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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => LAB: The Classic Live Audio Board => Topic started by: Sean Thomas on March 17, 2017, 03:14:58 PM
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Sound Theory 101 question:
Any inherent pros/cons to either of these designs?
With a symetrical design, you have 2 points of lows and 2 points of mids. As a listener moves to 50 degrees off axis (100 degree pattern),
the listener could be 30' from one low driver and 33' from the far low driver. Why is this not an issue? If it is not an issue, why are we so picky
about our sub placement, spacing, and alignment?
Thanks!
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You might want to peruse
https://en.wikipedia.org/wiki/Subwoofer
it goes a lot "deeper" (no pun intended) than a one paragraph explanation.
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Sound Theory 101 question:
Any inherent pros/cons to either of these designs?
With a symetrical design, you have 2 points of lows and 2 points of mids. As a listener moves to 50 degrees off axis (100 degree pattern),
the listener could be 30' from one low driver and 33' from the far low driver. Why is this not an issue? If it is not an issue, why are we so picky
about our sub placement, spacing, and alignment?
Thanks!
Simple answer, wavelength. At low frequencies the wavelength is so long they couple, effectively as one driver. The problem with all speakers, not just line arrays, is that these wavelengths get impossibly small the further up the frequency spectrum you go. This inevitably leads to comb filtering.
A good thing to do is to either google this or just lurk in the forums and pick it up piece meal, then ask questions to fill in the holes.
In sound systems there are no perfect answers just different compromises, then it's a question of finding the best set of compromises for you situation, not those that fit yours or others personal philosophy.
Good luck! ;)
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simply complex
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Both symmetrical and asymmetrical boxes have some lobing and acoustical sumation"problems". The trick is to keep them minimally audible. Some manufacturers do a much better job of that than others. The original research by Dr. Heil for L Acoustics explores that, and Danely has some interesting white papers on those problems and their solution. It will be interesting how Danely implements their solutions into a "line array looking" product for those that judge sound systems with their eyes.
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Simple answer, wavelength. At low frequencies the wavelength is so long they couple, effectively as one driver. The problem with all speakers, not just line arrays, is that these wavelengths get impossibly small the further up the frequency spectrum you go. This inevitably leads to comb filtering.
Agreed.
And just to add.
It is not the physical distance between the drivers (as many people think).
But rather it is the difference is distance to a particular listening position.
That is why, when you have spaced drivers (especially mids and highs), the sound changes (cancellation freq are different at different seats) because the distance between the drivers is different at different seats.
As a general rule, in order for drivers to couple well, (without noticable interference), they need to be within 1/4 wavelength of the highest freq that the speaker is producing.
For example: 100Hz is 11.3'. So the distance of arrival should be less than 2.8'.
At 1Khz, the distance is 1.13'-so less than 3.5".
At 10KHz the distance is 1.3". So now they need to less than 3/8" of an inch to avoid cancellation.
That is why multiple HF drivers interfere with each other much more so than subs.
The wavelengths are smaller-so the distances need to get closer and closer.
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Agreed.
And just to add.
It is not the physical distance between the drivers (as many people think).
But rather it is the difference is distance to a particular listening position.
That is why, when you have spaced drivers (especially mids and highs), the sound changes (cancellation freq are different at different seats) because the distance between the drivers is different at different seats.
As a general rule, in order for drivers to couple well, (without noticable interference), they need to be within 1/4 wavelength of the highest freq that the speaker is producing.
For example: 100Hz is 11.3'. So the distance of arrival should be less than 2.8'.
At 1Khz, the distance is 1.13'-so less than 3.5".
At 10KHz the distance is 1.3". So now they need to less than 3/8" of an inch to avoid cancellation.
That is why multiple HF drivers interfere with each other much more so than subs.
The wavelengths are smaller-so the distances need to get closer and closer.
Thanks Ivan - perfect answer, and exactly what I presumed. So if I check the specs of any major brands mid drivers highest xover point, the spacing will be or should be 1/4 wave or less? Is that an absolute design rule?
Also, if we apply this 1/4 wave rule to our sub placement - we could just line them up any where on the ground +/- a few feet (4' @ 75hz) and be ok..... but we don't.
Back to the original question - would an asyemtrical design be any better simply becuase it could never exhibit any of the symetrical "2 points/same band" issues as you move to the widest point of coverage where the distance becomes greater - even if the drivers are 1/4 wave or less?
