Small drivers vs big drivers

Forgot to include this: One area in which a vertical array of multiple small woofers has superior room interaction relative to a single large woofer is in the floor-bounce dip. The multiple small woofers will have their floor-bounce dips at different frequencies and so they will tend to fill in for one another. The single large woofer won’t get that benefit, though its dip will be smeared out a bit compared to a single small woofer, and therefore will be slightly less deep. The ear/brain system is fairly forgiving of the floor bounce dip because it occurs naturally all the time, but minimizing it is still beneficial.

Duke

Kosst, thank you for your reply. You are absolutely correct that I was not clear about what I meant by "good radiation pattern control".

First, I like for the pattern to be uniform over as much of the spectrum as is reasonably feasible, at least in the horizontal plane. Second, I would like for the pattern to be fairly narrow - say, 90 degrees wide (45 degrees on either side of the centerline) over as much of the spectrum as is reasonably feasible, at least in the horizontal plane. These characteristics tend to do two things: Give us a spectrally-correct reverberant field, and minimize detrimental early reflections. They also give us a very wide sweet spot with proper set up.

The midwoofer diameter usually sets the lower limit on radiation pattern control in the horizontal plane. Ideally we’d like to have the above-described "good pattern control" down to about 700 Hz, but that’s usually not practical. With a 12" midwoofer we can get down to about 1.4 kHz, which is definitely low enough to be a worthwhile improvement in my experience.

The idea behind all of this is to minimize detrimental room interactions by not causing them in the first place, and then to encourage beneficial room interactions. I happen to think this is something that matters a lot, and obviously most designers give higher priority to other considerations.

There are plenty of prosound drivers in the 10-15 inch range that perform well at these higher crossover points, but in turn they usually do not go down as low as most home audio woofers. So there is some compromise involved (in addition to the large enclosures required).

Some of these prosound woofers have well-behaved cone breakup, and then their accordion surrounds are generally superior to half-roll rubber surrounds from a damping standpoint. The downside is the stiffer accordion surrounds impose a higher resonant frequency.

The detriment from cone breakup is twofold: Peaks in the frequency response, and a slight smearing of arrival times from the surface of the cone. In many cases the frequency response peaks can be tamed via the crossover, leaving only a small arrival-time smear. A single small ultra-rigid cone is theoretically superior in this regard, of course. But TWO or more small ultra-rigid cones will often have WORSE arrival-time smear than a single large cone! So in this area an array of very expensive small cones is not necessarily superior to one big cone.

Instinctively people expect big woofers to be "slow". The 12" woofer I mentioned a couple of posts up has a motor-strength-to-moving-mass ratio almost TWICE that of the famously "fast" 5" Scan-Speak Revelator. So these prosound woofers give up nothing in that regard.

As a ballpark rule of thumb, a driver often has around 1 dB of thermal compression (or more precisely thermal modulation) at about 1/10th its RMS rated power. I like to have enough thermal headroom that the peaks are never going to be rounded off. The 12" woofer in my example above has about 1 dB of thermal compression at 112 dB (at 1 meter), which translates to somewhere around 100 dB peaks at the listening position once we factor in the other speaker + room reflections. This is 10 dB more thermal headroom than three 7" Scan-Speak Revelators. But the three 7" Revelators will go over half an octave deeper, so that’s something we trade off with the prosound woofers.

I guess it boils down to what problems one thinks are most in need of solving. I readily admit to being in the minority among speaker designers in that area.

Duke

Kosst: "I hate to break it to you, but you’re wrong about radiation patterns."

That’s possible. I’m not infallible.

Would you mind pointing out exactly what I said wrong about radiation patterns? I think it’s fair for me to ask that so I can take another look at whatever it was, especially given your tone of condescending certainty.

Thanks.

Duke

Kosst, of course we can compare arrays of smaller drivers vs large drivers.

"Array" is a rather open-ended term. How big is your array? Line array? J-array? Splayed array?

Arrays can get pretty big and pretty sophisticated.

So let’s do an actual apples-to-apples comparison.

