Sealed woofers are attractive with separate amp plus room equalization.
Our HT/stereo uses a computer to generate the crossover plus room equalization for a 3-way speaker with large sealed box woofers driven by a separate woofer amp. The combination of a separate amp + digital room equalization made a sealed woofer the best design choice. Sealed woofers with Qts = 0.7 have exceptional transient response, and their modest low frequency SPL drop-off more closely matches the natural room gain than a ported design. This simplifies room equalization vs. room placement issues. I will probably always favor a sealed woofer design when I have a separate amp and electronic crossover/equalization.
The other speakers in our home are bass reflex bass designs in order to get higher bass SPLs with a single modest power amplifier. Keep it simple.
I have developed a positive bias toward MLTL woofer box designs, since to my ears the MLTL reduces cabinet resonances that modulate a sine wave sweep on most ported designs.
Our HT/stereo uses a computer to generate the crossover plus room equalization for a 3-way speaker with large sealed box woofers driven by a separate woofer amp. The combination of a separate amp + digital room equalization made a sealed woofer the best design choice. Sealed woofers with Qts = 0.7 have exceptional transient response, and their modest low frequency SPL drop-off more closely matches the natural room gain than a ported design. This simplifies room equalization vs. room placement issues. I will probably always favor a sealed woofer design when I have a separate amp and electronic crossover/equalization.
The other speakers in our home are bass reflex bass designs in order to get higher bass SPLs with a single modest power amplifier. Keep it simple.
I have developed a positive bias toward MLTL woofer box designs, since to my ears the MLTL reduces cabinet resonances that modulate a sine wave sweep on most ported designs.
Actually I pretty much daily use a pair of speakers which you say would be terribly expensive and sound horrible. Believe me, that isn't the case- the cost to build them wasn't by any means excessive, and stereo imaging is excellent and I've never experienced listening fatigue with them.
The two-way system includes a 12" woofer with a rubber surround that retails for less than $50. The cross-over frequency is 2 kHz and the electrical roll-off rate of the cross-over network is second order. The specified upper limit of frequency response of the woofer is 3 kHz, so the 2 kHz crossover frequency should be okay. I will say that I toe the pair of them in and I think that probably listening to them in the sweet spot is the only acceptable position. At 2 kHz, the 12" woofer must be beaming considerably.
The woofer is just barely acoustically suspended (alpha = 3) in a box with an internal volume of 74 liters. Most people these days would describe my speakers as bulky, which is why the majority of speakers being manufactured now aren't acoustic suspension with a big woofer. There is a mania amongst the "regular" music listening crowd for small speakers. Apparently some are under the impression that speakers can be made to be infinitely small without a loss of proper bass response in the same way that a chip amp can perform as well as an amp that is a circuit board of discrete components.
I always felt that "Acoustic Suspension" was AR's marketing term. It isn't actually very precise.
I'm okay with reserving the term for high alpha sealed box designs (Vas significantly larger than Vb) but I wouldn't consider some particular border, such as an alpha of 3 as being a hard and fast rule.
In the end the terms are generally interchangeable.
David S.
I'm okay with reserving the term for high alpha sealed box designs (Vas significantly larger than Vb) but I wouldn't consider some particular border, such as an alpha of 3 as being a hard and fast rule.
In the end the terms are generally interchangeable.
David S.
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I've noticed this myself. It's like if you cannot bring XYZ device with you & stuff it into your pocket or backpack, it is old fashioned and just not worth thinking about.
Several members have written (I've seen this on other forums too) that a.s. enclosures tend to be larger than a b.r. enclosure for the same size woofer, but wasn't one of the main reasons a.s. was celebrated in the late 50s as a positive step forward because it was smaller than a b.r. design with the same bass frequency limit? Or was that before the T/S parameters revolutionized b.r. designs (many of the ported loudspeakers up to that time were enormous, with 4 to 6 cubic foot cabinets being a common sight)?
