Mach5Audio MJ-18 LLT

[kano32]

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.

[kano32]

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.

[kano32]

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.

[Sonnie]

12mm xmax... isn't that kinda weak? Seems like it would have a hard time producing much output.

[Darren]

Sonnie wrote:

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.

[SteveCallas]

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.

[punkrokr1701]

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

[kano32]

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.

[SteveCallas]

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.

[punkrokr1701]

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.

[SteveCallas]

For large diameter ports, most of us use Sonotube. Where the port meets the MDF, we use a roundover bit to create a semi flare - the larger the bit, the better.

I agree that bass in the 30hz range doesn't get enough credit, that's where a lot of the more agressive and even stomach tickling stuff is. And I also agree that impact occurs much higher, in the 70-200hz range. That said, there is still a pretty noticable difference between 30hz stuff and infrasonic stuff. One is stomach tickling, the other is fear inducing. If one has a concrete floor though, the infrasonic stuff isn't very fun at all.

[letzleta]

SteveCallas wrote:

If one has a concrete floor though, the infrasonic stuff isn't very fun at all.

Why do you say this steve?

[punkrokr1701]

yeh there is a difference between the 30Hz region and the infrasonic stuff, but on a low budget build getting a decent response that low that won't ultimately take performance away from the higher ranges is next to impossible, but not impossible, with some of the experience I've gained at DIYaudio forums I'd say that a horn is another choice is he wants low, but the sonotube seems best here, also another option that I'c ealways wanted to try myself is finding some tactile transducers like the Buttkicker 2 to go with this sub I want to get some cause I've felt them and even if you have a mediocre 10" sub adding one of these will bring those infrasonic frequencies to life because bass is felt more than heard the lower it goes and you'd have to have a wicked ear to be able to hear something like a 16 Hz tone.

[Chrisbee]

One can flare PVC pipe by heating it gently with a heat gun then forcing it rather gently over a suitable mold. It doesn't seem to like being reheated though and can buckle easily. Which can waste expensive pipe. Don't try flaring PVC freehand. It needs a form to get the desired shape. I doubt you can make a full trumpet flare like the pro models. Wear thick leather industrial gloves as the heat required to soften PVC will burn your skin very easily. If you can't smooth the hot PVC with your hands then you're stuck!

There are some PVC fittings (joints) which I believe could also be used if they were cut away carefully to leave just a flare behind. The pipe adaptors look like potential flares as do the surface mounting drain fittings. You just need the imagination to make the most of what is on offer for other purposes. In larger sizes the joints certainly aren't cheap though.

Asking a drainage contractor on (or off) a building site might get you something cheap if you ask nicely and show respect. Or it might not. I had some nice clean 10" PVC from a very long length that had been run over by a tractor. My taking it away as it was I saved them burning it on-site. They were glad to get rid of it before the boss noticed! Sheer luck though.

MDF/chipboard/plywood rings can be added on the inside or outside of a sub and flared with a rasp or Surform tool. (a course wood file) I used to do this when I didn't own a power router. You can buy rough wood cutting tools to use in an electric drill to round over the most part of the flare. Then you smooth it off with files and sandpaper wrapped round a big dowel.

A dirt cheap Chinese power router can be obtained easily these days and the router cutting tools come in cheap sets too. A pro or serious woodworker might squirm at the quality but for occasional speaker and sub projects these tools last long enough to be worth the small outlay. I built my IB array using just such a router working slowly to conserve the tools. The router cost me the equivalent of $35 at an Aldi supermarket! My wife finally bought me a better quality Bosch router for Xmas.

I think 16Hz would have to be played at over 110dB for most people to be able to recognise it as a tone. Most subs produce enough distortion for the second harmonic to be audible and then they claim they can hear 16Hz when in fact they are hearing 32Hz.

[kano32]

Chrisbee wrote:

One can flare PVC pipe by heating it gently with a heat gun then forcing it rather gently over a suitable mold. It doesn't seem to like being reheated though and can buckle easily. Which can waste expensive pipe. Don't try flaring PVC freehand. It needs a form to get the desired shape. I doubt you can make a full trumpet flare like the pro models. Wear thick leather industrial gloves as the heat required to soften PVC will burn your skin very easily. If you can't smooth the hot PVC with your hands then you're stuck!

