Lynn Olson said:
I *thought* there might be someone there who knew a thing or two.
Its good to hear that the less expensive 850PB is comparable to the neo version.
Keep thinking about that little tid-bit of info on compression relating to the driver itself.. NOW consider horn profiles in relation to this.. (i.e. a narrow dispersion horn vs. a broad dispersion horn).
For compression tweeters the beyma cp25 surpasses the "slot" version. However, its likely that if you are not terribly concerned with high output then the Fostex FT96H will perform slightly better.
About the RAAL ribbons - they are a bit different in design and sound. Reports from various sources are that they do sound more "dynamic" than other offerings. Frankly, I envisioned a custom driver similar to the 140-15D.. but larger, more eff., and capable of a 1.2kHz 2nd order crossover. Of course such a design would suffer from a decrease in horizontal off-axis output (at higher freq.s) because of the ribbons greater width (..but, for numerous reasons, I think that would be far less of a compromise than limiting off-axis output in other designs).
ScottG said:
Sooo ... reading between the lines here ... the "relaxed" sounding setup (which is for sure the sound I want) would be the low-compression-ratio Radian 850PB coupled to, say, the Azurahorn AH-550 with its 90-degree dispersion.
The AH-550 horn has a low expansion ratio, between its 2-inch throat and the 12-inch mouth, and the "antenna gain" from directivity is modest as well, since we're not talking a typical prosound 60 x 40 tight-pattern horn.
Am I following this line of reasoning correctly? As you may surmise from the other thread, yes, I'm aiming for headroom, but also an inherent smoothness and freedom from resonance as well. To me, this means not "pushing" any of the drivers (or horns) anywhere close to their limits, either in frequency extension, excursion, or acceleration. It's also important the drivers track each other dynamically - nobody runs out of gas before the others.
Lynn Olson said:
..though If I were you I'd check with Assistance Audio and see "whats-up" with DDS. DDS had a number of *very* nice large format horns, (100 and 110 2 inch jobs), none of which are listed on Assistance's site. (..these are horns I'd choose any day over the AH-550, at least for most designs).
..Note that "*very* nice" in this instance means horns similar to the Altec's you mentioned, but with better pattern control and VASTLY superior time domain performance. (..Multicells are terribly resonant buggers.) Because of the better pattern control they also have the ability to effectively "extend" higher in freq. and allow for a higher crossover point for a super tweeter (..if desired).
..again though, just a suggestion (..but the radian lead seemed to have paid-off.)
Member
Joined 2003
Lynn,
While on the mend, you may want to Google/download David McBean's "Hornresp". I found it extremely helpful in identifying the Horn/WG flare with the characteristics I wanted.
There are a few limitations, but Hornresp will give you an overall "feel" for the different flares (Expo, Tractrix, Obulate Spheroid, etc). Not all features are supported for all flares. For example, directivity is not supported for Spherical horns, and you can't add the mouth roundover necessary to reduce diffraction for an Obulate Spheroid.
So I recommend comparing Exponential vs Obulate Spheroid directivity and radiation patterns. That will give you some quick insight, then you can explore further from there.
Briefly, the flares with longer, narrower, throats tend to beam at HF. That helps offset driver rolloff by focusing the available HF energy on axis. The downside is that off-axis HF response rolls off quickly...so in-room power response rolls off (see Jeff Mai's comments).
For the "quick opening" flares like Obulate Spheroid, within the included design angle, on and off-axis FR tends to track driver output. This on/off-axis tracking (constant directivity) results in smooth power response. The downside for these flares is the EQ required for flat response...HF boost or MF cut.
It took a while but, for what I want to accomplish, Hornresp led me to Obulate Spheroid like MBK has illustrated here, and the spreadsheet Ed volunteered earlier (Ed's spreadsheet adds the roundover). That's how I ended up testing the constant directivity type waveguides shown earlier in this thread. Unfortunately for me I don't know of any commercially available round CD waveguides with controlled response in the 500-1k range...so DIY seems the only way!
Hope this helps get you where you want to go!
Hint: Print the Hornresp "help" file to use as documentation.
Paul
While on the mend, you may want to Google/download David McBean's "Hornresp". I found it extremely helpful in identifying the Horn/WG flare with the characteristics I wanted.
