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Old 12th July 2007, 11:07 AM   #1
Hyldal is offline Hyldal  Denmark
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Default Q in closed box design

I am mostly constructing vented boxes, but I will tra a closed design now.

What are your experinces with the system Q and the driver Q values.

I have head many closed systems that sounded to compressed, because of the air traped behind the woofer. How do you get a natural sounding bas, nor compressed but stil with control?
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Old 12th July 2007, 11:21 AM   #2
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I believe it's just your mind playing games with you if you think there is air trapped behind the woofer and that is making the sound compressed.

Maybe it's just the vented boxes you heard generally went lower, so you think that sounds more natural to you?

A closed box will always have more 'control' over the sound than a vented box.
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Old 12th July 2007, 02:39 PM   #3
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Default Re: Q in closed box design

Quote:
Originally posted by Hyldal
What are your experinces with the system Q and the driver Q values.
In my experiences, drivers with Qts values of roughly around .3 to .5 or so generally help lend to making a good sealed subwoofer. However, more often than not, these same woofers will usually work very well in proper vented alignments too. And of course, subwoofer drivers with a low free-air resonance tend to provide lower frequency response. And as with other designs, a good amount of linear xmax always helps.

As far as the total system Q, transient response tends to somewhat decrease with higher values, but the power handling of the system can increase a bit. A Qtc of 0.7 will usually give good results.

Quote:
Originally posted by Hyldal
I have head many closed systems that sounded to compressed, because of the air traped behind the woofer. How do you get a natural sounding bas, nor compressed but stil with control?
If I'm understanding you correctly, I think I can definitely relate to this statement and what you mean by this. Before I became so familiar with the different types of subwoofer systems and how they work, as well as all of the individual characteristics and Thiele-Small parameters of different subwoofer drivers used in these systems, I pretty much had the same feelings towards sealed air suspension subwoofer systems. I bought my first powered subwoofer (8" driver in a small sealed enclosure) for $150 when I was 10 years old to go with my $600 mini system. After hearing several of some of the cheapest vented subwoofer systems around that same time shortly after I bought mine, and not much higher in cost, I became very dissatisfied with the performance of my cheap subwoofer. Of course, some 14 years later now, I know quite a bit more than I did back then, and have listened to and toyed around with all kinds of subwoofers. And even now, those same thoughts I had toward sealed subwoofers 14 years ago are still somewhat the same in some aspects, but not exactly..

Basically, pretty much any subwoofer driver in a sealed enclosure isn't going to give as low of a frequency response as it would in a vented box, at least without some sort of EQing. So, does that mean that vented subwoofers are always going to perform far better than sealed enclosures? Absolutely not! It really all depends on the overall characteristics of the particular driver being dealt with, the rest of the system that the subwoofer will be used with, the room that it'll be used in, etc etc.

For example, I've listened to a couple of large custom-built subwoofers in the last year or so, specifically the ever so popular 'sonotube' designs that seem to be floating around everywhere these days. The main idea of this design is to tune the enclosure extremely low by making everything BIG. While this obviously raises group delay to the extreme, it also shoves this massive rise way down in frequency response, to where we're not so sensitive to it. As a result, the rise in group delay doesn't usually start to skyrocket until around 30Hz or so, while group delay above that is actually significantly lower than having that same subwoofer driver in a sealed box. As a major side benefit of all this, low frequency response is also extended as far as possible for the driver being used..

Anyway, having liked what I heard when I listened to these designs, I decided to gather some equipment, with plans of hopefully building one or two of these massive beasts in the future. A year or so ago, I ended up with an almost new Ascendant Audio Avalanche 15 (T/S listed below. Once I got it, I listened to that woofer in a small sealed enclosure for a good length of time, powered by a Dayton 1000 watt plate amplifier. If set up properly, it actually sounded REALLY good! Since then, I've obtained 3 more of these subwoofer drivers, and will most likely scratch my sonosub plans. Instead, I'm selling my current speakers, and going for open baffle...hopefully OB coaxials. I want to try using the open baffle L&R mains down to 35-40Hz or so, and using the 4 Avalanche 15 woofers from there down, in sealed enclosures with EQ. So yeah, basically augmenting the augmentors! With these particular drivers and this much cone area and excursion, I should be able to obtain around the same extension as I would using a large low tuned enclosure. So far, I think it should turn out pretty well.

While the Avalanche 15 would perform VERY well in a sonosub design, it's just too big for me (about 11 cubic feet EACH before displacement for a 14.6 Hz tuning!) But mainly, since I've decided to go OB with some major augmentation all the way down low, such a large vented enclosure isn't necessary anyway with all these woofers at the same time. And since I'd strictly be using them at the very lowest frequencies only, large low tuned boxes would probably do more harm than good.

If you haven't done so before already, I recommend you download WinISD (even the lesser beta version if you want, because it's much simpler)...and simulate a few good subwoofer drivers. Play around with box sizes for sealed enclosures, mess with all the configurations, and observe the outcomes of the phase plots and group delay as a result of your changes. At the same time, simulate these same drivers in their recommended vented alignments as well, observing and taking note of the system's characteristics simultaneously. After doing this, it'll become much more clear how everything works, as well as the reasons why sealed subwoofers often sound much more neutral and 'tighter' than ported enclosures.

Here are just a few of my personal recommendations of woofers to try...

