Once you have the driver T/S parameters you can pretty much design what you want...

 

...let's just assume for a second that XS30 dual opposed design is a standard (non-isobaric) design - ie the drivers move in and out at the same time (IMO a  reasonable assumption for a sub).

The drivers are 15" and the box dimensions aren't huge - I'd bet money that the XS30 has EQ applied out of the box.

 

Don't get me wrong - I love EQ in the bass end, and consider it essential - but don't head down a path attempting to replicate a commercial design that IMO has likely used EQ when you don't have any.

 

I would definitely plan and budget around including some DSP  EQ in your sub build (like a miniDSP 2x4).

 

Is there any specific reason you want to go dual opposed? I get that you want to replicate the commercial design, but why?

You'll achieve smoother "in room" bass response (but with more integration effort required) with 2 subs compared to a single sub.

Provided both subs are the same distance to the listening position you can run both from a single amp (assuming the amp has enough power, and is still able to drive 2 subs impedance wise).

 

cheers

Mike

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7 minutes ago, bjc said:

That's all the info Troy. I realised Power and xmax were missing. From my research and talking with the US PSA lads that this specific driver has a 380w power handling and xmax they say is 25mm which I don't doubt but I've kept it at 22mm in my sim which you can change. It will effect xmech (no biggy) and Vd (piston displacement at xmax).
Anyway, hope that helps and if any advanced people could chime in for sim advice that would be great....
I'd like a low freq tapped horn myself with these drivers but don't understand the horn software very well! Bassbox is easier.... 1d95409470dd6a1142b46a0f063db4c7.jpg

thanks

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just using the simple Rod Elliot spreadsheet that's a pretty big box to provide a Qtc of 0.71 - 190 litres

5a7eb09123741_troyusQtc.7.PNG.aea87065c4893bdb333a58d2fdbf9928.PNG

And the F3 (38.49Hz) is not in sub territory without EQ

adding EQ to hit 20Hz with the 190 litre box gives

5a7eb73c473e3_troyus190litreswiithLT.PNG.7d6ee8b073d2300194719327c8b30ee5.PNG

approx 12dB of EQ boost required to hit 20Hz

 

The commercial design (assuming normal box, not isobaric) of internal volume say 165 litres with 2 drivers (note I just divided the box volume by 2) would have a response like

5a7eb24801a20_troyus2drivers.PNG.19d44041116b57013e530bd5e03306db.PNG

As expected (2 drivers in a smaller box of 165 litres) the F3 (40.19 Hz) is higher and not in sub territory - more EQ will be required for sub performance.

Adding EQ to hit 20Hz with 2 drivers in 165 litre box (modelled as a single driver in 82.5 litre box)

5a7eb8b113da0_troyus2drivers165LwithLT.PNG.9b54e51b558c95f7f94aa39024249ca2.PNG

approx 15db EQ boost required to hit 20Hz - that's double the power of the 190litre box.

 

Too hard to seriously  consider the additional output of 1 driver vs 2 - I don't think it makes any difference in this case (the whole graph would be lifted with 2 drivers) - Hoffman's Iron Rule at play - smaller boxes need more power.

 

I hope the above illustrates to you that the commercial version is using EQ - and that you need to consider your sub design in this context - you won't be able to achieve the same performance as the commercial design without EQ...

 

...from my perspective every sub design needs DSP EQ, and for the best performance, the DSP ability to delay main speakers to time align with the sub/s.

 

cheers

Mike

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Thats a crazy amount of info, thanks Mike and BJC. So 165L is factory but its a small size so needs more boost down low to even it out. 190L would be better and less DSP needed.

 

I have the inuke6k DSP so I can add some power in down low, right? From what I have read it only allows adjustments to 20hz tho. The inuke has gobs more power than these subs can handle, is there any safety issues adding the bass in with a smaller box? 2000w RMS amp into 2x380w drivers has me a little worried.

 

Also, think this will sound any good?

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the inuke is a 2 channel amp, with oodles of power and EQ capability.

My recommendation would be to build 2 identical subs rather than a single dual opposed.

Keep shopping around if someone wants to charge you double for cutting the MDF for 2 identical subs (putting them together is twice the labour so that's OK)

 

On my quick scan of the inuke, what I couldn't find, but it may support, is the ability to take a full range line level input in, and provide a line level output (that would go to the amp for your main speakers) that can be delayed.

For me it's a fundamental issue when integrating sub/s and mains, it's usually the mains that need to be delayed to let the sub/s catch up. Being able to delay the sub/s further is just a band aid.

I've never come across a sub amp that could - but on my scan of the inuke specs I saw some stuff about delay line speakers for time alignment in large auditoriums - so your inuke just may be ideal (assuming you run a separate pre-amp and power amp).

