Better low end response from sealed enclosure?

[revboden]

I've found one the rss315ho-4 works in a 70l sealed cab with parametric eq fc=25hz, Q1.00,gain 5db. with 100w should work well to 104db. f3 = 28hz


http://www.parts-express.com/pe/show...number=295-466

[bbggg]

Originally Posted by christof123

I'm struggling to get a flattish response to extend the low end.
As can be seen in the image, i've currently used a 70L cabinet, as any bigger than this it becomes too obtrusive for the room

As you will have probably noticed, the closer you try to approach a driver's free air Q with a sealed box, box volume increases rapidly while the extra bass extension you gain for your pain becomes less and less. In your case you seem to be shooting for a Bessel alignment, and that's about all the extension you are likely to get. There is another thing you may have also noticed: while your curve changes with each simulation you try, the F6 (-6 dB point) stays pretty much at the same spot, like a hinge point. These are the physical constants of the system, and you cannot do much to get around them unless you turn the tables on them.

One solution is to just go for a bigger driver, preferably one with a higher force factor (Bl) and a lower Q. There are plenty of suitable 12''ers at the Parts Express site you mention, and prices are reasonable. You cannot have bass unless you move air volume and in this respect a bigger, stronger guy (woofer) will always be better suited.

The other two solutions were already proposed to you: either an LT, which will "cost" you amplifier power and extra displacement (ie increased distortion with increased loudness), or a reflex, which will save you power and displacement, but will cost you in time smearing and possible room mode excitation. Make sure to check amplifier requirements if you choose LT. If you find that you will run out of current, you may be better off choosing an 8 Ohm, or even a 16 Ohm woofer, although the latter are harder to come by.

I avoid reflex alignments, but one rough way to get a reasonably well-damped one is to model a box as big as a woofer's Vas (45 l in your case), and then add a port that tunes to the system's new resonance frequency. If I calculated this correctly -and I did it very roughly with pencil and paper- this will get you flattish down to around 36 Hz. If this frequency does not coincide with a major room mode, it's an option you can consider with a goodly chance of success.

[christof123]

Hi all.

Thanks for some really great responses.
Aren't LT and parametric eq just going to add distortion, and if i use it incorrectly, potentially damage the driver from over excursion?

I had initially wanted to avoid vented systems for the risk of a "blowy" boom, and honestly i'd rather have no bass than rubbish bass.

However, i've just heard a pair of Definitive Technology Mythos floorstanders. They use a small active sub, and 2 passive radiators. The response was UNBELIEVABLE from such a small system.
Should i bother investigating passive radiators? Not many people seem to use them?

[bbggg]

Originally Posted by christof123

Aren't LT and parametric eq just going to add distortion, and if i use it incorrectly, potentially damage the driver from over excursion?

The answer is no, as long as you know what you 're doing. If you use electricity incorrectly, you may electrocute yourself, and if you use water incorrectly, you may drown. Such is life, alas.

[18Hurts]

Originally Posted by christof123

Hi all.

I had initially wanted to avoid vented systems for the risk of a "blowy" boom, and honestly i'd rather have no bass than rubbish bass.

However, i've just heard a pair of Definitive Technology Mythos floorstanders. They use a small active sub, and 2 passive radiators. The response was UNBELIEVABLE from such a small system.
Should i bother investigating passive radiators? Not many people seem to use them?

I use a DIY passive radiator subwoofer, two Isobarik 15's face-to-face motivating a 18" passive tuned to 21 Hz. I chose the PR since I could easily change tuning frequencies on the fly, it has no port noise and various critters can't set up light house keeping in the enclosure. Modeled using a PR program, built it, tested it, changed the weights a little bit and my meter indicated 20 to 40 Hz +/- 2dB and I am done. Extra bonus, since the single PR is around a kilo of weight that is off balance--it will shake the floor during movie explosions to inform you of sub 30 Hz content. My son likes to lay on the floor during action movies for this reason.

There are downsides with PRs though. Cost being a main concern, it is a ported alignment so a piece of PVC is much cheaper! You'll need two passive radiators, one on either side of the box to prevent transferring vibration to the flood so cost/complexity goes up. It does have a phase shift at the tuned frequency but mine is so low I don't notice. The cut off below tuning is really steep--around 24dB per octave so if tuned high--best to use a high pass filter. During music, my 21 Hz tuned PR does not move so it acts more like a sealed box. No bass blowing through a port to muddy up the sound. Some people describe the "PR sound" as a hybrid between a sealed box and ported. Pretty close I would say, no sound coming from a port like a sealed box but a physical resonator for the ported punch around the tuned frequency.

The main downside of the PR is once you do it--you're stuck with it! Chopping additional holes in a box is rather permanent unless you don't mind making new boxes. Since I've always liked the Polk Audio SDA SRS/Klipsch and Definitive PR sound, it is not an issue. If you don't, then that alignment is not for you. If you don't like a box with a bunch of active/drone drivers and attempting to explain to people how it works--stay away from PR!

[chris661]

Originally Posted by christof123

Hi all.

Thanks for some really great responses.
Aren't LT and parametric eq just going to add distortion, and if i use it incorrectly, potentially damage the driver from over excursion?

I had initially wanted to avoid vented systems for the risk of a "blowy" boom, and honestly i'd rather have no bass than rubbish bass.

However, i've just heard a pair of Definitive Technology Mythos floorstanders. They use a small active sub, and 2 passive radiators. The response was UNBELIEVABLE from such a small system.
Should i bother investigating passive radiators? Not many people seem to use them?

Active subs. They have their own power amps, which will of course include some kind of signal processing for the subwoofers.
I do doubt that a single 6x10" driver could hit 14Hz (cone area is ~equal to an 8"), even at -10dB.

Be wary of following commercial designs with active crossover stuff, as they can be very complex in order to get the most out of limited cone area.

[herm]

If your budget can take it, a little DSP seems perfect for this task.

You can EQ the response to add a little low end, plus take care of
room modes with something like this:

MiniDSP kit | miniDSP

I have used similar devices and been very happy with the extra extension
and removal of boom...


herm