But like I said, I didn't think of it...
Hey, I didn't either
:Too many damn measurements thought of it for me
To counter your theory that there is a round trip from woofer cone to reflection point inside CD and back to woofer cone that results in a null that then propagates to the listener, I would point out that not all the reflected energy goes back into the port hole. In fact most of it goes down the horn.
I think you have to take the observer into account. If this were indeed quantum dynamics, there wouldn't even be a null unless a mic were there to measure it
If you want to listen for a null at the woofer cone, then what you say is true. The round trip path would then extend back to it and the null frequency would change when you re-position the woofer so that its cone moves towards or away from the port hole.
If you listen for that null anywhere else, the null frequency is independent of the distance from the woofer cone to the far side of the horn wall. The distance from the woofer cone to and through the port is common to both the direct and reflection paths. When you subtract the two, the result is independent of the distance from woofer cone to and throught the port hole. That is what I meant by "the term drops out"
This picture should make this clear:
I'm showing a slanted line from the mid port to the mic and an unslanted line from the CD reflection point to the mic. Thus it seems like the null frequency would be at least slightly sensitive to the listening distance. As you move the observation point out towards infinity (i.e. a few meters) this sensivity decreases, so its usually ignored, if thought of at all.
Perhaps there is some point source summation magic going on in the horn throat immediately adjacent to the mid port holes - perhaps a null forms there and propagates down the horn to the listener and mic. Since we usually count axial distance on the horn, not the distance along the horn wall as in my previous picture, when estimating null frequency, perhaps I should redraw this way:
The dashed lines show the previous point of view.
I'm trying to make the picture more realistic and also show how imprecise it is by way of the visible difference between the two points of view.
I am showing that there isn't just a single distance from woofer cone to the port hole but I haven't nailed it yet. I've drawn the port more as a point than as a hole. My experience is with relatively small holes appropriate for a 4" mid that I used only down to 250 Hz. Mark's holes are for a 12" woofer playing below 100 Hz.
When the ports get so large I can indeed imagine that the "acoustic center of the mid port" moves some distance inside the port hole and that that distance could indeed depend upon the distance from the horn wall to the woofer cone!
Or, more likely, that the acoustic center of the mid port moves along the horn wall, within the confines of the mid port hole, depending again upon the distance to the cone. When the port is aligned with an edge of the cone, most of the sound from the woofer cone comes from the other sides of the hole, those furthest from that nearby cone edge and so the acoustic center of the mid port isn't at the center of the mid port. When the port hole is aligned with the woofers dustcap, the sound comes equally from all sides and the acoustic center of the port is in the center of the hole.
I hope that makes sense and I haven't confused myself again. The lesson to me is to beware of simplistic models.
Attachments
Or to put it more simply,
when the woofer cone is centered on the woofer port, then the acoustic center of the woofer port will be at the center of the woofer port, perhaps some distance in or out from the horn wall but on the central axis of the port.
When the woofer isn't centered on the woofer port then its possible and perhaps likely that the acoustic center of the woofer port is off this central axis.
This could explain the change in reflection null frequency when the woofer was repositioned relative to the center of the woofer port...
when the woofer cone is centered on the woofer port, then the acoustic center of the woofer port will be at the center of the woofer port, perhaps some distance in or out from the horn wall but on the central axis of the port.
When the woofer isn't centered on the woofer port then its possible and perhaps likely that the acoustic center of the woofer port is off this central axis.
This could explain the change in reflection null frequency when the woofer was repositioned relative to the center of the woofer port...
could something like this be occurring Diffraction Through Slits – Sound science for schools and colleges
Great stuff, many thx. And yes, it did all make sense.
Maybe I'm giving too much of an effect, to in-horn cancellation, before exiting.
Like you say, most of the reflection off the CD is going out the horn and not back in the ports. I really don't know how to begin to portion the ratio there....based on horn perimeter at ports, the ports probably take up about 25% of the perimeter. But it seems area maybe the more appropriate apportionment.
I also need to keep thinking about the difference in direct path, vs axial path.
