Program for designing box by desired Q?

[Top Shelf]

Hi prickears, on several occasions I have read that a properly tuned "max flat" BR has an equivalent closed box. Qtc of 1.1 if that's what you're looking for. I suppose a "mistuned " box would produce a different "Qtc" as we'll as the associated response anomalies.

[prickears]

Thanx Jeremy
It is quite difficult to find the info on this. A deliberately 'mistuned' box is no longer mistuned unless you get it wrong!!!

infinia
That was the bit I am concerned about, leaning the bass out too much to find the extra bit of extension. I guess that's what makes it tricky, trying to balance this with the natural room gain.
I have four of these drivers, so they are a little bit bigger than their specs would suggest

Their job is to keep pace with four P13s, in a three/way, (active and tri-amped) although I haven't worked out exactly where to cross them yet. I'm really just weighing up my options and trying to find a good compromise.

Looking at your second chart post, again, the orange trace vs standard max flat, the orange is never more than about 2.2 db down between 100 and 80(?) hz, but then hangs in longer as room gain *should* be starting to give it a bit of help. Well thats the theory anyway. The fact that it differs from system to system and room to room is a bonus for a DIYer if not a headache at times!!

Mick.

[infinia]

That was the bit I am concerned about, leaning the bass out too much to find the extra bit of extension. I guess that's what makes it tricky, trying to balance this with the natural room gain.

yes the compromise of in between boxes, I like to go with designs that give options on the fly, like adding new ports, stuffing, plugs.
I like how the 11 liter 42 Hz box response tracks the slope of a closed box yet gives almost the same extension as the max flat BR at -10 dB. Group delay is tamed (monotonic) over this lower "pass band" as well.

About Q matching
What you could do is compare your modified BR designs step response to various closed box Qs in Unibox, and tune to that.

[prickears]

Originally Posted by infinia

About Q matching
What you could do is compare your modified BR designs step response to various closed box Qs in Unibox, and tune to that.

That might be the way to go I think.

The 11L 42hz Box has a 25.5 cm port even though it is only 5 cm dia (can you hear me breathing!?) so it can't really work in the real word. I know 23l works well, so I might just tweak the port and stuffing from there till it looks good.
The 23L boxes I already built have the port 'built in', so it is quite a pain to try to change the port length, but 23l was still quite boomy, so tweaking the port for a 23-25 litre box I think could be the way to go.

Thanx for your help/ideas/input thus far infinia !!!

cheers Mick.

[infinia]

Yes small boxes with unwieldy long ports are perfect for passive radiators , deja vu all over again. haha

Since you mentioned going active, how about going all the way, ie with a small sealed alignment with an LT equalizer? then you dial in the real Q by changing out a few R's and C's.

[prickears]

I did once try them in a 12 litre sealed box, but the estrogen levels of that system were a little too high........
They love a ported box, they are just a whisker tricky to tune is all, having said that, I would prefer to have the bass a little lean, rather than too boomy. Then there is nothing worse than a cliff face roll off, one bass note is loud and clear the next lower note all but disappears, I REALLY hate that.
I will get around to earning enough coin to build a proper sub one of these days.

[wintermute]

Hi Mick, sorry this reply is a bit late! The best I've found is akabak, it had multiple alignments for BR and shows you the transient response among other things, I'd say that selecting the alignment that gives you the fastest transient response might be what you are looking for!

Akabak Simulator

Its got a brutal learning curve if you want to use it to it's full extent, but should be pretty straight forward to just get some alignments out of it if you have a look at the dummys guide posted above

Hope you are well, and recovering/recovered from the injuries.

Tony.

[Don Hills]

The "ported.xls" spreadsheet from diysubwoofers.org allows you to enter the room response curve (resonances etc) and show the resultant response. It also has several filter options and room gain compensation. I use it a lot when working on designs outside the classic alignments.