Dual Shiva design

[AndrewM]

Ok, so I've been messing around with LspCAD (the Adire demo), and I modified one of the Low Q designs that Dan has on his site (I changed it from a Tempest to dual Shiva's). So here are the specs...
200 litre enclosure.
16Hz Port tuning
Twin 4" ports 25.7" long
50% fill
Qa 15.0
Ql 15.0
Group Delay of around 18ms @ 20Hz
I filled in my room dimensions (3x5x4 meters roughly), I also filled in a proposed front baffle size (.762x.559 meters again).
It says I should have in room that is pretty flat from about 50Hz on down to an F3 around 14Hz?! (with 500w of power).

The "Free Air" side says I should have an F3 around 22Hz.

So did I miss something here? Almost seems a little to good to be true for a "smaller" enclosure (for 2 Shiva's) of around 7cu/ft...did I miss something, make an error somewhere?

Andrew

[ThomasW]

Andrew

I don't have time today to model the design, probably can do it tomorrow.

But yes it sounds right. 7 cu ft is a pretty good sized box. Might try using a single 6" port.

Don't get too excited about the 14Hz with 500 watts thing. You wouldn't want to be in the room if the sub were being driven with that amount of power




theAudioWorx
Klone-Audio

[AndrewM]

Thomas,

Thanks I'd appreciate it. I did a little more thinking over the design, and the 200litres doesn't sound that small, I figure a regular SBB4 alignment Shiva (single) drops into 95litres, so two shiva's in 200l tuned a bit deeper isn't that far off. But any input on the design is of course always welcome.

According to the program the air speed of the dual 4" ports is under 10ms @ 20Hz (but is on an upward trend from there), I don't know where noise becomes an issue though. Also a 6" port would increase the port length from 2 x 25-26" long to a single 66" long port. And unfortunatly I couldn't get an approval for the tube idea. Of course it's going to be a monster sized cabinet (almost 3ft tall, almost 2ft square)...but with a cabinet I can put a little nicer finish on it (read: spending to much $$$ on veneer), but if it passes the spouce's approval and it gives me some very high quality bass, I'm all set. As to the 14Hz thing, that's not what I need (but I like the sealed-like response, and the safety of low port tuning)...since I still live in a town home (attached), being able to shake the neighbor 2-door's down pictures on the wall isn't going to make me Mr. Popularity. Not quite sure yet how I'd power the whole thing, Adire's HS500 looks interesting, but a little pricey...but I'm thinking that a decent pro-amp and 2-way active x-over (I like having more options than 80Hz) is going to cost more than $500....not sure if the AVA 250 would power it well or not (under 200w@ 8Ohm).

Andrew

[ThomasW]

Don't really know about the plate amps. I'm sure they're ok, but to me they don't seem like a good investment.

Not sure where you're going to get an amp and a outboard XO for $500.....unless you buy used.

The 2-4" ports will be ok, no real problems with chuffing particularly if you were to use dual flares for port. Basically adding dual flares makes the ports flow as if they were one size larger.

Consider using this Aerial photo for a building guide. This is the way to build regular boxes.






theAudioWorx
Klone-Audio

[AndrewM]

Don't really know about the plate amps. I'm sure they're ok, but to me they don't seem like a good investment.
Not sure where you're going to get an amp and a outboard XO for $500.....unless you buy used.

I did a little more poking around yesterday, and I found some pro-amps that are fairly cheap (from $199 up to $400 for my needs), the bigger problem comes with the x-over, I started going over Marchlands site, and it looks like some version of the XM9 is what I would need, but it's $240 (I'm comfortable putting electronics together at a component level).

But I looked some more, and saw the XM1...for $30. Now what's the difference here with these two, obviously the XM9 is a lot more complex, but do I really need that since I just need to keep everything from around 50Hz out of my mains, and everything below to the subs?

Consider using this Aerial photo for a building guide. This is the way to build regular boxes.

Actually I think the plan will be to use .75" or 1" marine ply for all the construction, and brace it much like the picture, however I'll add a couple of cross-braces. And then veneer over top of it all. Probably weigh in around 120-140lbs when it's done.

Andrew

[ThomasW]

Well let's see the XM1 is a single channel XO board. You'd need 2 of those plus a power supply, chassis, etc, etc.

If you get a plate amp most of those include a XO of some kind. Also most receivers have sub outs.

With MDF the idea is making the box so dead sonically that the resonant frequency of the box is lower than the operating frequencies of the woofer. Plywood is the opposite. If you go with plywood it should be several layers thick. The box must have a resonant frequency above the operating frequencies of the woofer.




theAudioWorx
Klone-Audio