Chops, the only real answer to that is measuring! I have found there is such a big difference between simulation and measurement that a guess based on what you hear might get you further!
I simulated a 50 Hz trough from room modes, but in reality I measure a dip around 80 Hz and a peak at 35 Hz with no room gain below that.
You could almost say that with typical 10-15db peaks and troughs that there is no such thing as in room F3!
Hmmmmm
13 x 17 x 8 = 3.9 x 5.1 x 2.4 that is almost the same as my room except the ceiling is higher.
What type of construction do you have? Solid means more modes, more severe and more room gain. Light means less severe modes (damped) and less gain or no gain.
You probably have less room gain due to the opening.
I simulated a 50 Hz trough from room modes, but in reality I measure a dip around 80 Hz and a peak at 35 Hz with no room gain below that.
You could almost say that with typical 10-15db peaks and troughs that there is no such thing as in room F3!
Hmmmmm
13 x 17 x 8 = 3.9 x 5.1 x 2.4 that is almost the same as my room except the ceiling is higher.
What type of construction do you have? Solid means more modes, more severe and more room gain. Light means less severe modes (damped) and less gain or no gain.
You probably have less room gain due to the opening.
Have a look at the FRDC website, they have an excel based room mode calculator.
I've seen some more around that are similar.
I doubt any of them are sophisticated enough to predict real world performance accurately though. You would have to enter in some fairly detailed data about the room and its construction for that.
Correction factors:
http://www.users.bigpond.com/bcolliso/SPL-corrections.htm
(Collo has put some very helpful info up there on his site!)
I've seen some more around that are similar.
I doubt any of them are sophisticated enough to predict real world performance accurately though. You would have to enter in some fairly detailed data about the room and its construction for that.
Correction factors:
http://www.users.bigpond.com/bcolliso/SPL-corrections.htm
(Collo has put some very helpful info up there on his site!)
paulspencer said:
Thanks for the tips and info!
If I have the time to get to it this weekend, I'll run this sub through its paces and see what it's capable of. I'm almost positive I'm getting usable output to at least 14Hz, if not lower.
And it amazes me how little power and how little cone movement there is at the levels this thing is playing at! I wish I knew what the total efficiency was on this sub.
Any ideas?
Again, thanks!
The room is mostly drywall/2x4 stud construction. The left and rear wall are interior walls, the front and right wall (with large sliding glass window) is concrete cinder block with drywall, flat drywall ceiling. The floor is a solid concrete slab.
Here's an older pic of most of the room taken with a Nikor 10.5mm fisheye lens on a Nikon D50 digital SLR, just to show the room. You can see the two bedroom doors on the left wall, bathroom door and hallway opening on rear wall, and sliding glass door on right wall.
Here's the freq test chart I just made. The subwoofer was tested from 10Hz to 50Hz at a constant 1 watt input and the Cornwalls were completely disconnected from the system. The SPL meter was on a Bogen 3001 tripod w/ 3265 "Pistol Grip" head at my listening seat set at "C" weighted and "Slow" response. Both bedroom doors and bathroom door in left rear corner were left open as well as the hallway opening which is always open.
Not a bad looking plot actually...
Here's an older pic of most of the room taken with a Nikor 10.5mm fisheye lens on a Nikon D50 digital SLR, just to show the room. You can see the two bedroom doors on the left wall, bathroom door and hallway opening on rear wall, and sliding glass door on right wall.
An externally hosted image should be here but it was not working when we last tested it.
Here's the freq test chart I just made. The subwoofer was tested from 10Hz to 50Hz at a constant 1 watt input and the Cornwalls were completely disconnected from the system. The SPL meter was on a Bogen 3001 tripod w/ 3265 "Pistol Grip" head at my listening seat set at "C" weighted and "Slow" response. Both bedroom doors and bathroom door in left rear corner were left open as well as the hallway opening which is always open.
Not a bad looking plot actually...
An externally hosted image should be here but it was not working when we last tested it.
That response looks very good! A pretty easy task to get it totally flat. I'm surprised because you seem to get the best of both worlds from that plot. I'd expect either ugly room modes and lots of room gain, or well damped modes and no gain or very little. I am looking at just those 15" drivers in a sealed box, right? It looks like you have quite a bit of room gain and very well damped modes!
Yep, the only thing producing any sound was the subwoofer. Nothing else was on. This test definately confirms my strong sense of output below 16Hz, like I thought. The only thing about this test is that I had the SPL meter about 8" behind my head, directly behind the couch/futon. Also, I had left the receiver's crossover point at 50Hz, so it was sucking out some of the output towards the top end.
After that test, I decided to put the meter on a small table-top tripod and place it leaning forward on the couch which placed the meter exactly where my head is while I listen to the stereo. There's a small change, but I doubt enough to make any difference.
Here's the charts. There's two different kind of charts, but both show the same plot. This time I bumped the crossover al the way up to 200Hz, and instead of doing the 1 watt reference, I set it to 95dB reference @ 50Hz. As you can tell, the only real change was on the top end, only because the crossover was set higher.
After that test, I decided to put the meter on a small table-top tripod and place it leaning forward on the couch which placed the meter exactly where my head is while I listen to the stereo. There's a small change, but I doubt enough to make any difference.
Here's the charts. There's two different kind of charts, but both show the same plot. This time I bumped the crossover al the way up to 200Hz, and instead of doing the 1 watt reference, I set it to 95dB reference @ 50Hz. As you can tell, the only real change was on the top end, only because the crossover was set higher.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
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