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Epique CBT24 Line Array Loudspeaker Review p2

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 testingR

The CBT24 speakers were tested on the ground since their emulated source point of acoustic radiation lay on the floor surface of their intended use. In other words, these speakers will not measure as well were they elevated in the fashion that I normally measure speakers, so in this case, I have tested them in the manner that they were designed to be used in. For the CBT24 speakers, this will be more reflective of the response that the end user will likely have in-room. No windowing was used since ground-bounce is not an issue with these speakers and does not interfere with their low-frequency response. Testing was mostly done at a distance of two meters with a one-meter height, and this would be a very typical listening position relative to speaker placement.

cbt24 dispersion response 3D

CBT24 speakers with MiniDSP equalization curve horizontal frequency response +/-90 degrees from axis: 3D view  

cbt24 dispersion response 2D 

CBT24 speakers with MiniDSP equalization curve horizontal frequency response +/-90 degrees from axis: 2D view  

The above graphs show the horizontal response of the CBT24 with the equalization curve provided by Dayton Audio for the MiniDSP. A lot of interesting features show up. One remarkable aspect is that there is barely any change in the directivity of the response up to 2.5 kHz, even out to 90 degrees. The speakers begin to get somewhat directional from 2.5 kHz to 5 kHz. Above 5 kHz, the CBT24s do lose their wider dispersion ability. The response also gets a bit rocky above 5 kHz as the 2.5” drivers can’t quite match the smooth high-frequency response of a dedicated tweeter. The direct-axis response becomes somewhat uneven above 7.5 kHz, and loses quite a bit of sensitivity above 15 kHz. The depression above 15 kHz isn’t really a big deal as there is very little content in that frequency range. There is a slight peak centered at 13 kHz, but it is too narrow of a peak in too high of a frequency to be a significant audible problem. One thing we do see is a nicely flat direct axis response at 5 kHz and below. The dips in the treble that we see above 7.5 kHz are not ideal, but they aren’t that problematic either; dips are much less audible than peaks, especially when they are sharp narrow dips such as these. Cumulatively, these dips might give the CBT24s a slightly recessed sound as compared to a speaker that had a perfectly flat response in this region. 

While the CBT24’s promise of extremely wide horizontal coverage looks to falter above 5 kHz, its promise of extremely smooth bass does pan out. Normally to measure a bass response that is as flat as this, I would have to place the microphone on the ground to avoid ground reflections. While that measurement technique will capture the loudspeaker’s intrinsic behavior in bass frequencies, it does not totally reflect a realistic behavior since few people listen to loudspeakers with their ears on the floor. In conventional speakers, the ground reflections that we discussed previously in the design overview section will affect measurements in the same manner that will be audible to listeners; we end up with a rocky and highly uneven bass response. This isn’t true with the CBT24 speakers. The bass response is extraordinarily flat no matter where the microphone is positioned with respect to the speakers.

It should also be noted that while the shown measurements were taken at a 2-meter distance with a 1-meter height, I measured these speakers at a variety of distances and heights, and the response remained very similar regardless of distance and height. The CBT24s maintained a very uniform response at any height and distance of a sensible listening position. In theory, there would be a sharp response roll-off not too far above the speaker’s height, but the speaker is five feet tall and it is unlikely that anyone has a listening position higher than five feet off the floor. Conventional speaker designs can have significantly differing response changes when moving from near-field to far-field, or especially when moving vertically on the speaker’s axis, but the CBT24s are essentially indifferent to these positional changes.  

 cbt24 dispersion response 3D no EQ

CBT24 speakers without equalization horizontal frequency response +/-90 degrees from axis: 3D view

The above graph shows the horizontal response of the CBT24 without equalization. We can see that the equalization chiefly shores up the response above 7.5 kHz where the 2.5” wide-range drivers are reluctant to play at the same level as lower frequencies.

CBT24 eq vs no eq 

 Comparison of equalization effects: direct axis of the CBT24 speakers with and without the equalization file supplied by Dayton Audio. 