There are a few limitations, but Hornresp will give you an overall "feel" for the different flares (Expo, Tractrix, Obulate Spheroid, etc). Not all features are supported for all flares. For example, directivity is not supported for Spherical horns, and you can't add the mouth roundover necessary to reduce diffraction for an Obulate Spheroid.
So I recommend comparing Exponential vs Obulate Spheroid directivity and radiation patterns. That will give you some quick insight, then you can explore further from there.
Briefly, the flares with longer, narrower, throats tend to beam at HF. That helps offset driver rolloff by focusing the available HF energy on axis. The downside is that off-axis HF response rolls off quickly...so in-room power response rolls off (see Jeff Mai's comments).
For the "quick opening" flares like Obulate Spheroid, within the included design angle, on and off-axis FR tends to track driver output. This on/off-axis tracking (constant directivity) results in smooth power response. The downside for these flares is the EQ required for flat response...HF boost or MF cut.
It took a while but, for what I want to accomplish, Hornresp led me to Obulate Spheroid like MBK has illustrated here, and the spreadsheet Ed volunteered earlier (Ed's spreadsheet adds the roundover). That's how I ended up testing the constant directivity type waveguides shown earlier in this thread. Unfortunately for me I don't know of any commercially available round CD waveguides with controlled response in the 500-1k range...so DIY seems the only way!
Hope this helps get you where you want to go!
Hint: Print the Hornresp "help" file to use as documentation.
Paul
That's exactly what I fear
... and the rent will go unpaid 
Looks like my WG design is file read properly and the setup seems straightforward. The first prototype will be in stacked plywood and then we'll see how the radiation patterns and all work out. As I said right now I just have 2 dome tweeter models to test this out, a Vifa silk dome and a Seas metal (ironically the 2 models Zaph tried out on WG's, the Vifa that worked and the Seas that didn't).
When I was at my friend's shop he showed me some lumber samples from Indonesia. Seems he has a friend with access to some very nice wood. There was some wonderful reddish, brown, and subtle olive tones, and one in ironwood. All these are meant for ... flooring
(the ironwood for untreated wet use, such as pool decks). In other words, should be good enuff for a horn . But that's for later, once a working design is confirmed by experiment...Some thoughts about decay, reflections and spaciousness
While trying to measure CSD of my woofer's in-baffle I reviewed a couple of things about the physics and hearing mechanisms involved. Here it goes:
Firstly, CSD measured in an OB like mine simply must have a lot of artefacts for a variety of reasons. With a path length difference of ca. 18" or 50 cm, the rear wave arrives about 1.5 ms after the front wave. 1.5 ms period or 50 cm wavelength correspond to 680 Hz. Take this and it is clear that the rear wave must influence the CSD very heavily below 1000 Hz and no amount of windowing can change that. Basically, just one cycle of 680 Hz will already take 1.5ms. So if we window at 1.5 ms for an already-lousy frequency resolution and add further time slices after that... we immediately get the addition of the rear wave to the CSD. It can in fact be seen in my CSD's, and Paul's as well, that soon after a first rapid falloff there is a lower level "shoulder" and I believe this is the attenuated rear wave.
Now, I think we agree that dipole midrange sounds airy, transparent and has "depth". [So do large ribbons, line sources, but not so many horns if one goes by anecdotal evidence]. Why do they (and especially, why if their CSD must look bad given the delays involved)? Well it appears that 0.7 ms is the absolute minimum integration time of the ear (and I wish I knew where I got that reference from). Signals closer together than this will get confounded by the ear, and if this time window contains reflections or other sound mirror images, there will be "smear", and below 0.7ms, the less delay of reflections/diffraction, the better (narrow baffle, say). 0.7 ms corresponds to ca. 25 cm or 10" path length difference.
Above this threshold, progressively, and especially >1.5ms, things get better again. While not capable of perceiving an echo yet, we then interpret the delayed signal as "airiness" and "openness". And such a delayed mirror image of the original signal could be a baffle reflection, room reflection, rear wave from a dipole, or the delayed signal from the far end of a line source. From this line of thought the above mentioned should sound open and airy, and they indeed do.
This effect works for1.5 - 10 ms delays, according to Griesinger's papers. Between 10 and 50 ms, reflections seriously impede speech intelligibility, the large room effect, and >50 ms is again less critical because we then perceive clear distinct echoes.