Axial path makes sense for hornresp inputs for sure, but measurements seem to tie with direct paths. Dunno what to think there yet.
Anyway, I'm pretty happy with the sound and measurements now, and am in the process of remounting the 12"s into permanent position, and trying to close up their rear chamber volume. Also need to play with reducing air volume under the cones.
Maybe I'm giving too much of an effect, to in-horn cancellation, before exiting.
Like you say, most of the reflection off the CD is going out the horn and not back in the ports. I really don't know how to begin to portion the ratio there....based on horn perimeter at ports, the ports probably take up about 25% of the perimeter. But it seems area maybe the more appropriate apportionment.
I also need to keep thinking about the difference in direct path, vs axial path.
Axial path makes sense for hornresp inputs for sure, but measurements seem to tie with direct paths. Dunno what to think there yet.
Anyway, I'm pretty happy with the sound and measurements now, and am in the process of remounting the 12"s into permanent position, and trying to close up their rear chamber volume. Also need to play with reducing air volume under the cones.
Even if the output of the port bounces in to the horn and back into the port, it could upset the cone movement a little bit, but it won't prevent the driver from making it's output.
One could probably measure the impedance of the driver on the horn to see if there's a wiggle at that frequency of interest in the impedance curve.
It should also show differences when the cone is moved in position over the port,for example the dome centered at the port or more sideways firing (dome not centered).
An impedance curve can come in handy to show the little things like if the bounce back has any effect on the driver itself.
One could probably measure the impedance of the driver on the horn to see if there's a wiggle at that frequency of interest in the impedance curve.
It should also show differences when the cone is moved in position over the port,for example the dome centered at the port or more sideways firing (dome not centered).
An impedance curve can come in handy to show the little things like if the bounce back has any effect on the driver itself.
@ turk 182, thx, good food for thought.
I especially like the double slit animations...makes me picture the 4 ports feeding the horn.
@ weysayso, good point. Impedance is such a great tool for fine tuning....I need to keep in mind it is also a good tool for basic understanding and diagnosis.
I especially like the double slit animations...makes me picture the 4 ports feeding the horn.
@ weysayso, good point. Impedance is such a great tool for fine tuning....I need to keep in mind it is also a good tool for basic understanding and diagnosis.
Ok, enough of measurement, trial and error, .....for now anyway
Happy enough with latest build, that I broke it down, and am putting it back together more permanent like....cones moved and their surround recesses rerouted etc.
Although it's still held together by only sheet rock screws....
It's officially syn #5 You guys all said be ready for plenty of iterations....
A few construction pics below.
To shed weight, and reduce rear chamber volume of the 12"s, I ditched the one big box enclosure and made separate small accesses as shown. Using foam board to further reduce volume.
The second pict shows the runners on the horn mouth for attaching the secondary flare assy.
The last is pict the detachable flare.
It's about the only way I can move the whole box around easy...having the frame detachable.
Oh, and for relatively easy moving, I also needed to make the CD and its small box removable. Makes CD exchanges easy too.
Happy enough with latest build, that I broke it down, and am putting it back together more permanent like....cones moved and their surround recesses rerouted etc.
Although it's still held together by only sheet rock screws....
It's officially syn #5
You guys all said be ready for plenty of iterations....A few construction pics below.
To shed weight, and reduce rear chamber volume of the 12"s, I ditched the one big box enclosure and made separate small accesses as shown. Using foam board to further reduce volume.
The second pict shows the runners on the horn mouth for attaching the secondary flare assy.
The last is pict the detachable flare.
It's about the only way I can move the whole box around easy...having the frame detachable.
Oh, and for relatively easy moving, I also needed to make the CD and its small box removable. Makes CD exchanges easy too.
Attachments
Progress report....
Well, happily, I think I've reached a new personal 'best sound to date'.
Lots more tinkering, trying different tunings, have somehow led to a really nice sound.
Hearing lyrics never caught before, vocal inflections, bass riffs, etc...with all the dynamics I'm so accustomed to.