The above graph shows the difference on the direct axis of the MiniDSP equalization curve supplied by Dayton Audio. The equalized curve here also had a high-pass filter applied at 80 Hz. We see that the equalized curve brings up the output above 7 kHz and also applies a small amount of boost in the bass for a flatter response in low frequencies. The difference is significant, roughly a 5 to 6 dB boost in certain treble frequencies. The equalized response is an overall flatter and fuller response and helps to shore up what would otherwise be a substantial flaw. Indeed, switching back and forth between the equalized sound and unequalized sound revealed a certain lack of clarity in treble frequencies on a variety of music without the equalization. This is the reason for Dayton Audio’s statement on the CBR24 product page: “Although the system works quite well on its own without EQ from below 100 Hz to 8Khz, the system works best with an active DSP...The DSP processor also provides touchup EQ to flatten the system’s overall response and to extend the system’s response out to the limits of hearing.”

CBT24 polar map 

CBT24 Polar Map of Dispersion 

The above graph is a polar map of the CBT24’s horizontal dispersion out to 90 degrees. This is with the equalization applied. It shows the same information that the preceding 3D ‘waterfall’ graphs do, but uses color to illustrate amplitude instead of a diagonal view of the Y-axis. This type of view can reveal different facets of the loudspeaker’s behavior. The polar map of the CBT24 gives us another view of its extremely wide dispersion out to 5 kHz, and this is a consequence of the small diameter of the drivers. There is some waist-banding above 2.5 kHz, and above 5 kHz the width of the dispersion narrows down to about 30 degrees off-axis. As we saw from the other dispersion graphs, the output is drastically reduced above 15 kHz. This graph tells us that for the best sound, the listener should be within a 30-degree angle of the direct axis since treble frequencies rolls off rapidly outside of that angle.

CBT24 impedance 

CBT24 Electrical Impedance and Phase 

The above graph shows the CBT24’s electrical load. It is specified by Dayton Audio to be a 4-ohm speaker, and that is true in a sense, but it is also a rather conservative rating. At no point in the CBT24’s response does it actually dip down to 4 ohms. Its minima occurs at 5 ohms, but it stays around 5 ohms for large swaths of frequency bands, and so it might be a bit taxing for low-budget amplification such as on entry-level receivers. Steep phase changes occur at high-impedance points, so it isn’t all that tough of a load. Heavy-duty amplifiers are not required to safely use these speakers, but users will want something more robust than a $300 AVR. More power capability is welcome, however, as the CBT24s can handle a lot of wattage (250 watts RMS according to the specs, but that is very much a conservative rating).

Conclusion

While I really enjoyed the CBT24 speakers, they are not aclose up 2 set of speakers that I would recommend unconditionally. First of all, the user should have a method to process the signal to equalize the dip in treble frequencies. The equalization curve provided by Dayton Audio for the MiniDSP is one way to do that, but the user would have to buy a MiniDSP unit along with the speakers, and that raises the cost by a couple hundred dollars. Room correction software should help. I did have the opportunity to listen to the CBT24s setup in a room equalized with Dirac Live software, and that made a significant audible improvement as well. So straight out of the box, I don’t really consider these ‘finished’ speakers; signal processing is needed to make them into high-fidelity speakers. Without that processing, these speakers are good but not great. Dayton Audio admits to as much on their product page.

Another caveat is that while they are large speakers, they aren’t really full-range speakers. As discussed before, their dynamic range in deep bass is nowhere near that of mid-bass and above. A subwoofer is needed for listening at more than moderate loudness levels. Something else to keep in mind is that there is no corresponding center channel at the present moment. The CBT24s are sold as a pair, not individually, and unless the user wants to buy a two-pack just for a single CBT24, some other speaker will be needed as a center, and preferably one that can actually keep up with them. One more caveat for some is their unusual appearance, but that will be an issue for some more than others. Personally, I like the way they look.

hero shot 2   pair angle

For those that can deal with these caveats, they will be rewarded with some pretty significant advantages. First of all, the sound, after equalization, is very nice. The sound of the CBT24s is smooth, wide, enveloping, and holds very good imaging, in both width and depth. The dynamic range, when used with subwoofers, is pretty much limited to whatever amplification can be supplied, so the sky is the limit. They can remain clean at VERY loud output levels, and this was made clear to me when I listened to them hooked up to an 800-watt amplifier provided by their designer, Don Keele, during a visit in which he explained aspects of the speakers and assisted with the setup. Most other speakers would have died under a load that they just laughed off. They have a good angle of coverage; the ‘sweet spot’ is pretty much anywhere within a 60-degree spread in front of them, and below 5 kHz that turns into a 180-degree spread. As previously mentioned, another neat attribute is they do not change much in loudness out to 10 feet. This makes them an ideal candidate for surround speakers where extra loudness due to closer proximity can degrade the immersion of the surround soundstage for anyone seated outside of a central position between all speakers. On a personal note, something else I enjoyed about them, as someone who moves speakers around a lot, is that they are quite light for such powerful speakers, at just a tad over 40 lbs. Pretty much any normally healthy adult can move these around with no problem.

