21 Inch Enclosure

Well. I wanted to try the 21" speaker MCM has. I don't know what to expect but the speaker should be in Thursday, or Friday. I will test it out this weekend. It’s a cheap speaker so I figured I'd give it a go. I've had 3 18"s from MCM and had no problem. I tested one 18" MCM next to a B&C 18", both in an enclosure at the size required by the speaker, and I tuned them both to ~50Hz. The MCM and the B&C both performed very well. I used a iNuke3000DSP to power them. The B&C started to smell after a blast of some sine waves even though the iNuke only puts out 450W at 8 Ohm. The B&C takes 600w RMS and 1200w max. The MCM on the other hand has a 300w RMS rating with a 600w peak. I never started to burn anything giving the MCM speakers the same power as the B&C. The MCM has been powered with the iNuke for almost a year and it still works fine I always gave it max power the amp would let me. (not bridged that is) Anyways the only audible difference is when you got to higher frequencies; the B&C produced crisper highs. Well, it’s a SUBwoofer, I don’t need it to play anything above 250 tops. Now I know there are times where you want the higher fidelity, like a theater, or a home theater. (The reason I used a B&C) But let’s be honest. If you have an EDM concert with 1000’s of screaming ragers, they won’t hear a difference in quality between a 21” that cost $800 or $100.

Anyways, getting back on topic, The design I modeled will give a response from 35-280hz at 97Hz +/- 3dB, and 130 dB max. The box is 36x24x24 with an internal volume of ~9 ft^3, with two 2"x22.5" ports.

[IMGHTTPDEAD]http://imageshack.us/a/img845/1692/freqres.png[/IMGHTTPDEAD]

If anyone can think of a better design feel free to post it!

My requirements:
-Low end to be about 35Hz (the lower the better)
-High end at least 120Hz
-Longest length has to be under 37"
-1w/1m SPL of 97dB+ (in a half space(
-Uses no more than one 4x8 sheet of wood, and one 49"x22"

If your design is better than mine I'll build and test that instead (my design is by no means all that great, it was just a simple enclosure with an okay response)

*Please note that the enclosure I showed modeled in post #3 has nothing to do with my 21" enclosure. I was just showing what Transmission Line could do*
 
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Hi,
Every driver I've bought from MCM has been far from spec with the exception of the 55-2421's.
Let us know how it turns out will you. With a tuning that high and a proper high pass filter excursion should not be a problem. What did you use to model your box? That FR graph looks nice...
 
NEO Dan, I used "Leonard Audio Transmission Line". It's a new software but so much easier to model in it.

Here's an example of a design:

I was reading Thawach's post about his "Thailand sub projects". I found an interesting sub that I tried to model in Hornresp, but just couldn't get it right. Here's the speaker plan:
[IMGDEAD]http://imageshack.us/a/img837/8409/thafhornnwdm.png[/IMGDEAD]

This is what I input:
[IMGDEAD]http://imageshack.us/a/img716/836/boxinput.png[/IMGDEAD]


[IMGDEAD]http://imageshack.us/a/img27/672/boxoutput.png[/IMGDEAD]


[IMGDEAD]http://imageshack.us/a/img811/373/driverinput.png[/IMGDEAD]

This software is still in beta testing. That's the reason I have these pictures, to point out some things I thought should be changed. The interface is still the same, though. Something else that's nice the software has, is that you can grap you design where it displays it and move it from there. Also you can change units, and graph extents. Here's a picture of the Setting windows, and ill toss in the Amp window to:

[IMGDEAD]http://imageshack.us/a/img705/5159/settingswu.png[/IMGDEAD]

[IMGDEAD]http://imageshack.us/a/img834/1692/freqres.png[/IMGDEAD]

Here's a link to the post:
http://www.diyaudio.com/forums/software-tools/220421-transmission-line-modelling-software.html

Here's a link to the software download:
Transmission Line
 
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tb46

Member
2006-01-09 7:04 pm
Texas
Hi abcdmku,

This sounds interesting. Could you share the model numbers for the MCM 18" and the B&C 18", and do you have measured T/S parameters for the MCM 18"? Finally, will you be measuring the T/S for the MCM 21"?

It should not be hard to get a good simulation out of Hornresp for this speaker, try it with the Compound Hor Driver Arrangement, that way you have something to compare to the transmission line software.

Regards,
 
tb46, I might measure the T/S for the MCM 21". Right now I'm just testing performance. Perhaps if one day I buy the Dayton Audio Test System, I'll measure quite a few MCM and other Drivers. For now I'll stick to Just using a Multimeter and Excel. I never got around to measuring the 18"s I already sold them, next time I buy an 18" MCM I'll be sure to measure the T/S. I still need to measure the RMS power out from the iNuke for my other thread about the new iNuke12000. (it lead to how reliable the iNukes are) I wanted to measure the iNuke last weekend, I'll probably end up measuring both the 21" and iNuke this weekend, when the 21" comes in.

For comparing Hornresp and Transmission Line, I already did some test, and the results were identical. One plus of Transmission Line, is that you can get a more accurate enclosure input.

