Originally Posted by notnyt
oh cmon, like nobody can hook up an SP or other worthwhile amp to some sealed subs and apply dsp/limiters correctly.... I understand you have a product to sell, but not everyone who DIYs is a moron.
Originally Posted by Mark Seaton
There's a lot more there than just the limiter. Unless you've tested many of the drivers, a DIYer has no way of knowing what the expected limits are vs other issues happening before those limits causing either distortions or highly audible sounds of distress. While anyone can, I suspect you would be surprised if you interviewed DIYers to see how many measured the behavior of the sub itself (NF in room to confirm performance is fine), and see similarly surprising responses when asking if they went through testing for any leaks, squeaks, or rattles with a test signal. While a few do, plenty of DIY-favorite amps don't have internal limiting, and a MiniDSP 2x4 does not include any features for limiting. Quick setting of limiters can result in noises that sound similar to hard clipping and just protect from death while still making bad noises. If more optimally dialed in, it's possible to increase useful playback levels by 6-12dB with very minimal audible changes in the first 6dB of that, and nothing offensive well beyond.
You are an experienced builder with a good deal of knowledge. Inside an echo chamber of a small DIY community it may feel like most should know these things and practice them, but that has not been the reality I have observed, where such cases are the exception. It has little to do with what someone *could* do, but rather is all about what people take the time and effort to do, or have the persistence to figure out the issue when things don't behave as expected. Companies producing other subwoofers on the market *could* do many of the things you might in a build, or similar things I do. The reality is that many don't. The reasons vary from feeling it doesn't matter, not seeing it as worth the time and effort, or in fact not knowing any better. Before starting Seaton Sound I thought the relatively elegant/simple sealed subwoofer that wasn't electronically castrated with a useful, starting low frequency extension was too obvious an offering to start out with and I started experimenting with more exotic solutions. Even after a few years of pointing other manufacturers to offer the right combo, almost none bothered, so I did. Fortunately there are many more such offerings available today, but most every manufacturer chooses to do things a bit different. The things I mentioned aren't about cost, they're about polish and refinement of the end product, and willingness to hold things up rather than ship out a an under-performing item.
I'd just like to add on to Mark's answer a little bit on why I think Mark's subwoofers are much more refined than what a DIY'er can normally achieve.
I deal a lot with limiters for my own speakers because it is a necessity when trying to get as much bass as possible from a small speaker. Before the journey I thought limiters are simple devices that'll just clamp the output from exceeding a certain threshold. Boy was I wrong.
Yes, the miniDSP has a limiter function, but I'd go so far to say that it is almost useless. Here's why
Simplistically, the miniDSP's limiter pretty much works like this: If it detects the signal exceeds the threshold, it reduces the entire channel's volume by the amount it exceeds the threshold by. For example, if a sudden signal comes in and it exceeds the threshold by 5dB, miniDSP will reduce the channel's volume by 5dB so it stays under the threshold.
The problem? This is not frequency aware, so instead of limiting just the frequencies that exceed the threshold, it brings down the whole subwoofer volume. Why is that a problem? Let's give an exaggerated scenario (which isn't too far from reality). Let's say you have a small sealed sub that uses EQ to boost the low end extension. Let's say the subwoofer is 20dB down at 10Hz. You'd put a 20dB shelf boost on the subwoofer so it'll be flat to 10Hz. Now, you put on your favourite vinyl album on, and the typical vinyl has a low frequency rumble in the single digits, let's say 10Hz. Let's say the vinyl track only has 40Hz bass, and the subwoofer can play 110dB at 40Hz and starts rolling off right after. Now because the EQ is boosting 10Hz by 20dB, this means that even though your subwoofer can play 110dB at 40Hz, the limiter will prevent the subwoofer from playing above 90dB because the 20dB of the EQ on 10Hz is causing the subwoofer to reach its limits already at 10Hz. That's bad to say the least. And this is exactly what the miniDSP and the iNuke limiters do, and this type of limiter is called a single band limiter. The only purpose they serve is to physically protect your speakers, that's it. For audio use, it is horrible and nearly useless.
So what we really want is to cap the 10Hz stuff at 90dB, and continue to let the 40Hz stuff play up to 110dB, and then limit it there. So what we do is to separate the bass into multiple bands. If we had 2 bands, <40Hz and 40-80Hz, then we can achieve what we want. But the problem still exists, just at a smaller bandwidth. So the solution is just to separate them into more bands to reduce this problem. This is called a multi-band limiter.
There are also various other issues with peak limiters like the ones described above. They introduce distortions and artifacts because they are analyzing signals in real time. For example, there is no way to know if a signal is 10Hz or 20Hz instantaneously. You need to wait at least the time needed for sound to travel the equivalent of the wavelength of the frequency. For example, the wavelength of 20Hz is 57 feet. It takes sound 50ms to travel 57 feet. So there is no way to know if that's a 20Hz sound for sure until 57ms has passed. But what happens if the signal has exceeded the threshold, how does it know if it should be limited? One way is just to clip the signal until it knows the frequency, and that's one source of distortion. And now what about the phase shifts that are introduced from the filters used to separate the bass into multiple bands? There are many other issues, and hopefully you see that a limiter design is much more complicated than one would think.
While I don't know what kind of limiter Mark does for his subwoofers, I can guarantee it is much more complicated and effective than what DIY'ers can do with miniDSP and iNukes. I can also guarantee all of you will underestimate the amount of time Mark spent on dialing in the limiters. If his experience is anything like mine, it involves lots and LOTS of listening sessions with only the subwoofer playing, listening to the same thing over and over again dozens and dozens of times, then repeat with different materials.