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Directiva r2 project: market requirements gathering

sarumbear

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Maybe borrow some aspects, but really not interested in doing an active knockoff.

[…]

If the main benefit is better bass in the room, controlled bass directivity may be worthwhile. There has been no discussion of a dipole bass module ala Linkwitz LX521. From what I have read, some have a major advantage as cabinet resonances are well controlled. See the gainphile speaker results on the Princeton site.
I urge the tweeter waveguide as that is the only way to have continuous directivity at the crossover. Don‘t you agree?

Siegfried’s design is bi-polar. I heard them at his house. They are very nice but they have to be placed away from walls to work well. They are very position sensitive. On most European rooms they will not work well as rooms are usually much smaller than you have in US.

May I suggest that we separate tweeter/mid-low transition and the woofer/enclosure separately to avoid confusion?
 

sarumbear

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dc655321

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If the speaker has only one sound source you are correct but in your case you have multiple sources.

You are considering the side vents to be secondary sources here?
That's debatable...

Moreover, in your suggested measurement there is the issue of diffraction; due to the reflected image of the loudspeaker, the baffle appears to be twice larger as it really is, causing a different diffraction response along the edge in contact with the ground. This will skew your measurement.

This effect is a "feature" of ground-plane measurements.
Lift the source above the ground by mic-to-source distance to decouple physical from virtual images.
 

tuga

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What about the Ktêma, it looks like an insteresting approach:


13087083_1726275880986816_9171437585684507204_o-1.jpg
 

617

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I urge the tweeter waveguide as that is the only way to have continuous directivity at the crossover. Don‘t you agree?

Siegfried’s design is bi-polar. I heard them at his house. They are very nice but they have to be placed away from walls to work well. They are very position sensitive. On most European rooms they will not work well as rooms are usually much smaller than you have in US.

May I suggest that we separate tweeter/mid-low transition and the woofer/enclosure separately to avoid confusion?

A waveguide is not necessary for smooth directivity if the driver size difference is small. 180mm to 25mm doesn't work but you can do well with a 120 or even 150mm woofer and a done tweeter.
 

sarumbear

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You are considering the side vents to be secondary sources here?
That's debatable...
If they are not sources why does your speaker not work as a closed box? It was said that sound coming out of the vents cancel the sound generated by the drive unit to reduce sound level at 180 degrees to form a cardioid like polar pattern.
 

sarumbear

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A waveguide is not necessary for smooth directivity if the driver size difference is small. 180mm to 25mm doesn't work but you can do well with a 120 or even 150mm woofer and a done tweeter.
Just check the plots of various speaker unit tested that does not use a waveguide. Also note @amirm ‘s comments on the effects when waveguide is not used.

I'm sure you can imagine the polar diagram difference between a 25cm diameter piston and a 5-6 times larger one.
 

dc655321

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If they are not sources why does your speaker not work as a closed box? It was said that sound coming out of the vents cancel the sound generated by the drive unit to reduce sound level at 180 degrees to form a cardioid like polar pattern.

Maybe I'm misunderstanding what you were saying?

It sounded like you were discounting the use of a ground-plane technique because there are secondary sources (slots) here.
My contention is that side-slots + driver act as single source and they should be treated as such (and GP is fine to use here).
 

fluid

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This observation pushes me to think that Harmonic distortion is not as big deal as we think it is, specially in upper and sub-bass. 10% 3rd-harmonic should be 'theoretically' very audible.
The desire to to have less of everything measurable is understandable. A considerable amount of work has been done by many that demonstrates clearly that THD is not very well correlated with sound quality. Making it as low as reasonably practical is good engineering but obsessing over it makes no sense.

http://gedlee.azurewebsites.net/Papers/Distortion_AES_I.pdf

I thought open baffle designs have lower sensitivity in general, isn't this theoretically something in between?

The voltage sensitivity of the driver doesn't change. What happens with a dipole, cardioid or other pattern that is created by destructive interference, is that it causes a rise in excursion when the drivers are equalized and more power used to reach the same SPL which is probably what you are thinking of as sensitivity. And where the rise in low frequency distortion comes from, increased excursion.

