For years I’ve mixed primarily on a pair of Focal Solo6 monitors.

---

I love the clarity and detail. They’re excellent speakers with plenty of low end for near field monitors. In fact, I never felt like I needed a subwoofer. Obviously I had a bit of a blind spot in the lowest octave but it really never caused me to do anything too dumb in the low end on my mixes.

But lately, I’ve been working on a lot of modern Reggae Music with my band, Noetic Sea. This genre features heavy low-end and I found that on some of my reference mixes, I was going a little bit over the top with the deepest tones of the kick and bass. I would only learn that during the car test which is not the most clinical listening environment. I decided I wanted to eliminate or reduce that blind spot and at least get another half octave or so in the studio below where the Solo6 monitors naturally begin to roll off.

More Rumblings of Change

The second clue came from a couple of outdoor live recordings of my band.

The recordings were made from the front-of-house mix and supplemented with a stereo room capture using the built-in X-Y microphones on a Tascam DR-40 (without a windscreen). A small amount of wind created significant low-frequency rumble.

Back in the studio, I applied filtering and thought I had removed it but out in the car, there was still a massive amount of rumble… way down there.

DIY Subwoofer – Design Goals

I wasn’t looking for a subwoofer that would shake the room or impress clients. I wanted a subwoofer that would subtly extend the response of the Solo6 monitors a little further into the bottom octave while remaining essentially invisible.

This project documents the design and construction of a compact sealed subwoofer built around a Peerless XXLS 10″ driver and a DSP-powered plate amplifier.

My priorities were:

• Small footprint
• Sealed enclosure
• Musical rather than theatrical
• Very low crossover frequency
• DSP control
• Clean integration with the existing monitors
• Ability to design and build it so I could learn something and have an interesting project.

Enclosure Design

The enclosure was designed as a sealed cabinet with approximately 37 liters of internal volume. The external dimensions are 17″ × 15″ × 14″. The speaker is front facing. Simple.

Why sealed?

A sealed box provides:

• Better transient behavior (not that I care about that in a sub)
• Simpler construction
• Much simpler design and avoiding endless trial and error of tuning a port.

The downside of a sealed box is efficiency, but per my design goals, I am just looking for a very subtle extension of the focals and since the subwoofer would be crossed over very low, efficiency wasn’t a concern. The upside of not having to deal with the complexities and trial/error of tuning a port far outweighed this. 37 liters of volume gave a decent curve in WinISD. In Hindsight, as long as I was going with 37, I might as well have gone to 43 liters. That would have extended the range only a few Hz but when you’re talking about 30 Hz, a “few” is pretty significant.

Driver Selection

After experimenting with several drivers in WinISD, I narrowed the choices to:

• Dayton RSS265HF
• Peerless XXLS-P835037

Either would have worked well, but the Peerless was available from DigiKey for about $111 compared to nearly $200 for the Dayton. I’m cheap like that.

The Peerless XXLS offered:

• Excellent reputation
• Long linear excursion (I was going to come close to the limit of either driver)
• Plenty of Power Handling

Amplifier

For the Amplifier, I wanted a plate amplifier with balanced inputs and built-in DSP for setting up filters, etc. The Dayton Audio SPA250DSP was an obvious choice. As of this writing (oct 2026), they are on clearance at parts-express so maybe they won’t be available anymore. It has the power and features I needed and it was about $270.

The 250 in the name means it’s a 250w, which is plenty.

The SPA DSP is purpose-built as a subwoofer amplifier. It takes in a stereo balanced signal (xlr or trs), sums it to mono, has some fancy DSP and a twisted pair of wires for the driver. It has built-in DSP for Low and High Pass Filters, Subsonic filter, Parametric EQ and as well as other delay and phase parameters. There is as USB port for programming it with a GUI but I had no luck getting that to work. Fortunately, there is a rotary encoder and LCD display that lets you easily program and store anything you need.

What I found interesting about this amplifier (as in disappointing) is that the High Pass filter had a minimum fc of 30Hz. The “subsonic” filter only goes to 25Hz (I wanted 10). More on this below.

