The Anatomy of the Acapella Violon - shocking find


For quite a while now I have been having trouble with the bass on my Acapella High Violon Suboktav 2001. With the help of a friend, we have dismantled this speaker and studied the internal construction and measured the crossover points. I am hoping that my findings will be helpful to all of you Acapella owners.

The bass problem is this: bass can not keep up with the speed of the midrange and top end. On some recordings, the bottom end becomes disconnected - you can hear music from the midrange and the top, followed by the bass response a microsecond later. Furthermore, the bass is poorly controlled and flabby. From my other Audiogon threads, you can see that I have been wondering whether the damping factor of my Cary CAD-211AE amps is sufficient to control the wild bottom end, and whether a solid state amp will cure this problem.

The current iteration of the Violon is Mk. IV. I am not sure what a "Violon 2001" is, I am guessing either Mk. I or Mk. II. Acapella's own website does not reveal any secrets, all it says is that the High version of the Violon has an additional driver inside.

Anyway, this is what we found.

PLASMA TWEETER: 4th order high pass crossover (24dB/oct) at 5000Hz. Measures very flat all the way to the limit of measuring equipment. Incidentally, Acapella marks the recommended tweeter level with a pencil mark on the tweeter volume pot. At the minimum recommended range, the tweeter comes in 12dB ABOVE the reference SPL. I had to wind the tweeter almost all the way down to get a flat response.

MIDRANGE HORN: First order high pass crossover (6dB/oct) at 450Hz, with a very gentle taper between 3dB/oct - 6dB/oct from 5000Hz and up. Goes all the way up to 10,000Hz. The shallowness of the low pass section of the band pass crossover makes me suspect that it is relying driver rolloff.

This is a surprisingly wide band of frequencies (4 1/2 octaves) to ask a horn to handle. As you know, horns are tuned to work over a fairly narrow frequency range and the response drops off at either extreme of this range. Wavelengths which are too long for the horn do not couple with the horn. Wavelengths which are too short will bounce around chaotically. That is only the theory however, because the horn measures very flat between 450Hz - 5kHz.

The integration between the tweeter and midrange horn is very good.

BASS UNIT. As advertised, there are two 10" drivers in the unit, and both appear to be SEAS drivers. The external driver is run through a passive crossover from the binding posts, with a low-pass first order crossover at 450Hz.

And now, the surprise. The internal driver is run directly from the binding post with no crossover in between. In other words, it is run full range, relying on driver rolloff only.

I can think of no advantages for a setup like this, only disadvantages.

Firstly, the drivers are wired in parallel. This will drop the impedance, making it difficult to drive them with valve amps (Acapella supposedly voice the speaker with the Einstein OTL).

Secondly, a configuration like this will result in destructive interference between the two drivers, ESPECIALLY if the crossover introduces phase problems in one of the woofers. Given the other woofer is crossover-less, any difference in phase will definitely cause interference.

Thirdly, running a woofer full range will cause cone breakup at the top, which will muddy the lower midrange (exactly what I have been hearing).

Possible solutions:
- wire both drivers to the crossover, maybe in serial configuration to increase the input impedance (Zin),
- disconnect and remove the internal driver, i.e. convert the speaker from the "High Suboktav" version to normal Violon,
- remove the passive crossover entirely and use a preamp-level crossover (active crossover).

Now, I am no speaker designer. I am just an enthusiast struggling to understand these things. But this just makes no sense to me. I am hoping that someone with more experience will be able to explain why Acapella made these design choices, and what you think of the possible solutions.
amfibius

Showing 2 responses by aaudio_imports


Dear Amfibius,

Before you start modifying your speakers I would suggest trying other amplifiers.

Consider this, Acapella has been building speakers for over 30 years, and the Violon's have been around for at least 10 years. Many pair of Violon's have been sold around the world, and I don't know of any owners that have thought about modifying their speakers. Unless you are an expert speaker manufacturer and can completely understand the design theory then you are probably going to make things worse.

As with many of the higher end speakers on the market, the designer of Acapella speakers has many proprietary things inside these speakers that can't be understood by you or me. They have tuned the speaker to perform a certain way. If we try to change this then we end up with something else that the designer didn't intend.

I used to own Cary amplifiers and they don't drive all speakers well. My experience with Cary amps is that they are better suited to 2 way designs with simple crossovers, which are an easy load. And even then they still have that Cary sound. Which on the right speaker's is very pleasing, but on the wrong speaker is a disaster.

Something that's important to know about Acapella speakers in general is that they need very good to excellent electronics, otherwise you won't get their true performance. Remember that you own one of the few true reference speakers in the world, so now you need to use equal electronics because these speakers will basically tell you what your system is made of.

Think of your High Violon's as a perfect measuring device for testing electronics, cables ect... At this point the problem is not the speaker, but the system you are driving the speaker with. The speaker is simply showing you what your system sounds like. Many other speakers may sound great with your current system, but that's because they are not capable of this level of fidelity.

Best Regards, Brian

Dear Amfibius,

I have dealers driving the Acapella speakers with Einstein, FM Acoustics, Jadis, Audio Note and Lindemann. These are all among some of the finest electronics that can bring out the qualities of Acapella speakers.

As with any high end speakers, you have to find the right synergy with your amplifier. I remember speaking with many Avantgard owners who went though several amplifiers until they found the right one. Many were just to noisy for these high efficiency speakers, and others made these speakers sound hard and forward.

I do suggest that you borrow other amplifiers from your dealer before trying to modify your speakers. If this doesn't take you into the right direction you would be better off selling your speakers rather than modifying them since this will kill the resale value.

I did speaker with Acapella and they did tell me that no upgrades will be offered from the previous Violon model to the latest MK4.

Dear Johnk,

Something that is unique with Acapella Horn speakers is that they have the performance of a horn midrange, without sounding like a horn. This is one of the reasons why they are not super high efficient like other horn speakers.

Best Regards, Brian