Trying to decide....

[bjm362]

The last thread I started here I got a lot of really good info/feedback, so I felt like this was a good place to talk about this.

 

I have a pair of 4 ohm 12s I am trying to decide what to do with. They are MCM 55-3242s, which are no longer in production.

 

Specs are:

General Specifications:

 

• Nominal Diameter: 12 inch
  
• Rated Impedance: 4 ohms
  
• Operating Bandwidth: 30Hz ~ 3.2KHz
  
• Power Handling Capacity: 350W RMS
  
• Sensitivity (1W/M): 96 dB
  
• Voice Coil Diameter: 2.5 inch
  
• Overall frame diameter: 12.28"
  

 

 

 

Thiele-Small Parameters:

 

• Resonance Frequency Fs: 36.23 Hz
  
• DC Resistance Re: 3.4 ohm
  
• Mechanical Q Factor Qms: 2.823
  
• Electrical Q Factor Qes: 0.446
  
• Total Q Factor Qts: 0.385
  
• Equivalent Cas air load Vas: 121.67 liters
  
• Efficiency Bandwidth Product EBP 81.2
  
• Voice coil overhang X-max 7 mm
  

 

 

 

Physical Information:

 

• Cutout: 11.10"
  
• Mounting Depth: 5.51"
  
• Basket: Cast Aluminum
  
• Magnet Type: 67 OZ
  
• Cone Material: Non-Pressed Paper
  
• Surround: Cloth
  
• Dust Cap: Paper
  
• Damper: Cloth
  

 

My original plan for these if I remember correctly was something similar to the original Peavey Triflex system. These being part of the sub box. Except instead of one 212 sub box, I was thinking two 112s (two 112s coupled being the same response as one 212). There are other potential uses, but something of that nature could come in real handy right about now. Especially being divided into two boxes for easier handling.

Links to good plans that would work well for light duty subs would be bonus. Even more bonus if they could be also used as moderate duty kick bins crossed over above my FH118s....

[isaac42]

Can't help you this time. I'm not familiar with either your drivers or the Peavey Triflex.

[bjm362]

Can't help you this time. I'm not familiar with either your drivers or the Peavey Triflex.

 

Thank you for taking a look anyway.

 

For anyone interested, here is a link to the oldschool Triflex system. Of course I would be using bigger better more modern tops, but that sub could be quite useful for smaller gigs.

It has been my experience that even at gigs where subs are not required everything still sounds better with them.

http://assets.peavey.com/literature/manuals/80370224.pdf

 

Some options I have been looking at.

Cubo 12

http://www.freespeakerplans.com/bass-cabinets/14-cubo-12

 

Punisher Horn MKII

 

https://www.freespeakerplans.com/plans/14-plans/basscab/45-punisher-mk2

 

 

 

 

 

 

[WRGKMC]

My favorite site for speaker building is Parts Express. http://www.parts-express.com/?utm_so...c&utm_camp aign=G+-+Brand+-+Main&utm_group=G-Brand-Main-Exact

 

Great people to deal with too. I had the wrong order shipped to me one and when I called they simply say keep it and we'll reship yours and they did so overnight. Not that what I got was worth much but its just the fact I didn't have to mess with sending it back.

 

Your specs seem to be for some kind of pro audio speaker form a PA cab or home system. 350W makes them good enough for small PA cabs or monitors. The lows are good enough for subs too if you choose but bass frequencies do eat up that wattage headroom very fast.

 

The speakers are good up to 3K and you could simply buy horns and use passive crossovers for monitors or PA cabs. The 4 ohm impedance is a bit troublesome. Most PA heads will let you run combinations of cabs down to 2 ohms but that's it.