Cabinet Construction

This cabinet was built out of 3/4″ birch plywood using fairly basic woodworking tools.

I don’t own a table saw.

All straight cuts were made using a circular saw and a straight-edge cutting guide

The driver opening and plate-amp opening were cut using a jigsaw.

The driver and amplifier were fastened in with M4 tee nuts and Phillips screws

The cabinet panels were glued together with internal corner supports and secured using an electric brad nail gun.

I’m a hack. My goal wasn’t a furniture-grade showpiece. My goal was a functional studio tool. Besides, it is mostly hidden under my studio desk anyway.

Parts List

• Peerless XXLS-P835037 Driver
• Dayton SPA250DSP Amplifier
• 3/4″ Birch Plywood (2 2×4 sheets were enough)
• Rockwool or similar Insulation
• M4 Tee Nuts
• M4 Screws 8mm length
• Wood Glue
• Wood Fasteners
• Paint/Primer or other Finish

The finished enclosure came out far better than I expected and looks completely at home in the studio.

Internal Construction

The enclosure is fully sealed and lined with Rockwool damping material.

The cabinet volume was chosen based on modeling for the selected driver, resulting in a compact enclosure with smooth low-frequency extension and excellent integration with the main monitors.

I did not put a stiffening “window brace” in this cabinet as my AI overlord suggested. It would have theoretically damped the box resonance, but it also would have robbed me of some internal volume (and been a bit of a pain to do). In operation, the box feels incredibly “still” and stiff so I think it’s fine for this size enclosure. If I went much bigger, I would probably stiffen it.

The Result

The most interesting thing about the finished subwoofer is that it doesn’t really call attention to itself.

The Focals still sound like Focals.

I use the Dangerous Music M-Box+ monitor switcher which allows switching in a sub. Turning it on gives the focals just a tiny extra something down there that sounds really nice.

When the low end is over the top in the car, it’s now over the top in the mix room too and that’s exactly what I was hoping to achieve.

---

Listening Impressions

The biggest success of the project is that the subwoofer doesn’t sound like a subwoofer.

The Solo6 monitors already provide excellent bass. What the sub adds is a sense of scale and weight in the lowest frequencies.

The deepest tones of the kick and bass can be judged much more accurately now.

Most importantly, my monitors still sound like the Focals I know and love.

Cone excursion is well within the 19mm max specified for the Peerless – even at higher than normal listening levels. I’m definitely well within the design limits of the amplifier and driver.

---

Measurements

I’m a by ear guy, I set up REW with my dbx reference mic to take some measurements.

The graph below shows the low-frequency response of the Focals alone (blue), the subwoofer alone (purple), and the combined system (red).

Yes, there is a little hump now at the bottom of the Focal’s range, but you can clearly see the extension of about half an octave with the sub engaged.

The exact shape of the room response is less important than the fact that the sub extends the system by approximately half an octave while remaining well integrated with the Solo6 monitors

The Amplifier is set up with a Lo Pass filter at 40Hz with a 24db/Oct slope. I have adjusted the relative volume of the sub to taste and I’m sure I’ll still be tweaking as I do more mixes with this system. My design in WinISD dictated a Hi Pass filter at 10Hz but it turns out that this is not possible with the Dayton amp. The HiPass only goes down to 30. It also has a subsonic filter, but that has a minimum frequency of 25Hz. This seems a bit strange for a purpose built subwoofer amp. I ended up switching on the subsonic filter at 25Hz with a 12db/Oct rolloff. Without it, the sub had quite a bit more cone excursion and the room response was still above 70db below 10Hz.

---

Final Thoughts

This project started as a small experiment and ended up being one of the most enjoyable DIY audio projects I’ve completed. And it was actually a pretty easy project.

The final result wasn’t a “cheap subwoofer.” Total cost was about 550 USD plus my extremely valuable time. There are several good choice one could buy off the shelf in that price range. This is probably a better subwoofer than those choices but they probably would have been good enough for my purpose.

