Sub output: Is it the woofer size or the rated RMS

A large driver in a large cabinet needs less power to produce deep bass. A small driver in a small cabinet must have huge amounts of power and much further excursion to produce deep bass. A small driver may seem like it would produce faster bass but in reality it must move further than a large woofer to output the same amount of bass. The laws of physics are constant and unchanging.

Elizabeth hit it right on the head and Rwwear went a step further.

But the small cone has more linearity in its movement. It is fascinating to see the large driver/small driver debate return again after we all thought it was settled. When I was young the bigger the better was the rule, EV had a 30" woofer, Hartley a 24". In music reproduction the last 40 years has seen a gradual reduction in driver size. This may or may not apply to HT. But the driver size or amp power alone tells you little about the quality of a particular sub, a good designer can use either paradigm. You have to match the performance of a particular unit with your requirements.

"But the small cone has more linearity in its movement"

Huh?....smaller drivers are made, so that you can use smaller boxes, so that the buyers wife will be happy, or at least, more happy than she would have been with larger boxes in her living room....(no other reason for doing it, purely marketing).

Dave

Excuse me , but that is ridiculous. Some of the best and most expensive speakers made use 10" or smaller bass drivers. In the 60s no self respecting speaker had less than a 15" woofer, they now are extremely rare. Look at the DIY speaker sites and see what is for sale there. They are hardly affected by marketing considerations. If you do not understand speaker design I can recommend some good books, starting with HIGH PERFORMANCE LOUDSPEAKERS by Martin Colloms. What part of my statement about cone linearity did you not understand?

Stanwal

Hummm, I wonder why all the best subwoofer designs, that have more than one size (10"/12"/15"/18"...charge more for the larger subwoofers?, if the smaller subwoofers are better?

You should quit reading, and get some practical experience.

The subwoofer drivers of yester year, were very large for a reason...more bass, with less power. The box design for the old 30" subwoofer you mentioned was huge (around 5' tall), and required only limited power supply....more in line with the technology of the day.

Dave

It stands to reason that for a given cost it is easier to design and manufacture a smaller driver that will be more accurate than a larger driver, with respect to the inevitable tradeoffs between cone resonances, stiffness, transient response, overhang (the ability to stop quickly when the music stops), various forms of distortion, etc.

It is also true, of course, that a larger driver in a larger enclosure will provide more bass for less power, everything else being equal. But so what? I don't think that Dave's insulting response to Stan's well intentioned comment was called for, and I don't think that "no other reason for doing it, purely marketing" tells the whole story.

Regards,
-- Al

More power in a sub can probably never hurt, but just be overkill perhaps.

Generally, a larger driver, properly driven, will facilitate better low end response but size alone is not enough. Its the quality of the driver and soundness of the overall design that matters most.

There are many things I could say to socalled sogood but will stop with saying that I have been in audio 46 years, some of it as a Krell dealer, have 4 pairs of subs, none of which I would trade for any of his, and will end with what my wife told me to tell him, " its not the size of what you have but what you do with it."

And I suppose she's an expert on........subs.

I just thought Stanwal's " cone linearity " statement was complete hogwash, and implying some advantage, towards smaller drivers.

Truth is, from 20-80hz (normal subwoofer range)...small drivers have no advantage over larger drivers.... at reproducing these very low freq's

Just trying to stop the spread of internet B.S. from taking over.

Sorry for being "insulting" in my approach....my bad...over and out.

Sobad

Its not your insults I mind ; its your stupidity. You obviously have no idea what you are talking about. I suppose you never heard of "speed" in a sub woofer. If all you are interested in is making noise then the HT set up you seem to favor is fine. For those interested in serious music reproduction other considerations come into play. Oddly enough, my motivation is exactly what you profess yours to be, the prevent the clueless from misleading the unwary. My two REL Stadium subs use one 10" Volt driver each and cost $3000 each. I suppose that is your idea of cheap. You appear to be one of those who thinks that because they have spent a considerable amount of money on their system they have some how acquired knowledge and authority. Making wild and unsupported statements is hardly the mark of knowledge.

