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Directiva r2 project: market requirements gathering

617

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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.

View attachment 160540 View attachment 160541
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)
View attachment 160544 View attachment 160545

Vertical normalized sonogram (vertical radiation)
View attachment 160546 View attachment 160547

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.
That's a clever way of implementing cardioid bass, could be done passive as well.

Can this be modeled in vituixcad directly I wonder?

I really need to learn akbak or whatever you use.
 

sarumbear

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That's a clever way of implementing cardioid bass...
If it works? Simple enough to build and test.

It is so simple that one asks why there are no designs like that around?
 

617

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If it works? Simple enough to build and test.

It is so simple that one asks why there are no designs like that around?
Much easier to interrogate strangers on the internet than make a prototype or boundary element model I suspect.

The issue if my memory of the old dipole website is correct, is that for passive systems you want relatively large distance between the front and back woofers for these passive systems. Active systems can use delay to create the desired interference.
 

sarumbear

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The issue if my memory of the old dipole website is correct, is that for passive systems you want relatively large distance between the front and back woofers for these passive systems. Active systems can use delay to create the desired interference.
That is why there are tries where they stuff the enclosure so much with rockwool that it is hoped the change in the speed of sound will create a delay. I have no understanding of the model and there are hardly any math around to make me to understand the concept. All we talk about is logical assumptions.
 

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Here is the music and design page on damped u frame woofer, which offer a cardioid like radiation:
 

sarumbear

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Here is the music and design page on damped u frame woofer, which offer a cardioid like radiation:
The H-Frame explained in the article was applied in the Bose Canon subwoofer. It was a huge device but worked pretty well. See below. Bose later tried a smaller version for cars called Bazooka but that wasn't very successful as it didn't work well. There lies the problem for home use; size, especially the large depth requirement.

_J8K0588.jpg
 
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Rick Sykora

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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?

Really want to avoid a waveguide unless it is part of the tweeter design. Amir has reviewed a number of speakers with good directivity without needing waveguides. This was already discussed in r1.

Linkwitz's design is a dipole and my question was around the OB bass module. Ofc, the upper part is going to need space as the those drivers are open baffle and have significant energy output from the back.

I had already planned a separate the bass module and upper monitor, so not sure where the confusion may be. The high level goal is to improve directivity over r1. So r1 is the reference. Am still not clear on where the most audible improvement in directivity may come from. At the risk of repeating myself, am interested in the audible benefit. Lacking this, not interested at all in something superficial like making a prettier polar map or chasing other cool designs without knowing the problem they are trying to solve...

For example, if controlling bass directivity has the benefit of clearer bass and better room integration, then this seems like a good goal. However, if improving the directivity above 5 kHz will be more audible, then would not spend time or money for better bass directivity. As I have not heard a kii 3 or the d&d 8c, am relying on others to articulate the benefits.

Hoping the discussion turns towards what benefits a given feature has and less of how a feature may have been accomplished. :)
 
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JRS

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A vent is a Helmholtz resonator, like the pipe of an organ, it resonates at a single frequency. Resistance simply changes the Q of the resonance. You can have multiple vents but that will make the FR non-flat.
I don't agree in this case. What instead is you have a leaky box--the "vent" is not storing energy, and instead is modeled as a resistor, Rx, whose value is independent of frequency, and introduces another order to the system with the loss the RC product of Rx and Cab (cabinet compliance). In any e-vent, the system is now 3'rd order and rolls off at -18dB/octave. Been kicking around for 50 years now, but is seldom employed except unintentionally by crappy cabinet construction . http://diyaudioprojects.com/Technical/Aperiodic/Aperiodic-Closed-Box-Loudspeakers.htm
 

JRS

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Because I'm curious on how these things work - this is my hobby (one of them) and since this is still not very well understood in practice, I'm trying to make sense of it all.

I'm sorry but I've made full 360° measurements before using the ground plane method, I've seen others do it. I've seen these measurements verified.. To be clear I'm not talking about simulating. I'm talking about making 36 measurements in 10° incrementations (or well, 18, for a symmetrical speaker)
This may help, the engineer sorts out the transfer function and vent considerations--bear in mind, that his intention is to take the twang out of a peaky box, getting some bass extension and better transient behavior in the deal. I wish I could remember where in DIY that I have seen this notion explored. I wonder if one could start with a 6 inch woofer in a small cardboard box to maybe get a handle on the parameters. Otherwise it could entail a lot of chopped wood.
 

voodooless

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

Horizontal normalized sonogram (horizontal radiation)
View attachment 160544 View attachment 160545

Vertical normalized sonogram (vertical radiation)
View attachment 160546 View attachment 160547

The results are not overwhelmingly good, but the directivity up to +-120° improves significantly below 500Hz, the rear radiation widens slightly
For a good comparison you need the three front plus rear enabled/disabled. Having 2 or three woofer on the front already changes directivity. I think things might improve when you filter the rear for < 500 Hz. Also try mounting the rear driver all the way down like Genelec goes. That will make the path length different to the listener longer. You could also experiment with an all-pass passive filter to make the delay longer. That won’t be cheap though…
 

jhaider

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However, if improving the directivity above 5 kHz will be more audible, then would not spend time or money for better bass directivity.

