MCM Electronics

21'' Die Cast Professional Woofer - 800W RMS By MCM Audio Select (55-2985) MCM Part #55-2985

3 stars 4 reviews
$139.00 
MSRP: $299.00
You Save: $160.00 (54 %)
Qty.Volume Price
4+$125.00
This product currently has limited stock.

21" Paper Cone Woofer

Low cost general replacement woofer is ideal in a two way cabinets or as a subwoofer. It is perfect for prosound applications and is ideal in sealed enclosures.

Specifications Top

    General Specifications:
    • Nominal Diameter: 21 inch
    • Rated Impedance: 8 ohms
    • Operating Bandwidth: 25Hz ~ 2.5KHz
    • Power Handling Capacity: 800W RMS
    • Sensitivity (1W/M): 99 dB
    • Voice Coil Diameter: 4 inch
    • Overall frame diameter: 21.26"


    Thiele-Small Parameters:
    • Resonance Frequency Fs: 25.9 Hz
    • DC Resistance Re: 6.3ohm
    • Mechanical Q Factor Qms: 3.51
    • Electrical Q Factor Qes: 0.43
    • Total Q Factor Qts: 0.38
    • Equivalent Cas air load Vas: 705.0 liters
    • Voice Coil Over Hang X-max 7mm


    Physical Information:
    • Cutout: 19.69"
    • Mounting Depth: 9.29"
    • Basket: Die cast frame
    • Magnet Type: 100 OZ
    • Cone Material: Treated paper
    • Surround: Cloth
    • Dust Cap: Paper
    • Damper: Cloth

    Part Numbers
    MCM Part #:55-2985
    MCM Audio Select Part #:55-2985
    Package Specifications & Dimensions
    Weight:35.32 lbs.
    Hazardous:Yes
    RoHS Comp:Yes
    Warranty:365 days
    Need to Return?
    Length:22.5 in.
    Width:22.5 in.
    Height:12.25 in.
    Shipping Information
    Extra Shipping Charge:No
    Drop Ship:No

Product Reviews Top

  • by praudio

    on 4/6/2016

    Where's the motor?

    Overall: 1 out of 5
    Value:
    Quality:

    After a 14 hr. break in at approx. 1.2x Xmax (one direction), and 4 days "recovery, using a Woofer Tester Pro through the low power port, the measured T-S paras are:

    Re = 6.1868 ohms
    Fs = 28.9966 Hz
    Zmax = 27.7265 ohms
    Qes = 1.7155
    Qms = 5.9725
    Qts = 1.3327
    Le = 1.5780 mH (at 1 kHz)
    Diam = 469.9000 mm ( 18.5000 in )
    Sd = 173420.6229 mm^2(268.8025 in^2)
    Vas = 422.6942 L ( 14.9273 ft^3)
    BL = 14.1448 N/A
    Mms = 304.4983 g
    Cms = 98.9373 uM/N
    Kms = 10107.4072 N/M
    Rms = 9.2887 R mechanical
    Efficiency = 0.5645 %
    Sensitivity= 89.5344 dB @1W/1m
    Sensitivity= 90.6506 dB @2.83Vrms/1m

    A "direct BL" test confirmed the "motor", meaning the rest of the measured parameters are likely close. The suspension might soften up further with more use, but this will not help efficiency / sensitivity at all, and in practical enclosures, won't help Q or the bass response much, either.

    Running MCM's specs through a modeling program gave a BL of 22.95. So, the question is, where is the motor? Motor strength is best given by ((BL)^2)/Re; by measurement = 32.34, per the mfgr. = 81.07. So, we've got about 40% of the specified motor. It actually "should" be possible to get a motor over "80" out of this size structure, and certainly around 60 -- many 18" competitors with from reputable vendors do.* But in this case, I can't figure out if this is a case of gross incompetence in the vendor's measurements, or if they just get the speaker "near" the magnetizer, at that point in the construction, most days. Friends tell me many of the larger MCM woofers are similarly afflicted, but I've never seen a case quite like this. That said, the Pyle 21", which appears to be built by the same "source", is very similarly "off" in its specs... It comes out as slightly "better" in an absolute sense because it has a double stack magnet and thicker top plate. QTS actually comes out under "1"!

