SVS is well known to two-channel-loving audiophiles and home-theater enthusiasts alike. Founded in 1998, the company began by producing subwoofers that quickly earned critical acclaim. In 2012, SVS added loudspeakers to its product line, and in 2015, cables, footers, and wireless products. Today SVS offers 12 subwoofer models, ranging in price from $500 for the SB-1000 and PB-1000 in standard Premium Black Ash finish, to $2500 for the flagship PB16-Ulta in Piano Gloss Black (all prices USD). They offer a total of six bookshelf and floorstanding models of passive loudspeaker, ranging from $270/pair for the Prime Satellite to $2000/pair for the Ultra Tower in Piano Gloss Black. There are also center-channel and surround models, to flesh out full surround-sound arrays.
For those interested in decluttering their lives, SVS offers a line of active, wireless (Bluetooth/Wi-Fi) models. These include the Prime Wireless Speaker system ($600/pair), which incorporates high-resolution (24-bit/192kHz) DACs and integration with DTS Play-Fi and Amazon Alexa products; and the Prime SoundBase ($500), which offers connectivity via Ethernet, Wi-Fi, and Bluetooth, accepts digital and analog inputs, and has line-level analog outputs (including subwoofer out), and a 150Wpc amplifier to drive even the most demanding speakers.
Wanting to learn about the thinking that goes into SVS’s subwoofer and loudspeaker designs, Doug Schneider and I sat down in my living room on April 19, 2019, for a teleconference chat with director of product management Smith Freeman, who joined SVS in 2013 and holds degrees in physics and acoustics.
Smith Freeman
Doug Schneider: Why does SVS make both ported and sealed subwoofers?
Smith Freeman: We know that every person has different requirements and goals for low-frequency output, and furthermore, no two listening spaces are the same. Basically, there’s no one-size-fits-all for subwoofers. Some customers have huge SPL goals with the emphasis on movies, while others have space and aesthetic requirements. With our series of products, we are able to respond to any and all customer situations and scenarios. For example, this is why we make the PC -- the ported cylinder. Some people may need a ported subwoofer for low-frequency extension at high playback levels, but can’t support the footprint of a traditional ported design.
I do think there will forever be personal preferences for sealed or ported subwoofers. As an engineer and designer, it’s my job to make sure they all exceed expectations, and provide the deepest extension and highest output possible.
Diego Estan: Many two-channel enthusiasts seem to cling to the notion that sealed subwoofers are better for music, and that ported subs are better suited to home theater. I have the sense that this may no longer be true with modern sub designs. Could you talk about the advantages and disadvantages of both types of enclosure?
SF: I do as much as I can to dispel this notion that ported subwoofers are inappropriate for two-channel music systems. Everything we do in our subwoofer designs is meant to ensure that our products are neutral and accurate, with speed and clarity, regardless of their acoustic alignment [i.e., whether they’re ported or sealed].
One of the key attributes of sealed and ported subwoofers is how they behave in and react to the room. In a sealed system, you have a slower low-frequency rolloff in the deepest frequencies. This yields a very different reinforcement from room loading as opposed to a ported system, which tends to have a steeper rolloff but at a lower frequency. A ported sub is generally a more efficient system, offering higher maximum output with the same amplifier power, which is especially beneficial for larger rooms. If either type of system is designed properly, there’s no reason why it won’t convey the subject material with neutrality, whether it’s an upright bass in a music recording or an explosion in a movie soundtrack. So what we’re doing at SVS is looking at every aspect of the system to make sure bass reproduction is true to the subject material.
DS: You mentioned speed and clarity as design goals. How do you define speed?
SF: What we’re talking about is the ability of a woofer’s suspension to control the position of the moving mass in space according to the signal. What we don’t want is any ringing or movement in the woofer after the signal has decayed naturally. We must ensure the suspension is tuned properly for the motor design, the cabinet, and the entire system. It’s not enough to have a giant magnet and voice coil; you need to be able to control the driver.
DS: And sealed vs. ported has no effect on that?
SF: It does. The volume of the cabinet has a direct impact on how a woofer and its suspension behaves. Likewise, the port is behaving as another transducer -- the volume of air in the port is also oscillating, which means the port is another acoustic element. The tuning of the port must be optimized, so as not to induce too much port-air velocity, but also allow it to contribute to the total output of the system. You can go in either direction, where the port is adding too much energy, or redundant energy at a particular frequency -- or, conversely, you could tune it so that the port’s contribution to total output is negligible.
DS: So sealed or ported subs can be equally good performers?
SF: Of course. But in a way, they’re like apples and oranges -- you must consider the space or room that they’re operating in. When we speak to customers to advise them on purchases, understanding their rooms and desired playback levels is important. This may drive a customer toward a ported vs. a sealed system, or multiple subs vs. one.
DE: Could you describe the main design considerations that determine the quality of a powered subwoofer?
