Sierra-1 NRC Measurements

I have had a few people ask us why the recent NRC measurements on our Sierra-1 do not look as flat as the measurements on our site. (http://www.soundstageav.com/onhifi/20070901.htm) There are a few reasons for this and I thought it would be a worthwhile thread and something that can be referenced to.

The two curves in question are actually quite close to each other. Attached is a picture overlaying our response curve on top of the response curve taken by the NRC. Our curve is green, the NRC curves are in black. It is important to note that the NRC graph shows on-axis, 15 degrees and 30 degrees off-axis. These off-axis graphs can be identified by the high-frequency roll-off. With my newfound Photoshop skills ;), I have precisely aligned the graphs.

In the range from 80Hz to 20 kHz, the NRC curve and our curve are within ± 0.5 dB, aside from a small peak at 800Hz that is 1.5dB higher then evidenced on our graph. That is remarkably close. The small 1.5dB difference is due to mic positioning. The NRC (where the measurement was taken) positioned the mic at tweeter level while our graphs are taken with the mic positioned precisely between the tweeter and woofer. It is important to note that most loudspeaker companies keep to a tolerance of ± 3dB (this is the audio industry standard.) Even SEAS themselves, a world renowned high-end tweeter manufacturer (who's tweeters we use exclusively) keep to a ± 3dB standard.

The closeness of these two graphs is a very good indication of just how tight our tolerances are. It would be highly unlikely that your non-Ascend left speaker matched your right speaker as closely as these curves match up :) and these were taken in different facilities using different equipment and using different Sierra-1. Our tolerances and QC procedures are the tightest in the industry.

I must also highlight that the NRC measurement does not include the output of the rear port, so that from 80Hz and lower, the NRC graph is not accurate (all you are looking at is the woofer output, no port). This is because the Sierra-1 is a rear ported loudspeaker and directly behind the speaker are 54" thick fiberglass foam wedges, designed to absorb all sound waves that hit them (the NRC is a true anechoic chamber).

The rear port of the speaker fires directly into these wedges, rather than firing towards the microphone, thus the output of the port is nearly fully absorbed. Where the rear port output begins to diminish and the front firing woofer takes over once again, this too is evidenced in the NRC response graph, where bass starts to increase in the 30-35Hz range. This is all clearly indicated on the impedance curve of the speaker where the impedance peak at 80Hz is where the port tube output begins and the woofer output begins to diminish, with the woofer output at its lowest point (port tube output is greatest) at the impedance saddle at 50Hz, and then woofer output takes over and port tube output is minimal at the second impedance peak at 30Hz. http://www.ascendacoustics.com/pages.../srm1meas.html

I have attached a picture of a speaker in an anechoic chamber to give you a visual representation of how a rear ported speaker would be "crippled" in an anechoic chamber (that guy is NOT me -- I don't even own a suit :p)

Hope you find this information useful!

Looks like a picture from a Si-Fi movie!

So... How low do the Sierras go, in a typical in-room situation rather than in that chamber? It sound like 35 hrz or so (which is all that many powered subwoofers give you, and kinda amazing when you think about it). Then again, I could be wrong about the frequency, it's just a guess based on some live familiarity with certain pipe-organ music I've been listening to.

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Originally Posted by robruffo

So... How low do the Sierras go, in a typical in-room situation rather than in that chamber? It sound like 35 hrz or so (which is all that many powered subwoofers give you, and kinda amazing when you think about it). Then again, I could be wrong about the frequency, it's just a guess based on some live familiarity with certain pipe-organ music I've been listening to.

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This is very room dependant, of course. I would say that in most rooms, one can expect clean output at 40Hz. Some of our customers have measured good output levels at even 35Hz and lower, but again, very room dependant.

Hi Dave,

Isn't the picture of the chamber from Mcintosh with one of their speakers??

Thanks,

Jim

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Originally Posted by buddhadas

Hi Dave,

Isn't the picture of the chamber from Mcintosh with one of their speakers??

Thanks,

Jim

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Hi Jim,

Hope all is well!

I can't remember where I pulled that pic from but it does indeed look like an older Mcintosh loudspeaker.

Here is a pic from the NRC (from SoundStage website)

http://www.soundstageav.com/images/r...cture_120w.jpg

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Originally Posted by davef

I must also highlight that the NRC measurement does not include the output of the rear port, so that from 80Hz and lower, the NRC graph is not accurate (all you are looking at is the woofer output, no port). This is because the Sierra-1 is a rear ported loudspeaker and directly behind the speaker are 54" thick fiberglass foam wedges, designed to absorb all sound waves that hit them (the NRC is a true anechoic chamber).

The rear port of the speaker fires directly into these wedges, rather than firing towards the microphone, thus the output of the port is nearly fully absorbed. Where the rear port output begins to diminish and the front firing woofer takes over once again, this too is evidenced in the NRC response graph, where bass starts to increase in the 30-35Hz range. This is all clearly indicated on the impedance curve of the speaker where the impedance peak at 80Hz is where the port tube output begins and the woofer output begins to diminish, with the woofer output at its lowest point (port tube output is greatest) at the impedance saddle at 50Hz, and then woofer output takes over and port tube output is minimal at the second impedance peak at 30Hz.

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I found this really interesting. I am not an Ascend owner (yet), and have a challenging installation issue. Ideally, I'd love to be able to wall-mount my main speakers. I've made the assumption that if a speaker is rear-ported, then wall-mounting isn't an option. However, reading these comments gave me a glimmer of hope.

Can I infer from the above comments that one can get away with wall-mounting a rear-ported speaker if I cross-over the sub at a relatively high frequency (say, 80-100Hz)? It would seem that maybe the port isn't doing anything above that frequency level. And would this logic extrapolate to other speakers (like the 170s and 340s)?

I'm not a speaker expert by any means, so I thought I'd ask...

Thanks in advance for any help!

(Feel free to move this if it doesn't belong in this thread...I'm not trying to take it too far off-topic.)

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Originally Posted by cynical2

Can I infer from the above comments that one can get away with wall-mounting a rear-ported speaker if I cross-over the sub at a relatively high frequency (say, 80-100Hz)? It would seem that maybe the port isn't doing anything above that frequency level. And would this logic extrapolate to other speakers (like the 170s and 340s)?

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Yes, absolutely. Wall mounting rear-ported speakers is not a problem, especially if you are high-passing them (setting a crossover etc.) at 80Hz or above. We have thousands of customers wall mounting our CBM-170 SE :D

By setting the speakers to "small", you are dramatically reducing the amount of low frequency information being sent to the speaker, thus dramatically reducing the output of the rear port. With an 80Hz crossover, the port will have little influence on the output of the speaker.

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Originally Posted by davef

Yes, absolutely. Wall mounting rear-ported speakers is not a problem, especially if you are high-passing them (setting a crossover etc.) at 80Hz or above. We have thousands of customers wall mounting our CBM-170 SE :D

By setting the speakers to "small", you are dramatically reducing the amount of low frequency information being sent to the speaker, thus dramatically reducing the output of the rear port. With an 80Hz crossover, the port will have little influence on the output of the speaker.

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Great news! Thanks, Dave!

baadman28 why are you going into every thread and posting the same thing???

There are invisible links in the posts....that's why. I will delete them all.

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Originally Posted by Madison

I could be wrong about the frequency, it's just a guess based on some live familiarity with certain pipe-organ music I've been listening to.

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Previous post was from 2008 so I, for one, am slightly confused by this post?

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Originally Posted by Mag_Neato

Previous post was from 2008 so I, for one, am slightly confused by this post?

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spammer trying to make the post look genuine...