    *Even Eminence' Delta Pro 18A manages to get a ((BL)^2)/Re of 67.4 out of it's (coincidentally) 67 oz. magnet and 2.5" voice coil.

    The only app. that would seem to make much sense for the 55-2985 is as an open baffle woofer, and even then the SQ is likely to be mushy. The old trick of damping material directly over the back of the woofer might be helpful.

    In other areas of comment: Indeed, the cone is quite "boingy", but if one uses the woofer from 100 Hz down, this should not be noticeable. The frame is VERY "resonancy" too, but damping applied to the basket, say, 50 yr. latex caulk, or 3M strip caulk, should help.

    Also, it should be pointed out that this unit (and the Pyle version) use woven-into-the-spider-cloth tinsel leads. In a former life one of my jobs was reliability testing of woofers. This type of lead will, if the speaker is pushed vigorously, fail every time, in anything from a few to 24 hours, right at the spider neck glue joint. In this case, if you rarely exceed Xmax, maybe (maybe) you'll be ok

    "Inexpensive" is no justification for specs that are not even close. MCM needs to hold their suppliers' feet to the fire! And this is going back, even though the shipping is a killer. I may never buy a large MCM woofer again.

    Dang, I hate giving bad reviews. But I have a good one next (28-21270). :-)

  • by tylerdrew47

    on 11/4/2015

    I have two of these

    Overall: 3.5 out of 5
    Value:
    Quality:

    I bought one for a sub and put it in a 7.5 cubic feet box. I did not get the bass out put I wanted the box is tuned to 32hz. So I bought another one and now have them in a isobaric configuration face to face style and now I have good bass response that I think is somewhere in the 30's. I have had this configuration for about a year and have not heard the ringing that one reviewer described. As far as power goes I can shake my whole apt. building but when I do crank it I run out of excursion with heavy bass drops its probably because of my isobaric configuration.

  • by jason tice

    on 6/28/2015

    BIG Disappointment

    Overall: 3 out of 5
    Value:
    Quality:

    ... I recently bought a pair of these, simply out of curiosity...Throughout the decades, I have seen a LOT of loudspeakers, and done a LOT of rebuilds and seen different build components, as I have been a re-comer for years.....
    As far as the quality of build, these are actually built well for being an import product. The frames are a nice cast aluminum, the cones are REALLY thick and heavy, and magnetic structures are fairly impressive as far as the size....
    I have quite a number of different enclosures, several of which are test boxes and I can simply change baffles to obtain different volumes/alignments/types of enclosures, including folded bass horns with compression chambers.....
    Welp, to get to the point, I've had 15's and 18's that perform better, play louder, have better efficiency, and play deeper than these do....
    Bass tonality of response is quite 'boinky', they have a serious problem with some sort of 'ringing', as well as cone edge resonance issues.... The CONE BODY resonance is REALLY high, so you have a massive bump in response from the 100-300hz range, but don't have much in the 20-80 range, which you would anticipate they would, as they do have an impressive size/perimeter...They're HUGE, they're heavy, and you simply don't get the perform,acne you think you would...The higher end 18's that MCM sells would be better choices if you';re looking for a decent subwoofer.These are more like giant mid-bass speakers.....

  • by allen banezz

    on 3/25/2014

    Air mover.

    Overall: 4.5 out of 5
    Value:
    Quality:

    I play in a band and DJ some times. These work well with a high powered amp. I made the mistake of using 2 of these 21" with 2 Gem Sound 3950 amps in bridge mono. Well the amps only put out 700 real watts to each woofer and burned one of the V.C. in the center. I bought another one and up graded the power amps to QSC 2450,s in bridge mono and they love it. These are the real deal for dance music. I use the MCM 18" for my live band because kick drum sounds more clear though them, But these 21" shake everything in almost any venue I work in. the 24" x 48" x 36" deep bass horn boxes I have them in weigh over 150 lbs but still vibrate across the dance floor plus I have to strap the mid/high cabs to them so they don't fall off. Power it right and these things are lethal.

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