MCM 55-2421 T/S Parameters and thoughts

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BillFitzmaurice

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Joined 2004
billfitzmaurice.com
You only need a horn if you require high SPL, for instance to run it with a low power tube amp or to match up with high sensitivity mains. For more normal SPL just model it up in WinISD in ported box, 4th order and 6th order alignments to find what suits your requirements. The Qts is a bit too low for a sealed box or TL. I also wouldn't be too concerned about trying to get flat to 20 Hz. down 10-15dB there is quite adequate, but if you really want that kind of extension you'll have to look at larger drivers.
 
Patrick Bateman

Patrick Bateman

Member
Joined 2006
Zaph said:
Actual measurements:

Fs=30.95 hz
Qms=12.2863
Qes=0.2365
Qts=0.2320
Vas=23.88 l
SPL=86.59 1w/1m
Re=3.4
Le=2.42
BL=13.15
Xmax=16mm P-P

This was from an early model, hopefully the specs have not changed.
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I bought four more of these this week. They look identical to what I bought twelve years ago. Here's the specs on one I just measured, after breaking it in with pink noise for a couple hours:

Fs=26.92 hz
Qms=9.5
Qes=0.2619
Qts=0.2549
Re=3.95
Le=1.41

My Re and qts always seem to measure higher than published specs. I think their are two main 'takeaways' from my measurement in 2017, my measurement in 2006, and John's measurement in 2004:

1) the driver hasn't changed
2) the published specs are inaccurate, but John's are accurate.
 
ODougbo

ODougbo

Member
Joined 2011
Patrick,
What are you planning on doing with them?
I have 4 left on my shelf also, and remember other posts with the same "on the shelf" responses,,,so they are out there.
My last experiment with a 2421 single woofer was in small sealed box and a inexpensive plate amp with boost. The bass was impressive, and probably be fine for a small car or room.

Any reason not to use them in a 3 way, crossed over very low?
E.g. Peerless reintroduced a affordable 5.25" with inexpressive flat response.
Peerless TPY05W08O0088 5-1/4" Heritage Family Woofer 8 Ohm
 
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portakalx2

Member
Joined 2017
Studio Au said:
@greg, may I ask where you purchased these drivers, wanting to make a push pull sub, like the one featured here.\

Building a Tapped Horn : 6 Steps (with Pictures) - Instructables

In Bristol too.

Thanks
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Has anyone built this tapped horn from instructables? And has anyone verified the design? The author's sketchup dimensions don't correspond to the Hornresp values. And he admits he has changed the design a bit. But looks like more like quite a bit. Anyone know anything about this design?

Best,

Selim
 
P

portakalx2

Member
Joined 2017
Brian Steele said:
Yup, I tried running that design through my BOXPLAN-THAM workbook. The numbers don't add up.
Click to expand...

Thanks for the reply Brian. I bought the two MCM woofers already and now I'm not sure about building the enclosure as per his dimensions without verifying them. I don't have enough experience in Hornresp and I'm new to the hobby, although I understand some basics. And I do want to build a tapped horn with these drivers. Do you have any suggestions on how to go about doing that?
 
freddi

freddi

Member
Joined 2005
not a "sub" but two BFM18 series connected in a corner should be pretty punchy

pcjeNNZ.png
 
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