Sigberg Audio Manta (12" wideband cardioid active speakers) development thread

[sigbergaudio]

Looks like tweeter is giving up above 15khz?

Not at all, but they do require a bit of lift to be flat. As this is a prototype thread and early days, you will be subject to less than perfect graphs. In post #19 (immediately above yours), the response is -3dB at 20khz 15 degrees off-axis, which I wouldn't go so far as to call "giving up". An on-axis measurement of that tune would likely be pretty flat to 20khz. Note that these are both responses of a speaker that has yet to be fully tuned, and also indoors measurements done during preliminary tuning, so not very precise.

Our SBS.1 speakers (that use the same coax, and thus the same tweeter) have a flat response on-axis to 20khz, and are about 1.5-2dB down at the reference axis (15 degrees).

 

[Ra1zel]

Not at all, but they do require a bit of lift to be flat. As this is a prototype thread and early days, you will be subject to less than perfect graphs. In post #19 (immediately above yours), the response is -3dB at 20khz 15 degrees off-axis, which I wouldn't go so far as to call "giving up". An on-axis measurement of that tune would likely be pretty flat to 20khz. Note that these are both responses of a speaker that has yet to be fully tuned, and also indoors measurements done during preliminary tuning, so not very precise.

Our SBS.1 speakers (that use the same coax, and thus the same tweeter) have a flat response on-axis to 20khz, and are about 1.5-2dB down at the reference axis (15 degrees).

I see, but now I also wonder what would Manta.1 give me that SBS.1 + 2 of your subs would not. I guess simply matter of price.

 

[sigbergaudio]

I see, but now I also wonder what would Manta.1 give me that SBS.1 + 2 of your subs would not. I guess simply matter of price.

There's a list of features as well as some comparison to the SBS.1 in the initial post in this thread, but I'm happy to elaborate.

First of all the Mantas also require subwoofers, so they won't replace SBS.1 + subs on their own.

The most obvious difference is of course size. While the design goals and desired sound signature are similar across both speakers, the MANTA.1 is simply bigger. The cabinet of the MANTA.1 is more than three times the size of the SBS.1. With that comes a high power, high sensitivity (~96dB) 12" midbass driver, which means a substantial increase in mid bass punch, attack, capacity and ability to sound "big". It's now a 3-way design so the coax is now used as a pure midrange + tweeter. The amplifier power is also doubled from the SBS.1, meaning it can play even louder and hit harder. While we are happy to recommend using SBS.1 with a single subwoofer, with the MANTA.1 we recommend going with two to better match the capacity.

Apart from the raw increase in capacity, the MANTA.1 feature acoustic slots on the sides of the upper chamber. In the current prototype this results in a partial cardioid effect, which further improve vocal presence, stereo perspective and soundstage compared to the SBS.1. The exact design (and thus effect) of this feature has not been finalized at this point.

 

[sigbergaudio]

Prototype stands have arrived. 30x30mm stainless steel painted black. They both feel and look very solid and robust. Damping feet made of silicone rubber at the bottom. The stands are designed so that they give a ~5 degree tilt to the speaker.

Tweeter height is 96cm.

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[sigbergaudio]

After some tuning and experimenting with cabinet damping/stuffing, it's time to share a bit about the effect of the acoustics ports on the side of the cabinets. Since the coax and the 12" is in individual chambers, the effect is naturally limited to the midrange with the current design.


150 degrees off-axis: green with open ports, orange with closed
Effect of ports: ~3-4dB attenuation from 450-2500hz

180 degrees off-axis: green with open ports, orange with closed
Effect of ports: ~4-6dB attenuation from 500-1500hz

The wavelet view also shows the reduced energy pretty clearly. Here we also see somewhat reduced energy even in the lower frequencies (180 degrees ports closed/open):

Preliminary results:
Depending on the angle, the rear radiation (and consequently reflection from the wall behind the speakers) are reduced by 3-6dB from 450-2500hz. This has an obvious audible effect through clearer more distinct vocals, and a generally more open and cleaner soundstage, very noticable in more complex or muddy recordings that traditional speakers often struggle with. The fact that the speaker has a wider baffle (35cm) than many modern speakers also contributes.

Objectively speaking, I think this has potential to sound pretty awesome (it does already)..

 

[sigbergaudio]

I've tried to inspect the normalized polar plots from Erins reviews of 8C and Kii Threee. Not 100% precise but I've tried not to exaggerate. Both Kii and Dutch are obviously better at 250hz since the lower chamber in MANTA.1 isn't cardioid, but from 500hz and up it looks pretty darn good. Again the wider baffle probably helps as well.

