The initial question was about the effect of recessing the driver, and the effect was clearly shown in the example measurements. If other, nearby structures (e.g. woofer surround) cause additional diffraction effects, that come on top to shown measurements and that may be another, different topic. I dont' get your point. So what is better than showing the single effect alone pointig exactly to the stated question, not mixed up with other things?
It's not the point I am making, but after reading this thread I have seen jmansion make statements like that more than once on this thread. So if we keep doing this, it will go on and on forever. You are happy with the data as presented from a tweeter flush mounted vs recessed, both mounted on a large baffle. Personally, I'd want to go one step further and would opt to include the enclosure shape to get the best out of the total package.
But jmansion had an even different view about it and most probably isn't going to be convinced that easily. I tried to prevent yet another back and forth as that had happened a couple of times already. I failed miserably as you did not get my point.
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I routed the recess in 19mm plywood, with a 6mm handheld router. I even cut the hole with the handheld router after I did the recess. I had a circle jig.
For someone who do this kind of thing maybe once in a lifetime, it was pretty intimidating and the potential for errors was great.
As many have written here, I did many light passes of a 2mm each. My tiny router was not the right tool, obviously.
And it did mess up, because I did not secure the rounded piece to my bench (in only clamped the baffle), and when I took the last pass, the circle jig was not secured to the baffle and the router dented the recess. I always keep the finger on the switch.
Next job, I will do the recess with the router and the circle jig, but I will probably use a jigsaw and a pattern bit for the woofer hole.
For someone who do this kind of thing maybe once in a lifetime, it was pretty intimidating and the potential for errors was great.
As many have written here, I did many light passes of a 2mm each. My tiny router was not the right tool, obviously.
And it did mess up, because I did not secure the rounded piece to my bench (in only clamped the baffle), and when I took the last pass, the circle jig was not secured to the baffle and the router dented the recess. I always keep the finger on the switch.
Next job, I will do the recess with the router and the circle jig, but I will probably use a jigsaw and a pattern bit for the woofer hole.
Except - that's on a 40by50 flat baffle? Which is exactly my concern - if the box its going to be in is not built with significant roundover (and even if it is, but quite small), then the effect may be secondary.
Maybe I should invest in some felt. I don't really have access to a space that is large enough to get much without doing artificial near-field - and its far too cold to go outside.
I was wondering last night what can be causing the effect. And whether these graphs are realy a good identification. The total sound energy is the same, and the frequency quite high, which suggests to me that the graphs would vary quite a lot with small changes in on-off axis listening, much as we see with coax/full range drivers. Sadly we don't have that in this case.
It also occurred to to wonder whether this is because of secondary radiation related to the diameter of the tweeter - or to the depth of the flange, but the flange is pretty thin and the phase rotation relatively large compare to depth/wavelength.
My suspicion is the former. As Troels points out you need to be within 0.1mm or there will be sufficient 'edge' that the effect returns. That's quite a big deal in terms of machining accuracy even with some CNC equipment, especially if you consider estimating for the depth of veneer and gasket tape - its not just depth but the fit of the driver in the hole.
Maybe I was the one who failed to get you point, and it was my mistake not to think about enough what you wrote.
Eventually it helps to separate and structure effects regarding driver recessing:
a) Recessing / not recessing a driver and the effect to the sound radiated by that driver itself
--> Mentioned, different measurements of tweeters(!) were shown
b) Recessing / not recessing a driver and the effect to the sound radiated by another driver nearby
--> I think this is what you wanted to point to?
Best regards
Peter
Here is a study I did where I tried to assess the effect of the midrange cavity on the tweeter response.
https://www.diyaudio.com/community/threads/interesting-diffraction-effect.374851/post-6727561
In this situation, the mid driver is mounted very close to the tweeter, and I measured a +1.5 / -2 dB from 900 Hz - 3000 Hz. It was not a perfect experiment, since my effort to cover the mid driver did not simulate a completely flat baffle. I also did not perform polar measurements, which I would do today if I repeated this experiment. Still, it does show a measurable effect. I found it very significant that @fluid was able to simulate an effect that was similar to what I measured.
j.