What do you mean by "improving" here? Wider? Narrower? Different shape?

IMO the biggest sonic distinction from R1 - possibly "improvement," I suspect that could be room dependent but maybe not- would be to extend pattern control lower. That's also the most complex and expensive direction to go.

There is a nice overview of these sort of speakers here

https://www.linkedin.com/pulse/directivity-control-part-1-survey-loudspeaker-systems-steve-mowry

and a follow up page with a design

https://www.linkedin.com/pulse/dire...se-article_more-articles_related-content-card

If rear rejection is not the most important aspect then a supercardioid has a higher DI in the forward direction and is what you tend to get with a rear cancelling driver like the W371.

That's a fascinating find - thanks! A similar design has been bouncing around in my head as a potential "phase 2" for our 2-channel system.

Isn't the author the brains behind a lot of the TC Sounds subwoofers in the past?

On the other hand both D&D 8C and Kii3 are extremely complicated speakers with multiple amplifiers. Kii3 has five power amps driven by an integral DSP in each speaker and has a remote control! Neither designs are within the realms of a DIY project.

I don't understand this. Why can't a DIYer handle a project (assuming stereo) 10 processing channels? Here's an easy route in terms of hardware:

miniDSP SHD or SHD Studio - gives you remote control, AirPlay streaming, other inputs (even vinyl, through e.g. a Parks Audio Puffin phono pre with digital output) room correction, 2 processing channels for your tweeters, and two channels to digitally pass to the next processor
miniDSP 4x10HD or 10x10HD - gives 8 processing channels with the ability to expand to even more over AES/EBU
So that's your remote, source, and processing.

Admittedly, miniDSP doesn't have a unified control software a la London/Audio Architect or QSC Qsys, so you'll need to use two different plugins to set up the crossovers. Still, it's not that difficult to do. Certainly easier and less time-consuming than simulating passive crossovers, building, and tweaking. Plus Dirac Live if you want.

Even the amp section is very simple and inexpensive. You could, for instance, use of the Lexicon/Crown/Savant "Drivecore" 1RU 8ch amps amps for most of the channels, and maybe something with better top end FR or lower noise for the tweeters. If you want higher quality there are single-unit multichannel Hypex-based amps from Buckeye, Apollon, etc. Or used ATI made "zone" amps sold under different brands. That's at most 2-4RU worth of amps. Building the amps into the speakers is kind of dumb anyway, when you don't have to on packaging efficiency grounds. (Kii, D&D, etc. would need to design a nice case and also new shipping carton, etc. for a proper external controller box - much cheaper to build the amps into the speakers.)

Four channel DSP plate amps are rather rare. Therefore, it would probably be desirable, if possible, to limit the project to 3 channels.
This means that only one DSP channel is available for the bass module.
...
Or am I missing a simple solution possibility?

If three processing channels per audio channel is the limit, one could do a hybrid crossover - passive MT unit (passive parts to roll off the drivers and correct for individual driver breakup, use the processing channel to set the response, a la JBL 7-series i-line) + bass. That gives you 2 channels for bass. However, I kind of hate plate amps generally. I much prefer keeping all the processing and amplification components in one rack and only running low-voltage cabling to the speakers.
 

abdo123

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I think we’re missing the OG (and the easiest) cardioid to make, the LXmini.

If we cross a dipole and an omni-monopole then we will have directivity in ~500Hz range for the bass module @ctrl simulated.

This would be by far the simplest way to control directivity. In terms of the DSP and DIY experience required.

1634883199767.png
 

TimVG

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

Ground plane measurements aren't new and when taking into to account certain precautions one can achieve correct full range measurements even for multiway loudspeakers

My own purpose for ground plane is limited to the lower range.

http://www.mh-audio.nl/Acoustics/Groundplane.html

 

tuga

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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

Don't HD and IMD go hand in hand?
And whilst a recording of the "girl-with-banjo" type may not be particularly challenging, orchestral music reproduction will suffer. The fact that it was dismissed by Harman is puzzling to say the least, considering it's level of complexity and dynamic range...
 
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tuga

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What about a coax in a sphere like the Gradient 1.4:

gradient-14-1.jpg


Nieren-Abstrahl_Charakteristik.jpg

"The orange curve indicates the desired radiation behavior of the gradient 1.4 in the important vocal range. For the frequencies above and below this range, however, the radiation looks completely different: in the bass all-round radiating, in the mid-high range increasingly directional" (google translation)

 

voodooless

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"The orange curve indicates the desired radiation behavior of the gradient 1.4 in the important vocal range. For the frequencies above and below this range, however, the radiation looks completely different: in the bass all-round radiating, in the mid-high range increasingly directional" (google translation)
Varying directivity is exactly not what one would want, is it?
 
