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 Post subject: New Altec Lansing FX-series PC speakers
PostPosted: Tue Nov 28, 2006 7:53 am 
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Since there's some speaker buffs here, I just thought that I'd comment on an intriguing new product line from Altec Lansing. I was walking through the Best Buy over Thanksgiving vacation, perusing the different offerings in the home audio and computer audio departments, when I noticed that Altec Lansing had introduced a new system in the $100-150 category. Usually there isn't a whole lot to get excited about in this price range, but the new FX-series from Altec Lansing does a couple things differently that I feel are worth mentioning.

The FX4021 is a 2.1-channel speaker system with two small, elegant 2-way satellite speakers with a 1" mylar semi-dome tweeter and a 2.5" cone midbass with a continuous-profile aluminum cone (most likely bonded to a paper cone behind it, though). The shape of the satellite speakers is a truncated square prism, and they have some nice-looking little stands as well. A square control pod is included, which I particularly like. It offers volume and mute control, as well as bass and treble adjustment. A large finger wheel provides the adjustment, while the changes are reflected in a small LED display around the rim of the finger wheel. Two other controls I don't typically expect to see on a speaker system at this price point are also present -- a 'loudness control' and something Altec Lansing calls SFX, which creates an expansive psychoacoustic effect. This effect causes the midrange to sound somewhat recessed, though, but I did not find this effect to be disturbing. The sound of the satellites can be quite natural with proper adjustment of the treble control, but it's also possible to cause them to sound shrill and harsh with the addition of too much treble EQ. The 2.5" midbasses exhibit a reassuring amount of excursion, letting me know that the satellite speakers work down to a decently low sub crossover point. There's plenty of detail retrieval here. At my neighborhood Best Buy store, the multimedia speakers are fed from a Sony SACD player, and I found the FX4021 satellites to be the best sounding ones in the price class. My own Cambridge Soundworks MicroWorks II satellites (which I use while at home instead of at school) have a slightly richer sound, but the FX-series satellites still have greater treble extension on tap than the MicroWorks' 3" full-range drivers, but both would be pleasant to listen to, and the FX-series offers the ability to dial-in your own frequency contour, which the MicroWorks do not. Lucky for the MicroWorks, they don't do much wrong in the first place.

The most intriguing facet of the new FX-series speakers, though, is the new subwoofer design. It's the only one in the price class that comes close to qualifying as a "true" subwoofer. As I listened, I was stunned at the real, deep bass coming from the FX series subwoofer's 5.25" cones -- this was even deeper bass than Altec's VS4221 which were sitting right beside, with their 6" subwoofer driver. The unconventional styling of the FX4021's subwoofer hides another unconventional technique, which is the secret behind the truly deep bass I was hearing. To tune a subwoofer to a low frequency, typically a large enclosure is needed, but a small enclosure with a very long bass port can be used to achieve the same tuning frequency. However, this small enclosure tends to produce a much higher acoustic impedance on the back-side of the driver, restricting the cone motion and requiring a large amount of force from the driver's motor. When the enclosure used is too small, the response curve appears to gradually roll off instead of exhibiting the proper vented box cutoff characteristics. By taking two drivers and coupling their diaphragms together, it is possible to produce a driver with twice the motor strength and suspension stiffness acting on the same amount of diaphragm area, allowing the required enclosure size for a given tuning to be reduced by half. This method of coupling two drivers together is called Isobaric* loading, because it creates a tiny chamber of constant pressure between the two driver cones, which is about as effective as coupling the voice coils of both drivers. Sometimes both drivers are facing forward, and an extra chamber must be built into the enclosure. However, another method of achieving Isobaric coupling is by taking the second driver and mounting it face-to-face with the first driver. Then, the second driver is wired out-of-phase with the first one, so that when the electrical signal is applied, both cones move in the same direction, even though both drivers are facing each other. This is called Isobaric Push-Pull, because one driver pushes while the other driver motor pulls. This has the added effect of canceling out asymmetries in the motor's magnetic field or the compliance of the drivers' suspension, lowering the distortion produced by the drivers when they are driven hard, for bass that's both deeper and cleaner. Isobaric push-pull doesn't double the effective diaphragm size, so it doesn't double the efficiency, but it does double the thermal power handling. The FX4021 delivers 24 watts to the subwoofer, but this is enough. It's possible to overdrive the subwoofer into "wubba-wubba" distortion by cranking both the bass controls and the loudness control to the max, but by this point the balance of the sound has already been shot to heck by the tweaking required to push the subwoofer into mud. On a heavy techno track, I managed to generate wind noise in the subwoofer's port. This sub is capable of generating a lot of air movement, but if you push it too far, you'll get both the Wubba-Wubbas and "Chuffing" from the port.

