Mach5Audio MJ-18 LLT - Home Theater Forum and Systems - HomeTheaterShack.com
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post #1 of 37 Old 01-19-07, 10:01 PM Thread Starter
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Mach5Audio MJ-18 LLT

I am low on cash so this will be a budget sub build. This sub will tide me over until my HT room is drywalled and I build an IB sub.

I have purchased a Mach5Audio MJ-18 but its back ordered until the end of the month. I have purchased 13ply oak plywood to use since I am tired of mdf and want to try something new. Here are the T/S Parameters - MJ-18 - 4 Ohms

Fs = 28 Hz
Re = 3.2 Ohms
Qes = 0.34
Qms = 4.99
Qts = 0.31
Mms = 229 grams
Rms = 8.1 kg/s
Cms = 0.14 mm/N
VAS = 208.4 litres
Sd = 1029.2 cm2
Xmax = 12 mm
Cone Diameter = 36.20 cm
Recommended Box Sizes:
Sealed: 80 litres (2.8 cu. ft.)
Ported: 128 litres (4.5 cu. ft.) 30Hz tuning
EBS: 250 litres (8.8 cu. ft.) 18Hz tuning

I am going with the 8.8 cu ft enclosure. 6" port, 21+" long. I've attached some WinISD info. The plots show spl and excursion with the input of 500watts. I am a little worried about excursion but we'll see.
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Mach5Audio MJ-18 LLT-mj-18-xmax.jpg  

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post #2 of 37 Old 01-19-07, 10:09 PM Thread Starter
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Re: Mach5Audio MJ-18 LLT

I will be making the enclosure a standing rectangle (like a sonotube) with intern"al dimmensions of 19"x19"x44". I will probably only feed the driver 500watts.
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post #3 of 37 Old 01-19-07, 10:17 PM Thread Starter
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Re: Mach5Audio MJ-18 LLT

I am also thinking of a slightly small enclosure, 7.5 cu ft tuned to 22Hz. It will have less low end extension but the driver seems slightly better protected.
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post #4 of 37 Old 01-20-07, 12:23 AM
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Re: Mach5Audio MJ-18 LLT

12mm xmax... isn't that kinda weak? Seems like it would have a hard time producing much output.
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post #5 of 37 Old 01-20-07, 11:16 AM
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Re: Mach5Audio MJ-18 LLT

Quote:
Sonnie wrote: View Post
12mm xmax... isn't that kinda weak? Seems like it would have a hard time producing much output.
The drivers have proven themselves in the IB world as a BUDGET driver. One Mach 18 driver pushes a lot LESS air than an RL-P 15" driver though because of the low xmax. I'd put the Mach 18 on par with a Dayton IB 15, maybe a little higher output.

Personally I wouldn't touch a lower xmax driver for a home theater sub. My experience is they can't handle my torture but they have been working for those on a strict budget.
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post #6 of 37 Old 01-20-07, 02:49 PM
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Re: Mach5Audio MJ-18 LLT

This driver isn't suitable for a LLT, namely the "low tuned" aspect. A more traditional, higher tuned and highpassed ported sub would be ok, but the enclosure would still have to be pretty large to maintain something resembling a flat response to ~20hz.


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post #7 of 37 Old 01-22-07, 07:01 PM
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Re: Mach5Audio MJ-18 LLT

I agree I'm also currently building 4 down firing subwoofer's (one for each corner in my room) using the MJ-18 and it is a budget sub and i found that this sub doesn't truly shine below 30 Hz I'm going with an 8ft^3 enclosure @ 34 Hz because that seems to be the most suitable enclosure for this driver and with 4 of those going with about 600 watts rms into each one the lower end extension will be better but as far as using one of these you can't get that much low end out of it or you'll have major distortion problems and you'll find that you won't get as much output out of it. Being that I'm only 15 I have to be pocket friendly and I'm a big fan of this driver until i can afford a few RL-s 15's. So I suggest you tune it up to 28Hz using the same box and all, just shorten up your port
post #8 of 37 Old 01-23-07, 12:42 AM Thread Starter
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Re: Mach5Audio MJ-18 LLT

Yeah, I know the driver isn't the best for the low end but this is on a tight budget. You know, one income + wife + 3 kids = tight budget. Considering that I do not have a sub right now, almost anything is better than nothing.
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post #9 of 37 Old 01-23-07, 10:45 AM
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Re: Mach5Audio MJ-18 LLT

Quote:
So I suggest you tune it up to 28Hz using the same box and all
Seconded. Rather than trying to stretch things out and end up watering down overall performance, let this woofer shine where it can, offering you lots of headroom from 30hz on up. Rather than shorten the 6" port though, I'd use an 8" diameter port that is 14" long. I'd also adjust the highpass center frequency on the plate amp to 22hz for better protection.


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post #10 of 37 Old 01-23-07, 11:55 AM
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Re: Mach5Audio MJ-18 LLT

This is off topic but where can I find 6" and on up ports? I've googled them a few times with no luck, I've thought about making my own with pvc piping but how would I flare pvc? I don't use a port unless it's flared. And the 8" is no problem like i always say bigger is better And besides one you get down in the 30 Hz range you'll hardly notice how it perform below 30 Hz unless you run some real low bass tracks through it or maybe in a few movies in a scene where there's some huge piece of rumbling machinery, b/c 30 Hz is pretty low although some like to make it seem like nothing, using heavy gauge string and down tuning my e-string to a D the lowest i can go on my bass is around 35 Hz at the most, and most bass that you actually feel in your chest occurs from 60Hz on up to about 200Hz. And with your enclosure the dimensions you gave give it about 9ft^3 leave it at that this driver does better with more space and tuning @28 would give you a almostt flat response down to 26 Hz which i say is a good comprimise on your budget between th cheap driver and a low frequency output.

Last edited by punkrokr1701; 01-23-07 at 12:32 PM.
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