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post #1 of 129 Old 11-02-2011, 10:07 PM - Thread Starter
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Here's the test results...

http://audioartistry.com/brochures/B...nts%20v8.1.pdf

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post #2 of 129 Old 11-03-2011, 04:34 AM
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These are some very nice results. Thank you Rick.
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post #3 of 129 Old 11-03-2011, 05:46 AM
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Those are awesome results in the vertical, just as predicted. The uniform ceiling interaction is probably the most useful part.

Although I understand why he uses the 801 as a yard stick as it adheres to the most commonly used approach, but I'd like to see his results versus a design that also controls directivity like a horn setup. Maybe when I get some SEOS 2-ways put together I'll haul them down to a Bloomington for a shootout. I'm always looking for an excuse to get back to B-town.

When I see the CBT I keep thinking of how it could be implemented with small horns. I know it wouldn't be cheap, but maybe possible with some custom molded horns. It might be more doable with ribbon or AMT drivers that can cross lower to the woofer section. That would definitely get pricey.
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post #4 of 129 Old 11-03-2011, 06:23 AM
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Rick,

How far away were all the other room boundaries to the DUT? Some of the dips in freq response seen could be some boundary interactions, as the measurements were gated with quite a wide gate (which is very helpful).

All in all, very comprehensive test. Would have loved to see 2m high off axis results, to see where the elliptical "sonic footprint" lies, but the nearfield results were pretty amazing......

JSS
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post #5 of 129 Old 11-03-2011, 06:27 AM
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Rick,

Will the CBT36's tweets be available as a separate part from PE?

JSS
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post #6 of 129 Old 11-03-2011, 06:43 AM - Thread Starter
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Quote:
Originally Posted by coctostan View Post

Those are awesome results in the vertical, just as predicted. The uniform ceiling interaction is probably the most useful part.

Although I understand why he uses the 801 as a yard stick as it adheres to the most commonly used approach, but I'd like to see his results versus a design that also controls directivity like a horn setup. Maybe when I get some SEOS 2-ways put together I'll haul them down to a Bloomington for a shootout. I'm always looking for an excuse to get back to B-town.

When I see the CBT I keep thinking of how it could be implemented with small horns. I know it wouldn't be cheap, but maybe possible with some custom molded horns. It might be more doable with ribbon or AMT drivers that can cross lower to the woofer section. That would definitely get pricey.

I'm sure Don would be welcome to have you visit; however, all of the arrays are here in Raleigh right now. We did CBT arrays with ribbons here at my church and I'm also designing a home audio / HT speaker with ribbons right now.

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post #7 of 129 Old 11-03-2011, 08:19 AM
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Excuse my ignorance, is this for sale? Is it a kit?

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http://www.avsforum.com/avs-vb/showt...1#post19489740
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post #8 of 129 Old 11-03-2011, 08:58 AM - Thread Starter
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Quote:
Originally Posted by maxmercy View Post

Rick,

How far away were all the other room boundaries to the DUT? Some of the dips in freq response seen could be some boundary interactions, as the measurements were gated with quite a wide gate (which is very helpful).

All in all, very comprehensive test. Would have loved to see 2m high off axis results, to see where the elliptical "sonic footprint" lies, but the nearfield results were pretty amazing......

JSS

I would have to go measure the distances but lengthwise (behind and in front of the speaker) there's plenty of space. The sides are closer and there's machinery everywhere so outdoors would've been better for the horizontal plots.

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post #9 of 129 Old 11-03-2011, 10:06 AM - Thread Starter
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Quote:
Originally Posted by maxmercy View Post

Rick,

Will the CBT36's tweets be available as a separate part from PE?

JSS

I'm not sure but I would imagine that initially all will be allocated to kits. I would email PE and ask them.

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post #10 of 129 Old 11-03-2011, 11:13 AM - Thread Starter
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Originally Posted by t6902wf View Post

Excuse my ignorance, is this for sale? Is it a kit?

Both kit and assembled systems will be available. The kit is going to be sold by Parts Express and I think they have targeted December for availability.

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post #11 of 129 Old 11-03-2011, 04:08 PM
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that is a pretty cool design.