The project achieved exactly what I hoped it would. The goal wasn’t to make the studio sound bass-heavy. The goal was to make low-frequency decisions in the studio translate more reliably to other listening environments.

For anyone curious about loudspeaker design, DSP, or studio monitoring, a small sealed subwoofer is an excellent entry point into the world of DIY speakers.

We have a

I used to dress up the mics with with Laser-Cut Nickel Badges. It looked cool. But if I’m honest: it was also the most stressful, anxiety-inducing part of the whole build.

Bending, aligning, and epoxying badges was a delicate game of “don’t screw this up.” One slip and the whole mic body had to be stripped or scrapped. I had bending jigs (various PVC Pipe pieces) for each mic body. The trick was to slightly over bend the badge (but not too much). I was spending way too much time playing arts & crafts when what I really wanted to do was focus on the guts.

Because the guts—the capsules, transformers, and circuits—have always been the point. And that hasn’t changed one bit.

Enter the Laser

Starting September 2025, epoxied-on badges are retired. Every RockScience Mic now ships with:

• A laser-engraved RockScience logo
• A permanent build configuration code, so you’ll always know what’s inside

It took a few ruined mic bodies and hours of testing to dial in laser settings for all the variations of material, color and diameter for all of the mics I work on. But now the process is clean, precise, and consistent. And yes, I look very relaxed in my green safety glasses standing next to the Omtech galvo fiber laser. Those “mistakes” will most likely end up in my mic locker – the same way the mechanic always has the most beat up car.

I spent time dialing in laser settings for black, blue, green paint on aluminum and brass – as well as settings for bare metal for aluminum and brass and anodized aluminum. For most of this, I used scrap pieces of metal to work out the settings. The laser reacts to all of these very differently so it’s a matter of tweaking the power, speed, frequency and number of passes for each variation.

That’s good TV right there

---

The Build Config Codes

This is actually the coolest part for me. I can’t tell you how many times I’ve had to open up a body during a session to remember which mic had which transformer or which was a TL, etc.

The format is

[CAPSULE][CIRCUIT].[VARIATION]

Section	Code	Meaning
Capsule Type	47	K47-style capsule
	12	CK12-style capsule
Electronics	TL	Transformerless
	TC	Transformer-coupled
Transformer Variation	C	Cinemag
	A	AMI
	3	3U Audio
	N	Neutrik (lo-fi)

Examples:
12TC.A → CK12 capsule, transformer-coupled with AMI
47TL → K47 capsule, transformerless
47TC.C → K47 capsule, transformer-coupled with Cinemag

---

About the Finish

I’ve got the laser looking great on Black, Blue, Green and bare metal. For the painted surfaces, the black shows the graphics with the most contrast – especially on aluminum mic bodies. For black anodized bodies like the 770, I’m suggesting sanding and applying a finish coat of the flat black (this covers up the usually dinged-up switch logos anyway). The laser cuts through the paint and the anodizing and it looks great. The blue seems to work about as well as the black. Green took a bit longer to dial in because it seemed to need a bit more power – but too much power and the metal underneath gets dull. It’s a balance.

No more Red. Red was always a problem color. It always took the longest to dry and cure and it seemed to be the softest and most easily dinged up color. I did one quick experiment with the laser and the results were not exciting. So it’s off the market for now.

As for bare metal, we need lots of power to really cut some material. To get the engraving to show up well, we have to actually burn the body a little bit. The trick is to do that just enough to show up but not so much that things get fuzzy. Again – lots of time have gone into figuring this out.

---

The Guts Haven’t Changed

This is important: the electronics, capsules, and mods are exactly the same. The only thing that’s different is how the mic looks on the outside.

So if you already own a RockScience mod with a badge or paint, don’t worry—you’ve got the same great guts. You just own a piece of RockScience history from the arts & crafts era.

The future, though? It’s laser-etched.

