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Rehousing a Peavey Speaker


Phil Starr
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Here's what I am thinking may be a possibility with an internal volume of 66L give or take made from 12mm ply. Unless anyone can see anything wrong I'll see if I can get a cut sheet together. I'm not sure on bracing which seems to be necessary on the 12 inch speaker build though. Dimensions are in mm 616W X300D X437H (external).

 

Screenshot 2021-11-14 at 18.09.43.png

Edited by Hacksawbob
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Its looking promising, good proportions. As you suspect  you'll have to brace. They are big panels for 12mm ply.

 

One place we've had problems with is the baffle particularly between the speaker and port. Plan to have some sort of bracing there and leave plenty of meat to fix to.

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I had another go ast the port design The first one for the external. The second one has a tighter curve, I had a read of that cookbook you mentioned Phil, there is some suggestion that asymetric ports may be beneficial. I'll print both and try them out.  I'm not sure whare to take the measurement from though for the port length? I'm going to get some ply  today.  I'm thinking the front baffle will be made of double 12mm ply which should give some stability there. I am hoping to keep the rear with just 12mm to keep the weight down.

 

 

 

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Edited by Hacksawbob
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That's looking really nice, if you fancied sending me a couple I'd love to get to see if it makes a measurable difference, I'd reluctantly return them to you afterwards. I'm sure @stevie would like to see them. He and I have slightly different positions on port noises where he is the perfectionist. Don't let him know but I think he's probably right.  A couple of these would help advance an interesting debate.

 

I'd just use the measurement from the outside edges as your length and the inside of the pipe as diameter. The computer software has a set of assumptions for making end corrections for port calculations but it makes a number of other assumptions too for things like leakage from the box. Consequently the calculated tuning is approximate at best (and varies with temperature and air pressure too) so we usually start off with the calculated length and then measure and re-tune. I doubt the manufacturers given parameters for the Scorpions are accurate for a 20 odd year old speaker too. The advantage of your end pieces is that you can cut the tube at will and always have a neat finish.

 

Out of interest what is the approximate cost of making these this way. I have no idea what 3D printing costs. 

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Hi Phil, for all the help and support you give here I'd quite happily send you a couple for for evaluation, you can keep them if you like them. If you have any design adjsutments just let me know, I can PM you the dimensions. Tricky to get an exact figure on 3D printing costs, electricity wear and tear etc it's probably about £5 per port + design hours and prototyping costs which you divide among the number you expect to sell which is an unknown :) 

 

Got all the plywood in today although the saw operator didn't seem to know the thickness of the kerf so I may have a few adjustments to make.

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I do have black pipe, I just used a spare bit of grey so you can see the join. It's not quite an interference fit on this but very close. I'm not sure how much variation you get in pipe, but better to be marginally over than under as it can always be glued, where as the other way means faffing with sandpaper. I did give this a quick sand to remove the supports and a quick coat of black paint 

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Edited by Hacksawbob
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I have a box of sorts, 24mm front baffle, approx 64L  internal after speaker and port subtraction I should be in the ball park of 55L Now, how to gain access if I need to. It will need to be top or bottom opener if I'm going to fix the front panel. I'm guessing some foam strips to seal it. If it's the bottom panel I guess the weight on it will be in my favour. I suspect the centre of gravity will be too far forward on this, a bit late now though :)

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Edited by Hacksawbob
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I've always used either the back or the baffle as my removable panels, usually the baffle because I've a tendency to re-use cabs for other projects and often re-cut new baffles. Mind you there's not much you cant do through a 15" hole.

 

I use draughtproofing strip to work as a gasket and get a seal.

 

Good to see it coming together, you aren't far off making your first sounds.

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So here is my attempt at rehousing the Scorpion speaker, not as nice as your workmanship! @anrque but it is functional. It  very loud, possibly louder than the original Combo amp. It's  a very full 'airy' sound that envelops you unlike the original cab which was quite punchy and focused, it is very responsive and manages the low B on the 5 string with ease. The weight is far more managable! 

 

  I used 12mm hardwood ply (B&Q) which is £34 a sheet and 4 2M lengths of 20x25mm batton (actually two of these were 1x1 inch from a local timber merchant after I ran out but it works with either of these) total cost was about £50

 

The screws for the carcass were 6X 1 1/4" or 3.5x30mm in new money. I am handy with drills and what not, but I am no cabinet maker so excuse the rough build quility, I'm more of an IT guy :)  I used some chunkier screws for the speaker itself, the baffle is held on whith coach bolts with some washers to spread the load, they just came out of one of those pick and mix bags you get from Wilkinsons (apologies if they are not in your area it might be more of a Northern thing.)  I originally designed the front baffle to sit back in a 12mm recess, but I used some 12mm foam sealing so it ended up being flush at the front which isn't ideal, I may well revisit this with some thinner material.

 

The ports are 3D printed to fit a 4" waste pipe, with a 73mm length, I measured this from the right angle mounting point so I think from memory it was about 38mm of waste pipe required which I cut on a chop saw and used mastic to seal it as it's so short I didn't need any additional support, the front is screwed on with the same screws I use for pickguards.  there is also a port flare on the inside. The port flare ends did a great job of hiding the dodgy jigsawing that I did in the baffle! They are printed grey stone type filament as I have a load of it to get rid of and I sent Phil my black ones, I decided to add some printed corner protectors in the same colour as well. Handle and feet on the bottom of the cab were robbed off the original amp.