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post #12 of 129 Old 11-03-2011, 04:49 PM
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Quote:
Originally Posted by Rick Craig View Post

I would have to go measure the distances but lengthwise (behind and in front of the speaker) there's plenty of space. The sides are closer and there's machinery everywhere so outdoors would've been better for the horizontal plots.

The wide gate used shows the upside of this speaker, and the upside that can be realized, as a wide gate more truly approximates what we get in-room. A much narrower gating or anechoic environment would make the 2 speakers appear more similar, deceptively so...

I bet the horizontals and all the measurements were affected by sidewall and equipment distance w/ a 50ms gate.....

Any subjective impressions between the two speakers in question?

JSS
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post #13 of 129 Old 11-03-2011, 05:22 PM
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Not to be a wet blanket, but doesn't the CBT solve two not so important issues and fail to address a single more important one?

The former being floor and ceiling reflections, and reduction in SPL vs. distance.

The latter being horizontal directivity (actually lack thereof) and its effects on early reflections and power response.

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post #14 of 129 Old 11-03-2011, 05:53 PM - Thread Starter
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Quote:
Originally Posted by maxmercy View Post

The wide gate used shows the upside of this speaker, and the upside that can be realized, as a wide gate more truly approximates what we get in-room. A much narrower gating or anechoic environment would make the 2 speakers appear more similar, deceptively so...

I bet the horizontals and all the measurements were affected by sidewall and equipment distance w/ a 50ms gate.....

Any subjective impressions between the two speakers in question?

JSS

The B&W does have some good qualities being very neutral and still holds it's own against many current point source designs. The main things I notice are dynamics and I get a better sense of immersion (soundstage,imaging,etc). The unifomity around the room is apparent as well.

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post #15 of 129 Old 11-03-2011, 06:08 PM
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Quote:
Originally Posted by noah katz View Post

Not to be a wet blanket, but doesn't the CBT solve two not so important issues and fail to address a single more important one?

The former being floor and ceiling reflections, and reduction in SPL vs. distance.

The latter being horizontal directivity (actually lack thereof) and its effects on early reflections and power response.

Yes. It, like every other design, has things it simply can't correct for....but 2 out of 3 is not bad....sidewall absorption and a proper crossover freq to multiple subs would be an option to mitigate its weakness....

Hard to place absorption on a floor that works low enough in freq, but ceiling is much easier.....of course, in a small enough room, front and back walls cause suckouts....

I think CBT is a good addition to the toolkit at our disposal, and used properly to exploit its strengths is the goal....it's not for everyone.

JSS
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post #16 of 129 Old 11-03-2011, 06:42 PM - Thread Starter
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Quote:
Originally Posted by noah katz View Post

Not to be a wet blanket, but doesn't the CBT solve two not so important issues and fail to address a single more important one?

The former being floor and ceiling reflections, and reduction in SPL vs. distance.

The latter being horizontal directivity (actually lack thereof) and its effects on early reflections and power response.

One distinct advantage is the even vertical coverage for a HT room with tiered seating. As far as the horizontal directivity and power response there is more control than you're assuming and Don Keele will address this soon. I can tell you from my experience at the RMAF show the horizontal power response wasn't a problem. The side walls were close to the speakers (13 ft. wide room in that location).

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post #17 of 129 Old 11-03-2011, 07:06 PM
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Originally Posted by Rick Craig View Post

One distinct advantage is the even vertical coverage for a HT room with tiered seating.

[me] That's easily handled by the 2-way WG speakers, or direct radiators for that matter; we're only talking a 10 - 15 deg vertical range.

As far as the horizontal directivity and power response there is more control than you're assuming and Don Keele will address this soon.

[me] Looking forward to it

I can tell you from my experience at the RMAF show the horizontal power response wasn't a problem.

[me] Power response as well as many other compromised performance parameters don't show up as problems in otherwise well-designed speakers until compared with one that does better in that regard.

p'fidojkr'po

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post #18 of 129 Old 11-03-2011, 08:52 PM - Thread Starter
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Originally Posted by noah katz View Post

p'fidojkr'po

One thing I forgot to mention. Due to the tapering of the drivers as you move up the line there is less output horizontally from the upper drivers.