I for one believe that a fast sub is not reproducing deep bass. The very thing that makes deep bass deep is the long wavelength. I am not saying a small sub can't make deep bass. It just takes much more power and further cone movement than a large sub. The further cone movement negates the quickness of the small sub because a small sub must move in and out so much further than a large woofer, it is just as slow.

I'm not an expert in this area, but I believe that what creates the subjective impression of "fast bass" is simply the ability to accurately follow the input waveform, without harmonic or intermodulation distortion, and perhaps most importantly the ability to stop moving quickly when the musical note stops.

Increased driver size obviously will produce more volume at lower frequencies than a smaller driver, everything else being equal. Or, as Rwwear points out, the smaller driver will have the disadvantage of having to move further to produce a similar output. On the other hand, as I indicated in my previous post, producing a larger cone that will be as accurate as a smaller cone within their respective ranges of motion is more expensive. Everything else being equal, a larger cone will have to be stiffer to avoid flexing (what I believe is called "cone breakup"), cone resonances, and other contributors to non-linearity and distortion. A stiffer cone, everything else being equal, will be heavier, have greater inertia, and be less able to stop abruptly. Implementing a better combination of stiffness and lightness will tend to require better and more expensive materials.

As Mapman said, "it's the quality of the driver and soundness of the overall design that matters most." And producing a larger driver of similar quality to a smaller driver simply costs more, particularly if the design doesn't require the smaller driver to provide the volume or bass depth of the larger driver. I would not say that "a fast sub is not reproducing deep bass," just that it can't reproduce bass quite AS deep and/or loud as a larger driver or a driver of the same size but greater excursion.

Regards,
-- Al

Almarg outlined the issues well I would say.

Sorry to have gotten irritated, I was upset at the idea that many manufactures are only concerned with marketing. I have known many , beginning with Sol Marantz and Stu Hegaman and by and large they were driven by considerations other than the maximum amount of money they could make. Of course there are those like Bose who are all marketing but they are rare. Most designers are trying to produce the best they can at a price they can sell their product for. The optimum size of woofers is a subject that has been debated for years and will not be settled in my lifetime and I respect anyone else's opinion. What I do not respect is unsubstantiated attacks on the motivation of people I like and , in many cases, admire. It has often been said that the way to make a small fortune in HI End audio is to start with a large fortune , sometimes good products are rewarded but often they are not. The lack of marketing skills has been far more prevalent in hi fi than an excess of them. The point I am trying to maintain is that it is possible to disagree about equipment without impugning the motives of those who make products we ourselves do not like. I have never succumbed to the charms of Magnapans but I do not think those that do are somehow defective in some respect. It would be boring in the extreme if everyone liked the same things. The older I get the more I realize that everyone hears things in a different way and what suits one will not work for another.

>In any subwoofer output, how important is the Watt output versus the woofer size?

Speaker efficiency is at best proportional to cabinet size and inversely proportional to the cube of the low frequency cut-off.

So all else equal, it's going to take 4X the power to maintain a given output level and bass extension in a 1 cubic foot box (like a Sunfire sub-woofer) versus a 4 cubic foot box.

You can't compare power without comparing box size.

Stanwal

I didn't attack manufactures at all, I simply stated that the reason they build small subwoofers is marketing. (the wife part was half in jest, and half not). A lot of people want subwoofers, in this day of hometheater. And many of those people can't, or won't buy huge boxes, they want small...and for many reasons.

Manfactures cater to market demands...thats called marketing, in case you didn't know?

I also didn't mention money (although you seem high on that subject...what a snob), didn't mention your $3,000 subwoofers, didn't mention my system...or my subwoofers...you did all that.

