The Incredible Shrinking Woofer

[JohnnyB]

When I got into audio 40 years ago, the speaker most of us lusted after was a high quality 12" 3-way "oversized bookshelf." That is, a cabinet about 25"h x 14"w x 12"d, finished in genuine oiled walnut veneer housing a 12" dia. woofer, a midrange usually around 4-6" dia. and a 2" or so tweeter. Let's call the oversized bookshelf enclosure the OSBS from here on. The good ones--JBL L100, Altec-Lansing 874A, AR 3a--were expensive at around $560/pair in 1972 or $2900 in today's money. Many of us who wanted 12" 3-ways either settled for cheap knock-offs or made do with a smaller-dimensioned 10"- or even 8" 2-way--just the woofer and the tweeter.

And yet, over time, 12" woofers were gave way to 10" woofers, and then 8", 6.5", and 5.25" or even less. Narrow floorstanders with two or even three 6.5" woofers are common now. Forty years ago 8" was considered an entry-level woofer. Today dual 8" drivers give you serious bass down into the low 20's.

How did that happen? Well, I'd say the first step that really got some traction was the Larger Advent Loudspeaker. Founder Henry Kloss and his team found that a 12" woofer displaces too much air to be managed by the OSBS.12-inchers need about twice that volume. He found that he got deeper bass from the OSBS with a smaller woofer, and could get as much displacement (which translates into "punch" or impact") by lengthening the cone excursion.

A 6" speaker with 1/2" excursion displaces as much air as a 12" with 1/16" excursion, which was typical of speakers of that era. To get that excursion, Kloss mounted a 10" diameter woofer in a 12" frame with a masonite spacer ring. He made a longer coil and magnetic gap to get the longer excursion, as well as a wider cone surround. When you subtract the spacer ring and the generous surround, the actual cone in the larger Advent was only about 7", and it made serious bass down to around 32 Hz. By contrast the JBL L100 was barely audible at 50 Hz.

There are several other advantages to a smaller cone woofer:

• Being smaller and lighter, the have better transient response, which means the bass driver is more responsive to the start and stop of signal. This makes the bass sound cleaner and more real.
  
• Being of smaller area, it's easier to control cone breakup with a small speaker than a large one. This reduces distortion at higher volume.
  
• The smaller the cone, the wider and more realistic the in-room dispersion. A speaker's dispersion narrows as the wavelength of the frequency approaches the diameter of the cone. A 12" woofer has about a 11" cone, meaning it is beaming its frequencies from 1200 Hz on up. a 6" cone doesn't start beaming until 2200 Hz, which makes it much easier to blend with a tweeter. The JBL 100 didn't cross to the tweeter until 6000 Hz, which means it beamed (i.e., had a room response suckout) spanning 2-1/2 octaves.
  
• The smaller woofer doesn't need a midrange driver, which lowers costs, eliminates a crossover network, and therefore provides a cleaner, more transparent sound.
  
• The smaller diameter woofer means the front panel can be much narrower, which improves dispersion and reduces reflections from the front baffle. This is what caused the OSBS to give way to tower speakers and mini-monitors.
  

To see what these developments have done to the price/performance ratio, the walnut veneer Advent was around $240/pair in 1972. It was considered the bargain of the decade and did in fact redefine what you could get for $200/pair. Yet that's $1240/pair in today's money. For $1250 today you can get this, which is better in every way except possibly for the last few notes in the bottom octave. Otherwise it bests the Advent in speed, clarity, transparency, room-filling dispersion, treble smoothness, detail, and extension, sensitivity (plays louder on fewer watts), dynamic range, maximum SPL, not to mention ease of placement and blend with room decor. If you shop around, for not much more you can get its bigger brother, the RX8, which adds a woofer and matches the Advent's bass extension while increasing dynamic range by 3 dB over the RX6. Here are the RX-6 and RX-8

Note another advantage this approach has to economy of scale: To get more bass, add another woofer and half a crossover. For the cabinet, the front baffles stay the same width and height. The manufacturer adjusts the size of the side walls to accommodate the need for more volume. Other manufacturers keep the width and depth the same while adjusting the height and bracing.