If you know about someone who loves to listen to music on their computer, but blasts it at high levels through ultra-cheap $30 JUSTer or OG speakers, this system would make a great gift for them. Or anyone who would enjoy decent sound from their computer. A 5.1 version is available, which steps up to 6.5" woofers in the subwoofer. I can only suppose that this further improves the already amazing bass for a product in this price range.

Here's a review of the FX4021 system, though the reviewer hasn't a clue about what is happening in the subwoofer. The main value is the pretty pictures.
http://www.techgage.com/article/altec_lansing_fx4021/2

*The proper spelling of the word is Isobaric. Sometimes, you will see this technique "Isobarik", because the Linn Products Company offered a loudspeaker using this principle, called the Isobarik. Linn has been known for their funky product names, but in this case we aren't referring to the Linn product, but to the design principle.

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 Post subject:
PostPosted: Tue Nov 28, 2006 11:18 am 
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Quote:
Altec Lansing notes that due to the "isobaric" woofer design, the bass output is deeper than that of a woofer twice it's size.


I am highly suspicious of this claim. As far as I know, isobaric enclosures allow you to reduce the box volume, not make the sound deeper.

Also, what do they mean by a woofer twice it's size? Do they mean they could make two 8" drivers have 'deeper output' than one 15" due to the "isobaric" design? Just sounds too far fetched to me.


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PostPosted: Tue Nov 28, 2006 11:23 am 
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Quote:
This sub is capable of generating a lot of air movement, but if you push it too far, you'll get both the Wubba-Wubbas and "Chuffing" from the port.


But the driver excursion is pretty crap no doubt which is why you get the "wubba wubbas". And your nicely marketed speech didn't mention driver excursion at all.


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PostPosted: Tue Nov 28, 2006 11:27 am 
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Well, the depth of the output of the speaker driver is primarily influenced by an increase in suspension compliance below the driver's resonant frequency, but some designs manage to tune below the driver's resonant frequency and then use a bit of equalization to compensate for the increasing compliance. If the equalization and the port tuning coincide, then the enclosure can really be energized by this approach and provide a lot of extra output without demanding much extra excursion from the driver, because the driver is being resonantly supported by the enclosure. Generally, though, you don't see a speaker tuned more than an octave below the driver's resonant frequency, particularly in passive designs like you'd use for high-fidelity applications.

In the case of the FX4021, Altec Lansing apparently decided not to actually make the box smaller, but to take advantage of the halving of the required volume to extend the low bass cutoff frequency even deeper. In light of the above, I figure that they probably developed drivers with an appropriately low resonant frequency to match the new low frequency loading that was possible. Any extra size to the enclosure beyond that which is necessary to allow operation in the low range increases the amount of resonant action assisting the driver, because it decreases the compliance of the air spring inside the enclosure, allowing the mass of air in the port to enjoy even longer excursions, though this can sometimes have the effect of creating a looser sound as 6th-order resonant operation is reached (with classic-alignment vented boxes typically being a 4th-order resonant system). I'm not sure how deep the bass was that I was hearing, but I wouldn't have been surprised if a solid 40 Hz was on order. The claims about bass extension are with respect to enclosure size, not the driver's diameter. The isobaric configuration with two woofers performs exactly as an enclosure twice its size would when loaded with a single one of the 5.25" woofers and tuned to the same frequency.