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tuga

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Varying directivity is exactly not what one would want, is it?

I don't know, are you asking for me personally or generally?
Most speakers are omni in the low-bass and sub-bass.

Is there consensus on whether it's better to have the sharp (off-axis) transition between omni and narrow-constant directivity of the 8c:

KteZOnp.jpg


Or a Kef-style more progressive increase in directivity:

uGoSwk3.jpg
 

fluid

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Linkwitz's design is a dipole and my question was around the OB bass module. Ofc, the upper part is going to need space as the those drivers are open baffle and have significant energy output from the back.
Dipole bass is good, but to go low it needs cone area, excursion or both. If any significant output below 50Hz is wanted or needed then subwoofers become necessary. It was my favourite part of the LX521 while I had them. Some space from walls is needed which tends to count them out for most on a practical level.
At the risk of repeating myself, am interested in the audible benefit. Lacking this, not interested at all in something superficial like making a prettier polar map or chasing other cool designs without knowing the problem they are trying to solve...

For example, if controlling bass directivity has the benefit of clearer bass and better room integration, then this seems like a good goal.
Perhaps you missed the link I posted before from kimmo here are some excerpts

"As we can see from measurements in the bathroom (with brick walls, concrete floor and ceramic tiles) and semi-open living space, leaking application is able to adapt to any room size/volume. Pressure below the lowest mode can be fully okay without level or tilt adjustment. In addition, mixed source is quite immune for source position. Those are clear advantages especially if owner does not prefer room EQ or multiple subwoofers or room is not dedicated for listening i.e. speakers cannot be anywhere ~ in the best places (vertically and horizontally) for bass performance with other source types".

"Axial modes exist also with mixed bass source so listening point should be selected carefully if rear side of the room is not diffusive or acoustically large. Reflections from solid flat rear wall (=behind the listener) can initiate quite massive dip to mid bass. Otherwise application is very flexible for almost any room size and typical speaker positions in living rooms which are difficult for monopoles and dipoles.

Ideal textbook cardioid is not very valuable. I prefer super-cardioid having lower total power to rear. Some...many resistance boxes are hyper-cardioids at midrange with only 6 dB attenuation to 180 deg. That probably needs some space on the back, but could create deeper sound stage (and higher DI) than ideal cardioid.

But if speakers can be in any ~ in the best places (close enough or far enough from front wall and corners) and also listening point can be optimized, there is not much need for cardioid bass. For example I can and have lived without, though possible locations for monopoles are limited. Dipoles would be in the middle of - everything which is no no for other family".

However, if improving the directivity above 5 kHz will be more audible, then would not spend time or money for better bass directivity. As I have not heard a kii 3 or the d&d 8c, am relying on others to articulate the benefits.
The last paragraph above spells out the reason to consider bass directivity. If you want to keep the cabinet to 10" woofers and don't want to add more amp channels the options for bass directivity shrink to very few.

A slightly smaller midrange would make for a more seamless transition between the DXT (or any other tweeter) if a custom waveguide is off the table and crossing it out to an 8" or similar woofer (or 2 or 4 ) would keep the midrange low excursion. Just having a line of woofers on the front like ctrl showed does help in room in a similar way to multiple subwoofers by spreading out the source. It's not as effective but it works and will tend to reduce the floor reflection notch. A driver on the back tends to dipole without the right filter in place to make it more cardioid.
 

tuga

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Dipole bass is good, but to go low it needs cone area, excursion or both. If any significant output below 50Hz is wanted or needed then subwoofers become necessary. It was my favourite part of the LX521 while I had them. Some space from walls is needed which tends to count them out for most on a practical level.

Dipoles are good at constant directivity but as @sarumbear said they are not suited to small UK sitting rooms.
Then there's multi-way horns but they are huge and extremelly expensive (so even less suited); and like dipoles they'll still need subs:

JQsgH2C.png
 

fluid

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Don't HD and IMD go hand in hand?
And whilst a recording of the "girl-with-banjo" type may not be particularly challenging, orchestral music reproduction will suffer. The fact that it was dismissed by Harman is puzzling to say the least, considering it's level of complexity and dynamic range...
I don't want to drag this thread way off course so if you want more than this it should be somewhere else.

Most distortion is 2nd or 3rd harmonic which despite popular opinion has been proven by many sources to not be very audible even in very large amounts, much more than almost any sensibly designed speaker would have. Higher order harmonic distortion and Intermodulation distortion are much more audible even in smaller amounts so minimizing them makes sense.

Alexander Voishvillo at Harman has done a lot of work on distortion and he does not seem to be of the opinion that it doesn't matter, but what matters is not what most people think.
 
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