There are some PVC fittings (joints) which I believe could also be used if they were cut away carefully to leave just a flare behind. The pipe adaptors look like potential flares as do the surface mounting drain fittings. You just need the imagination to make the most of what is on offer for other purposes. In larger sizes the joints certainly aren't cheap though.

Asking a drainage contractor on (or off) a building site might get you something cheap if you ask nicely and show respect. Or it might not. I had some nice clean 10" PVC from a very long length that had been run over by a tractor. My taking it away as it was I saved them burning it on-site. They were glad to get rid of it before the boss noticed! Sheer luck though.

MDF/chipboard/plywood rings can be added on the inside or outside of a sub and flared with a rasp or Surform tool. (a course wood file) I used to do this when I didn't own a power router. You can buy rough wood cutting tools to use in an electric drill to round over the most part of the flare. Then you smooth it off with files and sandpaper wrapped round a big dowel.

A dirt cheap Chinese power router can be obtained easily these days and the router cutting tools come in cheap sets too. A pro or serious woodworker might squirm at the quality but for occasional speaker and sub projects these tools last long enough to be worth the small outlay. I built my IB array using just such a router working slowly to conserve the tools. The router cost me the equivalent of $35 at an Aldi supermarket! My wife finally bought me a better quality Bosch router for Xmas.

I think 16Hz would have to be played at over 110dB for most people to be able to recognise it as a tone. Most subs produce enough distortion for the second harmonic to be audible and then they claim they can hear 16Hz when in fact they are hearing 32Hz.

Um, was this placed in the correct thread? I've made my own flared ports on many projects. I have a 3/4" round-over bit that will work nicely for the 6" port.

[Chrisbee]

kano32 wrote:

Um, was this placed in the correct thread? I've made my own flared ports on many projects. I have a 3/4" round-over bit that will work nicely for the 6" port.

Punkrokr15.5 asked about 6" ports a couple of posts above.... this is a thread about subs requiring large ports... I have a lifetime's experience in adapting simple manual skills and tools to woodworking and PVC fabrication problems on a limited budget using lots of patience.... so I volunteered some information ... is there a lack of bandwidth? Are there too many posts in the DIY section this week? Is the construction of proper flares common knowledge? Judging from my browsing around the subject of port flares it would seem not. A 3/4" roundover tool is not a proper flare....it is a bodge for low velocity ports.

[kano32]

Chrisbee wrote:

Punkrokr15.5 asked about 6" ports a couple of posts above.... this is a thread about subs requiring large ports... I have a lifetime's experience in adapting simple manual skills and tools to woodworking and PVC fabrication problems on a limited budget using lots of patience.... so I volunteered some information ... is there a lack of bandwidth? Are there too many posts in the DIY section this week? Is the construction of proper flares common knowledge? Judging from my browsing around the subject of port flares it would seem not. A 3/4" roundover tool is not a proper flare....it is a bodge for low velocity ports.

No need to be testy. The biggest roundover bit I have is a 3/4, so it will work nicely.

Anyway on to more important things. I finally got my MJ-18 in the mail!! I was on my way to work and had my wife meet me at the post office with the SUV. We opened the double boxed package and when we saw how HUGE the 18" driver was my wife exclaimed,"That's crazy!" I replied, "No, that's awesome!" I never realized how big the driver was until I saw it. I can't wait to get started!!

[Chrisbee]

kano32 wrote:

I finally got my MJ-18 in the mail!! I was on my way to work and had my wife meet me at the post office with the SUV.

Congratulations.

I remember seeing an 18" Fane driver in a music shop window when I was a kid.

That was the biggest thing I'd ever seen. :holycow:

It looked just like a radio telescope.

You could walk round it and have a picnic on the other side.

Enjoy!

[kano32]

Here's the MJ-18. It doesn't look big in the picture but it is. That's my 14yo son holding it. He took fifth in the State Wrestling Championships at 105lbs last week (can you tell I'm a proud dad). He won six matches (pinned five of his apponents) and lost two matches. Anyway, it's cold here but I hope to get started gluing up the plywood and mdf soon.

I ran some wires to it while the kids were playing xbox and it came to life. It may only have 12mm of excursion but it was moving like crazy. My wife came down stairs and stared at me. My daughters laughed and thought the driver moving like crazy was pretty neat. Shake the floor, shake the floor, woo hoo!