 

I'd be thinking along the mines of using a Plate Amplifier for them which you could easily add to the cab and simply run them as self powered cabs. Here's a whole page of them for different wattages and applications. http://www.parts-express.com/cat/sub...amplifiers/332

 

This one would be ideal. plus its got a 3db boost at 30Hz. for those earthquake tones. http://www.parts-express.com/yung-sd...30-hz--301-510 The price isn't bad either. Its nearly impossible to find a 300W head for $119 brand new. Your speakers are good for 350W so you have an extra 50W there clean headroom and could run the amps full up without blowing them. The bass frequency is tunable too from 30 to 200Hz so you can not only get the bet tone from the boxes if the resonant frequency is off you cant also tune the bass response to the room.

 

Next you can google up a speaker cabinet calculator on line. (Internet is great - I used to have to do this stuff long hand using a calculator back in the 70's when I first started building cabs). http://www.diyaudioandvideo.com/Calc...rBoxEnclosure/ I posted the results of one option in the next post.

 

Simply key in your parameters and it will give you the correct amount of cubic air you need for that particular speaker to get the best bass response.

 

As you can see in the next post, if you want to get the best low response with those speakers you need to use a ported box and learn how to tune the box. Premade plans are for specific speakers that match that cab. Low frequencies are tough because you have to correctly tune the cab to the resonance of the speaker, much like tuning a trombone by lengthening or shorting it pipe length.

 

Its not that hard really. I can give you some tips once you get to that point. You'd lengthen or shorten the port pipe until you get the maximum volume at the resonant frequency. You'd need the cab built and being pumped a 36Hz signal and have a multi meter connected to the speaker as well. Then you push the port pipe in and out till the meter reads the maximum signal. You then mark the tubes length with a marker, trim it off then glue it in place flush with the front of the cab and bang, you're done.

 

This is the only way you know the cab will have perfect tuning down that low. No premade specs or blueprints will be correct for any specific speaker. You may get lucky and you may get close through dumb blind luck but you know how awful a bass guitar can sound when its out of tune just a little bit. You want it dead on tined to that resonant frequency to get maximum decibels from that speaker too.

 

Bass and PA cabs that handle allot of bass are always Tuned when you're designing them. You can then use that formula to build others of course and if you dimensions and speaker tolerances are good. It wont matter if its off by a few Hertz.

 

So all you need to do from here is convert your Length Width and Height from one of these three designs. using this calculator. http://www.diyaudioandvideo.com/Calc...akerBoxVolume/ I messed with it based on VB of 3.66 ft3 for your speaker and up with W=17.67 X H=24 X D=18

 

You can of course play around with then various widths and depths to get the best shape you want and that page has alternate shaping for you. You can work the number to get an exact cube or whatever you want. Again, if you use a rubberized insulator inside or softer insulation you have to take those into account. That parts express site has all the extras from Grill cloth, Tolex, corners, Handles to insulation you can purchase to do a quality build.

 

I will note the cabs have to be fairly big to get all the way down to 36Hz. The sealed box gets you down into the 60's and probably have smaller dimensions. Most of the frequencies you hear form bass is comes from the first fundamentals so anything below 80Hz is going to have plenty of lows. at 30Hz you waste allot of power recreating low frequency noise. Nearly every recording you hear has everything rolled completely off below 40Hz or so its a matter of size vs essential ergonomics of what you actually need.

 

Back in the day Altec used to make bass bins 25 feet across to get good lows. They were only good in huge theatres where you had the space for those waveform can fully form. It takes about 56 feet for a 20Hz waveform to completely form. This is why many bass cabs are tuned higher. A bass cab that produces a string 80Hz can be much smaller and wave will fully form at 14 feet.

[WRGKMC]

Here's the cab dimensions I used for the one cab. You can calculate a sealed box or a simple port as well. I had issues trying to post them but the links are there and you can simply calculate them yourself. .

 

 

 

 

 

 

[bjm362]

Again, great post WRGKMC

I am familiar with Parts Express and count it as a resource. I have seen kits there and links to different companies "suggested enclosures". I will have to look for other speaker building plans/free resources on there.

