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Old 6th May 2007, 04:25 AM   #691
Variac is offline Variac  United States
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15"Deltalite ll:
http://www.eminence.com/pdf/deltaliteII2515.pdf

15" Kappalite
http://www.eminence.com/pdf/deltaliteII2515.pdf

15" Kappalite LF
http://www.eminence.com/pdf/kappalite-3015lf.pdf

If you look at the curves, you can see that the Deltalite is exceptional in the upper frequencies. not only are they smooth there, when they do drop off, there are no sawteeth and it's STEEP. You could probably run this driver with no crossover filters at all. Possibly a filter to reduce the rising rate. I did that with another 15" driver that had this same kind of response , and was very pleased with the final result.

The Kappas are fine-maybe better if you are crossing them at a low frequency, but the upper part of their curves are pretty typical Eminence..
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Old 6th May 2007, 08:02 PM   #692
mige0 is offline mige0  Austria
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Default missing colors / dissimilar woofers

Hi

Quote:
I could be 100% wrong on the "dissimilar woofers working in parallel" thing.
Well, I'd rather think so!

With a fairly smooth FR loudspeakers do not behave like TV or computer monitors where there are definitely not all colours available depending on make (DLP, LCD, Plasma...) and in addition to that there are also might be some missing spectral lines form the illumination source.

That there are sounds that can't be reproduced (accurately) is obvious for anybody. Thinking of it that there are "colors" that are missing is a nice concept but I don't think this holds true. At least unless we don't suffer from finite resolution of upcoming digital speakers. Anything could equally be explained with coloration and masking effects IF we had a better understanding about that.

While continuing my research about diminishing resonance effects in loudspeaker cabinets WITHOUT the use of damping material, I found it most interesting to first have a closer look at the effects that come up with different constructions.


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Note this is what we are used to see. Sharp high Q resonances fading away equally.




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Note that the resonance at 300 Hz starts lower but falls much less steep than the resonance at 180 Hz.




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Here the resonance at 300 Hz builds up and also shifts its frequency down to some degree




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Here we can observe kind of frequency swapping between 150 Hz and 180 Hz and kind of oscillation at very low frequency





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Here we can see decay in steps




Above gives a glimpse on how complex sound coloration might get. Sure, all measurements I presented were from speakers in cabinets and open baffle speakers are different.

On a smaller scale, I'll bet, same strange things happen with the speaker itself.

On an larger scale, we have to take room response also into account and a typical listening environment can always be seen as if sitting inside a loudspeaker cabinet. This is most obvious for those who like to build their speakers into the walls.

(By the way, my Avatar basically tells you the same story, showing the outspread of a single frequency wave from two loudspeakers into a simplified listening room.)


Coming back to overlapping frequency range with multiple speakers:
there was an experiment I was told of with one pair of very neutral sounding speakers against a pair of speakers where they throw a lot of resonating things into and guess what the multiple resonating pair was subjectively judged as the better one.

So at the end using different speakers over a broad range might balance also nicely.

Greetings
Michael
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Old 6th May 2007, 10:07 PM   #693
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Default Driver Resonances

Quote:
Originally posted by mige0
[BAbove gives a glimpse on how complex sound coloration might get. Sure, all measurements I presented were from speakers in cabinets and open baffle speakers are different.

On a smaller scale, I'll bet, same strange things happen with the speaker itself.

On an larger scale, we have to take room response also into account and a typical listening environment can always be seen as if sitting inside a loudspeaker cabinet. This is most obvious for those who like to build their speakers into the walls.

(By the way, my Avatar basically tells you the same story, showing the outspread of a single frequency wave from two loudspeakers into a simplified listening room.)


Coming back to overlapping frequency range with multiple speakers:
there was an experiment I was told of with one pair of very neutral sounding speakers against a pair of speakers where they throw a lot of resonating things into and guess what the multiple resonating pair was subjectively judged as the better one.

So at the end using different speakers over a broad range might balance also nicely.

