Better low end response from sealed enclosure?

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christof123

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Joined 2011
#1
Hello all.

Have been trying to design a sealed cabinet for mostly music uses, but very occasional movie use.

I've opted to use a dayton audio 10" driver as this seems to be highly recommended.
Dayton Audio RSS265HF-4 10" Reference HF Subwoofer 4 Ohm

Willing to fork out a bit more, if the quality will be noticeable.

I'm struggling to get a flattish response to extend the low end.

http://img193.imageshack.us/img193/2804/winisddayton10.jpg

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.

Any help on improving low end response or driver improvements will be greatly appreciated.

Thanks

Chris
 
#3
christof123 said:
Hello all...I've opted to use a dayton audio 10" driver as this seems to be highly recommended...Dayton Audio RSS265HF-4 10" Reference HF Subwoofer 4 Ohm ...I'm struggling to get a flattish response to extend the low end. .... i've currently used a 70L cabinet, as any bigger than this it becomes too obtrusive for the room. Any help on improving low end response or driver improvements will be greatly appreciated.
ThanksChris
Click to expand...

Hi there: Ran your driver RSS265HF4 through a box program LCD7 design suite:
sealed: 2.5 cf, F3=44hz, Qtc=0.56, Watts=31, SPL=99 about same as your simm
0.95cf, F3=42hz, Qtc=0.72, Watts=126, SPL=105 slightly better F3, ok Qtc
ported 2.5cf, F3=21.3, Qtc- n/a Watts=56, SPL=99 could port your box 3"dim x12.8"
1.55cf, F3=26.3, Qtc- n/a Watts=130, SPL=105, better SPL,lower F3,
and port 3"dim x 15.7"
Do not see lots of improvement possible with sealed enclosure from various sizes I ran, ported enclosure looks like it would meet your requirements. Hope this helps you make a decision and you will post your construction, and listening results (measurements if you do some). ...regards, Michael
 
#4
Hi,

ESP - The Linkwitz Transform Circuit

You can simulate a LT circuit in winISD - on the EQ/Filter tab, click Add, then choose Linkwitz Transform from the drop-down menu.
Set the two boxes on the right to the LF extension/rolloff you desire, and hit Add.

Now, go to (on the main drop-down menu) Amplifier Aparent Load Power (VA), and see how much power you'll need (keep an eye on excursion too). You'll notice at really low frequencies (sub 20Hz), you need a lot of power, and a lot of excursion. We need to cut that down, just in case something in a movie decides to wreck your subwoofer (and it will - the example I've just tried required 140x the nominal power at 5Hz).
Add a high pass at a low frequency, 2nd order minimum.

Hope this helps.
 
#5
Hi, thanks for the responses.

I wanted to avoid the ported route as I haven't yet heard a good one, so going with what i trust.

Transmission line? Surely this would end up being larger than a sealed? Also by occasional movie use I mean once every few months, so am designing towards a musical set-up.

Linkwitz transform - this looks very interesting, yet complicated. Are these commonly used?
 
#6
christof123 said:
I wanted to avoid the ported route as I haven't yet heard a good one, so going with what i trust.
Click to expand...

Ported designs sound excellent as long as you tune for max flat rather than a peaked up resonse at a higher frequency. Tuning hgher just like using too small a box for sealed subs, results in underdamped boom.

Tune deeper and its more damped. The best ported results are overdamped.

The distortion you will have pushing equalization to make up for the 44Hz tuning in a sealed box will outweigh any benefit. Keep in mnd that big power is needed to get a 10 to extend flat in room and even then, it will not make much bass being that its starting off down 12db at 25hz and having its rated power handling limit. Ported will require 1/4 the power in your case to extend to 20/25 and have a fraction of the distortion.
 
#7
If you look on Home theater shack there is some testing of LT subs of the same volume as ported using the same driver at the same output levels and in all cases the distortion from the LT is worse and in almost all cases the required power input is greater. It only makes sense to me if having a port would subtract significantly from the internal volume which in your case with 70L isn't the case. I would also investigate using two or more smaller subs as this works better in a given volume. If money is no object small isobarik equalized subs could be used.
 
#8
kipman725 said:
If you look on Home theater shack there is some testing of LT subs of the same volume as ported using the same driver at the same output levels and in all cases the distortion from the LT is worse and in almost all cases the required power input is greater. It only makes sense to me if having a port would subtract significantly from the internal volume which in your case with 70L isn't the case. I would also investigate using two or more smaller subs as this works better in a given volume. If money is no object small isobarik equalized subs could be used.
Click to expand...

Could you provide more details/a link about this test: it hardly seems a fair comparison to me.

I have used a Linkwitz Transform myself, thinking a pair of 8" drivers would be enough to hit 28Hz with any authority. I hadn't at that point discovered the Apparent Amplifier Load tab on winISD, and cheerfully chucked 14dB gain at them. The result was nice enough, but didn't stand being turned up. Power went up hugely (excursion followed), and the cheap amp probably didn't help.

IMO, take it for what it is. Provided you set off with sufficient driver/amp capability, you can get decent amounts of bass from cabinets that aren't huge.

Chris
 
#9
The HiVi sp10 is designed to be used with a Linkwitz transform. If you got one of them you could build a sunfire 10 clone. SUNFIRE: True Subwoofer EQ 10 - TS-EQ10

If 70L is it, you'll need to go with a folded slot port to tune low enough (~14hz) to keep the group delay low in the audible regions, if you were to think about going ported, as a round port would be too long and you'd get pipe resonances...
 
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#12
christof123 said:
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
Click to expand...
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.
 
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#13
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?
 
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#15
christof123 said:
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?
Click to expand...

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! :usd:
 
#16
christof123 said:
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?
Click to expand...

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.
 
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