Hi friends,
Thank you for your patience as I theorize again. I realized as I was looking at others discuss Synergy horns how little I know about horns and that some of my musings may have an answer already in terms of the physics. As you may remember I'm often wondering about how good a line array using a single driver type in a single line could be. Some of the most respected line arrays use multiple driver types for different frequency ranges so I'm trying to ask how we could push 4" drivers to wider horizontal dispersion.
At some random time I was also reading about the Doppler effect in large, wide band drivers as well. I had been thinking that maybe turning a line source sideways and slot loading it could solve a lot of issues at once:
Then to my surprise Monitor Audio did something very close with a concept speaker. The full speaker is a 3-way with separate mid/treble section but look at how they do the bass section. The two towers below are part of a single speaker:
So I guess before I even go very far, what are the physics of the slot? I mean, say I design a line array along these concepts. Two line arrays of 4" wide band drivers facing each other but 1" apart. Assuming the drivers could get to 20kHz on axis, what are the physics of the response when loaded essentially by a slot, as seen above?? Am I even going to get any treble at all? Is this essentially a very short horn?
Thanks!!
Erik
Thank you for your patience as I theorize again. I realized as I was looking at others discuss Synergy horns how little I know about horns and that some of my musings may have an answer already in terms of the physics. As you may remember I'm often wondering about how good a line array using a single driver type in a single line could be. Some of the most respected line arrays use multiple driver types for different frequency ranges so I'm trying to ask how we could push 4" drivers to wider horizontal dispersion.
At some random time I was also reading about the Doppler effect in large, wide band drivers as well. I had been thinking that maybe turning a line source sideways and slot loading it could solve a lot of issues at once:
- Eliminate Doppler/IM distortion by listening at 90 degrees to the piston
- Improve horizontal dispersion compared to using a front facing full range driver by using a relatively narrow exit slot, say 1"
Then to my surprise Monitor Audio did something very close with a concept speaker. The full speaker is a 3-way with separate mid/treble section but look at how they do the bass section. The two towers below are part of a single speaker:
So I guess before I even go very far, what are the physics of the slot? I mean, say I design a line array along these concepts. Two line arrays of 4" wide band drivers facing each other but 1" apart. Assuming the drivers could get to 20kHz on axis, what are the physics of the response when loaded essentially by a slot, as seen above?? Am I even going to get any treble at all? Is this essentially a very short horn?
Thanks!!
Erik
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Eric,
The slot will create an acoustical band pass filter, reducing upper response, while causing narrow "Q" peaks and dips in the frequency response, the spacing and depth depending on the "very short horn" dimensions and it's enclosed volume.
Here is an example of a slot 5.5" wide by 26" tall with 20.75" depth.
The peaks and dips would move up by ~an octave for each halving of dimensions.
The response simulated above is "kinda OK" for a subwoofer, but the frequencies that would "beam" with a 4" driver may be rendered useless by the slot.
The slot's acoustical band pass filter would reduce some high order harmonic distortion when the drivers are driven past Xmax, but won't reduce doppler/IM/AM distortion.
Art
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The one point I want to mention is that, unlike Pass's design, these are essentially two ported or sealed towers, and you can see through the slot. Essentially a bipole.
The real question is why the intense directive towards line sources when a point source is so much closer to how we identify and experience sound?
You can widen the directivity of a driver by experimenting with diffusion and acoustic lenses as JBL has done. Some of today’s 3” wide range drivers have quite acceptable polar patterns out to 10k…….but this isn’t the problem…..the problem is destructive combing that begins at the quarter wave of the distance from each drivers acoustic center…..at least where round transducers are concerned. Planar type drivers don’t have this issue…….but they won’t play low and the larger units don’t do well past 10k.
MEH and Unity are great…..they’re just big, wide and imposing…..a far cry from what works in the modern home.
What KEF has done with their coincident tech is where it’s at…….line source bass works combined with point source mids and highs….all in a slender, sleek system with a small footprint.…….
You can widen the directivity of a driver by experimenting with diffusion and acoustic lenses as JBL has done. Some of today’s 3” wide range drivers have quite acceptable polar patterns out to 10k…….but this isn’t the problem…..the problem is destructive combing that begins at the quarter wave of the distance from each drivers acoustic center…..at least where round transducers are concerned. Planar type drivers don’t have this issue…….but they won’t play low and the larger units don’t do well past 10k.
MEH and Unity are great…..they’re just big, wide and imposing…..a far cry from what works in the modern home.
What KEF has done with their coincident tech is where it’s at…….line source bass works combined with point source mids and highs….all in a slender, sleek system with a small footprint.…….
A slot itself is not a band pass filter, only that particular way of doing it. Compression drivers bring their output out of a reduced aperture with good high frequency performance.
The Monitor Audio is more of an insideout push-push box with both woofers in a single basket., and only the woofers. They had to do something different han KEF's.
Slot loading is studied fairly well with Nelsons’s slot loaded OB.
The compression of the chamber can provide some driver loading(something we have done forsone time with down-firing woofers.
Actual output far-fieldispretty much the same as if they were monted more congenitally,
dave
Slot loading is studied fairly well with Nelsons’s slot loaded OB.
The compression of the chamber can provide some driver loading(something we have done forsone time with down-firing woofers.
Actual output far-fieldispretty much the same as if they were monted more congenitally,
dave
Thanks, Allen.
I'm familiar with basic diagrams of compression drivers, and I guess that's what I wanted to do here. What's the difference between a compression driver and "slot loading" like Monitor Audio does here? Do the drivers need a mating surface to squeeze against?? Or is it a matter of the distance between driver and compression surface. I hope I don't sound like I'm asking hte impossible, more like I hope this helps me understand both compression drivers and slot loading a little better.
Thank you,
Erik
That design is a lot though. It's kind of open baffle. I couldn't find the original driver's FR chart so I'm not sure how I could assess the band pass limiting done.
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Nelson’s is an OB, the MA is not an OB. We are talking about the slot loading,something i have used for decades.
From the transparent image above, the hole at the base suggest there are 2 reflex boxes working as one.
dave
Right. What I meant is, that having never really seen any information about slot loading, I can't tell what Nelson's design is doing. He's just got a lot going on. Since I've never used one before, I don't know what happens in a case like the MA design instead of the Pass. I guess if I knew what slot loaded behavior was already the Nelson design would be a natural extension, but since I don't it just looks like an alien beast to me. 🙂
Yes, you read the MA diagram correctly. Just imagine two woofers each in their own enclosure (ported in this case, but not relevant) pointing at each other.
It is a compact mounting that provides some additional output nearfield, but that that disapates over distance. The air cavity it fires into can supply some loading on the woofers, like how adjustable height feet can be used to tune the bass of a dowbfiring woofer.
dave
The difference is that an acoustic bandpass has a cavity that the sound gets physically mixed up in, whereas the compression driver has a phase plug that carefully keeps it in order.
In addition to this, do a little research on line array horns that are designed to take compression driver output and extend it in one dimension.