Modding the Dayton Audio B652-AIR Bookshelf Speakers

Can $30 worth of materials improve these $40 budget champs?

I recently began putting together a 5.1.2 Atmos-enabled home theater system, with the goal of building it around a mid-range but fairly future-proof receiver (the Denon AVR-X3500H), starting with budget speakers, and upgrading the speakers over time.

Having listened to a variety of higher-end speakers recently, I became a huge fan of the sound of MartinLogan Motion 4i‘s and Motion LX16‘s. Their Air Motion Transformer (AMT) tweeters provided a clarity and transparency to music that I found lacking in all but the highest-end dome tweeters, without the harshness I normally associate with horn tweeters.

However, those speakers are not currently in the budget, so I decided to take a chance on the highly-recommended Dayton Audio B652-AIRs, with their own implementation of an AMT folded Kapton ribbon diaphragm, at an unbelievable price. I picked them up on sale for $40.70/pair at Parts Express.

First Impressions

The Dayton Airs, while no MartinLogans, definitely shared many of the qualities that impressed me with their motion series — the AMT tweeter design is just that good. They did run a bit hot on the treble, though, and bass is definitely not their strong point. I would strongly recommend pairing these with a subwoofer, whether you intend to use them in a 2.1 or a home theater setup.

Objectives

I wanted to see if I could improve the sound of the B652-AIRs, without spending too much time or money. Ideally, these mods would take an evening and cost less than the price of the speaker.

After reading about other modifications made to these speakers, I decided to add some mass to the decidedly thin cabinet walls to help reduce any boominess or coloration at the low end, add some acoustic stuffing, and add a 2 Ohm resistor in series with the existing 3 Ohm resistor to temper the slightly high treble response.

Although I will be using these in a 7.1.2 setup with the Audyssey MultEQ XT32 room correction system included with the Denon receiver, I wanted them to have a solid base upon which to work with, as far as correcting the frequency response. Any boominess or unpredictable resonances would be hard to work with, even with automated correction software. (Learn more about room correction systems here).

The tweeter polarity reversal mod previously recommended at noaudiophile is most likely no longer necessary. Newer B652-AIRs seem to be coming direct from Dayton Audio/Parts Express with the polarity already reversed at the tweeter. You can check this by pulling the tweeter and inspecting the wiring. If the black (negative) wire is connected to the wider (positive) spade, polarity is already reversed and no additional modification is necessary there.

I chose Noico 80 mil sound deadening mat as a low-cost alternative to a product like Dynamat, which IMO would be overkill on a $40 pair of speakers.

Here are the materials used for modification:

ItemSource
NTE Electronics 3W, 2 Ohm Resistor (x2)Amazon
Noico 80 mil 10 sqft car Sound deadening matAmazon
Poly-Fil Premium Polyester Fiber Fill – 16 Oz.Walmart
Total Cost:$29.95

Caveats

For frequency response testing, I used my iPhone 11 Pro’s internal microphone with the HouseCurve app. I realize this is no substitute for a properly-calibrated external microphone, but I wanted to look for rough overall relative changes, and wasn’t going for extreme accuracy in this case.

Process

The patient on the table, pre-surgery.
Dayton Audio B652-AIR Mods
Poly-Fil and sound deadening mat. Here you can see the factory-provided piece of foam that apparently qualifies as a dampening solution.
The interior cabinet walls have been lined with the self-stick Noico sound deadening material, and the additional 2 Ohm resistor (blue) has been soldered in place. I cut pieces roughly to shape, and tried to line as much of the interior cabinet as possible.
The B652 cabinets are approximately 50% filled with Poly-Fil here. I originally filled them to 100%, but subjectively, I didn’t like the sound as much. It seemed to suck some life out of the midrange.

Results and Conclusions

Dayton B652-AIR Frequency Response, Before Modifications
Dayton B652-AIR Frequency Response, After Modifications

The sound dampening material and Poly-Fil reduce some peakiness in the midrange, but it also lowered overall bass response somewhat.

If I were not augmenting these speakers with a subwoofer and using Audyssey XT32 correction, I would probably not bother dampening the enclosure based on these results. The low-cost woofers included with these speakers just don’t seem to have enough power to take advantage of stiffening the walls and stuffing the cabinet, as you might see with some higher-displacement drivers.

Oddly enough, adding the sound dampening material to the cabinet seemed to introduce a new resonant peak at around 3500 Hz, but it didn’t seem objectionable when listening to music. Although I didn’t save the graphs, I did some interim testing and saw this peak appear after adding the Noico material, but before adding the resistor.

The resistor modification was definitely worth it. I often use the Beatles’ Mr. Moonlight as a test for objectionable tweeters. The opening vocals on the track are loud and overdriven, and can be painful to listen to on many speakers at higher volumes. The stock B652-AIRs were not horrible on this track to begin with, but the resistor modification definitely got the vocals under control.

The good qualities of the AMT tweeter did not seem to suffer at all after adding the resistor — the excellent imaging, transparency, and soundstage were still intact.

Dayton B652-AIR speakers can be found at Parts Express and Amazon.

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