Example of a "Banana Curve"

[withTarragon]

I hear folks talk about the "Banana Curve" shape (frequency response) when a cabinet / port is set up and tuned.
However, after searching I have not been able to find an example (image / graph /sketch) of a prototypical banana curve.
Could someone point me to an example.

Thanks,
-Tom

[Mr. Widget]

I haven't heard that term myself, but maybe you are talking about a high Qtc box tuning? This will give you an elevated bottom end and depending on the performance of the woofer could give you a banana shape?


Here is a graph I grabbed from the internet. Typically we want a Qtc in the 0.707 - 1.0 range.


Widget

.

[Robh3606]

Figure .5- .71 on Widgets curves is about right. It's how Greg typically tunes his boxes. The anechoic -6 point seems high but with room gain or EQ it fills in nicely. An example the K2 9900 has a -6@ 48Hz


Rob:)

[Mr. Widget]

Figure .5- .71 on Widgets curves is about right. It's how Greg typically tunes his boxes. The anechoic -6 point seems high but with room gain or EQ it fills in nicely. An example the K2 9900 has a -6@ 48Hz


Rob:)Yeah, I think anything below 0.707 is on the anemic side... but it is a personal preference thing.

0.707 is the theoretical ideal.


Widget

[Robh3606]

Hello Widget

Don't you remember all the hub bub about the Everest having -6 @ 45Hz?? Same thing banana curve, did you find the Everest bass shy?? If you put them in a small room or close to room boundaries you don't end up an overpowering bass rise. I am using a banana curve on my DIY's but have a 6dB bump at 25Hz to flatten things out. So objectively I agree but it really is room dependent. I like the idea because it gives you more flexibility.

Rob :)

[Ian Mackenzie]

The term came about in Giskard’s posts describing the LF response shape of the newer soa systems.

The enclosure is tuned low and the drivers have a relatively low Q so the response tapers off at a pre determined point. The curve is akin to a banana. This is quite different to a maximally for response tuning like the TL QT3 tuning.

On paper these curves are calculated in free field conditions. In other words well away from any boundaries.

The effect of placing the loudspeaker in a room on the floor but away from any walls is associated with half space where mild low frequency loading occurs.

Placement near a wall boundary is associated with quarter space loading.

The idea of the banana tuning as Rob said is to self equalise and extend the low frequency response without undue humps in the 50-150 hertz region unlike a maximally flat tuning.

The thing is if you have always lived with loudspeakers with maximally flat tuning you may prefer them. This is a point of contention. Fortunately modern HT amps and processors have LF room EQ that assist in resolving the complex issues associated with room tuning.

In the case of the Everest’s Greg has recommended a mild LF shelf boost of 4 dB when triamping. This is because the passive crossover chokes influence the Q of the drivers and lift the low end response. Without the LF shelf they may sound a bit too dry.

I personally found the bass response of the DD67000 very natural and linear in a large room in triamp mode. The difference from conventional full passive operation is not subtle.

I think Bo ended up equalising his 4345s to be relatively flat and subjectively it’s excellent.

It’s a case by case thing and what one person experiences in one room can to quite different from another as the impact of a room on the response below 150 hertz can be unpredictable. And you also have personal taste which also comes into it. For example those in Hong Kong have different preferences to those in Japan and those in North America. So patience is a virtue in getting a system to sound just right in your own environment.

If and when things return to normal l will get back into these sorts of discussions on a practical level.

[grumpy]

:banana:


The term came about in Giskard’s posts describing the LF response shape of the newer soa systems.

The enclosure is tuned low and the drivers have a relatively low Q so the response tapers off at a pre determined point. The curve is akin to a banana. This is quite different to a maximally for response tuning like the TL QT3 tuning.

On paper these curves are calculated in free field conditions. In other words well away from any boundaries.

The effect of placing the loudspeaker in a room on the floor but away from any walls is associated with half space where mild low frequency loading occurs.

Placement near a wall boundary is associated with quarter space loading.

The idea of the banana tuning as Rob said is to self equalise and extend the low frequency response without undue humps in the 50-150 hertz region unlike a maximally flat tuning.

The thing is if you have always lived with loudspeakers with maximally flat tuning you may prefer them. This is a point of contention. Fortunately modern HT amps and processors have LF room EQ that assist in resolving the complex issues associated with room tuning.

In the case of the Everest’s Greg has recommended a mild LF shelf boost of 4 dB when triamping. This is because the passive crossover chokes influence the Q of the drivers and lift the low end response. Without the LF shelf they may sound a bit too dry.

I personally found the bass response of the DD67000 very natural and linear in a large room in triamp mode. The difference from conventional full passive operation is not subtle.

I think Bo ended up equalising his 4345s to be relatively flat and and subjectively it’s excellent.

It’s a case by case thing and what one person experiences in one room can to quite different from another as the impact of a room on the response below 150 hertz can be unpredictable. And you also have personal taste which also comes into it. For example those in Hong Kong have different preferences to those in Japan and those in North America. So patience is a virtue in getting a system to sound just right in your own environment.

If and when things return to normal l will get back into these sorts of discussions on a practical level.

[Mr. Widget]

Hello Widget

Don't you remember all the hub bub about the Everest having -6 @ 45Hz?? Same thing banana curve, did you find the Everest bass shy?? If you put them in a small room or close to room boundaries you don't end up an overpowering bass rise. I am using a banana curve on my DIY's but have a 6dB bump at 25Hz to flatten things out. So objectively I agree but it really is room dependent. I like the idea because it gives you more flexibility.

Rob :)Actually I don't remember any specific details on that discussion, but yes the E2 with twin 15" woofers is rather limited in the deep bass department. Actually from having experience installing these in a few rooms, I must say that it is not an easy speaker to deploy. The lower bass is what it is, but the upper bass is really hard to get right and can easily get a bit thick. I wonder if this isn't a function of the physical layout. I guess GT discovered this too and that is why the jumpers give you some ability to tune them.

Back to the original topic, I gather from these posts the banana curve in question is a downward curve and not the upward curve I originally thought.


Widget

[Ian Mackenzie]

I think any dual side side woofer system is sensitive due to the proximity of the outer woofers to side walls compared to the inner woofers when trying to get them in the optimal position for best stereo image. So you can get two different boundary loading effects.

While not directly on topic here Greg explained that he originally wanted the E2 to be a full Triamp enable system but marketing weren’t interested. Even so Greg incorporated additional binding post holes in the rear plate for triamping. The way the Triamp voltage drives are setup gives a far more coherent response below 300 hertz compared to the passive system and it’s noticeable subjectively. Biamp is a nice but Triamp mode is a real step up. We also introduced some room resonance EQ on Greg’s recommendation with some prototype analogue active crossovers. This clear up the sense of congestion in the lower midrange.

When things settle down some further evaluations will be arranged. Hopefully in the new year after 20/01/2021. We have have plans to provide the active analogue crossover with a measurement package which will support users to more readily achieve better and more consistent results.