Jack Caldwell wrote in his post ( http://www.diyaudio.com/forums/full-range/180185-new-frx-ob-driver-decware-4.html#post2549030 ) about the stiffened double surround fix of Deckert...
Quite frankly I am confused.
Making the surround stiffer should not improve the frequency response per se. What is needed is a surround that is more "lossy" or absorptive, thus keeping energy that is moving transversely across the surface of the cone from being reflected back. Not to mention keeping the surround itself from radiating unwanted energy.
The stiffness of the suspension/surround should not be "the thing".
To use the bell analogy, a bell hanging with nothing around the edge has an infinitely un-stiff surround. But the same bell with a rubber band around the same edge has an absorptive termination and has no change in the stiffness but a major change in the absorption.
Terminating the bell around the edge with a thin solid metal surround will kill the lower resonant modes but still permit the higher modes to operate...
In the case of a speaker, the stiffer suspension tends to drive the resonant frequency up. But this tells us nothing about the way that suspension absorbs or reflects energy - although it is likely that a stiffer surround will alter the break-up modes compared to a highly un-stiff one...
One could consider doping the existing surround?
One could consider doping the outer edge of the cone??
So, imo it is the way that the surround works to absorb and/or not reflect back energy that counts as far as the issues we've been talking about with the Dayton driver.
_-_-bear
Quite frankly I am confused.
Making the surround stiffer should not improve the frequency response per se. What is needed is a surround that is more "lossy" or absorptive, thus keeping energy that is moving transversely across the surface of the cone from being reflected back. Not to mention keeping the surround itself from radiating unwanted energy.
The stiffness of the suspension/surround should not be "the thing".
To use the bell analogy, a bell hanging with nothing around the edge has an infinitely un-stiff surround. But the same bell with a rubber band around the same edge has an absorptive termination and has no change in the stiffness but a major change in the absorption.
Terminating the bell around the edge with a thin solid metal surround will kill the lower resonant modes but still permit the higher modes to operate...
In the case of a speaker, the stiffer suspension tends to drive the resonant frequency up. But this tells us nothing about the way that suspension absorbs or reflects energy - although it is likely that a stiffer surround will alter the break-up modes compared to a highly un-stiff one...
One could consider doping the existing surround?
One could consider doping the outer edge of the cone??
So, imo it is the way that the surround works to absorb and/or not reflect back energy that counts as far as the issues we've been talking about with the Dayton driver.
_-_-bear
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It's more the matching...
Sorry if I wasn't clear. It's not JUST about making it stiffer, it's more about getting the mechanical impedances to match up properly, terminating them with a properly damped "load". It's the same as in electrical transmission lines where you get significant reflections if you don't use the proper impedance to terminate.
An overly soft surround will allow virtually unimpeded ringing modes, an overly hard one will constrain the driver and not allow it to move! (at the edges). The ratio of resistance vs mass and compliance (mechanical Q) of the suspension is crucial to good termination.
A good termination will absorb significant amounts of energy and significantly remove or damp out the edge resonances and the back-reflections that travel through the cone.
On top of this the "double roll" is apparently better at absorbing and dissipating these resonances. Don't take my word for, look for the Lowther information that discusses this rather cool technique. (I had it and lost it, if you find it please post it here!)
It apparently creates a progressively increasing stiffness that turns the motion into heat and voila, no more reflections! It clamps, it damps and it doesn't ring...
As can be seen in the Thiele-Small parameters, the Fs and mechanical Q have greatly changed on the FRX vs stock, so I suspect most of the change is to be found in the double roll. Time and experimentation will tell.
Also, your suggestion of applying damping along the interface of the cone and surround is a good one, many people do that. But it's not enough to overcome a big discontinuity in impedances.
Another option may be to apply the enAbl process, I have heard very good things about its ability to get the driver to operate more coherently - Dave at Planet10 is one of the main experts on this.
Anyhow, it's certainly worth experimenting with. I would love to try this on the drivers I'm using in my speakers but they already have a positive roll, and adding the extra roll would only work with very flat or inverted roll surrounds like the Dayton.
Of course until I've had a chance to mod a couple of the Daytons I won't know if my theory is correct or if it is the whizzer that needs attention.
And it may well be that the ultimate would be a combination of approaches including the double-roll suspension with a full enAbl mod by Dave.
Sorry if I wasn't clear. It's not JUST about making it stiffer, it's more about getting the mechanical impedances to match up properly, terminating them with a properly damped "load". It's the same as in electrical transmission lines where you get significant reflections if you don't use the proper impedance to terminate.
