Line Array in the works at Stryke Audio. (1 Viewer)

[Patrick Sun]

Modesty prevents me from thinking I belong in such esteemed company listed above, and I don't. My strength is in knowing that I know too little.

Okay, back to the Stryke arrays!

 

[John E Janowitz]

Chris,

In a line array you could make the cabinet curved. The top and bottom would curve in, making the path length from each driver to the listener the same. There are a couple problems with this. First off, it would be extremely difficult to build. Second, and more importantly, the curve would only time align things perfectly at one point in space. You would be limited to one listening position both vertically along the array, and distance from the line. That really gets rid of the benefit of the line array that it has a broad listening area.

The center channel will actually be curved the opposite way. The RTW2's have a very controlled vertical response, up to about 5 degrees off axis. When turned sideways, then they have a controlled horizontal dispersion. Putting 6 of them in a half moon shape with 10 degrees between them gives a very smooth coverage pattern to 30 degrees off axis horizontally. This is much better than a typical MTM laid on its side. Power response throughout that horizongal span will be very flat.

John

 

[Chris Tsutsui]

Makes sense.

Thanks

 

[ThomasW]

With any hybrid line array curved or flat, the signal can only be optimized to one specific sweet spot. It's just the nature of the beast when mixing cones and planars; each having a distinctively unique dispersion/roll-off characteristic.

That being said, IMO nothing beats a line array for a nice combination of low distortion, wide dynamic range and interesting imaging.

 

[Bill Fagal]

Hooray for arrays

A cautionary tale:

I've been loving my power-tapered raw-MDF homebrew arrays for nearly three years--until a yard sale got out of hand last Sunday, and I sold them for $50. I simultaneously traded my backup set for some vintage jensens that need refoaming. Now I'm listening to a 1961 Zenith console stereo until I can whip up some replacements from the pile of drivers cluttering my basement.

I do believe I am experiencing sellers remorse...:frowning:

The very definition of sad, wouldn't you agree?

Bill

 

[Brett DiMichele]

The way I see it.. Every speaker ever made has a compromise
somewhere and Line Array's have thier share. But no speaker
is perfect no matter how well the XO is designed no matter
how much research goes into the enclosure and no matter
what type of speaker it is. It all comes down to choosing
the type that best suits what your needs are and then
living with the comprimises. Like I said before, the
benefits of an LA outweigh the negatives that they have.

Low distorsion and better efficiency are just two of the
many great reasons they fit my bill.

 

[Brett DiMichele]

Chris,

Have you ever thought about a career as a stand up comedian?
I mean really, I am laughing


In all honestly though. Experimentation is fine if you are
not shelling out tons of money and sometimes learning the
hard way can be the best way to learn (so long as it's not
also the costly way to learn). But I would much rather rely
on those in the know, who have the equipment and skills to
offer a kit that will measure and perform well.

I suppose I
could invest a couple grand in drivers and throw them on a
board and call it a Line Array. But without the knowledge to
know how to design the crossover or how large to make the
baffel I am quite sure my results would be less than stellar.

For that reason I will let someone else do all the figuring
and then I can slap it together per instructions

 

[Jim Griffin]

The Stryke line array is very similar to the Linus II array designed by Rick Craig and me. The Linus II uses 10 Vifa TC14WG49-08 drivers for the woofer/midranges and 8 Silver Flute YAG20-1 planar tweeters per side. The TC14’s are very smooth and yield great sound in the Linus II sealed enclosure. The Madisound YAG20-1, the Stryke RTW2, and the Parts Express Pt2 tweeters are all the same component just under different brands. Eight tweeters are sufficient to cover either a seated or standing listener. Full details and information about specs, performance, plans, parts kit, and cost are given at Rick’s web site which is:

http://www.selahaudio.com/linus2.html

The Linus II represents a solid near field line array design and addresses several issues mentioned in previous postings in this thread. For example, a slight power taper of the woofers mitigates the path length issue and creates a unified sound wavefront to the listener. The Linus II has a relatively small foot print—12” W x 9.25” D—which is not much more than several monitor speakers on the market.

I know that John has been working with his array for several months and I’m sure that it will be good when he finishes. He has his work cutout to crossover from the 7-inch drivers to the planar tweeters. The tweeters need to be crossed over no lower than 2500 Hz. These woofers are a 7.4” frame diameter so with frames touching a wavelength center-to-center spacing would be 1832 Hz. Hence, to prevent the first cancellation (severe comb lines) at two wavelengths or 3664 Hz, John will need to have a pretty aggressive crossover at attenuate the woofer response so that it will not muddle the sound above their cutoff frequency.


