Drop off in high frequency

I decided to do some measurements of my own tonight and found out some good and bad information. The good news is that my room is almost dead flat from 20Hz up until over 10Khz (+/- 2 dbs). The problem is that at 13k (-8 DB) it starts to drop off and at 20k we are talking about -14 DB drop off from my 85 DB reference point. This was even after I maxed out the gain on the frequencies above 10k (manually correcting audyssey). I was wondering if anybody has any ideas to try to level out this void or correcting this issue?

First, what tool did you use to measure the frequency response?

But in general, all ML’s have a bit of a high-end roll-off. If they didn’t they’d be shrill. A line source speaker can really over-energize a small room with high-frequencies.

Actually, I believe one of the reasons so many people like ‘stealth tone control’ cables (that roll off highs due to capacitance) or tube pres and amps is that they all contribute to a softening of the highs. But that just my biased view

Also, if you are measuring a post-Audyssey corrected response, with the ‘normal’ Audyssey EQ in place (vs Audyssey ‘flat’), then you are ‘seeing’ the standard Audyssey target curve, which does feature a high-end roll off.

I’m not surprised that you have -14db total drop-off after 13Khz.

My system is also measures >10dB down at 15Khz and over 18dB down at 20Khz. Yet the balance is just fine.

If it weren’t for the room treatments everywhere dampening the resonances, I’d feel they might even be a bit bright (on Audyssey normal). On Audyssey ‘flat’, they’re noticeable brighter.

Also, are you using the ‘current’ source output of the Sunfire? If so, that might lead to that drop off as well. I’d recommend using the Voltage source, re-doing the Audyssey setup (including varying the height of the mic in at least two of the measurement positions to better capture the line-source pressure field.

I could go on but let’s get the answers to the above questions first.

Using the Auto-Equalize function on my Behringer equalizer boosted the 8k to 16kHz range, with the curve apex at 12.5kHz.
Since putting these diffusers in: http://www.martinloganowners.com/~tdacquis/forum/showthread.php?t=8793
I re-did the A-Eq which then boosted that same band section a little less than before and with a near flat profile.
However, I prefer the sound with the diffusers on the former Eq curve than with the latter. I haven't done the former curve with the new 8-16kHz profile to compare yet.
All I can suggest is to experiment with diffusion, though close to the source (speaker) rather than farther away where the variables can add up.
PS: Target eq curves were set at "flat"

JonFo said:

First, what tool did you use to measure the frequency response?

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Well, I did a 7 point Audyssey EQ and let the system do all the calibrations. Then, for kicks, I popped in a EQ cd (I believe the one burned off of real traps website) with test tones and took manual measurements with the Radio Shack SPL meter. The roll off started to occur after 10khz, but it now makes sense. I couldn’t imagine a 16k tone being at the same level, I could only listen for a few minutes before I would go crazy.

JonFo said:

My system is also measures >10dB down at 15Khz and over 18dB down at 20Khz. Yet the balance is just fine.

Click to expand...

Sweet, I for some reason though the reference point was flat from 20hz to 20khz. This is the happiest I have been with the sound in my room, I just wanted to see if this was normal. Like you said, “…the balance is just fine”. J

JonFo said:

Also, are you using the ‘current’ source output of the Sunfire? If so, that might lead to that drop off as well. I’d recommend using the Voltage source, re-doing the Audyssey setup (including varying the height of the mic in at least two of the measurement positions to better capture the line-source pressure field.

Click to expand...

I am using the current source to power the panels and the voltage source on the woofer. It really seemed to land the best of both worlds especially with the non-powered woofer box. Maybe now with the addition of the better subwoofer, I should go back to the voltage source with a higher crossover?

Thanks for all the responses.

tsmooth said:

Well, I did a 7 point Audyssey EQ and let the system do all the calibrations. Then, for kicks, I popped in a EQ cd (I believe the one burned off of real traps website) with test tones and took manual measurements with the Radio Shack SPL meter. The roll off started to occur after 10khz, but it now makes sense. I couldn’t imagine a 16k tone being at the same level, I could only listen for a few minutes before I would go crazy.

Click to expand...

The RadioShack SPL meter has itself a frequency response of 30Hz-10kHz.

It seems like I remember an article on audioxpress that put the Radioshack SPL meter as not being very flat above about 1khz. The other thing to be aware of is if you were using pink noise, which you should, there may be a weighting factor associated with them. C weighting rolls off on each extreme for instance.

Let me re-phrase that last part.

Pink noise has a constant power over its specified bandwidth. So if one is using 1/3 octave pink noise test tones the 1/3 octave from 25 to 31.5 hz has the same total power as the last 1/3 octave 16k to 20k even though the 16k to 20k slice has more bandwidth. This allows the SPL meter to give meaningful data since it's not frequency selective.

The A and C weighting on the Radioshack meter rolls of the ends of the audio band so a correction factor needs to be applied to the readings to get back to flat.

lhpcope said:

the Radioshack SPL meter as not being very flat above about 1khz.

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Yes, and the response is way down above 10 KHz, depending on which way it's pointed. Much more here:

Comparison of Ten Measuring Microphones

--Ethan

tsmooth said:

...

Sweet, I for some reason though the reference point was flat from 20hz to 20khz. This is the happiest I have been with the sound in my room, I just wanted to see if this was normal. Like you said, “…the balance is just fine”. J

Click to expand...

Yeah, the Audyssey target curve has a slight dip around 2.5Khz on purpose, then a gradual roll-off in the highs.

I looked for a graph, and realize I've not seen one published, so I'll do a screen cap from my Pro kit next time I have it out.

tsmooth said:

... I am using the current source to power the panels and the voltage source on the woofer. It really seemed to land the best of both worlds especially with the non-powered woofer box. Maybe now with the addition of the better subwoofer, I should go back to the voltage source with a higher crossover?

Click to expand...

Are you bi-amping as well?

Either way, use of the voltage source for the panel will give Audyssey less work, as it's going to be correcting the dip induced by the current sources resistance. The voltage source is also, ironically enough, able to delvier more actual current to your ESL due to lower resistance.

So as long as you use Audyssey, the best hookup is the cleaner one, Voltage source for the entire speaker.

As for crossover, leave it at around 80Hz to the sub. That will allow the ML's to do better in the mid-bass.