18" Mach 5 Sub - Check my graphs please? - Home Theater Forum and Systems - HomeTheaterShack.com

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post #1 of 3 Old 10-22-11, 07:49 AM Thread Starter
Join Date: Oct 2011
Location: London
Posts: 8
18" Mach 5 Sub - Check my graphs please?

Hello all,

A quick word to say that although I've only just signed up to be a member, I've trawled these forums for information in the past and can't say how helpful it's been so far!

As for myself, I'm a first-time builder looking to put together a decent subwoofer. My goal is for a speaker that will go loud and low, yet not boomy. Size is not the biggest concern provided I can get it through my door at uni! I've already given it some thought but I've decided it's time to ask someone else to check that I've understood the basics.

After throwing loads of drivers into WinISD I fell for the Mach 5 IXL 18.2.2 driver as it seemed to be able to go lower than anything else I found in the price range. My being based in the UK, however, makes this a little awkward. I've recently also discovered the Mach 5 Pi-18 which I can get direct through the iST website for ~£370.
I've been notified by iST that there is an upgraded version of the IXL 18.2.2 coming soon.

I have a few questions to the members of this board. The first few concern WinISD and what I should be looking for. I was comparing drivers before purely based on what I saw in the transfer function plots, although would I be right in saying that for comparing different drivers (with different power ratings) the SPL plot is a better comparison?

I've produced a few plots here and I hoped that someone could cast their eye over them and let me know if I'm at least along the right lines of choosing an enclosure size etc.

Green = Mach 5 Pi-18
Orange = Mach 5 Pi-18
Blue = Mach 5 IXL 18.2.2
Yellow = Mach 5 IXL 18.2.2

The orange plot is one suggested in a thread I read, but I can't understand why you'd choose that over the green alternative...why have it slope off when it can be kept flat for longer? These are the kind of thoughts I'd like confirmed or corrected!

Finally, although like these drivers I'm not dead set on anything right now. I want to do this right, and I also want to buy a good driver (in the £300 region) so that I don't simply replace it in the future, but work it in to future builds. Any of your info would be much appreciated.

Attached Thumbnails
18" Mach 5 Sub - Check my graphs please?-screen-shot-2011-10-21-12.22.05.png  

18" Mach 5 Sub - Check my graphs please?-screen-shot-2011-10-21-12.06.32.jpg  

18" Mach 5 Sub - Check my graphs please?-screen-shot-2011-10-21-12.07.06.jpg  

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post #2 of 3 Old 10-22-11, 02:44 PM
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Join Date: Apr 2007
Location: Chitek Lake, Sask.
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Re: 18" Mach 5 Sub - Check my graphs please?

When modeling use the SPL graph. When you input the rated power handling check the cone excursion graph to make sure the sub stays within Xmax and apply the necessary hi-pass filter if required.
In the case of the Pi-18 modeled in 170 liters tuned to 19 hz, with 1200 watts input power the driver reaches Xmax at 13 hz. At this frequency a hi-pass filter is not required in most cases. Shown below are the results of this modeling.

The orange plot is one suggested in a thread I read, but I can't understand why you'd choose that over the green alternative
There's is definitely something not right with your driver file, upload it here and I'll take a look at it.

18" Mach 5 Sub - Check my graphs please?-pi-18.jpg
Mike P. is offline  
post #3 of 3 Old 10-25-11, 05:56 AM Thread Starter
Join Date: Oct 2011
Location: London
Posts: 8
Re: 18" Mach 5 Sub - Check my graphs please?

Hey Mike,

Thanks so much for your reply, yeah I re-entered the T/S parameters into WinISD and I seem to be getting the same graphs as you do now. (although I've uploaded my driver file anyways).

You know what I've realised? When I said:

The orange plot is one suggested in a thread I read
it was YOU that suggested this in this post! Well now that that is cleared up (I can't believe I'd have casually marched ahead with making a sub based on incorrect models had I not posted! Thank goodness for the shack!!!) I think I'm confident that this is what I want to make. It seems to me to be a great driver.

So I will make a start on designing the enclosure now. I'm looking at:
Volume: 170L
Tuning Freq: 21.5Hz
Using a slot port like you mentioned in the other thread. (I'm aware I had chosen an ever-so-slightly higher tuning freq, so will change my slot port accordingly)

If you don't mind, once I have a design or two I will post them here. I don't mean to ask you to do everything for me or anything, but it's so good to have the reassurance that what you're doing has been looked at by someone else! I've heard that there is a 'Golden Ratio' for a rectangular sub enclosure, that minimises standing waves inside it etc. Is this to be followed? I wasn't planning to make a cube or anything but the suggested lengths I got (roughly equal to: 55cm x 88cm x 35cm) which is fine apart from the fact that the driver itself will have to go somewhere and with a diameter of 48cm I worry that I'll be cutting a hole too close to the edge in order to fit it in. By fiddling the numbers to more like: 65 x 78 x 35 I'm getting what's more like a square cross-section. In theory is this ok?

Anyways, gotta go to lectures. I'll get a provisional design or two up for a quick 'yes' or 'no' diagnosis!

Cannot thank you enough for your help!
sbriggsuk is offline  


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