DollarBill:

>>My point is that a large woofer will (should?) have more trouble reproducing the higher frequencies. 18s, taken by themselves, will not produce the higher octaves as well as 15s or 10s <<<

I'm sorry, but are dead wrong in your assumption that an 18" driver is somehow not fast enough to reproduce the higher end of the bass range. As I stated in my original post it is all about the size of the magnet / voice coil assembly in relation to the weight of the cone. The diameter of the cone has nothing to do with it - there can be and are 10" cones that are heavier than some 15" ones. The weight is the only determining factor, period. An 18" driver simply needs a larger motor assembly than a speaker with a smaller cone in order to have equal acceleration abilitiy, and therefore the ability to reproduce the higher end of the bass range as well as the smaller speaker. You are simply perpetuating an audiophile myth if you believe that you have to have a smaller woofer in order to have it respond up to 60Hz. That's just plain wrong. At the frequencies that a subwoofer reproduces, beaming is not a factor. Beaming only comes into play when the diameter of the cone becomes a significant ratio of the wavelength of the audio. The wavelength of 60Hz is over 18 feet. This is a small percentage of the 18" diameter of a woofer.

[This message has been edited by soundhound (edited April 07, 2003).]

Alright, I was more concerned about the large diameter woofer handling the higher frequencies. But since your point is that the diameter of the cone has nothing to do with the frequency response, then why do you think you can't use a smaller driver or drivers in a properly tuned cabinet to get bass as good as that produced from an 18 inch driver?

This is a matter of efficiency and low frequency extension. A larger cone moves more air than a smaller one, and therefore does not need to move as much in order to achieve the same SPL level as a smaller cone. With a larger cone, it is easier to achieve a low free-air resonant frequency, and therefore better low frequency extension. A small cone can have as low a free-air resonance, and reproduce low frequencies, but a 12" cone would have to move much more distance back and forth in order to reach the same SPL at the same frequency as an 18" driver. It would reach it's excursion limits at the lowest frequencies way before the 18" driver for equal SPL. This also means that the 12" driver would be more prone to non-linear behavior because of the distance the cone must travel, and therefore distort more. In addition, any port noise would be higher with the smaller woofer and cabinet.

I use four 18" subs, each in an 8 cubic foot cabinet in order to match the efficiency and output capability of my mains, which have efficiency of 106db/watt. My room also is 6,600 cubic feet. It would be impractical to have enough 12" subs to achieve the SPL and low frequency extension as the 18" subs. With my seup, response extends to 16Hz at 120+db SPL (my 1/2" Bruel & Kjaer instrumentation microphone clips before I can measure higher SPL).

If you don't need high output capability combined with good low frequency extension, a smaller subwoofer will work, however, as output and low frequency extension demands rise, the only practical solution is a large speaker driver, in a large cabinet.


[This message has been edited by soundhound (edited April 07, 2003).]

yeah...but it's way more fun to watch a 12" driver with a 30mm x-max push that amount of air.

i followed you up to the 'practical' part. the wife don't think it's very practical to have "those 2 ugly refrigerators" in the room. and, a good 18" driver ain't cheap.

i've been working on some 12" sealed, eq'd, adjustable Q, 2k watt, 1 cu ft subs. a lot of state of the art technology is required (the driver, small 2kw amp with no heat sink, power supply, battleship tight box, etc.), but it is available these days.

most people use those fast, tight, musical types of words but, the word really is overdamped. thus the adjustable 'Q' circuit. damp it to your liking. this, BTW, is where the discrete LFE comes in. 1 sub slightly underdamped, for effects, and the other, slighly overdamped, for music.

the advantages of the sealed design over the ported are better group delay, less critical box dimensioning, no port to make noise and smaller size. the price is gobs of power, a truly amazing driver and a very cool piece of hardware for mistake-free design of the precision eq.

my 18's have a 6mm x-max, the 12's are 30mm. at very low hz, the 12's are MOVIN'. the 18's movement is hard to notice, by comparison.

i'll miss one thing. the 4 ports are each aimed directly at the listening position. i like to set an unsuspecting friend up with a demo scene that has a sudden explosion type of low freq transient. a second later, the blast of air hits him right in the face. they always duck, as if they are under attack.-->fun<-- and it demonstrates how much air has to be moved to reproduce that kind of tone at that spl.