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post #19 of 129 Old 11-03-2011, 09:12 PM
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Quote:
Originally Posted by noah katz View Post

p'fidojkr'po

In case anyone's wondering, I put in some random keystrokes because it said my message was too short.

Anyone know how to embed responses to multiple statements within a quoted section?

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post #20 of 129 Old 11-03-2011, 09:52 PM
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Nope, not sure how to do that, Noah.

But 2-way WG speakers cannot eliminate a floor/ceiling/wall bounce below the woofers directivity control point to match the waveguide, nor a ceiling or wall (front/back or sides) bounce (NOR can CBTs below their control frequency). You don't see too many freq responses at people's seats from their individual L/C/R speakers due to this, unless it is quite strictly gated. Even coffee tables make freq responses look pretty terrible with wide gating. Is it audible? Some say yes, others no....some people will take the hit in freq response to be able to put their glass of wine down on something.

Woofer/WG speakers have a narrow sweet spot induced by nulls at the crossover frequency due to the C-C spacing between woofer and WG. Go past the nulls and you may find that output still exists past them, contributing to the reflected sound power unless dealt with by absorption/baffling/other means.

In a baffle-wall setup with an acoustically transparent screen and an absorptive ceiling and thick carpet with thick padding backed by thick felt, Woofer/WG speakers would be incredibly tough to beat. Without a baffle-wall, and no absorption on the ceiling, but good wall absorption hung on the walls (front/back and sides), a proper CBT using the ceiling as a groundplane could be very good, and provide all rows with essentially the same presentation, even with surrounds very close to listeners, the close and far listeners would hear an equivalent spl (if implemented properly), and the surround effects would not necessarily collapse to one speaker.

Do not get me wrong. CBTs have their shortcomings. 3dB per octave falling response in the high registers means equalization or careful crossover design is important. The low cutoff for directivity control is dependent on line height and curvature. Center-to-center driver spacing limits the frequency at which control is maintained in the higher registers. A near 1/2" C-C spacing on CBT36 means control out to almost (if not at) 20kHz. Most tweets are larger, and will have finite control limits. You also need to purchase many drivers (and drive many of them with less than full power, so some sensitivity is lost), and come up with an acceptable shading scheme and crossover. Your response in the transverse direction will be dictated by crossover nulls (just like vertical nulls in W/WG speakers) as well as the amount of curvature of the array. Small drivers that can dig deep enough to cross to subs and still play well up high enough to cross to small tweets are not easy to find, especially if you only have receiver power to feed a stack of them.

They also have distinct advantages over line arrays and point source speakers, as noted in the many papers Keele has put forth.

Like any speaker design, they are not a panacea (large Synergy horns need not necessarily apply here, as they are LARGE). They do fit a niche for certain directivity needs coupled by a nice form factor (tall/slim).

JSS
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post #21 of 129 Old 11-03-2011, 10:26 PM
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Quote:
Originally Posted by maxmercy View Post

But 2-way WG speakers cannot eliminate a floor/ceiling/wall bounce below the woofers directivity control point to match the waveguide, nor a ceiling or wall (front/back or sides) bounce (NOR can CBTs below their control frequency).

Correct, but they can at the midrange freq that affect imaging the most.

Quote:
Originally Posted by maxmercy View Post

Woofer/WG speakers have a narrow sweet spot induced by nulls at the crossover frequency due to the C-C spacing between woofer and WG.

The nulls are only in the vertical axis, which in an optimum HT design will have a narrow pattern (40 to 60 deg) anyway.

In the horizontal where it matters much more, crossing the L/R axes in front of the listening area gives a wide sweet area, keeps energy off of the adjacent sidewall, and sens it to the opposite sidewall for a spaciousness-creating late reflection.

Noah
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post #22 of 129 Old 11-03-2011, 11:08 PM
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Quote:
Originally Posted by noah katz View Post

In case anyone's wondering, I put in some random keystrokes because it said my message was too short.

Anyone know how to embed responses to multiple statements within a quoted section?

I do it manually by doing a copy & paste of the initial quote code and then end each of my responses with the ending /quote code. Works well but takes an extra minute or two.