I think the real breakthrough was just accepting that the straight sided conical horn was not going to give me a way of using the relatively automatic EQ process I've had so much success with on regular multi-ways. (Same thing might be said for what I need to realize regarding my last build attempts before the synergies...the straight and CBT line arrays...need to revisit them too I think).
I really softened the minimum phase EQs I would allow into the tuning, but still kept phase pretty flat.
I'm not talking about not allowing high-Q EQs, or excessive mag adjustments. I've known to avoid those forever.
It has ended up working better to softly 'eyeball average' all the tuning attempts (which were to particular spots or averages of spots), than to tune meticulously to averaged measurements. Hope that made sense.
No real clue why yet....
Another happily...don't think I need to add any bass reflex ports...at least not crossing to sub at 110Hz.
I'll need to get outside and really crank it up, to see if I can lower xover to 100Hz at full volume, which has been the design goal.
It should crank up pretty damn loud !
Rechecked sensitivity outside: all at 2.83v 1m.
mid 105.3dB : HF 110.4dB : VHF 106.6dB
That was with the dcx464 crossed at 3kHz. I've since moved xover to 4kHz just from listening tests...I should rerun HF & VHF sensitivity although I'm sure it won't change much if any. I'm a little surprised the VHF sensitivity is not up with the HF.
Should also add that I'm low-passing the dcx at 17kHz cause I think it's just burning current up there....needs real boost above 16k or so. (especially makes sense to low pass given my old ears.)
Anyway, my biggest problem now is that I like it so much I wanna build another to try out stereo
Well, happily, I think I've reached a new personal 'best sound to date'.
Lots more tinkering, trying different tunings, have somehow led to a really nice sound.
Hearing lyrics never caught before, vocal inflections, bass riffs, etc...with all the dynamics I'm so accustomed to.
I think the real breakthrough was just accepting that the straight sided conical horn was not going to give me a way of using the relatively automatic EQ process I've had so much success with on regular multi-ways. (Same thing might be said for what I need to realize regarding my last build attempts before the synergies...the straight and CBT line arrays...need to revisit them too I think).
I really softened the minimum phase EQs I would allow into the tuning, but still kept phase pretty flat.
I'm not talking about not allowing high-Q EQs, or excessive mag adjustments. I've known to avoid those forever.
It has ended up working better to softly 'eyeball average' all the tuning attempts (which were to particular spots or averages of spots), than to tune meticulously to averaged measurements. Hope that made sense.
No real clue why yet....
Another happily...don't think I need to add any bass reflex ports...at least not crossing to sub at 110Hz.
I'll need to get outside and really crank it up, to see if I can lower xover to 100Hz at full volume, which has been the design goal.
It should crank up pretty damn loud !
Rechecked sensitivity outside: all at 2.83v 1m.
mid 105.3dB : HF 110.4dB : VHF 106.6dB
That was with the dcx464 crossed at 3kHz. I've since moved xover to 4kHz just from listening tests...I should rerun HF & VHF sensitivity although I'm sure it won't change much if any. I'm a little surprised the VHF sensitivity is not up with the HF.
Should also add that I'm low-passing the dcx at 17kHz cause I think it's just burning current up there....needs real boost above 16k or so. (especially makes sense to low pass given my old ears
.) Anyway, my biggest problem now is that I like it so much I wanna build another to try out stereo
Progress report....
Well, happily, I think I've reached a new personal 'best sound to date'.
Lots more tinkering, trying different tunings, have somehow led to a really nice sound.
Hearing lyrics never caught before, vocal inflections, bass riffs, etc...with all the dynamics I'm so accustomed to.
I think the real breakthrough was just accepting that the straight sided conical horn was not going to give me a way of using the relatively automatic EQ process I've had so much success with on regular multi-ways. (Same thing might be said for what I need to realize regarding my last build attempts before the synergies...the straight and CBT line arrays...need to revisit them too I think).
I really softened the minimum phase EQs I would allow into the tuning, but still kept phase pretty flat.
I'm not talking about not allowing high-Q EQs, or excessive mag adjustments. I've known to avoid those forever.