Greetings
Michael [/B]
I strongly suspect the CSD measurements are actually showing cabinet modes, not the drivers themselves. I'll bet you two pixels that if the drivers were removed from the cabinets, mounted on a large flat baffle, and measured near-field (microphone 2 cm from cone), those low-frequency high-Q modes would all disappear.

The lowest-frequency departure from flat, resonance-free piston-band operation I've measured in a bass driver were spider resonances, typically around 500 Hz or higher. As it is, spider resonances are a design defect, and shouldn't be present in a monitor-quality loudspeaker. Spider resonances are sometimes disclosed by very small ripples in the impedance curve - and translate to severe, high-Q resonances in the acoustic realm. When the prosound manufacturers make obscure references to "silicon" damped spiders, they're trying to tell us the spider is damped with a silicone-rubber compound.

Resonances in a cone driver below 500 Hz hints at a gross design defect - the cone is flexing in a region where it should be rigid, some part is loose and buzzing, etc. I would be quite concerned by any driver resonance much below 1 kHz - it just ain't natural.

Conversely, we should ALWAYS expect to see severe cabinet resonances from 1 kHz on down. That's consistent with quarter and half-wave internal cabinet dimensions, and the fact that cabinet filling and damping materials on the cabinet walls have only modest effectiveness at lower frequencies. The region between 100 and 1 kHz is where cabinet colorations are measurably and audibly most severe - and coincidentally, where cone drivers are nominally in "piston mode" where they should be intrinsically flat.

In other words, cabinets are at their worst at the same frequencies where cone drivers are at their best! This is why I suggest getting the drivers out of the cabinets and measuring on a LARGE flat baffle in free air, or even measuring nearfield hanging from a string. Unless drivers have gone dramatically downhill from my Audionics days in the 1970's, I didn't see any narrowband resonances much below 700 Hz. Once you get below the spider resonances, drivers behave pretty close to Theile/Small models.

Now if drivers have degraded over the last several decades, I'd like to know. Last time I spoke with Linkwitz, he did say there were some famous, widely-used audiophile drivers with outright defective spiders.

------------------

Some very impressive links were sent to me by a reader - the webpage of David Griesinger. He makes a very strong case for separate stereo subwoofers that are positioned on the sides of the listener in this paper. Highly recommended reading!

The comments of audibility of the velocity wave is appropriate to this discussion - remember, measurement microphones are only sensitive to pressure, and as the articles show, equalizing for only the pressure term can be a mistake. Dipoles generate a strong velocity term close to the speaker, unlike a monopole, where it takes a LF room mode to create a velocity term (close to and right at the pressure null).

By the way, suggestions for "other" drivers like the PHY, Supravox, Fertin, and the Eminence Deltalites are very much appreciated, showing all of us what's out there. If a notch filter can be avoided, that's good!

As for mixing and matching, seriously, I don't know at this point. It's only an instinct that it would work well - in the bass region only. It's not something I'd try at higher frequencies, where crossover design, inter-driver phase relationships, and vertical and horizontal lobing become much more critical and hard to design. That's part of the reason the system has only one "real" crossover, around 1.5 to 2.5 kHz, depending on the properties of the widerange driver and the HF ribbon or horn tweeter.

Everywhere else, the drivers are close to phase-synchronous - and one reason I'm keeping a separate, isolated tweeter, and the possibility of a 5 to 10-degree slanted baffle, in the mix. Crossovers are much easier to design if the arrival times from the drivers are reasonably close together.
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Old 7th May 2007, 03:37 AM   #694
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This time I didn't draw the support structures - there are lots of ways to do this, from the steam-punk look of brass cylinders and adjustment thumbscrews to the modern-day black-painted space-frame. My suggestion for the tweeter is hanging it on threads, so it is isolated from the vibrations of the rest of the assembly. I think being able to adjust the tweeter front-to-back, as well as rotating it, might be a desirable option - this lets you fine-tune the system without wrestling with the main driver array.

