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Evidence-based Speaker Designs

andreasmaaan

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I am sceptical. I actually went to a manufacturers' symposium on such technology, and it is all about synthesising harmonics to create an impression of bass, limiting deep bass at high volume etc.
I'm deisgning a small portable speaker atm and am experimenting with Analogue Devices' subharmonic synthesiser, dymanic bass EQ and a few other DSP-based functions with this goal in mind. I'm not ideologically opposed, although I have to say I haven't been so impressed with the results so far. Perhaps I haven't found the sweet spot quite yet..
 

andreasmaaan

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Yes. Ideally the directivity of a woofer should match that of the midrange to which it is transitioning, and likewise the midrange directivity should match that of the tweeter - you will note the use of custom designed waveguides on some tweeters to improve this transition. Thinking about it, one of the most challenging designs is the very popular 8-inch two ways, especially those with no tweeter waveguide. A midrange speaker improves the design. Adding more subdivisions, up to a point, can also be beneficial. Obviously, three- and four-way designs require significant engineering effort to live up to their potential. The goal is a smooth DI.

If you read my book and/or papers it will be found that most people listening for recreation have a preference for wide dispersion, as a way to attenuate the basic limitations of conventional stereo.
Many thanks Floyd :) I have read a number of your papers and am very appreciative of the opportunity to be able to ask you a couple of direct questions here on the forum.
 

maty

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Most of the Finnish loudspeaker scene is pretty much dominated by Uniform Directivity (i.e. fairly linearly downward sloping on+off-axis power spectrum).

Examples of these, in addition to Jorma Salmi's (RIP) Gradient are:

Amphion Krypton series (hypercardiod diffusion pattern horizontally and vertically fairly directive)
https://amphion.fi/enjoy/products-home-audio/krypton-floorstanding-loudspeaker/
Talking about Amphion, one thing is the marketing and other the true reality.

[Polish] https://audio.com.pl/testy/stereo/zespoly-glosnikowe/f/1005-amphion

AMPHION Argon 7L

-> https://audio.com.pl/testy/stereo/zespoly-glosnikowe/2719-amphion-argon-7l

to English: https://translate.google.com/translate?sl=pl&tl=en&u=https://audio.com.pl/testy/stereo/zespoly-glosnikowe/2719-amphion-argon-7l



I know, it is other series but this graph is horrible, terrible... And others two speakers too.

The new, Amphion Argon 7LS only € 4100 !

With the speakers that there are with measurements, buy one that does not have them is like playing Russian roulette. The same with amplifiers and others audio hard.
 
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Ron Texas

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With the speakers that there are with measurements, buy one that does not have them is like playing Russian roulette. The same with amplifiers and others audio hard.
I used to think if an audio product got lots of good reviews it was a safe bet. The Schiit Yaggi kind of smashed that belief for me.
 

maty

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The more important, in reviews, is not the quantity but the quality. The problem lies in finding them and trusting the author.

How can a music system/hard be valued if the authors limit themselves to listening to modern recordings, so badly recorded and with low or very low dynamic range? I am talking about Amazon and other sites.
 

Ilkless

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Yes. Ideally the directivity of a woofer should match that of the midrange to which it is transitioning, and likewise the midrange directivity should match that of the tweeter - you will note the use of custom designed waveguides on some tweeters to improve this transition. Thinking about it, one of the most challenging designs is the very popular 8-inch two way, especially those with no tweeter waveguide. A midrange speaker improves the design. Adding more subdivisions, up to a point, can also be beneficial. Obviously, three- and four-way designs require significant engineering effort to live up to their potential. The goal is a smooth DI.

If you read my book and/or papers it will be found that most people listening for recreation have a preference for wide dispersion, as a way to attenuate the basic limitations of conventional stereo.
Thank you Prof Toole, I fully agree (and indeed why I started this thread). Smooth, accurate on-axis or even listening window appears to be generally accepted, but a smooth DI (regardless of width of dispersion ie. trend of DI with frequency) appears to remain fairly rare on the market.
 

Bjorn

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Constant Beamwidth Transducers (Dayton/DB Keele) - There are two CBTs you can buy as manufactured products: the CBT36 kit and the CBT24 kit/complete speaker, both offered by Dayton. The CBT24 is on sale for $1495/pr as of February 2, 2019. For mini-monitor money, you can get a bleeding-edge driver array, albeit limited by driver performance. I would personally love to see someone stick in Vifa TG9s or some other widebander with smoother dispersion and FR. Rick Craig of Selah Audio also does custom CBT work at a much higher price range. The CBT isn't a line array. Despite its looks it is as far as one can get from a line source. The curvature and gradually-decreasing SPL (called "shading") emitted by drivers as one moves up the array come together - as someone described brilliantly on DIYAudio - a "slice" (like an orange) of the wavefront of a perfect point source placed on the ground plane. Project an imaginary line backwards from each driver at the angle at which the driver is pivoted. Do you see the slice of a sphere now? Exceptionally uniform coverage both vertically and horizontally. No floor bounce because the speaker is on the ground plane. Floyd Toole mused that it could be the "perfect" surround loudspeaker due to the uniformity of coverage allowing similar sound over a larger seating area. There is more discussion on another ASR thread.