The CBT24s would make for great party speakers as well as great speakers for critical listening. Now when those of us in the audio press say a speaker is a ‘great party speaker,’ that is usually damning with faint praise; it typically means that the speakers aren’t very accurate but can get real loud. That is not the case here. Once equalized, they do sound very good and reproduce recordings with superb detail and imaging. By calling them a “party speaker,” I really do mean they would be good for parties. One reason is their indifference of amplitude to distance. Usually at parties, speakers are played loudly, and anyone standing close to the speaker gets blasted with deafening sound. The CBT24s aren’t really any louder at a one-foot distance then they are at a ten-foot distance. Furthermore, their 180-degree wide coverage below 5 kHz, which is where so much spectral content of music lay, means that everyone will be able to hear at least most of the music. So, everyone in the room gets a relatively uniform musical experience no matter where they are, in both loudness and tonality. And, of course, the CBT24s have adequate dynamic range capability for nearly any party (so long as they are crossed over to a subwoofer).   

To bring this review to a close, I am sad to have to send my review pair back. As I said when I opened this review, these are the type of speakers that keep me interested in audio: learning about a new way of doing things. Speaker science is not a settled matter and there will always be opportunities for improvement, and revolutionary changes in store for the future of loudspeaker design. The CBT24 is a fascinating and bold step in that direction. They aren’t a perfect speaker, but with digital signal processing to correct for the ragged treble response, they become a terrific speaker, and they demonstrate a promising future for the CBT technology. Note

Editorial Note by Don Keele:

As an addendum to our review of the Dayton Audio CBT24 "Epique" loudspeakers, we invited the CBT24 designer Don Keele to explain some of the unique aspects of the CBT design in more depth and the CBT24 in particular.  Don Keele's accomplishments in loudspeaker design is a long list, as is the list of awards he has received in this endeavor which includes a Scientific and Technical Acadamy Award from the Acadamy of Motion Picture Arts and Sciences for work he did on constant-directivity horns. In the Epique CBT24 Designer Note article, Don explains some of the features and science behind the CBT24 and what performance characteristics separates it from conventional loudspeaker design

The Score Card

The scoring below is based on each piece of equipment doing the duty it is designed for. The numbers are weighed heavily with respect to the individual cost of each unit, thus giving a rating roughly equal to:

Performance × Price Factor/Value = Rating

Audioholics.com note: The ratings indicated below are based on subjective listening and objective testing of the product in question. The rating scale is based on performance/value ratio. If you notice better performing products in future reviews that have lower numbers in certain areas, be aware that the value factor is most likely the culprit. Other Audioholics reviewers may rate products solely based on performance, and each reviewer has his/her own system for ratings.

Audioholics Rating Scale

  • StarStarStarStarStar — Excellent
  • StarStarStarStar — Very Good
  • StarStarStar — Good
  • StarStar — Fair
  • Star — Poor
MetricRating
Build QualityStarStarStarStar
AppearanceStarStarStarStar
Treble ExtensionStarStarStar
Treble SmoothnessStarStarStar
Midrange AccuracyStarStarStarStarStar
Bass ExtensionStarStarStar
Bass AccuracyStarStarStarStarStar
ImagingStarStarStarStarStar
Dynamic RangeStarStarStarStarStar
Fit and FinishStarStarStarStar
PerformanceStarStarStarStarhalf-star
ValueStarStarStarStarhalf-star
About the author:

James Larson is Audioholics' primary loudspeaker and subwoofer reviewer on account of his deep knowledge of loudspeaker functioning and performance and also his overall enthusiasm toward moving the state of audio science forward.

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Recent Forum Posts:

67-79 posts on March 29, 2019 12:04
Hi, im still on the market in audio. I spend 50$ per month in audio approx. I discovered this line array presentation for the first time today. Thanks, i will surrely experiment something in the coming weeks or maybe never but i will surrelly try to listen them soon.
honyewl posts on April 29, 2018 06:34
Hi James,

Thanks for taking the time to explain your idea of using 2 CBT24 horizontally for center channel. Fascinating!