I think any reader has now come to the point of understanding, that recessing speaker in the baffle is important for the end result, if it has been part of the construction.
Also, we now know that a Chassis will stick in a non recessesed baffle too, if the right screws are used, even if the plan calls for a recess.
Further, we all are warned that the most usefull tool to do recesses is loud, makes dirt, needs training to be used right, can harm untallented craftsmen and cost's about 50$.
Next, we have learned that one can build speakers from chassis combinations on different baffles, in different cabinets and with different crossover parts.
Then, we know understand that a speaker that was not build with the right recesses, cabinets, dimensions and crossover parts, does not sound identical to one build exactly to a well developed plan. For some, it may sound good enough, may be added.
Last it has become clear that in DIYS, any builder can do what he want's and ignore physical evidence, measured data and still fill a thread of more than 7 pages without beeing called a troll.
Conclusion: Members here are very tollerant and some don't respect scientific truth for unknown personal reasons.
Also, we now know that a Chassis will stick in a non recessesed baffle too, if the right screws are used, even if the plan calls for a recess.
Further, we all are warned that the most usefull tool to do recesses is loud, makes dirt, needs training to be used right, can harm untallented craftsmen and cost's about 50$.
Next, we have learned that one can build speakers from chassis combinations on different baffles, in different cabinets and with different crossover parts.
Then, we know understand that a speaker that was not build with the right recesses, cabinets, dimensions and crossover parts, does not sound identical to one build exactly to a well developed plan. For some, it may sound good enough, may be added.
Last it has become clear that in DIYS, any builder can do what he want's and ignore physical evidence, measured data and still fill a thread of more than 7 pages without beeing called a troll.
Conclusion: Members here are very tollerant and some don't respect scientific truth for unknown personal reasons.
Make sure to wear hearing protection, otherwise the sonic benefit of recessed drivers is wasted because of hearing loss!
Argh, this old topic again???
Here is my take on it: only matters for the tweeter. The worst case is a very small dome tweeter with an eg. 4" wide, thick mounting flange that is surface mounted.
Why?
Any spatial discontinuity on the baffle will cause diffraction. When there is a circular source like a dome or woofer cone, the worst possible shape for this discontinuity is a circular one centered co-axially on the driver itself. This is because the sound wave radiating out from the driver will reach the discontinuity all around its circular extent at exactly the same moment in time. This reinforces when the diffraction is occurring in time, and all the diffracted energy will reach a listener located on axis from the loudspeaker at the same instant, making it significant. This is mostly the case for a small dome tweeter and the classic circular discontinuity formed when it is surface mounted instead of flush mounted.
In contrast, this effect grows less and less as the size of the radiating surface of the driver grows, and as frequency decreases. For a cone driver, and a discontinuity at the edge of its mounting flange, the soundwave is eminating from different places on the cone (at high frequency) and these will all reach any one place along the discontinuity at different times. This smears out the diffraction in time. It is the same concept that explains why a large roundover can mitigate edge diffraction - the diffraction is now happening all along the rounded edge and so it is distributed in both time (when it happens) and space (where it happens), which tends to smooth out the effects. At low frequencies the "size" of the discontinuity that a surface mounted cone driver would represent starts to become too small compared to the wavelength of sound, so it doesn't appreciable diffract the sound wave produced by the driver.
The location and shape of the diffracting edge also plays an important role. For example, Troels Gravesen has published several loudspeaker designs that attempt to do some time alignment by recessing the section of the baffle in which the tweeter is mounted. This gives rise to a small "step" in the baffle just below the tweeter that might be 1cm or more "tall". I asked him about it once, and he said that he does not see any diffraction signature in his measurements. This is likely because the propagating sound wave coming out of the tweeter reaches different points along the "step" at different times, and this smears out the diffraction from it in time and space. For example:
http://www.troelsgravesen.dk/Illuminator-7751.htm
On the other hand it is hard to believe that diffraction is not a problem in this loudspeaker from Troels:
http://www.troelsgravesen.dk/Ellipticor-4.htm
Here is my take on it: only matters for the tweeter. The worst case is a very small dome tweeter with an eg. 4" wide, thick mounting flange that is surface mounted.