SH is dead-on correct with everything he said. velo's HGS-18 attests to it. plus...four 18 inch drivers for 60 hz and below....ya gotta love this guy. 120db at 16 hz....and you say MY system is miscalibrated?? 106 db, 1w-1m...gonna take more than 5 watts to equal THAT bass.

actually. LOTR has enormous LFE content. i have to back off quite a bit with certain scenes to equal gladiator or pearl harbor (or, are you saying it's the player or the preamp or the amp?)

Could it be the disc The unworthy asks the LFE experts? Making you wince away from your clip levels. Are you aware that there was a stink about the first LOTR disc released (although your Special E? Is that the 2nd release and I don’t’ know if that was the case with future releases). A reliable source said the disc was layed 10dB hot. And there were various threads around the forums about blown speakers in connection with LOTR.

It is a disc to use with restraint and moderation.

Bosso:

I just have to keep reminding my wife that the subwoofer cabinets are large enough to put her in if she gets out of line

I have modified the cabinets from what they were when I purchased them. They originally had three ports, and were tuned to around 25Hz. Working with the speaker's engineers, I blocked off two of the ports for a new tuning of 12Hz. This overdamped the system: essentially I traded efficiency for low frequency extension. I made up for the loss of efficiency by using 4 subs. They are driven by a 1000 watt MOSFET amp that has something like 16 output devices per channel.

LOTR? my subs aren't even breaking a sweat........


[This message has been edited by soundhound (edited April 07, 2003).]

It seems to me that if you have two woofers that have identical motor assemblies and are otherwise mechanically identical except for the area of their cones and their cones have the same mass (and thus the cone and coil assemblies will have the same mass), it seems to me that the one with the larger area will me more efficient.

Reasoning follows:

I am extrapolating from newtonian mechanics in that the maximum energy is transfered in two colliding bodies (such as billiard balls, for example) when the colliding bodies have the same mass.

In regards to dynamic woofers, the woofer moving system usually (cone and coil) has much more mass than the (nearby located) air it is trying to move. A larger cone is in contact with more air, so all else being equal, the mass of the (nearby located) air is more nearly equal to the mass of the woofer moving system of the woofer and so will transfere more energy from the moving cone to the air, thus the efficiency of the larger coned woofer will be higher.

Also, to reproduce the same SPL, the larger coned woofer will exercise (tax) the drivers mechanical suspension less, and beings many of the suspension compnents have elastomeric mechanical properties, the larger coned woofer will produce less distortion.

In either case, for subwoofer use, the upper limit of the frequencies that the woofer is being asked to reproduced is much, much less than what the woofer can reproduce without significant directionality and is established by the crossover. If this is not the case, then we are not talking subwoofer application or else we are talking about a driver of several feet in diameter.

So, size does matter.

Unless there are space constraints that rule out a big subwoofer (or WAF problems), bigger is better.

Paul

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the 1derful1

now that you mention it, i did hear something about DTS discs being 10 db hot because, when they did their own mastering, they weren't compensating for the LFE + 10db.

as i said, this weekend, i'll rent the disc and see what i find out.

no..my subs don't break a sweat at all either. they can handle 1kw each, continuous. it's definitely the signal from the disc.

bigger is definitely better. unfortunately, most people don't want the subs to dominate the landscape of the home theater (what's wrong with these people??). also, bigger is more do-re-mi.

BTW, i have 3 models of the same sub design (they differ in cosmetics only). one of them has the model # suffix: SLL, after a famous internet poster. as soon as the front panel is finished and attached, i'll post pix for a thumbs up or down.

ok...i couldn't wait for the weekend. just confirmed that my copy of LOTR has exactly 10db hot LFE track. (also confirmed, while i was at it, that my 950 outputs no LFE while in DTS-ES, which is actually a good thing for me.)

Lena...thanx very much for the info!

soundhound: LOTR, disc 2, chapter 9, at ref level + 10db, your sub's amp might sweat just a bit.

model # suffix: SLL, after a famous internet poster Famous or inFamous! I think I feel sorry for it. Would love to see pics when avail.

I need to get busy and order my ES kit. Of COURSE I wrote my serial #'s down. Of COURSE I can't find them. Time to pull out the flashlight. I keep meaning to buy a gooseneck!