size of the driver

Avs9 writes:
>But nowdays I am seing 6 inch drivers stated as "bass". Just curious how well those perform

They provide enough mid-bass output to meet a woofer for serious listening or a sub-woofer at polite but not realistic levels suitable for hold and elevator music.

>or in another words what is the secret behind those if they really can perform at the same level as the 12 inch ones?

They don't.

Output at the maximum linear excursion into full space for various representative drivers at 3 feet is as follows at 120, 80, 40, and 20Hz. Many drivers have less excursion and lower output. Subtract 3-5dB for living room dimensions and more for a larger space for the SPL at your listening position

You can add 6dB for a floor mounted woofer (as in many 3-ways), 6dB if there are a pair of bass drivers, and 6dB at the cross-over point to a sub-woofer.

Size Driver Sd (cm^2) x xmax (mm) 120Hz 80Hz 40Hz 20Hz
4 1/2" Seas W12CY001 50 x 3 89dB 82dB 70dB 58dB
5 1/4" Peerless 830873 88 x 3.5 95dB 88dB 76dB 64dB
6 1/4" Seas L16RN-SL 104 x 6 101dB 94dB 82dB 70dB
7" Seas W18EX001 126 x 5 102dB 95dB 83dB 71dB
8.5" Seas W22EX001 220 x 5 106dB 99dB 87dB 75dB
10" Peerless 830452 352 x 12.5 118dB 111dB 99dB 87dB
12" Peerless 830500 483 x 12.5 121dB 114dB 102dB 90dB

As a frame of reference I like my jazz at less than live 85dBC average levels which makes for peaks on good recordings with 20dB of dynamic range of 105-107dB at the speakers. The scale is logarithmic, so at 80Hz that's more than 10X what you can squeeze out of a 6" driver and 100X at 40Hz.

>And another question which I guess is too simple and too basic around here that's why I couldn't find some point to point answer - when we speak about sensitivity - would that be a true statement to say that higher level (say 92-95 db) will allow to extract "fuller" sound spectr at a lower level of volume?

Not with equal frequency response although design considerations mean you might get a boost in higher frequency bass output so it sounds that way.

Efficiency is at best inversely proportional to the cube of the low frequency cut-off and proportional to the size of the enclosure. To make a speaker play one octave lower using the same bass alignment (sealed, ported, band-pass) it needs to be 8X as big to maintain the same efficiency; or conversely at a given box size a speaker with one octave less bass extension can be 9dB more efficient (or 3dB for 1/3 octave).

When people build speakers with limited bass extension they often boost the output before the roll-off starts so there's the illusion of low bass and since higher frequencies have a lower threshold of hearing you can notice the extra bass at listening levels where you couldn't hear the real thing since our threshold of hearing and equal loudness curves require higher SPLs at lower frequencies.

Small and efficient speakers can't have low bass but are often built this way although that doesn't mean all efficient speakers are.

04-27-12
Responses
04-28-12: Jmcgrogan2
Smaller bass drivers have gained in popularity for two reasons.
>B) they may not go quite as deep, but the bass will be tighter.

Apart from physical limitations on the displacement needed to achieve a given SPL driver size has no bearing on bass quality.

>04-28-12: Sounds_real_audio
Boy you are old. Listening to music in the 70s. Smaller drivers are trendy because they go fast.

Driver size has nothing to do with "fast" or "slow". Twice the motor strength will accelerate double the mass as a smaller motor/mass combination whether we're talking about vehicles or drivers.

Smaller drivers are trendy because they're less expensive (which allows for bigger profits) and not as offensive to women who are more likely to contribute to the family pot and have a say in how it's spent than in the 1970s and before.

People retiring their tube gear in favor of transistors have also made smaller and necessarily less efficient enclosures practical. With 80 transistor Watts you can drive an enclosure with the same low frequency cut-off to the same SPL you could a speaker 8X the size with just 10 tube Watts.