I simply stated that your "cone linearity" statement was hogwash, and that the large drivers of old that you mentioned (and implied was the wrong direction), were a product of their time, and of that times technology.

Actually, the two huge drivers you used as examples, saw limited use....smaller 18", 15", 12" drivers were used in most designs as I recall it.

I fully understand that many manufactures make "very fine" small/med/large subwoofers for todays "market" needs....but they don't make the small subs, because they found out they were better than the large subs (although they probably are better than the large subs of years ago, given todays advanced technology).

I may be wrong, but I believe the Sunfire True Sub (I bought mine 2 months after they came on market)was the first "small" sub (12" cube). As Drew posted, it takes a lot of power to produce a FR response down to 16Hz in such a small enclosue (even though a 12" speaker is not "small").

Bob Carver designed the 2700w RMS amp to compensate for the small box. Was Carver motivated by market demand for a small sub? I think so and more power to him.

Sogood, it is strange to see me called a snob because I pointed out that not all subs that used small drivers were cheap. The idea that marketing was behind sub design implicitly assumes that it is money that drives the market. I will point out to you that Wilson has just replaced 2 18" drivers with ONE 12" in their latest sub, the Watchdog, which runs $10,000. Do you really thing that this is to make it more paltable to wives? The top REL sub, at the same price, uses 2 10" and is widely regarded , IN THE AUDIOPHILE COMMUNITY, as being possibly the best sub available. I am becoming aware that the HT community has a completely different set of priorities. When REL brought out the T series for HT use they were quite different from the S series designed for music reproduction. The T series has no real bass below 30hz ( as opposed to below 20hz for the bigger S series) and the lowest filter setting is 60hz. With my subs I start rolling them off at 22hz. The idea that cone linearity and speed are irrelevant can be instantly falsified by looking at the speaker compliment of large speakers. The new Snell Illusion , which is their best speaker, uses 2 10" magnesium cones and is specified to be -3db at 27hz. Do you think that when a company is trying to get $50,000 for a speaker they will not use the best possible driver combination? The Avalon Eidolon Diamonds , which are specified to be 1.5db down at 24hz use 2 11" woofers. They are about $34,000. Why do I mention money? Because I am a snob? No, it is to point out to you that at this price range the only consideration has to be performance. All of these are far out of my own price range, the $2600 I paid for the Duettas is my high water mark. Ah, you say, but these speakers are not subs; while smaller cones may have an advantage at the range these speakers operate in they do not at the low end. This assumes that there is some magic frequency at which physical law inverts itself and what was true at 100hz is no longer true at 50hz. Someone mentioned that smaller cones have no advantage in the range 20-80hz. If this were true why do the speakers mentioned above not use larger drivers? I have never heard anyone suggest that the B&W 800d needs subs, yet it uses 2 10" woofers. The less mass something has the quicker it can react. The smaller it is the more linear is the movement. this is simple physics. But, you say, speed in subs is unimportant/nonexistant. There we differ. The search for a sub that will mate with Quad electrostatics is over 30 years old. As they react much faster than cones most subs are hopelessly slow. But some do work; i.e. those with smaller drivers. It is also important in matching the main speakers, larger drivers have more momentum, they do not keep up as well as those 12" and below. All of this is regarded as self evident in the music reproduction community. The HT community obviously has different ideas. As I am not a member of the community, even though I do have a video system, I will refrain from deriding the ideas of its members if they will extend me the same courtesy,

>In any subwoofer output, how important is the Watt output versus the woofer size?

This also depends on the frequency range of interest.

The air you need to move quadruples with each octave decrease in frequency.

A driver with twice the area (say a 15" driver versus a 10" driver) can play 6dB louder. A longer stroke often goes with the larger diameter; if that doubled from 12 to 24mm you'd get a total of 12dB more output at low frequencies given enough amplifier power to use the excursion.

At higher frequencies you're limited by the power needed to overcome the stiffness provided by the air spring in the box + suspension; and at the highest frequencies you're limited by the power needed to accelerate the driver.