Why?
Any spatial discontinuity on the baffle will cause diffraction. When there is a circular source like a dome or woofer cone, the worst possible shape for this discontinuity is a circular one centered co-axially on the driver itself. This is because the sound wave radiating out from the driver will reach the discontinuity all around its circular extent at exactly the same moment in time. This reinforces when the diffraction is occurring in time, and all the diffracted energy will reach a listener located on axis from the loudspeaker at the same instant, making it significant. This is mostly the case for a small dome tweeter and the classic circular discontinuity formed when it is surface mounted instead of flush mounted.
In contrast, this effect grows less and less as the size of the radiating surface of the driver grows, and as frequency decreases. For a cone driver, and a discontinuity at the edge of its mounting flange, the soundwave is eminating from different places on the cone (at high frequency) and these will all reach any one place along the discontinuity at different times. This smears out the diffraction in time. It is the same concept that explains why a large roundover can mitigate edge diffraction - the diffraction is now happening all along the rounded edge and so it is distributed in both time (when it happens) and space (where it happens), which tends to smooth out the effects. At low frequencies the "size" of the discontinuity that a surface mounted cone driver would represent starts to become too small compared to the wavelength of sound, so it doesn't appreciable diffract the sound wave produced by the driver.
The location and shape of the diffracting edge also plays an important role. For example, Troels Gravesen has published several loudspeaker designs that attempt to do some time alignment by recessing the section of the baffle in which the tweeter is mounted. This gives rise to a small "step" in the baffle just below the tweeter that might be 1cm or more "tall". I asked him about it once, and he said that he does not see any diffraction signature in his measurements. This is likely because the propagating sound wave coming out of the tweeter reaches different points along the "step" at different times, and this smears out the diffraction from it in time and space. For example:
http://www.troelsgravesen.dk/Illuminator-7751.htm
On the other hand it is hard to believe that diffraction is not a problem in this loudspeaker from Troels:
http://www.troelsgravesen.dk/Ellipticor-4.htm
@CharlieLaub
If the woofer is close to the tweeter, recessing the woofer should impact the tweeter. So recessing the woofer is just as usefull IMO.
If the woofer is close to the tweeter, recessing the woofer should impact the tweeter. So recessing the woofer is just as usefull IMO.
Concerning power tools like a router,
they can negatively effect your hearing, your eyes and lungs, just as it's rotating part can penetrate any unprotected skin.
So better wear hearing and eye protection. Also wear at least a Corone mask, which I find very handy and cheap today, while
usinge some kind of vacuum to extract the dust. This reduces the mess you make to an accepable limit.
In a professional shop you are not allowed to use any wood working power tool without extraction system.
Yesterday I used a new kitchen knife. While I never hurt my self with a router, I cut my finger. Maybe I should quit cooking. Much too dangerous!
they can negatively effect your hearing, your eyes and lungs, just as it's rotating part can penetrate any unprotected skin.
So better wear hearing and eye protection. Also wear at least a Corone mask, which I find very handy and cheap today, while
usinge some kind of vacuum to extract the dust. This reduces the mess you make to an accepable limit.
In a professional shop you are not allowed to use any wood working power tool without extraction system.
Yesterday I used a new kitchen knife. While I never hurt my self with a router, I cut my finger. Maybe I should quit cooking. Much too dangerous!
No, not really. The woofer has a curved mounting flange - it's curved AWAY from the tweeter as a source. So, again, any diffraction from the woofer mounting flange will be distributed in time and space, and will not be significant.
This concern about diffraction from non-flush-mounted drivers is IMHO one of the old wives tales of DIY audio. Mostly it just "looks better" e.g. more professional when you do it, but in reality except for the tweeter itself, flush vs surface mounting has no effect sonically or otherwise.
Another aspect of diffraction that is not well appreciated is that the ratio of the diameter of the source to the diameter of the diffracting edge controls the amount of diffraction observed, when both are concentric and circular. Consider again the case of a dome tweeter with a round, thick mounting flange. Let's think about the extremes for the case of surface mounting this driver:
(A) when the mounting flange is much larger than the dome diameter
(B) when the mounting flange is only just a bit larger than the outer edge of the dome
For A the source is point-like. This means that for any point on the diffracting edge, all points on the source (the dome) are about the same distance away. This makes the output from the dome diffract coherently from any and all points around the edge of the mounting flange. This causes large diffraction effects.