An overly soft surround will allow virtually unimpeded ringing modes, an overly hard one will constrain the driver and not allow it to move! (at the edges). The ratio of resistance vs mass and compliance (mechanical Q) of the suspension is crucial to good termination.
A good termination will absorb significant amounts of energy and significantly remove or damp out the edge resonances and the back-reflections that travel through the cone.
On top of this the "double roll" is apparently better at absorbing and dissipating these resonances. Don't take my word for, look for the Lowther information that discusses this rather cool technique. (I had it and lost it, if you find it please post it here!)
It apparently creates a progressively increasing stiffness that turns the motion into heat and voila, no more reflections! It clamps, it damps and it doesn't ring...
As can be seen in the Thiele-Small parameters, the Fs and mechanical Q have greatly changed on the FRX vs stock, so I suspect most of the change is to be found in the double roll. Time and experimentation will tell.
Also, your suggestion of applying damping along the interface of the cone and surround is a good one, many people do that. But it's not enough to overcome a big discontinuity in impedances.
Another option may be to apply the enAbl process, I have heard very good things about its ability to get the driver to operate more coherently - Dave at Planet10 is one of the main experts on this.
Anyhow, it's certainly worth experimenting with. I would love to try this on the drivers I'm using in my speakers but they already have a positive roll, and adding the extra roll would only work with very flat or inverted roll surrounds like the Dayton.
Of course until I've had a chance to mod a couple of the Daytons I won't know if my theory is correct or if it is the whizzer that needs attention.
And it may well be that the ultimate would be a combination of approaches including the double-roll suspension with a full enAbl mod by Dave.
Lowther double roll suspension
Arrgh, I can't find the Lowther article anywhere on-line, seems to have disappeared...
Guess we'll have to content ourselves with this information from Deckert about how he modded the Fostex (gotta love those marketing names he comes up with... "Active Suspension System"... I can see why some people get steamed about the lingo.)
This quote is from DECWARE - Audio Paper - New Full Range Driver DFR8, edited for brevity. Check out the paper though, it is informative. Here goes:
The DFR-8 active suspension system
The original FE206EM used an inverted roll cloth surround that is attached to the under side of the speaker cone. It offers no damping like butyl rubber but then butyl rubber is high mass, less strong, and slow.
If you look at Lowther speakers they typically use polyether foam, not unlike that found in many hi-fi speakers....
We have added a specially matched positive roll polyether foam surround to the top of the cone, while leaving the existing inverted cloth surround in-tact.
This creates a more linear resistance on the cone in both directions. It also by nature adds some damping to the cone, another reason Lowther probably uses it.
But in the case of this driver, having both (positive and negative roll suspensions) creates a dead air space that is sealed (but with a high Q loss from the original cloth to the inside of the enclosure) that effectively becomes a perfect absorber for the midrange frequencies that are most effected by modal resonance's...
So there you have it, the dual-roll info as presented by Decware.. and Lowther before him.
It appears that the dual-roll mod IS the reason for the reduced resonances, certainly the response of the modded Fostex shows similar changes.
Of particular interest on the graphs in his paper is the distinct change/improvement in HF performance and linearity. Here the question becomes: is it the dual-roll or is it the treatment he did on the cones and whizzers? My guess is both.
Arrgh, I can't find the Lowther article anywhere on-line, seems to have disappeared...
Guess we'll have to content ourselves with this information from Deckert about how he modded the Fostex (gotta love those marketing names he comes up with... "Active Suspension System"... I can see why some people get steamed about the lingo.)
This quote is from DECWARE - Audio Paper - New Full Range Driver DFR8, edited for brevity. Check out the paper though, it is informative. Here goes:
The DFR-8 active suspension system
The original FE206EM used an inverted roll cloth surround that is attached to the under side of the speaker cone. It offers no damping like butyl rubber but then butyl rubber is high mass, less strong, and slow.
If you look at Lowther speakers they typically use polyether foam, not unlike that found in many hi-fi speakers....
We have added a specially matched positive roll polyether foam surround to the top of the cone, while leaving the existing inverted cloth surround in-tact.
This creates a more linear resistance on the cone in both directions. It also by nature adds some damping to the cone, another reason Lowther probably uses it.
But in the case of this driver, having both (positive and negative roll suspensions) creates a dead air space that is sealed (but with a high Q loss from the original cloth to the inside of the enclosure) that effectively becomes a perfect absorber for the midrange frequencies that are most effected by modal resonance's...
