Everything you always wanted to know about cardioids* (*but were afraid to ask)

[sarumbear]

The F205 has radiation control with acoustic ports and several internal chambers, with ports inside the cabinet. There is a rendering (picture below "Technology" section) which shows some of the internal construction, without damping materials.

The purpose of those internal chambers and ports and damping material is to shape the frequency response and delay of the sound emitted from the acoustic ports. This all works together in a rather complex way, that is only possible to see properly using simulation of the acoustic system.

The cabinet with the ports and internals is one part of the design - the choice of radiation pattern is also a part of the design process. A desired pattern is defined, and then the cabinet is optimized to create this pattern, by placement and size of acoustic ports, and tuning of the internal chambers.

I read it. Cool stuff.

However, I wouldn’t call your design a horn. An acoustic horn converts large pressure changes within a small area into a low pressure changes within a large displacement area. As far as I can see that’s not how your subwoofer works. Am I correct?

 

[Kvalsvoll]

I read it. Cool stuff.

However, I wouldn’t call your design a horn. An acoustic horn converts large pressure changes within a small area into a low pressure changes within a large displacement area. As far as I can see that’s not how your subwoofer works. Am I correct?

They generally have too small mouth radiation area for pattern control, so in that context, they are certainly not horns. But where do we set the limit - where does it stop being a horn - not many bass-horn designs that can be called a real horn, if the mouth must be large compared to the wavelength. But they do actually convert a large force/pressure into higher velocity/lower pressure - they act as an acoustic transformer - and that is what a horn is. Even the very small T6 does that, and compared to a typical ported design, the acoustic loading works across a much wider bandwidth - from 30Hz up to around 100Hz in the T6.

The acoustic ports for radiation control in what we call passive cardioid does not work like horn loading or like a typical reflex port - they do not provide acoustic loading, and they do not contribute to increase low frequency extension. In a typical bass port, the sound emitted from the port has a 180 degrees phase shift, so that the port output then sums in-phase with the sound radiated from the front of the cone. The ports in a cardioid emit sound that is in-phase with the sound emitted from the back of the driver - the sound inside the cabinet, so the port output is out-of-phase with the sound from the front of the cone. The sound is not totally cancelled, because the port output is at a different location - which creates a delay, and typically at a lower level. Off-axis and backwards, the timing between the port output and the cone output changes, so that the cancellation effect increases.

 

[sarumbear]

where does it stop being a horn - not many bass-horn designs that can be called a real horn, if the mouth must be large compared to the wavelength. But they do actually convert a large force/pressure into higher velocity/lower pressure - they act as an acoustic transformer - and that is what a horn is. Even the very small T6 does that, and compared to a typical ported design, the acoustic loading works across a much wider bandwidth - from 30Hz up to around 100Hz in the T6.

Your design certainly is an acoustic transformer but horn is just one type of acoustic transformer. As far as I can see yours does not achieve that with a horn. In a horn there is a tapered waveguide as the sound guide. As far as I can see (not much) you do not have that. I am also not sure if you actually increase efficiency as much as a horn will do.

Do please realise that I am talking about semantics here. You have a unique design. I congratulate you. I do have a question though: why are you so worried about the (low) loudness capacity of your speakers? What is stopping you to build larger versions?

 

[Kvalsvoll]

Your design certainly is an acoustic transformer but horn is just one type of acoustic transformer. As far as I can see yours does not achieve that with a horn. In a horn there is a tapered waveguide as the sound guide. As far as I can see (not much) you do not have that. I am also not sure if you actually increase efficiency as much as a horn will do.

Do please realise that I am talking about semantics here. You have a unique design. I congratulate you. I do have a question though: why are you so worried about the (low) loudness capacity of your speakers? What is stopping you to build larger versions?

They follow the same principles of physics as all speakers do - which means size, low frequency extension and efficiency follow a fixed relationship. For any given size, there is a limit for low freq and efficiency.

