Is mixing different subwoofers a good idea is an age-old debate for which there’s no definitive answer.
Maybe you already have two different-sized subs and don’t want to spend extra money, or maybe you’re quite satisfied with the mid-range bass and would just like to get some deep, low-frequency bass. There are plenty of reasons why you’d like to do it.
Altough the rule of thumb is that you do not mix different subwoofers, there are situations when we can make an exception.
But what’s the knowledge behind not mixing subs? Can you do it without compromising quality?
People mix subs with promising results, and you’ll see intentional use of this method with dedicated home theaters.
Different subwoofers can be mixed, but one must account for maximum output discrepancies. If your subs are drastically different in size, your maximum output will be defined by the smaller subwoofer.
In this article we’ll look at both sides of the discussion and try to explain when and how to mix subwoofers of different sizes and brands.
Mixing Different Subs – Overview
Many would argue that running multiple different subs of different sizes, brands and/or models can get a canceling effect and reduce your bass output.
While that is true, it is fine to mix different subwoofers so long as you’re not maxing out one sub or the other during normal operation. You can go along with the standard operation of combining each subwoofer with optimal positioning, EQ, delay, and level adjustment.
Put the smaller sub as close to the listening position as attainable so that you don’t need to drive the gain as high (obviously, don’t be foolish and do something that will end up being distracting).
Subwoofers of different sizes will work up to whatever volume your low-end sub can handle. If one sub goes lower than the other, I could envision a problem.
Your auto-setup would set the level, possibly based on an average of how both subs reacted during the level test.
As the one subwoofer, which did not go as low, begins to roll off, the other subwoofer will be mainly responsible for the output at lower frequencies even though it goes lower. That might result in it not performing quite as well as anticipated.
Be cautious when mixing ported and sealed subs. The sound coming out of the ported will be out of phase with the sealed sub, and you can occasionally get some cancellation down low.
Imagine a ported sub as a two-driver speaker. The driver crosses over to the other driver (out of phase under Port tune). They don’t play simultaneously, but a sealed sub has only one driver, so if you mix the two, the sealed subwoofer will be out of phase with the driver or the port.
From my experience with mixing different subs, I found that it is best to mix subs with a similar f3 (the lower the f3 parameter, the deeper the bass will sound) and low-frequency roll-off. Otherwise, the subwoofers with the higher roll-offs will adversely impact the overall depth of the system.
Regarding the level setting, something closer to gain-matching has advantages as it controls the sub or subs with the lower output capacities from achieving their limits before the others. That will maintain the whole bass system cleaner up until it reaches its limitations as a whole.
Why Mixing Two Different Subwoofers Isn’t Optimal
There are three cases of mixing different subs, which some experts don’t recommend. Here’s why.
Case #1 – Subwoofers with different outputs
In this case, the subwoofer with lower output can restrict the sub with higher output. The lower-output sub may go into compression, distortion, and perhaps bottoming before the stronger subwoofer.
The best option is to restrict the higher output subwoofer to the level of the weaker subwoofer.
Of course, you can mitigate this to some degree with the nearfield placement and level reduction of the weaker sub.
Nevertheless, if you’re purchasing a new subwoofer to couple with a current, it’s WAY better to pick a subwoofer with matching output capabilities.
Case #2 – Subs with dissimilar low-frequency extensions
The subwoofer with lower extension will add to the levels at all frequencies beyond the -3 dB level, but it will add almost nothing below that.
When the mixed levels of the subwoofers are calibrated to the speakers, they’ll set the level on the fused levels.
That will reduce the levels of both subwoofers, but the subwoofer with a lesser extension will have its deeper extension decreased, disabling the deeper extension.
Using two matching subwoofers won’t increase the extension of either sub, but it will increase the useful levels of the deepest extension of the combined output.
Case #3 – Sealed with ported subwoofers
A ported sub has a “Tune point” of the port. At that frequency, the output of the port is predominant, and the back wave of the driver drives it.
Thus, the output of the ports is, by definition, out of phase with the remainder of the output, driven by the driver’s front wave. Sealed subs don’t display this phenomenon.
If you combine a ported sub with a sealed subwoofer, they may be in phase with each other at all frequencies except at the frequencies near the Tune point of the ported sub, where they’ll be out of phase.
You Can Still Mix Two Different Subs
Altough I wouldn’t advise dissimilar subwoofers if you have to purchase them, if you already have them, or the second sub is extremely affordable, I think the odds of improvement are fantastic.
I say this based on my own firsthand experience. I’ve accomplished it, it works, and there was no rupture in the space-time continuum.
Single subwoofers with room mode response problems always produce spacially uneven bass coverage. Multiple subwoofers correctly located mitigate modal points, even if they’re not the same.