So conclusions? Here are my half-educated guesses:
1) does decay not matter below say 1k? No necessarily - *if* the delay of the rear wave in-baffle (or line source delay, or room reflection, or large baffle diffraction, or horn reflections and mouth diffractions) is >0.7ms and ideally >1.5 ms then the rear wave will not get perceptually "smeared" together with the direct sound. Then the decay of the original signal does matter.
2) how to measure decay below 1k? Either Linkwitz style or CSD with driver in box or in-wall. Possibly unbaffled driver for a very short rear wave delay and peace after that for an undisturbed decay.
3) how to make horns sound "airy" and "open"? No horn reflections in the 0.7 ms window (good horn profile, rapid expansion, dampening materials), and either
- a wide angle WG to allow for decent amounts of room reflections, especially laterally, or
- a horn mouth large enough to put secondary signals produced by edge diffraction outside the 0.7 ms / 25 cm window, calling for a diameter of ideally, 50 cm or more
- in combination with a large mouth, possibly a conscious provocation of edge diffraction to add the "air": say in my case the WG will have a smooth roundover to a flat baffle, but the baffle then continues until a total width of 60 cm (24") with just a 1" roundover to a 90 degree baffle edge. So I'd expect this project to sound "airy" now to satisfy my grand theories here
- variation of the above: staggered diffraction edges on the horn mouth, sort of a coarse, fractal like feathering, to get a whole spectrum of delayed mirror images. Say, a mouth termination that starts at 20" diameter and irregularly extends to say 30", in spiral fashion, with lots of "ears" of different sizes and shapes etc.
Such a horn would then sound airy and open even without any room reflections.
Thoughts?
While trying to measure CSD of my woofer's in-baffle I reviewed a couple of things about the physics and hearing mechanisms involved. Here it goes:
Firstly, CSD measured in an OB like mine simply must have a lot of artefacts for a variety of reasons. With a path length difference of ca. 18" or 50 cm, the rear wave arrives about 1.5 ms after the front wave. 1.5 ms period or 50 cm wavelength correspond to 680 Hz. Take this and it is clear that the rear wave must influence the CSD very heavily below 1000 Hz and no amount of windowing can change that. Basically, just one cycle of 680 Hz will already take 1.5ms. So if we window at 1.5 ms for an already-lousy frequency resolution and add further time slices after that... we immediately get the addition of the rear wave to the CSD. It can in fact be seen in my CSD's, and Paul's as well, that soon after a first rapid falloff there is a lower level "shoulder" and I believe this is the attenuated rear wave.
Now, I think we agree that dipole midrange sounds airy, transparent and has "depth". [So do large ribbons, line sources, but not so many horns if one goes by anecdotal evidence]. Why do they (and especially, why if their CSD must look bad given the delays involved)? Well it appears that 0.7 ms is the absolute minimum integration time of the ear (and I wish I knew where I got that reference from). Signals closer together than this will get confounded by the ear, and if this time window contains reflections or other sound mirror images, there will be "smear", and below 0.7ms, the less delay of reflections/diffraction, the better (narrow baffle, say). 0.7 ms corresponds to ca. 25 cm or 10" path length difference.
Above this threshold, progressively, and especially >1.5ms, things get better again. While not capable of perceiving an echo yet, we then interpret the delayed signal as "airiness" and "openness". And such a delayed mirror image of the original signal could be a baffle reflection, room reflection, rear wave from a dipole, or the delayed signal from the far end of a line source. From this line of thought the above mentioned should sound open and airy, and they indeed do.
This effect works for1.5 - 10 ms delays, according to Griesinger's papers. Between 10 and 50 ms, reflections seriously impede speech intelligibility, the large room effect, and >50 ms is again less critical because we then perceive clear distinct echoes.
So conclusions? Here are my half-educated guesses:
1) does decay not matter below say 1k? No necessarily - *if* the delay of the rear wave in-baffle (or line source delay, or room reflection, or large baffle diffraction, or horn reflections and mouth diffractions) is >0.7ms and ideally >1.5 ms then the rear wave will not get perceptually "smeared" together with the direct sound. Then the decay of the original signal does matter.
2) how to measure decay below 1k? Either Linkwitz style or CSD with driver in box or in-wall. Possibly unbaffled driver for a very short rear wave delay and peace after that for an undisturbed decay.