---

🔧 Nerd Alert: The Laser

For those who like to peek behind the curtain: I’m using an Omtech 20W Galvo Fiber Laser with a Rotary Chuck to do all engravings. Powered by LightBurn, it’s basically the “DAW for lasers.” Settings have to be tuned for each mic body’s finish — stainless, brass, painted aluminum. The diameter and taper of each mic body has to be carefully meassured — and I’ve wrecked more than a few bodies figuring it out.

Here’s a little LightBurn screenshot for the curious. This is the file for a painted 990

Laser For Hire

I’m not going into the engraving business, but I’m considering opening up this laser engraving as a service for other DIY-ers. Got a body you want marked with your logo or config? Let me know — if there’s enough interest, I’ll make it a thing.

Introduction

The MXL 5000 is a sleeper hit in the world of affordable large-diaphragm condensers. With a sturdy metal body, a well-designed headbasket, and—unlike many budget mics—built-in pad and high-pass filter switches, it’s already a solid contender. But what if we could elevate it even further?

I’ve been refining the BFM (Big F’m Microphone) circuit, a design inspired by the Neumann KM84, and now I’m bringing it to the MXL 5000. This isn’t just a component swap—it’s a complete circuit replacement, featuring transformer-coupled output and a custom PCB that fully utilizes the mic’s existing pad and filter switches!

As usual, I’m offering multiple transformer options (Cinemag, Tab-Funkenwerk, or 3U Audio) and your choice of capsule (CK12 or K47 style), allowing you to fine-tune the mic’s character to your taste. This board also has the optional internal Pattern switch to select Cardioid or Omni modes. The body must be opened up to access it, but on those occasions when you want an OMNI, it’s nice to have that trick.

In this post, we’ll break down why this mod takes the MXL 5000 from “good” to studio-grade exceptional.

Why Modify the MXL 5000?

The stock MXL 5000 is no slouch—it’s built like a tank, has a decent k67 style capsule and external switches on its TL circuit. But like many budget transformerless mics, it is over-bright, sibilant and harsh.

Our BFM rebuild addresses key limitations:

• Transformerless stock circuit → Now transformer-coupled for added depth, weight, and vintage vibe.
• Basic FET amplification → Upgraded with low-noise, hand-selected transistors for better clarity.
• Generic capacitors/resistors → Replaced with premium WIMA, polystyrene, and metal film components for improved signal integrity.
• Capsule flexibility → Choose between CK12 (bright, open) or K47 (warm, smooth) styles.

The Circuit: KM84-Inspired BFM Design

The BFM board is a refined take on the Neumann KM84—a circuit renowned for its balanced midrange, smooth highs, and natural tonality. There is very little in the audio path in that circuit: FET->Capacitor->Transformer—that’s it!

Transformer Options: Pick Your Flavor

As usual, you can choose your transformer, each imparting a unique character:

• Cinemag  – Clean, detailed, with a slight midrange push.
• Tab-Funkenwerk  – Vintage-style warmth, reminiscent of old Telefunken mics.
• 3U Audio  – A modern take with a slightly lighter low end.

This flexibility lets you tailor the mic to your preferred tonal profile—clinical and accurate? Warm and colored?

Capsule Choices: CK12 vs. K47

This build allows a choice of two capsule styles, each suited for different applications:

• CK12-style – Brighter, more open, with enhanced presence. Great for vocals that need air or acoustic instruments.
• K47-style – Warmer, smoother, with a slight low-mid richness. Ideal for darker voices, electric guitars, or bass-heavy sources.

---

Component Upgrades: What’s Inside?

A great circuit is only as good as its parts. Here’s what we’re using to maximize performance in all of our BFM builds:

• Polystyrene Capacitors – Critical for clean high-frequency response.
• Low-noise metal film resistors – Reducing thermal noise for a blacker background.
• Selected FETs – Hand-biased for optimal distortion characteristics.

---

Sound Comparison: Stock vs. Modded

Stock MXL 5000:

• Decent clarity but can be slightly harsh in the upper mids.
• Transformerless circuit – Lacks low-end weight and harmonic richness.
• Good features (pad/HPF), but the electronics limit its potential.

