Sonosub Calcs

[bikedave]

Well, I have been looking around this forum for a while and am now ready to post. I appreciate all the expertise which haunts these threads. I recently purchased a 15" sub as described here: XJ-15. I also have a Carver Pro amp rated at 450watts (2 channel) @ 4ohms and 900watts bridged @ 8ohms to push it. I picked up a piece of 20" sonotube about 41.5 inches long recently as well which I would like to use. I have been modeling it in Unibox to help design it. The manufacturer recommended that I not use a box smaller than 7cf for this sub, which is almost exactly what I have in the sonotube. Now, I know that more volume is better for reproducing the low frequencies, and I would like to tune the thing to below 20hz if at all possible. I have been thinking about mounting the tube in a box inorder to gain some more volume. So the rub comes when I model larger boxes in Unibox. I find that I exceed the xmax of the driver when I go over around 250liters and keep it tuned low. But if I leave it tuned to say 15hz at 200liters it is ok, although SPL goes down. So, I guess my question is, should I worry about building a bigger box or keep it at 7cf to maintain low tuning? Maybe I am not modeling it right. Any input would be appreciated. I will post the T/S below in case the link above doesn't work.

XJ-15 Parameters:
Re: 3.95 ohm
Qts: 0.578
Qes: 0.673
Qms: 4.095
Fs: 24.5hz
mms: 130g
cms: .300mm/N
BL: 11
Vas: 284L
Pmax: 600W

[---k---]

You should post your models. I've never modeled that driver, so I can't tell you anything quickly.

Did you see this post? http://htguide.com/forum/showpost.ph...7&postcount=36

(take a look at the posts below that one too.)

300L w/ a 15 - 18 hz tune looked good. So how big can you go?

Not sure how putting the tube inside a box is going to increase your volume, you'll have to explain that one. And, exceeding xmax at very low frequency is something that could be a problem (bottoming your driver), but generally with a little caution, it is okay.

[bikedave]

Sonosub Calcs

Thanks for the prompt response!
By mounting it in a box I mean to construct a 4-5cf reinforced box from MDF with the driver mounted in one of the walls. Then cut a 20" hole in the top and slide the sonotube in a few inches and secure it. The tuning port would mount in the Sonotube cap. I will post some of my models when I get a chance this afternoon. Thanks for the links as well, its good to see what a good response curve should look like.

[Kevin Haskins]

If you use the tube you have (41.5"), tune it to 17-18Hz. For a 6" port that is about 28". Measure the inside diameter of your tube carefully to calculate volume. Also measure your 6" port. The sonotube varies in dimension so your values can be off if you trust their measurements. Line the walls of the cabinet with the stick-on foam to achieve a 10-15% fill.

Here is 200L tuned to 18Hz.



If you wanted a larger enclosure I'd just buy a bigger piece of sonotube. The 300L tuned to 17Hz works fine too.... gets you some more extension.

Here is the 300L tuned to 17Hz.

[bikedave]

Alright, here are some of my models for this sub in various volumes at different tunings. It looks to me like there is a fairly significant different between the 200 and 300l configurations. Even though it is just a few decibels I know its a logarithmic function and exponentially louder. There seems to be between 2 and 4db increase all the way up to 40hz. Because I am wanting to fill in the bottom end of my sound system it would seem like that is the best option all the way around.

I also have a BFD 1100. Will this work as the primary eq/xover for this sonosub? Do I just put it in line before the power amp? I'm still pretty new to this and the pro side is a little confusing at times. Thanks again for the responses!

[bikedave]

A few more quick questions/observations:
In playing with Unibox, it recommended that with a 300 liter box tuned to 17hz that I have a port bigger than 6 inches. So just for fun I bumped the port diameter up to 8 inches and noticed that it lowered the SPL about 1db across the curve, but it also seemed to keep the driver further from xmax. Do larger ports tend to protect the driver from over extension? Will I have port noise issues with a 6" port?

[---k---]

You sure? If you kept the volume and the tune the same, port diameter shouldn't have an effect (I think). I just tried it with my RL-p15 models and I didn't see a change, except for the location of the squiggle for the first resonance.

[Kevin Haskins]

A few more quick questions/observations:
In playing with Unibox, it recommended that with a 300 liter box tuned to 17hz that I have a port bigger than 6 inches. So just for fun I bumped the port diameter up to 8 inches and noticed that it lowered the SPL about 1db across the curve, but it also seemed to keep the driver further from xmax. Do larger ports tend to protect the driver from over extension? Will I have port noise issues with a 6" port?

Your only going to run into a problem with a 6" port at extreme SPLs. I wouldn't worry about it. If you want, add a couple flares with a 3/4" roundover.


You probably made a mistake when you bumped up the diameter. I don't have Unibox so I'm not sure if it simulates port compression or not. But that is the only reason a larger port would have more output with the same tuning frequency.

Port compression is basically when the port contribution is lower than the theory would predict due to turbulence loss. There is a correction factor used based upon calculated turbulence in the port. The more turbulence, the less output from the port and you may have seen a consequent reduction of output near the port tuning frequency simulated by Unibox. I find that in real life, the compression is not as significant as the simulated compression.

The driver excursion is less because the acoustical impedance, seen by the driver, is higher when the port is highly resistive. Its becomes more like a lossy sealed box rather than a resonant system.

[CraigJ]

sub listening assistance

I just completed a pair of Sonosubs. I used the RS390 instead of the xj-15, in a 320 L tube, with a port tuned to 17.5 hz. Currently, the subs are powered with an older Luxman Receiver, which I believe is rated at 115 amps @ 8 ohms. I use a front projector, so the subs are located on each side of the screen; like giant pillars 8O This may appear to be a silly question, but I've never owned a sub before, so besides my house rumbling, what exactly should my subs sound like. Also, my basement HT is 20'x14' with a drop ceiling.

Thomas, thank you for sharing the instructions and pictures of the Sonosub build. Using your design made building very easy and straight forward. Now that I have the Sonosub and the Isiris, I'm feeling very "boxless".

Craig