Note that the CBTs will require subs and ideally DSP to equalise driver response. Don Keele (ex-JBL, designer of the JBL biradials before the CBT array for audio) has an excellent lecture series that examines the properties of CBTs:
I hope it's ok that I point that I'm working with Don Keele on a new CBT speaker and possibly other versions as well down the road. Our preliminary website is here:
https://www.keele-omholt-technologies.com/

This CBT speaker we're designing now works very well without any subwoofer by the way but does require an external crossover and 4 channel amplifers.

Below is in room measurement of the left CBT prototype without any room correction. Distance from speaker to mic is approximately 2.7 meters and speaker was placed 1 m to closest boundary/front wall. Placing it closer to a boundary and especially corner will give more low frequency gain.
CBT1 left position 2 in the room.jpg
 

Ilkless

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I hope it's ok that I point that I'm working with Don Keele on a new CBT speaker and possibly other versions as well down the road. Our preliminary website is here:
https://www.keele-omholt-technologies.com/

This CBT speaker we're designing now works very well without any subwoofer by the way but does require an external crossover and 4 channel amplifers.

Below is in room measurement of the left CBT prototype without any room correction. Distance from speaker to mic is approximately 2.7 meters and speaker was placed 1 m to closest boundary/front wall. Placing it closer to a boundary and especially corner will give more low frequency gain.
View attachment 21593

Impressive, does it have a MF/HF crossover like the CBT36, or are you using wideband drivers?
 

Bjorn

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Impressive, does it have a MF/HF crossover like the CBT36, or are you using wideband drivers?
It's 2-way design similar to CBT36 but with better drivers and a lower crossover point. This is a first prototype and we plan to swap to another woofer for several reasons. The new woofer performs better in every aspect and is round as oppose to the square one used in the prototype below.
CBT pair 2 (Stor).jpg
 

Juhazi

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Horizontally a CBT is nothing special, but room response is actually 3D directivity plus time including reflections and modes. CBT helps helps a lot with reflections.
 

Ilkless

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It's 2-way design similar to CBT36 but with better drivers and a lower crossover point. This is a first prototype and we plan to swap to another woofer for several reasons. The new woofer performs better in every aspect and is round as oppose to the square one used in the prototype below.
View attachment 21594
Is a one-piece curved ribbon with smoothly decreasing drive level (eg. through the physical design of the motor) feasible as an extreme implementation?
 

Bjorn

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Horizontally a CBT is nothing special, but room response is actually 3D directivity plus time including reflections and modes. CBT helps helps a lot with reflections.
That's not true.

First of all, one can't make a general statement about the horizontal directivity of a CBT. Why? Because it can be implemented in various ways. Both with various kinds of directivity and with different types of shading networks that will effect the performance.

If you take the first CBT on the market, CBT36, it has a constant and wide horizontal directivity down to approximately 400 Hz. While it's not perfect and has a few side lobes, it's still very uniform and certainly way above most speakers out there. You can see that clearly illustrated in Don's video where he measures it one the sides in real time. Look after 6 minutes in video part 8.
CBT36 2.jpg


CBT36 1.jpg


While it's not perfect and as good as it is vertically, it's quite spectacular.

Either way, as mentioned previously a CBT can be designed in various ways which will effect the horizontal dispersion. There are several ways to improve the horizontal and ways where it will practically have no side lobes whatsoever.

One really cool way is illustrated below. We have called this "The Matrix".
The Matrix.jpg

It would have controllable beam width. It could do very narrow dispersion till very wide with far more directivity options compared to Beolab 90. I dare to say it would be a Belob 90 killer. However, it would require a lot of amps and not be cheap. But hey, if someone has the money and are interested, contact us!
 

Bjorn

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Is a one-piece curved ribbon with smoothly decreasing drive level (eg. through the physical design of the motor) feasible as an extreme implementation?
Would you be able to change the level at exact certain places?
If so, it should be possible.

However, I'm uncertain what level and distortion it could achieve below the midrange. While one can use a separate subwoofer for the lowest frequencies, the mid - and upper bass is still crucial for a great design IMO.
 

12B4A

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Would you be able to change the level at exact certain places?
If so, it should be possible.

However, I'm uncertain what level and distortion it could achieve below the midrange. While one can use a separate subwoofer for the lowest frequencies, the mid - and upper bass is still crucial for a great design IMO.
I think this could be done with magnepans by just slightly canting the fixed magnets assembly a little so that their field strength has a weaker interaction with the ribbon the further up the assembly.
 
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