Please help me build a cab

[leosep]

Hi, how are you all?

I have some old driver and i want to use it to make a little PA subwoofer for a small room.

The only specs about the driver that i have are:

Speaker:
General Specifications:
Nominal Diameter: 12 inch
Rated Impedance: 4Ohms
Operating Bandwidth: 35 ~ 3.2KHz (-3dB)
Power Handling Capacity: 350W RMS
Sensitivity (1W/M): 96dB (±3dB)
Voice Coil Diameter: 2.5 inch

Thiele-Small Parameters:
Resonance Frequency Fs: 36.23Hz
DC Resistance Re: 3.4Ohms
Mechanical Q Factor Qms: 2.823
Electrical Q Factor Qes: 0.446
Total Q Factor Qts: 0.0.385
Equivalent Cas air load Vas: 121.67 L
Surface Area of Cone Sd: 0.0552 m2
Efficiency Bandwidth Product EBP 81.2
Voice Coil Over Hang X-max 7 mm

Physical Information:
Cutout: 11.10"
Mounting Depth: 5.51"
Basket: Die cast aluminum
Magnet Type: 67 oz.
Cone Material: Non pressed paper
Surround: Cloth
Dust Cap: Paper
Damper: Cloth

Any ideas of the size of the cab? sealed, ported?

Thank you in advance!

 

[academia50]

Creo que esto te ayudara


I think this will help you

Designing and Building a Speaker Box Example

 

[leosep]

Thanks,

I tried to calculate my cabs in the past but i think i'm doing something wrong. I cant
get enough bass. I'm not sure if i'm doing it right. I don't know how to calculate for a bass sub-woofer and i don't know if it's the same method when calculating for full range.

 

[freddi]

a problem with most of the MCM-Newark Chinese made woofers is in-correct specs. Qes can be double what's published.

https://www.newark.com/mcm-audio-se...55-2982&ddkey=https:en-US/Element14_US/search

Here's a thread with what I believe is your woofer - after the owner got his impedance jig set up correctly, qts was running in the 0.6-0.7 area.

It probably a good speaker other than the qts figure. I wonder what magnet material is used as many of these speakers have large magnets but what looks like low magnetic strength.

I would ignore trying to get an alignment, and not make the boxes too large.

There's probably more info including successful boxes if you search MCM 55-2982

MCM 55-2982 T/S Params and a Ghetto System

Here's AmpsLab's measurements and suggestions for that woofer:

MCM 55-2982 12″ Die Cast Woofer Thiele/Small – AmpsLab

I think Brian Steele might offer some thoughts on your woofer.

 

[freddi]

using Ampslab's spec - here's what it does in a rather large (110 liter) bass reflex tuned to 36Hz

 

[leosep]

Thank you all

The driver is a 55-3242

Should I build a sealed cab or ported?

 

[freddi]

I figure its about the same driver as before other than 4 ohm nominal impedance.

there's no measured specs that I see so its probably like the AmpsLab measurement for 55-2982.

I just got a 10" MCM and its qts >0.7 - should have looked it up
as one measurement showed qts 1.3 ! - mine is strong in comparison



55-3242

55-2982

An externally hosted image should be here but it was not working when we last tested it.

 

[NEO Dan]

Agreed, MCM is notorious for its deviation from specifications.

 

[freddi]

here's some stuff based on AmpsLabs spec of the 8 ohm version

hey NEO Dan - I've got a knockoff of 8pe21 - superficially looks similar including big magnet and shiny backplate - - qts must be around 0.65

There is one MCM which is on spec ant that's the paper DVC 12 used by the late Marshall Leach Jr. in a sub - sat system.

A 450uF low loss capacitor would flatten and extend the 8 ohm version in a 40 liter sealed box.

 

[freddi]

kooky idea - maybe if sim works then good for some other drivers

 

[freddi]

with a good capacitor and low impedance driving amp - 40 liters sealed would work.

 

[academia50]

Should I build a sealed cab or ported?

If the transducer is very variable in its specs, as you have already been told, then the logical choice would be sealed.
The main advantage of the sealed cabinet is that you have less chance of sounding bad because of deviations in the calculations, the big disadvantage is that you need more amplifier power to achieve the same SPL than in a ported cabinet.


Types of enclosures - speaker boxes - easy explanation

 

[NEO Dan]

hey NEO Dan - I've got a knockoff of 8pe21 - superficially looks similar including big magnet and shiny backplate - - qts must be around 0.65

There is one MCM which is on spec ant that's the paper DVC 12 used by the late Marshall Leach Jr. in a sub - sat system.

Hi Freddi,
The only driver I ever got from them that was on spec was the 8" tang band copy.

 

[leosep]

Thank you for your help. I'll start to test the info you gave me and see what happens.

 

[HammerSandwich]

The main advantage of the sealed cabinet is that you have less chance of sounding bad because of deviations in the calculations

And, if you have DSP available, you can use a Linkwitz Transform.

 

[academia50]

And, if you have DSP available, you can use a Linkwitz Transform.

Of course, and he can buy it now or make it himself ....😀


Linkwitz Transform

Linkwitz Transform Subwoofer Equaliser

 

[oldmanaudio]

Being you don't know how accurate the specs are building a vented system would be prone to possible alignment issues(tuning). A sealed box about 1.5cuft should be in the size range that will work. The specs we do have don't favor ether sealed or vented. You are going to use it for a PA right?