Everybody wins: the speakers are cleaner and more articulate, energize the room more uniformly, and cost less.

The level of finish is much higher too. Here's the front baffle of the original Advent with the grill removed. It looks like a garage project:

However, Advent was moving us in the right direction. The JBL L100 was $560/pair ($2800 in today's money) and the Advents bested them in almost every way at 40% of the price. Two pairs stacked were still 15-20% less and was one of the best sounding rigs available at the time regardless of price. They also started the trend to smaller, faster woofers that don't look as impressive but woof better.

[mathman]

What I lusted after and eventually got sometime around 85 right after I got my first credit card was this with it's 15 inch woofer. The bass player in me wanted the biggest woofer I could get. I had those speakers for over 20 years and loved them. They weren't top of the line but they sounded great to me! Now I have a 10 inch subwoofer that blows them away in the bass response. It is a different world these days.

[unfun75]

Realistic Mach Two!

The last great Radio Shack product.

[django49]

Good write-up.

Sorta like how my Mesa Mk series with 60 watts into one (Okay, 12") EV totally blew away my original Dual Showman with those 2 big 15" JBLs, I guess, despite those HUGE cabinets.

Still miss those big old Klipschorn corner speakers, but do NOT miss the size.

[JohnnyB]

Good write-up.

Sorta like how my Mesa Mk series with 60 watts into one (Okay, 12") EV totally blew away my original Dual Showman with those 2 big 15" JBLs, I guess, despite those HUGE cabinets.

Still miss those big old Klipschorn corner speakers, but do NOT miss the size.

The biggest casualty in downsizing the speakers is sensitivity. The Klipschorns make 105 dB from 1 meter away with 1 watt input. That's pretty screaming loud. Altec Voice of the Theaters have a similar sensitivity. Such speakers harken back to the days of mono (when you could fit one big speaker in the living room) and power it with a 10-15 w tube amp. Sensitive speakers have a certain ease and immediacy about them--they make a lot of sound from a very little input.

By the time we got to the AR3a and Advent loudspeakers, sensitivity had dropped to about 84 dB with 1w input at 1M. You'd need 128 watts to hit that same 105 dB that the Klipsches make at 1 watt. This is what prompted Bob Carver to come out with the Phase Linear 700 and then 400 power amps making 350 and 200 wpc respectively. OTOH, you could fit two Advents on bookshelves (if they were built-in wall units), and they extended easily down to 32 Hz where the Klipsches were gone by 40-50 Hz depending on the room.

Today's home audio speakers have a sensitivity somewhere in between--around 88-93 dB at 1w/1M. They are livelier than the old acoustic suspension designs. It's for the same reason your Mesa kicks such ass: big, clean power and much better driver design with more powerful magnets, bigger voice coils, more rigid frames, more compliant and higher excursion surrounds, and lighter yet stiffer cone materials. All these elements make for a more responsive speaker that is sensitive yet can handle a lot of power and play louder than the speakers from the '70s and '80s.

[gorch]

When it comes to speaker design, I have in mind that amp and speakers build a duo. So, when talking about speaker changes over the years, certainly improvements, amps may have changed and improved over time too. JohnnyB, did you make your examination with respect to the amps?

[hamerhead]

I still want this:

[JohnnyB]

Anybody remember this?

http://youtu.be/-DP89iMe0BY

Those speakers are the JBL Century L100's mentioned in the original post.

[ArnieZ]

Great historical perspective! I have some personal experience with much of this. I owned a double advent speaker system and a 250 watt/channel power amp to drive them. One of the best bottom ends I've experienced that didn't involve a sub. The above referenced JBL's were very efficient but had a fatiguing upper mid spike. The Advents eventually were replaced with the Dalquist dq 10's which ironically used the Advent woofer. Those were repalced with Thiel 04A's which was my entry into the small but mighty woofer. Ultimately replace with Definitive Tech BP10's and then I just stopped changing. The Definitives also use small long throw woofers and have a solid bottom, even without a sub. Next????

