All amp manufactures boast a plethora of features, ranging from flux capacitors to lithium ion fission generators. Many of these features are impossible to test/understand to the normal end user. I'll run through some of the features listed by Massive for their D800.4, focusing on the ones that I can tangibly identify and experience.
Filters - These are listed at 18db slope. The frequency response of both HPF and LPF is 50-750hz. The filters are able to be fully defeated by sliding the switch to "FULL".
While I would love to see a x1/x10 multiplier of the internal crossover, allowing for a more flexible crossover, there aren't many amps that include such a feature. The only ones that I've tested lately that have such flexibility have been the Zuki Eleets, and the Zed Audio Leviathan. The frequency response of 50-750hz is a bit limiting for the amp. The only scenario I see this crossover being useful is to push 4 sets of components, or 2 sets of components plus a small sub. Most users will not be using 4 sets of components, or trust "only" 240 bridged watts to push their sub, so these scenarios are a bit far-fetched. I feel that anyone running an active setup will use the internal crossover in "full" position.
As for the choice of an 18db slope, I tend to prefer 12db slopes, as I personally feel that they allow for better integration between drivers. Some prefer 24db slopes since they like to run their drivers close to their useable frequencies and need the steep drop-off. Massive's choice of an 18db slope is a smart one, as it effectively provides the best of both worlds, and does provide good phase response, so the user doesn't have to worry about connecting speakers in/out of phase. I tested the functionality of the internal crossovers using an RTA on my test bench, and am happy to say that they perform the way they are advertised.
This all being said, this amplifier was tested by me using active setups, including a pioneer DEH-p99rx, a JBL MS8, and a Pioneer DEH-p880rs. I suspect that many users looking for a high powered 4 channel amplifier will be running an active setup anyways, and won't be depending on the internal crossover.
High Power Output
This amp is listed at 120x4 at 4 ohms. It has a good power supply which allows it to also make 240x4 at 2 ohms as well. I tested this amp pushing several power hungry woofers. I was able to audition the amplifier with Seas' ER18RNX (8 ohms), ID OEM V1s (4 ohms), and Exodus Audio's Anarchy midwoofers (8 ohms). I am happy to say that the amp delivered as advertised. It was able to push all of these woofers to very high effect, without displaying any signs of distortion or loss of control at high volumes. The speakers that I auditions are by no means efficient, and provided a very strenuous test for the power output of the amplifier. That being said, power ratings of amplifiers can most often be taken with a grain of salt, as some amps are rated rather optimistically, and others conservatively (Zuki @ 5 watts anyone?). I feel that a challenging test of power hungry woofers is the best indication of just how good an amp's power rating is in the real world, and The Massive D800.4 passed with flying colors.
Noise Rejection Circuit
This may sound pretty gimmicky, and if you had asked me about this a couple of years ago, I probably would have agreed. That is until I recently ran into an install where I used a very high quality amplifier that had garnered a lot of praise from all comers. It sounded great, but I could NOT get rid of electrical/alt noise no matter what I did. I finally gave up after checking all of the common answers like grounding points, RCA runs, etc, and simply swapped the amp out for a JL HD. This totally eliminated the noise. I changed absolutely nothing else. I was absolutely mystified and I bugged JL about the reason behind this. I found out that JL actually spends quite a bit of time engineering a noise rejection circuit, tying the grounds of the RCA's to the common ground properly, as well as other amplifier design practices that apparently work to reject noise, instead of cutting corners.
Luckily, I still had access to the "problem" car, and installed the Massive Audio D800.4 into it. I am ecstatic to report that the D800.4 rejects noise just as well as the JL HD in this case. There is absolutely nothing worse spending hours of time chasing phantoms when the problem could have been solved with careful product selection.
Honda Accord Coupe 2008
Source - Pioneer deh-p99rx
Front Stage - Hybrid L1v2/Hybrid L3/Exodus Audio Anarchy
Subwoofer - SI BM MKIII
The small size of the amp provided tons of options. I tested it for fitment in a variety of unique locations:
Rear deck underside (where factory sub option would mount subwoofer)
Underneath passenger seat
Behind rear seats (you could probably fit 6 of them back there!)
Underneath front carpet in passenger footwell
If I were to use this amp in a brand spanking new install, I would most likely locate it on the bottom of the rear deck where the factory option subwoofer would go. It fits very nicely and could be easily mounted with bolts from the top of the deck, or with self tapping metal screws from the bottom. Wires could be cleanly run and you would give up 0% of your cargo space. I know that many of you like keeping rear fill. Using this amp to push 4 sets of components would be a very good choice and would get loud enough to make you cry.
If it was up to me, for maximum value, I would use this amp to push a set of components in the front doors and use it to push 2 x 6.5 inch subs on the rear deck. After spending some money on deadening, you would have a bad-ass system that would murder anything stock, premium or otherwise. The internal crossover points of this amp would allow this to be easily done, as you could easily pass frequencies of ~ 80hz and up to the components in the front doors, and frequencies 80hz and lower to your rear subs. Keeping the subwoofers on the rear deck would keep the trunk nice and clean so you could put your folding baby stroller, dead body, skis, penguins, wild tigers, etc into the trunk without a problem.