Btw Radio Shack's "mighty mouse" Minimus 7 is one of the models I think of when discussing the potentia) size advantage of a classic acoustic-suspension design. RS used to sell that 4" woofer the 7 used, and it had the heavy cone and compliant suspension I associate with an a.s. speaker, along with a large motor structure nearly as large as the cone itself (the woofer utilized that strange shiny greenish foam-ish material that only RS used and doesn't seem to be susceptible to rot, even after three decades!) ---> page 23 and listed - click on page to enlarge - as a "long throw woofer" along with a brief spec chart.
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Actually they aren't, but where does one seemingly cross over to the other? Infinite Baffle is the term I normally see used for large sealed boxes, but there are others.
The problem is that basic principle (air spring) which denotes an AS cabinet isn't necessarily as large, robust, nor a profound factor, in many larger cabinets.
Best Regards,
TerryO
4-6 cubic feet would look small next to my speakers.
Mine too..
I have always used the various terms more or less interchangeably, and I suspect imprecisely, but then when I think of acoustic suspension, sealed box or infinite baffle I think Advent, AR, KLH, EPI etc.. Seems to be a trend here..
Even the original Radio Shack got its start here in MA.. And I now like JBL and Altec stuff from the times when boxes were big, suspensions stiff, and there were various odd holes and collections of bent wood (horns) in boxes. California stuff..
I've noticed this myself. It's like if you cannot bring XYZ device with you & stuff it into your pocket or backpack, it is old fashioned and just not worth thinking about.
Several members have written (I've seen this on other forums too) that a.s. enclosures tend to be larger than a b.r. enclosure for the same size woofer, but wasn't one of the main reasons a.s. was celebrated in the late 50s as a positive step forward because it was smaller than a b.r. design with the same bass frequency limit? Or was that before the T/S parameters revolutionized b.r. designs (many of the ported loudspeakers up to that time were enormous, with 4 to 6 cubic foot cabinets being a common sight)?
Btw Radio Shack's "mighty mouse" Minimus 7 is one of the models I think of when discussing the potentia) size advantage of a classic acoustic-suspension design. RS used to sell that 4" woofer the 7 used, and it had the heavy cone and compliant suspension I associate with an a.s. speaker, along with a large motor structure nearly as large as the cone itself (the woofer utilized that strange shiny greenish foam-ish material that only RS used and doesn't seem to be susceptible to rot, even after three decades!) ---> page 23 and listed - click on page to enlarge - as a "long throw woofer" along with a brief spec chart.
The AR's were much smaller than the large horns, etc., that were "the standard" for deep bass at the time. The advent and use of the T/S parameters were actually the first time that it was possible to get a fairly accurate idea of how to model Bass Reflex enclosures, down to a more reasonable size that has become increasingly important.
Best Regards,
TerryO
The tweeter has an Fs of 600Hz. If I cut the crossover to 1200 or 1600 from 1800 with a steeper fourth order crossover, might that be moving in the right direction?
That's a common problem with most 2-way speakers using a large diameter woofer. Even horns and wave guides, which can used to advantage in this situation, are often getting pretty close at these frequencies. Really, a three-way is perhaps the ideal, although it requires quite a bit of work to get the crossover voiced.
As for your question, you're correct, it is a move in the right direction.
Best Regards,
TerryO
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In efficiency constant terms it is true that a vented box can be smaller for a given efficiency and cutoff but...if you take a given woofer and model the ideal sealed and the ideal vented cabs for it you will find the vented cabinet will be approx twice the size.
It takes a lot of driver changes to achieve the smaller vented box with same sensitivity and cutoff, primarily heavier cone and much bigger magnet.
Regarding the AR's, I always felt their invention was not to have high alpha, i.e. Acoustic Suspension, (RCA had published papers about that previous to the AR patent) but they were the first company willing to pile on the mass and give up sensitivity to achieve deep bass in a relatively small cabinet.
David S.
