Understanding Measurements (Off Axis Question) Comparing Speakers

[Cos]

After Swerd's helpful post on measurements and off axis, I have been going back on old reviews and resources on audioholics to better understand what the measurements mean and what to look for.

I was hoping for a little more help in understanding the measurements of why Speaker A will measure better than Speaker B. So I wanted to use the Triton 7 measurements against speaker B and if someone can explain which measures better and why?

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[Dennis Murphy]

I'm not sure there's much to choose between in the off-axis department. Ignoring the bass region, which may just reflect differing measurement techniques, both speakers have a fairly peaky response in the critical 2-5 kHz region in a + - 15 degree listening window, and that will probably be audible. The first graph has 10 dB vertical scaling, so the deviations are larger than they may appear. I don't think there's anything to be concluded about in-room performance other than both speakers may sound edgy. I always get uncomfortable when I read debates about the importance of off-axis response. It obviously figures into what we hear from delayed arrivals, but we don't know how much weight the ear assigns to differences in arrival times, particularly since they will be lower in amplitude. One of the speakers I sell has pretty much text-book roll-off to the sides. A much cheaper speaker in my line has the more customary flare in off-axis response at the crossover point, where the dome tweeter has much greater dispersion than the midwoofer. Yet when I compare them in instant volume-compensated A-B trials, I don't really hear a brighter sound in the lower treble. What I hear is dominated by differences in lower bass and extreme upper treble response, inherent driver quality, and depth of sound stage (which results mainly from an open-back midrange vs a close back). I'm not saying that off-axis performance isn't important--it's just that I don't think we know exactly how important it really is.

 

[Swerd]

I prepared an answer, but I see Dennis has already spoken. Dennis probably knows (and has forgotten) much more about speaker measurements and listening impressions than anything I've ever learned (mainly from him) to repeat .

Here's my longer answer (that says less) anyway:

It's always hard to compare frequency response (FR) curves when they were done with different measurement rigs (microphones, software, rooms, and people). If you see differences, were they due to the speakers or the measurement methods? That's why the many speaker measurements published by Sound Stage (done by the NRC) and by Stereophile are so useful. You can believe that their skill, experience, and standard methods allow comparison among different speakers.

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Reviews | Stereophile.com

Below 200 Hz, the NRC trace looks rather smooth, and the other trace (different speaker?) shows large peaks and valleys. When making measurements in normal rooms, the long wavelength bass reflects off of walls, floor and ceiling, and arrive at the microphone with a bit of delay compared to the sound coming directly from the speaker. Depending on the distance the reflected signals travel, these waves arrive at the microphone in or out of phase with the sound coming directly from the speaker. The direct and reflected sounds add or cancel, causing those large up and down excursions in the graph. Moving the speaker or microphone to different spots in the room will change the frequencies of the peaks and valleys.

At roughly 200 Hz and higher, as the wavelengths get shorter and shorter, this becomes much less of a problem. The NRC has a true anechoic room – little or no reflected sound. They measure the bass response (below ~200 Hz) separately from the rest of the audio frequency range response above ~200 Hz, and later splice the curves together. Stereophile does something similar. I’m don’t know what was done for the second graph you attached, but looking at the frequency response below 200 Hz, I’d guess it was measured in a room without any making corrections or splicing. So, ignore the apparent differences below ~200 Hz between those two FR graphs.

 

[Cos]

That was a measurement reported from speakers by audioholics.com the RBH 8300SE/R. What I was trying to discover is one substantially better than the other by looking at the graphs and if so, what on the graph would represent this.

http://www.audioholics.com/tower-speaker-reviews/rbh-8300ser/rbh8300-measurements

Given the fact that they're are so many discussions about what speaker measures better off axis, etc., I am trying to learn what to look for when I am doing my research.

I appreciate the information and comments, I am trying to become more educated on what I am looking at when everyone is posting graphs.

 

[GranteedEV]

It obviously figures into what we hear from delayed arrivals, but we don't know how much weight the ear assigns to differences in arrival times, particularly since they will be lower in amplitude. .

