Hi John, thanks for the informative measurements.
Judging from your plots - there is a distinct qualitative difference regarding the low pass filter effect of the damping material varying with the density of stuffing.
Comparing the curve of no filling with the trace if lightest filling there can be seen a lot of dampening of the peaks but almost *no* low pass filter effect as the green trace touches the red one several times even *above* the main peak
Down from lightest filling to heaviest stuffing the traces go almost in parallel – as if applied a low pass filter with increasingly lower cut off frequency (overlaid by a left shift of the traces in general due to "virtual volume enlargement" / mass coupling respectively).
Would you agree with my observation / analysis?
Michael
Judging from your plots - there is a distinct qualitative difference regarding the low pass filter effect of the damping material varying with the density of stuffing.
Comparing the curve of no filling with the trace if lightest filling there can be seen a lot of dampening of the peaks but almost *no* low pass filter effect as the green trace touches the red one several times even *above* the main peak
Down from lightest filling to heaviest stuffing the traces go almost in parallel – as if applied a low pass filter with increasingly lower cut off frequency (overlaid by a left shift of the traces in general due to "virtual volume enlargement" / mass coupling respectively).
Would you agree with my observation / analysis?
Michael
mige0 said:
You have to consider that the resonance can create peaks and dips in the response. The damping plays dual roles: 1) the low pass filter effect and 2) damping resonances. So id the resonances are damped you can see a reduction in the peaks as well as a filling of valleys. Also recognize that as the damping increase the corner frequency of the LP filter shifts down in frequency. If you look at a mean slope I think you will agree that the red trace has a lower Fc that the green as well as being "smoother". The trend continues as the damping is increased.
Here are some additional plots that may be of interest. The black line is the envelope of the input burst. The first is the near field response of the OB system to a shaped 5 cycle burst:
Next is the near field response to the same burst for the undamped sealed box:
Last is the same sealed box with 4 oz fiberglass fill.
The 200 Hz frequency was chosen because the undamped box has a nasty resonance there. Perfect response would be the red plot contained within the black envelope.
I'll point out, without posting a graph, that at 200 Hz the undamped U looks very similar to the OB result because the undamped U has no resonances at 200 Hz.
An externally hosted image should be here but it was not working when we last tested it.
Next is the near field response to the same burst for the undamped sealed box:
An externally hosted image should be here but it was not working when we last tested it.
Last is the same sealed box with 4 oz fiberglass fill.
An externally hosted image should be here but it was not working when we last tested it.
The 200 Hz frequency was chosen because the undamped box has a nasty resonance there. Perfect response would be the red plot contained within the black envelope.
I'll point out, without posting a graph, that at 200 Hz the undamped U looks very similar to the OB result because the undamped U has no resonances at 200 Hz.
So you didn't actually read the interview because you have already made up your mind. Too bad.
Fincham's opinion of Dolby is highly tempered:
<i>"he single-handedly allowed the recording industry to change – even if not always for the better."</i>
Give Fincham credit, his activities certainly led some loudspeaker makers to improve their products.
Your host on this thread probably would agree.
I think you are letting your personal experience colour your view - Taking the particular case and applying it to the general one.
The gold in that interview comes after you stopped reading it and it explains why Geddes might be talking to Fincham.
Some nuggets here, for instance:
john k... said:
Yes, I agree on that F-res is lowered and the (fluffy) red curve has gotten smoother - but what I wanted to point at was that we don't see the red and green curve in parallel - indicating a shift in conrner freqeuncy - ig indicating a low pass behaviour.
The low pass behaviour is clearly visible for the denser stuffings for me though.
Michael
FrankWW said:
Not exactly – put it that way:
my personal experience *is* my view !
FrankWW said:
No problem – many people around this forum did as well... no glorification needed
FrankWW said:
Almost anything discussed here earlier
+++++
Please don't take my sidenote personal – my point just was that nobody around has to quote any THX guy to impress someone as they are BS'ing as anybody else in the biz – and certainly Earl's point of view always is appreciated by its own (though not always shared)
Michael
mige0 said:
I think it's is a matter of how you interpret the data.
An externally hosted image should be here but it was not working when we last tested it.
Hi Telstar,
My premise was not wrong; just not analysed.
Hi John,
Why is the burst shaped like that ?
Take bass guitar picking. The first cycle suddenly has the greatest amplitude !
I have some notes here - http://www.gmweb2.net/new_page_1.htm
Cheers ...... Graham.
My premise was not wrong; just not analysed.
Hi John,
Why is the burst shaped like that ?
Take bass guitar picking. The first cycle suddenly has the greatest amplitude !
I have some notes here - http://www.gmweb2.net/new_page_1.htm
Cheers ...... Graham.
Priority List.
Hi to Mige0 and Lynn,
First of all Michael a huge thank you for your most illuminating white paper on thermal compression in loudspeaker drivers.