ArnieZ

[tomteriffic]

Had the double Advent rig back when and loved it. They got driven by a variety of stuff, but my fave was a NAD integrated that matched up nicely, despite its modest power rating. One my neighbors is a vintage hi-fi fan and has two pair of the Advents. But he's not really all that knowledgeable and I'm trying to work out a trade. At the studio where I worked in the '70's, the "home audio" reference speacers were the higher power-handling studio versions of the L-100's. They really were fatiguing, especially when you were in front of them all day. Going back to the Voice of the Theaters was a blessed relief.

Oddly enough, the front of my HT system these days is JBL, the Studio Series with 8" 3-ways on left and right and the matching center 2-way. They cross over farily low and have very good dispersion. And while some additional cabinet volume might help the low end, they're still honest down to a low E on the bass.

The surrounds (as well as the mains in the bedroom system) are the good ol' Athena B-1's. Best cheapo hi-fi tip I ever got from John. The laws of physics do impose some limits eventually, but these are some very satisfying 5" 2-ways. At the price ($100/pr when they were being closed out) they fill the bill nicely.

[LostArt]

I think a lot of it has to do with cabinet design.

I have altec 19's in my home studio along with a set of the modern jbl lsrXXX I forget the model but they are powered monitors.

IMHO you need to push air for bass and you do that with larger speakers. I have not heard a bass rig for performance that I liked that had small speakers

some of them are good for example phill jones but most lack and the lower priced stuff is just awful

[Mitch]

Thank God for psychoacoustics.

[JohnnyB]

ArnieZ: We're from the same audio era. I sold home audio my first year out of college. The first store had all the cool stuff including Advent, Dahlquist, Ohm, ESS, and Bose and JBL to get people in the door. Electronics included Pioneer, Kenwood, Marantz, Yamaha, Crown, and Accuphase. Being part of an old and venerable audio enterprise in SoCal, our store was on the itinerary when Saul Marantz made a tour to promote the Dahlquist DQ-10s. We also had the assumption that the DQ-10 used the Advent woofer, but Marantz told us that they were in fact different woofers with different designs, but with very similar appearance. He said that both the Advent and Dahlquist woofers were sourced from the same supplier and that they had to uniquely label each production run to make sure they didn't send Advent woofers to Dahlquist and vice versa. Since the Advent speaker predates the DQ-10 by a few years, I have no doubt that Marantz "borrowed" the idea of a 10" woofer in a 12" frame from Henry Kloss, but other things were different. That could include the magnet size and flux density, cone material, voice coil depth and winding, etc. To me the best proof is that the DQ-10 just didn't have the bass extension of the Advent. Probably the woofer enclosure wasn't large enough.

Anyway, what to follow the BP 10's with? There are lots of possibilities. One would be Def Tech's spiritual successor, the GoldenEar Triton 2 towers, or for $1K/pair less, the Triton 3. GoldenEar was founded by Sandy Gross, co-founder of Def Tech and Polk. The Triton towers have the advantage of built-in amps for the low woofers, giving strong, clean bass extension down into the 20's. Another interesting candidate with tiny woofers is the Atlantic Technology AT-1, which--through ingenious management of the woofers' backwave--manages to get usable bass down to 29 Hz from a pair of 5-1/2" woofers in a modest-sized column. Animated illustration here and comprehensive review here.

TomTerrific: The pro studio monitor version of the JBL L100 was the 4312.

You can see that it uses the same box and drivers but arranges them for vertical placement, whereas the L100's drivers and controls are situated for sideways (i.e., bookshelf) placement. And you're right about the L100/4312. With their boosted midrange and punchy bass, they made a good impression on rock and pop in demos, but were tiring to live with. The quickest way to show their shortcomings was to play some classical music through them, where the violins turned scratchy and screechy, whole parts of the orchestra receded to the back and it revealed how little true low bass these speakers had.

LostArt (AlPep): Altec 19s? Go Al !

My first stereo was an all-Altec rig and I became an Altec fanatic for the next several years. My wet dream speaker at the time was any form of the Voice of the Theater (VOTT). The 19 is a nicely finished home version of the VOTT. In my junior year of college our band bought a used pair of Altec 9845a's for our PA system. In between gigs they were hooked to my stereo in my dorm room. 40"w x 28"h x 24.5"d and 140 lbs. each.

