Are Two Subwoofers Better than One?

How to Get your Wife to Say Yes to a Pair of Twins

Are two subs better than one??? The answer to this question is typically yes, assuming you’re comparing one vs. two subs of the exact same brand and model #. In almost all circumstances, installing multiple subwoofers in your theater room will yield significantly better and smoother bass response across a wider listening area due to modal averaging. We’ve covered this topic thoroughly, so I don’t want to re-invent the wheel.

Recommended Reading on the Benefits of Multiple Subwoofers:

• Place for Bass – Subwoofer Calibration

• Multi Subwoofer Connection Tips

• An Easy Solution To Subwoofer Calibration

 The Benefits of Multiple Subwoofers for Home Theater

The Argument for Two Subwoofers

What I’d like to explore however is comparing 1 LARGE sub vs. 2 smaller subwoofers to determine if the multiple subwoofer advantage will still hold true. This is a common decision people face when setting up a home theater. Usually the wife will tolerate one subwoofer if it’s placed out of view, but two is a hard pill to swallow, unless both are small and inconspicuous.

I chose to perform this experiment in the Family Room system of the Audioholics Showcase home. This room is quite typical of what I’ve seen in many homes. It has 10ft ceilings and is open to the rest of the house which makes it quite challenging to get good sound in, let alone respectable bass response. For the past three years, I was using the venerable Axiom EP500 subwoofer located towards the left front of the room behind one of the couches. For a single subwoofer installation, I found this to be the best location for performance and aesthetics as the couch and blinds did a great job hiding this beast.

Considering the room dynamics, I was mostly pleased with the results. What really impressed me was the ability of the EP500 to shake the entire room which if you factor in the kitchen is about 10,000 ft^3 of listening space. Bass was well extended and tactile. In fact for the left couch where the sub was placed behind, it was a bit too tactile which unfortunately lend itself to being localized for the listeners that got stuck sitting there, usually my mother-in-law. Another thing I wasn’t t pleased with was the rather drastic change in quality of bass from sitting in the sweet spot to the mother-in-law position. Even the sweet spot at times gave away the subwoofer location in the sense that I could tell I was listening to a satellite subwoofer system and not a large pair of bass capable speakers. With a sub as tactile as the EP500, getting too close to it can often give its location away just from its sheer output and resultant pressure waves it produces.

I suppose I am spoiled as I am so used to listening to multi subwoofer home theater systems. This was the only system of the three in the Audioholics Showcase home that hasn’t assimilated that design philosophy mostly because of aesthetics.

I had to figure out a way to remedy this while also keeping the WAF high. After all this is a family room and not a dedicated home theater room. The ideal solution would have course been two EP500 optimally located within the listening space. Luckily I had the foresight when building this home to pre-wire all the good possible locations with RCA terminations and power for the eventual integration of multiple subwoofers. At the time I told the wife those were auxiliary video ports for kids gaming systems or flat panel TV hook ups. It’s doubtful that she bought that, but it was enough to not raise too many questions and years later, here we are with the ability to run a multi-subwoofer system. As time progressed I slowly convinced my wife of the benefit of multiple subwoofers and how it would eliminate that boomy effect she experienced in this system but not the other two. In addition, I told her how her mom would especially appreciate this when she sits in her favorite seat to watch movies with us. I got a provisional green light to go forward but with one caveat – each sub must be significantly smaller than the original sub and also be a better blend with the room décor. Well that pretty much ruled out a second EP500 and most of my other favorite subs. So the search was on to find a small compact yet potent sub with a custom real wood finish that would “blend” into the room. While there were many good options out there from the likes of JL Audio, and Velodyne, I came back to Axiom because of their ability to do custom real wood finishes. I chose two EP400’s in a semi gloss cherry Bordeaux veneer with gray grills. I also decided to hold onto my black EP500 to do a face off comparison to ensure I made the right decision.

The Axiom EP400 vs. the EP500

Spec Comparison

On the surface, it appears two EP400s (116dB + 3dB = 119dB) would have near equivalent max SPL of 1 EP500 (120dB). But what the manufacturer is not showing you is the bandwidth vs. max SPL output of both subwoofers in their spec sheet. In fact, it’s interesting to note they show you a graph for the EP500 but not the EP400. Factoring in the laws of physics that the single 12” driver found in the EP500 still has 12% more surface area than two EP400 8” drivers not to mention the driver to box ratio of the EP500 is at a great advantage to the EP400 and one wonders why I would even consider doing this exchange.

