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Peterson combo driver upgrade


Pea Turgh
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Hello.  I have an old Peterson P150 combo, with a lovely mahogany cabinet, and a now departed EV12L.

The stupid bit: I actually sold the driver because I wasn’t that enamoured with the sound, and it weighed as much as a caravan full of tigers.

I had considered just selling the combo as a whole a few times before pulling the driver, but I like the way it looks, and very, very occasionally I develop sentimental attachments to objects, this being one of them.

So, I know the cabinet is just shy of 35 litres, which ain’t fantastic for bass, but it is what it is, so I’m just after getting the best out of those dimensions.

Now the tricky bit:  the ports are slots either side of the cabinet.  41cm high, 3cm wide, 24cm deep, but, the slot ports are fed by a 1cm x 41cm gap at the back of the enclosure.  How do I work out port dimensions for that odd shape?!

If any speaker cabinet ninjas could point me in the direction of a suitable, light-ish 12” that will work in that space, with those weird ports, I would be very happy and grateful!!!!

 

Edited by Pea Turgh
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I reckon you have about 30 litres net. The tuning appears to be in the region of 80Hz, which is OK for a vocal cab or a guitar cab, but not good for bass. To make matters worse, as Downunderwonder correctly points out, the rear entrance to the ports is constrained. It looks like the designer didn't know what he was doing.

If you block one of the ports and open up the rear of the remaining port, you'll have a fighting chance. That will probably tune the cab to around 60Hz. It's difficult to be accurate here because the proximity of the ports to the rear baffle affects the tuning.

You might like to get hold of a Celestion 12BN-300S, which is claimed by many to be close to the EV you sold. No guarantees though.

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Thanks for the replies so far.  I’m certainly not expecting much from it, however I did gig it regularly (sometimes without PA support) for about ten years, so it wasn’t unusable with the EV.  Just really heavy!

I’ve got a Barefaced/Ampeg gig rig now, so this is just a pretty combo for the studio, but might take out occasionally.

I suppose I could plug the rear vents and pop some ports around the driver?  I’ve got space, just... 

 

Edited by Pea Turgh
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Hi there, How much woodwork do you want to do and how much do you want to spend?

As it happens this 30litre net cab is the same size as the ones we've been playing with recently. I've tried out the Beyma 12CMV2 in it and it works better than the SM212 the cab was originally designed for. Recently Stevie has designed a 110 plus horn cab which is also based upon the easy build 30l design. Both of those could work in the cab you have with a bit of carpentry. The advantage is that they are both tried and tested designs.

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3 minutes ago, Phil Starr said:

Hi there, How much woodwork do you want to do and how much do you want to spend?

As it happens this 30litre net cab is the same size as the ones we've been playing with recently. I've tried out the Beyma 12CMV2 in it and it works better than the SM212 the cab was originally designed for. Recently Stevie has designed a 110 plus horn cab which is also based upon the easy build 30l design. Both of those could work in the cab you have with a bit of carpentry. The advantage is that they are both tried and tested designs.

Thanks!  I’ve been following all the build threads - you guys are awesome!

Still at the pondering stage, really.  I want to get it useable again, but need to examine the construction to see how easy it would be for me to do.

As a dad of 3 young’uns, I always have an extensive list of “more important” things to do first, so this may take a while!!!

I will, of course, keep everyone updated here!

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You could just drop a 12CMV2 in. The cab won't be tuned optimally but it will work for not a lot of money. It wasn't really tuned for the original speaker anyway probably.

Then when you have time you can mod the ports the way @stevie suggested.

Plan B would be to block off the slot ports completely and cut holes for a couple of drainpipe ports as in the easy build cab.

Did you ever put the ports in your house amp?

 

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13 hours ago, Phil Starr said:

You could just drop a 12CMV2 in. The cab won't be tuned optimally but it will work for not a lot of money. It wasn't really tuned for the original speaker anyway probably.

Then when you have time you can mod the ports the way @stevie suggested.

Plan B would be to block off the slot ports completely and cut holes for a couple of drainpipe ports as in the easy build cab.

Did you ever put the ports in your house amp?

 

That sounds like a good way forward.  At least I’ll have it ready to mod properly when a spare block of time arises!

Re: The house combo - still no ports fitted! 🤦🏻
 

Another one of those things on the to do list!!!

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  • 4 months later...
58 minutes ago, Pea Turgh said:

Ta da!!!  New driver courtesy of @Chienmortbb

Plan is to add a new front baffle with port, pop a vintage looking cloth grill on and polish up the cabinet so it looks lush.

 

Now to put it in a corner for another 6 months before I muster the drive to complete it 😂

444B8924-EC6D-4277-86D0-A4A74D6717E4.jpeg

2A964607-78F6-4516-A677-F95992E8BBA8.jpeg

I'm glad it is being used Pete.

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  • 10 months later...

Now that I’ve completed my micro cab, I’m feeling confident about my chances of not screwing this up either. 
 

Been out to the shed to cut some wood for the new full-width grille.  Expect an update soon.  Maybe even before 2023.

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  • Pea Turgh changed the title to Peterson combo driver upgrade

Right, I have some 68mm drainpipe as per the Basschat micro cab & easy build 12” cab, so I’m going to pop a round port in the front, and block up both slots at the front, flush with the baffle.  But, I will leave the internal walls in place.

 

 By these calculations, I have just over 43 litres (not taking in to account the derrière end of the driver).

 

What length port (64mm internal diameter) would tune this bad boy to a usable frequency for the Beyma 12CMV2?

 

Highly technical drawing:

 

 

 

7A965BF8-8E45-43D5-B184-FE76469D2493.jpeg

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9 minutes ago, Downunderwonder said:

You could get a lot of useful cab volume by whacking out those 'port' shelves altogether.

 

Possibly you could trim the 1cm openings back to a usefully tuned length of proper shelf ports. 3cm is still pretty skinny though.

I’m abandoning the slot port idea.  They seem problematic!  I did think about removing the internal ‘box’ bit and putting a fresh new full width baffle on the front, but it’ll be quite destructive, and I ‘m not kitted out for the job (probably need one of those oscillating cutters).  Blocking the front slots and cutting a circle I can manage!

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You may be over thinking this, by blocking just one of the ports you will reduce the tuning down to about 50-55 Hz. (I'd rather they left something bigger than a 1cm gap at the back but you've said you dont want to do major surgery)

 

That gives you a 2db peak in the upper bass and a -3db of around 60hz, both acceptable if not exactly neutral sounding. There are commercial cabs worse than this. Give that a go and see what you think of the sound and let us know.

 

This is the sort of bass end response you ought to get this way

 

 

image.png.f2b3274d4b4656d32946b138f266fb1f.png

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14 hours ago, Phil Starr said:

You may be over thinking this,

It’s my super power.

 

I’ve got it in my head to block up both slots and fit a new full-width grille for aesthetic reasons.  Popping a round port in the front seems an easier way of getting the tuning right, too.

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I think that would be a great solution. Your problem is that the ports will then be quite small and you'll have problems with wind noise in the ports. If you can fit in two drainpipe ports that will help a lot or use a single 10cm port. Two ports 13.2cm or a 10cm port 14.4cm long.

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