Dave, I believe you are quite familiar with the loudspeaker industry; having worked in it. Are the requirements to manufacture an acoustic suspension woofer any more stringent than a vented cabinet woofer? or is the reverse true? (i.e. are AS woofers more expensive to produce than vented cabinet types?)
A bas-reflex has more sub-bas at a same size compared to e sealed one at same efficiency.
And has better controlled sub-bas at tuning frequency. If port size is big compared to Sd 30% or bigger. To small port leads to muddy bas response.
Above tuning it is like a closed box only the first port resonance is the negative influence to take care of.
I let confuse me for many years people saying closed box is better and on stands is better. Now I know better people who say that do not like good sub-bas or hate to hear sub-bas.It is their taste.
It is not difficult to make a tight sounding bas-reflex and also with low group delay. Although group delay is the result of the resonant system and questionable if it is audible. The tuning controls the woofer at tuning so good it almost doesn't move and the positive effect reduces cone extrusion at low frequency (so less dopplereffect when used as basmid).
A low groupdelay basreflex design for AS lovers.http://www.diyaudio.com/forums/multi-way/183727-ciare-design-idea.html
And has better controlled sub-bas at tuning frequency. If port size is big compared to Sd 30% or bigger. To small port leads to muddy bas response.
Above tuning it is like a closed box only the first port resonance is the negative influence to take care of.
I let confuse me for many years people saying closed box is better and on stands is better. Now I know better people who say that do not like good sub-bas or hate to hear sub-bas.It is their taste.
It is not difficult to make a tight sounding bas-reflex and also with low group delay. Although group delay is the result of the resonant system and questionable if it is audible. The tuning controls the woofer at tuning so good it almost doesn't move and the positive effect reduces cone extrusion at low frequency (so less dopplereffect when used as basmid).
A low groupdelay basreflex design for AS lovers.http://www.diyaudio.com/forums/multi-way/183727-ciare-design-idea.html
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Couple drivers that could be good in sealed box are :
Peerless SLS12 bit high Fs
SB Acoustics 12 SB34RNX75-6 bit heavy cone, but low Fs
I would say less stringent but most of the same difficulties apply to both. The biggest issue I dealt with constantly was DC offset and other misbehavior under high drive. Wiik of SEAS wrote a great paper years ago about improving DC offset with a properly progressive spider. (A non-linear spider would actually give lower distortion.) I found I agreed with his findings and did a lot of work trying to find spiders with just the right progressive characteristics.
It is a little more of a problem with vented boxes because the box unloads at low frequencies and DC offset (a temporary shift of the center point) happens more frequently.
Other woofer problems: suspensions that soften up when you overdrive the unit for long periods (resin crumbles and sheds). Also, the 1000 watt small subwoofer imposes huge stress on woofers and surrounds that rip, and spiders that break down are a constant battle.
Regards,
David S.
As I understand, an acoustic suspension system is one wherein the enclosed air is predominant over the surround in providing the restoring force on the cone of the woofer. I've read an explanation of acoustic suspension as being an attempt to reduce the interior volume of the closed-box system without sacrificing the bass cut-off frequency. That is, the surround is made more compliant which lowers the free air resonant frequency of the woofer. Then the box volume Vb can be smaller without raising the system resonant frequency higher than previously and the enclosed air is providing most of the restoring force.
So, yes, this thread really should be a discussion of whether or not the acoustic suspension technique IS effective at reducing the size of the box without reducing bass response (probably so) or being defective in some other way. One concern that has been expressed is that the floppy surround of an AS driver (floppy to the extent as proposed by Villchur) can't keep the cone of the driver moving as a piston.
Regards,
Pete
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Pete,
The linear motion of a driver is pretty much determined by the spider with a bit of help from the surround. In an Acoustic Suspension box the air spring provides the damping.
The problem is that most OEM manufacturers want to cover a lot of bases with any given driver, while a driver designed for an acoustic suspension is very much limited to that "specific" application alone. There are any number of build houses that will produce drivers to your specs, but they want a minimum order and that's after the up front tooling and development costs are paid for.
Best Regards,
TerryO
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