4-way Truncated Line Array Nearfield Studio Monitor
This is an ambitious project, and I suspect that it will take plenty of time and patience to reach a final design/revision.
My goal is to create a superior version of this monitor: Barefoot Sound >> MiniMain12
Yes, it is massive. And, yes, it is actually used a nearfield quite frequently. The reviews are stellar, and the price is high (22k). As you can see in the pictures, the mm12 uses mostly Dayton and Peerless drivers that are easily sourced on Parts Express. I can't afford 22k, but I am proficient in Solidworks and woodworking and can afford a slew of drivers that are supposedly better than what is found on the mm12.
I have been doing tons of research on loudspeaker design, and my initial choice of strategy is to design the entire speaker around the midrange. As indicated in the title, I would like to utilize line array configuration for this monitor. For the midrange, I would stack 5-7 midrange drivers in a vertical line array. To the right of this array would be a line array of tweeters, packed as close as possible to the midrange line array. To the left of the midrange array would be 2-3 7" woofers. And, of course, there would be 2 isobaric dual-opposing 12" subwoofers on the side of the cabinets.
Right now I am mainly wondering about which drivers to use for the midrange and tweeters. Here are my current contenders and thoughts. My current proposed combination is the following:
Dayton RS75T
Dayton Audio RST28F-4
Dayton Audio RS180-4
Dayton Audio RSS315HO
Feel free to add suggestions!
Midrange:
Dayton RS75T
Great reviews by Timothy Fileppa as a midrange driver and, being a truncated design, is designed for line array duty. Bass extension stops at 170Hz. Frequency response not super linear but can be corrected with DSP perhaps?
RS100T
Same design as RS75 but useable down to 80Hz. Flatter frequency response from 1k-4k but dispersion falls apart pretty fast beyond 4k. More sensitive than RS75T.
Peerless by Tymphany NE123W-08
I have heard the 5" version of this driver, and it sounds excellent, especially in lower mids. Barefoot uses the 5" in their mm27 gen2, which I own. Frequency response is not that flat and dispersion falls off a bit in upper midrange. Not truncated and thus spacing will be more difficult to get within one wavelength of upper crossover frequency
Dayton Audio RS52AN-8
Flat midrange frequency response and excellent dispersion. Ugly. Not truncated and would probably need frame modification to achieve spacing within one wavelength of upper crossover.
Tweeters
Dayton Audio RST28F-4
Nice frequency response. Good reviews. Ugly. Can be mounted to truncated frame (5$/frame), which supports use in line array that requires tightest packing possible.
Peerless by Tymphany XT25TG30-04
Great Reviews. Not truncated, so spacing for line array would require modification. Off-axis response possibly not the best but might be mitigated with line array.
Peerless DX25BG60-04
Not much written about this one. Looks like it might be the same as the tweeters that ATC used before going in house. Big spike at 10k+ on axis. Not truncated.
Peerless by Tymphany D27TG35-06
Good reviews. Could also be the tweeter that ATC used before going in house. Same 10k+ spike as DX25BG60-04. Not truncated.
Woofer
Dayton Audio RS180-4
Great Reviews. Aesthetically consistent with my top choice mid range driver
Peerless by Tymphany NE180W-04
I know firsthand that I like this family of sound.
Subwoofer
Dayton Audio RSS315HO
Great reviews again. Consistent aesthetics with my top choices.
This is an ambitious project, and I suspect that it will take plenty of time and patience to reach a final design/revision.
My goal is to create a superior version of this monitor: Barefoot Sound >> MiniMain12
Yes, it is massive. And, yes, it is actually used a nearfield quite frequently. The reviews are stellar, and the price is high (22k). As you can see in the pictures, the mm12 uses mostly Dayton and Peerless drivers that are easily sourced on Parts Express. I can't afford 22k, but I am proficient in Solidworks and woodworking and can afford a slew of drivers that are supposedly better than what is found on the mm12.
I have been doing tons of research on loudspeaker design, and my initial choice of strategy is to design the entire speaker around the midrange. As indicated in the title, I would like to utilize line array configuration for this monitor. For the midrange, I would stack 5-7 midrange drivers in a vertical line array. To the right of this array would be a line array of tweeters, packed as close as possible to the midrange line array. To the left of the midrange array would be 2-3 7" woofers. And, of course, there would be 2 isobaric dual-opposing 12" subwoofers on the side of the cabinets.
Right now I am mainly wondering about which drivers to use for the midrange and tweeters. Here are my current contenders and thoughts. My current proposed combination is the following:
Dayton RS75T
Dayton Audio RST28F-4
Dayton Audio RS180-4
Dayton Audio RSS315HO
Feel free to add suggestions!