So there you have it, the dual-roll info as presented by Decware.. and Lowther before him.
It appears that the dual-roll mod IS the reason for the reduced resonances, certainly the response of the modded Fostex shows similar changes.
Of particular interest on the graphs in his paper is the distinct change/improvement in HF performance and linearity. Here the question becomes: is it the dual-roll or is it the treatment he did on the cones and whizzers? My guess is both.
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Ok, well a gas filled balloon as a surround (the dual half round foams) will be a non-linear suspension. I believe that as you create excursion, there will be increased compression within the half rounds, creating both a spring effect and an increased resistance with Xmax.
I'd like to see what "Kippel" has to say about it...
In effect I am saying that this is some sort of mechanical compresson/limiter effect - greater at higher excursions than low... perhaps at low excursions it is sufficiently linear, and perhaps if the F3 of the system/speaker is sufficiently high the Xmax is never pushed enough for this to be a practical issue... I guess in that case it would be a good thing...
Interesting approach no matter what.
Now the question is what is/was the treatment on the whizzer cone and how come that is so flat??
One could experiment with cheap speakers with whizzers I suppose. I suppose they still exist out there. At one time cheap-o speakers with whizzers were easy to find... or one could buy some whizzers and retrofit them to existing cheap-o drivers for experimental purposes... if you want to talk about an unterminated "bell", that whizzer qualifies it would appear? 😀
_-_-bear
I'd like to see what "Kippel" has to say about it...
In effect I am saying that this is some sort of mechanical compresson/limiter effect - greater at higher excursions than low... perhaps at low excursions it is sufficiently linear, and perhaps if the F3 of the system/speaker is sufficiently high the Xmax is never pushed enough for this to be a practical issue... I guess in that case it would be a good thing...
Interesting approach no matter what.
Now the question is what is/was the treatment on the whizzer cone and how come that is so flat??
One could experiment with cheap speakers with whizzers I suppose. I suppose they still exist out there. At one time cheap-o speakers with whizzers were easy to find... or one could buy some whizzers and retrofit them to existing cheap-o drivers for experimental purposes... if you want to talk about an unterminated "bell", that whizzer qualifies it would appear? 😀
_-_-bear
a Bell you say?
That one rings true !! (Sorry, couldn't resist...)
Yeah, I think I'd want to experiment on cheap-o whizzers before ruining any $200 a pair Daytons... that gets a little costly. Maybe Deckert would sell a less expensive version without the magnetic coupling, just the suspension, cone and whizzer mods and just make it easy for all of us who don't have the long green to lay out...
On the subject of the gas filled balloon...
with one roll going positive and the other one inverted roll, how much compression do you suppose is going on?
My guess is probably not too much until you get to pretty far out excursion, and at that point it might actually lower the distortion, acting like a rubber bumper that offers soft clipping and keeps the driver from "jumping the gap" or bottoming...yeah, a Klippel test comparison would be really interesting on that mod.
But to get a 5X decrease in compliance, either 2nd roll suspension is really stiff or the trapped air is really stiffening it it up. Hmm... a gas filled shock absorber for your speakers...
Even if the mod is glorious, the driver Xmax is only 5mm, and I don't think this would be the best choice to run it as a full range if you want to get some halfway decent max SPL... especially on an open baffle! Might be OK if you never go above 90dB or so...real nice with chamber music...guitar... solo voice... but not rock or full scale orchestra classical! Deckert himself alludes to something like this in his discussions about the modded Fostex in his ZOB
But... for those who are LOUD-iophiles... this could make a very interesting combination with a pair of Eminence Alpha 15a in an 18" wide OB about 45" tall.
Connect a 4.5mH inductor in series to a paralleled Eminence pair... this corrects for the OB bass drop-off and provides near ideal bass level between 40Hz to 200Hz, with a 1st order rolloff starting at 250Hz....
then we just cross in the Dayton with a 250Hz high-pass, also 1st order, and voila a pretty nice system that clocks in at 95dB at 2.83V/1m... and sooo easy to build...
acoustically phase coherent at listening axis if it is sloped back at about 15 deg... hmm... I might just have to try a pair!... a combo like this could probably play at more satisfactory levels...models out at 115dB+ for peaks.
Loud enough for some of us...others, maybe not...
Eh? What's that you say? Huh?... I can't hear you....🙂
That one rings true !! (Sorry, couldn't resist...)