Many people still achieve good sound  in their rooms with subs without delaying their mains. If your inuke can't delay the mains (or you run an integrated amp without pre-out/power amp in), try to position your sub/s closer the listening position than your main speakers.

 

All that aside, coming back to your sub (or subs), the drivers seem relatively efficient (89.58 1W/1m) and have good Xmax (25mm), and you have plenty of power and DSP EQ available, so you're in a good place to start :)

 

You need to decide on 1 sub or 2 - with your 2 channel inuke, as I said above I'd go 2 identical subs - simple cubic boxes with decent internal bracing.

Your SPL and low frequency target will influence the design and how long your drivers survive, I don't think you'll run out of power (should probably do a "back of the envelope" check - EQ down low does chew up amp headroom).

If you want 120dB SPL at the listening position at 20Hz, then I suspect you'll hit thermal and/or mechanical limits on the drivers pretty quickly.

That said, most music doesn't have a lot of content below 35Hz, and action movies with explosions etc have much lower content, but it's transient not continuous - provided you're not hitting the excursion mechanical limits on your drivers, or running 20Hz test tones for more than a few seconds, you'll be fine.

 

Because you have EQ and plenty of power and Xmax, you could go for a box say 100litres for a single driver.

That provides a Qtc of 0.83 - and requires about 14dB of EQ boost to get to 20Hz, which is a lot of boost, but not ridiculous

If you build a cube that's 465mm internal each way.

You can change any dimension to suit but keep the volume the same.

litres = length (mm) x width (mm) x depth (mm)/1 million

A cube just makes the maths easier

litres = (internal dimension mm)^3/1 million, or

internal dimension (mm) = litres^(1/3)*100

 

I wouldn't go smaller than 100litres per driver if 20Hz is your target - I'd go larger

 

If you really have to build a dual opposed box, just double the volume - 200 litres is a cube of 585mm internal.

 

Coming back to some "back of the envelope" calcs

Let's make the numbers easier and say your drivers are 90dB/1W/1m

Your inuke has 3000W/channel into 4ohms

Ignore for a second that your drivers are rated to 380watts continuous - we won't ignore it for long...but provided your drivers aren't hitting mechanical limits (Xmech), then they can take much higher power for short periods (like explosions in a movie).

 

With no EQ boost and using a rough estimate of 6dB reduction in SPL between 1m from the speaker and the listening position you'd need

 

2048W for 123dB @ 1m and 117dB @ the listening position

 

if you really needed 15dB boost (from above 14dB to hit 20Hz in 100litre box)

2048W for 108dB @ 1m and 102dB at the listening position

 

Pushing subs lower consumes a lot of power - I'd need to run the numbers, but going to 200litres per driver would significantly reduce the boost and power required to hit 20Hz.

 

Coming back to the 380W continuous spec on your drivers, that would give you about 108dB SPL without EQ or 93dB SPL with 15dB of boost - but this is a very very rough guide.

Your sense of smell is a much better guide for exceeding thermal limits of drivers - shut down immediately if you smell something odd from your drivers - sealed boxes don't have ports to let heat out/pump air out of the cabinet.

 

Muck around with your speaker modelling tool of choice - I like the spreadsheet I linked to, but WinISD and others are way more powerful.

 

cheers

Mike

 

 

 

 

Edited by almikel
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20 hours ago, almikel said:

Is there any specific reason you want to go dual opposed? I get that you want to replicate the commercial design, but why?

You'll achieve smoother "in room" bass response (but with more integration effort required) with 2 subs compared to a single sub.

Provided both subs are the same distance to the listening position you can run both from a single amp (assuming the amp has enough power, and is still able to drive 2 subs impedance wise).

Thanks for the info above mike. I missed this question above.

I liked the idea of 2 subs per box for extra power and since one of them will be a coffee table, dual opposed reduced vibrations seemed like a good idea. So then of course we need 2 seperate subs to reduce nulls so I’m planning 2x2 dual opposed subs. 1 will be nearfield at the end of the couch, beside me. The other near the tv or in the corner. Placement is a bit flexible there.

 

to that end, the inuke 6k dsp only outputs 4ohm min, so I purchased 2x2ohm speakers per subwoofer box so everything works out. So I couldn’t even run 1 in a box if I wanted. Plus the inuke 2k power seemed better used for 2 380w subs rather  than 1. (Inuke 6k has been measured to only but out about 2k rms btw)

 

this is for a basic loungeroom so no seperate amplifiers for each listening speaker I’m afraid.

 

so from all this measuring above, it seems to come down to ‘bigger box is better.’ ? No specific size, just it would work better with more space? Better as in less boost needed to reach 20hz.

Edited by Troyus_
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The XS30 was about 5.27cft external so 4.27 internal or there abouts. Tom's designs were based (not solely) on using natural room gain in the low end to enhance most of that range of subs which is why when a basic simulation is run the graph is peaky like a mountain! Until you check the figures or overlay something similar then you realise....