Midrange:
Dayton RS75T
Great reviews by Timothy Fileppa as a midrange driver and, being a truncated design, is designed for line array duty. Bass extension stops at 170Hz. Frequency response not super linear but can be corrected with DSP perhaps?
RS100T
Same design as RS75 but useable down to 80Hz. Flatter frequency response from 1k-4k but dispersion falls apart pretty fast beyond 4k. More sensitive than RS75T.
Peerless by Tymphany NE123W-08
I have heard the 5" version of this driver, and it sounds excellent, especially in lower mids. Barefoot uses the 5" in their mm27 gen2, which I own. Frequency response is not that flat and dispersion falls off a bit in upper midrange. Not truncated and thus spacing will be more difficult to get within one wavelength of upper crossover frequency
Dayton Audio RS52AN-8
Flat midrange frequency response and excellent dispersion. Ugly. Not truncated and would probably need frame modification to achieve spacing within one wavelength of upper crossover.
Tweeters
Dayton Audio RST28F-4
Nice frequency response. Good reviews. Ugly. Can be mounted to truncated frame (5$/frame), which supports use in line array that requires tightest packing possible.
Peerless by Tymphany XT25TG30-04
Great Reviews. Not truncated, so spacing for line array would require modification. Off-axis response possibly not the best but might be mitigated with line array.
Peerless DX25BG60-04
Not much written about this one. Looks like it might be the same as the tweeters that ATC used before going in house. Big spike at 10k+ on axis. Not truncated.
Peerless by Tymphany D27TG35-06
Good reviews. Could also be the tweeter that ATC used before going in house. Same 10k+ spike as DX25BG60-04. Not truncated.
Woofer
Dayton Audio RS180-4
Great Reviews. Aesthetically consistent with my top choice mid range driver
Peerless by Tymphany NE180W-04
I know firsthand that I like this family of sound.
Subwoofer
Dayton Audio RSS315HO
Great reviews again. Consistent aesthetics with my top choices.
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Are you sure you want to build a line array? Its spectral balance for a finite one changes if you move closer of further away, which seems problematic for a studio monitor to me. It happens because the transition from near field to far field is frequency dependent. Near field they drop off with 3 dB per doubling of distance, far field it's 6 dB.
That is certainly a good question. Just because we can build it does not mean we should. I based most of my assumptions on this paper: https://audioroundtable.com/misc/nflawp.pdf
The following is from the paper:
A near field line array provides a different listening experience versus point source speakers. Among the distinctions that characterize line arrays are: · Near constant sound levels throughout the listening room · A wider soundstage · An image ‘sweet area’ and not an ‘sweet spot’ · Recreates live event sound dynamics
One observation from in-room listening to line arrays is that the stereo sound stage is very wide with a large side-to-side and front-to-back sweet spot. When first heard this enhancement of the stereo image area is in stark contrast to listeners who are familiar with pin-point sweet spot listening from point source speakers. Again the broaden image area is a line array manifestation as the near field sound fall off versus distance from the speakers is less for both side-to-side and front-to-back directions within the room. As you move within the room you can hear the opposite speaker when you are a few feet in front of the nearest speaker. With a good line array system you can walk-up beside the speakers and hardly sense that they are producing the sound that you hear. In a way, near field line arrays will redefine your listening experience. Line arrays can reward the listener with more enjoyable music.
The following is from the paper:
A near field line array provides a different listening experience versus point source speakers. Among the distinctions that characterize line arrays are: · Near constant sound levels throughout the listening room · A wider soundstage · An image ‘sweet area’ and not an ‘sweet spot’ · Recreates live event sound dynamics
One observation from in-room listening to line arrays is that the stereo sound stage is very wide with a large side-to-side and front-to-back sweet spot. When first heard this enhancement of the stereo image area is in stark contrast to listeners who are familiar with pin-point sweet spot listening from point source speakers. Again the broaden image area is a line array manifestation as the near field sound fall off versus distance from the speakers is less for both side-to-side and front-to-back directions within the room. As you move within the room you can hear the opposite speaker when you are a few feet in front of the nearest speaker. With a good line array system you can walk-up beside the speakers and hardly sense that they are producing the sound that you hear. In a way, near field line arrays will redefine your listening experience. Line arrays can reward the listener with more enjoyable music.
Especially for NEAR field use, I'd foresee lots of problems with side-by-side line sources (as you say a line of 5-7 midrange units stacked vertically, and a few tweeters stacked tightly in a vertical line beside it.