Stanwal

Some good points, so I'll keep this short:

Regarding Wilson:

(They have Thor's Hammer subwoofer?)...two 15's

Regarding Rel subs:(and in no way intended as a knock)

(Fine subs, but mostly over rated at Audiogon, and probably under rated, at most other forums? To be honest, there has never been a time as now, when so many good subwoofers are in the market, and we are very lucky. The "AUDIOPHILE COMMUNITY" is much larger than Audiogon, and much of the hype around Rel subs stays here, or at least your statement about them " being possibly the best sub available")

Regarding subs, or mains using multiple drivers:

(Multiple drivers give you more cubic inches, they move more air...see the Wilson Thor as an example that works along with your examples. Multi driver subwoofers were not in my subject line, they are a "whole nother subject"...although an interesting one that does bring some advantage, in some systems. My Apogee MiniGrand subwoofers use a pair of 8" drivers in each cabinet, and my VMPS subwoofers use a 12" and 15" driver in each cabinet, and a single VMPS subwoofer, uses only a 12" driver).

Like you, I'm not a hometheater guy...although I wouldn't be without one, and I do enjoy it now and then. My main music system is no longer using subwoofers (except when I play my little MiniGrands). My Duetta Signatures don't need subwoofers to keep up with the MiniGrands, and the large subwoofers rarely came into play, when I did use them for music in the past (so, I thought it a poor return on value)....and I moved them to the movie system where they get more work.

Regarding 20-80hz:

(Two octaves, the first one....one 15" has a clear advantage over one 10" driver in the 20-40hz range)....the winner?, the 15"

(The second octave, 40-80z?...I can't think of any reason, why a single 10" would have any advantage here either)....the winner?, probably an "equal result" at best.

This would seem to give the larger driver an edge?....a 50% win rate at least, while the smaller driver gets no clear win...0% win rate from 20-80hz.

At freq's above 70-80hz, and using a subwoofer at these higher freq's, your on to something, or at least your ear may be....as the small driver, begins to take any advantage away from the larger driver...no rocket science here.

Regarding hometheater subwoofers:

While they do make hometheater subwoofers (I like to call them "west coast subwoofers"....I'm sure you remember the west coast sound)...any "good" subwoofer can reproduce music and movies just fine.

Regarding Quad and subs:

Dipole bass and monopole bass, does not sound the same. In order to mate "monopole subs", with dipole speakers (at least in my experience, and to my ear)...you must use a filter slope that does not allow the sub, to be active above 40-50hz... 70hz max. (lower is always better)....it's not a speed thing at all. While subwoofers do need to be "linear" (except the west coast ones(-:)...they don't need to be fast? If any one driver is playing faster than another, it's playing a different freq. yes?

Any driver only needs to play, as fast as the freq. calls for, and no faster. Large drivers do have a speed limit, because of their size and weight, but 20-80hz is well within that limit for a 15" driver.

So, I'm going to end this short post, and say I agree with you 50% on subwoofers...and 100% on speaker choice...(-:

Dave

>A driver with twice the area (say a 15" driver versus a 10" driver) can play 6dB louder. A longer stroke often goes with the larger diameter; if that doubled from 12 to 24mm you'd get a total of 12dB more output at low frequencies given enough amplifier power to use the excursion.

Also note that since drivers are rated based on total basket diameter and that doesn't grow as much with the rest of the driver the surface area differences are greater with smaller drivers.

An 8.5"/22cm driver can have nearly twice the area of a 7"/18cm driver. (220 vs. 126 cm^2)

I'm not sure if this is relevant, but the flagship Ampeg concert bass guitar amp/speaker cabinet is one of the most popular among rock musicians.

The amp does 300w @ 4ohms. The cabinet has 8 x 10" woofers. Low FR is 58Hz @ -3dB and 40Hz @ -10dB. SPL is a thunderous 130dB.