The delay of the horn compression driver, or ribbon tweeter, is approximately correct - about three inches behind the voice coil of the widerange driver. So if a ribbon is used, yes, it'll be in about the same place as the compression driver drawn here. The prettier look of aligning the faceplate of the tweeter with the front panel means more work on the crossover and accepting time and frequency response that isn't quite as good - your choice.

There is a possibility of a OEM version of 100 dB/metre ribbon specifically designed for studio monitors, with a suggested 1.5~2 kHz crossover. Stay tuned for more news on this front.

I'm still leaning towards the 18Sound driver array, with the 12NDA520 for the 12" driver, and the 15NMB420 for the midbass and bass drivers. The Eminence Deltalite-II 2515 looks entirely suitable as well.

It's interesting many of these drivers have a minor (3 dB or less) peak at 2.2 kHz. If you don't want to use a notch filter, they could be crossed over with a low-Q (0.5 or less) lowpass filter somewhere around 1.5 to 2 kHz - the net acoustic result of the minor peak at 2.2 kHz and the low-Q 2nd-order filter would result in an acoustic 3rd-order Butterworth lowpass filter around 2.2 kHz.
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Old 7th May 2007, 06:35 AM   #695
mige0 is offline mige0  Austria
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Hi

Quote:
I'll bet you two pixels that if the drivers were removed from the cabinets, mounted on a large flat baffle, and measured near-field (microphone 2 cm from cone), those low-frequency high-Q modes would all disappear.
You won!
Of course all measurements show cabinet behaviour not speaker behaviour.

Don't get me wrong, omitting the cabinet seems to be the best way to get rid of cabinet coloration, making cabinets small compared to the wavelengths involved is an other possibility especially suitable for subwoofers.
Showing the backside of a coin though, can bring up the real juicy stuff!

The mechanisms demonstrated like:

- non linear decay
- frequency shift and interaction
- Q blurring
- small interval echo

basically apply to any more complex resonating system, is it a cabinet, a speaker or a listening room.

The point here was, that there is plenty of coloration going on with audio playback at different scales but I didn't find any evidence for the concept of missing sound colors so far.





Greetings
Michael
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Old 7th May 2007, 07:37 AM   #696
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Quote:
Originally posted by mige0

Showing the backside of a coin though, can bring up the real juicy stuff!

The mechanisms demonstrated like:

- non linear decay
- frequency shift and interaction
- Q blurring
- small interval echo

basically apply to any more complex resonating system, is it a cabinet, a speaker or a listening room.

The point here was, that there is plenty of coloration going on with audio playback at different scales but I didn't find any evidence for the concept of missing sound colors so far.

Greetings
Michael
I couldn't agree more. Loudspeakers do many dreadful things to the signal, especially long-term high-Q storage effects - one of the more bizarre effects I discovered in that MLSSA series of tests were resonances that swept in frequency as they decayed, like chirp radar!

Room resonances can be resolved by the hearing system, while cabinet resonances follow the direct sound so quickly they can't be separated out. The first in a long succession of room reflections typically arrives 5~7 mSec after the direct sound, while cabinet resonances start within a millisecond. This falls within the interval used by the location-sensing mechanism, and also degrades the impression of timbre - especially vocals, which not surprisingly sound they are coming from a box. They are!

By partitioning the spectrum, we can use devices in the region where they perform the best. Subwoofers, whether monopoles or W-box dipoles/cardioids, operate with an enclosure a small fraction of a wavelength. This is good; all the box has to do is be rigid, and not generate high-order decay harmonics in the several-hundred Hz region.

If we avoid the region where boxes go into characteristic modes (as a function of their size), the drivers can operate in the piston region, and deliver inherently flat response. The 1/f characteristic of dipoles can be equalized, or compensated by bringing in additional drivers to keep efficiency constant.