I think we both agree that the on-axis / listening window frequency response is paramount. The nature of peaks and dips - broad being more readily audible even at low amplitudes - is what I would focus on.

However as far as what you say in the quoted part - i don't think it would matter. That's because different rooms have different arrival times and amplitudes for reflected - and absorbed - sound.

So i say smooth off-axis response is important not because it "always" influences sound perception but precisely because we can't usefully predict how much it might. The best we can do is feel "less-at-risk of excessive room influence" when "edging towards" speakers with a smoothly tapering power response. The research definitely shows some degree of correlation to audibility.

Of course, the more neutral (generally properly treated) the room, the more even the amplitudes of reflected sound. The larger the room, the later the arrival. In both scenarios, you're going to have more direct sound arriving early. There's no consensus on how much reverberation is best for music (in stereo) or a method of predicting what a person's room constraints will be. I think by looking at off-axis response we can still make valuable educated guesses on what kind of speakers are appropriate for a given space, though.

 

[AcuDefTechGuy]

I like those off-axis graphs on Stereophile better than Soundstage or anywhere else. They may be easier to differentiate among the speakers.

 

[konajoe]

OK. I'm concerned about having a really bright, reflective room. I've been doing tons of reading. Some solutions include headphones (eliminates reflections), room treatments (low WAF), and having speakers very close to the seating position. These three options all increase the percentage of direct sound from the speakers, compared to reflected sound. Wouldn't 'beamy' speakers with poor dispersion also help?

I completely understand the idea that a speaker with the best attainable off-axis response would make the speakers sound like the musicians were right there in the room. But the fact is, some of us have rooms with crappy acoustics. So, if there was actually live music in the room, it would sound terrible.

 

[Swerd]

OK. I'm concerned about having a really bright, reflective room. I've been doing tons of reading. Some solutions include headphones (eliminates reflections), room treatments (low WAF), and having speakers very close to the seating position. These three options all increase the percentage of direct sound from the speakers, compared to reflected sound. Wouldn't 'beamy' speakers with poor dispersion also help?

I completely understand the idea that a speaker with the best attainable off-axis response would make the speakers sound like the musicians were right there in the room. But the fact is, some of us have rooms with crappy acoustics. So, if there was actually live music in the room, it would sound terrible.

Don't talk yourself into doing something you might later regret (getting 'beamy' speakers with poor dispersion) just to avoid a problem that might not be as bad as you think. In addition to that "ton of reading" you've done, re-read these statements:

I always get uncomfortable when I read debates about the importance of off-axis response. It obviously figures into what we hear from delayed arrivals, but we don't know how much weight the ear assigns to differences in arrival times, particularly since they will be lower in amplitude.

I'm not saying that off-axis performance isn't important--it's just that I don't think we know exactly how important it really is.

… So i say smooth off-axis response is important not because it "always" influences sound perception but precisely because we can't usefully predict how much it might. The best we can do is feel "less-at-risk of excessive room influence" when "edging towards" speakers with a smoothly tapering power response. The research definitely shows some degree of correlation to audibility.

 

[konajoe]

When a subjective, non measured speaker review says that a speaker 'benefitted from being toed-in, and pointed toward the listener', is that an indication that it wouldn't measure well off axis?

 

[Dennis Murphy]

When a subjective, non measured speaker review says that a speaker 'benefitted from being toed-in, and pointed toward the listener', is that an indication that it wouldn't measure well off axis?

Well, it could indicate that the dispersion is on the narrow side. It wouldn't necessarily mean the off-axis response was ragged. Or the reviewer could have imagined the whole thing. When you see a speaker pointing right at you, your ears and brain can play tricks. This is another area where a blind test is needed.

 

[konajoe]

Are there examples of speakers that people really like, but measure poorly off axis?

 

[PENG]

Are there examples of speakers that people really like, but measure poorly off axis?

B&W 802D for sure. Probably 802 diamond too because they are similar, but I have not heard those.