Why We Call These Perfect Filters

Max Bass and Protects Drivers? Perfect.


The below text is a transcription of the video.

Hey there, John Hunter with REL here. We’re going to explain a little bit of our perfect filters. These are incredibly important in the last generation or so products that we’ve been developing. They’re all tailored to individual units. This particular S812 that we’re using is a perfect example of it, but we use these in everything from our HTs to our TXs, to our SS ’s. Significantly, we do not use perfect filters in our reference. Why? When we get up to the reference, we don’t hold anything back. And that means that we can perfectly size the volume of the cabinets to what the driver needs. So the point of a perfect filter is this. If you stuff a massive 12 inch long stroke driver into a relatively small cabinet like this, it’s not ideal for the driver. Normally, this thing would need a cabinet roughly twice the size to really use all the capacity of the driver.

So how does that manifest itself? Well, when you put it into too small of a cabinet, and the smaller the cabinet is, the more dramatic this happens. What winds up happening is base is dropping off at an incredible pace below about 50 hertz, all right, down to 50. You can make it sort of look fairly accurate, and then it just goes, why? Because it’s fighting the limitations of the cabinet. We get a little bit of help on some of our units that have very specially developed passive radiators down below that will bring it in. But those really help at the lowest base. So how do we get it to be more linear in sort of the 30 hertz region? We’d say below 40 hertz is really, 40 to 25 is where the perfect filters really do amazing work. We can electronically in the crossover section of our filters, elevate that region.

So if you think about it, if the subwoofer is rolling off like this inside that cabinet, if we have a little bit of an inverse and it’s so easy to get caught up in the math and oh, well, it looks like this, all I have to do is this. It’s never that simple. You really have to listen very carefully and really iterate exactly what the human ear wants to hear out of it. But the reality is that if we have a generally upward sloping compensatory filter, what we wind up with is something that is much closer to linear, much lower. So rather than, for example, falling off from 50 hertz and below, it’ll get a little bit bumpy in the sort of 40 down to 30 hertz region. But it’s doing it, it’s doing it at 90% of what you need it to do.

And then the secret we just developed in the latest HTs is that we actually have an analog subsonic filter, way down low, five hertz, eight hertz. That takes out all the infra base. So the subwoofer isn’t being tasked with trying to inaccurately replicate massive movements down at 12 hertz, at 13 hertz, where all you’re going to do is wind up honestly damaging a driver or worse damaging an amplifier. So the perfect filter compensates for what is essentially too small of a cabinet. And I know most civilians would look at this and go, that’s a pretty good size subwoofer, John. Not for the physics of what drivers really need to see. This same thing, for example, roughly the same size driver finds itself in our new brand new No.31s, and that cabinet is 30% larger by volume than this one.

And that driver’s a little different. So that one is a custom tailored suit made on Savile Row. These were taking things that are not intended to be happy together and really making them happy, elevating electronically with a lot of power. That’s why our newer designs have far more horsepower in the amplifiers, and we’re using some power and some equalization, very gentle to elevate that up, get it, instead of falling off like this, to go along like this, take it way down low, and then it starts to roll off in the twenties. Well, that’s what the perfect filters do. It’s a great combination of technology, very simple analog technology, and just good application of physics to make these produce things they could never have done five years ago.

May 22, 2023 - Posted in: Sound Insights