Questions About Ascend Speaker Measurements

[theophile]

...So if I calculated this correctly I guess that this is not problem. I just need to get an amplifier that can cleanly put out 250 W to 300 W peaks.

Back to my original question. If our amplifier can cleanly put out 300 W peaks, is the output from the speaker still clean at those 300 Watt peaks (Note that a 105 dB peak will be very close to needing 300 Watts at 4m away.)? Or would we be hearing distortion or compression when the speaker is driven with that amount of power?

NB,

You are in the right church, right pew!!

A good amp capable of clean 300 watts\channel (from 6 to 8 ohms output) will meet your peak HT audio realism goals! I see no problem with the S2's (barring any severe room nulls or response voids) maintaining their response integrity with 105db musical peaks. On the other hand, Your Ears may start distorting (becoming fatigued\ringing) due to excessive high noise (music, sound, volume) with long term listening (105db safe "continuous" unprotected sound exposure is under 15 minutes-as per OSHA)?!

Ted

[N Boros]

Ted,

I do not at all plan to listen to 105dB on average. I am only talking about peaks at a fraction of a second. Per OSHA 85 dB on average with 105 dB peaks is supposedly safe for up to 8 hours per day. The recording engineers for movies that aren't deaf in their older age give some weight this these figures. My plan to make sure that I can cleanly play at 85 dB on average with 105 dB peaks because that is the absolute loudest I would ever listen to a movie. Usually I might be at -15 or -20 dB under 85 dB average volume, but every now and then we might crank things up and I want to be sure that my equipment is safe in doing so.

I'm hoping that Dave might be able to let me know that if we push the Sierra 2 close to the 300 W for peaks that if the peaks are clean in terms of no distortion or compression going on there. I'm still trying to understand what "unclipped peaks" mean.

[davef]

One small correction on the sensitivity though. Since this is a nominal 6 ohm speaker it is actually 1.33 Watts to produce 87 dB at 1 m away from the speaker.

Incorrect, minimum impedance is not nominal impedance. The minimum impedance of the Sierra-2 is ~6.3 - ~6.4 ohms. This meets IEC impedance specifications of being a nominal 8 ohm impedance speaker.

It is a bit more complicated than this as one must / should also look at the speaker's reactance at its minimum impedances and in the case of the Sierra-2, reactance is mild - making it an exceptionally easy nominal 8 ohm load.

Back to my original question. If our amplifier can cleanly put out 300 W peaks, is the output from the speaker still clean at those 300 Watt peaks (Note that a 105 dB peak will be very close to needing 300 Watts at 4m away.)? Or would we be hearing distortion or compression when the speaker is driven with that amount of power?

Nick, the problem here is that you are asking for a definitive answer to a question that simply can not be definitively answered. It is basically the same as asking if the car I am buying, which is rated at 30 mpg highway, will I also get 30 mpg when I am driving it?

There is nearly an impossible number of variables here.

First off, amplifier power ratings are determined using purely resistive loads. Speakers present a reactive load to an amplifier - and how that amplifier will react to the complex impedance of a specific is unknown, as every model speaker presents its own unique load. An amplifier might be "clean" at 300 watts into a static 8 ohm load (I am not sure what your definition of "clean" is) - but this same amp may very well start to clip under a reactive load, even at well under rated power - or produce distortion that the speaker in question does not handle well.

As far as hearing distortion or compression, it is entirely unknown at what percentage of distortion is typically audible with human hearing. There are also many different types of distortions - some more audible than others.

I believe, theoretically, what you are asking is if at an amplifier's peak power delivery of 300 watts, how different will the output of a speaker be compared to the source?

Assuming the source is bandwidth limited pink noise (limited to the real world capabilities of the speaker), and the speaker is a purely resistive 8 ohm load, and the amp is rated at 300 watts peak at 8 ohms, and the speaker is rated at 300 watts peak (and a peak is defined by a typical 1.414 crest factor over a max of 5ms) - the speaker should "cleanly" reproduce this peak.

But what is defined as clean? Also, music and home theater sources are not bandwidth limited pink noise. Hit any ported speaker with a frequency below port tune, and the power handling of that speaker will drop considerably (as will the reactance presented to the amplifier). The converse is also true -- high frequency switching noise of class D amps is typically not a problem for any dome tweeter as they can't reproduce it and it is just dissipated as heat in the voice coil - but true ribbon tweeters are different and will try to reproduce it, and this can be problematic as well.

I hope you see my point. The only way to answer your question is to actually match your amp with the speakers in question, combined with an appropriate source signal and test - or simply just listen for yourself and if you hear distortion or mechanical distress, turn the volume down.

We have had no issues reaching 105dB peaks with a pair Sierra-2 crossed to a sub at 80Hz at ~11ft with a well designed 150 watt class A/B amplifier.

And just to add to the complexity of this, Ted's post (which is very good) does not factor in variances in room / boundary gain. We are overly conservative with our in-room sensitivity specification - real world scenarios would typically add 3-5dB to our anechoic sensitivity spec - and this will vary considerably regarding different placements within that room.

Hope this makes sense

[sludgeogre]

This has quickly turned into a great thread! Lots of information here.

I have to say that with 300 watts behind my towers, they will absolutely terrify you with how crazy loud they can get. When I first got them and was getting used to them, I kept finding scenes in movies with clipping and I could hear it. I thought something was wrong with the speakers or setup at first, but it only happened on certain scenes, so it turned out to be the movie tracks themselves and not the speakers. Play that same movie on a less resolving speaker and you don't hear any clipping at all.

The Sierras will effortlessly reproduce whatever you throw at them, be it clean or dirty or anything in between, so you have to be careful with confusing things that you're hearing with equipment specs. I thought I was providing a clean signal all the time, but it turned out that Hollywood isn't always as careful as they should be. Just keep this in mind when you start playing your music really loud and you hear things that you don't think you should be. If your gear is operating as it should and is capable of doing what you're asking, the problems you hear are from the source material and you're just hearing it the way it actually exists for the first time.

[N Boros]

Dave and Ted,

Thanks for the replies! This has been very helpful in understanding the limitations of measurements and specs in some cases. The fact that I didn't look as carefully as I should have and thought that the minimal impedance was the nominal impedance is actually helpful though, after thinking about it a bit. These frequencies with the lowest impedance present the most difficult challenge to the amplifier. So if I can just about hit the reference volume peaks at my seat with that impedance, then it is likely that it should be no problem for the rest of the frequencies.

Your gas mileage example gives a great analogy to help understand what is going on. It is funny. I drive an older Honda Civic that according to the EPA testing standards should get 30 mpg for city and 40 mpg for highway. At my previous house I had about a 50/50 mixture of city and highway driving and usually I would get around 35 mpg. Now, I have a very very short commute to work and just about everywhere else I drive to is a similar short distance. Now I am only getting between 25 and 30 mpg. At first I was upset and thinking something might be wrong with my car. But, after thinking about it a bit I realized that I wasn't driving under the conditions that the car was driven in where the EPA tested it under. This is exactly what some of the measurements for the Sierra 2 mean. They can be a good for guidelines to get us in the ballpark of where we want to be. But, likely they are not going to perfectly tell us how the speaker is going to perform in my particular room. There are simply too many variables to know for sure. It does sound promising that by the theoretical calculations I can hit the peaks that I would like and from your experience in your rooms you have hit 105 dB peaks with only a good 150 Watt amp. So it is likely that I should at least get close to being able to do so as well. Thanks again!