Linus II Link

 

[Patrick Sun]

Welcome Jim to the HTF!

For those not familiar with Jim, he's an all around nice guy, and has plenty to share in the speaker building spectrum ranging from making big tall line array speakers to very small full range speakers that sound mightily sweet. Make him feel at home, folks!

 

[Brett DiMichele]

Welcome Jim,

As far as the LA's go.. I am sure John will get the XO's
worked out for his design. I certainly have the utmost
respect for his work with those of us who choose not to
buy prebuilt speakers. The LinusII's are also a very sweet
looking (and I am sure, sounding) Line Array!

 

[Brian Bunge]

Jim,

You are going to bring those to the Atlanta DIY event this year, right?

 

[Jim Griffin]

Brian,

I'll probably bring two new arrays--Linus II and Needles. Both are shown below. I look forward to seeing you in Atlanta.

Jim

 

[Mark_J_H_Jr]

Brian,

Could you give some details on the Atlanta DIY event. I would love to attend. Gotta check out Jim's creations! They look impressive.

 

[Patrick Sun]

Mark,

Check out this webpage for details on this year's DIY Atlanta event.

 

[John E Janowitz]

Hi Jim,

Glad to see you around here. The Linus Array and Linus 2 are no doubt very good systems. My intent with this array is actually to improve upon a few issues that I see with the Linus. The first issue is the length of the line itself. As seen in Roger Russell's patent, to correctly approximate an infinite line source, you not only need to have a line long enough to keep the listener in the near field, but the array must also extend infinitely in the room, floor to ceiling. It is this infinite line that gives the well controlled early reflections from the floor and ceiling. One of the key benefits of a line array.

While this array will be 88" tall, it comes closer to approximating this infinite line. The difference between 72" and 88" may not seem like a whole lot, but when I did some experiments, you could see differences in the impulse response due to the floor and ceiling reflections. If I get a little more time, I will do some impulse responses with various numbers of drivers. I'll start with just a single driver, then a group of 4, 8, and 12.

In a standard impulse response you can see the inital impules, and then pick out reflections further down the line. Typically the shortest distance in the room is the height, so the first or earliest reflection is the one off the floor and ceiling. Where in time this reflection occurs is related to the path length difference from the driver to the listening position, and the driver to the ceiling and back down to the listener. The idea with the line array is to get the lenght from the top and bottom drivers to the listener to be the same as the reflected path length. This gives the most "control" to the reflections. Again, I'll try to do some impulse plots with various numbers of drivers and overlay them to illustrate just what I mean by the reflections being controlled. Another thing interesting to do is time gate to show ONLY the response of the reflections, not the initial impulse. This way you can see exactly what the response is that is being reflected to you from the ceiling.

As for the power tapering, I don't quite agree with this method.

For example, a slight power taper of the woofers mitigates the path length issue and creates a unified sound wavefront to the listener.

Tapering the power can lead to a flatter response in some cases, but also has drawbacks. You will get less comb effects at high frequencies, only because you are cutting down the magnitued of output from the outside drivers. Now as you go up or down within the line, the sound changes. The tapered power also does not do anything with regards to the path length issues. Whether the outer drivers receive less power or not, their signal still arrives at the same time. Giving them less power at the end of the line does the same as shortening up the line. It negates the benefits of the infinite line for controlling the vertical reflections, and the system begins to act more like a point source than an infinite line source.

The footprint on this new array will be larger than the Linus 2. There are a couple reasons for this. First, the large 2" radius roundovers on the corners help to smooth edge diffraction effects. Adding a 2" roundover to each side means the cabinet needs to get 4" wider. Thus, it will be 16" instead of 12". IMO, this 2" roundover also looks very cool. I'll let everyone else decide in a few days when I have cabinet pics up. The cabinet will also be a little deeper, about 12". The extra volume is useful for two reasons. First, as a sealed system, they Qtc comes in at .6 with typical box fill. This will give very well damped and accurate bass response. The system ends up with an F3 point around 70hz and F6 point around 50hz. My intent was to have this crossed to a subwoofer around 50hz, and with typical room gain from 50-70hz this should work very well.

