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Basschat easy-build lockdown cab project


stevie

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12 hours ago, carnabass said:

Hello Again!

 

Well.... the teeny tiny cab is together and has been tested

 

It's definitely easy build

 

I haven't applied any finish to the cab or a grille as this was a test version (although i'm falling in love already)

 

I made the crossover on a piece of thin ply. 

 

It really is a compact cab. 

 

I used araldite to glue the port extension on and then stretched some gaffa round it nice and tight for support

 

One point I would bring up (and I could be talking rubbish here).... The port ends closer to the rear wall than I would have expected to be ideal. My thoughts were that you needed at least the diameter of the port. Any thoughts on this chaps? (port length 170mm) Or does it not matter? 

 

I coupled up my BH800 and played some tunes through it via an ipod. I was very pleasantly surprised. Nicely balanced with neutral equalisation and with a good dispersion of higher frequencies.

 

My better half said "that sounds nice" - praise indeed.

 

I've played my precision through it for a few minutes and its great! Not bottom heavy, but then I didn't really expect it to be. 

 

BUT

 

It's clear, punchy and responds very well to EQ changes. 

 

Would I gig with it? Probably not unless it was a small room.... Would I gig with it plus another cab (minus the tweeter section) yes definitely!

 

Its probably a bit unfair to do a review after such a short time, but I promised myself that i'd contribute to this project as well as gain from it. I'll report back once i've done a rehearsal with it

 

Anyone can make this cab. The joy of hearing your creation come to life is soooo worth it!

 

I am v tempted to knock some 12mm versions together (although the V3 basschat design is calling me)

 

Thank you to all who are involved in this wonderful little design

 

Pics attached - drill shown for scale 😊

 

Jon

 

 

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That's a great job ,well done. Apply 2 or 3 brush coats of Tuff-cab first  to level the surface then a couple of texture roller coats and you'll have a great looking and sounding cab. Great job.

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Wallop! 

 

Not quite tuffcab paint - Rustin's step paint from Toolstation

 

Rough finish, but it'll do

 

I did the good old rice test this morning and got 52hz. I'm guessing i need to add a few more millimetres to my port length - i'll give it a go

 

Not sure what to do grille wise. I have some cloth, but I quite fancy some perforated aluminium sheet. 

 

I've installed the tweeter so that the 90 degree dispersion is in the vertical plane. 

 

Feet on 2 sides so I can use it in both planes

 

My little ipod into my BH800 and through this tiny cab is really, really nice. Nicely balanced. Added a little bottom end via the EQ makes it even better

 

Second, tweeterless cab is on the cards now

 

Weight - My scales (which always seem to lie to me when I get on) say 11.5kg 

 

I've already lined up some more scrap 15mm ply for the second one 😁

 

Grille to go! 👍

 

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Edited by carnabass
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Looks fantastic.  A 2nd  speaker only cab would give you a handsome rig with loads of H##t. Gold star and take a £1 out of the till on your way home.

Edited by JohnDaBass
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What you are experiencing with your port depth being so long is because the port area is too large for the driver and displaced volume. As the port becomes more than a few times the diameter of the port, there can be non-linear terms that affect the tuning (one reason why calculated and measured port responses can vary). Also, the resistance (or lossy) term of the port can add a non-linear variable, especially when the end of the port gets close to t he back of the cabinet.

 

The way to prevent this is to calculate the port area and length, then verify that the length is reasonable. If not, you may need to adjust the port area to get length down to a reasonable value... though there are those who will bend the port like a pipe with an elbow (but this too adds non-linearities).

 

In general, a port length of less than 2x the diameter ends up to be a reasonable compromise IME.

