[draki]

Hello all. This is my first post here, hope to get some feedback. The forum is great and very informative, but I still thought I will post this question since I do need a second opinion.

The bass is Eminence Delta15-LFA (Fs 39/ Xmax 4.8 / Qts .48).

I am considering either slot-loaded (as per N.Pass article) or U or H frame - single driver per side.

Regarding the slot version: from what (I think) I know, the slot area should be 3:1 ratio to Sd - so for a 15" of abt 900 cm2 Sd the slot area should be abt 300 cm2, making it 7 cm wide for 42 cm height. The back would be winged to form "L". I am sure you know what I am trying to picture.   

The U and H versions are obvious: 42x42cm with about 15 cm(U) or 30 cm(H) depth

In all three versions the bass element (almost wrote "box"!!) would be about 45 cm high - housing the 15" plus some material thickness top and bottom - as the upper/mid/high will be plain OB with MTM consisting of 2X8" plus Eton ER4, and will be positioned on the top shelf of the bass , erm, element.

What would you recommend: slot, U or H?

Listening room about 30 m2.
Crossover DCX2496 (modified)
Equalaizaton DEQ2496
Various amps (class D and SS)

Thanks in advance.

Draki

[matevana]

Where do you plan to cross the Delta 15-LFA?

[draki]

I plan to cross it not higher than 100-120 Hz.
Slope to be determined by listening/measuring , with DCX.

[Nate Hansen]

I'm using the same 15's, in an open U frame. It's sort of a trapezoid shape, and the wings taper.....but it's about 7" deep.  With fairly heavy eq they're -3db at about 38hz, which for me is fine for music.

Hp at 35hz lr24, lp at 250 lr24.

I can eq them into the low 30's if I really want, but the distortion rises and the sound is muddied up........the hp filter makes a big difference here as well.

That said I'd like to build some bigger frames and play with rear damping, I think cardiod may be a better option for my room.......although I am pretty happy with the Deltas as is. Just can't stop making "improvements"!

[draki]

What are the width/height of your panel?
Crossing active I suppose?
Can you tell what EQ are you using - I wouldn't like to have to use more than 4-5 dB top.

[Nate Hansen]

Like I said it's a bit of a trapezoid shape......20" at the bottom and 16" at the top, x 20" tall. That baffle is tilted back about 25 degrees, and the wings are 9" deep at the bottom, up to 6" deep at the top.  This shape was mostly for aesthetics, to match a separate baffle for an 8" fullrange that I used to run above the woofer.

Yeah, it's active via miniDSP. Good luck with that 4-5 db of eq though, unless you run a massive baffle and only go down to 50hz or so.  I've got a high-shelf filter -12db at 300 hz (rather than boosting the dipole roll-off, I don't think the miniDSP would allow that much boost!). There's several boosts of 5-7 db below that, and I've got a 14(!)db boost at 40hz, with a Q of 2.  I use REW to set all the filters, then export to miniDSP, then measure and tweak from there.

I've also damped and felted the frames of the Deltas, as well as magnet mounted them, with a brace running from the magnet to the baffle wings on either side. I'd say this brought a big improvement......

[draki]

The baffle you are using is about the same that I intend to use if going for U-baffle. Can't accommodate bigger that that bcs the width is an issue in my room.

That was the reason I was asking about the recommendation for slot, U or H (or maybe N, the 45 degrees variant of H): which would give the lowest extension - even at the cost of lowered SPL - but within about 18" or so baffle width? Remember the LP would be not higher that 100-120.

The slot with L-winged side could be made even narrower (maybe up to 15" - if the slot is abt 2,5" for 3:1 ratio, plus the depth of the bass units plus some space behind up ti the "L" side) AND it supposedly has the lowest extension (lowest Fs and increased Qts) but lowest SPL, IIRC.

The H falls between the slot and U, wheres the U has the highest SPL with the Fs and Qts unchanged from that of the driver's free-air spec.   

Where would you put "N" baffle? This can also be made narrower at front (like GR "V"). Does it behave like H or U ?...

[draki]

Regarding the magnet mounting: do you use extra insulation on the basket rim or the unit's own is sufficient? You don't use any screws at all? 

[Nate Hansen]

Regarding the magnet mounting: do you use extra insulation on the basket rim or the unit's own is sufficient? You don't use any screws at all?

I screw the basket to the baffle as well. These were just "temporary" baffles, so I made them from chipboard, but they are pretty solid with the magnet mount tying it all together. The bass response seemed to tighten up quite a bit......

[THWO]

All options may give you a deeper but possibly muddier sound. The more airload gets into the woofer´s way, the muddier but deeper.  The most precise reproduction may be achieved with a strait open baffel without anything else "around", but then with the baffle step rolloff. So it may depend on your own preference - or compromise.

This is my own subjective experience until today and, therefore, will certainly not be correct in all aspects, i.e. as I did not listen to a slot in front of a woofer before.

OK, this will not help you much with your very question. But trying to combine both your question and my a.m. thought, the solution could be: If the airloads of slot, H-frame and U-frame where equal, there shouldn´t be much of a difference. The design with the lowest airload could be the most accurate one together with a little bit modest lowbass, the one with the maximum airload may show the deepest but may be "softest" bass.

Is it adequate to put it this way or is this thought a too simplified one?

Regards,
Till

[draki]

This is more or less the same I envision the specifics of slot, U, H, OB-plain ... Since the project is still not ready (await the delivery of Delta's), at this point I rely on the knowledge and information from this and other forums.
What I think would be the starting design is the U - 16x16x7. Let's see how it will perform, that will be the first experience with 15" Pro driver in OB. Let's say it will be up to the expectation. After allowing some time for a break-in, both the speakers and the listener, I guess some more tweaking/testing might follow:
- an extra front baffle with a circular opening of about 7" in diameter (abt 30% of the Sd) to simulate the slot loading and see how that will alter the sound;
- an easy-to-do increase of the system Qts with a resistor in series - between 1R5 and 2R - which should bring the Qts to 0.7;
- a combination of the above;
While there is no substitution for one's own experience, I would just like to check if the above holds water, specially with those who already have the practical experience and maybe tried one or all of the a/m variants.