Sound Advice - Home Audio Related Q&A
Q. What is your "claim to fame"?
A. Without a doubt, our pro-grade ribbon or planar tweeters on larger die-cast wave-guides. This combination provides 30kHz. top-end FR, lower distortion and ringing, a more-uniform sound dispersion and higher-efficiency anywhere from >100db 1w/m down to 1kHz.
The Spectral Decay Plot for a state-of-the-art compression driver at Left shows severe ringing, especially at typical power levels.
The Spectral decay plot for the SA 8535 Ribbon/planar tweeter at Right, shows much less mid-range ringing and almost no High-Freq. ringing, with much smoother and more extended high-freq. response!
The above plots explain why pro-high-freq. compression drivers sound harsh and quality planar tweeters sound natural. Also, the small ribbon & planar tweeters, used by others, only go down to 2 to 3kHz. and don't have uniform dispersion (compared to ours).
Few-costly brands are offering such quality planar tweeters in their production loudspeakers. These high-SPL ribbon/planar tweeters are matched to large planar (or pairs of high-quality cone) MF drivers; it is important to match dispersion from MF to HF, also an unusual feature.
Q. How does the sound quality of your speakers compare?
A. By including premium concert-sound woofers (w/low moving mass & high motor strength) between the true sub-woofers (with ultra-long-stroke/excursion) and the mid-range drivers we are able to provide a much higher sound-level-output (hi-SPL) and exciting/"punchy" bass along with more extended low-frequency response than commonly offered to the concert & studio loudspeaker market.
Q. Does woofer size matter?
A. Yes, woofer size is very important; assuming the use of a quality driver, the woofer cone and voice-coil size are the primary factors in predicting maximum sound-level-output. The box-enclosure size is the primary factor in predicting how low (in frequency) a woofer can play in combination with efficiency; while enclosure type and how low the woofer resonate frequency is, will also be factors.
Classic pro-sound woofers are very efficient, but needed very large enclosures to provide any low bass. Some newer pro-sound woofers work in smaller enclosures by adding some mass (like hi-fi woofers but less so) and/or by requiring equalization to get full low-frequency extension (40 to 50Hz.).
Modern hi-fi sub-woofers tend to be in small-sealed enclosures with a built-in amplifier & equalization to get full low-frequency extension. While a small sub-woofer can sound decent at low sound levels, the notion of a small sub-woofer is basically a contradiction in terms. A small sub-woofer can not be made to:
- Play as loud (max. SPL) as a larger unit
- Have as low-frequency extension (<30Hz.), and
- Have superior dynamic range.
These features are mutually exclusive in a small-sub-enclosure. It's like the old sign in many quick-print shops: "quality, low-price, speed; choose any two".
Mass market consumer (home-stereo) loudspeakers have been getting smaller and lower-cost. Many people don't seem to notice that the sound quality goes down with the size and price.
Q. What are the best types of bass/woofer box/enclosures?
A. The best woofer box type is dependent on your usage (music style & sound level), listening skill, box/room size/space constraints and budget.
Design Goal: Add-on subwoofer for small-room (home) system, low cost, good transient response, small box. Sub system: Typical premium-brand Sealed enclosure with a built-in amplifier & equalization to get full low-frequency extension. But remember that size matters.
Design Goal: High-end home & studio applications; size no object; excellent transients.
Sub system: Infinite or TL type very-heavy walled boxes; subwoofer drivers 12-15″ long-excursion, Subwoofer drivers powered by a >1kW, dedicated amplifier(s) (with DSP EQ/XO).
Ideally, the subwoofer is a bi-amped 2-way system including a short-coil (pro-sound) woofer with a stiff cone for the upper-bass "punch/slam" range (50-150Hz.) and a separately powered larger or pair of opposite-mounted long excursion subwoofer(s) for the lower bass range (15-50Hz.).
Design Goal: High SPL concert sound reinforcement in large spaces, size no object. Mid-Bass using 10-12″ drivers and Sub system using 15-21″ drivers:
A. Multiple-large-Tapped or large-folded-horn subs or,
B. Multiple-large ported boxes (premium-pro-brand).
Ideally reversed cardioid subs added for directional control.
Subwoofer drivers powered by >3kW, dedicated amplifiers with DSP EQ/XO.
For more on sound design in large spaces see my design site at www.D-K-A.com.While the list of bass-box types in the following section Q3 is available online (for the most part), there is not good consensus on the list, much less are the best choices explained nor suggested. This outline above is an attempt to clarify and summarize our subwoofer suggestions and preferences, based on the differences in application, cost, performance and size.