The other option is to use the same enclosure, but vented instead of sealed. As I stated before, this gives an F3 point of about 49hz, with a very shelfed off low end that will work well with room gain, giving in room response down to 25hz or so. In many rooms, this could be sufficient without a subwoofer.

As far as the Xover goes, there is always a challenge in any system. The RTW2 has a resonance from 1-2KHz, therefore you need to cross higher to avoid that. Also as Jim said, severe comb lines are noticeable around 3.6KHz. This means there is only a small region that is acceptable for the crossover. It may be necessary to use higher order filters to make sure these problem regions are well supressed. The higher order filters also give more ability to fine tune things to get proper phase coherency, and in an array that has 12 mids and 12 tweeters, an extra inductor and capacitor will not affect the price much at all.

John

 

[Jim Griffin]

John,

On the number of tweeters needed in a line array my research tells me to design so that the listener is within the near field (hence the direct sound to the listener predominants over any reverberant sound) and that the listener is covered both while sitting or standing. Hence, for 2500 Hz (about the RTW2s lowest practical frequency of operation) and if the listener is 4 meters (13.1') away from the source, then the minimum tweeter line height needs to be about 1.14 m (45 inches). As frequency increase the near/far field transtition increases directly with frequency. The difference in sitting and standing positions (at ear level) is about this 45" length as well. Hence, a line of 8 RTW2 tweeters will be sufficient unless one listens lying on the floor or is over 6'6" tall. This would give you more than 54" of tweeter length which is OK.

Furthermore, if the speaker is operating in the near field, then its vertical radiation is perpendicular to the array and very little sound impringes off of the ceiling or floor. Bottom line is that if you create a near field array situation, then ceiling and floor reflections are minimal and should not adversely impact the speaker's performance. More than 8 tweeters in this case should not sufficently impact the sound heard by the listener.

Finally, the operative word in my power tapering statement was 'slight'. The trick here is to taper just a little so that the precedence effect (loudest first arrival sound captures the brain's ability to discriminate sound coming from different directions). If properly done the tapering would not significantly impact the basic line array effects nor would it foreshorten the array. The key is to reduce any unnatural sound bloom effects versus frequency--that is the impact of the different path lengths to the listener.

I agree with you on the box tuning statement. While line arrays of little drivers are nice, a bass head would want a subwoofer for going low.

On the round over there are two schools of thought on the diffraction effects. One way to think is to use the larger round over as you have designed. The other way to think about these ribbon and planar tweeters is that they really work their best (their widest horizontal disperion) when they have little if any structure around them. It would be interesting to see measurements and listening tests to explore this aspect for your array.

Jim

 

[Scott Pultz]

Hi Jim,

Can you tell us how much you power taper the array by? What is the power of a driver at the end vs the power of a driver in the middle? If this is confidential (ie you sell your x-over or whatever) then don't worry about it

Thanks,
Scott

 

[Jim Griffin]

Scott,

The proper way to power taper is to center weight the feed around the listening height. Thus, feed more power to the center than the outer drivers. You do this by series/paralleling the drivers in different numbers. Notice that all power is conserved--no resistors or power is lost--but just distributed differently across the aperture. One example for 11 drivers is to parallel 3 series groups of 4, 3, and 4 drivers. This is a 4/3/4 feed.

Jim

 

[Chuck Bogie]

So, with 16 drivers, Do you think that the best solution would be 6/4/6? But wait a minute... Wait - paralling three series... Sheesh - six 8 ohm speakers in series...

4/3/2/3/4?

Now if I can just figure out the ohmage involved here... I start looking at this stuff, and my brain goes into protection mode...

The good news is that I've been practicing my soldering.

 

[Jim Griffin]

Chuck,

A lot of combos out there to try. The way to figure the resultant nominal impedance of the array is to use the parallel formula for the strings in series:

Z(array) = 1/(1/Impedance of First Series String + 1/Impedance of Second Series String + ....)

For that 6/4/6 arrangement for 8 ohms drivers it would be:

Z(array) = 1/(1/6x8 + 1/4x8 + 1/6x8)
= 1/(1/48 + 1/32 + 1/48) = 9.6 ohms

Other combos to consider are 5/3/3/5 for 7.5 ohms, your
4/3/2/3/4 for 4.8 ohms, and so on.

Does that help?

Next week's lesson will be how to estimate the resultant SPL gain for the array.

Jim