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Thanks Ivan - perfect answer, and exactly what I presumed. So if I check the specs of any major brands mid drivers highest xover point, the spacing will be or should be 1/4 wave or less? Is that an absolute design rule?
Also, if we apply this 1/4 wave rule to our sub placement - we could just line them up any where on the ground +/- a few feet (4' @ 75hz) and be ok..... but we don't.
Back to the original question - would an asyemtrical design be any better simply becuase it could never exhibit any of the symetrical "2 points/same band" issues as you move to the widest point of coverage where the distance becomes greater - even if the drivers are 1/4 wave or less?
There is a bit of a "grey area".
1/4" is (should) be the design target. If it is a little larger-then there will be more interference.
How much more? It depends. How much is tolerable? it depends.
When some says "turn it down". Is 1dB enough? You "turned it down-but not enough for them to notice.
what about 10? Would 3 do it, or maybe 5.
As I often say, there is no simple answer that is correct.
But you need a guideline.
Many people are simply not aware of the "patterns" they are creating by placing subs where they do.
Sometimes you have no choice.
Often times there is no "right for everybody" position. It can be good for some people, but bad for others.
That is why it is ALWAYS best (no matter the manufacturer or product) to use a SINGLE sub and SINGLE full range cabinet.
As soon as you start to add more-you start to add problems.
But sometimes the end result is better than the problems it creates.
What IS important-is to understand how the interactions work, the penalties for doing so etc.
This way at least you have an educated idea of what to do and what might be the best compromise.
If you don't understand what if going to happen with various placements, then you are just "hoping" for something that may or may not happen.
VERY OFTEN, the result of adding more speakers is NOT AT ALL what most people think (or would like) will happen.
It is MUCH more science than voodoo. An accurate model (that is taking phase into account) will show these interactions.
A simple "amplitude" model will not show this and "assumes" (wrongly) that everything is "playing nice" with each other.
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You might want to peruse
https://en.wikipedia.org/wiki/Subwoofer
it goes a lot "deeper" (no pun intended) than a one paragraph explanation.
This is what happens with point sources and their various spacing relative to wave length.
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I believe your question is in respect to line-array design. This is a very rough sim of what happens with your T12s at their low / mid crossover of 420Hz with the spacing they have used. The FR plots are 0 degree and 45 degrees and there is a 100Hz HP.
The Mid / High crossover of 2.0 kHz does not work quit as well - you can see what happens modelling it with Ease Focus 3 (bottom picture)
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There is a bit of a "grey area".
1/4" is (should) be the design target. If it is a little larger-then there will be more interference.
How much more? It depends. How much is tolerable? it depends.
When some says "turn it down". Is 1dB enough? You "turned it down-but not enough for them to notice.
what about 10? Would 3 do it, or maybe 5.
As I often say, there is no simple answer that is correct.
But you need a guideline.
Many people are simply not aware of the "patterns" they are creating by placing subs where they do.
Sometimes you have no choice.
Often times there is no "right for everybody" position. It can be good for some people, but bad for others.
That is why it is ALWAYS best (no matter the manufacturer or product) to use a SINGLE sub and SINGLE full range cabinet.
As soon as you start to add more-you start to add problems.
But sometimes the end result is better than the problems it creates.
What IS important-is to understand how the interactions work, the penalties for doing so etc.
This way at least you have an educated idea of what to do and what might be the best compromise.
If you don't understand what if going to happen with various placements, then you are just "hoping" for something that may or may not happen.
VERY OFTEN, the result of adding more speakers is NOT AT ALL what most people think (or would like) will happen.
It is MUCH more science than voodoo. An accurate model (that is taking phase into account) will show these interactions.
A simple "amplitude" model will not show this and "assumes" (wrongly) that everything is "playing nice" with each other.
I agree completely with the fundamentals you're referencing & trying to analogize--But aren't there circumstances where it's possible to place multiple cabinets in an array so that the combined performance would be fully complimentary?
Take, for instance, the EAW BH760 OR KF940 Bass horn cabinets: They're 100% DESIGNED TO FUNCTION BEST in arrays of 4 or 8 pieces, stacked with the horn mouths adjacent & Coupling, effectively pieced together onsite to create a much larger single "bass Cabinet" which arguably acts better-behaved /is more directional than the generic common solutions available to those that either throw longer distances & provide more "tactile punch in the gut".