Q. What are the various types of loudspeaker & sub-woofer (bass-box) enclosures?
A. To achieve full low-frequency extension, some sort of loudspeaker box/enclosure is needed. Since the box affects mostly the bass frequencies and bass-box is a more all-inclusive label than sub-woofer, we will use the term bass-box here.
There are several types of bass-boxes; they are well documented in several loudspeaker books (from amazon.com & other web sites) and on several loudspeaker web sites including www.wikipedia.org/wiki/Loudspeaker_enclosure, www.buyingloudspeakers.com and www.diysubwoofers.org. So our comments here will be brief as possible, omitting history, with minimal technical details.
Over 90% of the hi-fi speaker/subwoofer box types in mass production are Sealed or Vented boxes. Over 90% of the studio and concert-sound bass/speaker/subwoofer box types in mass production are Vented boxes. The most common types of bass-box systems are briefly covered here (Aperiodic, Isobaric and other rare-esoteric bass-boxes will not be discussed):
- Open Baffle: AKA dipole type speakers, have the back of the cabinet left open, or just a Baffle/panel. No longer typical for hi-fi systems, dipoles are still common for planar drivers and guitar amplifiers. The baffle's edges are sometimes folded back to reduce its apparent size, creating a sort of open-backed box. These speakers are said to have a more "open", live-sound like, due to the less "boxy" ringing (common in many bass/speaker boxes). The baffle (open box) dimensions are chosen to obtain a particular low-frequency response, with larger dimensions giving a lower frequency extension before the front and rear driver waves interfere and cancel each other out commonly supplemented with a true sub-woofer (or extensive eq.) to handle the lower freq. A dipole enclosure has a "figure-of-eight" radiation pattern, which means that there is a reduction (cancellation) in loudness, at the sides as compared to the front and rear. This is useful if it can be used to prevent sound reflections from the side walls; the greater directionality together with the lower ringing make for a following from many audiophiles.
- Infinite Baffle: A variation on the open baffle approach is to mount the speaker driver in a ultimately large-sealed enclosure, providing a low air-spring restoring force to the driver. Some infinite baffle enclosures have actually been wall-mounted through to an adjoining room, basement or attic. The special woofers and custom (impractical) mounting are unpopular (but quite effective).
- In-wall (flush-mount and on-wall speakers) are new/loose categories, rarely even listed elsewhere. In-walls are a variation on the Infinite baffle; they include a wide and growing selection of cheap (poor sounding) as well as good sounding, along with some exotic loudspeakers (Infinite, Sealed or Vented box types). The typical-modern wall construction in the US is of framed Gypsum panels, and it has been shown that such construction is inferior (in sound and durability) to typical MDF loudspeaker enclosures. So the better in-wall loudspeakers (including studio monitors) include enclosures made of MDF and better drivers, and quality crossovers (sometimes using ribbon tweeters). Superior in-wall subwoofer boxes could be custom-built on-site of massive materials, like concrete, stone or brick, using one of the larger and better box types (like IB or TL).
- Sealed and "acoustic suspension" enclosures are common for small-modern (mass market) hi-fi speakers. They can sound good at low sound levels with more dynamic (life-like sound) than vented boxes (due to less ringing), but a small-sealed loudspeaker box can not match the sound level or quality of much larger enclosures. Because the enhanced suspension linearity of this type of system is offset by rather low efficiency.
- Vented (bass-reflex or ported) boxes are more efficient (play louder) than Sealed enclosures, but are larger and add low freq. ringing. Predictable vent size (bigger is better) and tuning changes the low-frequency extension and amount of ringing. This type of bass-box is dominate for pro-sound and is very common for hi-fi systems; it provides the maximum deep-bass output for a given enclosure volume and is economical to build. Many people like the sometimes-hyped "boomy" bass. Even so, many audio¬philes seek a more neutral, dynamic and life-like sound, with less low-frequency ringing.
- Passive radiator speakers use a second "passive" driver, or drone, to extend low-frequency response, similar to vent/ported enclosures. The passive driver is not wired to an amplifier; instead, it moves in response to changing enclosure pressures. These designs are variations of the vent/ported type, but with the advantage of avoiding unwanted sound leakage, and a relatively large port/tube through which air moves, (smaller ports are noisy). Box size can be smaller than a well-vented box, with similar efficiency, low-frequency extension and ringing.