For (B) it's the opposite. For any given point on the diffracting edge there are a wide variety of distances from points on the dome surface to it, and at high frequencies this causes the phase of each part of the source (every little infitessimal area of the dome) to be different. When you add up lots of different sources, each with a different phase angle, the result is not a strong signal. Thus diffraction is very weak even though the tweeter is surface mounted.
A similar case happens for a source in the end of a cylinder. Olson studied this, and this is why many people think that a round baffle is terrible, the worst ever, do not use it! But what is not appreciated is that in Olson's study the "source" was a special full range driver that was IIRC about 7/8" in diameter, while all the shapes he studied were 24" wide. Thus the source is "point like" and, yes, when you put a point-like source in the center of a round baffle you will get the strongest edge diffraction possible. But in the case of a woofer or cone driver in a round baffle that is not much larger in diameter than the driver mounting flange, the source is no longer point-like compared to the diffracting surface (the end of the cylinder) and diffraction signature is actually very weak. This is also why small "mini-monitor" speakers often have a very smooth response through the top of and above the baffle step. In this sort of speaker the cone of the woofer is almost as wide as the baffle and thus not point-like, and so the baffle step response is very smooth.
(A) when the mounting flange is much larger than the dome diameter
(B) when the mounting flange is only just a bit larger than the outer edge of the dome
For A the source is point-like. This means that for any point on the diffracting edge, all points on the source (the dome) are about the same distance away. This makes the output from the dome diffract coherently from any and all points around the edge of the mounting flange. This causes large diffraction effects.
For (B) it's the opposite. For any given point on the diffracting edge there are a wide variety of distances from points on the dome surface to it, and at high frequencies this causes the phase of each part of the source (every little infitessimal area of the dome) to be different. When you add up lots of different sources, each with a different phase angle, the result is not a strong signal. Thus diffraction is very weak even though the tweeter is surface mounted.
A similar case happens for a source in the end of a cylinder. Olson studied this, and this is why many people think that a round baffle is terrible, the worst ever, do not use it! But what is not appreciated is that in Olson's study the "source" was a special full range driver that was IIRC about 7/8" in diameter, while all the shapes he studied were 24" wide. Thus the source is "point like" and, yes, when you put a point-like source in the center of a round baffle you will get the strongest edge diffraction possible. But in the case of a woofer or cone driver in a round baffle that is not much larger in diameter than the driver mounting flange, the source is no longer point-like compared to the diffracting surface (the end of the cylinder) and diffraction signature is actually very weak. This is also why small "mini-monitor" speakers often have a very smooth response through the top of and above the baffle step. In this sort of speaker the cone of the woofer is almost as wide as the baffle and thus not point-like, and so the baffle step response is very smooth.
Why would you cut a recess into the baffle when you can just use a circle jig to cut two panels and then laminate them??? Lot easier and if you botch a cut you don't loose the entire baffle.
Rob 🙂
Rob 🙂
It is not a bad idea to use this method. The results are just as good as the other method. The only thing that I see as a concern is to get the two sheets to become one after gluing and proper clamping. not a hard thing to accomplish but must not be overlooked.
I agree with the idea that you have multiple chances to get it right, and even if you choose, to use a different material for each panel, assuming that each might have their benefit to add.
I agree with the idea that you have multiple chances to get it right, and even if you choose, to use a different material for each panel, assuming that each might have their benefit to add.
I agree with experimenting. We can sometimes get these stiff opinions about what is right and so on. I have used the green glue in structural applications. Wasn't really about audio as much as being too close to a neighbor.
I read Tom Danely write something similar on a thread at ASR; he phrased it as 8 inches rather than 20 cm. But he didn't explain why it mattered. Your post filled that piece of the puzzle for me. Thanks. Do you happen to know if there is an original source for that distance? Or, alternatively, maybe it is common shared knowledge among experience listeners.