This Bass Horn Coupling I'm speaking of is much more noticeable & drastic than the much smaller benefits you'd reap attempting the same geometrical layout with "standard"Front-loaded Stadium Bass increase in in efficiency & low frequency linear extension by up to 10HZ or more
I also Design in-car Hi-Fi / High-End Custom Car audio systems that are designed with the intent of Getting Loud while Still sounding GREAT that Use similar principles--As a matter of fact, My current main Rear Subwoofer Temporary setup has three JBL Differential Drive W12GTI subs placed inside a large Enclosure to effectively create a single point-source via a large slot /round point for the Bass to emanate from, thus avoiding unwanted frequency cancellations & lack of in-phase cohesion.
(https://uploads.tapatalk-cdn.com/20170319/26389567aad571def0a988d682a95125.jpg)
(https://uploads.tapatalk-cdn.com/20170319/0d4ccbf810d9420a9acd835af0d2dc58.jpg)
(https://uploads.tapatalk-cdn.com/20170319/0b5dba7639f4736a7dc51cbe96066dcf.jpg)
The port fires up, at a vertical but slightly non-parallel angle to the inward on the rear hatch glass & Creates a cohesive pressure wave thru-out the car that HITS SO FAST & HARD that I could do nothing but smile after putting them In that way!
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I agree completely with the fundamentals you're referencing & trying to analogize--But aren't there circumstances where it's possible to place multiple cabinets in an array so that the combined performance would be fully complimentary?
Take, for instance, the EAW BH760 OR KF940 Bass horn cabinets: They're 100% DESIGNED TO FUNCTION BEST in arrays of 4 or 8 pieces, stacked with the horn mouths adjacent & Coupling, effectively pieced together onsite to create a much larger single "bass Cabinet" which arguably acts better-behaved /is more directional than the generic common solutions available to those that either throw longer distances & provide more "tactile punch in the gut".
This Bass Horn Coupling I'm speaking of is much more noticeable & drastic than the much smaller benefits you'd reap attempting the same geometrical layout with "standard"Front-loaded Stadium Bass increase in in efficiency & low frequency linear extension by up to 10HZ or more
I also Design in-car Hi-Fi / High-End Custom Car audio systems that are designed with the intent of Getting Loud while Still sounding GREAT that Use similar principles--As a matter of fact, My current main Rear Subwoofer Temporary setup has three JBL Differential Drive W12GTI subs placed inside a large Enclosure to effectively create a single point-source via a large slot /round point for the Bass to emanate from, thus avoiding unwanted frequency cancellations & lack of in-phase cohesion.
The port fires up, at a vertical but slightly non-parallel angle to the inward on the rear hatch glass & Creates a cohesive pressure wave thru-out the car that HITS SO FAST & HARD that I could do nothing but smile after putting them In that way!
Hi
“ But aren't there circumstances where it's possible to place multiple cabinets in an array so that the combined performance would be fully complimentary? “
It’s a source spacing issue as illustrated in Peters graphic, consider that if one had two simple identical direct radiating sources and has a source to source spacing of about ½ wl or more, then one has two independently radiating sources which raises the total SPL 3dB compared to one, four of the same sources more than ½ wl apart gives you +6dB more sound.
Conversely a direct radiating subwoofer example, two close coupled (less than ¼ wl apart) gives your +6dB more sound and four of them gives you +12dB more sound.
Fwiw, WL in inches roughly 1130*12 / frequency.
Bass horns fall in here too although they are not as straight forward as the direct radiating case as the horn gain stops increasing at the same rate.
While not serving the normal “sell the most boxes” goal, aside from the intelligibility considerations in the Hopkins Stryker equation and those that followed, there is a very strong acoustical reason to use the close coupled “coherent addition” approach so far as minimizing the total number of boxes / sources and cost, with enough sources acting as one acoustic source (with one source time arrival at any location) it is possible to provide “hifi” sound in large stadiums and outdoor venues with very few cabinets, in some cases one or two if you only have 30K-50K seats.
