Bass-reflex vs. acoustic-suspension: need refresher course!

Discussion in 'Audio Hardware' started by Taurus, Nov 17, 2009.

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  1. Nonhuman

    Nonhuman Forum Resident

    Location:
    Waverly, NY, USA
    I still love the sound of a pair of Klipsch Cornwalls. I don't care if they aren't accurate. They are lively. At a certain level of quality I think my sensitivity to harmonic distortion gets diminished. The one thing I can't tolerate is missing low bass (30HZ) response.
     
  2. ROLO46

    ROLO46 Forum Resident

    passive rads were popular in the 70,s (isobarrics,kef 104 etc)
    now its stiff drivers in sealed boxes with plenty of current
    in the 50's diy depended on open baffle or tuned ports with 15wpc
    it all works
    my main set up is3 sealed boxes (with 12x8inch lf)
    my second system sealed 10inch woofs bur 18inch ported sub
    both excellent
     
  3. jorgeluiz

    jorgeluiz New Member

    in 70's i had 2 Acoustic Suspension speakers and had amazing basses.
    no more A.S. made in Brazil and to import from others countries have too HIGH taxes(more than 100% sometimes :realmad:).

    i want to 'build' my own box(wood) speakers, who know pages/urls with free projects?
    (google is not so friendly as the users in the forum to help)

    great thread, coments and links posted!

    cheers!
     
  4. kevintomb

    kevintomb Forum Resident

    Passive radiators were still very popular with POLK AUDIO well into the 90s, I have a pair of RTA-11T polk towers that have (2) 6" woofers, and (2) 8" Passive radiators, each tuned to a different frequency. VERY impressive deep bass for such small drivers, and fairly efficient also. Only weak point, limited very deep bass power handling. Its still amusing to watch the lower tuned radiator slowly move back and forth SO FAR, during deep bass notes!
     
  5. Nonhuman

    Nonhuman Forum Resident

    Location:
    Waverly, NY, USA
    I run a pair of Klipsch Forte II with passive radiators. I send the full bandwidth to the Fortes but still complement them with a Klipsch 10" powered subwoofer dialed in to add bass at 34HZ and below. I don't use tone controls on my McIntosh MA230 integrated amp, and have never enjoyed equalizers etc. I turned my back on EQ decades ago. This system reproduces whatever frequencies are present in the recordings to my satisfaction.

    I am strongly beginning to consider a pair of Klipsch Cornwall III. I bought the Fortes second hand as a matched set with satellite rear channel speakers and a matching shielded center speaker. I've never used the satellites/center speakers. I don't have the slightest interest in 5.1 sound. I guess I'm perfectly focused on old school audio. I think the physics of sound reproduction is quite well understood today. Most of the people I know that decided to build a set of speakers have found their projects very rewarding. I designed mine from a book on loudspeaker and crossover design. That was before the internet was a reality. Today there must be an amazing number of online sources for drivers and design software. I don't think there is any money to be saved in building your own, but the satisfaction of bringing a set of speakers to life is priceless.
     
    eyeCalypso likes this.
  6. Taurus

    Taurus Forum Resident Thread Starter

    Location:
    Houston, Texas
    You know, I've never thought about that. I always thought bass reflex had been around forever but actually, they only really became popular when Thiele and Small published with their now classic Thiele/Small parameters in the early 1970s that made designing a ported system MUCH easier and much more consistent (before it was mostly trial & error along with experience....which translated to $$ as far as a manufacturer's time was concerned). And AFAIK horn systems shared the same R&D difficulties, not to mention the expense of building the horn itself.

    I think another reason ported systems became popular, despite their relatively less accurate bass output, is that they could produce higher volume levels with less-gutsy amplifiers (which was also very easy to demonstrate at the retail level to music fans who weren't familiar with audio i.e. "See, this speaker is better because it's louder"). As cybermantis alluded to, most receivers back then were built like tanks, even the entry-level 20 watt/channel models: that was mostly so could supply enough power so AS speakers could perform at their best.

    But those receivers were costly to build because of all that iron and copper in their hefty power transformers, the metal in their thick heat sinks & the heavier chassis to hold all of this together (can you imagine the reaction to such designs today from the many consumers who are trying to "go green"?). I think a solution to this for large AS systems could be the use of an internal digital amplifier - much more efficient & less expensive than the typical class A/B amp - for the woofer and allow the owner to use his own amp for the tweeter/midbass driver array.