Here's what Ampeg has to say about choosing an array of 10" woofers over larger woofers:

"Why do we use eight 10” speakers? Because we learned early on that 10” speakers work much more efficiently than fifteens or eighteens—and if you put eight 10” speakers together, you can move a much larger column of air. In fact, you’d need five 18” or six 15” speakers to move as much air as the SVT-810AV! And they simply wouldn’t be able to respond to transient peaks as quickly as our tens."

"And they simply wouldn’t be able to respond to transient peaks as quickly as our tens.""

Smaller dynamic drivers do have an inherent advantage in regards to transients over larger drivers even if disadvantaged in regards to reproducing the lowest octaves.

I've always leaned towards smaller drivers in conventional dynamic speaker designs in general as a result.

For subs, I've heard it done well with both larger and smaller drivers, again depending on the robustness of the overall design more so than just pure driver size.

Sometimes it's simply a matter of Proportion, like sticking a babies head, on a 250# man. Or building a huge state of the art hometheater sound system, and then watching the movie on a 27" screen....it's just not right.

The design is of the utmost importance for a sub it's true. It's just easier as the driver size increases. That being said a system with multiple small drivers would probably be the best but would require a lot a of equalization and power to have real low bass.

"Why do we use eight 10” speakers? Because we learned early on that 10” speakers work much more efficiently than fifteens or eighteens—and if you put eight 10” speakers together, you can move a much larger column of air."

Mmarvin19 - excellent point. Bass players know that 10" speakers provide the best compromise between power and bass definition and use arrays of many 10" speakers.

Speakers in array made in the same enclosure work better. (Acoustic impedance lowers, resonance frequency drops down) Making simple reasoning 18" speaker moves 3.24 times more air than 10" speaker. To avoid membrane bending (cone breakup), that Almarg mentioned, membrane has to be 3.24 time thicker and in order to keeps everything proportional coil and magnet have to be 3.24 times larger to move 3.24x heavier membrane with 3.24x more air pressure. Am I right? Speaker people - are you there?

One correction - membrane of 18" speaker should be 10.5 times heavier because it should be 3.24 times thicker and the area is 3.24 times larger. That is probably why definition is getting poor (too heavy).

>One correction - membrane of 18" speaker should be 10.5 times heavier because it should be 3.24 times thicker and the area is 3.24 times larger. That is probably why definition is getting poor (too heavy).

It's entirely about extended frequency response, which only matters when you're using the driver at high frequencies as in a musical instrument amp. It's not an issue for sub-bass drivers in multi-way audio playback systems.

In spite of the name, bass guitars generate harmonics out to 5 kHz which is well into tweeter territory. Punch can be an 800 Hz phenomenon.

No matter what you do with the motor, larger diameter speakers without a phase plug have reduced power response (total power output in a sphere at a given frequency) at high frequencies the problem being that their radiating diameter is large compared to the wave lengths being reproduced so the sound from two points can be out of phase and cancel or at least add incoherently for less total output. For instance, a hypothetical 18" diameter cone (maybe a 21" driver) would have the 90 degree off-axis output 180 degrees out of phase at 376 Hz (sound travels at 1130 feet/second in air; 1130/2/1.5 = 376)

The force generated by the motor is a product of the magnetic field strength
(B), length of wire in the magnetic gap (L), and current flowing through the wire. Current is voltage divided by impedance. Voltage is fixed - it's just the instantaneous musical signal.

There are limits to how strong you can make the magnetic field especially given money, space, and or weight budgets - 40 pounds of motor isn't cheap or small so to overcome more moving mass (Mms) means a longer wire (L). More wire means more resistance which reduces current at all frequencies. You can increase the voice coil wire diameter for less resistance to compensate at the expense of weight and a wider magnetic gap which in turn means less field strength. Wire coils form inductors, and more turns mean more inductance. Inductor impedance is proportional to frequency (2 pi f * L) so current is less at high frequencies with the net effect being a heavy speaker cone + strong motor has less high frequency output.