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I think that's all fair comment, though I only built the cab @stevie did the tuning and he did this on the basis of measurement of the final cabs response. The original design was shaped by the need to keep everything easy to build and the availability in the UK of a ready made port was an important factor. We were looking for something cheap, easy to obtain and sourced from a well established supplier so likely to be available for a few years. This one also has a decent lip to cover up any dodgy cutting of the hole. When I did the modelling on WinISD I found my 'best' response was higher than the final tuning and that the original port without the addition of extra length would give that tuning. The extra card extension was added as a result of frequency tests on a built prototype. The frequency plots are there in the text somewhere.

 

In my original version of the cab I used plastic guttering down pipe. One of the things we discovered testing is that two narrow ports start to make port noises (chuffing) at lower power levels than a single bigger port with the same cross sectional area. We hadn't seen this in any literature. Like @agedhorse I shudder at the idea of folded ports.

 

Like all the commercial designs we have looked at and pretty much any practical cab there are compromises in this design. Like the crossover design and choice of drivers the port was an issue of cost and availability. Actually 52Hz sounds about right, I measured 53Hz by looking at impedance on mine. I don't think it is worth re-tuning unless Steve comes along and says there is a problem, my cab sounds great given the cost of the components and pretty much as i'd have expected from the design software.

 

 

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I must confess I'm a bit of a Beyma fan

 

This evening, I've been comparing the pulse 10 (£60 free carriage) to the 10CMV2 (£53 £7.93 carriage) 

 

I put them both into winisd

 

Cab size (nett) 30L

 

Tuned to 55hz

 

1 x 10cm dia port

 

The CMV2 looks rather tidy

 

Am I missing something? 

 

Doesn't seem to exceed xmax @ 250 watts (down to about 45hz)

 

Equals or betters the pulse throughout the response curve

 

Is it worth investigating? Or am I getting excited and not spotting a potential issue?

 

Voice coil is 0.5" smaller than the pulse, yet rated to 50 watts more??

 

I'm assuming it'd need a re-think on the crossover side of things :( enough to notice???

 

Could any clever beans offer me any advice? Even if it's shut up and finish your cab off 😁

 

 

 

 

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16 minutes ago, carnabass said:

I must confess I'm a bit of a Beyma fan

 

This evening, I've been comparing the pulse 10 (£60 free carriage) to the 10CMV2 (£53 £7.93 carriage) 

 

I put them both into winisd

 

Cab size (nett) 30L

 

Tuned to 55hz

 

1 x 10cm dia port

 

The CMV2 looks rather tidy

 

Am I missing something? 

 

Doesn't seem to exceed xmax @ 250 watts (down to about 45hz)

 

Equals or betters the pulse throughout the response curve

 

Is it worth investigating? Or am I getting excited and not spotting a potential issue?

 

Voice coil is 0.5" smaller than the pulse, yet rated to 50 watts more??

 

I'm assuming it'd need a re-think on the crossover side of things :( enough to notice???

 

Could any clever beans offer me any advice? Even if it's shut up and finish your cab off 😁

 

 

 

 

Cost and performance wise the CVM2 range are excellent and I have two of the 12" 12CVM2 drivers for sale on here at the moment.

In my opinion modelling Celestion Drivers perform better than they model. Without the ability to measure the response you are better sticking with @stevie's design.

Edited by Chienmortbb
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9 hours ago, Chienmortbb said:

In my opinion modelling Celestion Drivers perform better than they model.  @stevie

+1

Took the combo I posted previously on this thread to a band rehearsal in a smallish rehearsal studio last Friday and it had absolutely no problem at all keeping up with 2 loud guitarists, shed building drummer and keys. I was amazed how the little combo performed and I don't think my BF One10 would have been able to cope. Badge for Mr  @stevie  and Mr @Phil Starr please.

Edited by JohnDaBass
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19 hours ago, carnabass said:

Even if it's shut up and finish your cab off 😁

 

 

 

 

Shut up and.... no I can't be so rude :)

There are a few Beymas that are really good value, the CMV range are across the board good value. It's a shame they stopped making the SM212 though. 