RockScience BFM Mod:

• Smoother, more balanced highs – No harshness, just detailed air.
• Transformer-enhanced lows – Fuller, more controlled low-end.
• Lower noise floor – Cleaner signal for critical recordings.
• More “pro” vibe – The KM84-inspired circuit adds a touch of vintage Neumann magic.

Best Uses for the Modded MXL 5000:

✅ Vocals (especially with the K47 capsule for warmth)
✅ Acoustic Guitar (CK12 for sparkle, K47 for body)
✅ Drum Overheads (transformer helps with punch and depth)
✅ Kick Drum – with K47 (get your 47FET mojo)
✅ Electric Guitar Cabs (K47. The pad handles high SPL with ease)

---

---

Final Thoughts

The MXL 5000 has always been a solid platform, but with the RockScience BFM treatment, it becomes a true studio workhorse. Whether you want a vintage-voiced vocal mic (Tab-Funkenwerk + K47) or a detailed acoustic instrument mic (Cinemag + CK12), this mod delivers.

Ready to transform your MXL 5000?
📩 Contact us for pricing and lead times.
🛠️ Check out our Mod Services page for more details.

---

What’s Your Dream Mic Combo?

CK12 + Cinemag for clarity? K47 + Tab-Funkenwerk for vintage warmth? Let us know in the comments!

I just sat for the AWS Certified Cloud Architect Exam. And I even passed!

Pivoting to the software development side of RockScience, Here are some lessons learned around taking AWS Certification exams.

You’ve spent weeks or months studying and taking practice exams, building your own practice infrastructure and it’s finally time to sit for the exam. The last thing you need right now is a logistical gotcha. Here are some tips to avoid those.

Call me Robert

When you sign up for certifications at https://aws.amazon.com/certification/, you will be asked to create a Builder ID. This is where you set up the account for your certifications. This account info is then propagated to Pearson who actually administers the proctored exams.

When I did this, as usual my browser auto filled me as “Bob” and I just went with it as usual. MISTAKE!!!! The key here is to enter your name exactly as it appears on the identification document you are going to use (drivers license, passport, etc).

When I took the Cloud Practitioner exam, the proctor didn’t catch the discrepancy between my account name and the name on my license (Robert). I took (and passed) that exam. When it was time to sit for the Solutions Architect exam, the proctor bounced me because of the name mismatch.

Here’s the problem – if I didn’t already have any exam history, I would have been able to self-serve the name change in my account. But because the first proctor let me slide, the name could no longer be changed without opening a ticket with AWS. What a pain. On the other hand, it gave me more time to study. The issue was sorted within two days (and lots of back and forth), but it was a real hassle. On top of that, not only could I not use the voucher from the first exam to get half off, I had to pay full price again for the exam. So instead of $75, it was $225! I probably could have fought that, but was too exhausted and stressed by then.

Running the system check

DO run the system check! You don’t want any surprise on exam day. I suggest setting up your testing area exactly as it will be (I suggest even doing this for the practice exams). Make sure you have power, good internet and your wireless mouse is well charged up. You can’t have multiple monitors. If you have them, take them away so there is only on on the desk. If you are not doing this on a laptop, make sure your webcam wire is long enough that you can walk around your testing area (they will ask you to do this at check in).

The system test is going to look for applications and services that shouldn’t be running. Things like Dropbox and other sharing apps will be tagged. You need to figure out how to stop them running.

On a windows 11 laptop, one annoying one is going to be “tabtip.exe”. What the heck is that? It’s the virtual keyboard that pops up when you are using your laptop as a tablet. If you stop that in the task manager, windows re-launches is immediately. Here’s how to stop it. In settings, set this to “Never”. I burned up a few hours figuring this one out.

Download the system check each time you want to run it!