Wow does not begin to do it justice and I think it should be recognised as essential reading by all commercial driver and complete loudspeaker designers.
Obviously it will be of huge assistance to all DIY speaker builders as well. Thank you once again.
Lynn & main contributors,
In the new (to me anyway!) light of Michaels TC paper I have been reviewing my own list of speaker design priorities and it occurred to me that maybe Lynn and the main contributors to his thread could post an updated top 5 or top10 priority list which reflects some of the content and (hopefully!) lessons learned over the last 2 years and 210 pages of this highly informative thread.
My own list is still in a state of flux (bad pun!) as I am still rearranging things to allow for the new entry...TC!
Far from definitive, but as a starter for ten here goes...
(1) Budget: entry level or lottery win! Ease of build and time frame.
(2) Driver type: Pistonic (including all stats, ribbons and AMT variants) Bending Wave, Plasma (tweeter only at the moment) or something else...
(3) Driver Choice: Specification, measurements, sound quality, ease of matching, long term reliability / repair and appearance.
(4) Bandwidth / SPL goals: Music only or AV, or both?
(5) Crossover type: DSP or analog. Active or passive crossover (if full range ) single driver if limited bandwidth / SPL.
(6) Cabinet / loading : Sealed box, ported ABR, Trans, Line, Open Baffle, hybrid, remote subs, one piece cabinet or modular....
(7) Two way, three way, 4 way, full range plus sub(s) ....
(8) WAF, appearance (the speaker not wife!) : do you have your own AV room...?
(9) Room size / acoustics : Is this it, can it be modified, what if you move house....
(10) Upgradable : Modular, with an eye on future upgrades or this the last pair I'll ever build.
That's my list, the order can vary and there is overlap, minimising Thermal Compression issues now dominates my thinking with numbers 2, 3, 4, and 5.
Now I've written this I actually feel a bit nervous!
But I think it will be of great help to many DIYers if enough of the "big hitters" contribute a list and we can all then cross reference the most important points.
All the best
Derek.
Hi to Mige0 and Lynn,
First of all Michael a huge thank you for your most illuminating white paper on thermal compression in loudspeaker drivers.
Wow does not begin to do it justice and I think it should be recognised as essential reading by all commercial driver and complete loudspeaker designers.
Obviously it will be of huge assistance to all DIY speaker builders as well. Thank you once again.
Lynn & main contributors,
In the new (to me anyway!) light of Michaels TC paper I have been reviewing my own list of speaker design priorities and it occurred to me that maybe Lynn and the main contributors to his thread could post an updated top 5 or top10 priority list which reflects some of the content and (hopefully!) lessons learned over the last 2 years and 210 pages of this highly informative thread.
My own list is still in a state of flux (bad pun!) as I am still rearranging things to allow for the new entry...TC!
Far from definitive, but as a starter for ten here goes...
(1) Budget: entry level or lottery win! Ease of build and time frame.
(2) Driver type: Pistonic (including all stats, ribbons and AMT variants) Bending Wave, Plasma (tweeter only at the moment) or something else...
(3) Driver Choice: Specification, measurements, sound quality, ease of matching, long term reliability / repair and appearance.
(4) Bandwidth / SPL goals: Music only or AV, or both?
(5) Crossover type: DSP or analog. Active or passive crossover (if full range ) single driver if limited bandwidth / SPL.
(6) Cabinet / loading : Sealed box, ported ABR, Trans, Line, Open Baffle, hybrid, remote subs, one piece cabinet or modular....
(7) Two way, three way, 4 way, full range plus sub(s) ....
(8) WAF, appearance (the speaker not wife!) : do you have your own AV room...?
(9) Room size / acoustics : Is this it, can it be modified, what if you move house....
(10) Upgradable : Modular, with an eye on future upgrades or this the last pair I'll ever build.
That's my list, the order can vary and there is overlap, minimising Thermal Compression issues now dominates my thinking with numbers 2, 3, 4, and 5.
Now I've written this I actually feel a bit nervous!
But I think it will be of great help to many DIYers if enough of the "big hitters" contribute a list and we can all then cross reference the most important points.
All the best
Derek.
I want to thank mige0, Dr. Geddes, John K, and Derek for their contributions. The disagreements are fine - I don't expect audio designers, even the most famous and well-respected ones, to agree with each other. Go back 40 to 50 years, and the engineers at Altec, JBL, Quad, KEF and the BBC Research Labs all took completely different paths to design loudspeakers - and all of them produced what many of us would consider "landmark" loudspeakers.
Despite far superior measurements and modelling techniques, I don't expect any more agreement now. Look at the cosmologists - they have the best mathematics, theory, and measurement tools in all of science, and they disagree with each other! The models of the meta-universe are wildly different from each other.
Regarding the 414's vs the 12NDA520's, they're still around. They will be auditioned in due course. I have a completely unscientific subjective bias in favor of Alnico, and have to confess that in advance.
