On this episode, our very own subwoofer enthusiast, Stephen Entwistle drops by. Hello, and welcome to Ask the Expert. My name is Christopher and I'm your host. So as you might can see, we've changed the venue for this episode but don't you worry we're still right here in Skanderborg, at our HQ. With us today we have Stephen, and Steve can you start by telling us a little bit about who you are. - I'm one of the senior acoustic designers here. I've just done the last four subwoofers we've just launched. They're a bit more than just subwoofers, but I've done quite a few in the past as well. - So, you know a thing or two about subwoofers. - Yes. - Cool, and we have a lot of questions today, so I think we should just jump straight into them, is that okay? - Great. - Perfect. Stephen, I think we should get started with a question about what makes a subwoofer sound tight and punchy? It's from Sandy and just to paraphrase the question what are the key parameters of making a subwoofer sound tight and punchy? - Yeah, there is only one thing and that's BL. So, BL is the force factor in the drive unit and it's to do with the voice coil and the strength of the magnet. And the higher the BL, the more the drive unit follows the voltage from the amplifier. So an amplifier tells the driver to move, it moves, and when it tells it to stop, it stops. So, you can kind of say that the BL factor tell us a little bit about how well the amplifier controls the drive unit, or? - Exactly, yeah, it's the way they're coupled together. So, it's just - one is voltage coming from the amplifier, the driver moves and the higher the BL, the more it wants to follow that voltage. The less the other electro acoustic parameters of the drive unit have influence on that. - And that control you have over the drive unit actually makes the subwoofer sound tight and punchy because when it says stop, the amplifier says stop, the woofer stops moving. - Exactly. - Okay. So, BL factor is just the key parameter when you talk about tight and punchy bass. - It's the most significant one I would say, yeah. - Let's go with that. Our next question, Stephen is from Brian and he wrote so if we assume that you already have a really good room correction system at home, what would the benefit of considering a sub six with its advanced DSP and pre-sets, be compared with considering a sub three? - That's two kind of different products, in many ways. The sub six is a more advanced subwoofer, you know. We developed the drive unit from the ground up specifically for maximum subwoofer performance. So, we've got the new cone, a new diaphragm, a new surround to allow it to move more. So, there's a whole load of benefits on the for the sub six over the sub three, just pure audio performance. The features that we also are able to add in to the sub six over the sub three is the better integration in a 2.1 setup. So, if you don't have a room correction and you aren't able to time align your subwoofer with your speakers because your subwoofer's in an odd location. You have that ability inside the subwoofer to do that. So it's an extra level of functionality and we are able to tailor the filter specifically for our products. So, you get a perfect integration whether you're using a Special Forty or an Evidence Platinum. - So, what I'm hearing you say is that even if I did have a room correction system at home that is really advanced and really good, it still makes sense to consider the larger sub six compared with the sub three because there are more benefits with that product? - Completely, just from a raw performance point of view, the sub six plays louder, it plays lower, you have the balanced drive unit so it doesn't shake around the room, when you're really playing low bass. The integration with your main speakers, You can handle that in your processor with your room correction, that's fine. - So, you're not just buying a couple of pre-sets? - No, no, no, you're buying a lot more than just a couple of pre-sets... - I hope that answers your question, Brian. Stephen, if you already have a pair of loudspeakers that go really low, what is the benefit of adding a subwoofer? It's a question by Peter, and I think that it's a really good one. - It goes lower, for starters. - But I guess there's more to it than it just goes lower, right? - Yes, I mean a lot of subwoofers are used for movies, that big boom, or that big bang, but there's so much more to it than that. So, if we take an Evidence and then we add a subwoofer that's properly integrated, you know, we may only abstend that response by 10 Hertz, but the way the subwoofer integrates with the loudspeaker you get so much more. There's often in recordings, the cues that we pick up on for localization, they're all in the reverberation cues. - Just one, can you talk a little bit about reverberation and what that is? - Reverberation is a fancy way of saying echos. - Okay. - So, if you go, if you're in your bedroom, it's got a fairly low reverberation time. If you're in a cathedral, that will have a very long reverberation time. - Because the room is really big, right? - It's really big, there's lots of hard surfaces, not a lot of absorption. And in the big spaces as well, particularly the low frequency reverberation gets even bigger. And when you add a subwoofer in, you're able to reproduce that reverberation more accurately. And you might think oh but who cares about that, but that reverberation gives you cues all the way up the frequency scale. So, you know, kind of going back to our Evidence, Evidence, you know, you put a violin on the Evidence and you hear the violin and it sounds really good, and you can picture it in the space. You add the subwoofer, the violin stands more real, the position becomes more pinpoint and it's just an overall more immersive experience by adding the subwoofer. - And we were actually most of the time before we do an episode we actually do an article and we were talking a couple of weeks ago about this. And it really struck me as quite interesting, because I don't think that a lot of people actually consider that the subwoofer can add information, not just in the lower frequencies but in... in the middle and in the high frequency as well. And it really does, right? - Yeah, I mean everything interacts with each other in different ways, so you know. The subwoofer will change your perception of how the tweeter sounds the tweeter will change your perception about how the subwoofer sounds. If you've got a misalignment with the integration between