The technical problem doing this is our hearing spans a 1000:1 range of wavelengths so while it’s trivial to arrange a few subs to add fully but at 20KHz, the wavelength is only about 5/8 inch and for most uses, having directivity that is as constant as possible vs frequency is similarly challenging but also addressable.
How sound behaves depends strongly on the size of the physical objects compare to the wavelength of concern.
Best,
Tom
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I agree completely with the fundamentals you're referencing & trying to analogize--But aren't there circumstances where it's possible to place multiple cabinets in an array so that the combined performance would be fully complimentary?
Take, for instance, the EAW BH760 OR KF940 Bass horn cabinets: They're 100% DESIGNED TO FUNCTION BEST in arrays of 4 or 8 pieces, stacked with the horn mouths adjacent & Coupling, effectively pieced together onsite to create a much larger single "bass Cabinet" which arguably acts better-behaved /is more directional than the generic common solutions available to those that either throw longer distances & provide more "tactile punch in the gut".
You MUST use your full real name to participate on this forum or threads will get locked or your posts removed
As Tom said-it all has to do with wavelength.
Everything I said holds true-once you start to think in terms of wavelength vs size. Even for the cabinets you are talking about.
Actually the bass horns you mentioned were NOT designed to work together.
They were DESIGNED as smaller horns that could be transported easily.
Yes they will work together and in multiples they each help the impedance load of each other-so the end result is that they do couple.
A single larger horn would be a better "design", but then it becomes impractical to move around.
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I agree completely with the fundamentals you're referencing
Please go to your profile and change the "Name" field to your real first and last name as required by the posting rules displayed in the header at the top of the section, and in the Site Rules and Suggestions (http://forums.prosoundweb.com/index.php/board,36.0.html) in the Forum Announcements section, and on the registration page when you registered.
Mac
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You MUST use your full real name to participate on this forum or threads will get locked or your posts removed
Actually the bass horns you mentioned were NOT designed to work together.
They were DESIGNED as smaller horns that could be transported easily.
Yes they will work together and in multiples they each help the impedance load of each other-so the end result is that they do couple.
A single larger horn would be a better "design", but then it becomes impractical to move around.
Ivan, you may be thinking of the wrong box - these were all stadium sized horns designed to work in blocks of 4 or more for the best results - http://eaw.com/docs/2_Legacy_Products/Loudspeakers/BH/BH760/Spec_Sheets/BH760_SPECS_rev1.pdf
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Ivan, you may be thinking of the wrong box - these were all stadium sized horns designed to work in blocks of 4 or more for the best results - http://eaw.com/docs/2_Legacy_Products/Loudspeakers/BH/BH760/Spec_Sheets/BH760_SPECS_rev1.pdf
I am aware of the cabinets.
I still say the "design" was a smaller cabinet that when combined with others, would smooth out the response.
If the "design" was a single large horn, to then be cut into smaller pieces, it would look different.
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I am aware of the cabinets.
I still say the "design" was a smaller cabinet that when combined with others, would smooth out the response.
If the "design" was a single large horn, to then be cut into smaller pieces, it would look different.
If 52” x 36"x 24” x 376 lbs (KF940) is a small sub with respect to this forum … you guys at Danley need to rethink your packaging :D :D
This is what the manufacture says – “Widely known as the SuperSub,the KF940 is engineered to be used in arrays of four or more to produce extremely high output sub bass response to the very bottom of the audible spectrum.”
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Please go to your profile and change the "Name" field to your real first and last name as required by the posting rules displayed in the header at the top of the section, and in the Site Rules and Suggestions (http://forums.prosoundweb.com/index.php/board,36.0.html) in the Forum Announcements section, and on the registration page when you registered.
Mac
Got it--Thanks!
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I agree completely with the fundamentals you're referencing & trying to analogize--But aren't there circumstances where it's possible to place multiple cabinets in an array so that the combined performance would be fully complimentary?
Yes at long wavelengths, that is what was discussed. The spacing between subs are pretty small related to the wavelengths, specially in the subs you are referencing and being stacked together. You still cannot create a large omni-directional source. What was mentioned and is still being mentioned is you need to decrease the distance to at least 1/4 wavelength. If you put a high enough frequency sine wave through even those subs and walk the room you will find that they start lobing just like was shown above because the spacing between the drivers are larger than the 1/4 wavelength requirement.