Extension and max SPL isn’t everything. Quality of bass and how well it integrates into a system is paramount. I can’t tell you how many homes and demo rooms I’ve been in with refrigerator sized subwoofers that sound like a teenager car stereo system. That’s not how I like to roll. I don’t consider an install a success until you cannot locate the subwoofer(s) in a system and the bass just sounds like its emanating from the speakers across the entire listening area. If I have to sacrifice a bit of extension and SPL to achieve this, so be it.

The Set-Up

I left my EP500 towards the left front corner behind my couch as it has been for the past 3 years. I placed one EP400 on top of it and the other EP400 diagonally located towards the back right of the room. Luckily the distance between both EP400s was relatively equal to the primary listening area making it much easier to integrate them and not have to worry about bass cancellations due to mismanaged time alignment between the two subs. I checked the phase and found they integrated best with both subs set to 0 degrees (default). I always recommend using symmetry when placing your subwoofers relative to the primary listening area.  If for some reason you can’t, then it’s usually best to average the distance between the two subs for the electrical delay in your processor and tweak from their using variable phase or EQ to better hone in your response. The electronics include the new Yamaha RX-Z7 A/V receiver, Denon DVD-2930CI DVD player, Emotiva MPS-1 7CH power amplifier, APC H15 power conditioners and a 57” Samsung DLP RPTV. All HDMI and toslink cables are Sonicwave from Impact Acoustics and all speaker cables (10awg) and interconnects are from Blue Jeans Cable.

The Analysis

When setting up subwoofers in a home theater system, I always measure the response to ensure I am at least in the ballpark for great bass. I run sweeps using LMS or my Sencore SP495C Audio Analyzer, adjusting placement, crossover settings, phase and electrical distance until I measure the most linear response at my two primary listening positions. I tweak as needed to improve the other seats but usually if I get at least the two money seats right, the others aren’t so bad, especially with the multi subwoofer advantage.

After level matching the EP500 and two EP400s, I was ready to do a direct comparison between them integrated into my family room theater.

EP500 vs 2 x EP400s at Primary Listening Seat

The purple trace represents the single EP500 while the green trace represents two EP400s. As you can see the dual EP400 response is much more linear across the entire frequency range. Gone is the 10dB suckout centered around 48Hz. This is a fairly narrow suckout with a Q roughly 4.8 so it’s possibly audible and really only fixable with multiple subs rather than EQ’ing. On the downside, some output was lost in the 25-30Hz region going from the EP500 to the 400s but the response was much flatter as well. Looking at the overall response of the EP400s you will notice an in-room bass response of 20Hz to 90Hz +-3dB. Not bad considering no electronic room correction was used to optimize the response.

EP500 vs. 2 x EP400s at Secondary Listening Seat

This is the mother-in-law seat we discussed earlier. As you can see in the purple trace, the bass response of a single EP500 at this listening position suffers a huge 12dB low Q (1.7) peak centered around 42Hz. This is clearly audible at that seat and makes the bass sound very boomy and muddy. While this could be tamed a bit with EQ, I’d risk adversely affecting the other seats since it’s a rather drastic problem needing a lot of cutting to resolve. The best solution of course it adding a second subwoofer as can be seen in the green trace via the dual EP400 subs. This response is much better and certainly far easier to optimize via EQ than the purple trace is.

Because I wanted to directly compare the audible sonic differences between the single EP500 and dual EP400s on the fly, I did not create a customized EQ response for both. As a result, my listening tests were conducted at the two listening positions measured above with no further changes.

EP500 vs. 2 x EP400s at Primary Listening Seat LOUD

I was curious to see how the response between these subs changed at high SPL levels so I turned it up to near house shaking levels in my room. It’s rare we ever listen to higher sustained levels except perhaps during big party events which most of our guests are usually a bit too buzzed to take notice of the bass response. You can see the limiting the EP400 is doing below 28Hz to keep things clean and distortion free. To look at it another way, the bass response is only shelved down 4dB below 28Hz at these high output levels to match the rest of the bass spectrum. This is a very smooth and linear response.