    I do think HT receivers can sound good, but as far as their relatively low power output is concerned, that's easy to understand because what is the most popular speaker system for use with such components? ---> Five small satellites that use a couple of 3" midbass drivers or a single 5.25" woofer. Those don't require much power at all to operate properly, even before you include the fact that the receiver's speaker management system has filtered out the bass below @100Hz (the self-powered sub reproduces that portion of the audio spectrum), which significantly lightens the load on the receiver's power amplifier section.

    One of my favorite systems & can produce some really extended bass because a PR is much heavier than the air in a port tube, but I think they generally fell out of favor* because a port paired with a simple plastic tube is much less expensive than what is essentially a woofer with no magnet or voice coil assembly.

    I'm surpised more speaker companies haven't utilized the aperiodic system the classic Dynaudio A-25 used in the early 70s, a hybrid of the AS and ported configurations. It was supposed to have been tricky to get right, plus each A-25 had to be individually hand tested to make sure the stuffing in the "port" was correct in amount and position. Computer modeling should take care of the most of the R&D issues and modern production techniques should eliminate the hand testing, but the aperiodic design itself must be lacking something to keep modern manufacturers from using it.



    * I think many of those small "Mighty Mouse" subs, the ones small enough to fit inside a toaster oven, still use them because of this design's favorable physics
     
  7. misterdecibel

    misterdecibel Bulbous Also Tapered

    The Linn Isobarik is not a passive radiator system. The passive radiator is a form of reflex port, Isobarik is two active woofers in acoustic series. It's a rather extreme form of Acoustic Suspension.
     
  8. Taurus

    Taurus Forum Resident Thread Starter

    Location:
    Houston, Texas
    Just a random story: back when I was building speakers, I wanted to build a design described in the Radio Shack design book I used for the other two speakers I built. It was a dual-chamber bass reflex, utilizing an 8" woofer operating in the largest chamber (which was ported in the normal manner), with an internal port connected to the other smaller enclosure (also normally ported). The two chambers were tuned to different frequencies so provided reinforcement over a broader range than a single chamber design. A pretty large enclosure, totally nearly 3 cu/ft, for such a relatively small driver so it wasn't "practical" but I'll bet it sounded good. But I was attending college at the time so couldn't afford the materials and had nowhere to put it together in the first place.

    If anyone's interested, on page 61 of their 1982 catalog is the woofer Radio Shack sold for this purpose (woofer "B", bottom right of that page; click to magnify). They also used that tough little driver with its thick/heavy cone and compliant surround for many of their own completed speaker systems over the years, including their first passive radiator design and a transmission line(!!) design. I always liked that you could see the aluminum voice coil through the thin dust cap which aided cooling. Unfortunately later versions were "wimpified" when they substituted a 2-layer voice coil for the 4-layer one.
     
  9. e630940

    e630940 Well-Known Member

    Location:
    Canada
    You should have. I did build that double chamber design - modified somewhat for better frontal dispersion . It was tough to build and tune but well worth it. I even later upgraded the drivers to Scanspeak and Morels. A lot of my buddies thought it was reference quality and wanted a pair.
     
  10. misterdecibel

    misterdecibel Bulbous Also Tapered

    George L. Augsperger published a similar design in Speaker Builder magazine, claiming that the performance of the box was largely independent of the driver's T/S parameters. So I built a pair for a friend to use his KEF B200s, since they weren't really suited to either an "ideal" ported box or Acoustic Suspension, and it worked a charm. The only time I ever heard standard B200s work well.
     
  11. Freako

    Freako New Member

    Maybe a little off topic, but just to share my opinion: Between the sealed and the ported sub, there are many options (sort of like acoustic valves). I have side speakers way too close to the wall, why I have "tuned" the ports on the backs of the speakers with woolen socks, rolled hard together. This has allowed me to remove the bass "hump" at about 70-80 Hz. Also I have tuned my sub exactly the same way, but not to remove any "humps", more in order to make the slam from the sub, much dryer and faster. Much listening joy can come from well-tuned ports, although it may take a lot of time and effort to get it right :)
     
  12. darkmatter

    darkmatter Gort Astronomer Staff

    Interesting, I'll have look that design up :)
     
  13. seed_drill

    seed_drill Forum Resident

    Location:
    Tryon, NC, USA
    When I moved into my house 6 years ago there was still a Bozak mounted on the living room coat closet door. Unfortunately, it was mono, and, even more unfortunately, it was cut into a solid American chestnut door, but it got me into Bozak, and I still use a pair in my vintage system downstairs.
     
