Steve F Posted October 24, 2016 Report Share Posted October 24, 2016 From the Cat Dragged in LST thread: Hi Jerry, What great replies! First of all, I, too, didn't realize that speaker companies who built vented enclosures paid too much attention to small air leaks; however, I can see where it could give a problem. I think what Steve is referring to regarding the "their lower 3dB down points" is the lower fc of many vented designs, but the 24 dB/octave rolloff below resonance in vented vs. the 12 dB/octave in acoustic-suspension designs. Thus the vented design obviously rolls off very rapidly below resonance compared with a/s designs. Vented designs are certainly more efficient, and I agree about the ported designs' tendency to exhibit "one-note bass," and although there is usually plenty of punchy low-frequency energy, it always seemed (to me at least) muddy or less well-defined than sealed systems, but there were some exceptions. If one is listening to a lot of jazz with kick drum or orchestral music with big orchestral bass drum, organ or electronic music with lots of low-frequency energy, the acoustic-suspension system seems to have a significant advantage. Ported or vented systems do just fine with probably 90% of all recorded music, especially rock or popular music. But overall, I think acoustic-suspension systems are much cleaner than vented systems in reproducing fundamental energy, usually with flatter response and lower harmonic distortion, but many will argue that some vented designs that are certainly excellent as well. I'd written about this topic in great length (over 1500 words--about four pages) back in 2002. I guess it's time to summarize that post again now, so here goes. Yes, the “tuning frequency” of a correctly-designed vented speaker with a woofer of appropriate T-S parameters will allow it to reach a lower -3dB point for a given enclosure size compared to a sealed speaker of the same size. In the early 90’s timeframe, for instance, the PSB Alpha was reaching, say, -3dB in the low 50’s Hz compared to our sealed Boston Acoustics HD5, which was down 3dB at about 65Hz. That was terrifically audible in a retail A-B demo comparison. The fact that the HD5 had more output at 30 or 35Hz because of its 12dB/oct rolloff compared to the PSB’s 24dB/oct rolloff was essentially meaningless, for two reasons: 1. They were both so far down in level at 30Hz (these were small 5 ¼” 2-way bookshelf speakers for about $200/pr. at the time) that it didn’t matter at all if one was down 15dB and the other was down 24dB. Neither had any impactful output down there, so the HD5’s sealed “advantage” was no advantage at all. 2. These were speakers that would be used to play popular music in stereo, where the lowest bass content in the program was in the 40-60Hz range. The PSB just sounded so much “fuller” and richer than the HD5. The fact that the sealed HD5, 7 and 8 were getting killed at retail was the driving factor that lead to the CR Series that replaced them being ported speakers. Which leads us to the next big point: It’s waaaaaay past time to totally debunk that tired old cliché about “Ported speakers are boomy and one-notey and ‘thick’ sounding compared to the ‘fast, tight’ sound of acoustic suspension speakers.” That may have been true in the ‘50’s and ‘60’s, but only because designers didn’t have fully fleshed-out T-S parameters and modern computer modelling to work with. So, ported speakers were hit-or-miss, “cut-‘n-try,” etc. A lot of shooting in the dark. Not any more. I defy anyone to listen to a really excellent Aerial or B&W or KEF or Legacy Audio—name a good company, your choice—and tell me that their bass isn’t excellent. It is excellent. “Tight, crisp, well-defined, fast, articulate, musical, muscular, athletic, accurate, natural,” etc. Pick your adjective. Pick your music. Sealed had a huge advantage when design practices were unsophisticated, because the acoustic suspension design principle enabled designers to optimize a truly excellent system by jockeying and adjusting only a few variables. Presto: Combine 17Hz Fs, high compliance, 1.7 cu.ft. enclosure and you get 3a bass. Duck soup. But to build and test dozens of variations of woofer parameters, port length, port diameter, vent shape, vent location, etc., etc. and come up with an optimized vented design was just not practical in 1966. However, it is now. Press a button and see 12 vented design options in a second. Press the button again and see another 12. You couldn’t build and measure 24 of them in 1966. Now you can do it in an hour. So, you can now get that lower -3dB down point and get bass that’s all the above good things. Why do you think nothing’s sealed any more? Don’t misunderstand my point—the 7, 4x, 2ax, 3a, et al. had—and have!!—terrific bass. It just that now there’s no barrier to getting great bass from ported designs, with their advantages, but without the drawbacks of 50 years ago. Steve F. Link to comment Share on other sites More sharing options...
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