My priorities are:
1A) Rapid settling time from each of the drivers and associated horns, enclosures, dipoles, etc.
1B) Within that settling time, freedom from "buried resonance", as it was defined by D.E.L. Shorter and Laurie Fincham 30 to 40 years ago.
1C) This is not the same as endorsing "linear-phase" crossovers that can reproduce square waves et al. I am not convinced that allpass phase rotation is that audible, compared to the previous driver-originated problems mentioned above.
2) Flat response at the most widely used listening positions, and freedom from narrow directional "spikes" in the response, especially problems that are only a few inches wide (which would produce imaging artifacts).
3) Dynamic range, headroom, and efficiency comparable to professional studio monitors.
4) Pleasant subjective qualities on voice, massed chorus, and large-scale symphonic music. Movie playback, THX or otherwise, is not a design goal.
I am seeing good measurements and subjective reports from 288 & AH425 owners. I've heard the RAAL 140-15D's successfully matched with compression drivers and horns. I now want to explore cardioid LF systems with the goal of reducing settling time.
Despite far superior measurements and modelling techniques, I don't expect any more agreement now. Look at the cosmologists - they have the best mathematics, theory, and measurement tools in all of science, and they disagree with each other! The models of the meta-universe are wildly different from each other.
Regarding the 414's vs the 12NDA520's, they're still around. They will be auditioned in due course. I have a completely unscientific subjective bias in favor of Alnico, and have to confess that in advance.
My priorities are:
1A) Rapid settling time from each of the drivers and associated horns, enclosures, dipoles, etc.
1B) Within that settling time, freedom from "buried resonance", as it was defined by D.E.L. Shorter and Laurie Fincham 30 to 40 years ago.
1C) This is not the same as endorsing "linear-phase" crossovers that can reproduce square waves et al. I am not convinced that allpass phase rotation is that audible, compared to the previous driver-originated problems mentioned above.
2) Flat response at the most widely used listening positions, and freedom from narrow directional "spikes" in the response, especially problems that are only a few inches wide (which would produce imaging artifacts).
3) Dynamic range, headroom, and efficiency comparable to professional studio monitors.
4) Pleasant subjective qualities on voice, massed chorus, and large-scale symphonic music. Movie playback, THX or otherwise, is not a design goal.
I am seeing good measurements and subjective reports from 288 & AH425 owners. I've heard the RAAL 140-15D's successfully matched with compression drivers and horns. I now want to explore cardioid LF systems with the goal of reducing settling time.
Could anyone explain to me how Geithain achieves cardioid bass dispersion?
http://www.me-geithain.de/index2.html?eng
It is linked to adjacent to the picture of the
Studio Monitor Speaker RL 901K
http://www.me-geithain.de/index2.html?eng
It is linked to adjacent to the picture of the
Studio Monitor Speaker RL 901K
Lynn Olson said:
Lynn,
I have addresses this before in several posts but it doesn't seem to make an impression. There are two things to consider with regard to settling time and LF systems; the acoustic response of the system and the motion of the mechanical part of the system, that is, the motion of the driver's moving mass. Cabinet resonance aren't much of an issue here because the frequency is typically well below any cabinet resonance and we are dealing mainly with potential panel flexing in a compliance dominated region, which may be addressed through good cabinet design.
For the point of view of the free field acoustic output of the system polar response makes no difference. If the on axis, free field acoustic response is that of a Q = 0.7, 25 Hz HP cascaded with a 100 Hz Q = 0.7 LP then the impulse associated with the free field acoustic response will be independent of polar pattern. The only difference is that if the source is not a monopole the amplitude will be a function of position. Form to point of view of the moving mass, starting with the monopole, the source must provide the volume velocity required to produce the desired band pass acoustic output. For a cardioid or dipole, the volume velocity of the source starts with the same volume velocity as the monopole plus a 6dB/oct boost as the frequency decreases to compensate for the 1st order gradient roll off of dipole and cardioid sources in the free field. The only impact of polar response is in the amplitude, not settling time. The resulting impulse for the acoustic response of any format (monopole, cardioid, dipole) is shown in the plot below in red. This is also the impulse associated with the moving mass of the monopole source. However, for the cardioid or dipole the impulse of the moving mass is as shown in blue.
An externally hosted image should be here but it was not working when we last tested it.
Now another issue with dipole and cardioid sources is that the acoustic response of the system in a non reflecting environment is a function of distance. See this link for a discussion with respect to dipoles. The same applies to cardioids.
However, all this actually pales compared to the in room response for which settling time is dominated by the room acoustics. Of course, this doesn't negate the deisre to have a LF system with good mecahincal and free field characteristisc. But the idea that a cardioid or dipole would offer better settling times than a monopole is incorrect. Given the same bandpass response it can only be the same or worse than a monopole, depending on listening distance and on whether acoustic or mechanical settling time is examined.