Hon Yew
shadyJ posts on April 28, 2018 20:39
honyewl, post: 1245408, member: 85573
Hi James,

I bought a pair of CBT24 in September last year. I have a 5.1 home theater setup - for both stereo/surround music and movie with a fixed projector screen. The CBT24 replaced my previous conventional 2 tower speakers. The Pros list in your review captured perfectly how giddily ecstatic I have been with them: “Excellent.., Extraordinary.., Superb.., Remarkably smooth..”!

However, as you rightly pointed out, there's no center. And trying to match them with “…preferably one that can actually keep up with them” has been a frustrating experience. My existing center (which I used to like a lot) now just sounds, well, underwhelming. I have also tried a center from a respected brand with concentric design, but again, it just couldn't keep up.

So I did something that I never thought I would do - I removed the center and settled on a 4.1 configuration! Except for listening positions way to the side of the movie screen (92“ diagonal), the phantom center works remarkably well.

I do want to explore having a CBT24 as a center. But not sure how it will work with overhead projector. If I used a drop down acoustic transparent screen, only part of the speakers is behind the screen - not sure if this will screw up the CBT characteristics. Perhaps a big enough screen that will ”cover" all three CBT24 - and the screen will have to reach the floor? Anyway, appreciate if you or Don have any advise and comments on this.

What speaker configuration did you use for testing the movies? Do you add a CBT24 central?

Thanks again for the nice and informative review.
Glad to see you are enjoying your CBT24s as I did with mine!

Per your questions, as you say, the way in which you outline the possible use of a CBT24 as a center does negate a couple of their advantages, but I think it would probably still work OK and sound fine. If you used a screen that reached to the floor, that would work to solve that problem, but that might make for a sub-optimal viewing angle. Depending on your viewing position, that still might be doable though.

One interesting idea might be to take two CBT24 speakers, omit the base, and attach them at the bottom for a larger arc, and then use that horizontally. This way, the shading between the drivers will be consistent for that kind of use. Here is a pic of what I am talking about:


Of course, if you elevate that off the ground, you do get floor bounce, but that isn't the end of the world for the sound. And that would be one hell of a center, it would easily keep up with your left and right fronts. You would want an outboard two-channel amplifier for a center like that, and use a splitter on your center channel pre-out. Since you can not buy these things individually, you would have a spare CBT to do this with anyway. The caveat with a center like that would be it would have wide vertical dispersion, and not so wide horizontal dispersion. This might not be a bid deal because the response of the vertical dispersion of a CBT24 is so uniform, and the pasting it into a center like that makes it so wide that even though it won't shoot out sound at a wide angle, it will still cover a large area. I will see if I can rope Don in here to comment on this potentially dumb idea.

By the way, for my own surround sound listening, I just used my Infinity Primus p362 center. That isn't a big fancy center, but it is a real over-achiever as far as center speakers go. I have yet to see a center speaker that measures better.
honyewl posts on April 28, 2018 12:06
Hi James,

I bought a pair of CBT24 in September last year. I have a 5.1 home theater setup - for both stereo/surround music and movie with a fixed projector screen. The CBT24 replaced my previous conventional 2 tower speakers. The Pros list in your review captured perfectly how giddily ecstatic I have been with them: “Excellent.., Extraordinary.., Superb.., Remarkably smooth..”!

However, as you rightly pointed out, there's no center. And trying to match them with “…preferably one that can actually keep up with them” has been a frustrating experience. My existing center (which I used to like a lot) now just sounds, well, underwhelming. I have also tried a center from a respected brand with concentric design, but again, it just couldn't keep up.

So I did something that I never thought I would do - I removed the center and settled on a 4.1 configuration! Except for listening positions way to the side of the movie screen (92“ diagonal), the phantom center works remarkably well.

I do want to explore having a CBT24 as a center. But not sure how it will work with overhead projector. If I used a drop down acoustic transparent screen, only part of the speakers is behind the screen - not sure if this will screw up the CBT characteristics. Perhaps a big enough screen that will ”cover" all three CBT24 - and the screen will have to reach the floor? Anyway, appreciate if you or Don have any advise and comments on this.

What speaker configuration did you use for testing the movies? Do you add a CBT24 central?

Thanks again for the nice and informative review.
gene posts on April 27, 2018 01:14
Don Keele's Designer Note and Review Feedback
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