 

I have built some cabinets before (sealed), and may wind up having to do a bass reflex design with this. I no longer have a Bass Box pro, so finding an online calculator would be a plus if I do that kind of cabinet. I have reworked some bass reflex cabs too, but not while I had BB Pro. I did not do any while I had the benefit of that resource.

 

Part of what I am trying to accomplish is a reasonably priced, compact, not too heavy, very productive and also versatile (at least can be used as a light duty sub in a lower powered system and midbass in in a bigger system) cabinet. Yeah, I realize there are going to be some compromises between these goals.

I feel like you may want to look at the links I provided though. It may interest you quite a bit. More so the current designs than the oldschool Triflexes.

 

Your point about them making good PA tops is very valid. That was one of the things I had considered when I bought these.

Unfortunately that really is not what I need most right now.

 

Power sources available already varies dramatically. Peavey XR-684, T-Pro 1000, Pyle PTA1200, Behringer NU4-6000. So at 4 ohms I CAN look at 200w,360w, 600w, 880w, 3000w depending on which amp and in what configuration.

[isaac42]

One interesting tidbit: a lot of professional 'subwoofers' cover the second octave, 40-80Hz. That's plenty low enough for almost all live performance situations.

 

Subwoofers for high fidelity systems typically cover the first octave, from 20-40 Hz.

 

I'm not sure how applicable that is to the current discussion, but we were talking subs.

[bjm362]

The fact that Sub-woofer as a term used in my trade is a misnomer and what it actually means is relevant as far as I am concerned. A true sub-woofer would operate in the sub human hearing range (below 20hz). That is what the term actually means, but is not how it is used. Hifi subs as you pointed out typically operate down to 20 hz, but in live sound generally reproducing anything below 40 hz is a waste of resources.

The BR boxes WRGKMC is recommending are capable of a pretty good deal of what I am trying to do. They will operate well down to 45 hz as a light duty sub. They won't be excessively heavy and they will operate even better in the other role I want them for. Even though they operate better there, that is actually where they fall short on what I am trying to do. Support above my subs (80hz to 200 or 300hz) in a big system. I am just trying to get as much out of this all the way around as possible.

That is why one of the examples I was looking at is a tapped horn/chamber load hybrid. It is productive deeper than traditional horn theory says it should be. The Chamber loading helps it get deeper, while the tapped horn uses energy from both sides of the driver in correct phase to almost double its output ability. The downfall of this is a narrow operating range. Outside of that range the tapped horn is no longer in phase on both sides and creates cancellation.

The other horn design meets the range and production goals with this driver, but is bulkier,heavier and a bit more difficult to build.

The old Triflex subs would be a good compromise between all of the goals, but even having used them myself, I do not have sufficient details to build. Plus I would still want to be able to divide that box in two.

 

I may be trying to get too much out of this, but the time to weigh it out is before I build....

[bjm362]

I have went to the link used to make his example box. That example is a good starting place to design a box. It is similar to how Bass Box Pro worked. I am also looking at some other links to replace some of the design functions that were available in that program. If I build a BR box though I feel like I should design a diffuser to increase loading.

Looking at the box in the example also kind of makes me more interested in two things for these drivers. Saving them longer until I can build some tops with them. Then I only need to design my own crossovers. I already have ample links for that. Or trying my hand at my own ideas for a hybrid sub. Before I go buy wood I am taking a harder look at BR boxes thanks to the input here.

As always all input is appreciated, especially that that has provided additional resources for making this decision!

 

[bjm362]

I had found something like this years back, but just saw this. I think some of you guys may find this interesting too.

 

http://dbdynamixaudio.com/quarter-wave-flared-vent-t-line-horn-bass-reflex-enclosure-calculator/

[bjm362]

This box is closer to what I actually want to build with these. there is a improvement I know I can make with these that does not add significant weight, but does increase their versatility quite a bit!

http://dbdynamixaudio.com/single-fold-on-axis-transmission-line-enclosure-calculator/