# sirbOOm's Stereo Integrity BM mkIV Review (Finally)



## sirbOOm (Jan 24, 2013)

Late last year, I went through a nightmare with ZED amplifiers that held up for months my build in my (now previous) ride: a 2014 Chevrolet Silverado Double Cab. In the end, I dumped the ZEDs and went with Alpine PDX amps with no issues. But, in all of that commotion, I never posted a dedicated review of the pair of Stereo Integrity BM mkIV subwoofers that turned out to be the star of the system.

_Well, here is the review._ Late and, well, probably not as viable given the mkV will come out soon. Well, I have PM’d with a couple dozen people about this sub and hopefully they all bought one!

System Profile:
- OEM Head Unit
- RF 360.3
- Alpine PDX-M6 (underrated 300 watts RMS to each sub)
- Alpine PDX-F4 (underrated bridged 200 watts RMS to each midbass) 
- Alpine PDX-F4 (underrated 100 watts RMS to tweeters and midranges)
- Pioner Stage 4 3-way (active configuration)
- (2) SI BM mkIV subwoofers in .55 cf per champer sealed box with no stuffing
- Eventually tuned by Scottt Buwalda at Hybrid Auto Salon

Review #1 – Test Phase:
I started with one of these mkIVs in a temporary setup sitting in a .6 cf sealed box in the front passenger foot well of my truck just to screw around with placement. Then I tried it in the rear. My truck’s sweet spot for cabin gain in all the right places is most definitely in the front of the vehicle, not the rear. That is why I went ultimately with two mkIV subs instead of the original single sub plan. A lack of performance alone in the rear of the cabin is not the mkIV’s fault – my truck is just not a great environment to create bass without a lot of tuning and a couple woofers to compensate.

I will focus on the single mkIV up front, though.

I believe at the time I had it hooked up to a JBL GTO 1000 watt amp running at 8-ohms for, what?, 250-300 watts to the sub? First, those JBL amps are really quite good for the money. But, getting to it here, I must say that I have never heard deeper bass in the cabin of a pickup truck… ever. I have installed subs in quite a few trucks and they always get real bad below 40 Hz. I’m no expert as to why but in every truck I’ve heard (that wasn’t a blow through or some sort of SPL nightmare), low end bass was crap. Well, except my previous truck which used a ProBox design that actually performed very well. But this SI sub got down and dirty without issue – and it did its job across the range I gave it (20 to 80hz) with a butter smooth sort of enveloping result. The bass never kicked you in the chest or squeezed you. There wasn’t enough wattage for that. But that isn’t to say it wasn’t loud – I had a lady dancing in the car in front of me when I was playing some rap song once… so it was loud. But I kept wondering when it was going to screw something up, and it didn’t. Dubstep drops: done better than anything I’ve had in at truck (some loss of intensity at the lowest point of the drop but… find me a sub that doesn’t do that in a teeny box in a truck cabin). Heavy metal double bass drum: keeps up, delivers the sound of the actual drum (you know this sound when you hear it) and not a sort of BFFFFF mushy mess. Rap beats: done. These aren’t hard to do for any sub if you think about it but rap beats sounded different. Good recordings of rap songs have great basslines that this sub did not fault or alter. It is no SPL sub, but it did deliver a tough Italian hug (not a punch) when every bass note hit, which I very much liked.

There was just no way to keep the sub up front but for that period of time I had it there, I was sold.

Review #2 – Final Design:
In the end, two of these went into a dual sealed box that I adjusted a bit to get to be .55 cf per chamber (added some wood block inside to take up .1 cubic feets. Yes, it was a prefab box. So sue me.

Now, I’m going to jump straight to the best compliment of all. The words of Scott Buwalda. After he tuned my system for me, he told me that they needed a lot of EQ to get right but they took every bit of it and they were “the star” of the system. Indeed, especially after his tune job, wow… they got nasty low for a flatty and even for any sub. And when they were doing their job at the lower end of the spectrum, two of them created the punch that was missing from just one. They also had that sort of rumble you feel in your chest when loud bass at the lowest range is playing – that duh duh duh duh duh essentially replicating the movement of the cone I guess. It was buttery, but you could feel the waves so to speak like you do when you’re stupid enough to sit in an SPL truck (only it wasn’t pure gross distortion-filled burp tones or horrible rap music beats, it was quality sound – butter, just buttery butter).

Before Scott’s tune, I was having issues with them being a bit one notish. Around 50hz they would boom like crazy, much lower and they died off. Much higher and they didn’t blend as well as I wanted. This, my friends, is what always happens in a truck cabin IME. But I’ve never heard a down-firing, non-tuned sub sound better in a truck cabin right off the bat – the SI just gets to work and, when the time comes, seemingly can be tuned even “a lot” to sound right and take it. Very good, very good.

What happened, unfortunately, is that my midbasses in the Pioneer set were not able to keep up with the capability of the sub. They were not particularly happy at 200 watts. Before I sold the truck, I ran them down at 100 watts and they calmed down – sounded the same but didn’t get stress at high volume). I wish I had the tune done that way but whatever.

I sold the truck recently as, quite frankly, I didn’t need a truck. I sold my old Lincoln, my Harley, I was done with home remodels, and I drive 52 miles to my full-time job per day and for me to get to Sound Sensations is about 50 miles ONE WAY. I was burning oil fields. I now drive a Volt!

Conclusion:
I don’t know how these perform in cars. Well, I do – I’ve heard one up front in a BRZ, of course. But in the trunk of cars is what I mean. I can’t attest to that. And I won’t guess. But what I do know is, I do a lot of pickup trucks (or hear them after the install is done) at my shop and not once, even with a 360.3 or some other tuner and tune job, have I ever heard better low end extension in a truck cabin. Obviously we must exclude people who have blow through jobs or sit two W7s in a big ported box on the back seat or remove the seat or stuff like that. Talking under seat downfire or even upfire box. 

The point being… these are the sub to get if you have a pickup truck and the place you’re going to put your subs is under the rear seats. There is no question in my mind that you will not find anything better that fits in that tight space, that doesn’t require ridiculous power, and that can be tuned safely to your liking. Unless you just like Kicker-square style loud and boomy bass for some reason, you will love these.

Things I Don’t Like:
Has to be said: the rubber surround thing is annoying to work around when screwing it down and it makes the sub’s diameter noticeably larger than the metal actually is. In tight spaces, I’d rather not use the rubber thing but the sub needs it otherwise it looks goofy. Also, I’d rather have a sub that sits more flush in the box vs coming out about, what, 1-1.5”. That’d require more box depth but that’s not the problem. The problem (with downfire boxes) is the space between the box and the carpet. With the mkIV, I had JUST enough space. Like… a gnat’s pubical hair type space left to cover excursion. Yikes!






Hope this helps. Buy one new, buy one used, whatever. You won’t need an mkV to be happy. Check my build log for various photos.


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## seafish (Aug 1, 2012)

NICE job on the review, can't wait to get one of these in my truck, down firing in the center console...Does this mean your NOT gonna sell me your "extra" MKiv..lol??


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