CBT36 Line Array has arrived!

[MSaturn]

Re: CBT36 Line Array has arrived!

anyone spending $2000 on a pair of speakers minus the amps, crossover, and whatnot shouldn't be averse to measuring if they wish to use their own crossover. I would also go miniDSP, probably.

[rickcraig]

Re: CBT36 Line Array has arrived!

Actually the inclusion of the Behringer was initiated by Marshall since he's very familiar with it. The DEQX unit is also mentioned because of my suggestion and I set up the DSP used for the CBT36 at the RMAF show. I did talk with Marshall and Don about the miniDSP and am sure they would be open to trying it in the system.

I jumped the gun at first.



Same transfer function? If used properly, the only difference will be that the passive one will require more power for an equivalent SPL, due to losses.

And yes, I use and have a miniDSP, albeit currently only on subs (not mains, though that's certainly an option in the future). I've also seen enough measurements of it to know that it's perfectly fine.

Note that John K uses it fairly extensively as well. As does Bill Waslo.



Fair enough. One thing about the miniDSP that is HIGHLY relevant to the instructions for this kit is that PE doesn't sell miniDSP's, but does sell an alternative in the Berry box. Nothing wrong with PE being self-interested enough to exclude mention of a part they don't sell, in favor of a part they do sell.

[charlielaub]

Re: CBT36 Line Array has arrived!

Same transfer function? If used properly, the only difference will be that the passive one will require more power for an equivalent SPL, due to losses.

The hurdle that must be overcome with the MiniDSP is that the user cannot implement any old transfer function unless you are fairly knowledgeable and can calculate the biquad transfer function coefficients and enter them in the "advanced" plug in. I had to develop a spreadsheet for this very thing as part of my active crossover developer spreadsheet tools, so that I could first test out the active transfer functions withe the MiniDSP.

If the CBT people want my calcs that implement analog transfer functions for the MiniDSP, they are welcome to contact me.

-Charlie

[cargilljc]

Re: CBT36 Line Array has arrived!

Not just arrived at Parts Express, but shipped from PE and arrived at MY HOUSE too!!! Yeah! Did some sanding over the weekend, and tomorrow will drop off at a cabinet maker for priming, sanding and final coat(s). Managed to tag on to the end of a production line of cabinets and kitchen isle being finished in semi-gloss black, and cabinet maker is charging me $40/speaker to finish. Seemed reasonable.

I am replacing some venerable old Infinity Prelude Compositions (linear array stacked over a subwoofer). I have wanted speakers with CBT36 properties for a long time. I did my MS at the Naval Postgraduate School. The fellow who roomed next to me was in Air Ocean Interface Sciences (academic euphemism for sonar geek). I heard unclass info about the need to not light up you own vessel with rear and side lobes and how much more coherent the return signal was when frequencies maintained their relative sound power levels over distance, and more so given temperature, salinity, sheer velocity gradients. Very heavy duty math. Since then, I have wanted a set of speakers that did not have back or side lobes and would not radiate off the ceiling. JBL patents and various literature suggest that I have found what I am looking for. Sure ought to make room corrections less radical. Will let you know how it turns out.

[rickcraig]

Re: CBT36 Line Array has arrived!

Not just arrived at Parts Express, but shipped from PE and arrived at MY HOUSE too!!! Yeah! Did some sanding over the weekend, and tomorrow will drop off at a cabinet maker for priming, sanding and final coat(s). Managed to tag on to the end of a production line of cabinets and kitchen isle being finished in semi-gloss black, and cabinet maker is charging me $40/speaker to finish. Seemed reasonable.

I am replacing some venerable old Infinity Prelude Compositions (linear array stacked over a subwoofer). I have wanted speakers with CBT36 properties for a long time. I did my MS at the Naval Postgraduate School. The fellow who roomed next to me was in Air Ocean Interface Sciences (academic euphemism for sonar geek). I heard unclass info about the need to not light up you own vessel with rear and side lobes and how much more coherent the return signal was when frequencies maintained their relative sound power levels over distance, and more so given temperature, salinity, sheer velocity gradients. Very heavy duty math. Since then, I have wanted a set of speakers that did not have back or side lobes and would not radiate off the ceiling. JBL patents and various literature suggest that I have found what I am looking for. Sure ought to make room corrections less radical. Will let you know how it turns out.

Cool - looking forward to your impressions.

[Pallas]

Re: CBT36 Line Array has arrived!

Note that John K uses [the miniDSP] fairly extensively as well. As does Bill Waslo.

