Originally Posted by Cvetan1
Explain to me how the 7"Vifa M18 drivers outperform the LSi 5 1/4" drivers? I'm quit curious how you come to this conclusion?
This is a VERY complicated topic and I can't get into a full-blown discussion here. But I will give you one simple example of how these drivers differ.
You will notice that both speakers have an identical F3 (the point where the bass response falls off 3db on the low end). But the way they reach that point differs.
The 5 1/4" drivers used in the LSi9's require ports in order to extend the bass response to the speaker's F3 point. This is because the drivers themselves cannot play that low in a sealed enclosure.
Since the speakers will be used in some situations where rear porting may not be feasible, the ports were placed on the front of the speaker. While this is often done, it is far from ideal. In fact, you will rarely see it done with extremely high-quality speakers. The reason is simple.
If you think about it, what sound is coming out of the ports? It is the sound generated by the rear side of the speaker cone. As it is created, this sound is exactly 180-degrees out-of-phase with the sound coming from the front of the driver. If you were somehow able to combine both the sound generated on the front and rear of the driver, they would completely cancel each other out.
The sound generated by the rear side of the cone bounces around in the interior of the cabinet and eventually exits the port. Some frequencies take a more direct route than others based on their wavelengths and the internal dimensions of the cabinet.
At certain frequencies, the sound exiting the port will be in phase with the sound coming from the front of the drivers and will reinfoce it. Other frequencies will be 180-degrees out of phase and cancel it out. Most will be somewhere in between.
Even if the driver exhibited perfectly flat response (which no driver does) to begin with, it would no longer be flat once the sound eminating from the front of the driver combines with the sound exiting the ports. The result will be dips and peaks in the summed frequency response.
Keep in mind that the main reason front ports were required is because the driver used could not generate the required bass extension without them. If the ports had been on the rear of the cabinet, it would have been far less problematic. But that would have limited the speaker's use in certain applications and, thus, limited its marketing potential. In most (if not all) cases, the decision to use front ports is a marketing decision, not a speaker design decision.
When we set out to design the HTS series speakers, we too wanted a speaker that could be used in virtually any application (which was also why we designed three crossover options). So the first part of the design process was to locate a driver that could generate the desired bass response in a smaller sealed enclosure. This pointed us toward a 7" driver and, while it was more costly, the M18 seemed to be a perfect candidate. While not as detailed as the Seas Excel W18's use in our Veracity models, it can deliver deeper bass in a small sealed enclosure.
By selecting a driver well-suited to the task at hand, we were able to deliver the same F3, but totally avoid problems related to front porting.
While this is only one of many, many criteria used to evaluate drivers, it should provide at least a glimpse into the complexity of this aspect of speaker design. You can add cone materials, motor structure, frequency response, distortion and a long list of T/S parameters to the mix.
There have been a few very good books written on the topic. If you are truly interested, I would suggest getting your hands on one or more of them. They won't be easy to digest, but when you do, you will be well on your way to being able to evaluate speaker drivers.
I hope this helps.