As far as driver excursion goes, I didn't actually hit the Wubba-Wubba region until I had completely maxed out the bass control on the control pod and activated the 'loudness' control as well, and cranked up the level to the point where other people around me in the store were looking at me like I was a nut. Excursion is a concern with isobaric systems, but it seemed like these drivers were pretty well behaved up to the point where I was asking positively stupid things from them, indicating that they probably have sufficiently long voice coils to keep some wire in the gap even when being run very hard. The tradeoff made when deciding to put two woofers together in an isobaric configuration is the fact that the piston area is still only equal to that of one driver, while the excursion demands from added bass extension are increased. Thankfully, Altec Lansing seems to have tuned their enclosure well enough to support the drivers' low extension. Excursion of a driver in a vented enclosure is greatly reduced to nearly zero at the tuning frequency of the port, as the enclosure assumes almost the entire acoustic load. Vertigo is right, however -- if we were dealing with a sealed enclosure, driver excursion would rapidly increase to unsafe levels. When I finally did hit Wubba-Wubbas, there was plenty of turbulence noise coming from the port as well, indicating that the vent was working very hard. The thing to be careful of in a vented box, however, is the fact that below the vent tuning, the drivers can unload catastrophically, creating all kinds of nasty sounds and even causing driver damage. I don't know if Altec included a subsonic filter in the subwoofer -- perhaps I should shoot them an email to see if they'll answer an engineering-type question like that.

Addendum: Checking the PDF file for the FX4021, the subwoofer provides usable output to 32 Hz. From 5.25" woofers, this is insanely deep.

(Between you and me, I'd eventually like to get into writing review pieces of audio gear, including speakers. It seems like PC speakers are ready to be reviewed more critically with high-fidelity criteria.)

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 Post subject:
PostPosted: Tue Nov 28, 2006 12:10 pm 
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Quote:
Thankfully, Altec Lansing seems to have tuned their enclosure well enough to support the drivers' low extension.


Ok, so they use filtering to lower the 'hump' and thereby get a lower response more cheaply, but how does that affect the phase of the signal? I hate laggy bass.


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PostPosted: Tue Nov 28, 2006 12:11 pm 
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Quote:
the subwoofer provides usable output to 32 Hz


If companies like Wharfedale insist on simple vented designs with no fancy filters, there must be a reason for it.


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 Post subject:
PostPosted: Tue Nov 28, 2006 12:29 pm 
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Just like any vented box, the output from the vent is 90 degrees out of phase with the driver diaphragm. At these frequencies, group delay above 100ms is practically inaudible (limited by the size and shape of your head and the spacing of your ears), and the group delay peak occurs at the enclosure's tuning frequency. The bass seemed very coherent with the main speakers in the system I listened to. Its tuning frequency is not so high relative to the resonant frequency that a "boom" effect is generated. Quite the opposite, in fact, which is why I even went back for a second listen.

Wharfedale probably uses a single driver in a relatively large box (as compared to the sub in the FX4021) because isobaric loading becomes expensive with larger drivers, and consumer expectations of enclosure size allow Wharfedale to build a larger enclosure to support the bass extension, while the customer expectation for computer subwoofers is that they will both be small and have a small footprint. I'm not saying that the FX4021 subwoofer would be any kind of match for a good 10" powered sub -- just comparing the size restrictions. As far as subsonic filters are concerned, most high-end consumer subwoofers have them as well, to prevent their drivers from unloading at low frequencies with today's DVDs. Less high-end subwoofers actually have bass boost circuitry, usually centered around 30-40 Hz to create the impression of deeper bass.