3) how to make horns sound "airy" and "open"? No horn reflections in the 0.7 ms window (good horn profile, rapid expansion, dampening materials), and either
- a wide angle WG to allow for decent amounts of room reflections, especially laterally, or
- a horn mouth large enough to put secondary signals produced by edge diffraction outside the 0.7 ms / 25 cm window, calling for a diameter of ideally, 50 cm or more
- in combination with a large mouth, possibly a conscious provocation of edge diffraction to add the "air": say in my case the WG will have a smooth roundover to a flat baffle, but the baffle then continues until a total width of 60 cm (24") with just a 1" roundover to a 90 degree baffle edge. So I'd expect this project to sound "airy" now to satisfy my grand theories here
- variation of the above: staggered diffraction edges on the horn mouth, sort of a coarse, fractal like feathering, to get a whole spectrum of delayed mirror images. Say, a mouth termination that starts at 20" diameter and irregularly extends to say 30", in spiral fashion, with lots of "ears" of different sizes and shapes etc.
Such a horn would then sound airy and open even without any room reflections.
Thoughts?
Member
Joined 2003
MBK,
I think you are thinking too hard for a Friday.
I believe driver CSD on a small open baffle should show some influence of the rear wave. After a speed of sound delay, an attenuated rear wave will arrive at the microphone. Attenuation should increase with frequency and phase will likely be random...so there should some +/- undulation in the decay display. For driver decisions, I doubt this is a big deal because we can see what the driver is trying to do in the first few time slices. On the other hand, if we were preparing driver marketing sheets, we'd want to use an infinite baffle for the cleanest possible chart...no wrap-around and no diffraction. Measurement closer to the driver will improve the S/N ratio (noise being the rear wave). So, at least broad brush, I think we agree so far.
However, my personal experience is the fewer reflections from anything within 6 feet or so of the drivers, the better. This includes walls, furniture, cabinet edges, and sharp-edged waveguides. At least for me, getting rid of the close-in hash improves clarity/articulation. (this preference shows in the 8" radius roundovers in my avatar and near constant use of felt to attenuate the rear wave) While I don't care for reflections coming from near the speakers, I really do like the lack of box coloration. Of course this is just one person's opinion...YMMV
If you're interested in staggered diffraction edges, there is a patent showing a dish antenna shaped like a scalloped star with rounded major and minor points. This might do what you are thinking but the inventor's purpose was to reduce the diffraction signature by spreading it out. If you can't locate it on Free Patents, I have it somewhere.
Paul
I think you are thinking too hard for a Friday.
I believe driver CSD on a small open baffle should show some influence of the rear wave. After a speed of sound delay, an attenuated rear wave will arrive at the microphone. Attenuation should increase with frequency and phase will likely be random...so there should some +/- undulation in the decay display. For driver decisions, I doubt this is a big deal because we can see what the driver is trying to do in the first few time slices. On the other hand, if we were preparing driver marketing sheets, we'd want to use an infinite baffle for the cleanest possible chart...no wrap-around and no diffraction. Measurement closer to the driver will improve the S/N ratio (noise being the rear wave). So, at least broad brush, I think we agree so far.
However, my personal experience is the fewer reflections from anything within 6 feet or so of the drivers, the better. This includes walls, furniture, cabinet edges, and sharp-edged waveguides. At least for me, getting rid of the close-in hash improves clarity/articulation. (this preference shows in the 8" radius roundovers in my avatar and near constant use of felt to attenuate the rear wave) While I don't care for reflections coming from near the speakers, I really do like the lack of box coloration. Of course this is just one person's opinion...YMMV
If you're interested in staggered diffraction edges, there is a patent showing a dish antenna shaped like a scalloped star with rounded major and minor points. This might do what you are thinking but the inventor's purpose was to reduce the diffraction signature by spreading it out. If you can't locate it on Free Patents, I have it somewhere.
Off to New York tomorrow to see the toys at HE2007...I'll let you know if I hear any "transparent" line cords
Paul
Re: Some thoughts about decay, reflections and spaciousness
MBK,
Some very interesting thoughts, indeed! A lot to digest there. What makes a sound or sound field "open and airy"? It's a good question.
I'll bet the boys at LEXICON could tell us a thing or 2. They have been doing that sort of stuff for over 30 years, and doing it very well. Of course they are treating audio signals in the electrical domain, where as you are talking about the physical domain. But the results can be the same.