On-axis this is compensated some by the driver coupling more efficiently to the air as its diameter becomes large relative to the wave length produced.

Cross the sub-woofer over at 40-120Hz and it's not an issue. With a good motor design you can even mate a 15" mid-bass to a wave guide at 1Khz.

161 ten inch woofers have met their match!

http://www.ohgizmo.com/2006/03/06/the-biggest-subwoofer-ever-made/

Kijanki: Membrane of 18" speaker should be 10.5 times heavier because it should be 3.24 times thicker and the area is 3.24 times larger. That is probably why definition is getting poor (too heavy).

Drew_eckhardt: It's entirely about extended frequency response, which only matters when you're using the driver at high frequencies as in a musical instrument amp. It's not an issue for sub-bass drivers in multi-way audio playback systems.

Drew -- doesn't your response overlook bass damping, inertia of the cone and the other parts of the moving assembly, and the ability of the cone to stop quickly when the input signal stops? All of which I think support what Kijanki was saying.

Regards,
-- Al

Interesting debate. IMHO, there is no question that a larger well built subwoofer will sound better than than ten small cheap ones sharing a box. The issue is that the single large woofer may cost up to $2K! Most high quality 15" subs are expensive and most will use 3 or 4 inch voice coils - not your regular 1 inch VC found in most WAF friendly speakers. This all makes the amplifiers tough job as easy as possible which is what it is all about ....effortless clean dynamic sound with little or no compression is generally why a single large driver matched to an amplifier works well.

I do agree that 10 inch woofers with a whizzer cone tend to work well for a bass player (as in Zu) because there is a slap sound to the bass which is up around 3 to 5 K HZ. But this is not a valid reason to say that a 10 inch for a subwoofer is ideal. Certainly a 10" sub is likely far better than a 6 inch but likewise a 15" will be a lot better than a 10" (assuming good quality in both drivers).

IMHO, ideal is a super big sealed box with low Q (0.5 or so) and a large woofer. The very large woofer and super big box allow for the very poor efficiency of a low Q design.

the ability of the cone to stop quickly when the input signal stops?

That would be system Q or damping. An overdamped design would be extremely inefficient (low SPL output at 20 Hz) with a small woofer in a small box.

Compare a WAF friendly product with an ugly DIY brute. (Source HT Shack subwoofer tests)

Both probably sound equally as good but the brute is going to play a whole lot louder cleanly and effortlessly.

Shadorne - I wasn't thinking of slap and 5kHz when I mentioned 10" woofer's bass definition - for that bass enclosures have tweeters. I was thinking of low frequencies. 10" woofer arrays have better controlled/damped (shorter) bass while 18" woofers tend to produce "woolly" bass. The question is what is cheaper - 18" woofer or 3 x 10" woofers (to obtain the same surface area).

>Drew -- doesn't your response overlook bass damping, inertia of the cone and the other parts of the moving assembly, and the ability of the cone to stop quickly when the input signal stops? All of which I think support what Kijanki was saying.

Bass damping is a separate issue which also isn't related to driver size.

It's determined entirely by the transfer function.

How you get to a given Q (the ratio of stored to dissipated energy) isn't relevant to decay. Even convolving the input to a sealed or open baffle enclosure with a Linkwitz-Transform or shelving low-pass filters works (although with a small box the distortion from air-spring non linearities and power required make a large box more desirable).

Resonant devices (ports and passive radiators) rely on stored energy and may cause audible problems when within the musical power spectrum, but work fine to gain infrasonic extension.

Stored energy in the room is a much bigger problem than in sub-woofers built for flat response, with decay and the resulting amplitude response being very frequency dependant.