 

You could always build them so the sub is facing down. Then you can build two cabs with one sub in each and have your coffee table as it won't bounce around. 

Tom had a sealed and ported version of these I'm sure in his line up?  

 

Doesn't the iNuke do 2ohm stereo per ch? Otherwise you do what I do with multiple subs and chain gang them via speaker wire outside there cabs to a single input to make up your 4ohm..... 

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19 minutes ago, bjc said:

You could always build them so the sub is facing down. Then you can build two cabs with one sub in each and have your coffee table as it won't bounce around. 

Tom had a sealed and ported version of these I'm sure in his line up? 

Thats the plan for the end table one. One driver facing down to clear the dust from under the couch and the other facing up to look cool with some glass over the top.

 

The other one will be more normal in the corner somewhere. Front and rear facing drivers.

19 minutes ago, bjc said:

Doesn't the iNuke do 2ohm stereo per ch

Not the inuke 6k DSP. I think the Inuke4 6k does, from memory.

 

Either way Im happy with the dual opposed idea.

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On 2/11/2018 at 2:36 PM, Troyus_ said:

 

so from all this measuring above, it seems to come down to ‘bigger box is better.’ ? No specific size, just it would work better with more space? Better as in less boost needed to reach 20hz.

Yes, a bigger box requires less EQ to hit 20Hz - this is Hoffman's Iron Rule at play...

...pick any 2 out of the 3:

  • low bass
  • small box
  • high efficiency

with a total of 4 drivers across 2 boxes with your amps I think 100 litres per driver is about right (200 litres each box) - if you go smaller then you'll just need more EQ - and it will come down to your SPL targets and the capability of your mains (if you need to dial back your subs to match your mains then you just picked up headroom on your subs).

 

You could also take the approach that the coffee table sub is the "heavy lifter" and make it bigger (to improve efficiency), and compromise on the size of the corner sub and not push it so low.

 

On 2/11/2018 at 4:34 PM, Troyus_ said:

One driver facing down to clear the dust from under the couch and the other facing up to look cool with some glass over the top.

Cool idea - careful with rattles, and ensure enough space for Xmax (or preferably Xmech) excursion.

Low bass "should" pass straight through the glass depending on it's thickness, but don't be surprised if drinks/objects move around when the wick is turned up (nothing to do with cabinet vibrations which would be cancelled with the dual opposed config - all to do with many watts of acoustic energy going through the glass)

 

cheers

Mike

 

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19 hours ago, Troyus_ said:

I’ve heard polyfill or insulation make s the sub sound bigger. Is there a prob adding this to it? Does this allow for a smaller box?

I don't know about "sound bigger"

 

... but right amount of absorption inside the box, will make the box seem bigger to the driver.... by up to 10% or so.

 

 

In most subwoofer designs none of this stuff is at all critical.     Much (understatement) more critical is the in-room frequency response, which is determined by positioning of the source and listener, and by the EQ applied.

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20 hours ago, Troyus_ said:

I’ve heard polyfill or insulation make s the sub sound bigger. Is there a prob adding this to it? Does this allow for a smaller box?

3 minutes ago, davewantsmoore said:

.. but right amount of absorption inside the box, will make the box seem bigger to the driver.... by up to 10% or so.

 

agreed - and the 10% increase in "apparent" volume won't make up for making the box much smaller and can also reduce efficiency (so more EQ and power needed to hit SPL targets with stuffing).

So if getting away with a smaller box by adding stuffing was the goal, don't bother - you have EQ and power to manage a smaller box.

 

Have a read of a Data Bass article where they tested stuffing/no stuffing here:

http://data-bass.com/data?page=content&id=79

 

I haven't been on Data Bass for a while, so I read their article on "room gain" another time

In summary room gain is very room/speaker position/listening position dependent, and the room can provide positive and negative gains depending on frequency - still worth a read - also the bit at the end of adding an additional identical sub - which is almost what you're doing.

http://data-bass.com/data?page=content&id=80

 

How small were you intending to go? and how important is high SPL at 20Hz?

At 50 litres per driver, the lower F3 point is 43Hz, and because the box is small it has a high Qtc (1.04) and the response is dropping fast. This means lots of EQ and amp power to push the speaker lower - more than an octave - but you have EQ and power and decent Xmax!

 

Depending on your SPL target, in your room you could still hit 20Hz with EQ (especially with 2 subs) - it depends on dave's comment below

46 minutes ago, davewantsmoore said:

Much (understatement) more critical is the in-room frequency response, which is determined by positioning of the source and listener, and by the EQ applied.

The thing is it's hard to predict before you build the subs.