I might be interesting to do some experiments with a good pair of headphones and a nice delay/reverb unit like a Lexicon. You could simulate the delays and reflections that you are thinking about very easily. That might allow you to hear directly what the different delays and offsets are doing.
Thanks for the nice post!
MBK,
Some very interesting thoughts, indeed! A lot to digest there. What makes a sound or sound field "open and airy"? It's a good question.
I'll bet the boys at LEXICON could tell us a thing or 2. They have been doing that sort of stuff for over 30 years, and doing it very well. Of course they are treating audio signals in the electrical domain, where as you are talking about the physical domain. But the results can be the same.
I might be interesting to do some experiments with a good pair of headphones and a nice delay/reverb unit like a Lexicon. You could simulate the delays and reflections that you are thinking about very easily. That might allow you to hear directly what the different delays and offsets are doing.
Thanks for the nice post!
MBK..
wow.. that WAS a lot of thinking for a friday..
However I've seen this problem before.. (your delayed and reduced in level "parallel" decay pattern between 600 Hz and its nasty resonance at 2 kHz).
Its incredibly ironic though, considering how this deviation from linearity is generated, when comparing a good bit of this thread's content..
Its a bad horn.
I.E. directivity has its price when "paid through" cone geometry.
You'll get this same effect in-box as well (..a long with other "perpendicular" decay artifacts generated by box resonances).
This was something I was trying to caution Lynn on early in his Ariel + thread.
wow.. that WAS a lot of thinking for a friday..
However I've seen this problem before.. (your delayed and reduced in level "parallel" decay pattern between 600 Hz and its nasty resonance at 2 kHz).
Its incredibly ironic though, considering how this deviation from linearity is generated, when comparing a good bit of this thread's content..
Its a bad horn.
I.E. directivity has its price when "paid through" cone geometry.
You'll get this same effect in-box as well (..a long with other "perpendicular" decay artifacts generated by box resonances).
This was something I was trying to caution Lynn on early in his Ariel + thread.
ScottG said:
Point taken - and part of the reason I want to keep the door open with 2" compression drivers and a generous-sized horn, so I have the option of moving the crossover downward if I want to. The option appears to be more or less foreclosed with 1" CD's and smaller horns. Put another way, it's a halfway house between the smallish typical HF horn/driver and the monster Oris/Lowther setup that's popular in Northern Colorado.
We saw an interesting idea quickly flash by in an earlier post, and I want to draw more attention to it. Simple in concept: cut Karlson slots into the edge of the OB, with the "point" of the slot facing the driver. Not many slots, either. So if a driver is fairly close to one edge (i.e. 7" from centerline to the edge), but is farther away from the opposite-side edge (11.5" from centerline to other edge), you cut a Karlson slot into the farther edge of the OB.
I think you guys can see what I'm trying to do - blur the wavefront coming around the edge of the OB. Similarly, 3 or 5 Karlson slots could be cut into an (expendable) plastic horn, which should diminish the symmetric standing waves. This should be easy to check - just look for the characteristic triple peak in impedance to diminish (the most direct evidence of HOM's in horns).
Lynn,
that kind of "Karlsson slots" was exactly what I had in mind when talking about staggered diffraction edges for the horn mouth termination edges - only that I thought the outline itself could also be variable in diameter, like an expanding spiral, rather than round. For the OB itself, in the lower midrange this may not matter anymore though since the wavelength is considerably larger than any path length variation you could achieve with this technique.
To clarify my talk about CSD shoulders - I was exclusively talking about *OB's* - not horns - it's what I get when measuring my 40"x24"x7" OB. That's when the rear wave comes 1-1.5ms after the direct sound. Listening impression of this configuration is a very nice depth, like the main singer standing in the room in 3D at a specific location. That's what got me into the delay tangent, why this type CSD leads to this type of listening impression.
Pano - Lexicon: no coincidence here: Griesinger whom I quoted for all the delay references *is* the Lexicon physicist-in-residence.
Paul - "dish antenna", yeah that could also be a way of describing what I have in mind. And, have fun with the line cords!
that kind of "Karlsson slots" was exactly what I had in mind when talking about staggered diffraction edges for the horn mouth termination edges - only that I thought the outline itself could also be variable in diameter, like an expanding spiral, rather than round. For the OB itself, in the lower midrange this may not matter anymore though since the wavelength is considerably larger than any path length variation you could achieve with this technique.