It has ended up working better to softly 'eyeball average' all the tuning attempts (which were to particular spots or averages of spots), than to tune meticulously to averaged measurements. Hope that made sense.
No real clue why yet....
Another happily...don't think I need to add any bass reflex ports...at least not crossing to sub at 110Hz.
I'll need to get outside and really crank it up, to see if I can lower xover to 100Hz at full volume, which has been the design goal.
It should crank up pretty damn loud !
Rechecked sensitivity outside: all at 2.83v 1m.
mid 105.3dB : HF 110.4dB : VHF 106.6dB
That was with the dcx464 crossed at 3kHz. I've since moved xover to 4kHz just from listening tests...I should rerun HF & VHF sensitivity although I'm sure it won't change much if any. I'm a little surprised the VHF sensitivity is not up with the HF.
Should also add that I'm low-passing the dcx at 17kHz cause I think it's just burning current up there....needs real boost above 16k or so. (especially makes sense to low pass given my old ears
Anyway, my biggest problem now is that I like it so much I wanna build another to try out stereo
Glad to hear it has all finally come together; somewhat surprised it was all in the tuning - except it wasn't: the throat piece and the secondary flare, felt on the vertical flares.
Confirmation that one can get there with a conical horn is good news because conical horns are very buildable, whereas the more ideal profiles are often out of reach.
I wonder which I would prefer if I could A/B them - my line arrays or my conical synergies?
Thanks Jack,
Yeah, I'm kinda surprised it was all in the tuning too, and how long it took me to find it...especially given that tuning is the one aspect in DIY speaker building where I feel I have some real competence. Maybe not, LoL.
I've ended up not needing the felt strips. And I think the secondary flare does more to effect pattern control, making bass from an adjacent sub sound more localized to the horn, than it does to change waist-banding higher in freq. But that's just an impression at this stage. I do still think the throat mod helped patterning.
A big change in thinking about measurements and measurement averaging, occurred at a Rational Acoustics training class I recently went to. The class discussed averaging quite a bit, and how nulls can at times inappropriately average down peaks in the summed measurement , peaks we would like to EQ down. I think I saw Gmad talking about this in another current thread.
That's what led me to a psuedo-averaging the on and off axis processing curves made for each location, instead of making a processing curve based off the measurement average of those locations.
The conical just has alot of stuff going on that measurement averaging seemed to be missing.......
I think the good news for a DIY synergy builder, who needs straight sided walls for simplicity, is identify the major trends on and off axis...treat those trends loosely and nothing more. Maybe it's why Danley's relatively simple passives work as well as they do...????
Oh, and yeah, it's a nice problem to have wondering which of your speakers, line array or syn you would like best ! Congrats
I think you have the same problem (which of your children to you love the most?) to a higher order, with all the speakers you have done. When you get the tuning and the integration with the room right, and operating the speakers within their limits, will there be reason to prefer one over the other? (that was the question behind my comment)
probably not at the primary LP but likely over a wide area simply based on different directionality/dispersion characteristics
The problem I had with my Synergies was their floor and ceiling bounce made it impossible for me to get clean measurements at the LP so I tuned them based upon 1m measurements. But they still sounded great at the LP despite the imperfections I saw in measurements taken there and it provided great background music to the rest of the house.
With the LAs, I get clean measurements at a 4M distance (so I can actually do room equalization) but I also have more treatment and in a totally different room. I think they would be equally capable of filling an open floor plan house with good sound once moved in from the garage. The reason I built them was for their small footprint, which isn't so small if you include the subs.
probably not at the primary LP but likely over a wide area simply based on different directionality/dispersion characteristics
The problem I had with my Synergies was their floor and ceiling bounce made it impossible for me to get clean measurements at the LP so I tuned them based upon 1m measurements. But they still sounded great at the LP despite the imperfections I saw in measurements taken there and it provided great background music to the rest of the house.
With the LAs, I get clean measurements at a 4M distance (so I can actually do room equalization) but I also have more treatment and in a totally different room. I think they would be equally capable of filling an open floor plan house with good sound once moved in from the garage. The reason I built them was for their small footprint, which isn't so small if you include the subs.
