Floor-to-ceiling array vs CBT

[keyser]

bbutterfield posted some interesting simulations with respect to line-arrays in this topic: Wave-front shape and impulse response: spherical, cylindrical, plane-wave

 

[jeno]

It has been allmost 5 years since I started this thread, and it is time to make some sawdust.

The fullrange driver floor to ceiling line array has grown popular, so I think I will go that direction too. The Tymphany TC9 drivers seems like the obvious choice. The fiberglass TG9FD10-04 are on sale at Madisound for $9. The paper cone TC9FD18-08 are about $10 at Parts Express.

Is there any reason besides price to choose the fiberglass version? If not I think I will go for the black paper cone as I find it visually more attractive.

 

[Zarathu]

When I built my first line arrays back 2007, I used 3.5 inch Sammi’s with similar characteristics to the Tympany’s. I turned them on first as full range speakers. I was astounded as to how good they were. But then, I turned on the electronic crossover to the 30 ND20s(with cut flanges to c-to-c of .87) and suddenly a whole new range of sound opened up. And then I added the 12 inch woofers crossing at 125hz, and suddenly what I didn’t think I needed was there.

If the range isn’t there, then your brain will create it. But when its suddenly there, you realize what you are missing.

 

[jeno]

I will probably build the arrays first, and add some subs later. I realize the bass quality from the arrays may be good, but in the end they only have so much displacement.

 

[wesayso]

TG9 vs TC9 is a tough one. They are more alike than they are different. A definite family resemblance there. The one on sale is a little more different though with it's 4 ohm motor design.

Personally I'd go for the TC9 FD 18-08 again without blinking, but that doesn't mean I did not seriously look at the TG9FD 10-08 for a long time to make up my mind. The 4 ohm version never made it to my shortlist.
For a lot more money, the Scan Speak 10F would be the one to beat. The TG9 FD 10-08 gets a little closer to the 10F if we look purely at the published measurements etc.

Ultimately, it's your pick. I don't regret mine. An array full of: etc... just didn't do that well for me (lol)

About bass performance, if and when placed close enough to the wall, with a bit of care to prevent early reflections, the arrays might surprise you in the bass department. I was expecting a lot but got more than I ever envisioned.
How you EQ the line will be very important, a clean DAC (at least 24 bit) and a good power amp are a must. The TC9 in a 25 driver array can handle about 240 watt before it gets into trouble. There are limits, for pure Home Theatre goals I'd add subwoofers to handle the first octave.

 

[Omholt]

However I sometimes see the claim that a floor-to-ceiling array will overcome the problems of straight arrays and eliminate the need for a CBT?

You don't overcome the phase issues between the drivers by adding more. On the contrary the spacing increases with more drivers, thus you have more lobing and comb filtering.

Obviously there may be some benefits in building it from floor to ceiling, but this doesn't negate the added superposition.

 

[Zarathu]

The real question, and the one that Russell, Keele, Griffin among others, whether you can hear it. You can measure it; but can you hear it.

With my floor to ceiling midrange line, and 30 inch tweeter line, I could not, and that was more than 10 years ago. Of course I did follow Jim Griffin’s Nearfield Line Array White Paper, TO THE LETTER.

 

[Omholt]

How do you know you can't hear it before you've heard one that doesn't have these problems (like the CBT) in comparison? And preferably in a AB test.

We can adopt to a lot of things and accept them. But it's not necessarily before one has done a comparison or get better references we notice them. That's the case with many areas within audio.

Personally I'm convinced that phase issues like these are very audible in a living room. You need a distance that's not possible indoor before the drivers sum properly. After all, we are very sensitive to timing issues. To my ears, traditional line arrays sound messy compared to something without the serious superposition. Making it taller (from floor to ceiling) will simply make these areas worse.

Not sure why you're mentioning Keele here. Since he has designed a speaker (CBT) that actually overcomes these problems. That also why it has a new name (constant beamwidth transducer), to distinguish it from a traditional line array.

 

[wesayso]

Did you read the theory thread of infinite lines? Infinite Line Source: analysis
Bending the array backwards and using shading is a pretty cool concept for shorter arrays, no argument there. However a floor to ceiling array has advantages over a straight short array.
The papers from Speaker Dave also have an interesting view on that: http://www.diyaudio.com/forums/multi-way/165596-constant-beam-width-transducers-line-arrays-6.html#post2257395
This is what makes a floor to ceiling array different in behaviour from a finite array.

 

[jeno]

Thanks for input wesayso, I think I'll probably go with the black paper cones. Don't expect too much activity until the autumn, but I will be starting collecting drivers and do the detailed planning.