Listening Tests

I started out with some 2 channel music played in PLIIx Music Mode which is what we use on this system 90% of the time for listening to two channel sources. I got jiggy with some DJ Jazzy Jeff. With the EP500, the bass was well extended and tactile but not particularly as tight as I’d like it. Switching over to the dual EP400s was a real eye opening experience. I noticed that the bass no longer sounded like it was emanating from the front left of the room but instead sounded like it was coming dead center near the plane of the main speakers. The dual EP400s were creating that “virtual” subwoofer effect making it hard to pinpoint exactly where the subs were. This is how bass should be! The effective bass response of the dual EP400s was much tighter with a lot more mid bass punch. I was definitely down with the improvement I was hearing from the dual sub system.

It was time to go a little lower so I fired up my Rhapsody service featured in my Yamaha RX-Z7. I searched out some bass tunes popularized by teenage car audio enthusiasts back in the 90s. I am not a fan of this crap but I wanted to really test out the low end and this was the easiest way to do an instant comparison of the low end bass response. The EP500 was at a big advantage during this test. It played down lower and created a much LARGER tactile response than the dual EP400s. The single EP500 rattled my walls while the dual EP400s did so but at a much reduced level and tactile presence. Overall the bass of the dual 400s was smoother and more defined but true bass heads that listen to this type of so called “music” will prefer the bigger woof that the EP500 offers. For that crowd, I encourage you to consider an EP800 or two.

Next up was the Beatles Love DVD-A disc. I listened to bass heavy tracks like “Tomorrow Never Knows” and “Hear Comes the Sun”. The low end bass drop towards the middle of “Tomorrow Never Knows” did have more tactile feel with the single EP500 but the bass quality of the dual EP400s was clearly superior. The system bass response of the dual EP400s sounded more fluid and the blend between the subs and the main speakers was nearly perfect. In fact the advantages of the dual EP400s were even more apparent when I sat in the mother-in-law seat. With the EP500, the bass was distracting at that listening position. It was entirely too boomy and localizable. The EP400s produced a much more blended and pleasant experience. I was happy to report the wider improved listening window we always tout about multiple subs was being clearly demonstrated in a real world listening environment. The bass definition I was hearing on “Hear Comes the Sun” via the EP400s was above and beyond what I was able to muster from a single EP500 in my room.

Left Pic: Beatles Love DVD-A ; Right Pic: Horton Hears a Who DVD

I did extensive movie watching ranging from Star Wars Episode III “Revenge of the Sith” to “Horton Hears a Who” and the results pretty much mimicked my music listening tests. The starship explosions during the opening battle scene of Star Wars was a great experience with both subwoofers but the bass again proved a bit overpowering on the far left coach with the EP500. At times I preferred the extra tactile response of the EP500 but the mid bass punch and overall smoothness of the dual EP400s ultimately won me over. The fact that one could now get a similarly good movie watching experience across all the listening seats was worth sacrificing a bit of low end extension at high listening levels. Not once did I hear the EP400s strain to produce satisfactory bass response at near reference listening levels. The advantage of Axiom’s DSP driven technology was really proving itself, as subs typically this size would tend to bottom out or distort when attempting to play at reference levels in my largish room. This is a true testament to a properly engineered sub as it’s not all just about max SPL and extension. Designing a sub to be free from mechanical noise at all power levels is no trivial matter.

One thing I did notice over a course of a few days, the extension seemed to deepen a bit on the dual EP400s as they broke in. I am normally not a proponent of driver break in, unless you’re dealing with high mass, high excursion drivers like the ones found in Axiom subwoofers. That being said I couldn’t help but wonder what the result would be if Axiom offered an EP450 with dual 8” woofers or a single 10” in a slightly larger enclosure. Hmm, maybe this article will get the wheels spinning over in Canada as the ice thaws out and spring arrives :)

Recommendations

When you’re getting ready to pick out a new subwoofer for your home theater system, I’d highly encourage you to instead choose two subs. The benefits of multi-subwoofer systems are well documented and proven. The only circumstance where I would choose a single sub over dual subs is if your budget and placement are constrained and you listen at a single position only. If budget is a factor, then I’d recommend spending a little less on that first sub now with the intent of adding an identical second sub at a later date. If size is a factor when choosing between adding one or two subwoofers to your system, consider doing what I did and go with two smaller but potent subwoofers. If it’s a hard sell for your wife on getting two subs, just tell her you’re doing it for the benefit of her mother.