About sub boxes..

tigox

Member
2012-07-10 7:24 pm
Hey, i've always seen big subwoofer boxes that give a hell load of bass...
but what i never in my life got is how do companies like samsung that make home theater subwoofers , like subs with 6.5 inch drivers and have a tiny box and with a port almost the size of my fist and still ratter my house???!!

Shouldn't smaller boxes give less bass?
And shouldn't big ports be long??:( :confused: :(
 

kouiky

Member
2009-06-18 4:42 pm
Often, its the same way Bose achieves an acceptable response from mere pedestrian grade components- generous electronic equalization and high excursion combined with low Fs and Qts, neither of which make the driver better sounding on their own. Bose and JVC used two different orders of bandpass alignment and Bose patented their quarterwave rear loading of the bass driver in the waveradio and later models of the acoustimass. For the most part, the eq plays a large role. I find it funny they patented a technology that they didn't invent, and had been used by others generations earlier.
 

tigox

Member
2012-07-10 7:24 pm
doesn't bass boost supposably make the subwoofer distord a bit ?

And also i don't understand very much about fs and qts etc.. combinations , can someone make me understand a little bit or does somebody have any wbe page on this subject?
Tnak you guys :DD
 

wg_ski

Member
2007-10-10 5:21 pm
If you boost the hell out of a frequency that the "sub" has no problems reproducing and it will sound bassy. Give it 20 dB of boost at 90 Hz and filter everything below 50 (to keep it from falling apart) and you have the impression of "good bass". Until you hear a real system and then everything changes.
 

kouiky

Member
2009-06-18 4:42 pm
Better than webpage or whitepaper, I can explain the important basics right here. There is more to reproducing low frequencies than just a large driver in a large box. A woofer/driver has certain electrical and mechanical characteristics derived from its moving mass, magnet flux strength, coil impedance, suspension linearity and native compliance, diaphragmn displacement, inductance and several other characteristics. Years ago, two researchers set out and mapped how these interact with each other to form the basis we use today to model and make modern bass enclosures. The driver has a natural mechanical resonance frequency, a note at which it moves the easiest and requires the least input power to produce movement. This frequency also tends to be near the lowest frequency that the driver will realistically produce, although there are a few exceptions. The Qts is the relationship between mechanical and electrical characteristics and total compliance of the driver. A low Qts driver can, with the correct combination of other factors, produce prodigious bass in a small or sealed enclosure compared to a high Qts woofer, which will be more linear in a horn or transmissionline cabinet. A specialized 6.5" woofer can extend deeper than an 18" woofer if the T&S parameters are idealized for the application. There are other factors but that is the readers digest version.

EQ can attenuate very low frequencies to reduce driver diaphragmn movement while accenuating bass just above this region to allow for good extention without out of control distortion.
 
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tigox

Member
2012-07-10 7:24 pm
If you boost the hell out of a frequency that the "sub" has no problems reproducing and it will sound bassy. Give it 20 dB of boost at 90 Hz and filter everything below 50 (to keep it from falling apart) and you have the impression of "good bass". Until you hear a real system and then everything changes.

yeah but when i tested the ps-cw0 subwoofer from the samsung ht-c550 home cinema system i did it comparing it side by side with my jbl gt5-1204br car subwoofer ( a beast by my begginer standarts), and also th samsung subwoofer gives a looot of bass in my living room without giving the freaking vibration my jbl sub does, how it that possible?
 

kouiky

Member
2009-06-18 4:42 pm
The driver may have a generous amount of excursion, ie cone travel, and that combined with its resonance frequency, Qts tuning and finally the box tuning, can produce a relatively large peak in a narrow bandwidth, making it more efficient in that bandwidth. The right woofer and the right box size & port can yield a 5 to 10 dB peak, making it very loud. Add some EQ just above this quasi resonance point to smooth it out and suddenly we have loud deep bass from a shoebox. It will not offer any real extension in the deepest regions but will give the impression of being larger than it is, for a while. A bigger woofer will have a greater moving mass and physical reactance will vibrate the surroundings far more than a 6.5" woofer below the passband.
 
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tigox

Member
2012-07-10 7:24 pm
The driver may have a generous amount of excursion, ie cone travel, and that combined with its resonance frequency, Qts tuning and finally the box tuning, can produce a relatively large peak in a narrow bandwidth, making it more efficient in that bandwidth. The right woofer and the right box size & port can yield a 5 to 10 dB peak, making it very loud. Add some EQ just above this quasi resonance point to smooth it out and suddenly we have loud deep bass from a shoebox. It will not offer any real extension in the deepest regions but will give the impression of being larger than it is, for a while. A bigger woofer will have a greater moving mass and physical reactance will vibrate the surroundings far more than a 6.5" woofer below the passband.


So, something like this?
[IMGDEAD]http://i49.tinypic.com/2r72hbn.png[/IMGDEAD]
 

kouiky

Member
2009-06-18 4:42 pm
Generally, a Qts lower than .6, an Fs in the region that you wish to realistically reproduce without EQ, and a very low Vas, indicating a stiff mechanical compliance. The Hi-Vi SP10, Dayton Ultimax and Scan Speak aluminum 9" subwoofer each fall under the category by some means. They all will produce extended bass to 20Hz or lower in relatively small enclosures requiring no EQ. Now to answer your question- what woofer characteristics would offer a wide Q peak and maximum band gain in a small box? I can't think off the top of my head because its exactly the type of system I avoid. LOL It can however be achieved by using a low Vas/ low Qts driver in a box too small. A high Qts driver can have an unwanted narrow FR peak, like the one in the picture you generously provided.
 
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kouiky

Member
2009-06-18 4:42 pm
At this point one may pose the question: "If I can get great extension from a driver that makes deep bass in a small enclosure, why would I ever consider using a driver that requires a box the size of a refrigerator to do the same thing?" The answer is because they do not do the exact same thing. This brings us back full circle to efficiency and compliance. Low Vas drivers have large magnets to help overcome the high losses of stiff controlling suspension, but are still lower in efficiency compared to high Vas drivers. High Vas compliance drivers do not fight rigid suspension that is set in concrete, but often need support in the lowers frequency region. You've probably read "high efficiency drivers sound more detailed and lifelike" from many high efficiency builders, and to some degree there is truth in this. However, I've found its often mitigated by the fact that you can get superior performance from drivers in intermediate efficiency dB range that rival or outright trump many high efficiency drivers, and thus I prefer to find my intermediate point where I get the best of both worlds.
 
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It really can't.

oh ok, but what i don't get is how can a subwoofer work in such a small space?

If you run test tones you will see very little (sub) output for a given number of watts fed into it. Those micro subs may have a nice peak at 50-60hz but drop off fast below tuning.
High excursion drivers and ton's of power/eq can work in a small box but hoffmans iron law is still in working against it.
 

tigox

Member
2012-07-10 7:24 pm
^ +1

Also, electrical compression is often used to reduce the peak power into the subwoofer (you can hear it cut in occasionally when cranked).

Hook a "sub" like that up to a clean, powerful amplifier and see what it can actually do.

Yeah i hooked it up to my kenwood car amp and it was freakking amasing o_O , very good quality/power this kenwood amp, very worth the price :D


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So this got me thinking, how do i calculate a box that "pulls some plugs" in these subwoofers to have a good bass for the size?