SF: With subwoofers, you need them to play low and loud at the same time, which is not always achievable. For example, you can have very deep low-frequency extension, but only at very low levels, which is not useful. You also need to control the higher-frequency response, so that the subwoofer blends well with whatever speakers you’re combining it with. The subwoofer must also be appropriately designed for control so that it has the transient speed to play whatever material you’re throwing into it. These are the general performance goals that we’re always trying to hit on every subwoofer -- or, any properly designed subwoofer should be able to do all those things well.
When we make our choices from a design standpoint, it’s not enough to narrowly look at individual parts of the system -- you must consider the system as a whole. And, as in any system, you’ll be limited by the weakest link. For example, if we make a super-rigid, well-braced cabinet, and we put a massive amplifier in it with a huge woofer, but we put a tiny motor on that woofer, the motor would limit the whole system. The SVS engineering process is rigorous on every front -- we’re always evaluating and tuning each element of the system. This process encompasses everything, even the screws we use. That being said, the main parts of the system are the cabinet, the driver, the amplifier, and the software.
DS: What aspect or part of a subwoofer most drives up its cost? Is it overall physical size, which of course is linked to the driver and cabinet?
SF: The cost is the sum of the parts, so we must balance this equation when trying to meet a price point. For example, how much amplifier power do we need to drive a particular woofer? Is the cabinet braced enough for the output we’ll get from the amp-driver combination? Is the output going to overwhelm the size of the port? Every aspect has to be weighed for performance and cost together. Take the dual ports on the PB-3000: We’ve received questions from customers about whether the PB-3000 will have the option for a second tuning mode, with one port open and the other closed. We said no, because the single-port performance wouldn’t satisfy our requirements for that system, and while you’d gain additional low-frequency extension, we concluded that the negative consequence of the port noise would outweigh the benefit. So, for the PB-3000, there are only two tuning modes: two ports open or sealed. Contrast this with the larger PB-4000 and PB-16 Ultra subwoofer, where we have greater port-opening surface area, so we’re able to offer two- and three-port tuning modes in addition to the sealed modes.
DE: I’m sure that most owners of SVS subs are home-theater enthusiasts who’ve been using the room equalization built into their A/V receivers for some years now, but I think room EQ is now gaining traction in two-channel circles as well. Has any thought been put into incorporating room EQ in future SVS subs, and providing calibrated microphones and maybe partnering with Audyssey or Dirac Live?
SF: What I can tell you is that we are constantly evaluating all of the auto-EQ solutions that are possible. I would love for us to release a room-EQ solution for our subwoofers, but we’re only going to do it if it’s the right solution, without compromise.
DE: The Ultra Tower loudspeaker has dual, horizontally opposed woofers, which offers advantages such as cancellation of mechanical vibrations. Has any thought been put into releasing an active subwoofer with the same sort of driver mounting?
SF: I would love to make something like that! It’s true that the benefit of dual opposing drivers is fantastic, and I’m a firm believer in that alignment. While I can’t say what we’re working on specifically, I can tell you that I’m super busy, and that there’s a ton of products we’re working on -- all flavors of products.
DS: Can you tell us what makes a good loudspeaker?
SF: A good loudspeaker should be faithfully neutral to the source material. In an ideal sense, it should be omnidirectional, and offer no coloration or temporal changes. It should just present the source material as close to what was originally recorded as best it can. In the frequency domain, a loudspeaker should present every frequency equally, without prejudice for or against any particular band. With that in mind, you need to pay attention to the total sound power and the off-axis responses, and make sure that all the drivers’ polar responses behave well together and don’t create any lobing effects or other acoustic augmentations of the original source material. And then you take the room into account, and how the total output of a speaker system in a space is received at the listening position.
DS: So you’re going for a flat frequency response, as well as wide and even dispersion?
SF: You got it!
DS: I’ve seen some speakers display messy off-axis frequency responses, but when you sum the total -- that is to say, the polar response -- it looks quite flat and smooth. Any thoughts?
SF: The on-axis frequency response of a loudspeaker is a critical part of how we hear a speaker, but it’s not nearly the entire story. While this is the “first arrival” to our ears, the total sound power of a loudspeaker also takes into account the off-axis response. The off-axis response will be more likely to reach our ears later in time, [because it’s first] interacting with walls or other boundaries. While the on-axis frequency response will control most of the total sound-power frequency response, we must also consider the off-axis response and how the speaker behaves in a real room, not just an anechoic chamber.
It’s normal to see some rolloff in off-axis response, but it’s important to make sure there are no severe dips or peaks. When tuning the crossover, I pay a lot of attention to the polar response of the drivers and the system. In particular, as a midrange or woofer approaches its higher operating frequency, it becomes less omnidirectional and will start to beam more, and lose control of the off-axis response. This is part of the reason why the tuning of a speaker and its crossover is so time consuming, and requires constant measurement and listening sessions.
DS: In the Prime Pinnacle, the midrange driver is mounted above the tweeter. Was this choice based on acoustics or cosmetics?