This post from Kimmo explains more and has some good insights

https://audiosciencereview.com/foru...dspeakers-are-they-worth-it.21942/post-753582

and one of his old webpages

https://web.archive.org/web/20160405235024/https://kimmosaunisto.net/CardSub/CARDSUB.html
 

abdo123

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The desire to to have less of everything measurable is understandable. A considerable amount of work has been done by many that demonstrates clearly that THD is not very well correlated with sound quality. Making it as low as reasonably practical is good engineering but obsessing over it makes no sense.

http://gedlee.azurewebsites.net/Papers/Distortion_AES_I.pdf



The voltage sensitivity of the driver doesn't change. What happens with a dipole, cardioid or other pattern that is created by destructive interference, is that it causes a rise in excursion when the drivers are equalized and more power used to reach the same SPL which is probably what you are thinking of as sensitivity. And where the rise in low frequency distortion comes from, increased excursion.

This post from Kimmo explains more and has some good insights

https://audiosciencereview.com/foru...dspeakers-are-they-worth-it.21942/post-753582

and one of his old webpages

https://web.archive.org/web/20160405235024/https://kimmosaunisto.net/CardSub/CARDSUB.html

So if I understood you correctly, the sensitivity remains the same but more excursion is used for the same amount of volts?
 

sarumbear

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Maybe I'm misunderstanding what you were saying?

It sounded like you were discounting the use of a ground-plane technique because there are secondary sources (slots) here.
My contention is that side-slots + driver act as single source and they should be treated as such (and GP is fine to use here).
Lets start from the beginning. What’s the purpose of those slots?
 

sarumbear

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Are you doing this deliberately, or is there still wine involved?
Not yet. :)

I maybe slow to understand and/or read between the lines but certainly and never, ever, deliberate. I value your posts and interested in them.
 

ctrl

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So folks, I've simulated the easiest to implement version of a bass module (BM) with some directivity control in the frequency range below 500Hz.

It consists of three 8'' woofers on the front of the cabinet and one 8'' woofer on the back which is connected with reverse polarity - something like a cardioid arrangement, but without the possibility for a delay.

The dimensions are W (0.3m) x H (0.8m) x D (0.5m). Possibly, if this is pursued further, the enclosure depth should be reduced somewhat.

1634855489615.png 1634855504741.png
The virtual microphone was located at the height of the top edge of the cabinet at a distance of 2m, as indicated by the coordinate system in the sketches.

As a comparison, I show how a bass module with only the top two woofers would behave. A bass module with four woofers on the front would behave almost identically (but this is not possible with 0.8m height).

First BM with two woofer on the front, second BM with 3 (front) + 1 (rear) woofer

Horizontal normalized sonogram (horizontal radiation)
1634856003914.png 1634856019893.png

Vertical normalized sonogram (vertical radiation)
1634856037333.png 1634856056477.png

The results are not overwhelmingly good, but the directivity up to +-120° improves significantly below 500Hz, the rear radiation widens slightly.

For those who want to play around with it, I have attached the VCAD project.
Important: Set the frequency range in VCAD to 50 - 2000Hz, only in this range the simulation is valid.
 

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thewas

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Getting the passive delay elements in the rear and slots for a wide frequency band is as expected the biggest challenge, ME-Geithain does successfully so since more then 20 years, here are independent measurements of one of their models https://www.hifi-selbstbau.de/mobile/testberichte/fertiglautsprecher/536-me-geithain-804k

Now about the "active" methods, other than the active crossover with delay it can be done also with 2 woofers and a passive crossover using different enclosure resonance frequencies as described here (use deepl or google to translate to English):


 
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sarumbear

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Getting the passive delay elements in the rear and slots for a wide frequency band is as expected the biggest challenge, ME-Geithain does successfully so since more then 20 years, here are independent measurements of one of their models https://www.hifi-selbstbau.de/mobile/testberichte/fertiglautsprecher/536-me-geithain-804k

Now about the "active" methods, other than the active crossover with delay it can be done also with 2 woofers and a passive crossover using different enclosure resonance frequencies as described here (use deepl or google to translate to English):


I saw (and auditioned) one of their speakers, Geithain RL944K, when it was reviewed for the Sound on Sound magazine back in 2016. They use the same acoustically filtered side exit method D&D use on the 8C.

Definitely a very accomplished and engineering minded company. Their website is refreshingly devoid of market speak. The German wiki page is unteresting read.
 
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fluid

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So if I understood you correctly, the sensitivity remains the same but more excursion is used for the same amount of volts?
The sensitivity remains the same because that is a property of the driver, more volts are fed in to account for the equalization needed to return the response of the driver to flat. It is the increase in power that results in more excursion.

This is what a Cardioid looks like on axis (taken from the links I posted above), so you can see that it needs equalization. The directivity comes at the cost of output at low frequencies.
On axis Cardioid.png
 
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