>Bigger drivers can still have that old school sound. Bigger drivers move more air but tend not to be as accurate and have trouble keeping up with a 5" midrange so you can loose cohesiveness.

Nope.

04-28-12: Ngjockey
>Although bass extension is generally less with smaller drivers, some of the dynamics can be equivalent or even superior with multiple drivers.

Right. Looking at the table I provided you'll note that with 10 6" drivers you can match the headroom for dynamic peaks you get with a single 12" driver. Where you only get 2-4 6" drivers the smaller drivers can fall short.

>04-28-12: Johnnyb53
>More or less true, but bear in mind that a 12" woofer has *at least* twice the mass of a 9.5" woofer, and perhaps more because it will probably have a thicker cone to counteract breakup. All things being equal (which they're not), a 12" woofer has 3.5 times the mass of a 6.5" woofer, so by your reckoning it would need a magnet 3.5x as powerful.

The 12" driver's excursion and acceleration requirements are also scaled down to create a given frequency + SPL sound wave compared to the 6" by the ratio of their surface areas. Using the Peerless XLS12 and Seas L16RN-SL as examples it's less than 1/4 the distance and acceleration (483 cm^2 for the Peerless XLS 12 vs. 104 cm^2).

I don't have the magnet strength on the Peerless; although if you compare the Seas L26RO4Y 10" driver (BL 18, 1.1 Tesla in the gap, mms 173g, Sd 363 cm^2) to the L16RN-SL (BL 6.2, .88 Tesla, mms 14.8g, Sd 104 cm^2) with force / mass * Sd to make a meaningful comparison the big driver comes out ahead at 39.93 vs 37.44 for the small.

I could also point out that the smaller driver probably has a higher resonance which in turn means more group delay from the inherent minimum phase response of a driver+enclosure combination although all this would still remain irrelevant for purposes other than internet arguments based on inapplicable science.

Your brain needs a lot more than a fraction of a cycle to pick up a sound and assign direction, and where transients are of interest they split into low and high frequency components which are sent to the tweeter courtesy the cross-over network.

>Maybe, maybe not. However, speed aside, the the large driver still has a disadvantage in driver blending because its dispersion pattern turns into a beam at a lower frequency. A 12" cone starts beaming at 1100 Hz; a 6.5" at about 2K Hz. Guess which is easier to cross over to a tweeter at 2K Hz while maintaining uniform dispersion?

Those are arbitrary numbers (it's a continuum - you could say that the 12" driver is 6dB down at 45 degrees off axis by 1400Hz, or -3dB by 900Hz) although the 12" would work better provided that you didn't do anything contraindicated by decades of subjective listening impressions and research.

You can put the tweeter on a wave guide so the directivity matches the 12" driver at the cross-over point. This produces much smoother spectra in the side-wall first reflections which contribute to perceived timbre than the 6.5" driver with narrowing dispersion crossing to a 1" tweeter on a non-waveguide baffle which has near uniform radiation across its front hemisphere.

You can use a more conventional 3-way design with a relatively small cone or dome midrange between woofer and tweeter with a cross-over to the midrange at a few hundred hertz. This produces more nautral sounding side-wall/front-wall/ceiling reflections with improved vertical polars coming from reduced driver spacing compared to the 6.5" 2-way.

You can use a mid-tweeter that accomodates a very low cross-over point. For instance the 1.6" Aura "full range" driver does well at the sort of moderate SPLs a 6" mid-bass limits you to with a 1KHz cross-over (the big voice coil does roll-off at high frequencies, although most of us can't hear that and where we can it can be compensated for in an active cross-over).