Yeah, I think I'd want to experiment on cheap-o whizzers before ruining any $200 a pair Daytons... that gets a little costly. Maybe Deckert would sell a less expensive version without the magnetic coupling, just the suspension, cone and whizzer mods and just make it easy for all of us who don't have the long green to lay out...
On the subject of the gas filled balloon...
with one roll going positive and the other one inverted roll, how much compression do you suppose is going on?
My guess is probably not too much until you get to pretty far out excursion, and at that point it might actually lower the distortion, acting like a rubber bumper that offers soft clipping and keeps the driver from "jumping the gap" or bottoming...yeah, a Klippel test comparison would be really interesting on that mod.
But to get a 5X decrease in compliance, either 2nd roll suspension is really stiff or the trapped air is really stiffening it it up. Hmm... a gas filled shock absorber for your speakers...
Even if the mod is glorious, the driver Xmax is only 5mm, and I don't think this would be the best choice to run it as a full range if you want to get some halfway decent max SPL... especially on an open baffle! Might be OK if you never go above 90dB or so...real nice with chamber music...guitar... solo voice... but not rock or full scale orchestra classical! Deckert himself alludes to something like this in his discussions about the modded Fostex in his ZOB
But... for those who are LOUD-iophiles... this could make a very interesting combination with a pair of Eminence Alpha 15a in an 18" wide OB about 45" tall.
Connect a 4.5mH inductor in series to a paralleled Eminence pair... this corrects for the OB bass drop-off and provides near ideal bass level between 40Hz to 200Hz, with a 1st order rolloff starting at 250Hz....
then we just cross in the Dayton with a 250Hz high-pass, also 1st order, and voila a pretty nice system that clocks in at 95dB at 2.83V/1m... and sooo easy to build...
acoustically phase coherent at listening axis if it is sloped back at about 15 deg... hmm... I might just have to try a pair!... a combo like this could probably play at more satisfactory levels...models out at 115dB+ for peaks.
Loud enough for some of us...others, maybe not...
Eh? What's that you say? Huh?... I can't hear you....🙂
Eo really be able to compare t/S data the drivers need to be measured under the same connditions. Both weather & instrumentation. One can get "greatly" changed parameters just by changing the instrumentation (if they measure under different drive conditions).
dave
Parameters
Dave, that's very true, especially with temperature changes.
However, the calculated Thiele-Small parameters for the FRX and the Dayton seem to be very much in line with a simple change of compliance.
I went through the calculations and if the Cms is reduced by about 5x the way this affects the other parameters Qmd, Qed, Qt, Vas, and the calculated changes in those shows up pretty much exactly as the figures Deckert published on the FRX, within less than a very small variance...
so's I suspect it's the only major structural change, i.e. not much added mass or mechanical resistance, and certainly not a change in motor structure or BL.
I don't think the differences are due to the weather in this case!
Dave, that's very true, especially with temperature changes.
However, the calculated Thiele-Small parameters for the FRX and the Dayton seem to be very much in line with a simple change of compliance.
I went through the calculations and if the Cms is reduced by about 5x the way this affects the other parameters Qmd, Qed, Qt, Vas, and the calculated changes in those shows up pretty much exactly as the figures Deckert published on the FRX, within less than a very small variance...
so's I suspect it's the only major structural change, i.e. not much added mass or mechanical resistance, and certainly not a change in motor structure or BL.
I don't think the differences are due to the weather in this case!
From the experiments others have done it works. Some tuning of transformer ratios & inductance to get the optimum results.
I'd suggest that a digital EQ (ie miniDSP) would get as good and more versatile results. Cheaper too. Extra front suspension (or something) likely still needed to kill off (some?) resonant modes.
dave
I'd suggest that a digital EQ (ie miniDSP) would get as good and more versatile results. Cheaper too. Extra front suspension (or something) likely still needed to kill off (some?) resonant modes.