I have noticed this too. At first I tried various EQ settings, even very rigorous suggestions by REW. But 'softer settings' generally sound much more natural than getting the measurements looking ruler flat - even if you try to average measurements from different locations. It's as if your brain subconsciously tells you something is not sounding quite right if you apply heavy EQ with high Q's, but you can't exactly tell what it is, while all the while your measurement mic says it's all good
.So you haven't even built a stereo set. Wow, that'll be a big difference then. Every time I hear them I am amazed at the sound stage they create. It truly is as if you're wearing big headphones with immaculate positioning, depth and sound quality
. Get the second one done!!!Which of my kids do I love the most?
That's easy, whichever one is not trying to withdraw from the Bank of Dad
But seriously to your question, which speaker will be preferred once fully tuned and integrated into the room....
There, almost sadly, I still find it's album by album, track by track.
I mean, I have some old Bose 901's hanging in the garage...you know smear city, almost totally reflected sound. And worse ...no highs, no lows (so you know it must be Bose
) But yet, some (fortunately very few) tunes sound better in the garage than on any system I have.
Do you find the same song by song vagaries/preferences?
I have noticed this too. At first I tried various EQ settings, even very rigorous suggestions by REW. But 'softer settings' generally sound much more natural than getting the measurements looking ruler flat - even if you try to average measurements from different locations. It's as if your brain subconsciously tells you something is not sounding quite right if you apply heavy EQ with high Q's, but you can't exactly tell what it is, while all the while your measurement mic says it's all good
So you haven't even built a stereo set. Wow, that'll be a big difference then. Every time I hear them I am amazed at the sound stage they create. It truly is as if you're wearing big headphones with immaculate positioning, depth and sound quality
That makes a growing set of us I think, regarding our experiences with trying to EQ the synergies to a spot or spot averages.
I forget who, but some helpful soul recently posted this link to John Sheerin's site, about conical horn issues, LeCleac'h horn vs Conical Horn
And yeah, time to get to work on the other side of the headphones
Which of my kids do I love the most?
That's easy, whichever one is not trying to withdraw from the Bank of Dad
But seriously to your question, which speaker will be preferred once fully tuned and integrated into the room....
There, almost sadly, I still find it's album by album, track by track.
I mean, I have some old Bose 901's hanging in the garage...you know smear city, almost totally reflected sound. And worse ...no highs, no lows (so you know it must be Bose
But yet, some (fortunately very few) tunes sound better in the garage than on any system I have.
Do you find the same song by song vagaries/preferences?
I auditioned Bose 901s once back in the 70's but mostly what was demonstrated to me was how loud they could go - and that was impressive. LOUD meant a lot more to me then than it does now.
My first real purchase was Carver Amazings which I enjoyed until the woofer surrounds rotted. I wish I still had them and could DSP them, perhaps put AE woofers in them, because they were amazing. In hindsight, they could have been tuned better.
When some tracks don't sound right I take that as I sign that I'm not done with the crossover or equalization.
I can't say whether i would have track by track preferences from one speaker to another because I can't do real time compares; probably I would because I recall the Synergies doing better on complex orchestral works at volume. But then there is the literature on the need for double blind preference testing.
Good stuff.
My first real purchase, other than building dynaco kits and buying their speakers, was a pair of Acoustat-X electrostats in the late mid 70's. Huge expense for me at the time. They have a unique direct drive high voltage tube amp, and still reside in my bedroom.
Glorious sound, and one of the reasons I keep finding a song by song preference.
Honestly, I no longer blame my tuning for song by song variances, anywhere near as much as i blame mastering inconsistencies. If the differences were CD by CD, I might still think it's my tuning or crossovers etc. But when even on the same album/CD, I hear significantly different spectral balances, I'm like "it ain't me!"
And I guess when I'm down to differences that need to be double-blind testing, well....I don't care anymore..they are both good.
The test of time for me is on lots of different material,... in the sweet spot, all around the room, heck even in other rooms (one of my favorite ways to evaluate) is pretty much all I trust anymore.
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