To clarify my talk about CSD shoulders - I was exclusively talking about *OB's* - not horns - it's what I get when measuring my 40"x24"x7" OB. That's when the rear wave comes 1-1.5ms after the direct sound. Listening impression of this configuration is a very nice depth, like the main singer standing in the room in 3D at a specific location. That's what got me into the delay tangent, why this type CSD leads to this type of listening impression.
Pano - Lexicon: no coincidence here: Griesinger whom I quoted for all the delay references *is* the Lexicon physicist-in-residence.
Paul - "dish antenna", yeah that could also be a way of describing what I have in mind. And, have fun with the line cords!
In truth.. it isn't that big a deal as long as the standing wave "resonances" are down low enough in level (less than 9db) and it isn't "too" high in freq. (..i.e. keeping it under 1kHz should be fine.. and in fact most crossovers will overlay more linear decay distortion, though the distribution will be more uniform and completely "die" a lot sooner). It does *look* odd though.
I'm not sure I "get" the shape of the Karlson coupler for open baffle.. The only OB designs I've seen for this have been fairly normal "Karlson" positioning for a sub (and also a "split" sub).. (..presumably to give a bit more air compression effects in the upper bass response, i.e. make it more "energetic" sounding.)
If the desired result is to reduce diffraction effects for an open baffle then I'd think the best bet would be an edge, (..at least for the baffle's sides), similar to the trailing edge of flaps on an airplane:
i.e. the little tear drop shape at the back of the wing here:
http://en.wikipedia.org/wiki/Image:Flaps.png
The intention here would be to minimize the edge itself for a maximal null (particularly at the edge). You would want to keep air speed loss to a minimum (to reduce stored energy) - i.e. no edge "padding" with a lossy material like felt. You could however keep friction low and still have some sound attenuation via silica borscilate added paint for that last 1/4 inch of the baffle's edges. You would also want the edge's material to be very non-resonant.
The biggest problem then is the cavity resonance of the baffle near the back of the driver (..for its "insert", assuming the driver is "flush" mounted to the front of the baffle).
I'm not sure I "get" the shape of the Karlson coupler for open baffle.. The only OB designs I've seen for this have been fairly normal "Karlson" positioning for a sub (and also a "split" sub).. (..presumably to give a bit more air compression effects in the upper bass response, i.e. make it more "energetic" sounding.)
If the desired result is to reduce diffraction effects for an open baffle then I'd think the best bet would be an edge, (..at least for the baffle's sides), similar to the trailing edge of flaps on an airplane:
i.e. the little tear drop shape at the back of the wing here:
http://en.wikipedia.org/wiki/Image:Flaps.png
The intention here would be to minimize the edge itself for a maximal null (particularly at the edge). You would want to keep air speed loss to a minimum (to reduce stored energy) - i.e. no edge "padding" with a lossy material like felt. You could however keep friction low and still have some sound attenuation via silica borscilate added paint for that last 1/4 inch of the baffle's edges. You would also want the edge's material to be very non-resonant.
The biggest problem then is the cavity resonance of the baffle near the back of the driver (..for its "insert", assuming the driver is "flush" mounted to the front of the baffle).
For the OB <1k, I think that a plain rectangular shape introduces enough path length variation, so I wouldn't think slots are needed. Plus the wavelengths are too long <1k to make a few inches worth of slots meaningful.
For a large horn and >1k it could make sense/ I imagined it looking like an array of flower petals of varying sizes. The horn I'll have made will have no termination (ends flat) so I can experiment with various terminations - insert into flat baffle, classic roundover, or "petals".
Re: CSD, with the 7" deep OB I have no obvious pure resonance problems, except for the bump at the onset of the rolloff, around 180 Hz. This ca 6 dB Q 1.7-2.0 bump is described in detail by SL, he explains it as a result of the lowpass filter formed at the rear of the driver. I had it in all driver and baffle combinations I tried and it must be EQ'd. Once done that it seems to be harmless.
The question of X-O and other resonance peaks is a valid one. Any CSD should actually be carried out on a driver that is already EQ'd flat, and only has meaning far from X-O or driver induced rolloffs - because by definition any wiggles or rolloffs *will* show up as energy storage.
For a large horn and >1k it could make sense/ I imagined it looking like an array of flower petals of varying sizes. The horn I'll have made will have no termination (ends flat) so I can experiment with various terminations - insert into flat baffle, classic roundover, or "petals".