SF: The choice was largely acoustic and mechanical. Getting the height of the tweeter right for real-world living spaces is important. I’ve seen some systems where the tweeter is mounted very high, which is not something that works for a lot of people’s homes. We know our customers will mix and match different speakers, so we want to be able to maintain a coherent acoustic image traveling throughout the soundstage. We also found, during our listening tests, that we were getting better results with the midrange mounted above the tweeter.
When we set out to build the Prime Pinnacle, we thought it seemed simple. We assumed it would just entail building a bigger version of the Prime Tower. In the end, we went through about five major redesigns and revisions. Each revision represented updates to the acoustic and mechanical design, from the position of the midrange to how many woofers, how many ports, the bracing, and so on. Each time, we would tune the crossover, measure, and listen to the system against the previous revision and the Ultra Tower and Prime Tower. I think it was version 5.5 where we finally settled on the acoustic and mechanical alignment for the tweeter, midrange, three parallel woofers, and three port tunings.
DS: When in that design process did you decide to place the midrange over the tweeter?
SF: It’s a little difficult to describe, but we were doing A/B listening tests with the Prime Tower, Ultra Tower, and two identical versions of the Prime Pinnacle, the only difference being the tweeter and midrange positions. It was really arduous work doing the voicing work on both speakers, but in the end, we found that the midrange and vocals sounded most honest and transparent when the midrange driver was mounted above the tweeter. We were basically observing better diffraction qualities due to having the midrange up at the top of the cabinet. With that, we had to study the crossover points very closely to make sure the crossover point between the midrange and the woofers blended well, and that ended up at around 300Hz.
DS: What is the crossover frequency for the midrange and tweeter?
SF: About 2.1kHz. We keep this tweeter crossover point the same for almost our entire product line. That’s a big part of how we ensure coherent voicing across all of our products.
DS: How do distortion measurements factor in?
SF: Distortion is one of many parameters that are scrutinized early in the design process for all our products. When talking about driver-borne distortion, we review each driver, from their core parts and materials, from the start. Before that, we determine the target driver complement and the frequency-response range that each driver will be asked to reproduce. For example, we’re not going to ask a 6.5” woofer to operate at 10kHz. Once we know the operating range for each driver, we can optimize the cone material and shape, suspension, motor parts, and voice coil to ensure the best measured performance and lowest THD [total harmonic distortion], plus some headroom.
As an aside, headroom is a major consideration for all our products. In particular, one of the reasons we use very high-powered amplifiers in our subwoofers is because it gives the system performance headroom. When the system has this extra operating capability, the system will perform with lower distortion through more of its operating range. This goes for every part of every model we produce.
DS: You mentioned that many of your customers are home-theater enthusiasts. Many mass-market A/V receivers may have a hard time with low impedances -- when do sensitivity and load impedance factor into the design process?
SF: For a passive speaker, we address the sensitivity right away. Again, we start with determining the driver complement for a speaker, and from there we can target the desired impedance for each driver and the system all together. Most passive speaker designs operate under similar principles. The system impedance is a critical dimension we must pay close attention to when we get into crossover design. We have to track the impedance dips for each driver in the system, whether it’s sealed or ported, and make sure we’re not creating points in the system impedance that will be too low for most electronics to comfortably drive. If we find we’re asking a driver to play too close to a low impedance point, we may take a step back and look at the driver design to try and push those driver resonances lower, or revisit the crossover point. This is especially important when you start wiring several drivers in parallel, because the total system impedance is being driven down significantly. For example, the 6.5” woofers we use in the Pinnacle are totally unique to the Pinnacle. They were specifically designed for the Pinnacle line, nothing else. We had to start with an all-new woofer, and all woofers are wired in parallel, each mounted in a unique ported enclosure. We needed to make sure that the resulting total system impedance didn’t present a troubling load for lower-power receivers.
DS: Would it make sense to combine your knowledge of active subwoofers and passive speakers in a single loudspeaker design?
SF: There are some benefits to this approach. We are not currently working on anything with that alignment, and that’s because we feel that the best results still come from one of our subwoofers paired with one of our speakers.
DE: So you feel that a separate active sub and passive speakers is the better way to go? If so, why? I ask because that’s how I have my own system set up.
SF: Generally speaking, an important hurdle to overcome with any passive speaker system is controlling cabinet resonances. How do you not compromise the performance of that passive speaker when you’ve mounted a high-power, high-excursion subwoofer inside it? A good subwoofer is an absolute workhorse for output. It’s also a very difficult system to design so that there are no extraneous vibrations or any other mechanical issues with its own internal components -- and now I’m going to attach a full-range passive speaker to it! There are ways to do it, and many manufacturers have done it, with tremendous results -- but this type of design makes for a far more complicated system, and the only real benefit is to aggregate two different speakers into one box. From my experience, if the goal is honest, neutral playback and absolute immersion, the best results still come from discrete, purpose-built subwoofers.
. . . Diego Estan
diego@soundstagenetwork.com