 

I will add the cut sheet, this assumes a 4mm blade thickness which will just allow you to get the cuts on a 1.22X2.44 Meter sheet, (total 1.212M of material) You might want to check with the saw operator what the kerf is as they can vary between setups, also, bring a tape measure and check each cut as it comes off. I have added the amp front to this cut sheet which I wasn't sure about the exact dimensions so is missing from the photo. I have allowed for 4X front and back panels, this would allow you to make either or both 24mm thick by screwing and glueing them togeher, (or to allow for a mistake cutting the baffle)

 

 

Things to do:

I am toying with the idea of adding a 4 inch tweeter as the TNT160 has a crossover out, and piping this to a second practice amp which I can fit under the main amp, this might also help to balance out the head as the transformer weight makes the head carry at an angle. Also, I might add some wadding/foam internally once I have had a chance to put a frequency sweep through it. Speaker needs some protection, not sure which way I'm going to go with this possibly some speaker material rather than a grill as I think they look a bit pants.

IMG_20211128_141138(1).thumb.jpg.1ad05ed2d3775c34355190746f090364.jpg

 

 

Cutsheet TNT160 cab and head.pdf

Edited by Hacksawbob
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Well done, it's great to get to this stage and now you can take an empirical approach of trying things and using that to improve your cab.

 

I like the idea of doubling up the baffle if you are happy with the extra weight. I'm a little worried about that baffle TBH. You have a lot of speaker in a small cab and most of the baffle is cut away leaving it inherently less stiff.

 

Have you just used the bolts to secure the baffle? The foam strip you mention will ensure the cab is airtight but just fixing at the corners isn't enough. At higher power levels the panel will want to resonate and flex. I like a removable baffle but I use screws with a minimum 10cm spacing. That should crush the foam seal and give you a bit more depth for the grille cloth.

 

I'm particularly loving the printed port termination, it looks really good and those small radius cut outs for the port are really hard to do tidily.

 

I'd always go for some wadding on the rear panel and usually do the top bottom and sides as well. Now you have a cab you can add and remove it at will and do listening tests. Keep it away from blocking the port though. You might also want to add some top to bottom and side to side bracing. Again you can do this by testing your nearly finished cab.

 

Well Done :)

Edited by Phil Starr
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Hello Hacksawbob,


I'm a bit late to this party, but with reference to your & Phil's post from the 23rd November, it is my understanding that Port Tuning & size is based upon using the internal paralllel surface of the port; the flares are ignored, regardless of their curvature. The flares are there just to reduce turbulence.


Your "Cookbook" source and the winISD website may have some info as well as various "hi-fi" component supplier web-sites.

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34 minutes ago, Balcro said:

Hi @Balcro thanks for that. The port flare I printed has a compound radius rather than a simple circular radius which most design calculations use. There is a gradual decrease in radius as you transition from the straight pipe to the external.  I picked the right angle face mounting to give a reference point for measurement, it might not be the optimum and some other point further down might be 'correct' resulting in a slightly longer internal pipe it's just starting point and may indeed need adjustment after I have tested it further. Hopefully when Phil gets a chance to test them out I'll know better.

 

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Yes @Phil Starr  just the 4 bolts at the minute, I'll add some screws at some point but the 24mm thick baffle is pretty solid despite the holes in it,I'll add some more bolts at the cardinal points when I can get a trip to Wilkos.  At the moment I have the back on and off almost daily, once I have setled on a design I'll seal it off properly. I have added carpet tiles on the internal panels with spray adhesive and staples. Seemed like a good idea with the rubberised back and carpet material on the front. I have run some frequency sweeps and what I thought was some distortion was actually a computer case that was rattling at about 60Hz :)

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The picture of the Scorpion that Hacksawbob is showing has a hole in the rear magnet assembly. On my Scorpion that was filled with a foam plug to prevent debris from falling in. The issue is that after 20-30 years, the foam disintegrates on touch and "becomes" the debris. Hacksawbob's may have already disintegrated since it looks like nothing was there.

 

Progress on my combo to head/cab has been slow. I was back at work and also applying for a new role (which I did not get after a month of interviews, grrrr!)

 

I did get the headshell glued up and just sanded down the  finger joints over the US Thanksgiving holiday. It looks like this now:

 

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I need to pull out the router table and mount my 1/2" Bosch router with roundover bit. I'll be moving the work instead of the tool this time and hopefully have an easier time than I had routing the finger joints. Even with the finger joints and clamps while gluing I had a bear of a time trying to get this to come out square. I was not entirely successful. :(

 

My cabinet will be larger in depth than my Porter Cable dovetail jig allows, so when I eventually get to the cabinet, I think it will be butt joints.

Edited by anrque
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 Looking good  @anrque I'll take a look inside and see if there's any debris. I have a router but it scares me using it, I toyed with the idea round over but it is so full of screws now it's probably not a good idea.

Here's my latest handy work Whith the carpet tiles on the inside. Also testing a couple of smaller radius port terminations to get a what the cookbook mentions as an asymentric port. This one has a hard edge on the underside and in my 'armchair audio designer' head I think it might be better with a teardrop profile, so printing a replacement now.  I'm also going to need a few differrent pipe section lengths cut for port length testing, but the chop saw was a bit tricky trying to rotate a long pipe length to get a clean edge, so I might make a jig out of the spare ply. Also added 4 more bolt fixings to cinch down the middle of the baffle, I bought an adapter for the drill so I can get the 10mm screw bolts out quickly.

 

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Edited by Hacksawbob
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@HacksawbobDefinitely DO NOT use a router and carbide cutter on wood that has metal fasteners already in place. That is a recipe for a hospital trip. If you did butt joints and biscuits or dowels you would be fine, but screws/nails -- no way.

Your progress looks good. You've gotten a lot further along than I have. :)

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