Hi Jvillas,
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I Have owned my Ascends now for 3 weeks. Prior to my purchase I did my research, and noticed at least in my price range $500. dollars or less that the vast majority of speakers are bass reflex design. Not so long ago this was not the case. Most designs were Acoustic Suspension. Why has this happened?
I don't have an exact answer for you but my guess is that it is becoming easier for a designer to get the bass reflex design correct. A ported design is more complex than an acoustic suspension system and if you get it wrong, it can really sound bad -- muddy, boomy - often with excessive ringing. In my opinon, it is easier to design an acoustic suspension cabinet. Loudspeaker modelling software has become easier to use and the results (if one is able to plug in the correct data) are generally very close to real world performance. Thus, it has become easier to design good sounding bass reflex systems.
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Bass reflex designed speakers were also considered highly efficient. It was a selling point. I f you had a low powered amp you could get a big sound using bass reflex speakers. This no longer seems to the case. Today they are no more efficient than acoustic suspension.
Bass reflex designs, when compared to an acoustic suspension design, are only more efficient in the range of where the port has been tuned. They actually become less efficient below the port tune range. They give you that "bigger" sound simply because, when properly tuned, they will have a lower -3dB point then a similar acoustic suspension design. For example, an acoustic suspension design that is -3dB at say 80Hz, can be made into a bass reflex design (with changes to the cabinet and woofer) that can then be -3dB at 50Hz. The acoustic suspension design at -3dB at 80Hz will sound thin, so the designer will sacrifice overall efficiency to gain a lower roll off so the speaker will not sound as thin. To keep the speaker balanced, the efficiency of the woofer and the tweeter must be decreased, thus the overall efficiency of the loudspeaker is decreased.
The low end -3dB point of a loudspeaker is directly related to efficiency. If cabinet volume remains the same, the only way to improve the -3dB point is to decrease efficiency (either by changing the mass of the woofer cone or specific types of compensation circuits in the crossover) A bass reflex design is inherently more efficient at the range of the port tune so this is a way of achieving a better -3dB point without sacrificing efficiency...
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While the reflex design speakers have tremendously improved and are very very impressive. I use to consider this design to be nothing more than a big boom box, not well designed and often poorly executed.
And I think that directly relates to what I stated above -- it is now easier to get it "right" :D
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Why is the reflex design so dominant, (at least in the price range I'm looking at).
Because it will tend to have a warmer more pleasing sound while at the same time requiring about 1/2 or even 1/4 the amplifier power (very important considering many people are running 5 - 7 speakers off a single amplifier).
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Are there any advantages left to this design over acoustic suspension.
Yes! Besides what was already discussed above, a properly designed bass reflex system will have considerably less distortion in the port tune range than a sealed design. In a bass reflex system, woofer excursion will decrease as you approach the port tune frequency. At port tune, the woofer is barely moving. Distortion (and many other negative characteristics) increase as cone movement increases. With an acoustic suspension design, woofer excursion simply increases as frequency decreases. In a bass reflex design, woofer excursion will increase dramatically below the port tune frequency, soon surpassing the excursion of a similar acoustic suspension design, thus distortion will increase.
Look at the distortion measurement graph for the classic CBM-170 http://www.soundstagemagazine.com/me...ascend_cbm170/
Notice how it dramatically decreases below 100Hz, reaching a minimum point at around the port tune frequency of the speaker. Distortion then begins to dramatically increase at frequencies below the port tune. Another reason why rolling off the bass can be so important...
Hope this answers your questions!