So no you cannot place multiple cabinets in an array so the combined performance would be fully complimentary across the entire frequency range unless the cabinets are infinitesimally small which needless to say is at present impossible.
I believe the original theory behind line array was an infinite length of infinitesimally small drivers. It works for subs and also in antenna arrays purely due to the wavelengths being reproduced but as the frequency gets higher you stop being able to use line array theory.
Most line array manufacturers use line array theory up to a point and then switch to manifolds or horns above that purely because it is a better compromise.
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If 52” x 36"x 24” x 376 lbs (KF940) is a small sub with respect to this forum … you guys at Danley need to rethink your packaging :D :D
This is what the manufacture says – “Widely known as the SuperSub,the KF940 is engineered to be used in arrays of four or more to produce extremely high output sub bass response to the very bottom of the audible spectrum.”
It just depends on how you look at what is called "design".
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It just depends on how you look at what is called "design".
Hmmmm ...
"The design was based on a block of four, but they work fine one at a time or two at a time. Using fewer than four does not change the shape of the response, so the same processor settings will work no matter how you stack them.
Dave Gunness
(designer of BH760)"
http://forums.prosoundweb.com/index.php?topic=2376.10
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Hmmmm ...
"The design was based on a block of four, but they work fine one at a time or two at a time. Using fewer than four does not change the shape of the response, so the same processor settings will work no matter how you stack them.
Dave Gunness
(designer of BH760)"
http://forums.prosoundweb.com/index.php?topic=2376.10
Peter,
As you know, Dave also designed an asymetrical "line array" the EV MT4 system.
Anyone that has deployed those systems, or the more current EV asymetrical line arrays,
knows, or should know ::) if not set up "mirror image", you will be stuck with a response that sounds quite different
from one end of a centered mix riser to the other.
Greg Huber was experiencing that problem at the Minneapolis First Avenue night club,
the installers had not mirror imaged the cabinets, he dropped and re-hung, instant "success",
the system now has the same different sound on either side of dead center ;^).
Art
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Peter,
As you know, Dave also designed an asymetrical "line array" the EV MT4 system.
Anyone that has deployed those systems, or the more current EV asymetrical line arrays,
knows, or should know ::) if not set up "mirror image", you will be stuck with a response that sounds quite different
from one end of a centered mix riser to the other.
Greg Huber was experiencing that problem at the Minneapolis First Avenue night club,
the installers had not mirror imaged the cabinets, he dropped and re-hung, instant "success",
the system now has the same different sound on either side of dead center ;^).
Art
Art you make an interesting point - here is the frequency response plots of the T12 I mentioned above. You can see the results of the asymmetric design. The T12 is actually an excellent design. It should be noted that there are also big problems trying to produce good horizontal patterns with a symmetric design. Often the drivers are spaced too far apart either side of the HF horn to achieve good summation and horizontal pattern control.
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Art you make an interesting point - here is the frequency response plots of the T12 I mentioned above. You can see the results of the asymmetric design. The T12 is actually an excellent design. It should be noted that there are big problems trying to produce good horizontal patterns with a symmetric design. Often the drivers are spaced too far apart either side of the HF horn to achieve good summation and horizontal pattern control.
Peter,
Excellent design other than the 8 to 10 dB off-axis suck-out at 2000 Hz ;^).
I had the same problem with my year 2000 line array, except the crossover was lower.
The off axis suck-out in the crossover region with "side by side" layout is a problem with no solution, which is why we prefer multi way virtual point sources using shared horns for mid/high or low-mid/mid/high.
Art
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Excellent design other than the 8 to 10 dB off-axis suck-out at 2000 Hz ;^)
Peter and Art,
What would be cuasing the 10dB cut at 2k? Is that calculation
model accurate? It looks like your Listener Position is no where near the 100˙ pattern edge.
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Peter and Art,
What would be cuasing the 10dB cut at 2k? Is that calculation
model accurate? It looks like your Listener Position is no where near the 100˙ pattern edge.
Yes. Because the signals at that freq are coming out of 2 different drivers-which are in two different positions in space, the different time arrivals will cause combfiltering.
As you move (and change the difference in signal arrivals)-that notch will change freq.
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Peter and Art,
What would be cuasing the 10dB cut at 2k? Is that calculation
model accurate? It looks like your Listener Position is no where near the 100˙ pattern edge.