For scale, those are 15" woofers in there. The better VOTTs had a more robust treble driver pushing the crossover frequency down to 500 Hz. A 15" driver starts beaming at about 1200 Hz, so this kept the dispersion and power response more uniform. They were amazing. We were listening to the Beatles' Please Please Me and noticed that John and Paul started to sing different lyrics on the 3rd verse and were singing while trying to suppress their laughter. All these VOTTs made around 101 dB on 1 watt input with a max. spl of 117 dB. This means a 15-25 wpc tube amp was plenty to light them up. My 9845 monitors were 16 ohm which would have made them even easier for tube amps with small output transformers. Tubes also smooth out the treble on those compression horn transducers.

And yes, the matching the enclosure to the bass drivers is critical to getting the best performance. For many years speaker manufacturers were sort of clueless about this. That's what made the Advent special: they kept that popular OSBS box but put in a smaller diameter woofer and got better bass. A couple of audio engineers, Thiele and Small, put together a guidebook of sorts that showed the relationship between driver size and box size, and whether the enclosure was sealed or ported. This work is called the Thiele-Small parameters. It was first published in Australia in 1961 but didn't become widely known until it was published stateside in the AES journal 10 years later. As previously mentioned, on average a 12" woofer needs to be in a 4.8 cu. ft. enclosure and the OSBS is exactly half that--not nearly big enough to get full bass extension from a 12-incher.

The 40+ years since have seen great advances in backwave management to get ever stronger and deeper bass from modest enclosures. The Atlantic Technology AT-1 above is a great example of this--29Hz extension from two 5-1/2" woofers in a 9"x13" x 42" tall compact tower.

[django49]

I have built a couple of the Thiele enclosures, using the EVM instructions for their 200 watt speaker. They are very precise measurements. It was a good learning experience.....VERY solidly built, great BIG sound. Also a good learning experience for how to fit tolex and grill cloth, as well as cab construction itself.

[HSB0531]

Bose pioneered small speakers.

Why didn't you mention the Bose 1-inch subwoofer.

Designed for mice in small cubicles.

[JohnnyB]

Bose pioneered small speakers.

You could rightfully say that Bose redefined the small speaker, but they didn't pioneer it. That distinction has to go to Acoustic Research and their first product, the AR-1 introduced in 1954. When the AR-1 came out, any other speaker with high fidelity aspirations was a huge floorstanding cabinet. AR originated what I call the OSBS with dimensions of 14" x 25" x 11"d. Compared to the Klipschorn, the Bozak Concert Grand, the Altec Voice of the Theater, or the 250-lb. JBL Hartsfield, the 50-lb. AR-1 was petite. (See this.) Acoustic Research was founded by Edgar Villchur and Henry Kloss. In 1957 Kloss left to found KLH, and then in 1968 went on to found Advent.

The Bose 901 isn't really much smaller than the OSBS. The 901 is about 21" x 12.75" x 12.75". The Bose had more room-filling ability because of the multiple angled drivers and required placement close to the back wall, which not only gave you the wall of sound but also provided boundary boost to the bass.

The reason I didn't mention Bose is because I was specifically talking about how the 12" woofers of the '60s and '70s--even in bookshelf units--were replaced over time with 10", 8", and now 5" to 6.5" woofers, often in multiples. And that was because the designers started using the Thiele-Small parameters to match the driver displacement to the cabinet size. Over time other benefits of doing this emerged, such as more uniform dispersion throughout the speaker's operating range, improved imaging because of the narrower front baffle afforded by small-diameter woofers, faster bass response, and attractive small-footprint columns that are easier to place in-room.

One thing I find interesting, however, is that the radiating area of nine 4" drivers (Bose 901) is exactly the same as that of a single 12" driver. The Bose 901 had a lot of impact through the 1970's, but not really much influence, as no one else of note made a direct/reflecting speaker comprised of multiple full-range drivers. Nor do they follow Bose's 11% direct/89% ratio of direct to reflected sound. I have a great pair of omnidirectionals but they have a 60/40 front/back radiation pattern.