dave
Hello all, I have the FRX drivers now. Its about one week since I have received them. Right now I wont provide a review since they are open sitting on a box & connected to amplifier. But sure will give you a quick first impression. From appearance stand point, its 5 out of 10. Steve needs to make it more attractive for the price. First day when I plugged in I really hated the speakers. They were unbearable, very bright (two surroundings). I gave couple of days to loosen up. Now treble is very different then what I am used to listening to (even compared to the SS aircircle tweeters I have). They are very clean and true to the instrument tone. Vocal sounds very clean and little forward like singer is in the room. Since speakers are without any panels, vocal does not have body which will change with ZOB box. Will let you know how the bass is when it goes on ZOB. But otherwise all instruments sound distinct and clear. I am discovering a lot of details in my music. Music sounds very natural with real tone. You got the idea, I have only good things to say about it. Also let me just share that I do not know Steve and this is my first purchase from him. You might ask how they measure. Unfortunately I have Radio Shack SPL meter which is not calibrated or accurate. I have just downloaded the REW software and planning to measure them if I can figure out the setup. Meanwhile happy listening.....🙂
Would be cool if you could get them on temporary baffles or something to get some separation between the front and rear wave, then listen to them and give some impressions on the sound.. Raw drivers just plugged in on their own are not really going to shine or show their true potential as you already noted etc. Maybe a simple pair of 5'x3' baffles could be an easy way to get to know how they really could sound 🙂
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One sheet of MDF cut in half with a hole slightly off center would do the trick for a "cheap and dirty" means... most of the "Home Improvement" stores will chop a sheet in half in the store, no charge... then you have to bang a hole, mount screws... 😀
Instant OB...
OR better still - IF you have a pair of windows in ur LR on the same wall, make a simple bit of MDF or plywood with a mounting hole, and put that with the driver mounted in the WINDOW! 😀
Instant almost perfect IB conditions - you might be VERY surprised.
_-_-bear
Instant OB...
OR better still - IF you have a pair of windows in ur LR on the same wall, make a simple bit of MDF or plywood with a mounting hole, and put that with the driver mounted in the WINDOW! 😀
Instant almost perfect IB conditions - you might be VERY surprised.
_-_-bear
Measurement of FRX
Hello All, attached is the frequency & waterfall response measured with my PC card and uncalibrated mic. This is a quick and dirty measurement. But I am very happy about what I am seeing. Comments are welcomed.
-creek
Hello All, attached is the frequency & waterfall response measured with my PC card and uncalibrated mic. This is a quick and dirty measurement. But I am very happy about what I am seeing. Comments are welcomed.
-creek
Attachments
Speakers are without any baffles so the frequency response is dropping after 1K. The mic is at about 5 - 6 inches from center.
The graphs look good! 🙂
Maybe Decaware will force full range (kicking a screaming) into a different direction? Thank you very much for throwing you money at it so see what happens. An 8" FR that does 18KHz down to 40 Hz within a 3dB window and have decent sensitivity would be a world class design. If it can do 30 to 20KHz at 94dB or higher--I'll be saving my coins! 😱
It takes time for everything to break in, take your time and looking forward to read about the final result.
OB in a window? Now that is an interesting idea--have a sawzall and a garage... hmmmm.
Maybe Decaware will force full range (kicking a screaming) into a different direction? Thank you very much for throwing you money at it so see what happens. An 8" FR that does 18KHz down to 40 Hz within a 3dB window and have decent sensitivity would be a world class design. If it can do 30 to 20KHz at 94dB or higher--I'll be saving my coins! 😱
It takes time for everything to break in, take your time and looking forward to read about the final result.
OB in a window? Now that is an interesting idea--have a sawzall and a garage... hmmmm.
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What is in the center of the speaker in your picture??
That's not what the stock driver has in the center... what are we looking at??
_-_-bear
That's not what the stock driver has in the center... what are we looking at??
_-_-bear
I think maybe the mic far too close to the driver. Mic needs to be in the far field for a valid measurement. 4-5 times the driver diameter would be a good start.
dave
dave, I don't agree about that... depends on what "validity" you seek??
Up close but a little bit farther away than in the speaker gets you a good idea of
what the IEC response might look like, since there is more direct radiation and less everything else... of course too close and where the mic is positioned can radically change what is picked up and how the curve looks...
About 12" away is not a bad place to start in some instances...
Was that a mic??
_-_-bear
Up close but a little bit farther away than in the speaker gets you a good idea of
what the IEC response might look like, since there is more direct radiation and less everything else... of course too close and where the mic is positioned can radically change what is picked up and how the curve looks...
About 12" away is not a bad place to start in some instances...
Was that a mic??
_-_-bear
NEW THREAD on Dayton 8" Driver
I've started a new thread on the Dayton 8" FR driver here:
http://www.diyaudio.com/forums/full-range/191302-dayton-8-fr-ps220-discussion.html
I figured it deserves consideration on its own and WRT mods...
_-_-bear
I've started a new thread on the Dayton 8" FR driver here:
http://www.diyaudio.com/forums/full-range/191302-dayton-8-fr-ps220-discussion.html
I figured it deserves consideration on its own and WRT mods...
_-_-bear
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