The reason we "accept" the vertical lobing (radiation nulls over swept FR) you get in a normal setup like a vertical stack of bass-mid-tweet is that you get a wide angle of horisontal coverage where the frequency response is similar to the on-axis response.You can move the listening point sideways without getting huge changes in the perceived FR and phase through the audible range.
When you put two line sources next to each other and try to x-over between them at a frequency higher than the half-wavelength distance between the lines, the trigonometry of your listening point relative to the speaker lines change hugely (relative to the wavelength) when you move it sideways. So say 12cm is the distance. Half-wavelength is 12cm >>> full wave is 24cm = 0.24m
Frequency = speed of sound 340m/s divided by wavelength (0.24m) = roughly 1600Hz
If you try to x-over this solution at 1600Hz, you will get quite big changes in FR just by moving the listening point a few degrees sideways, making the listening impression very unstable. This is why many (?) solutions I've seen try to use the line source efficiency and power spread over many drivers to move x-over points lower in frequency than what a single driver of the same kind would tolerate - to get less angle dependent FR and phase response. Moving the x-over point down to half the half-wave point, and keeping the x-over slopes pretty steep will minimize, but not remove the problem. For very far-field applications like large PA and so on, line sources tend to blend much more naturally, but this also largely stems from a passive change in the trigonometry - if you move 1m left, that's a very small angle if you're 15m away from the source. OTOH, if you're only 2m from the source, 1m is a huge shift in angles, giving huge changes in FR - something your listening impression over time will protest very strongly against.
Note that the high-mid to tweeter arrangement in the speaker you linked to is extremely compact, with very short c-c distances... I'd also imagine that the real acoustic power phasing of the three drivers is extremely sensitive to tweaking. Very, very small changes in the x-over characteristics will have huge impacts on the frequency response of the listening field of the speaker...
I'm not saying "don't do it" though - just be aware that some parts of the layout/setup/x-over will take some extra care in planning... Maybe look at some of the available simulation softwares before proceeding? There are a few applications out there that can model the kinds of setup you described.
The reason we "accept" the vertical lobing (radiation nulls over swept FR) you get in a normal setup like a vertical stack of bass-mid-tweet is that you get a wide angle of horisontal coverage where the frequency response is similar to the on-axis response.You can move the listening point sideways without getting huge changes in the perceived FR and phase through the audible range.
When you put two line sources next to each other and try to x-over between them at a frequency higher than the half-wavelength distance between the lines, the trigonometry of your listening point relative to the speaker lines change hugely (relative to the wavelength) when you move it sideways. So say 12cm is the distance. Half-wavelength is 12cm >>> full wave is 24cm = 0.24m
Frequency = speed of sound 340m/s divided by wavelength (0.24m) = roughly 1600Hz
If you try to x-over this solution at 1600Hz, you will get quite big changes in FR just by moving the listening point a few degrees sideways, making the listening impression very unstable. This is why many (?) solutions I've seen try to use the line source efficiency and power spread over many drivers to move x-over points lower in frequency than what a single driver of the same kind would tolerate - to get less angle dependent FR and phase response. Moving the x-over point down to half the half-wave point, and keeping the x-over slopes pretty steep will minimize, but not remove the problem. For very far-field applications like large PA and so on, line sources tend to blend much more naturally, but this also largely stems from a passive change in the trigonometry - if you move 1m left, that's a very small angle if you're 15m away from the source. OTOH, if you're only 2m from the source, 1m is a huge shift in angles, giving huge changes in FR - something your listening impression over time will protest very strongly against.
Note that the high-mid to tweeter arrangement in the speaker you linked to is extremely compact, with very short c-c distances... I'd also imagine that the real acoustic power phasing of the three drivers is extremely sensitive to tweaking. Very, very small changes in the x-over characteristics will have huge impacts on the frequency response of the listening field of the speaker...
I'm not saying "don't do it" though - just be aware that some parts of the layout/setup/x-over will take some extra care in planning... Maybe look at some of the available simulation softwares before proceeding? There are a few applications out there that can model the kinds of setup you described.
er, quad amped.
Definitely quad amped. That's how the monitor I linked is implemented
. It's pretty easy to do with DSP and class D amps.Thanks so much for this post! Do you know offhand what software packages are able to simulate such an arrangement?
I was thinking of crossing over from the midrange array to the tweeter array at roughly 4-5k, which would require a distance of 85mm to satisfy the one wavelength requirement set forth in the aforementioned paper. Is there something special about the mid to tweeter crossover that would require the more restrictive 1/2 wavelength distance requirement that is mentioned in the paper?
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