In this case the choice of the Celestion Pulse was a good one mainly because of it's mid-range performance. Most bass/mid speakers have a pronounced peak at cone break up. At high frequencies the out part of the cone can't keep up with the centre and the cone starts to flex and this creates frequency anomalies. For a 10 the response is fairly flat and rolls off evenly and this makes adding a horn driven through a simple high pass filter relatively simple. To get a flat response from most bass/mids you need to have a 'proper' crossover and control the roll off for the bass unit. The inductors for this tend to be large and relatively expensive and beyond that you often get other frequency problems which need extra components and design work to tame. You'd be amazed at the manufacturers who don't bother doing more than a cursory job on their crossovers. It's probably why some bassists don't like horns; there's nothing wrong with the horn but the crossover leaves little frequency peaks that sound harsh/distorted/honky.

 

So Win ISD models the bass response and you may well find better 10's but the Pulse was chosen because it gave good enough bass but a really helpful treble that enabled a good response with just three cheap components in the crossover.

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Posted (edited)
On 24/07/2021 at 19:15, carnabass said:

 

One point I would bring up (and I could be talking rubbish here).... The port ends closer to the rear wall than I would have expected to be ideal. My thoughts were that you needed at least the diameter of the port. Any thoughts on this chaps? (port length 170mm) Or does it not matter? 

 

You're making some good points. The gap between the end of the port and the back panel certainly matters but the rule you mention applies to slot ports. If you have a full-width slot port, you should leave a gap equivalent to at least the height of the slot port between the end of the port and the rear panel of the cabinet. Otherwise, you’re constraining the air flow into the port, which will speed it up and cause turbulence. Designers have been trying for decades to find ways of reducing turbulence in ports – so this is the last thing you need. 


Round ports are different. You can go closer than the diameter of the port. The main thing is that the flow of air into the port isn’t constricted. You need to visualise it and use a bit of basic geometry. On your speaker you should have about 40mm of space behind the port. That’s fine. You could actually go closer than that without restricting the air flow. 

 

Nice work, by the way.😊

Edited by stevie
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Didn't want to come across as negative when I mentioned that and thank you for the ace explanation (as always)

 

I'm certainly learning more about design for sure

 

The little cab is going to get a test tomorrow night - I already know that my fellow band mates will scoff at it's tiny..ness

 

Tweeterless (or tweetered but with an on/off switch) cab to follow. Will commence this weekend once i've collected the scrap ply from my friend

 

Be good to see a few more attempts popping up on here ;)

 

Jon

 

(ps - is there any way of changing username? carnabies were my old band and i'd like to change it)

 

 

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Posted (edited)
On 25/07/2021 at 23:43, agedhorse said:

What you are experiencing with your port depth being so long is because the port area is too large for the driver and displaced volume. As the port becomes more than a few times the diameter of the port, there can be non-linear terms that affect the tuning (one reason why calculated and measured port responses can vary). Also, the resistance (or lossy) term of the port can add a non-linear variable, especially when the end of the port gets close to t he back of the cabinet.

 

The way to prevent this is to calculate the port area and length, then verify that the length is reasonable. If not, you may need to adjust the port area to get length down to a reasonable value... though there are those who will bend the port like a pipe with an elbow (but this too adds non-linearities).

 

In general, a port length of less than 2x the diameter ends up to be a reasonable compromise IME.

 

As I explained to Jon in an earlier post, there isn’t a problem with the port length. 


Also, a 4-inch port isn’t too large for a 10-inch driver – that’s just a completely weird assertion. As far as port nonlinearity is concerned, the number one priority (by far) is maximising the size (and optimising the shape) of the port. The maximum vent air velocity in the cab at its rated output is currently about 14m/sec/Hz, which is very good and I dare say better than virtually any commercially built small bass guitar cabinet. Reducing the area of the port would mean going to a 3-inch port, which would nearly double the vent speed. In fact, 80W through the 3” port will take the vent air velocity to the same level that the 4” port experiences at 200W. 
  