The relative significance of time and amplitude aberations is not well understood here. Stimulating fewer room resonances through directional bass works well (this implies dipoles which are dumping most of their power into an acoustic short circuit). Equalizing for flat steady state amplitude response seems to work. Sub-woofers at a null or two sub-woofers centered on the null work according to literature. Catch-throw arrays look real interesting.

Two sets of two (mounted push-pull to cancel even order harmonics) dipole sub-woofers equalized to a second order roll-off with poles at 20Hz (Q=.5) did produce the most natural bass I've heard from any room-loud speaker system in spite of having only 13x19x8' to work with and no acoustic treatments.

>Shadorne - I wasn't thinking of slap and 5kHz when I mentioned 10" woofer's bass definition - for that bass enclosures have tweeters. I was thinking of low frequencies. 10" woofer arrays have better controlled/damped (shorter) bass while 18" woofers tend to produce "woolly" bass. The question is what is cheaper - 18" woofer or 3 x 10" woofers (to obtain the same surface area).

You can't extrapolate from instrument speakers driven with a wide bandwidth signal (even with a tweeter you may be running the main driver out to 2Khz) that are engineered to break up in a pleasing way to hi-fi drivers run in a narrow bandwidth (not even out to 200Hz) containing entirely wave lengths that are much larger than the speaker that are supposed to be true to whatever signal you're feeding them.

Just because a driver is large doesn't mean it will sound less good. Remember it is trying to reproduce such devices as ten foot bass drums and long stringed instruments. In order for ten inch drivers to play deeply enough they will require much more equalization and power than an eighteen inch model. doubling or tripling drivers does lower their f3 point. It just decreases their distortion and increases power handling and output.

This is the best lecture series I have ever had, and I have attended a few to get a Ph.D that made me prematurely bald in the process.
I am no student of wave physics. I am only interested in fiddling with mammalian genes. But I wanted to learn more about the components I listen to and what affects their output. I got a treat.

Thanks guys. And I mean that.

Shadorne: ... That would be system Q or damping... An overdamped design would be extremely inefficient (low SPL output at 20 Hz) with a small woofer in a small box .... IMHO, ideal is a super big sealed box with low Q (0.5 or so) and a large woofer. The very large woofer and super big box allow for the very poor efficiency of a low Q design.... The issue is that the single large woofer may cost up to $2K!

Drew_eckhardt: Bass damping is a separate issue which also isn't related to driver size. It's determined entirely by the transfer function. How you get to a given Q (the ratio of stored to dissipated energy) isn't relevant to decay.

I don't doubt that what you are both saying is correct, but it seems counter-intuitive to me. It seems to me that to provide accurate "piston-like" motion, with minimal flexing of the cone, a larger driver would have to be thicker and heavier (as Kijanki stated), especially if we want to limit the cost increase associated with it.

It seems to me that a bigger, thicker, heavier cone would have reduced "compliance," if that is the right term, and therefore require a greater degree of damping than a smaller, lighter cone. Why would bass damping be independent of this?

Putting it another way, couldn't the smaller, lighter, more compliant driver get away with a higher-Q enclosure, which would partially offset its limitations in low frequency extension and volume?

Dogmatix -- Although your kind acknowledgement is more relevant to some of the other contributors to this thread than to mine, let me say that it's nice to see such words here.

Regards,
-- Al

It seems to me that a bigger, thicker, heavier cone would have reduced "compliance," if that is the right term, and therefore require a greater degree of damping than a smaller, lighter cone. Why would bass damping be independent of this?

Good point. It is actually quite complicated because designers can also make choices about voice coil diameter, magnet size, VC length and mag gap length etc - to compensate for added cone weight.

However, simply put - the big advantage that a large woofer has over a small one is simply that it moves much less for a given output. Smaller long throw cones with long coil in short mag gap (large Xmax) tend to be less well controlled than larger short throw cones (short coil large mag gap). Another issue is heat - small long voice coils have more trouble getting rid of heat and the amp loses control (as impedance rises). Wiring many small woofers together is also going to dilute the "control" that the amplifier exerts over each woofer.