An interesting thing about the system check app, is that you download an instance of it for each time you want to run it. If you go to your downloads folder and just rerun the same instance again, it will almost succeed but will mysteriously fail the network check. That wasted a few panic stricken hours the night before my first exam. The key is to just follow the link from your email and download a new instance if you want to run it again.

Check in Procedure

This is fairly straightforward. You can start the process 30 minutes before your scheduled exam and if you get through it quickly, you can start the exam early. Take off your watch (see below)

You are prompted to take photos of your test area, a photo of your ID document and confirm your system settings (again). When you are done with your mobile phone and your ID, you are told told that from then on, you are being recorded and must follow the exam rules – including that you can not leave the field of view of your webcam. Your phone and ID card have to be out of arms reach, but you also may need them again if there is an issue. So when you are done with the phone, put it out of arms reach but in a place where you can get it while staying on camera.

Follow all the other rules too. Make sure the space is quiet around you. If they hear any voices (yours or anyone else), they will revoke the test. Schedule your test accordingly.

The Queue and the Greeter

You will be shown your position in the queue. It’s not unusual to be 10th-ish in the queue but it goes by pretty quick. Soon you will be Up Next! and a popup message from the greeter will say they are going to call you through the computer. You say OK and a voice chat starts. Here is where they ask you to pick up your laptop (or other webcam) and show the whole testing area once again. Then they’ll be asking you to show on the webcam that you are not wearing a watch. I’m sure that soon, you’re going to have to prove that you’re not wearing any kind of “smart” glasses.

Within a couple minutes, you are in the test. Hopefully you are ready and pass with a great score.

Learning Tips

This post is mostly about avoiding logistical issues, but I have some thoughts on how to study for this too. First of all, I highly recommend the Udemy courses and in particular the ones by Stéphane Maarek. But it can’t hurt to buy one of the other instructors’ courses too. They are cheap! I bought two courses and I also bought the set of practice exams from Stéphane. In total, I had six practice exams. My suggestion is to take the first one without looking up anything (cheating) to get a baseline. If you do great, then great! If you’re like me, you barely passed. For the subsequent exams, I did them as “open book” and I looked up and learned details right then and there for any questions I had doubts about. I think this made a huge difference for me.

Are the practice exams realistic?

This is the big question. I passed every single one… until the very last one (the morning of exam day). That one was massively harder than any of the others and I failed it miserably. That gave me a psychological whammy to deal with. For me, the real exam was maybe just slightly easier than the average of the practice exams. But that’s just my impression and I wouldn’t count on it!

Good Luck! Build something cool! Hire me to help!

I’ve been building Transformer Coupled LDC mics for a while now. My BFM (Big F’n Microphone) circuit is adapted from the Neumann KM-84 (kleines Mikrofon – 84) circuit with very minor differences from the original. I have finally gotten round to building some SDC mics with another adaption of the BFM circuit called the TFM (Tiny F’n Microphone).

Donor Bodies

Donor bodies are plentiful for these mics. From MXL alone, there are 551, 991 603s and 840 (and maybe more). The 551s and 991s are usually in a set with a 550 or 990 respectively, but sometimes we can find them alone.

TFM Circuit

The TFM really is pretty tiny. There is not a lot of wiggle room on the board – especially when a large chunk of the board is taken up by the Transformer. Fortunately the KM48 and our derivation of it is a very simple circuit and within a few revisions of the board, everything is fitting and working out well. As with the LDC bards, the capsule and FET wiring is off board and using Keystone insulated turrets for the point-to-point wiring.

Transformers and Capsules

I’ve been building my BFM boards with either CineMag or AMI transformers, but will now be offering the 3U GZT-84 Transformer. The tone is slightly brighter than the CineMag or AMI and it it seems to have a bit more harmonic distortion in the low frequencies than the others. And this is largely what gives transformer mics their sound.

For capsules, I am offering options from 3U Audio. Their capsules come in several polar patterns apart from the standard cardioid and they sound amazing. Because the capsule is easily field-replaceable, you can get several capsules for your mic and swap in the one that is appropriate for what you are trying to capture.