How To: Converting Passive Speakers to Active Speakers

Four years ago, I posted a thread about using Behringer B215XL 2-way passive PA speakers for home theater applications. Thanks to the low price and high performance of the speakers, the idea caught on and resulted in an epic thread. Then, about a year ago, I tried out another highly affordable passive 15″ PA speaker, the Monoprice Stage Right ($190 on Amazon) and really enjoyed the way it sounds. In that review, I promised to explore converting the Monoprice 15s into active speakers, which brings us to this post.

While both the Behringer B215XL ($220 on Amazon) and Monoprice 15″ PA speakers sounded good unmodified, they are simplistic designs that sacrifice a degree of potential fidelity for the sake of maximum output (spec’d at 126 dB).

The main compromise employed to achieve DJ-friendly output levels is a fairly high crossover point between the 15″ woofer and the compression-driver horn-loaded tweeter. But what I found was that PA speakers have the headroom to accommodate some modding, in particular to bring down the crossover point to a range where the dispersion of the woofer and tweeter more closely match.

The listed crossover point for the B215XL is 2000 Hz and for the Monoprice Stage Right 15″ it’s 3300 Hz, whereas ideally the crossover for coupling a 15″ woofer with a horn tweeter would be in the 800 Hz to 1200 Hz range. Because I have no soldering skills, I took a digital approach to creating a new crossover by using a DSP-based active crossover and bi-amping the speakers.

For this project, I used a MiniDSP DDRC-88A 8-channel Dirac Live room correction processor with built-in bass management to go active with the Monoprice Stage Right 15″ speakers. The DDRC-88A has the BM (bass management) upgrade, which allowed me to create custom crossovers for the speakers. The best part is Dirac Live took care of the little details—including tweaking output levels and distances.

First and foremost, this is something you can do. Not necessarily something you would do, unless you already had the gear sitting on hand. I already had the gear.

The result of the switch to an active approach, and the reconfigured crossover, is transformative. Granted, using Dirac Live on the speakers with their stock passive crossovers also produced an improvement in tonality, but with the horn taking care of business all the way down to 1000 Hz gave the speakers more definition in the frequency range of human vocals.

The switch in crossover points allowed the speakers to sound more focused and better defined. Now, this change assuredly comes at some cost to the tweeter’s peak output, but what I found was that in a high-sensitivity speaker already designed to handle 250 watts RMS with 1000-watt peaks, there’s lots of headroom to handle this mod.

A few salient points regarding this endeavor

First of all, I cannot live without subwoofers, and in this instance subwoofers are a necessity regardless because these PA speakers are not designed to play as deep as even a residential bookshelf speaker. But, they do play low enough to use a standard 80 Hz crossover. Therefore, in order to add enough bass to keep up with these active speakers, I used a total of four subs: Two KEF R400b subs that feature dual-opposed 9″ drivers and to JL F112 V2 subs that feature high-excursion 12″ drivers and tons of power. It’s a combo that’s good for reference-level output down to 15 Hz in my listening room.

I employed two AVRs to make this system work, a Denon AVR-X4300H and a Marantz SR7010, with the Denon serving as a pre/pro and the Marantz acting as amp. The MiniDSP DDRC-88A BM sat between the two, performing its DSP magic.


I used two AVRs and a MiniDSP DDRC-88A BM to create the active speaker system.

This particular configuration utilized six of the eight channels on the DDRC-88A, with four dedicated to the active speakers and two dedicated to the subwoofers. The result is a 2.1-channel system that shows how AVRs, room correction, multiple subs and what amount to “cheap” PA speakers can combine to offer jaw-dropping fidelity based on precise imaging, a smooth yet detailed sound, notable neutrality and gargantuan dynamics.

Setup

Here is exactly how I set this system up:

  1. Open the rear panel of the Monoprice Stage Right 15″ speakers and disconnect the passive crossover. Conveniently, these speakers house the crossover in a discrete chamber for easy access.
  2. Wire the speaker drivers to the Marantz SR7010, using the left and right front as well as left and right surround channels.
  3. Adjust the output levels of the channels powering the tweeters to -10 dB, to compensate for the intrinsically higher efficiency versus the woofers (the passive crossover uses resistors). Notably, there was no audible hiss whatsoever coming from the tweeters.
  4. Set up the Marantz to act purely as an amp by turning off all processing, bass management, and adjusting all speaker distances to the same values and then engaging “Pure Direct” mode.
  5. Configure the Denon AVR-X4300H for a 2.1 speaker configuration with an 80 Hz crossover. Disable all room correction and EQ. Also, set the distances of the speakers and sub so they are the same.
  6. Configure signal routing and DSP crossovers in the DDRC-88A. In this case applying a 24 dB/octave slope centered around 1000 Hz.
  7. Connect the DDRC-88A to the two AVRs and the subs.
  8. Run Dirac Live.
  9. Measure the resulting response of the now active speakers using REW.
  10. Pour beer. Drink beer.
  11. Listen to favorite tracks on the resulting system… loud.


The Monoprice Stage Right 15″ PA speaker’s passive crossover.

Dirac Live helpfully provides graphs of the raw sound from each microphone location, offering useful insight into both the raw response of the drivers, and how the tweeter and woofer are handling the new crossover settings.