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yeah that's what I usually do but was feeling lazy

but it's good to know I haven't been wasting effort doing it the hard way, thanks

Noah
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post #24 of 129 Old 11-04-2011, 12:35 AM
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Rick

I saw in another post (?) that you mentioned the deqx with this, and that has also been mentioned in the pdf.

For a lot of potential DIYers of the kit, the cost of that might be a factor. (I use a deqx, and am kinda curious about the kit). In any case, it does say a processor (right word?) is needed, I assume not a passive design then.

Can you expand on any of this? Seems it is needed data for people to evaluate.
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post #25 of 129 Old 11-04-2011, 06:11 AM
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Quote:
Originally Posted by maxmercy View Post

Nope, not sure how to do that, Noah.

But 2-way WG speakers cannot eliminate a floor/ceiling/wall bounce below the woofers directivity control point to match the waveguide, nor a ceiling or wall (front/back or sides) bounce (NOR can CBTs below their control frequency). You don't see too many freq responses at people's seats from their individual L/C/R speakers due to this, unless it is quite strictly gated. Even coffee tables make freq responses look pretty terrible with wide gating. Is it audible? Some say yes, others no....some people will take the hit in freq response to be able to put their glass of wine down on something.

Woofer/WG speakers have a narrow sweet spot induced by nulls at the crossover frequency due to the C-C spacing between woofer and WG. Go past the nulls and you may find that output still exists past them, contributing to the reflected sound power unless dealt with by absorption/baffling/other means.

In a baffle-wall setup with an acoustically transparent screen and an absorptive ceiling and thick carpet with thick padding backed by thick felt, Woofer/WG speakers would be incredibly tough to beat. Without a baffle-wall, and no absorption on the ceiling, but good wall absorption hung on the walls (front/back and sides), a proper CBT using the ceiling as a groundplane could be very good, and provide all rows with essentially the same presentation, even with surrounds very close to listeners, the close and far listeners would hear an equivalent spl (if implemented properly), and the surround effects would not necessarily collapse to one speaker.

Do not get me wrong. CBTs have their shortcomings. 3dB per octave falling response in the high registers means equalization or careful crossover design is important. The low cutoff for directivity control is dependent on line height and curvature. Center-to-center driver spacing limits the frequency at which control is maintained in the higher registers. A near 1/2" C-C spacing on CBT36 means control out to almost (if not at) 20kHz. Most tweets are larger, and will have finite control limits. You also need to purchase many drivers (and drive many of them with less than full power, so some sensitivity is lost), and come up with an acceptable shading scheme and crossover. Your response in the transverse direction will be dictated by crossover nulls (just like vertical nulls in W/WG speakers) as well as the amount of curvature of the array. Small drivers that can dig deep enough to cross to subs and still play well up high enough to cross to small tweets are not easy to find, especially if you only have receiver power to feed a stack of them.

They also have distinct advantages over line arrays and point source speakers, as noted in the many papers Keele has put forth.

Like any speaker design, they are not a panacea (large Synergy horns need not necessarily apply here, as they are LARGE). They do fit a niche for certain directivity needs coupled by a nice form factor (tall/slim).

JSS

That is an excellent summation JSS. IMO, the CBT is truly an exceptional breakthrough. I would expect nothing less from Keele. That doesn't mean they are superior in every situation. For pro applications, I could see it doing very well in medium sized rooms where people are very spread out. It wouldn't have the output capacity of arrayed horns, but for moderate output needs it would be great.

My theater is a horn baffle wall setup like you describe. I don't see the CBT besting my setup in this case. I don't have ceiling treatments yet, but I plan to address that at some point. I control directivity vertically down to about 700hz presently. My vertical coverage for two rows at 12' and 18' is great. Of course, it is not as good as a CBT's. I might switch to a 3-way with a midhorn at some point and that will control vertical directivity lower.

Would using gradually thicker acoustic foam at the top and bottom of a flat or less curved array work to both delay and attenuate like the CBT model? It could eliminate the crossover complexity and make it easier to construct a small CBT. Something like 2ft tall.

Specifically, I'm thinking about something like what RAAL does with the foam on their ribbons which helps to reduce the beaming inherent to a tall ribbon.
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post #26 of 129 Old 11-04-2011, 10:06 AM - Thread Starter
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Quote:
Originally Posted by maxmercy View Post

Nope, not sure how to do that, Noah.