Although most bass guitar cabinet designs would actually meet the two-to-one ratio requirement, it is purely arbitrary with no real basis. Try designing a compact subwoofer with those constraints in place and you won’t get very far. In fact, you can make a port as long as you like as long as you know how to deal with the trade-offs.


We’re using a 100mm diameter port 170mm long. So that’s all right then. 🙂

Edited by stevie
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I have only been on the periphery of @stevieand @Phil Starr's designs so I cannot make definitive comments* however that one thing I have learnt is that you cannot design a cabinet purely by modelling and that the traditional "rules of thumbs" similarly should be used for guidance. One thing you can be sure of is that the designs that are published are rigorously tested and measured then gigged to ensure that they meet the original design criteria.

 

Of course there are small compromises, there is always a little more that can be gained by making the box  bigger, a more expensive driver but in many cases the extra is not worth the extra.

 

 

 

 

* I do lay claim to the phrase "squeezing the balloon" when describing how changing any on parameter of a design affects many others>

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On 26/07/2021 at 21:47, carnabass said:

I must confess I'm a bit of a Beyma fan

 

This evening, I've been comparing the pulse 10 (£60 free carriage) to the 10CMV2 (£53 £7.93 carriage) 

 

 

Adding to the previous comments, although the Beyma would probably work quite well in this cabinet, I can't see any real benefit in using it. The xmax is about the same. I'd be suspicious about the 250W power handling, as the driver only has a 1.5" coil (compared with the 2" coil in the Celestion).

 

It does seem to be slightly more extended in the HF, due I expect to the smaller coil, and its main breakup point is higher, which is a plus point. Unfortunately, this means that the crossover won't work as well as with the Pulse 10 and you'll get a peak at around 3.5kHz. Probably not a biggie in a budget cab. If you already owned the Beyma, I'd say - sure, try it. But otherwise, I'd stick with the Celestion personally. It's up to you: if you feel like experimenting, there's nothing to stop you and I certainly wouldn't expect it to be a disaster.

 

 

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3 hours ago, carnabass said:

 

The little cab is going to get a test tomorrow night - I already know that my fellow band mates will scoff at it's tiny..ness

 

Tweeterless (or tweetered but with an on/off switch) cab to follow. Will commence this weekend once i've collected the scrap ply from my friend

 

 

 

If the results of the rehearsal are positive, then I would be inclined to build a duplicate of what you have achieved and fit a tweeter switch to both. That way you will have 100% redundancy in the event of a cab failure. Normal use with 2 x cabs with only one tweeter switched on to avoid the issues already explained.   

Edited by JohnDaBass
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10 hours ago, stevie said:

 

As I explained to Jon in an earlier post, there isn’t a problem with the port length. 


Also, a 4-inch port isn’t too large for a 10-inch driver – that’s just a completely weird assertion. As far as port nonlinearity is concerned, the number one priority (by far) is maximising the size (and optimising the shape) of the port. The maximum vent air velocity in the cab at its rated output is currently about 14m/sec/Hz, which is very good and I dare say better than virtually any commercially built small bass guitar cabinet. Reducing the area of the port would mean going to a 3-inch port, which would nearly double the vent speed. In fact, 80W through the 3” port will take the vent air velocity to the same level that the 4” port experiences at 200W. 
  
Although most bass guitar cabinet designs would actually meet the two-to-one ratio requirement, it is purely arbitrary with no real basis. Try designing a compact subwoofer with those constraints in place and you won’t get very far. In fact, you can make a port as long as you like as long as you know how to deal with the trade-offs.


We’re using a 100mm diameter port 170mm long. So that’s all right then. 🙂

Respectfully Stevie, I have designed commercially successful bass guitar and pro audio cabinets for over 40 years, including compact LF cabinets. Not just a few dozen or a hundred cabinets but tens of thousands of cabinets.