The T12 uses LR filters between the Mid and HF – because of the spacing between the MF and HF there is a parallax time error that causes cancellation off axis as Ivan said. This happens with most “standard” designs.
If you could run the HF crossover down to 1000Hz the problem would be almost gone, but that causes a different set of performance problems.
Another solution is to use synergy horns like Danley does, this however is not without design challenges
.
http://www.rane.com/note160.html
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The T12 uses LR filters between the Mid and HF – because of the spacing between the MF and HF there is a parallax time error that causes cancellation off axis as Ivan said. This happens with most “standard” designs.
Peter - would FIR filters (steeper slope) fix most of this issue at the xover point?
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Peter - would FIR filters (steeper slope) fix most of this issue at the xover point?
A steeper slope narrows the bandwidth of the "hole", but won't change the cabinet layout, there will always be an off axis dip if the spacing of drivers is not within 1/4 wavelength at the crossover frequency.
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A steeper slope narrows the bandwidth of the "hole", but won't change the cabinet layout, there will always be an off axis dip if the spacing of drivers is not within 1/4 wavelength at the crossover frequency.
Hi Art,
FWIW here is a graphical representation of what you described -
http://www.felusch.com/ton/Lake/004_Tech_Papers/Lake_Technology_-_Linear_Phase_Brick_Wall_Crossover.pdf
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....here is a graphical representation of what you described -
Nice info Peter. I assume this graph is for a generic 2 way speaker with the xover at 1k? The spacing between the low and high will change where your freq. dips are?
I read the LAKE pdf that you posted. Looks like the linear brick wall filters fix most of the issue. I assume that is FIR.
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Nice info Peter. I assume this graph is for a generic 2 way speaker with the xover at 1k? The spacing between the low and high will change where your freq. dips are?
I read the LAKE pdf that you posted. Looks like the linear brick wall filters fix most of the issue. I assume that is FIR.
Sean,
FWIW I decided to jump in the deep end a while ago and design and build my own line–array.
The design has a single 8” LF driver with a horizontal phase plug and a horn loaded AMT HF driver. It uses an FIR crossover - 1150Hz @ 72 dB per oct.
By doing that I achieved 1/4 wavelength spacing on the adjacent LF drivers and almost 1/2 wavelength spacing between the 8" and HF horn.
The horizontal directivity of the 8” and horn are very similar at the crossover point. When you model these two including their directivity there is only very minimal lobe-ing at the crossover point. By combining this with an almost brick wall FIR crossover there are no noticeable directivity artefacts.
I also looked at using a symmetrical design however the spacing between the two 8” drivers becomes problematic and results in reduced horizontal coverage and lobe-ing issues below the crossover frequency.
To solve this, the width of the horn I selected would have to be reduced but in doing so the pattern control of the horn would be compromised. You could also tuck part of the 8” drivers behind the horn flare to reduce the distance they are apart and reduce the horn width a little as a compromise, or have some the energy from the 8” drivers enter in through the HF horn mouth like dB Tech VIO or even as EAW have done with their KF730.
At the end of the day there is no simple answer to your question … as Ivan says “it depends” ;)
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Peter, I applaud you for having the guts to design and build your own system, and for the finished product. It looks very good. Is it a double 8" with one of the 8's rolled off or just a single low driver? How are the Air Motion Transformers holding up? I assume you tested and they have the efficiency to work with the 8" driver chosen.
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Peter, I applaud you for having the guts to design and build your own system, and for the finished product. It looks very good. Is it a double 8" with one of the 8's rolled off or just a single low driver? How are the Air Motion Transformers holding up? I assume you tested and they have the efficiency to work with the 8" driver chosen.
It uses a single 8" - 300 W 96 dB/W/m... The ATM's are rated at 120 W continuous and 104 dB/W/m so they don't seem to be having any trouble keeping up.
The sound quality using the ATM's is absolutely stunning. Their distortion levels are typically 20 dB less than a "standard" compression driver.
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Thanks Peter. I appreciate the answers. I somehow missed the single 8" as you clearly stated. Again, a great looking result. I'll bet the AMT's do sound good. I've heard some really good ribbon drivers in cabs (I don't want to start an argument but NOT the Versarray 112), but most ribbons usually can't handle the crossover point needed and input levels. To me, your system looks to be very well matched. Good job!