But 2-way WG speakers cannot eliminate a floor/ceiling/wall bounce below the woofers directivity control point to match the waveguide, nor a ceiling or wall (front/back or sides) bounce (NOR can CBTs below their control frequency). You don't see too many freq responses at people's seats from their individual L/C/R speakers due to this, unless it is quite strictly gated. Even coffee tables make freq responses look pretty terrible with wide gating. Is it audible? Some say yes, others no....some people will take the hit in freq response to be able to put their glass of wine down on something.

Woofer/WG speakers have a narrow sweet spot induced by nulls at the crossover frequency due to the C-C spacing between woofer and WG. Go past the nulls and you may find that output still exists past them, contributing to the reflected sound power unless dealt with by absorption/baffling/other means.

In a baffle-wall setup with an acoustically transparent screen and an absorptive ceiling and thick carpet with thick padding backed by thick felt, Woofer/WG speakers would be incredibly tough to beat. Without a baffle-wall, and no absorption on the ceiling, but good wall absorption hung on the walls (front/back and sides), a proper CBT using the ceiling as a groundplane could be very good, and provide all rows with essentially the same presentation, even with surrounds very close to listeners, the close and far listeners would hear an equivalent spl (if implemented properly), and the surround effects would not necessarily collapse to one speaker.

Do not get me wrong. CBTs have their shortcomings. 3dB per octave falling response in the high registers means equalization or careful crossover design is important. The low cutoff for directivity control is dependent on line height and curvature. Center-to-center driver spacing limits the frequency at which control is maintained in the higher registers. A near 1/2" C-C spacing on CBT36 means control out to almost (if not at) 20kHz. Most tweets are larger, and will have finite control limits. You also need to purchase many drivers (and drive many of them with less than full power, so some sensitivity is lost), and come up with an acceptable shading scheme and crossover. Your response in the transverse direction will be dictated by crossover nulls (just like vertical nulls in W/WG speakers) as well as the amount of curvature of the array. Small drivers that can dig deep enough to cross to subs and still play well up high enough to cross to small tweets are not easy to find, especially if you only have receiver power to feed a stack of them.

They also have distinct advantages over line arrays and point source speakers, as noted in the many papers Keele has put forth.

Like any speaker design, they are not a panacea (large Synergy horns need not necessarily apply here, as they are LARGE). They do fit a niche for certain directivity needs coupled by a nice form factor (tall/slim).

JSS

Very good points! I have tested other tweeters in CBT designs, including a 3/4" dome and a few different ribbon tweeters. The spacing does affect the control in the upper octaves; however, the audible effect can be very subtle (depending on the driver size / radiation). With the larger ribbons it is more noticeable so that's why I'm using a smaller RAAL ribbon in a design I'm currently working on.

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post #27 of 129 Old 11-04-2011, 10:27 AM
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Quote:
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In a baffle-wall setup with an acoustically transparent screen and an absorptive ceiling and thick carpet with thick padding backed by thick felt, Woofer/WG speakers would be incredibly tough to beat.

JSS


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post #28 of 129 Old 11-04-2011, 11:43 AM - Thread Starter
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Originally Posted by terry j View Post

Rick

I saw in another post (?) that you mentioned the deqx with this, and that has also been mentioned in the pdf.

For a lot of potential DIYers of the kit, the cost of that might be a factor. (I use a deqx, and am kinda curious about the kit). In any case, it does say a processor (right word?) is needed, I assume not a passive design then.

Can you expand on any of this? Seems it is needed data for people to evaluate.

A DSP crossover is best but it doesn't have to be a DEQX. You could easily use a Behringer, DBX, etc. if your budget is less than $2K. A passive design isn't possible with this kit but there are other driver combinations that will allow for that.

Selah Audio

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post #29 of 129 Old 11-04-2011, 01:12 PM
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How many channels of EQ per speaker are required?

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post #30 of 129 Old 11-04-2011, 09:48 PM - Thread Starter
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Originally Posted by noah katz View Post

How many channels of EQ per speaker are required?

Any of the DSP crossovers are fine, such as DEQX,Behringer,etc.

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