One more to add, from someone for a long time thought that active units were a waste of time and money compared to passives at that:

I was also inclined to do this because the prices for active DSP modules have become quite attractive (unlike past attempts at using active crossovers). I have opted to start using the MiniDSP module because it appears to be the best value in the marketplace. I am aware of the supposed "issues" with this unit, but from what I have seen thus far I do not believe that these issues are a real concern for me. I plan on doing more testing.

Source: http://www.geddes-audio.com/forum/sh...tus-March-2012

[rickcraig]

Re: CBT36 Line Array has arrived!

One more to add, from someone for a long time thought that active units were a waste of time and money compared to passives at that:


Source: http://www.geddes-audio.com/forum/sh...tus-March-2012

Another option I failed to mention is the Digmoda amp. It has built-in DSP for the crossover function and can be purchased with a 2-way or 3-way amplifier section. I've used them with good results.

[cargilljc]

Re: CBT36 Line Array has arrived!

Have the CBT36 nearing completion.
Have DEQ2496
Have DCX2496
Anyone have recommendation for class d amp and power supply.
As for the person who was looking for CBT36 tweeters, if you are doing a curved line array, making that front baffle would be a real bear. I was impressed with the CNC quality. I thought I was pretty good at wood working, but I would not have been able to pull off the drilling for the 72 tweeters on their little circuit boards.

[MSaturn]

Re: CBT36 Line Array has arrived!

four of these

one of these with the proper voltage

[cargilljc]

Re: CBT36 Line Array has arrived!

MSaturn,
Thanks for the tip on Connexelectronics CxD400 and SMPS2000R power supply. I am going to look into those items more closely. They really look nice. I have asked for the spec sheets, but am guessing that they are at least up to a good standard. Have you used the amp module you recommended?
John

[jeffs_partsexpress]

Re: CBT36 Line Array has arrived!

Hey John,
Can you send us any pictures of your assembly of the CBT36? Especially of the painted cabinets. BTW great deal on the painting cost! I am looking forward to building a set of these myself some day.

Thanks Jeff

[MSaturn]

Re: CBT36 Line Array has arrived!

I've used other (older) versions of the IRS amplifiers, and can recommend them.

[cargilljc]

Re: CBT36 Line Array has arrived!

Cristi at Connexelectronics recommended their scalable IRS2092 Stereo Amplifier or their scalable single channel IRS2092 Modular Amplifier over the CxD400 "entry-level" single channel amp. Anyone on this thread have any feelings one way or the other. My building background has been amateur radio and williamson push-pull tube amps, so I don't have a clue other than looking at the specs of other Class D amps and loving the flat portion of the power curve relative to THD+Noise.

[aarond]

Re: CBT36 Line Array has arrived!

As for the person who was looking for CBT36 tweeters

That's me;)

If you are doing a curved line array, making that front baffle would be a real bear. I was impressed with the CNC quality. I thought I was pretty good at wood working, but I would not have been able to pull off the drilling for the 72 tweeters on their little circuit boards.

You are probably right as far as your statement goes but I would more than likely do the baffle in a segmened arc. There are other ways to do this too. Even if CNC is the most practical option it's not like the suppliers of this kit have a monopoly on CNC equipment.

In my opinion there aren't many/any good performing and affordable tweeter choices for an array. It doesn't seem like that big of a deal to offer the CBT36 tweeters seperately from the kit. Of course price is what would determine if it a good option for the consumer (I obviously can't address that one). Also, I don't think a seperate tweeter option would hurt CBT sales since you are probably talking about two different types of customers. I'm not going to buy a CBT kit regardless but I will continue to wait for an option that is better than what is on the market.

[cargilljc]

Re: CBT36 Line Array has arrived!

Aarond,

Good point about the various categories of DIY'ers. At various times dependent upon time, age, affluence, etc. I think I have been in every category.

On the other hand, I found it well worth the kit cost to have those many tweeters mounted on printed circuit boards that I did not have to make. That saved a lot of effort and precluded the possibility of wiring one of the 144 tweeters out of phase (not that would ever admit to having done that sort of thing in the past....). Heck, I cannot pop the tops of 144 consecutive cans of beer without making an error. I am not sure I can do anything 144 times without deviation or error. That would be 288 solder joints just for the tweeters -- I am sure, even with an RF background, that I would have to trouble shoot those connections.

One speaker down, the other wired but baffle with drivers not yet put into the cabinet. Next step will be the class D six channels of amplification.