Here are the model numbers and links to the datasheets:

B&C Speaker (18PS76):
http://www.bcspeakers.com/PDF/PRD/18PS76.pdf

MCM Speaker (55-2954):
http://www.mcmelectronics.com/content/ProductData/Spec%20Sheets/55-2954.pdf

Oh and please note that the enclosure I showed modeled up there has nothing to do with my 21" enclosure. I was just showing what Transmission Line could do.
 
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The B&C started to smell after a blast of some sine waves even though the iNuke only puts out 450W at 8 Ohm. The B&C takes 600w RMS and 1200w max. The MCM on the other hand has a 300w RMS rating with a 600w peak.
If you have an EDM concert with 1000’s of screaming ragers, they won’t hear a difference in quality between a 21” that cost $800 or $100.
B&C uses the AES power ratings which have a 6 dB crest factor, sine wave testing only has a 3 dB crest factor.
Beware that if you use 600 watt sine wave (about 70 volts into 8 ohms) you are at double the power of a 600 watt AES rating.

Be careful, keep sine wave tests short.
Also beware that clipped sine waves have even less crest factor, a "450 watt" clipped amp could potentially put out a lot more than 450 watts.

As far as hearing a difference between speakers, if one has double the Xmax of another, properly powered in a properly designed box, it will be capable of 6 dB more output, a difference easily detected by almost anyone not totally wasted.
Generally you get what you pay for, high Xmax 21" need huge expensive magnets.
If cabinet size is a concern, they may be worth it.
If cost is a concern, TH can beat out BR by 6 dB or so, but require more cabinet volume.

Art
 
haha, I was a little shocked to see this post on the front page. I'm currently working on this. Anyways, The 21" does move a lot of air, but doesn't make all that much noise. Also can't handle as much power as the 55-2954. I abandoned this project because my dual 18"s in a smaller box preformed a lot better. Speaking of which I need to get going, I'm on my way out to pick up the wood for my new 18's. I was just making the cut sheet for it when I saw this. I will post a more detailed response later today or tomorrow.
 

revmark

Member
2015-04-15 10:03 pm
I'll give it a try for my A/V Project studio....

Thanks for the dimensions for this project! I think I'll give it a try and let you know how it turns out. I'm currently using twin 12" Rockfordfosgate P1S412 in an enclosure from the specs of the PDF file I got from them. I'm not happy with them at all...I'm pushing 1000 watts wired in Parallel while it is a dual enclosure each side is 14H x 18W x 10D inches for an internal size of
1.02 Cu ft Vb, F3 of 43 HZ...at least that's the specs they gave me. My Satellites for my system are some old school 12 Inch 3 way Utahs that I've modified by just changing the midranges to some nice 4 inch paper cone mids and some nice 3 way crossovers. The Utah's are very nice and smooth as silk. Powered by a Carver Receiver for the front and a couple of class D amps for the center with a nice walnut converted 1970's HI-FI with dual coaxial speakers for the front. and rear speakers. All of this is ran by my dell computer with a PCI Soundblaster PCI card that I have a nice project studio to do church music on and listen to (Plus some old classic rock) Biggest problem not enough bottom end! When I went to the vendor I bought the Midranges and saw that they carried 21" woofers I thought, YES! I'll sell my old dual 12 in Boat anchor and get 2 of these with seperate enclosers...But being an amatuer at speaker box building what size. Thanks for your post! It's easy and to the point! I'll keep you posted on my Old School meet's high end with some pic's when I get done!
 

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These drivers and the cab recommendations are for a mobile audio app. For HT sub duty, each driver needs at least 2.88 ft^3 and preferably more, though they still won't be all that loud unless a relatively large 6.35 ft^3 [or more] vented alignment tuned to 20 Hz or less is used.

GM
 

revmark

Member
2015-04-15 10:03 pm
Bigger is better?

These drivers and the cab recommendations are for a mobile audio app. For HT sub duty, each driver needs at least 2.88 ft^3 and preferably more, though they still won't be all that loud unless a relatively large 6.35 ft^3 [or more] vented alignment tuned to 20 Hz or less is used.

GM

So If I were to put these subs that I have right now into much larger cabinets I would get the sound I seek?
 
So If I were to put these subs that I have right now into much larger cabinets I would get the sound I seek?
I'd say there's a good chance you could redesign something that requires a larger cabinet but provides more output. If that's a sealed box, almost definitely. Ported boxes have much better output capability.

Cars tend to offer pretty huge gain at low frequencies. A lot of car audio boxes depend on that fact and are really pretty anemic down low. As soon as you take it out of a car it's gonna sound a lot less impressive. That could be exactly what you're experiencing.
 
So If I were to put these subs that I have right now into much larger cabinets I would get the sound I seek?

Well, you didn't provide any specific performance goals, I just pointed out that these RF drivers want to 'feel' large vented cabs tuned low to get the most gain BW out of them, which in theory will be near/at THX reference in room if up against a sturdy wall and maybe even exceed it a little if corner loaded.

GM
 
Well, it does unless a MLTL alignment is used, so ideally should either be a tall or folded pipe design.

GM
I see what you mean. I was just saying you can get a similar but slightly less flat and less sensitive design by giving it a smaller port with a similar resonant frequency. Given the space I'd build it as is.
qWCQoYg.png

Like here you shrink the port by 40L and you keep the response reasonably similar.
 
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