 

[sigbergaudio]

Loudspeaker development in Norway..

 

[bigjacko]

Looking nice! What is happening at around 450 Hz at horizontal directivity? There seems to have a dip. Also why are you using three slots? Does it has any benefit or some effect?

 

[sigbergaudio]

Looking nice! What is happening at around 450 Hz at horizontal directivity? There seems to have a dip. Also why are you using three slots? Does it has any benefit or some effect?

As I'm currently measuring under less than ideal conditions, I have some reflection from the ground, so I'm EQing them out of the measurement. When moving off-axis that wreacks a bit havoc with the measurement. Should have removed it again at that point, but didn't at the time. So it's an artifact of the measurement not the actual response.

The form and number of slots affect the effect and response (how much is attenuated and at what frequencies), the reason for this initial design was partly to be able to experiment with different variations of it. The final design may look different.

 

[sigbergaudio]

Updated concept drawing for the next iteration of the cabinet:

 

[sigbergaudio]

Onwards with the next major iteration.

 

[sigbergaudio]

This might be interesting for some. There's been some discussion about the distortion / THD in Cardioid speakers. I did a compression test of the MANTA.1 in the first iteration (12" chamber still sealed) and in the second interation (cardioid / acoustic slots on both sides). The distortion more than doubled around 100hz, but otherwise stayed basically the same.

The 12" driver is pretty capable, so in absolute numbers it's pretty low even in the cardioid configuration.

 

[sigbergaudio]

With ports only in the upper chamber we saw a cardioid effect down to about 450-500hz. We now see a signifcant effect below 1khz and all the way down to 100hz. The slope is also pretty even across the entire frequency range despite being measure at 180 degrees (directly behind the speaker). The drop above 1khz is primarily due to the baffle.

This graph shows on-axis (green), 180 degrees with a traditional sealed cabinet (orange), and 180 degrees with ports in both the upper chamber (coax) and the lower chamber (12" midbass).

 

[sigbergaudio]

Third iteration cabinet design

 

[kma100]

What’s on each side of the tweeter?

 

[sigbergaudio]

What’s on each side of the tweeter?

Openings / cutouts in the baffle to trick the midrange into "seeing" a more narrow baffle, and thus better match the directivity/roll-off of the rest of the frequency range. I plan to measure the effect of this today if all goes well.

 

[bigjacko]

Nice, I am glad to see the cardioid goes down to the woofer. Can I ask did you cut the holes at the side with any simulation or calculation in mind, or just cut the holes first then worry about how to tune the port? How easy is to tune the damping if the hole is randomly cut, or the other way tune the hole if the damping is already in the box? Thank you very much for answering.

 

[sigbergaudio]

Nice, I am glad to see the cardioid goes down to the woofer. Can I ask did you cut the holes at the side with any simulation or calculation in mind, or just cut the holes first then worry about how to tune the port? How easy is to tune the damping if the hole is randomly cut, or the other way tune the hole if the damping is already in the box? Thank you very much for answering.

I don't think you can tune your way out of the wrong position/size of the hole. On the other hand I can say that while the position / size / number of holes matter, it's not like either it works perfectly or it doesn't work at all. So you can get a reasonable result without everything being perfect.

I did not cut randomly, but I was prepared to experiment. It's hard to calculate exactly how this works.

 

[sigbergaudio]

So what do those holes in the baffle do? They alter and improve the dispersion characteristics from around 800hz and way up in the high frequency area. How? The coax driver "sees" a more narrow baffle, which is now suddenly 185mm as opposed to 350mm.

Please ignore irregularities in the frequency response here, this is measured under less than optimal conditions (reflections from the ground and nearby objects). It's the dispersion characteristics which is the point, not the frequency response as such.

Notice how 30 and 60 degrees off-axis no longer crosses the on-axis response at 2khz, and the off-axis response now tracks the on-axis response better all the way from 1-8khz as opposed to with the closed / traditional baffle.

It sounded damn good to begin with, but the difference is clearly audible as an even more balanced, effortless and open midrange as a result of less off-axis energy in this area and reduced early reflections.

My objective assessment is that these speakers already sound incredibly good!

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[diyhobby]

Is your solution somewhat similar to Seas KingRoy Kit or any fundamental differences besides the woofer size