the subwoofer and the main speaker, that will completely ruin your experience. - Of the entire system. - Of the entire thing. Yeah, not just because you've got a cancellation or something... - So adding that subwoofer's not just about, you know, adding a lot of punch and boom to your action movies. It's about adding all of the information that was in that cathedral when it was recorded. - Yeah, even if you look at modern pop music, or rock music it's still, they still use the same effects, you know. It's not been recorded in a cathedral, but they have a reverb unit that they add, to give you that kind of spatial feeling. And it's just as valid for an artificial reverb as it is for a real reverb. And interesting thing for me, you know, Everybody's like oh you know, what's your wife going to be like? I took the subwoofer home, and my wife was just like finally music's starting to sound like it should. And it's not because I've got bad speakers at home, but she's just used to real life music in concert halls and things... - So, I guess that this long talk if we had to sum it up, and give Peter an answer, you add so much more to your speakers, when you add a subwoofer. - Yes, it's not just a frequency response. - Cool. Okay, Stephen, we have a question from Tim, and before I ask it to you I just want to tell the viewers that last time on Ask the Expert we covered room acoustics with Kristoffer And from that episode I know that, you know, placing speakers in a room can be a pretty big topic, and that leads to Tim's question because he wants to know how to put his speakers, his subwoofer, where to put them in his room... And as I said, it's a huge topic, but could you try and help Tim out just a little bit, and maybe not going in way deep into detail but giving a couple of pointers for people out there to think about when they put a subwoofer into their room. Yeah, when you put your subwoofer into the room most rooms are fairly small compared to the wavelengths that are happening from the subwoofer. So the placement in the room is critical, mainly for model behavior, which is room acoustics. On top of that we have time alignment issues, so you need to find a compromise between time alignment and model behavior and to fully explain that it's going to be more than two minutes. - Yeah, Kristoffer's episode was 32 minutes So, It is a big topic, but are there any hints or points, or things to think about that we could explain in a couple of minutes here? - Yeah, time alignment, I definitely want to time align the signals between the subwoofers and your main speakers. You can do that in a processor, our bigger subwoofer you can do that inside the subwoofer as well for a stereo system. That's really going to help, and to think about room modes there's lots of information about room modes available on the internet, so you can position your subwoofer to kind of ameliorate the blur, the room modes. - And I know that you can use more subwoofers to help out, but that adds another set of things to worry about, I guess. - Yeah, there are... With more subwoofers you can position them differently in the room so you activate or cancel room modes differently. So it gives you another layer of control. So you can control the room modes with position and acoustic treatment. And then you need to think about time alignment to make sure everything adds up properly. - And going back to the time alignment thing, you were talking about you can use processors, our bigger subs, they have pre-sets that help you out. If you don't have any of that stuff I guess it's again I remember the first episode you were on, we talked about the circle around you, the equilateral triangle, it's about getting the subwoofer in line with all of that stuff, right? - Exactly, you want the subwoofer... If you don't have any delay available, or room control available, get your subwoofer in line with your speakers. - And that means just the same distance away. - Same distance away, yeah. Ideally in front of you, but if you have to put it behind you It's maybe not so bad, but. - Maybe not so bad, so put it in front of you if you can. - Yeah, definitely. - And I guess that's where we should close this topic, because we could keep going for hours and hours, right? - Yeah we could go for a long time on this. - We were talking about it took you four years to come to an understanding of it, so maybe we can't really cover it in a couple of minutes. - No, not easily. - Thanks, Steve. Stephen, we are at our final question and it's from René and he asks if you can comment on fast bass. What he means is that people often tend to believe that bigger drivers are slower than smaller ones. - I prefer kind of tight bass or boomy bass instead of fast and slow, but they're kind of interchangeable. - And just for my sake, can you maybe define what you mean of a fast and tight, or slow and booming bass. - So, fast bass is like *snaps* that. And boomy bass is *buh*. - Okay, I get that. - And yeah, generally, you know, bigger drivers... We're back to the BL - From earlier question... - You know, they tend to have different parameters so the BL isn't as good and then they tend to just react a bit slowly. So, they don't have that *snaps* snap, that tightness. It's easier to achieve that with a smaller driver. Having said that, I've had heard some really slow and boomy small drivers, like eight inches. But some really tight and fast drivers particularly in PA, like 21 inch driver. - Pretty big. - Yeah, you know and you really need to hear that. That's an experience all by itself. - So, just to sum it up here, it doesn't really have anything to do with the size of the woofer, but if the control of the amplifier has over the cone? - Yeah, it's an interaction of the two. You always gonna have to move a fair amount of air. We talked about that in our white paper, you know volume velocity, you still have to do that but how you do that, and the control you do that generally smaller drivers it's easier to achieve than on a bigger driver. Okay, so is all the way back to the first question about the BL and watch that again, and then you get a little bit closer. - Yeah. - Perfect. Steve, I feel like I've been getting myself into some pretty big topics this time and the time before with room acoustics. - Yeah, certainly. - But even still, I want to say thank you for being here today It's been a pleasure. - Same here. - The next episode of Ask the Expert will be in January so stay tuned for that, and keep the great questions coming.