Long spurned by the audiophile community, the Bose 901 seems to be regaining some respect recently, given the ongoing improvements and the relatively high value of a product long in production. See this review by the editor of ToneAudio, an online high end audio magazine and website. When the 901s came out in 1968, they were around $450/pair, or about $2800 in today's money. Since that was also the price of the top dogs at the time, the JBL L100 and AR-3a, they were an attractive alternative. Today the Bose 901 is $1400/pair, still made with real walnut veneer in the USA. So they're half their original price adjusted for inflation. At that price they're still viable, depending on what you want in a loudspeaker.

Why didn't you mention the Bose 1-inch subwoofer.

Designed for mice in small cubicles.

Ha-ha! Like Scotty on Star Trek said, "Ya canna break the laws of physics," and a couple of 5-1/4" drivers in a small box will give you some bass, but it won't give you subwoofer bass. Low bass has to be a combination of driver size, enclosure size, and available power. Bob Carver invented the compact subwoofer under the Sunfire brand, a 12" cube that could really make 22 Hz at 100 dB. But to do it he had to include an 1800 watt class D amplifier.

[stobro]

Let me just throw this out there:

When Altec developed their Voice of the Theater loudspeaker (I worked for Altec Lansing back in the mid-'80s), it was specifically for movie theaters. They were typically installed behind the screen (many movie theaters were converted from live stage theaters, so there was plenty of space behind the screen) and had to fill the room. Power amplifiers at the time were very low power compared to even modest home theaters of today. So, while size wasn't a concern, efficiency was. Folded horn LF drivers and directional horn loaded HF drivers were state of the art for many years. As power became cheaper with the advent of solid state and later digital power amps, manufacturers abandoned complicated horn-loaded designs for much cheaper to build sealed or T-S aligned vented boxes.

Bill Fitzmaurice today has several horn-loaded designs that use modern drivers. If you're into the simple, pure low power tube hi-fi thing, he's worth checking out.

[JohnnyB]

Stobro's post introduces another part of the story and a niche market offshoot. When enthusiast or high end audio began to develop in the '50s, there were no quality home speakers per se. So enthusiasts had to adapt what was available from PA and studio monitors. Hence, Voice of the Theater, JBL, Klipsch, etc. All directional and highly efficient. But then, speakers pretty much had to be because all amps were tube amps back then and 30 watts was near the top. Fortunately, these horn-loaded speakers could produce 100-105 dB from 1 watt input (measured from 1 meter away).

However, the smaller, far less sensitive "bookshelf" speaker didn't come about because of the sudden availability of more power for less money. The original AR-1 came out in 1954, four years before the first stereo LP and about 7 years before solid state amps started to make inroads in the home audio market. However, with bookshelf-sized speakers already available from AR, KLH, and Harman-Kardon, these companies were already in the favorable position when stereo LPs came out (1958) and now you needed two speakers instead of one. It was certainly easier and more affordable to fit two AR3a's in a living room than two VOTTs. Soon after was the rise of solid state, where you could buy 40 wpc in a lighter, cooler, lower maintenance unit. The higher level of power became necessary as that these bookshelf speakers were far less sensitive than the big old horns. Given that it takes at least four times the power to bring an air suspension bookshelf speaker to the same SPL as a big horn speaker, the next step was the introduction of the super power amp, ushered in by Bob Carver's Phase Linear 700, a 350 wpc power amp that could finally make the AR3a come alive.

Along with the general resurgence of tube amplification over the last 20+ years has come a niche within that, the Single-Ended Triode (SET) amp. Usually based on the Western Electric 300B tube (making about 5 wpc) or the 2A3 (making about 2 wpc), these amps are used to power high sensitivity speakers and within that category are single driver speakers.

Two popular suppliers of these crossoverless full range drivers are Fostex and Lowther. Many boutique operations create elaborate horn systems to extract maximum frequency extension from these drivers. Example:

The SET plus full-range driver approach requires more owner involvement. But when you combine a single-ended amp with a high-sensitivity driver with no crossover, there is a transparency and immediacy that is elusive in more conventional configurations.

[JGale]

Has anybody here actually spent some time with a Lowther or similar single driver system. If so, what are your impressions with various musical genres?

Now that I have a workbench, the tinkerer in me is intrigued.