Subwoofer suggestion for L`acoustic 108p

0krizia wrote:

i also could not get more than 80DB out of the sub at 4m away with 700W and low cut at 40hz last time i used it. It was a 10X10m room with 5m under the roof ish. i was hoping i could get more out of it.

(mesured with "A" weight in SPLnfft app)

OK, couple of issues coming to light now.

First, A weighting is used where you want to focus on mid frequencies so will always give poor results for sub - it's artificially reducing your 40Hz SPL by approximately 34dB! That means that you should really have about 114dB at 40Hz.

Always use unweighted for sub measurements.

Second, you may be driving that cone well beyond where it can stay linear, which would increase distortion and account for a lot of your muddiness.

Here's what WinISD thinks is happening at 700W. Yellow is your box, green is the same volume tuned down to 35Hz.

First graph is SPL, it predicts just a little bit higher than 114 at 40Hz, once you get rid of the weighting.

Second is Group Delay and you can see there where tuning lower to give a flatter frequency response gives less group delay over most of the band, at least until you get to the new low frequency corner.

Third is excursion, and it looks like with either tuning 700W is just a bit too much for this driver, so it will probably not sound at its best unless you back it down a few dB. Don't worry about excursion going off the scale below tuning - your HPF should take care of that, but it's still leaving a lot of excursion in the 45-70Hz range, which may result in excess distortion, muddying up everything for you. I didn't try to model the exact HPF as you didn't give the order & alignment I don't think.

Thank you for this information David.

So if i wanted a clean sound down to say 35hz, i should tune it lower than 35hz in order to have less group delay. Ill lose alot of output in that way tho. guess thats where bigger driver comes in (-.-)

Yes, you can see that the excursion problems would get worse if you tuned lower (as well as losing a couple of dB of level around 40Hz too), which is why bigger/better drivers that can make up for that without going over Xmax would be beneficial if you really want to minimise GD.

i was hoping i could get away with a small sub.

But i dont think group delay is the problem when the muddy sound is not only below 60hz but in the whole spectrum the sub is capable of playing in.

There's a thing in speaker design called Hoffman's Iron Law - which basically means that you have to trade off box size, loudness and LF extension against each other, so if you want small at least one of the other two is going to suffer.

As can be seen above, tuning low can help Group Delay and give good extension but often at the expense of Excursion which can lead to distortion, which I think might be the most likely reason for your box not sounding good across it's whole range.

If you can live with running it on less power (about 3-4dB less should keep the excursion under control) you might notice the sound cleaning up, but then you might not feel it's loud enough.

Edit - wrong image (and diagnosis) posted earlier, now fixed.

Edited by DMorison - 17 February 2016 at 9:05pm

0krizia wrote:

i have read about a guy giving 1200w to the 12n630 with no problem with low cut at 38hz.
I think he was named Tony on this forum. so why does your graph show to high xmax at 700w?
http://forum.speakerplans.com/q12-12-sub_topic28555.html

I also dont get the spl mesuring. I have been on a metal concert where they played at 110db and that its crazy loud!!
That beeing said, i have experienced a Rammstein concert where they played 120db in avrage and that was unbearable, my eyes was blurring with the kick drum, i could even feel all my clothes vibrating and a pure sensation of mild pain in my ears.
I dont understand how a simple 12" can achive anything even close to those sensations. What am i missing?

Tony's box was smaller, which always helps control Excursion, and he (usually) used EQ or boosted alignments to flatten the low end (that project was -6dB at 38Hz on its own), and the boost/EQ uses up a bunch of the stated power so he most probably did not have all that power dumped on the driver at the frequencies where excursion was highest.

(Excursion is low right near the box tuning frequency, so if you chose the shape of the boost carefully you can often throw more power at a driver at those particular frequencies to flatten the response without so much of a problem with distortion.)

Regarding overall SPL's, our ears are more sensitive to midrange frequencies, so 110dB for a full band mix will always sound a hell of a lot louder than 110dB just at 40Hz.

Edit: Tony's project was also tuned higher to start with, which also reduces excursion in-band.

Edited by DMorison - 18 February 2016 at 1:32pm

0krizia wrote:

Is it the presure in a small box that makes it less prone to excution?

So what i need to match up against my top speaker is atleast 1 15 inch sub, since it can move more air with less excution? If so, any light weight recomandations?

Think about it like this:

If the speaker has a surface area of 500cm², and you want it to move 1cm each way, then it has to compress the air in the box by half a litre extra, and stretch it out by the same amount for every cycle.

If the box is 50l, then that half litre is 1%, but of the box is 100l then that half litre is only 0.5%, so it represents less resistance to the physical movement of the speaker cone.

For light 15's, the big brother of your current one isn't bad, but does want a rather bigger box to get reasonably low.

You might also look here, another poster had similar goals: http://forum.speakerplans.com/ciare-punisher-sub-br011_topic87634_page2.html

MarjanM wrote:

You have only one subwoofer?

If yes, then that is one of your problems. Ideal subwoofer/top ratio is 2:1. Not 1:2.

The 108 is a very small box designed for small speech applications and install applications etc so 1 sub is probably about right for what it's designed for.

If your trying to have a "rave" with it then it's the wrong box for the job.

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