Ascendant Audio Avalanche 15:
Qts- .31
Qms- 3.5
Qes- .33
Fs- 15.7 Hz
Vas- 300.6 l
Re- 3.20 ohm
Le- 2.40 mH
Xmax- 27 mm
SPL- 87.50 dB
Pe- 800 W
dia- 15 in.
Sd- 750 cm^2

CSS Subduction SDX15:
Qts- .39
Qms- 3.65
Qes- .44
Fs- 19.20 Hz
Vas- 218.4 l
Re- 3.60 ohm
Le- 1.80 mH
Xmax- 30 mm
SPL- 87.30 dB
Pe- 1000 W
BL: 16.50
dia- 15 in.
Sd- 660 cm^2

TC Sounds 18" LMS-5400 DVC:
Qts- .37
Qms- 13.01
Qes- .39
Fs- 18 Hz
Vas- 216 l
Re- 3.47 ohm
Le- 3.10 mH
Xmax- 38 mm
SPL- 88.10 dB
Pe- 2500 W
BL: 26.50
dia- 18 in.

TC Sounds 15" TC-2000:
Qts- 0.321
Qes- 0.347
Qms- 4.264
Fs- 18hz
Re- 3.19Ω
Ls- 2.45mH
Lp- 5.87mH
Rp- 4.30Ω
Dia- 320mm
Vas- 267l
mms- 296g
cms- 260um/N
bl- 17.2T*m
Spl- 88.5dB

SoundSplinter RL-p 18 D2:
Qts- .44
Qms- 4.54
Qes- .48
Fs- 20.71 Hz
Vas- 314.2 l
Re- 3.74 ohm
Le- 3.32 mH
Xmax- 27.4 mm
SPL- 89.45 dB
Pe- 1000 W
BL: 19.50
dia- 18 in.
Sd- 1188 cm^2

Mach 5 Audio IXL-18.4:
Qts- .37
Qms- 5.59
Qes- .39
Fs- 17.70 Hz
Vas- 274.1 l
Re- 3.40 ohm
Xmax- 22 mm
SPL- 89 dB
Pe- 800 W
dia- 18 in.
Sd- 1029.2 cm^2

Dayton Titanic 15:
Qts- .38
Qms- 5.89
Qes- .41
Fs- 19.93 Hz
Vas- 220.6 l
Re- 3.68 ohm
Le- 3.84 mH
Xmax- 20.5 mm
SPL- 91.70 dB
Pe- 800 W
BL: 15.79
dia- 15 in.
Sd- 735 cm^2

Adire Tempest Classic:
Qts- .39
Qms- 6.70
Qes- .40
Fs- 18.80 Hz
Vas- 317 l
Re- 3.50 ohm
Le- 2.90 mH
Xmax- 16.4 mm
SPL- 89.10 dB
Pe- 750 W
BL: 14.20
dia- 15 in.
Sd- 779 cm^2
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Old 12th July 2007, 02:51 PM   #4
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Well, the previous post shows I'm full of baloney, but I've always been under the impression that there aren't that many drivers out there suited to sealed boxes. The Fs is usually too high, though Q is less of a problem. The sealed boxes I've built were generally unsatisfying unless I went for a finished Q higher than the usual 0.7- a value up to 0.9 or so was much better. For many years I valued flat response above all things, knowing that anybody who liked a little thump in their bass just wasn't a purist. I've gotten over that and stopped being so attached to Butterworth. Definitely run the simulations on various drivers. Though it kills efficiency, I've also had some good results adding a bit of mass to drivers to alter their parameters.
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Old 12th July 2007, 03:25 PM   #5
Hyldal is offline Hyldal  Denmark
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I feel many closed boxes sounds like they are not allowed to open up and sound free. The sounds "over controlled" but if the right system Q is chosen i guess, it should be no problem, I would just like to here if someone have some experinces to take this "over controlled" sound away, without loosing control and the sound gets muddy
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Old 12th July 2007, 03:28 PM   #6
BHTX is offline BHTX  United States
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Quote:
Originally posted by Hyldal
I would just like to here if someone have some experinces to take this "over controlled" sound away, without loosing control and the sound gets muddy
...Yeah, it's called infinite baffle.

Impossible for me at the moment, though.
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Old 13th July 2007, 08:24 AM   #7
Hyldal is offline Hyldal  Denmark
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I probably need to invetigate this when I find the time. I think I will use a drive with dual voice coils, and put a potentiometer on the one coil and drive it on the other, then i can vary the Q, with the potentiometer, and se how the Q influence the sound.
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Old 13th July 2007, 10:43 AM   #8
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Maybe you only heard lower-Qtc boxes before? Try for Qtc around 1 and see what you think.
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Old 13th July 2007, 12:06 PM   #9
Hyldal is offline Hyldal  Denmark
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Yes maybe a higher Q is better for me. Or maybe I simply should stick to reflex boxes or Dipole.
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Old 13th July 2007, 12:33 PM   #10
BHTX is offline BHTX  United States
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IMO, more often than not..

Infinite baffle, then large low tuned, then sealed with lots of needed EQ, then a vented with flat response

..In that order, from best to nastiest...different drivers used for each alignment that are optimized for that particular type of system, of course. And, depending on specific needs/wants..OB or dipole bass is always nice, with the main factor being whether or not the roll off will be an issue for you in your particular situation.

Once again, this is all just my personal opinion...and one that greatly depends on many different variables, at that. I'm really not biased towards any enclosure type, and have heard all kinds that performed very well and sounded great.
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