- Compound or band-pass enclosures have two chambers. The dividing wall between the chambers holds the driver; typically only one chamber is ported (4th order), or the enclosure on each side of the woofer has a port in (6th order). These are considerably harder to design and tend to be very sensitive to driver characteristics. They are more efficient (play louder) than Sealed enclosures, but have limited range and ringing issues (don't sound "punchy"), thus are not typically used for critical applications.
- Bass horns use a flare to better match the driver cone to the air, this improves the coupling and controls/confines dispersion, both improving efficiency and transient response; thus sounding more "punchy" (on axis), partly due to the lower moving mass and tight suspension used in the compatible drivers. Properly designed horns for low frequencies (under 300 Hz) are massive, dozens of feet, but factories have produced folded low-frequency horns, which are smaller, but are still very large and expensive.
- Tapped horn: Both sides of a long-excursion high-power driver in a tapped horn enclosure are ported into the horn itself, with one path length long and the other short. These two paths combine in phase at the horn's mouth within the frequency range of interest. This new design is especially effective at subwoofer frequencies and offers reductions in enclosure size along with more output. More to come from Danley Sound Labs on this innovative design.
- TL: A transmission line enclosure is a waveguide in which the structure shifts the phase of the driver's rear output by at least 90°, thereby reinforcing the frequencies near the driver's Fs (and low end). Transmission lines tend to be larger than ported enclosures of approximately comparable performance, due to the size and length of the guide required. The design is often described as non-resonant, and some designs are sufficiently stuffed with absorbent material that there is indeed not much output from the line's port. But it is the inherent resonance (typically at 1/4 wavelength) that can enhance the bass response in this type of enclosure, albeit with less absorbent stuffing.
- Variations on the transmission line enclosure are the Acoustic Labyrinth and Tapered tube, with the port having a smaller area than the throat. The tapering tube can be coiled for lower frequency driver enclosures to reduce the dimensions of the speaker system. Famous brands have used this design, but due to their greater size and cost (& lack of hyped bass) they are not highly popular in most countries. Even so, many audiophiles and loudspeakers engineers (including the author) consider the TL to be the ideal (except in auditoria), but most complex enclosure with which to load a moving coil driver (woofer); providing higher sound level and quality than Sealed or Vented boxes.
- Tapered quarter-wave pipes (TQWP) are examples of a combination of transmission line and horn effects. Although large (and thus unpopular), it is highly regarded by some speaker designers. The concept is that the sound emitted from the rear of the loudspeaker driver is progressively reflected and absorbed along the length of the tapering tube, almost completely preventing internally reflected sound being retransmitted through the cone of the loudspeaker. The lower part of the pipe acts as a horn while the top can be visualized as an extended compression chamber. Excerpt from Wikipedi (author has no opinion on this variation)
Q. Are pro-sound woofers better than hi-fi types?
A. For the most part, yes. High-quality pro-sound woofers have many advantages over hi-fi type driver/woofers. Pro-sound woofers are commonly better built (heavy magnet & cast frame & larger voice-coil), to handle the more abusive use in concert-sound & studio applications, so tend to be stronger and handle high power (avg. 1,000W RMS). Pro-sound woofers are much more efficient than hi-fi woofers (typ. 6-9dB greater or more), so they can play much louder or can be used with a lower-power amplifier (like tube amps).
More importantly, pro-sound woofers are more dynamic and life-like sounding because their more powerful magnet and/or lower stored energy, due to lower moving mass (Mms) of the coil & cone; especially when they are mounted in a very-large specialty box/enclosure (bass horn, TL or IB), detailed in post above.
The down side of most pro-sound woofers, is that while they are typ. designed for max. output at mid-bass frequencies (80-800Hz.), they don't have the long excursion nor low-resonate freq. needed for true sub-woofer use, so (multiple) true sub-woofer drivers would be needed as well, to cover the lower <30-80Hz. range. Heavy equalization can be used to extend the lower range, but doing so reduces the maximum sound level.
Note that there are some costly car stereo (competition) driver/woofers that are well built and high-power, but they tend to be high-mass, so more for true sub-woofer use (30-80Hz.) and of low efficiency.
Some great sounding hi-fi mid-bass drivers/woofers are available (from factories like Seas). Hi-fi mid-bass drivers go much lower in freq. (30 to >2kHz.) than what pro-sound people call a mid-bass driver; pro-sound people would call them a woofer. The better hi-fi mid-bass drivers have low moving mass and heavy cast frames, but smaller voice-coils; larger voice-coils (for higher-power) would add too much moving mass or require a much bigger magnet, so they have less max. sound level than (more costly) high-quality pro-sound woofers.© 2010 David Kennedy, Audio Engineer
Feel free to contact the author for more info.