Box size with DEQ2496

[thymej]

My Goal
Use 2 Dayton 12” RS HF drivers (maybe 4, in a 2 per box configuation).
Sealed Box Q of 0.577
Use BFD or DEQ2496

My question
When using a BFD or DEQ, do I still need to make that big box to get the benefits of a large box or Will the BFD/DEQ nullify the benefits of the low Q box? The box size for a .577 is just too big where I want to put it (but I really want the benefits the low Q gives me). I might be able to get away with a .6 or .642 Q box size.

So knowing the fact that I will use a BFD/DEQ, can I build some filter(s) that would give me back some of the benefits the DEQ takes away?

thymej

[ThomasW]

With the DEQ you can create a Linkwitz Transform circuit. That allows you to electronically create a lower "Q" in a small box. This can't be done with the BFD.

can I build some filter(s) that would give me back some of the benefits the DEQ takes away?

I have no idea what you're asking here....?

[thymej]

Sorry for being confusing, may be this might help.

I like the sound of the more musical subs. I here low Q boxes sound less boomy and more tight (as I read somewhere possibly because of good group delay).

Do I gain anything if I build a box that gives me a Q of .5 vs .642 with the DEQ in the loop? Will the DEQ make it a moot point between the .5 and .643 box sizes (when the DEQ is used as a LT and or PEQ to smooth out the room in the 20-80Hz or so range).

Secondary question: What other benefits does a large box give you besides good group delay? And with a DEQ in the loop acting as a LT and PEQ, witch of the benefits does the DEQ interfere with that you gain with the large box?

[Dennis H]

Group delay only depends on the frequency response, whether you get there with box design or EQ. However, small boxes have more air spring distortion than large boxes so bigger is always better with the ultimate sealed box being an IB where the volume is on the order of 10x Vas.

[Victor]

However, small boxes have more air spring distortion than large boxes so bigger is always better with the ultimate sealed box being an IB where the volume is on the order of 10x Vas.

Very true indeed. Having been considering the issue of box volume verses sound quality myself, I am beginning to realize that while the small box will certainly lead to a higher distortion, as you noted, it is also true that if you turn down the volume a bit and is willing to live with a lower SPL, then the distortion numbers will be down again.

More specifically, - the LT turns the small box high Qtc into a critically damped Qtc of 0.5 at the expense of the overall lower SPL. So, - with this in mind I am wondering, can I expect the same distortion out of the small box system with LT in the loop while operated at lower SPL as I would get from an IB system?

Well, I guess I am asking what is the SPL penalty here, in order to get the same sound quality with the small box verses an IB- does anyone know?

Victor

[thymej]

Group delay only depends on the frequency response, whether you get there with box design or EQ. However, small boxes have more air spring distortion than large boxes so bigger is always better with the ultimate sealed box being an IB where the volume is on the order of 10x Vas.

If group delay is a certain group of frequencies being delayed (e.g. 20-50Hz) how does one use EQ to correct the delay?

So larger still, even with EQ/LT, has good things, lower spring air distortion. Hmmm, more things to think about.

I might only be able to make as big as I can in the spot I'm allowed to put the sub. That might only be 5cu.ft for 2 Dayton 12" HF drivers before bracing and driver displacement.

[ThomasW]

in order to get the same sound quality with the small box verses an IB- does anyone know?

Prior to building my first IB I had dual 15"s in individual Qtc 0.5 boxes. IMO the IB is much better.

[Dennis H]

According to SL's worksheet:

(Air spring distortion %) = 140 * (driver 1-way Vd) / (box volume)

So, cutting the SPL 6dB cuts the Vd in half and cuts the distortion in half.

[Victor]

Thomas,

Yes, I understand. I am sure there are other things at play here that we may not be able to simply quantify with numbers. IB is not in store for right now, - too bad.

I was all set to start working on my tubezilla clown to house my 2 Ave 15 drivers. I even got the 48-inch long 18-inch diameter tube for that. Well, my ‘better half’ has gone to the barricades opposing the tube!

I am now back to considering two separate sealed boxes. Oh well, do not want to hijack this thread, but I’ll be posting soon and asking to check my numbers before I start cutting things. I need small boxes and I want big low distortion sound!

Dennis,
Thanks for the formula.

Victor