 

There’s nothing “weird” about my assertion, when the port depth extends to within between 1/2 and 1 times the diameter of the back of the cabinet, additional lossy (and non-linear) terms enter the calculations for the dynamic tuning of the cabinet (ie. the tuning varies with level). 
 

With many (not all) 10” drivers suitable for bass guitar, it’s not uncommon to find that in a compact cabinet a 4” port results in a depth that’s too deep for commonly accepted cabinets.
 

When encountering this condition, the options are to either make the cabinet deeper or to reduce the port area to reduce the depth. For example, if the ratio of depth to area is 2:1, a reduction of port are by only 10% affects the depth by (roughly) 20%. This might be enough to mitigate the issues without impacting port velocity significantly.
 

I never suggested decreasing the port diameter to 3”, just to be aware that sometimes, recognizing that there may be an issue, a small adjustment may be helpful.
 

It’s all part of managing the trade offs. That’s all, nothing more.

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Respectfully, agedhorse, you barged onto this thread, which was proceeding in a nice, friendly, positive manner, and claimed that the porting of the cabinet was flawed. The professional thing to do, as a member representing a commercial entity on here, would have been to send me a pm saying ‘I think there might be a problem with the porting of the box’. But no, you post on the thread that the “port area is too large for the driver”. 

 

So I had to spend time that I can ill afford explaining why this is not the case.

 

The professional thing for you to do then would be to say simply, ‘it looks like I might have been wrong here’. That’s obviously not your style. No, you then double down and post in a really aggressive manner, implying that you can’t be wrong because ‘look who I am’ – really not impressive (a technique honed to perfection by Donald Trump if you don’t mind my saying). You don’t even acknowledge that you might have been a bit hasty and proceed to repeat your assertions about port aspect ratios, which you haven’t made any effort to substantiate and, frankly, I don’t think anyone has the slightest interest in. They’re certainly not pertinent to this thread.

 

The only reason I responded to your first post was to explain for the benefit of the people already building the cab that the design was fine. I have already explained why I don’t agree with some of your ideas (which you have ignored) and I’m not in the slightest bit interested in arguing about them now. I was enjoying seeing the builds come together and hope we can dispense with this nonsense, call a halt here and resume the constructive spirit of the thread.

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13 hours ago, agedhorse said:

I have designed commercially successful bass guitar and pro audio cabinets for over 40 years, including compact LF cabinets. Not just a few dozen or a hundred cabinets but tens of thousands of cabinets.

 

Units manufactured, presumably, or individual designs 🙂

Edited by Stub Mandrel
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6 hours ago, stevie said:

Respectfully, agedhorse, you barged onto this thread, which was proceeding in a nice, friendly, positive manner, and claimed that the porting of the cabinet was flawed. The professional thing to do, as a member representing a commercial entity on here, would have been to send me a pm saying ‘I think there might be a problem with the porting of the box’. But no, you post on the thread that the “port area is too large for the driver”. 

 

So I had to spend time that I can ill afford explaining why this is not the case.

 

The professional thing for you to do then would be to say simply, ‘it looks like I might have been wrong here’. That’s obviously not your style. No, you then double down and post in a really aggressive manner, implying that you can’t be wrong because ‘look who I am’ – really not impressive (a technique honed to perfection by Donald Trump if you don’t mind my saying). You don’t even acknowledge that you might have been a bit hasty and proceed to repeat your assertions about port aspect ratios, which you haven’t made any effort to substantiate and, frankly, I don’t think anyone has the slightest interest in. They’re certainly not pertinent to this thread.

 

The only reason I responded to your first post was to explain for the benefit of the people already building the cab that the design was fine. I have already explained why I don’t agree with some of your ideas (which you have ignored) and I’m not in the slightest bit interested in arguing about them now. I was enjoying seeing the builds come together and hope we can dispense with this nonsense, call a halt here and resume the constructive spirit of the thread.

Stevie- Wow, your response is not just off the mark but is insulting as well (complete with a Trump reference which is totally uncalled for). Why do you think it’s necessary to act like this towards others?
 