Each of us picks out about $300 worth of drivers for their hypothetical speaker. You specify the shape of your array. Then let’s look at thermal and mechanical limits, radiation patterns, and bandwidth.

I’m picking a $210 woofer (Eminence Kappalite 3012LF), a $45 compression driver (Celestion CDX1-1446), and a $14 horn (Dayton Audio H6512), Parts Express retail prices. That comes to $269. These are all components that I actually use.

You pick your ballpark $300 worth of array drivers, tell me how they arrayed, and let’s take a look at the thermal and mechanical limits, radiation patterns, and bandwidths. I have a modeling program that can model radiation patterns fairly accurately, "Enclosure Shop" by LinearX. I will post my analysis of how your array would perform, and of how my giant driver two-way would perform. You are of course invited to do your own analysis.

Let’s get specific. Maybe you are right, maybe your array will be better across the board. Let’s go apples-to-apples and find out.

Duke

Kosst, I think you are resorting to straw-man arguments; that is, putting words into the mouths of those you disagree with in order to make them appear foolish.

I design speakers having what you would probably call "giant drivers".

The primary reason we use them is for radiation pattern control, to minimize detrimental early reflections and create a spectrally-correct reverberant field.

One secondary benefit is improved dynamic contrast. Our giant drivers have negligible thermal compression at home audio SPL’s.

Another benefit is compatibility with a wider range of amplifiers.

Another benefit is a larger sweet spot with proper set-up.

Like just about everything else in audio, driver size is a juggling of tradeoffs.

Duke

Yes, excursion distance before bottoming out is another factor to be taken into consideration.

This is whole thread shows why I find the Raidho (and similar) philosophy totally unconvincing.

mzkmxcz wrote: "Soundstage is the off-axis of the speaker."

Well, I have a somewhat different opinion:

A wider radiation pattern results in early sidewall reflections which increase the apparent image width. This is usually judged to be a pleasing effect (according to Toole), but it is not without its downsides.

First, early reflections are more likely to impose colorations and/or degrade clarity.

Second, early reflections tell the ear/brain system that you’re in a small room, and this can constrain soundstage depth and the sense of being immersed in the acoustic space of the recording.

Spectrally-correct late reflections are generally beneficial, enhancing timbre and a sense of immersion without degrading clarity or imposing colorations.

A fairly narrow but well-controlled (i.e. uniform over most of the spectrum) radiation pattern can result in more precise imaging and a deeper soundstage along with better clarity by minimizing early reflections, and if you want a wider soundstage too, move ’em a bit further apart.

Duke

dealer/manufacturer

It's not just a question of whether a 7" driver can produce 20Hz, it's surely a question of at what level.

BTW, 3 x 7" = approximate surface area of 1 x 12" driver.

To make the situation more complicated, some speakers have small drivers but there are many of them. Can many small drivers compensate for the size limitation

I don't know which specs determine a wide sound stage

@shadorne raises an important point. During heavy excursions of its cone, a woofers voice coil heats up, changing the drivers electrical characteristics, and therefore its sound. One of the functions of the Servo-Feedback circuit in Rythmik subs is electronic compensation for the change in the woofers electrical characteristics due to voice coil temperature. No non-feedback woofer or sub is capable of that feat, one of the reasons for the uniquely clean (low distortion) sound of Rythmik subs. Sound like a sales pitch? Too bad ;-) .

The Servo-Feedback circuit also minimizes differences between the 12", 15", and 18" Rythmik woofers. Their sound characteristics are identical, the difference between them being in their maximum SPL capability. Rythmik also offers subs with 8" woofers, for those clinging to the idea that smaller woofers are "faster" than larger ones.

The ability to create a wide/big soundstage and the ability to reproduce low frequencies are two completely different matters (except that the sound of a large recording venue---cathedrals, churches, theaters---are of very, very low frequencies).

The size of the drivers in a loudspeaker, assuming you are talking about cone/dynamic drivers, has nothing to do with the speakers ability to create a wide/big soundstage. The size of a woofer, on the other hand, is very much related to how much air it can move at low frequencies. But size isn't everything, right girls? ;-)