Performance and Listening

I used REW to measure sine-wave sweeps from various spots within my listening area. This revealed a very well-behaved system that—with the help of the four subs—covers 16 Hz to 16 kHz with very close tracking to Dirac Live’s default room response curve. The only significant weakness in the measured result is a lack of high frequency extension above 16 kHz, so one of my future projects will likely consist of adding a super-tweeter. But pragmatically speaking, unless you have a teenager’s ears, these active speakers are full-range as-is.


Here’s the average frequency response of the system post-Dirac Live.

When I reviewed the Monoprice Stage Right 15″ PA speakers, I only discussed their performance as passive speakers. And they did a very good job considering they cost only $160 each. But, in that review I noted the day would come where I modded them, and the result of converting to active speakers is nothing less than a revelation.

There’s no question that the compression-driver tweeter is better able to deliver the micro-dynamics that midrange frequencies demand, as compared to the (inexpensive) 15″ woofer. Moving the crossover point from 3000 Hz to 1000 Hz “fixes” the main design flaw of these speakers when used at home for music or movies. On the other hand, if you are a DJ I suggest using these speakers unmodified since you’ll probably blow a tweeter if you take this approach. But when used in a residential context, these speakers play as loud as any I’ve reviewed and have not failed me yet.

By lowering that crossover point, you better match the dispersion of the horn to the bass driver. Smaller woofers allow for a higher crossover, with a 15″ you have to scrape the lower limit of what an inexpensive compression driver tweeter can offer to meet this objective.

Why bother? Because a lot of what you hear is no direct sound, but rather reflected sound. And if the dispersion narrows and then suddenly widens again, the overall tonality—taking the room into account—can wind up sounding less balanced.

I’m especially enamored with how I can use the volume control on the Marantz SR7010 to adjust the level of the speakers without affecting the subs. This gives me an instant subwoofer level control while the Denon AVR-X4300H provides gain control for the entire system.

When it comes to music, I found that the dynamics and clarity I achieved with the active speakers configuration made it easy to listen to great recordings at concert levels. I’ve experienced this with other gear that blends pro audio with consumer sensibilities, but never from speakers as affordable as these. You want precise imaging? Dirac time-aligned the drivers as a matter of course, and consequently the soundstage produced by this system is very focused and holographic.

Specific examples of music that I am deeply familiar with and that possessed something “extra” when played through this system include Air’s excellent album 10,000 Hz Legend with the opening to “Electronic Musician” immediately demonstrating the powerful performance it can provide. I immediately forgot that AVRs had anything to do with what I heard, and I bet if this system was behind a black curtain, even trained listeners would mistake these inexpensive active speakers it for something high-end.

The new album by German electronic, ambient, new-age, and space rock legends Tangerine Dream is a thick, velvety, rich, deep, multi-layered soundscape that epitomizes “deep listening.” Ambient pads of varying flavors and arpeggiated leads build up with the almost-realized beats that never quite dissolve into pure rhythm. The soundstage is huge, and when you are within its embrace it’s hard to not be impressed.

The final track on Quantum Gate, “Genesis Of Precious Thoughts” filled the holographic soundscape with delightful details that showed off why compression-driver horn tweeters can be so seductive. When the beat stops at 2:22, the spacious ambience surprises with its vastness. Meanwhile, a lone violin sounds authentic and emotional and as textured as you could wish for.

My perennial favorite torture track, “Disc Wars” by Daft Punk from the Tron: Legacy soundtrack did manage to find the limits of what these active speakers can resolve. I’ve heard clearer renditions of the track, albeit not always with as much impact as this system provided.

Dub Meltdown by Bill Laswell and Style Scott is an ambient dub reggae classic that’s smoke-thick with fat bass, blissed-out synth work, and lots of reverb plus echo effects. In other words, it’s excellent chill music and also a great recording. When the thunder hits at 1:20 in the opening track “Crooklyn Dub Syndicate” the Monoprice speakers render the dry crackle with appropriate immensity as Style Scott taps aways at his drum kit, thusly providing an entrancing rhythmic foundation to the proceedings.

This system let me experience the albums at a higher overall volume level than was comfortable when using residential “cone and dome” speakers that cost multiple times more than the Monoprice 15s. It also provided clarity and neutrality that was not present in the unmodified, passive versions of these speakers. I don’t merely regard it as a success, I consider this a foundation to build upon. For example, upgraded compression drivers are worth considering.

Conclusion? More like what’s next!

The next step—upgrading the drivers—is a project I plan to pursue sometime in the next few week. I’m already so thrilled with the result of going 2-way active, it’s energized me.

Fortunately I’ve got two more channels on the DDRC-88A and the SR7010 to work with, so going 3-way active using super-tweeters is totally doable. But ideally, new compressions drivers would do the trick.

For now, I’m totally thrilled with the fidelity the crossover-modded Monoprice Stage Right 15″ PA active speakers offer. But, because there is clearly room for improvement. Therefore, in the eternally famous words of the T-1000, I’ll be back.


SYSTEM

Sources

PC running Tidal HiFi and Google Play Music
Sony PlayStation 4 Pro

Processing and Amplification

Marantz SR7010 AV Receiver
Denon AVR-X4300H AV Receiver
MiniDSP DDRC-88A BM 8-channel Dirac Live processor

Cables

Blue Jeans Cable

Speaker Stands

IKEA FNISS, black