The entire point of my comment was to share information, specifically related to the question of the port being so deep that it comes within 1/2-1 diameter of the back of the cabinet and the aspect ratio of the smaller ports with equivalent area chuffing (as Phil had mentioned).  Specifically, what Phil experienced is an example of the aspect ratio non-linearity that I had addressed that can introduce additional factors and calculation errors with regards to tuning suitability. Just because you are unaware of this or don’t agree doesn’t make the information wrong, or me arrogant.

 

When a port comes to between 1/2 and 1x the port diameter, the static pressure of the air mass against the back of the cabinet can come into play, this too is a non-linear term. Non-linear terms result in a cabinet’s tuning changing with level (all cabinet tuning will change to some extent, but the more non-linear the greater the shift with level. This is especially problematic in compact cabinets. Have you ever modeled the non-linear math behind this?

 

Stevie - my comments were general in nature, not specific to your precious design. Perhaps you should re-read my comments with your big boy comprehension. 

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6 hours ago, Stub Mandrel said:

 

Units manufactured, presumably, or individual designs 🙂

Yes, units manufactured.

 

I mentioned this because these sorts of issues tend to show themselves after many speakers are out in the field used in a variety of applications.
 

Same sort of thing often occurs with fatigue related reliability issues, which is one reason why more comprehensive modeling and aging analysis is done in higher volume commercial products (especially if a long warranty is offered).

 

I thought that some folks here might be interested in the information I provided, if I was wrong then I’m sorry for wasting my time.

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long thread warning..

 

Hello All

 

First outing with the scrap ply cab last night

 

I loaded the car and looked at this little black box in the corner of my boot and though “I don’t think I’m going to have enough grunt tonight”

 

I play in a Glam band with 2 excellent guitarists who really like to noodle and a solid drummer

 

The cab was plonked on the floor (in landscape mode if that makes sense) and hooked up to my TC BH550. I tilted the cab back very slightly with a high tech lump of wood

 

No pedals – just a lead and a classic vibe precision. A tad of compression on the amp.

 

Low bass turned down a bit to avoid pummelling the pulse 10. Mids and top enhanced a tad

 

I tried it out whilst others were setting up and thought “Blimey - I might just get away with this”

 

Began rehearsing and I got a little lost in the mix.

 

Turned up a little between songs and I was there. I sat right in the mix with a smile on my face.

 

I usually use 2 x 50L cabs with Beyma SM212’s. We rehearse in a steel stockholders, so it’s quite ringy and boomy. The 212’s used to sound very muddy (but sound great outdoors or in a dead room). I think the band used to play louder because of this boom

 

With the new cab, we played a bit quieter (lovely) and my tone was right there. Highs were clear without being obnoxious. Bass was enough for it not to appear like I was using a practice amp

 

Compliments during the break along the lines of “I can’t believe that little thing”

 

The Pulse 10 is quite a little powerhouse. I was dubious as to whether it’d cut the mustard, but I’m pleased to say it does

 

Remember this is a 1 x 10” 200 watt small enclosure so it’s not going to shake your fillings out. It will be easy to transport, make you grin when you look at it and it’ll hold it’s own with a band who aren’t prone to inducing tinnitus

 

So – 1 cab for a rehearsal? For me, yes indeed. Would 1 cab suffice for a gig? Hmmm. Jury is out on that one. Tiny pub? Yeah. 100+ room?…. I’d be wanting a bit more grunt for peace of mind

 

BUT – Given I now have the ply, speaker and hardware for a second one, I think we know where this is going

 

I may make the second with a removable baffle, so I can try the 212’s in a smaller enclosure.

 

Top hats to be fitted too so I have an emergency PA system. 

 

Thanks once again to the people behind this thread/design for a great little build

 

I would say to anyone thinking of having a go to just get on with it! There’s loads of helpful people on here.

 

Bring on the next design 😉

 

Jon

 

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