The delayed rear-wave coming around the edge of the baffle can be smoothed out by using asymmetric shapes, Karlson slots, or open-mesh resistive grilles to smooth out the delayed-arrival signal. Rather than guessing as is traditional for OB, MLS can be used to inspect the delayed-arrival signal and confirm the smoothing techniques are working. True, these are some of the same techniques used inside boxes, but it has the merit that we're dealing with one signal coming around the edge, not hundreds of internal reflections.

At higher frequencies, we shift technologies again, and select tweeters that with low time storage - to match the performance of the OB drivers. A real hard-core purist might insist on dipole electrostats or planars in the 700 Hz to 5 kHz region, just to avoid cone-driver resonances, but that would discard the high dynamic range (and efficiency) of prosound drivers, and would certainly add to system complexity. Harmonizing the sound of cone drivers to electrostats and ribbon tweeters sounds like an awful job.

The trick is to find tweeters with very high dynamic range and low energy storage, two things that don't usually go together. The candidates are compression drivers + advanced profile horns, modern versions of the AMT, and studio-monitor-grade ribbons.

What's so interesting about OB is that this is largely uncharted territory for loudspeaker design: Siegfried Linkwitz was one of the first to discover what it can do for modern systems, but there's lots more to territory to explore. It's amusing is that Americans are so late to the table on this one - I was surprised at the 2004 ETF that OB was so well established in Europe, while it's really radical here.
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Old 7th May 2007, 07:46 AM   #697
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Speaking of Siegfried Linkwitz, what are your thoughts on his recent epiphany re: dipolar HF? Do you think this should be part of the basic configuration for this project?
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Old 7th May 2007, 08:06 AM   #698
mige0 is offline mige0  Austria
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Hi

Nice coincidence about Griesinger's interesting research about room behaviour - I read some of his stuff (really a lot !) just two days ago and was considering to cite this namely page.

What a pity that his cure treatment with F and Q matching isn't more efficient.

Greetings
Michael
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Old 7th May 2007, 11:41 AM   #699
fiacono is offline fiacono  Australia
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Hi Lynn,

Correct me if Im wrong but your image refers to high Qts drivers. The 18Sound are low Qts drivers. The 18Sound come in 8 ohms, you have 2 x 15 and 1x 12 driver, does that imply a 3 way crossover (12 bandpass filter)?

regards
Frank
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Old 7th May 2007, 10:00 PM   #700
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Quote:
Originally posted by Russell Dawkins
Speaking of Siegfried Linkwitz, what are your thoughts on his recent epiphany re: dipolar HF? Do you think this should be part of the basic configuration for this project?

Quote:
Originally posted by fiacono
Hi Lynn,

Correct me if Im wrong but your image refers to high Qts drivers. The 18Sound are low Qts drivers. The 18Sound come in 8 ohms, you have 2 x 15 and 1x 12 driver, does that imply a 3 way crossover (12 bandpass filter)?

regards
Frank
Russel, I'm surprised he liked forward-facing treble in the first place. True, it's the "traditional" sound from conventional speakers that we're used to, but SL was trying to get away from that and move towards something more like real life. Just because we disagree with Amar Bose's 901 concept doesn't mean there isn't something worthwhile in there.

In my own experience, the challenge with rear tweeters is rear sound sneaking around towards the front, and degrading coherence from the front driver. This is no problem with a true radial tweeter (Walsh, MBL, etc.) which radiates from one point (OK, one radiating surface), but is awkward with multiple radiators that are spaced apart. One solution to this is hiding the rear tweeter behind the rear of the speaker, and shaping the highpass filter so not as much sound diffracts around the front.

When I tried this with my first speaker for Audionics in 1975, I wasn't completely happy with the sound - it was more spacious, true, but there was an artificial, pasted-on quality to the HF dimensionality. But that was a conventional forward-facing speaker, a really big transmission line with four drivers and four-way crossover.