Bjørn,
This will be a design for a small living room, so a curved array will take up too much floor space. I might try a cbt later on. I made detailed plans for 32 mids and 32 ribbons allready 6 years ago, using active shading (1 amplifier for each bank of drivers) but have not had time, space and money to make it happen. Maybe some day... In the meantime I may live happily with some straight full length arrays.

 

[Zarathu]

And preferably in a AB test.

Yeah.... one could find one of those anywhere. I’ll just zip down to my local grocery store.

 

[Bob Richards]

CBT is a BIG mistake. You want to have all the drivers at similar max amplitude, so they can handle lower frequencies adequately (at a decent SPL). It's about effective cone surface area. The closer the end drivers are to acoustically reflective floor and ceiling, the better it will work acoustically. The TG9 driver has less of a frequency response peak at around 10kHZ, compared to the TC9, (according to the published FR graphs) so is slightly better, unless it's easy for you to EQ that several dB peak out.

I highly recommend googling "Roger Russel", former speaker designer at McIntosh, who now makes and sells straight line arrays in his retirement. He has a great website with lots of incites about his line array projects. Also, the 8 ohm version of the TG9 appears to have slightly more extension of FR at the high end, relative to the 4 ohm version, which may be significant.

 

[Patrick Bateman]

CBT is a BIG mistake. You want to have all the drivers at similar max amplitude, so they can handle lower frequencies adequately (at a decent SPL). It's about effective cone surface area. The closer the end drivers are to acoustically reflective floor and ceiling, the better it will work acoustically. The TG9 driver has less of a frequency response peak at around 10kHZ, compared to the TC9, (according to the published FR graphs) so is slightly better, unless it's easy for you to EQ that several dB peak out.

I highly recommend googling "Roger Russel", former speaker designer at McIntosh, who now makes and sells straight line arrays in his retirement. He has a great website with lots of incites about his line array projects. Also, the 8 ohm version of the TG9 appears to have slightly more extension of FR at the high end, relative to the 4 ohm version, which may be significant.

"big mistake" is a little harsh. CBT arrays are just different. A CBT array approximates the behavior of a point source.

This is particularly nice for prosound; I'm so sick of going to concerts where the line arrays are melting your face in the front row.

If you've heard a CBT, they have a surreal ability to sound the same no matter where you are. The Danley SH50s do this too. It's very odd that you get closer and closer to the loudspeaker and the speaker doesn't seem to get louder. With an SH50 you can stick your head in it, and it's not particularly apparent where the sound is coming from.

Basically if you want to put sound in a room and you want even coverage, CBT is tough to beat.

They are admittedly less efficient. But power is cheap and you can make a CBT with very cheap drivers (since you're using so many.) You can get twenty 2" drivers from Tymphany or AuraSound and achieve power handling of around 50 watts with a CBT, at a total cost of about $200 per side. That's good performance for not a lot of money.

 

[Patrick Bateman]

I highly recommend googling "Roger Russel", former speaker designer at McIntosh, who now makes and sells straight line arrays in his retirement. He has a great website with lots of incites about his line array projects. Also, the 8 ohm version of the TG9 appears to have slightly more extension of FR at the high end, relative to the 4 ohm version, which may be significant.

Russel writes this on his site:

"I have now spent several years living with the IDS-25. I have not been seriously listening to any other speakers during this time. I recently brought out one of my earlier favorite designs from several years ago, the XR250. I had many good things to say about this speaker. One was the use of the new LD/HP woofers that lowered the distortion by a factor of ten.

Now, on first listening to the XR250, I could not believe what I heard. First, I noticed the imaging was very confusing and I couldn't locate the instruments in Copland's Billy the Kid as well as what I had been accustomed to with the IDS. The sound seemed to come from a wide area and didn't vary as much from instrument to instrument. The sound field had little relative depth and was more like a flat plane between the speakers. The difference was so great I thought perhaps I had wired the 250s out of phase by mistake but a battery test showed they were correct.

The second thing was glaringly obvious having a complete lack of life. There was no punch in the bass drum or other instruments as well. Even the piano seemed lifeless. It was a complete relative loss of transients and peak output. I was so used to the percussive sounds becoming alive that now they seemed dead in comparison. The third thing was the need for a lot more power. I usually set the volume control at 9 o'clock. Now it must be at 12 o'clock for the same listening level. There was no deep bass and the highs seemed to be a little clustered in one frequency area.