  14. Miguel Sanchez

    Miguel Sanchez New Member

    Interesting...
    I have the oportunity of hear almost all technologies.
    Still remember the sound of my father AR3a an the previous AR-2( and in perfect conditions still Works) to the AR-6 a bouth for a personal proyect (cabinet, that I still Use).
    The bass is clear and soft. Really a good speaker, for vinil LP, and realistic music. Using a clásical DYNACO 120..superb.
    But... Its performance with electronic music ... I dont agree. All of them are Acoustic suspensition sealed cabinet.

    KOSS on the other hand Works impresive with the new modern an electronic music.
    They sound great clean an without to much color...
    Incredible designs with bass réflex...

    The new designs are a incredible mix...
    For example the CREATIVE LABS low cost small size speakers mix a small closed, sealed, plastic cabinet (Clearly AS...for mid/hi freq) satellite speaker; and a full bass reflex for the sub woffer.
    With a reduced frequency response is the ideal for MP3..( and the compressed spectrum...100-15,000 Hz). This where ideal for games also. Ther are non realistic sounds so distortion is not a isue.

    Wich you prefer..depends of with sound you reproduce; and with what tecnique where recorded, and the Price yo can pay..
     
  15. bhazen

    bhazen Fab Fourever

    Location:
    Newcastle, WA
    Would someone care to riff on placement issues with acoustic suspension speakers? ...

    I've ordered a pair of ATC SCM7's, to be delivered in a few weeks. They are standmounts, approximately the same size as LS3/5A's or P3ESR's. Might they have the same characteristics as ported minimonitors, i.e. need to be out in the room a bit from the back wall? Or might they be more amenable to wall placement? I've mainly had ported speakers in this place, so I realized I have a gap in my practical experience.
     
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  16. Lester Best

    Lester Best Well-Known Member

    Location:
    Bklyn NY
    Acoustic suspension, ported, & transmission line are all a matter of implementation.
     
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  17. F1nut

    F1nut Forum Resident

    Location:
    The Mars Hotel
    You can place AS designs much closer to the back wall, which will also reinforce the bass.
     
    bhazen likes this.
  18. P2CH

    P2CH Well-Known Member

    I feel ported cabinets rely on external reflecting surfaces. Like how Bose reflects them to create a larger sounding system. When back waves get delayed, bass is extended. IMO

    Or using a small cabinet but also utilizing the surrounding area to maximize dynamics.
     
  19. JBStephens

    JBStephens I don't "like", "share", "tweet", or CARE. In Memoriam

    Location:
    South Mountain, NC
    Rebuild the crossovers with good caps and inductors, and bypass the thermistor (I just soldered a bridge across it). It makes a difference. Good speakers to have sitting atop the subs, I bring mine in at around 80 Hz and knock down the low bass with an EQ.
     
  20. JBStephens

    JBStephens I don't "like", "share", "tweet", or CARE. In Memoriam

    Location:
    South Mountain, NC
    A ported cabinet is a Helmholz resonator, nothing more. Like blowing across the top of a bottle. And you tune that resonator to match the woofer and your design goals. So to work, the port output must be 360 degrees behind the cone. But then, below Fs the cone unloads, so it can do destructive things at extremely low frequencies. Ported = lower F3, sharp rolloff, sealed = higher F3, but shallow rolloff. Building speakers is about choosing which compromises will work the best for youl.
     
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  21. bhazen

    bhazen Fab Fourever

    Location:
    Newcastle, WA
    Talk to me about siting classic AR's, Advents etc.; up against the wall? Out in the room, on stands? What's your experience?
     
  22. Adam9

    Adam9 Senior Member

    Location:
    Toronto, Canada
    My Large Advents are on approximately 12" stands, so that the tweeters are at ear level. My Smaller Advents are on somewhat higher stands so that the tweeters are at ear level also. Both sets of speakers are about a foot away from the back wall.
     
    bhazen likes this.
  23. Richard Austen

    Richard Austen Forum Resident

    Location:
    Hong Kong
    This is a 7 year old thread.
     
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