Shadorne - I was thinking of three 10" woofers versus one 18" woofer (same area).

>It seems to me that a bigger, thicker, heavier cone would have reduced "compliance," if that is the right term, and therefore require a greater degree of damping than a smaller, lighter cone.

By the time you've built a speaker with a given pair of high-pass poles it doesn't matter whether the driver in question is a 26 gram 8" mid-bass, 166 gram 12" sub-woofer, something smaller, or something bigger.

Most of the damping is electrical. For instance, the Peerless 830452 bass drivers in my Orions have an electrical Q of .22, mechanical Qms of 3.90, and total Qts of .21 (those drop a bit in the H-frames due to the mass of the air).

When you make the motor stronger to maintain efficiency in spite of the heavy cone and stiff air spring, it's stronger when braking too.

>Putting it another way, couldn't the smaller, lighter, more compliant driver get away with a higher-Q enclosure, which would partially offset its limitations in low frequency extension and volume?

No. Qs higher than .707 produce a pass-band peak which is audible.

While a reasonable psycho-acoustic trick to give the impression of missing octaves for tiny speakers you don't want it in sub-woofers where tightly spaced equal loudness curves make a small peak especially noticeable. High-Q resonances are what give box store sub-woofers that anoying one-note boom-boom quality.

Isn't Q the dude from Star Trek w/ God-like powers?

I don't understand 1/2 of what you guys are saying. Alls I know is, for home theater I want 2 passive cabinents w/ 2 x 15" JBL woofers in each driven by 2 mono 1000w Boulder amps. For stereo music, I'll take a pair of 12" RELs.

Or, I'll take either of the subs (I think its the gigantic one that comes w/ extenal amp & XOver) from Wilson Audio. With Wilson, I wouldn't need more than one sub.

>Shadorne - I was thinking of three 10" woofers versus one 18" woofer (same area).

That's a bad comparison, because the bigger driver can have more excursion. The bigger surround can move farther, bigger basket accomodates a bigger spider which can move farther, etc.

You'd need 6 long-throw 10" drivers (DPL10 with 333 cm^2 Sd and 19mm xmax) to match one healthy 18" driver (Maelstrom 18 with 1182 cm^2 Sd and 33mm amax).

>You'd need 6 long-throw 10" drivers (DPL10 with 333 cm^2 Sd and 19mm xmax) to match one healthy 18" driver (Maelstrom 18 with 1182 cm^2 Sd and 33mm amax).

It's probably a bad specific example (the DPL is a high-Q driver appropriate for dipoles and infinite baffles) but there just aren't a lot of high-quality 10" drivers out there.

Drew - Thanks. I forgot about xmax.

Isn't Q the dude from Star Trek w/ God-like powers?

Maybe, but he was also the guy who created James Bond's gadgets. :)

Shadorne & Drew -- Thanks! I guess we've established, at the very least, that there's a lot more to it all than just WAF and marketing.

Regards,
-- Al

I'd add that long throw tends to rely on long coils and you get less driver control. The relationship between back EMF and inductance is a factor. Long throw designs of any size (even the TC sounds monster drivers) tend to have less control ("braking" if you will or the ability to stop on a dime and change direction).

I agree with Drew Q is very important. Think of damping like your "storm door" - a Q of around 0.3 - 0.5 will be just like you storm door closing - it is extremely controlled and you get absolutely NOTHING other than the input signal coming out (no extra oscillations and no resonances as everything is damped) Like the storm door it is very inefficient (lots of energy to get little output). If you remove the piston from the storm then it wil flap around inteh wind or oscillate freely - this would be like having a q of 1.1 or higher. A Q of of .7 is flat and a good compromise between a good response and decent SPL output but ultimately for high quality you probably want something highly dampedwith a Q lower than that and in order for this to work at reasonable SPL you meed very large drivers or the SPL is to weak.