Of course traditional 2-way cone and dome speakers aren't worth considering where your first priority is sound quality especially where you do not limit yourself to simple music at background listening levels. They vary from each other in how their mediocrity comes out (inaccurate timbre, low SPL capability, limited bass extension) but as a listener you're better off skipping the genre and building or buying something excellent. OTOH as a speaker manufacturer this is OK because people buy based on appearance and price and as a competent cabinet maker you can make building such speakers a full-time job. Cabinet/furniture makers with more refined ears do use low cross-over points with extra-beefy tweeters like the Seas Millenium for better directivity matches at the cross-over point so the results needn't as bad as they can be.

There's a lot of latitude in how you get to "excellent" with the many possibilities producing sound more similar than different. You can use acoustically small cones and domes on acoustically small baffles with uniformly broad dispersion like the B&W Nautilus or Linkwitz Pluto (still somewhat dynamically limited). Wave guides work well to bring the high frequency dispersion from acoustically small drivers in line with the lower midrange for moderate dispersion as in the Revel Salon 2 or more directivity like the Gedlee designs or Danley Synergy Horns. Acoustically small dipoles work great where cancellation from the sonic short circuit between front and rear waves brings directivity at lower frequencies in line with higher for each driver like John Krevosky's NaO Note or Siegfried Linkwitz's Orion.

FWIW, in 2004 Sean Olive produced a pair of numerical definitions for "excellent" which correlate exceedingly well with blind subjective speaker rankings. Monotonic off-axis response curves and bass extension are significant where physics dictate conventional 2-way cone and dome speakers lack at least one.

Any one interested in sound reproduction owes it to themselves to read _Sound Reproduction: Loudspeakers and Rooms_ by Floyd Toole where chapter 20 (Closing the Loop: Predicting Listener Preferences from Measurements) is especially relevant. While not "light reading" at 500 pages it's a lot more digestible and affordable than the decades of JAES and other papers it summarizes.

For more conventional designs on more finite budgets you can do better with more less expensive drivers than fewer pricier ones, especially where the speaker maker adjusts the cross-over to compensate for the manufacturing variations (Dunlavy did this) you get at lower price points since polar response has a lot more to do with how close you get to "excellent" than other metrics like on-axis response flatness and stored energy. It's nice to have a scientific explanation for what you hear or suggestion on what to audition next.

If you want a thin spouse-friendly cabinet at the same time you can do it with a side-mounted woofer or W-frame dipole.

(You can tell I'm a bit cranky - I spent my day periodically staring at the boards which will become my next two pairs of cabinets contemplating which grain and figure combinations will look best where instead of making sawdust).

04-29-12: Sounds_real_audio
>If 12" drivers were as fast and accurate as 4" drivers we wouldn't need any midrange drivers.

It's a function of system design. You're not going to beat a 12" midrange paired with a like sized wave guide for sound quality although the 30" high x 15" wide "stand mounted monitor" combining the two may be hard to get past your spouse.

Your brain hears timbre as a combination of the direct sound and what it identifies as reflections with the later coming off the speaker at extreme angles (> 70 degrees for the side walls depending on toe-in).

So to get a natural sound you need drivers to have similar behavior both on-axis and at those extreme angles.

Drivers also become increasingly directional as their dimensions grow large compared to sound wavelengths. By 900Hz a 12" driver has lost 3dB 45 degrees off-axis and by 1400Hz it's 6dB down.

At those frequencies a 1" tweeter on a flat baffle is omnidirectional.

The two won't match like the waveguide does. A 12cm cone or 5cm dome will match on a flat narrow baffle.

>04-29-12: Bombaywalla

> You can add 6dB for a floor mounted woofer (as in many 3-ways), 6dB if there are a pair of bass drivers, and 6dB at the cross-over point to a sub-woofer....

>>Drew, why are you adding 6dB? It's power output, you should be adding 3dB in each case.

That's the sound increase you get when you run the drivers out to their physical limits although it'll take twice the power to get there as with a single driver. With the example 5.25" driver I listed 2.83V (1W into 8 Ohms or 2W into 4) will get you to xmax at 80Hz with one driver or a pair in parallel with power around 0.25W for a single driver and 0.5W for a pair (impedance increases as you approach resonance so power drops).