With a dipole with a generous amount of rear-directed energy over the full spectrum, a rear tweeter is a different matter. In that event, you want the spectrum coming out of the back of the speaker to have a similar character to the front - maybe not identical, but similar. So you now have the fun task of measuring the speaker over the front listening angle (a 60-degree sweep), at the sides (what's the null look like?), and across the back (is the spectrum continuous, or are there holes?).

Exact one-to-one spectral matching is less important than gross discontinuities - big peaks and holes at certain angles. I'd look for the most trouble at +45, +135, -135, and -45 degrees, where the the drivers are reaching the edge of their polar pattern, and the sound from the front and back are meeting, resulting in a partial null. This is where the spectrum is going to be the roughest, and time response most distorted.

I suspect it all comes down to quality of implementation. Dissimilar front and rear tweeters, with different sonic characters, is asking for trouble. HF response shaping for the rear tweeter is fairly sensitive, since you're controlling the polar pattern in the horizontal plane with the phase relationship between front and rear.

Frank, there are several ways to go with this concept - none of them wrong, just different. First, pick any widerange driver you like, 8, 10, or 12 inches. Second, choose the bass-assist drivers - one or two, 12 or 15-inch, or a combination of 12 and 15-inch.

If the same amplifier is going to drive the entire front panel, a pair of 16-ohm Tone Tubby's, either 12 or 15-inch, fills the high-Q Midbass and Bass requirement. All of the cone drivers have a cascade crossover, starting with a 12 dB/octave lowpass at 2 kHz. This is connected directly to the widerange driver at the top of the baffle. (The Widerange driver has an inductance-correcting Zobel network so it presents a resistive load to the 12 dB/oct lowpass and the other drivers.)

After going to the widerange driver, the signal flows to a tapped lowpass inductor (transformer-grade iron-core) tunable between 160 and 250 Hz. The Midbass driver is connected to the other side of the inductor, and also has a Zobel network to compensate for its inductance.

The signal continues to another tapped lowpass inductor, tunable between 80 and 125 Hz. The Bass driver is connected to the other side of this inductor, and has its own Zobel network.

All three drivers, working at parallel at the lowest frequencies, present a nominal 4-ohm impedance, and are in-phase with each other. The overall slope of the network gradually steepens for each driver in the cascade, but the Q is very low, since the poles are spread quite far apart.

If 16-ohm drivers are not available, and/or the Qts is in the more conventional 0.22 to 0.4 range, then multi-amping and equalization is a good idea. The high-quality amplifier is reserved for the widerange driver and its tweeter (which are crossed-over passively). Any equalization of the widerange + tweeter is done by the passive crossover, not active EQ, partly because I strongly recommend drivers that don't need much equalization in the first place.

Things are different once you get to 250 Hz and below. The room response merges with the what the speaker does - in fact, the room cannot be distinguished by ear, or far-field measurement, from the speaker. This is where individual L and R channel parametric EQ to remove peaks created by room modes is a good idea - but trying to "fill in" room nulls is a bad idea, creating massive distortion and overloading the drivers and the amplifier to no good effect.

Equalization is most useful in the range covered by the midbass and bass drivers - 80 to 250 Hz. I'd still recommend connecting the Midbass and Bass drivers in parallel, as in the example above, with the Bass drivers additionally lowpass-filtered by a tunable 80 to 125 Hz inductor. This controls the overlap between the drivers, and allows response and phase shaping in this critical region.

For the region from 60~80 Hz and lower, stereo subwoofers, located as far apart as possible, or even at the sides of the listening room, are a good idea. I feel it is quite legitimate to put the stereo subs on each side of the listening chair or couch, for example - it decreases power requirements, and increases the tactile sensation. If the subwoofers are conventional monopoles, choose drivers with the lowest distortion possible, to match the dynamics and low-distortion character of the rest of the system.

In the multi-amping example, this is a good application for obsolete Dolby Surround home theater receivers, or Class D or T amps. I'd reserve the quality amplification for the 200 Hz-on-up range.
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