Jay QSC K10 Tips applied to the K12?

brokenvail

brokenvail

Fractal Fanatic
After reading Jay's sticky I wondered if any one has every looked into if the K12 has the same design flaw? I know he said it was for the K10 only but that doesn't mean the K12 was even looked at. He said these finding only happened becaue he was looking at Scot's K10.
 
I don't know if I would call it a design flaw so much as a design choice. Anytime a HF and LF driver are mounted separately on a flat surface (most FR cabinets) certain phenomena come into play that cause undesirable and uncorrectable anomalies. Different designers use various tricks to move the anomalies around and mask them in different ways, but they are always there. Many companies are good at pushing the limits of this design. Many of these type of cabinet sound quite good. They just don't sound anywhere near as good (to me) as a properly designed co-axial cabinet. The problem with co-axial is that it is significantly more difficult to design a proper system. The required information/knowledge base is somewhat arcane and as most industry people have not heard or don't care about the difference, we are mostly stuck with an inferior design paradigm.

Regardless of the quality of any given FRFR cabinet here is where we get boned trying to use the Axe FRFR with non-coax:
A friend of mine played through my rig the other night. I got to listen from an audience position about twenty feet away. The tone was much better to me than what I hear sitting close to the monitor. I experienced a phenomena Jay has explained to me that I believe causes lots of Axer users to struggle with FRFR systems. The closer you place yourself to a non-coax FR speaker the more you will be affected by your ears' position relative to the LF and HF drivers. Moving around and turning your head will radically alter the way the frequencies reach your ears. This is not subtle. The problem gets worse if you turn any given cabinet sideways and use it like a wedge. Now the HF and LF drivers are side by side on a horizontal plane. One ear is tracking more HF driver and one ear is tracking more LF driver. if you are standing close to the cabinet things can really get weird and Axe patches, which we subject to highly critical listening tests, can all of a sudden sound not so good. If you close-monitor or close-backline yourself with a non-coax FRFR speaker this phenomena is not correctable and (to me) very noticeable and highly undesirable.

Anyways...
Jay only tested a K10. Does the K12 have the same HF issue? Don't know. Regardless, the issue is subtle. If you aren't somewhat happy with the K12 as it is built the slight adjustment of moving the HF notch won't make things that much different. The over emphasized low end issue of the K10 is very easy to hear and and extremely noticeable. If you are not happy with your K12 try putting the PEQ last in your chain as in the K10 instructions and see if you like the overall presentation better. Try moving the shelf around a bit in terms of frequency and dB and listen to what it does. In the case of the K10 adjusting the lows improved the presentation of the mids and highs.
 
Last edited:
vestapol said:
FWIW read what QSC had to say about it here:
Click to expand...
Yeah. The miracle of stonewalling and censorship. I sent Bob Lee an email with all the pertinent points spelled out and quotes from various posts. I suggested that he might be working with insufficient data from QSC design staff. No reply. I forwarded the email to QSC tech support. No reply. Jay posted on the QSC forum and clearly spelled the issue out and QSC deleted the reply and left the information they want you to have.

Having said all that, don't pick on QSC. They are using a common trick that allows them to get the best test results from one position. Lots of FR speakers by various manufacturers are designed this way. In relation to common industry practice it is not "wrong". It is most definitely wrong-headed. They are either doing this in lemming mode because they don't get it or it's just a marketing decision, or both.

I have owned a K12. I have been using a K10 recently with decent results. QSC K series is good equipment. It is not great equipment.
 
Last edited:
I just picked up a brand new K10; however I'm not sure if this mod is still applicable. Are they still shipping with the reversed polarity? Thanks for any input.
 
Considering that QSC denies that the way they did it was wrong, it's a good bet that they're still doing it the same way.
 
Well... They are not denying it. But, they are definitely giving a test to make sure that they are in phase. I'll need to figure out how to do this.

-Nate

QSC Audio Rep said:
Do a frequency response sweep on the loudspeaker. If there's a noticeable notch in the 1.5 to 2 kHz range, then one of the drivers is out of polarity with the other. If there is no notch, then they are in polarity with each other.
Click to expand...
 
nateb said:
Well... They are not denying it. But, they are definitely giving a test to make sure that they are in phase. I'll need to figure out how to do this.
-Nate
Click to expand...

The statement by the QSC rep is meaningless. The proposed test proves nothing about phase. Do a search on this forum and you'll find Jay Mitchell's explanation as to why. All K10s are factory wired with the HF driver out of phase to the LF driver.
 
burningyen said:
Considering that QSC denies that the way they did it was wrong, it's a good bet that they're still doing it the same way.
Click to expand...
They are not doing it wrong. The phase reversal is an old trick used by many manufacturers to achieve optimal test results from one listening position without regard to what is happening in all the other listening positions.

By correcting the phase of the K10 you will get slightly worse performance from one listening position but noticeably better performance from a bunch of others.
 
I have the equipment to make this same measurement on my K10's. If they are really all out of phase, that is bad for imaging (phasing of harmonics) in the azimuth plane. The simpler fix is to just flip the phase of the woofer, that brings the impulse response back and imaging would be better (given the complications of getting to the HF driver leads). I (personnaly) have never really seen/heard absolute phase be a factor (High end stereo experiments).

Any thoughts, Scott or Jay?
 
I would suspect directly in front (azimuth and elevation)... at all other positions, the path difference adds to the time delay/phase (more in elevation).

The goal is to have all harmonics of the fundamental to be maintained in relative phase (even when off axis). I thought the Kseries had a DSP based low pass/high pass with delay correction for time alignment of the HF driver. There is likely more going on here... I have not yet measured my K10s.. They sound good to me at present, but may check and modify a pair to see if this yeilds a better sound (as well as time/phase alignment)..


Perfect world would be a sphere that expands/contracts in sync with the input source... they have done this with HF drivers (modulated plasma) in the past... lots of ozone though.. This is why coaxial drivers have some advantage (but with other difficulties).
 
You must log in or register to reply here.
Back
Top Bottom