This isn't the first time I've ever seen an Isobaric system before. I'm just marveling at how practical it is for computer subwoofers, where the drivers are inexpensive, but the size constraint is there. The effect was decidedly a good one.

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PostPosted: Wed Nov 29, 2006 1:54 am 
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I'd have to listen but small subs I've heard either have boomy bass or laggy bass (or no bass), to the degree that I won't buy computer speakers with a subwoofer.

My wharfedale diamond 8.1's don't sound too bassy and are rated to 55 Hz which is why I don't trust frequency ratings too much. However, they do sound awesome, it must be said.

So if my vented 5" speakers are rated to 55Hz and don't sound bassy, I would hesitate to trust a 5.25" sub rated to 32Hz. I am suspicious of such claims and would always listen to them first.


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PostPosted: Wed Nov 29, 2006 11:06 am 
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Vertigo.... have any alternatives in mind in the $100-150 price range that you could suggest?

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PostPosted: Thu Nov 30, 2006 1:48 am 
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Quote:
Vertigo.... have any alternatives in mind in the $100-150 price range that you could suggest?


I don't, I don't like the look of any of them. I'm not too useful...

I've looked and the closest I saw was the Abit DS500 (without sub, the sub looks like it sucks completely) but they are ridiculously overpriced, I would never pay that price for them.

Computer speakers are just bad...

(oh hang on, there seems to be more models I didn't see)


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PostPosted: Thu Nov 30, 2006 10:57 am 
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vertigo wrote:
Computer speakers are just bad...


I've noticed that. Sigh.

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PostPosted: Thu Nov 30, 2006 11:01 am 
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I agree -- though there are a few that aren't as bad as others. The bigger Klipsch ProMedia sets are basically their Quintet system paired with a subwoofer. You do what you can with the budget you have, and I was surprised by what that particular model of PC speakers had to deliver.

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PostPosted: Thu Nov 30, 2006 11:22 am 
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I haven't looked at the 5.1, but the Klipsch Promedia 2.1 has its crossover frequency set at 5kHz. In other words, everything below 5kHz is mono. At least they are honest, the sorry excuses companies call satellite speakers probably can't go much below that... :)

But seriously, that would probably sound pretty close to a mono system. Also, you would probably want to put the 3" woofer on the desk where it belongs, which would be a space-issue.

Perhaps the 5.1 is an improvement.

Edit: Ok, it's not as bad as I thought, it has a 6.5" sub, not 3" like I thought. I saw 3" woofer and assumed. But it still belongs on the desk with its 5k xover.


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PostPosted: Thu Nov 30, 2006 1:08 pm 
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vertigo wrote:
I haven't looked at the 5.1, but the Klipsch Promedia 2.1 has its crossover frequency set at 5kHz. In other words, everything below 5kHz is mono. At least they are honest, the sorry excuses companies call satellite speakers probably can't go much below that... :)

But seriously, that would probably sound pretty close to a mono system. Also, you would probably want to put the 3" woofer on the desk where it belongs, which would be a space-issue.

Perhaps the 5.1 is an improvement.

Edit: Ok, it's not as bad as I thought, it has a 6.5" sub, not 3" like I thought. I saw 3" woofer and assumed. But it still belongs on the desk with its 5k xover.


What they oughta do IMO, is just not have crossovers built-in and let you do it yourself through your sound card.

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PostPosted: Thu Nov 30, 2006 2:06 pm 
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5kHz is above the frequency that most high-fidelity tweeters cross over to the midbass or midrange (usually around 3k). Perhaps the internal crossover between the 3" woofers and the mylar tweeter is 5kHz, but I can't imagine (having heard the Promedias on many occasions) that the sub crossover is above 200 Hz. But even that would be pretty high -- it's probably around 160 Hz.

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PostPosted: Fri Dec 01, 2006 11:06 am 
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Ok, I think I read a bum review. No excuses though.


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