Re: CSD, with the 7" deep OB I have no obvious pure resonance problems, except for the bump at the onset of the rolloff, around 180 Hz. This ca 6 dB Q 1.7-2.0 bump is described in detail by SL, he explains it as a result of the lowpass filter formed at the rear of the driver. I had it in all driver and baffle combinations I tried and it must be EQ'd. Once done that it seems to be harmless.
The question of X-O and other resonance peaks is a valid one. Any CSD should actually be carried out on a driver that is already EQ'd flat, and only has meaning far from X-O or driver induced rolloffs - because by definition any wiggles or rolloffs *will* show up as energy storage.
MBK said:
Hmm.. a "high knee" low pass filter... *hinky*!
That "high knee" "high q" bump is slang for resonance. So while it may act as a low pass filter above that resonance - it sure isn't *at* that resonance.Whether EQ will do it or not largely depends on the driver and the filter vs its operating passband. With a low mass driver (for a given sd), this can become a serious problem with or without eq. IF its present in the driver's intended operating passband.
Some one of "long ago" did an empirical study on various shapes for this problem.. Darned if I can't remember who..
just a thought...
you have been discussing such things as Karlson tapers on open baffles along with other termination techniques. I wonder if any of you have ever been out at dusk and been spooked by an owl flying low overhead (letting you know that he/she would rather you were not in the area scarring off the mice)? They are already past you or at best you just catch them in your periferal vision as they fly past. The spooky part is that you realize that you never hear them fly by, they are totally silent unlike say a duck whose wings make a whir you can hear comming at over 50 yards from behind.
The reason why owels are so silent when they fly is so they can pounce on a mouse looking the other way. The mouse usually never knows what hit him it's over so fast. How they fly so silently is because of the way thier wings are feathered. On the leading edge of an owles wing (the front curved edge) every other feather is missing along the edge of the wing. This makes for (in effect) narrow slits that allow the air which is parted by the wings edge to slip quickly and smoothly over the top and bottom half of the wing. It might be interesting to cut a baffle with saw kerf wide slots that are an inch or so long starting flush on the baffle and that progress to say 1/8 or 3/16 if an inch deep at the baffles outer edge. This would break up the form of the wave as it "breaks" over the edge of the baffle. In othe words some of the wave would slide off of the baffle faster than the rest would. Just a thought. Regards.
you have been discussing such things as Karlson tapers on open baffles along with other termination techniques. I wonder if any of you have ever been out at dusk and been spooked by an owl flying low overhead (letting you know that he/she would rather you were not in the area scarring off the mice)? They are already past you or at best you just catch them in your periferal vision as they fly past. The spooky part is that you realize that you never hear them fly by, they are totally silent unlike say a duck whose wings make a whir you can hear comming at over 50 yards from behind.
The reason why owels are so silent when they fly is so they can pounce on a mouse looking the other way. The mouse usually never knows what hit him it's over so fast. How they fly so silently is because of the way thier wings are feathered. On the leading edge of an owles wing (the front curved edge) every other feather is missing along the edge of the wing. This makes for (in effect) narrow slits that allow the air which is parted by the wings edge to slip quickly and smoothly over the top and bottom half of the wing. It might be interesting to cut a baffle with saw kerf wide slots that are an inch or so long starting flush on the baffle and that progress to say 1/8 or 3/16 if an inch deep at the baffles outer edge. This would break up the form of the wave as it "breaks" over the edge of the baffle. In othe words some of the wave would slide off of the baffle faster than the rest would. Just a thought. Regards.
No question the dipole "bump" is a resonance. But I don't think it's a 1/4 wave resonance of the 7" depth. Also my point was, *only if you EQ* this and other resonances and rolloffs away, can you then see the actual driver constributed stored energy decay.
I actally think these are all windowing artefacts from the CSD, which itself has a 0.2ms window rise time. Not to mention that say, 417 cycles corresponds to a period of 2.4 ms, so the 2.4 ms "decay" duration shown in my CSD plot only corresponds to *one* full cycle at 417 Hz, and less below that.
I actally think these are all windowing artefacts from the CSD, which itself has a 0.2ms window rise time. Not to mention that say, 417 cycles corresponds to a period of 2.4 ms, so the 2.4 ms "decay" duration shown in my CSD plot only corresponds to *one* full cycle at 417 Hz, and less below that.
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