My New Line Array--It's a Modified CBT24

The sensitivity of CBT24 is only 87 dB. However, it looses much less dB per meter compared to a traditional speaker. With 3 m distance the loss with a CBT is 5 dB, whereas it's 9,5 dB with a regular loudspeaker.

Without room gain, 50W will play about 102,6 dB at 3 meters (9.8'). With 200W and same distance, you'll reach approximately 108,6 dB (still without room gain).
 
My current 50 watts receiver is more than enough for the arrays as is. As Omholt and wesayso point out the arrays have virtually no volume fall off in the room akin to near field line array characteristics.

Once the 1200 watts matching powered subs are finished, I can use the 125 watts per channel vintage Yamaha R9 receiver that powers the 10" passive subs in the photos for the arrays. Power will not be lacking.
 
I'm not a tweaker without a reason kind of guy. I like to listen for a while, measure frequency response and decide how to address any shortcomings. Then rinse and repeat if necessary. These CBTs sound good as they are without EQ but they may have a soft upper frequency end which is typical for full range drivers in an array.

By design I attempt to not have any EQ by the choice of components, proper design approach to mitigate potential issues and such.

My bag of tricks for the CBTs include applying Audyssey in this case--easy to do with my receiver and retry as needed. I also have a minidsp 2x4 HD to try with the CBTs and and beyond that perhaps my DEQX Calibration processor. My opinion is less or little EQ is better than overdoing it. At some point I may try some of the computer based techniques suggested by others for their work in this forum.

Jim
 
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Hank,

Thanks for the note. I've been on a Florida vacation for the last five weeks so my new arrays have not been played until I returned this Sunday. After missing 5 weeks of play memory I am recovering my knowledge of how good these arrays really are. I'll be running some full listening room responses next week followed by a Audyssey MultiEQ tests. I'll everyone know what I see/hear. My previous measurements of this type were outside so it will be a difference experience with these new guys.

I really don't have a driver to recommend (other than the SB65s) but I can talk about process. I spent a while monitoring the experiences of others on their line array and other projects. The testing by XRK on DIYaudio and elsewhere gave me some insight on several drivers to consider. My approach included data sheet reviews of many 2.5" to 3" diameter drivers. I looked for smooth (or EQ-able) frequency response from 125 Hz to about 18 kHz. I prefer a rising response above 10 kHz and with a reasonable slope that can be EQ'ed. Notice that I'm planned to have subwoofers below 125 Hz. My towers are sealed so I did not intend to have heavy EQ on the low frequency end of the response.

Specs that I liked about the SB Acoustics SB65 units were their smooth frequency response curves (no breakups until 30 and 60 degrees off axis above 18 kHz and 16 kHz respectively), reasonable sensitivity at 83.5 dB for 2.83 V/m), a 5.3 mm linear coil travel (p-p), free air resonance of 115 Hz. The SB65 has an aluminum cone, copper cap, and a low damping surround and a linear neodymium motor for reduced distortion. Also these drivers can be mounted on a 2.626" c-t-c distance for a close array.

Let me hear if you need more insight from me.

Jim
 
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Quite the vacation, Jim. I'm looking forward to your opinion of just how much EQ your CBT's will need. Hopefully not so much that you'd need to insert your minidsp into the chain. My plan is to cross to my two Rythmik Audio F12G's at about 100 Hz or so. I just stumbled onto this Dayton 4" full-range and cursory glance at the specs make it interesting: Dayton Audio PS95-8 3-1/2" Point Source Full Range Driver 8 Ohm I think I'll buy cabs from Kevin - will be nice to not deal with sheets of MDF and the dust for a change ;-)
Thanks for your sharing your design and I look forward to your tweaks.
 
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Hank,

The Dayton 4" PS95-8 driver that you mentioned is 'huge' compared to the SB Acoustics 2.5" SB65s. We are talking 98.2 mm (3.866"round frame) vs. the 64 mm (2.519") square frames of the SB65. So we have a 34.2 mm or about 1.346" width dimension difference per driver. Hence, the 24 driver array width the same spacing of my project would be 32.3" longer. The SB65s have a total array baffle length (stretched out) of 65" or the same as Don Keele's Epique version. Hence, larger size drivers would significantly lengthen the array and likely harm the high frequency performance as the c-t-c spacing of the drivers increase by that 34.2 mm value.

More promising in matching the scale of the Epique or my modified CBT24 arrays is to start with a 2 to 2.5" dimension driver sizing and go from there. Some possible drivers from the Parts Express line include the

Dayton Audio ND64-16 2-1/2" Aluminum Magnesium Cone Full-Range Neo Driver 16 Ohm

which is a 16 ohms unit similar to the Epique's 16 ohms unit (may be the same driver). Several other drivers come close to the sizing for the scale of the CBT24s arrays. You can review the various other drivers among the 20 or so in the 2.5" size in P-E's offerings for fit checks.

Another new driver in the P-E line is the Eminence Alpha 2-8 which is a nominal 2" driver

Eminence Alpha 2-8 2" Full-Range Speaker 4 Pack. Another 2" driver is the Fountek FR58EX 2" Neodymium Full Range Speaker Driver

Some of these other drivers may need vented enclosures to lower the cross over to your preferences but that should be doable. Having good driver drawings is key to judge between each unit. Again I can not make expert recommendations on drivers without a lot of comparisons, even testing, and adding your constraints.

On the shading networks for the CBT24 arrays: Don provided me the shading network for his 16 ohms driver version and I scaled it to 4 ohms driver for my arrays. 8 ohms driver shading will take some thinking to achieve the proper weights but that is mathematics.

Going with Kelvin is an easy choice given his ability to derive a CNC'ed array for these small drivers.

Jim
 
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Hank,

You can study drivers all day but I would still go with the SB Acoustics SB65s over any other driver that I've considered even though it isn't as price friendly as some of the others. Given the performance/quality that you seek they are worth the cost. See if you can get volume pricing from Madisound and Meniscus Audio for starters and check other suppliers if possible.

Jim
 
Founder of XSA-Labs
Joined 2012
Paid Member
The SB65 is an excellent driver that probably has the highest smooth (no breakup) reach of any full range driver. It resembles a 1in aluminum dome tweeter in some ways. My main complaint is lack of sensitivity but when in an array that’s not an issue. The Faital Pro 3FE25 in 16ohms might be worth looking at as well. Super sensitive and quite smooth.

If you want the close CTC distance the Fountek FR55EX is also worth a closer look. Also Nd magnet and aluminum cone.
 
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Instead of the FR58EX I think xrk971 meant the Fountek FR58EX. I mentioned the FR58EX as well.

The Faital Pro 3FE25 is excellent as well but it is 81 mm diameter vs. the 64 mm wide dimension of the SB65. In this case that 17 mm additional c-t-c spacing is very critical in sizing the array and overall performance. Essential the application really needs a 2.5" dimension driver vs. a 3" unit.
 
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