All together it was very disappointing for my pet XR250s. I had thought I might live with them for a while but I prefer not to go back now that I know what I am missing in the recordings. The lack of dynamics alone is enough to turn me off. Better dynamics was one of the first things I noticed when first hearing my 4" wide-range single column version but this is much more obvious now with the IDS-25. The sound of the experimental system had kept me pursuing this idea. I suppose it is somewhat from my listening experience over the years and learning what to listen for. Many people are used to inaccurate sound and perhaps have not made many comparisons with live music. They may be happy just enjoying the music with the sound as it is. When an improvement comes along, although it is heard, it may not be recognized right away unless it is pointed out to the listener.

Although the XR250 was unquestionably the best sound at the time, it must be realized that almost thirty years have gone by and improvements in sound are inevitable. A single, wide-range column system was on my mind for many years as the next step for improvements. The result was even better than I had hoped for."



I think he's experiencing a couple of things here:

1) A conventional line array isn't going to 'illuminate' the ceiling and the floor very much. For instance, his line array looks to be about two meters tall. That means that it will control directivity in the vertical axis down to 340Hz. I believe that would be the main reason that he finds that the line array images better.

2) He complains that his old direct radiator design is not dynamic. This is a no-brainer; the line array is more efficient and handles more power. This one is important and I think it's fairly easy to achieve in most loudspeakers. I believe it was Greg Timbers, from JBL, who wrote that dynamics was the most important criteria in his loudspeaker designs.


Here's the thing: line array isn't the only solution here. Prosound speakers are pretty darn dynamic. Waveguide speakers can image really well. If he REALLY wants to have his mind blown, he should go listen to a cardioid.

I'm not saying those are the BEST solutions, just saying they're definitely options. For me, one of the things that consistently puts me off with line arrays is that the treble sounds 'off' to me and they tend to make everything sound BIG. I keep doing Unity horns because they do that thing that CBTs can do, but the treble sounds more natural.

At some point I'm sure I'll build a CBT though. Won't be my main system but I need to have one in some room of the house.

 

[Patrick Bateman]

Did you read the theory thread of infinite lines? Infinite Line Source: analysis
Bending the array backwards and using shading is a pretty cool concept for shorter arrays, no argument there. However a floor to ceiling array has advantages over a straight short array.
The papers from Speaker Dave also have an interesting view on that: http://www.diyaudio.com/forums/multi-way/165596-constant-beam-width-transducers-line-arrays-6.html#post2257395
This is what makes a floor to ceiling array different in behaviour from a finite array.

McIntosh line arrays have been mentioned in this thread. If I'm not mistaken, Dave Smith worked on those.

Here's a couple of data points that might be of interest:

1) Dave Smith is currently doing arrays at Bose, and he's mentioned the use of log spacing. As I understand it, log spacing is used for shading. (I've posted some threads on how to do it.) Basically log spacing is a way to shade an array without throwing power away in resistors. It's a cost saving measure. My sims indicate that power tapering works better, but it sure gets expensive. (With power tapering, you're not only throwing power away, but you also have to purchase additional drivers. A log spaced array basically has "holes" in the line.)

2) Someone had mentioned on here that they'd visited Dave Smith at his home, and listened to his reference. Though he's worked on a gazillion line arrays, his reference speaker was the Snell eXpanding Array.

 

[Omholt]

A synergy horn is very interesting, but I'm a little skeptical to the additional holes and how it might effect the impulse response, hence sound quality. Hard to say and probably dependent on the size of the horn.

 

[Zarathu]

For me, one of the things that consistently puts me off with line arrays is that the treble sounds 'off' to me and they tend to make everything sound BIG.

Since you posted this in the multi-way section rather than the full range section, one might believe that you were talking about multi-way range line arrays not full range but then the only ones you mention are full range(one speaker 25 times in a row, for example).

Have you listened to a 4 way(a line of 25 - 2.5 inch mid, a line of 12-3 inch planars, a 8 inch mid woofer, and a 12 inch DVC 15 mm xmax sub woofer equalized to 27hz--PER SIDE) multi-way, line array that is driven by four separate amps in a fully electronic crossed 24 db/oct L-R system?

I suggest that the ones you have listened to have serious deficiencies.

 

[Patrick Bateman]

It's a tradeoff, no doubt. I was actually measuring a bunch of my waveguides yesterday to see which produced the smoothest frequency response.

The thing I noticed yesterday, which I think was interesting, was that the AXIS that you listen on seemed to have the greatest impact on the overall smoothness of the response.(1)

For instance, nearly every waveguide that I measured had the lumpiest response ON AXIS!

Charles Sprinkle wrote this about his "image control waveguides":

"“The Bi-Radial horn that we have had for decades was a 90x60 horn, and not the best match for the low frequency device in the M2,” Sprinkle says. “This horn is 120 degrees horizontal and 110 degrees vertical. We knew that if we wanted a good directivity transition between the woofer and the high frequencies, we had to have that amount of pattern, so the waveguide was designed to have a pattern consistent with what the woofer was doing with no discontinuity at the crossover point, which is 800 Hz.