If you want to combine different subs, you must know how to measure the system and optimize it.
The major problem we address with multi-subs is room modes. These result in massive response variations, location, and frequency-specific, and are somewhat inconsistent in location and magnitude.
You can never eliminate a mode; in fact, you don’t want to. Having two subwoofers that produce dissimilar modes lowers the impact of any one mode.
Even if you have exact subwoofers, putting them in separate locations outcomes in radically different modal equations for every location.
They aren’t there to subtract or add out of phase with one another. They serve as a stimulus for various modes that fill in response gaps.
Last but not least, aside from general potential problems getting multiple subwoofers to work together happily in any room, the problem we’re solving for multiple different subwoofers links to frequency response.
If one sub is flat to 30 Hz and the other to 40 Hz, you may never use them both and be flat to 30. You need to have a 3-6 dB dropoff of about 30 Hz when one of your transducers stops contributing to the sound in the room.
Of course, if the weaker subwoofer makes ugly noises when it runs too loud and too low in frequency, the rest of the system may make them obvious.
How to Mix (Integrate) Different Subwoofers?
Subs don’t need to be exactly the same to integrate them, but they must cover a similar frequency range.
We can bump up against some frequencies via EQ utilizing a mini DSP 2×4 (I bought this one from Amazon) or a similar instrument, but there’s a limit to it.
How does the tune/test work?
From the MLP, and with room correction off:
- Turn on the first subwoofer
- Turn off the second subwoofer
- Run a test tone that’s in the center of your sub’s FR (say 45Hz)
- Adjust the first subwoofer’s gain to a particular level (many opt for 70dB, I’m going with around 65dB as I don’t listen to reference levels) on your SPL meter.
- Turn off the first sub
- Turn on the second sub
- Adjust the gain on the second to match the level on the first.
- Run your room correction on the AVR.
If the subwoofers are drastically dissimilar:
- Gain-match the subs
- Perform the pub crawl with each
- Run room correction
This is similar to what I explained above, but each subwoofer is calculated in the center of the room with the meter an inch or so from the middle of the cone to ease room modes.
I have three dissimilar subwoofers in my theater, and room correction is not an issue. A pre/pro with two separate LFE outputs combined two subwoofers to each one and ran Audyssey.
If you’re determined to employ a sub you have, you can also build new enclosures that can go deeper and utilize your current amps/drivers.
Most folks match the box tunes with mixed drivers but doing it that way offers mixed results; some like it, some don’t.
This makes for more comfortable integration but also makes it harder to tune specific frequencies, and if you have them in diverse corners of the room, it gets even more tricky.
Mixing Subwoofer Brands Can Be Beneficial
Mixing and matching different brands of subwoofers is totally acceptable because there is no tone matching with subwoofers.
However, it would be best to avoid adding a second subwoofer if it is not at the same level as your first one, sound and quality-wise.
If you have one subwoofer subordinate to the other, you might be better off staying with one high-quality subwoofer so that the subordinate one isn’t tearing down the all-around sound quality.
If they are both high-quality subs, having two different brand subwoofers might even be more reasonable!
My argument for different brands would be that each sub has its own strengths and weaknesses. With the non-directional sound of the subs, each can help balance the weaknesses of the other.
In my system, my HTD subwoofers are actually a bit different. I added the second one much later, and they have a slightly diverse enclosure. Also, one has a digital amp, etc.
Acquiring a receiver/pre-processor with Audyssey XT32 will likewise assist the subwoofer and help you balance them.
My Onkyo TX-NR6100 didn’t do the subwoofer levels well like my recently added Marantz NR1711 (Amazon link).
If you have to set the levels unaided, I advise you to turn one on and off simultaneously and set the active subwoofer to 72db.
Then when both subs are turned on, it should result in approximately 75db (the 3db gain from doubling the output).
If you don’t measure the 3db gain when the second sub is turned on, you might need to try various positions or set them out of phase. I nowadays appear to have the best luck with the subs in phase.
Why It’s Better to Integrate Two Different Subs Than Stick With Single (If You Need More Output)
The crucial question here is, why are you adding the second subwoofer? Is your existing extension okay, but you want more output? Is your existing output okay, but you want more extension?
Even matching subwoofers won’t perform identically when positioned in separate locations. They’ll be radically dissimilar.
It’s never just about the subwoofer; it’s about the room and the subwoofer.
For the multi-sub idea to succeed, it already needs to be “radically different.”
So, if you end up with drastically different subwoofer performance when using identical subs in different positions, using different subwoofer designs in different positions is not much of an issue.
…so long as you know and use their performance limitations effectively.
Not to shy away from the fact that identical subs make it a bit easier, especially in the extreme LF, high SPL area.