My recommendations would be:

  • build 1 sub first, as big as you can get away with, at least 50 litres per driver - bigger is better.
  • Get a measurement rig (mic + mic stand + REW + a USB sound card if your mic requires phantom power - not required for USB connected microphones like the Umike).
  • measure the 1st sub in the room from the listening position and keep a very close eye on driver excursion and listen for speaker stress/distortion when applying EQ
  • muck with position of sub and/or listening position to optimise the sound with 1 sub
  • apply learnings from 1st sub when building 2nd sub (assuming a 2nd sub required)
On 2/10/2018 at 10:09 PM, Troyus_ said:

The inuke has gobs more power than these subs can handle, is there any safety issues adding the bass in with a smaller box? 2000w RMS amp into 2x380w drivers has me a little worried.

I find in DIY that being sympathetic to my system helps a lot in preventing catastrophic failures.

  • I watch drivers for large excursions
  • I monitor pre-amp and power amp levels for clipping
  • I listen for driver stress
  • I can smell when my power amps are getting worked hard

Most of my equipment failures have occurred when I'm not controlling the volume.

 

Any 380W woofer driver will fail pretty quickly with a 380W continuous test tone of any frequency.

 

Music isn't like that - in normal home setups, subs don't work that hard, they just tick over

Even movies don't stress subs much - low bass is quite transient.

Night club volumes and electronic music with lots of bass content could stress a home sub/s.

 

There are 2 things that wreck woofers:

  • thermal stress - the voice coil gets so hot from continuous high current that the glues on the voice coil begin to fail
  • exceeding the excursion limits (called Xmech) - slamming the voice coil on the end plate (known as "poling" the driver), fortunately if pushing the voice coil forwards so far it leaves the gap, the magnetic force disappears, so frontwards Xmech is rarely exceeded

As long as you don't exceed either of the above, then a 2000W amp with 380W drivers is not an issue.

Typical woofers if kept within their excursion limits can take a lot more power than their rated spec until they hit their thermal limits.

The challenge is there's no easy way to tell if a driver is hitting its thermal limits - if you can smell it, then it's likely you've gone too far - turn down/off immediately - a very different smell to an amp working hard.

 

Remaining sympathetic to your stereo is very important if you choose to push it to its limits (DIY or not) - sight, sound and smell are key indicators.

 

I can hit night club volumes with my setup in my room with better bass than any night club/venue I've ever been in - but I know I'm pushing the boundaries on all my kit - preamps/amps/drivers...

,,,and especially neighbours (so far no complaints).

Any hint of stress, I turn down (power amp smell is normal when amps are working hard - clipping lights aren't).

 

Where you run into problems is when you're not around and someone else is dialing up the volume without a sympathetic ear.

 

Clearly every stereo needs decent "headroom" deigned into it - but it's easy for "less informed" users to "break stuff" on a stereo if the stereo is running close to limits (for example dialing up the bass further on the sub if it's already close to amp and Xmax limits).

 

cheers

Mike

 

 

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  • 1 month later...

First design of subs by a local guy here that made my arcade cabinet. Really nice guy. Sheets are 16mm mdf only but it’s heavily braced so that should be ok, right? In these pics he has double thickness all around but I only want double for the baffles. He’s on it. External dimensions =6.7cf or 190l. I can change the size but this seems to be getting large to me. 

I will have 100mm casters on the bottom and 100mm glass top stood off from the top.

 

7FDC9FCD-311F-4231-8CDF-06D9AE6DB7EF.jpeg

4C008CD2-ABAC-434E-9877-BA73595F7029.jpeg

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Next design a lot closer. Less material.

 

he hasn’t built subs before so he is putting in dowel screws the same as he does for his arcade machines to hold it together. I’ve said I’ll be using wood glue but these dowel screws should lock it together while it dries. No need for sash clamps, nice! Gunna be a big jigsaw puzzle with no cutting. I hope.

 

he says he can adjust sizes once the design is right as I want another one the same but different.

 

*edit. Oops sides are still double thickness. I’ll get on that.

 

 

575D5591-8F82-4E94-95BB-7E80F8EB9E18.jpeg

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5 hours ago, almikel said:

10mm?

the box looks fine, but ensure the drivers fit

 

Mike

10mm seems safest. They can make the size whatever so we will measure my subs. Still not sure on recessing them. Then that only leaves 1 sheet of mdf that they are attached to really.

 

New design single walls with cam locks.

4.jpg

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  • 5 weeks later...

Got 2problems. 

1- There is a gap around some edges that needs filling. What can I use that fits in, is flexible, won’t fall out and can be sanded and painted? See the pic.

 

2- in the pic you can see a round hole. This is where the cam lock cut out was too thin and I’ve sanded through to it. I’ll have to pop out the round bit and fill the hole somehow. As above, what’s best to use for this bigger gap that can withstand pressure from in the sub? I was thinking Selly’s Kneed it.

 

 

B077FBF8-C81F-454E-AF49-948CB575A9AF.jpeg

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