“The second thing we did was use a blending geometry—there are no straight lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an infinite number of reflections, and the net effect is that it smears the reflections coming back down the horn and negates them."

So one of the things that I've been doing with my waveguide designs lately is that I've been making them asymmetrical. And I don't just mean the beamwidth, the axis of the waveguide is asymmetrical too.



JBL DD55000 is the only speaker I'm aware of that's done this.

My thinking is that the *symmetry* of the waveguide is the reason that waveguides measure worse ON axis than OFF. So breaking up the symmetry should improve things, is what I'm thinking.

And the difference isn't subtle either; for instance the JBL PT waveguide measures about +/- 1.5dB on axis, but OFF axis it's about +/- 0.5dB!



I'm too lazy to dig up my measurements, but here's a measurement that Geddes did of his oblate spheroidal waveguide from the Abbey. Note how it's smoother off axis than on. That behavior seems to be typical of waveguides.

Of course, Geddes probably knew this, and that may have contributed to his setup recommendation, which is to listen to his speakers off axis.

(1)Frequency response is a derivative of impulse response, so you can "fix" the impulse response by flattening the frequency response.

 

[Patrick Bateman]

Since you posted this in the multi-way section rather than the full range section, one might believe that you were talking about multi-way range line arrays not full range but then the only ones you mention are full range(one speaker 25 times in a row, for example).

Have you listened to a 4 way(a line of 25 - 2.5 inch mid, a line of 12-3 inch planars, a 8 inch mid woofer, and a 12 inch DVC 15 mm xmax sub woofer equalized to 27hz--PER SIDE) multi-way, line array that is driven by four separate amps in a fully electronic crossed 24 db/oct L-R system?

I suggest that the ones you have listened to have serious deficiencies.

Oh yeah. I have a huge preference for arrays that don't have a tweeter line. In the article that was posted earlier, the author writes:

My Experience with Column Systems

"To put it simply, a multi-way system by its nature chops up the signal from the power amplifier into 2 or 3 or more frequency ranges using crossover networks that destroy any coherence in the original signal."

IMHO, this statement is misguided. In a loudspeaker array, the main advantage of using a line of very small drivers playing out to 20khz is because it's practically the only way to get the polar response to look decent. Check out Keele's own measurements of his two-way CBT; there are significant issues with the horizontal polar response. Heck, I'd argue that there's a lot of good reasons to take Keele's two-way CBT and listen to on it's side! Monte Kay's CBT basically does this.

Every line array that I've ever heard that had a seperate tweeter line array exhibits this issue. Once I noticed it, it kinda made them unlistenable really. I mean, they do lots of things right, but I could never get over that.

Keep in mind, it's possible that my brain is kinda 'dialed in' for hearing that, because I generally listen to loudspeakers with waveguides, and waveguides arguably produce the best polars. Same thing with HOMS, after living with Gedlee Summas for half a decade, I'm really attuned to hearing HOMs. I can play pink noise over a waveguide and hear if there are HOMs with a single sweep, takes about ten seconds.

I came pretty close to buying the CBT Epique, and I know there's another person on this forum who replaced his Gedlee Abbeys with a two-way CBT.

 

[Omholt]

Charles Sprinkle wrote this about his "image control waveguides":

"“The Bi-Radial horn that we have had for decades was a 90x60 horn, and not the best match for the low frequency device in the M2,” Sprinkle says. “This horn is 120 degrees horizontal and 110 degrees vertical. We knew that if we wanted a good directivity transition between the woofer and the high frequencies, we had to have that amount of pattern, so the waveguide was designed to have a pattern consistent with what the woofer was doing with no discontinuity at the crossover point, which is 800 Hz.

“The second thing we did was use a blending geometry—there are no straight lines, you’ll notice—that has a generally decreasing radius,” he continues, “forming an infinite number of reflections, and the net effect is that it smears the reflections coming back down the horn and negates them."

Seems like an example of moving away from a true high-end solution IMO. They could have used a midbass horn to match the directivity of the older bi-radial horn. But obviously that makes it too big to market.

The polar response of the bi-radial horn used in JBL monitors 4430 and 4435 were almost perfect. The M2 and PT waveguides are clearly a step or two back in the power response. Even with a 1.5" exit driver, they beam more than the old horns with a 2" exit and are generally less even. But they measure better on-axis. Some of that might be related to the driver though.

Getting both a flat on-axis response and a great polar seems to be a conflicting matter in a horn. The question is how much is minimum phase behavior, thus can be EQed.