The narrow horn channel increases slightly in area, and it is long compared to wavelength, this is different from a typical ported box where the port is very short compared to wavelength, and acts like a pure acoustic mass.

It is capacity at the lowest frequencies that sets the limit for a bass-system, especially for movies. The acoustic loading makes it possible to achieve good low frequency output utilizing drivers with more powerful motor system and less moving mass, thus increasing output capacity at higher frequencies.

Once the required extension is in place, a larger bass-system can be created by stacking more units. A very large subwoofer is impractical - it is hopeless to handle, ship and place.

 

[sarumbear]

They follow the same principles of physics as all speakers do - which means size, low frequency extension and efficiency follow a fixed relationship. For any given size, there is a limit for low freq and efficiency.

On a pure horn, the standard efficiency relationship of Vb * f3^3, which is the fundamental formula of all electromagnetic drivers in an enclosure, doesn’t apply. I do however agree that the overall size and f3 still affect efficiency.

 

[Kvalsvoll]

On a pure horn, the standard efficiency relationship of Vb * f3^3, which is the fundamental formula of all electromagnetic drivers in an enclosure, doesn’t apply. I do however agree that the overall size and f3 still affect efficiency.

Yes, for horn the efficiency also depends on the design, still there will be a similar trade-off between size and low cut-off and efficiency.

But for a modern design, it is all about max output capacity - once, when a 20W amplifier was considered powerful, we have much more cheap and good power available, and drivers that can handle this power. Relevant for cardioid - or acoustic ports for pattern control - is that this principle also trades efficiency for better radiation pattern, but this does not matter in the end, because you just add more power and end up with sufficient capacity still.

But it is better with a larger radiating mouth area - it couples better. There is a difference in perceived sound from the smaller versions of my subwoofers to the larger ones - larger sounds more powerful.

 

[MikeFromNorway]

Just the thread I was looking for.
It seams to me like there is a trend of making Cardioid speakers latly. Kvasvoll, Sigberg audio (both from Norway), D&D are all active on the front. This might be a stupid queastion for you technically enabled guys. But still I wonder. What are the main differences between cadiod and dipols? expet the obvious designs.

I'm asking because I have followed Forsman and Likwittz speaker designs the last 20 years and am a happy owner of the D2-10s for the last 4 years. Rarly do I hear speakers comparable when it comes to ease of room integration, imaging, stage and depth. The only pitfall I encounted is the bass. Less then 1m from the backwall and its gone. I use Sonarworks for room correction and get good measurements from 27hz. The placement issue can be easily fixed with separate subs thought.

Forsman - legendariske høyttalere - med norsk patent

Forsman høyttalere har en lang historie i Norge, og er et lite stykke ingeniørkunst. Her kan du lese mer om disse legendariske høyttalerne!

www.forsman.no

Linkwitz Lab - Loudspeaker Design

Design and consultation in electro-acoustics. Fundamental concepts of sound reproduction in rooms. Detailed design information for DIY construction of a subwoofer and an open-baffle speaker with exceptional fidelity. Dipole loudspeaker design for true to the original sound reproduction with...

www.linkwitzlab.com

 

[sarumbear]

...the last 20 years and am a happy owner of the D2-10s for the last 4 years.

What make is that model D2-10s?

 

[MikeFromNorway]

As linked. Forsman.

 

[MikeFromNorway]

D2 Series

 

[D4C_20]

Hey guys, I was just curious - been trying to understand loudspeakers and room interactions a little better lately

As an example of how dipoles can give a smoother response due to their dispersion pattern interacting less (or in a more unique way?) compared to more traditional designs - which got me thinking...could it be fair to describe a cardioid design as basically being similar to a dipole, but that you're catching the rear wave?

Essentially, you're "catching" and dealing with the rear-circle of a dipole's figure-8 pattern, such that it's really only the forward part of it that's being sent out into the room?

Does that make sense to you guys?
(Not sure if I'm wording the pieces correctly here, but I feel like y'all catch what I'm trying to describe)