>04-30-12: Unsound
Some have argued that larger drivers will have greater energy storage, and correspondingly slower energy release.

They don't store energy and ring longer. Ringing at resonance is purely a function of driver + enclosure Q.

04-29-12: Johnnyb53
>04-29-12: Tamule1
>real bass comes from moving a large surface area gently -not a small surface violently . 6.5" is not a woofer size IMO

"Violent" isn't a problem until you reach the linear or physical limits which geometry dictates you do when using such small drivers.

>And you base this opinion on what?

I draw upon personal experience with speakers including transmission lines built with similarly small drivers (I've heard various examples and owned Definitive BP8s when I was young, naive, and less proficient with power tools ) and identify the underlying physics which cause such issues. They get strained at moderate listening levels when the source material contains bass, where that's low bass you get doubling where you hear tones at twice the fundamental frequency due to distortion which although inaccurate isn't too bad, and the IM distortion happening to midrange frequencies is offensive.

These are some of the same reasons "audiophile" speaker demos are done with female vocalists and not orchestral music.

>What then shall we call all those 5.25" and 6.5" drivers that provide real bass extension down to 25-30 Hz?

Having more measurable bass extension at low to moderate listening levels than stand mounted monitors with similar drivers, good marketing, or fiction depending on your perspective.

>You also left out the part about how the back wave is managed, which accounts for why the Atlantic Technology AT-1 extends usable bass to 29 Hz from a pair of 5-1/4" woofers.

Assuming the 88cm^2 Sd and 3.5mm xmax of the 5.25" drivers I used in my example with driver output attenuated per the Stereophile measurements they'd reach their linear limits with program material calling for 94dB 1 meter from the speaker at 60Hz (one driver will net 83dB, two 89db, and the Stereophile nearfield measurement has the drivers -5dB down with the remainder coming from the port/transmission line hybriddrivers and 89dB (one will net 71dB, two 77, and they're 12dB down) at 30Hz.

As stated I like my jazz at a moderate less-than-live 85dBC SPL average which can yield peaks 105-107dB 3 feet from a speaker.

Pulling _Take Five_ from _Time Out_ off the CD and feeding the two channels through second order IIR Butterworth low-pass filters at 60Hz using GNU Octave I find right channel peaks at -10dB below the full-range peaks; or 95-97dB SPL.

The arithmetic explains why such speakers don't work well - up to 9dB shy is off by a factor of 8.

This is also an optimistic simplification. Distortion product SPL is more a function of total driver displacement although the fundamental output is dropping for a given excursion at lower frequencies so you might find only half the total linear excursion is clean.

>Next thing we'll need a disclaimer:
"No violence was committed in the generation of these low frequencies."

I'd like something quantitative such as output levels and distortion numbers for given input frequency + level combinations like independent testers are starting to do with sub-woofers plus a practical frame of reference: In our small and large listening rooms, we could average xx and yy dBC SPL with Sir Solti conducting the Chicago Symphony playing Beethoven 9. Elevator music averages xxdB, the typical middle aged male gets to yydB when his spouse is home, and the average audiophile prefers zzdB in a darkened room with a tumbler of single malt.

05-01-12: Waj4all
>I wonder as to whether the experts in this thread would have a theory as to why the double-stacking of small speakers causes a subjective increase in the robustness of lower-midrange tones? This has been my experience, and I've seen where others have spoken of this phenomenon.

Wave lengths are longer at lower frequencies so the path length differences in the direct sound and reflections result in a lesser phase shift compared to the higher frequencies so the lower frequencies sum closer to +6dB compared a single speaker while the higher frequencies have lesser gains and even some comb filtering.

>And similarly, is it a fact that large mid-woofers are intrinsically more robust or warm at lower-mids than small-coned designs, perhaps, because of the same surface-area effect?

No.