Crossover frequency bass - midrange Reference, Kappa

[Fleime]

Hello,

Still planning on restoring a Reference 60 when something caught my attention concerning the crossover frequency between the woofer(s) and the midrange driver, compared to e.g. Reference 50 and Kappa 6.1i.

The Reference 60 has double 8 inch IMG woofers and a 5 inch IMG midrange driver. The crossover frequency between these is set at 250 Hz.

For comparison, the Reference 50 has one 8 inch IMG woofer, same midrange driver. The crossover frequency between these is set at 300 Hz. The Kappa 6.1i has the same (as far as I can tell) woofer and the crossover frequency with the polydome is set at 500 Hz.

Although I have done some research and have some ideas, I am still not certain why the crossover frequency for the Reference 60 is set at 250 Hz, the lowest compared the those mentioned above. Can someone clarify this for me?

Also, doesn't this crossover frequency 'demand' too much from the midrange driver by having it produce frequencies down to 250 Hz (and up to 4000 Hz)?

Thanks.

 

[swechsler]

In a well designed speaker, crossover frequencies are chosen first by their best theoretical values based on the performance and graphs of the drivers. But the specs for drivers (woofers in particular, but realistically any driver that isn't fully sealed from the factory) change when the driver is installed in a cabinet, and the original crossover values will need to be modified based on that. The different models you've mentioned have different cabinet sizes. Presumably it's a combination of listening and instrumented testing. Also, the Reference series is a sealed design while the Kappas are ported, so I wouldn't assume that they use the same woofer (I originally thought these models corresponded to the North American Reference 1-6, but the Ref 6 is a single woofer design, so the Reference 10-60 models may be a unique series not sold in NA).

ETA: Infinity is notorious for the complex crossovers in their higher end models. While the Reference Series is more a midrange system (with the SM on the lower end and the Greek-lettered models on the higher end), it wouldn't surprise me to learn that the crossovers in these speakers were not a simple 2nd order design.

 

[Fleime]

Ah, my dear swechsler, thank you for enlightening me. I had not considered these other factors and now feel slightly embarrassed. My knowledge is not big enough to understand the exact consequences of different cabinet sizes and the presence, or lack thereof, of ports, and perhaps other factors as well, but I can understand these can make a difference.

And I stand corrected about assuming the Kappa 6.1i and the Reference 60 using the same woofer, according to their technical manuals they are different (or at least have different part numbers).

Indeed the Reference 10-60 models were meant for the European (and perhaps elsewhere) market. The Reference Six and the Reference 60 only have the amount of drivers in common, but the former is a 4-way system en the latter a 3-way system with double woofers. The Reference 50 more resembles the Reference Five, both being 3-wat systems, but with a different woofer size. I do not know if there is a difference in build quality between the 'European' and the 'North-American' References.

My knowledge on crossover designs is small, e.g. I do not know what a 2nd order design means. If necessary I can educate myself on (the basics) of crossover designs. I am still planning on posting a picture of the crossover in my other thread concerning the Reference 60, however I have gotten a hold of the technical manual and will add it here.

 

[swechsler]

This article gives a (somewhat complicated) explanation of some different crossover types.

Just out of curiosity, do your speakers say where they were manufactured? Some of Infinity's speakers (for example, the Delta series, the last Infinities with EMITs, which was apparently sold around the world) were made in Denmark, but the majority of models sold in the US were made there as well. The styling of the Reference 10-60 is very similar to that of the Reference 1-6, but even the ones that are similar, such as the models 5 and 50, are obviously not identical; compare, for example, the grill peg positions.

 

[StimpyWan]

The dome mids, in the 6.1's probably couldn't respond as low as the cone mids, so that's most likely the reason it cuts off at 500Hz. With the Ref 60 using dual woofers, a lower crossover point would most likely be used to roll off the woofers sooner, so as to not cause any bass bloat, or vocal chestiness, through that range. The Ref 50's single woofer could respond higher, without any upper band beaming as well. It's easier to cross it higher, without introducing any sonic issues.

 

[Fleime]

@swechsler Thank you for the reference on crossover types. The speakers say made in the USA, with the circuit board made in Mexico. I have added some pictures in my other thread.

@StimpyWan Thank you for further adding to my understanding of the workings / choices behind these speaker designs.

For that matter, any ideas on why they have chosen for double woofers? I can understand the cost reducing effect in crossover design of the Reference 60 (3-way) versus the Reference Six (4-way), but is there really an audio benefit over one woofer? Or is it perhaps also for show?

 

[swechsler]

A double woofer setup increases the amount of air the bass portion of the system can move. In a properly designed speaker, it can theoretically go lower than a single woofer design, or have a higher maximum SPL, without some of the disadvantages of larger woofers. Infinity has used multiple woofers in many different speakers over the years.