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360ｰ speaker users: flat pink noise response?

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Posted on January 14, 2017 at 19:38:58
dave789
Audiophile

Posts: 559
Joined: September 21, 2001
 If you use 360 degree radiating high-end speaker (MBL Radialstrahler, German-Physiks DDD, etc.), do you let your system exhibit flat RTA response on pink noise signal at your listening position?

Or do you let the curve slope down toward 20kHz? If so, how much down and from what frequency?

 

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RE: 360ﾂｰ speaker users: flat pink noise response?, posted on January 16, 2017 at 12:29:06
AJ
Audiophile

Posts: 532
Joined: February 24, 2001
 I'm very interested in the response to this question.

I have 180 deg radiating Beveridge Electrostatics.

Thanks

 

RE: 360ﾂｰ speaker users: flat pink noise response?, posted on January 16, 2017 at 12:56:28
DrChaos
Audiophile

Posts: 2063
Location: San Diego
Joined: July 13, 2009
 Is there a reason to suppose that the proper FR at listening position is different for an omni versus a conventional speaker?

I would assume without further information that the preferred FR is from humans and should be the same, and therefore downward sloping.

I would use the Harman curve or something close to it.

I don't have measurements, but hearing MBL 101 in a large room at a show, I didn't think they were particularly bright so I would guess the FR measured in that way at listening position would also be downsloping correctly.

 

RE: 360ﾂｰ speaker users: flat pink noise response?, posted on January 24, 2017 at 08:27:14
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 I've owned Planars and the Obelisk from Shahinian, as well and messed a lot with Bose 901's in various setups and rooms. An Omni always provides an "on-axis" response independent of the orientation of the speaker (at least horizontally). In my opinion i get the best sound with a flat response on the intial arrival - however if you are playing steady pink noise, the pressure you get at the microphone in a somewhat reverberant room will have a reverberant component that roles off with frequency and a direct component that is usually louder. in the higher frequencies (say above 5kHz) most rooms with have very little reflective energy - so you can set the pink noise response flat above 5kHz and be pretty much assured that you are measuring the initial arrival.
In the Presence range (1-5kHz) yo can find a lot of reflected energy in a room - so the continuous pink noise level should drop 2-3 dB in this range. Below 1KHz you will find room geometry based reflections for reinforcement or cancellation - so here it is important to average several microphone positions to find an Average level to match up to that presence range level.
For the room modes frequencies (150-300Hz and Down depending on room size) - loudspeaker placement and sub integration with Bass management needs to be used. That is complicated and independent of the directivity of the loudspeaker - but is important to be smooth for playback of music.

Sometimes this leads to a slightly valley like response for a pink noise target. Note, The Shahinians were pretty much spot on out of the box! Only a little bass EQ used in a 17 x 12 room - speakers 42 inches our from the short wall.

FYI I use precision measurement instrumentation with a free field microphone to measure loudspeaker response. Note that many measurement microphones are not free field - though a 1/4 inch omni "Random" capsule is pretty good to 8kHz

Full disclosure: I work for Bruel & Kjaer and using accurate instrumentation is not a problem.




"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: 360ﾃつｰ speaker users: flat pink noise response?, posted on January 24, 2017 at 09:52:39
Inmate51
 "a reverberant component that roles off with frequency"

"I work for Bruel & Kjaer"...

Two things:

A real-time continuous pink noise source has useful aspects for analyzing the soundfield in a room, and outdoors. But, in a home living room, it doesn't tell us much about the important aspects of what we hear. A swept sine wave tells us much more. A "chirp", aka TEF/ETF, tells us even more. The IRIS system tells us yet more, since it contains directional information.

So, except for outdoor systems, a pink noise source is fairly crude at analyzing the soundfield.

Secondly, since you work for a noise/sound/vibration equipment manufacturer, and I don't mean to denegrate either B&K or you, you really should use the right word: It's "rolls", not "roles". This kind of incorrect word usage blows a big hole in your credibility. It's akin to saying "base" instead of "bass".

:)

 

RE: 360ﾃδづつｰ speaker users: flat pink noise response?, posted on January 24, 2017 at 11:43:21
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 No worries, I'll roll with the punches.

Of course, a processing technique (there all all kinds) that allows you to separate Direct and reflected arrivals are much better than continuous pink noise that the OP asked the question about. My experience in the field - and even ancient old B&K application notes say you can do a fine job with pink noise...

Check out the old real time 1/3 octave analyzer on the cover (the world's first digital filter RTA) and used for the measurements


"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

RE: 360ﾃδεつづδづつｰ speaker users: flat pink noise response?, posted on January 24, 2017 at 16:24:23
Inmate51
 Hahahahaha! Glad you're a good sport!

Excellent call on the Application Note!

(You did see my "Caption this pic" post, right?)

:)

 

RE: 360ﾂｰ speaker users: flat pink noise response?, posted on January 24, 2017 at 20:36:46
BigguyinATL
Manufacturer

Posts: 3475
Joined: April 10, 2002
 Caption this is great free publicity !

FYI that old measurement setup on the cover would have set you back about $40K in 1974 dollars!

I was graduating high school that year - selling Wi-Fi that summer for Cal Stereo in LA


"The hardest thing of all is to find a black cat in a dark room, especially if there is no cat" - Confucius

 

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