[DMurphy]

The board has been a little quiet of late, so I don't think one semi-off-topic thread will hurt.  This relates to work I do at the Federal Trade Commission.  We currently are reviewing our Amplifier Power Rating Rule to see whether any changes need to be made in the way the rule applies to multichannel amplifiers in home theater.  I don't want to get into a discussion of the "right" power rating system because that really would muck up the forum.  But I would like to get a better feel for how the use of a separate powered subwoofer affects the power demands placed on the main home theater receiver (amplifier).  In my system, I set all of my front and back speakers to small, and play all the bass through my sub, crossing at 60-80 Hz, depending on the mood I'm in and the phase of the moon.  That should place a little less stress on the main amps. I have an old Outlaw receiver without a lot of options.  How else can bass be managed in current systems?  Suppose you're running HT3's as the L & R, the monster center (the size of Nebraska), and HT1's in the rear.  What are all the options for bass management?  If I want the fronts to cross at 40 Hz (assuming my receiver has that option), what setting would I use?  Do I still select small for all the speakers?  Is there any reason, and any way to bring the sub in at 40 Hz, and still run the HT3's and center full range?  Or, stated a little differently, is the signal going to the sub in 5.1 or 7.1 unique, in the sense that it's not just the bass component of whatever is going to the fronts and centera?  Would I want the fronts and center to run full range if they can go low enough?  Or do I want to cross in any event, the only question being at what frequency?   Hope you can figure out what I'm asking.   Thanks.

[randybessinger]

I do not have it anymore, but the Lexicon MC12 had one of the better bass managment systems, that I have seen.  On that preamp, you could select different crossover points for the mains, center, side surrounds and rear surrounds.  Many recievers/preamps can do that now, but you could also select large and select a crossover point.  As I understand it, the .1 would go to the sub but the other speakers bass below the crossover points would go to the lowest of your 5 or 7 speakers.  So if you had say HT3's and a large center, you could route bass below the higher frequency cutoffs to say the mains and then everything below that cutoff went to the sub.  You could also duplicate the bass in the .1 channel to the mains  as well as going to the sub.  Many of the preamps and receivers can do that these days (although I recall that Lexicon did not recommend it).  I think the idea would be that you could have a sub and mains that play very low and get better bass distribution in the room.

Some of the new auto setups also determine the crossover frequency and the size the speaker should be set-up, but you see many complaints that they do not do a good job setting them as large when they are bass limited and vice-versa.  Hope that helps.

[DMurphy]

Thanks.  If you choose to duplicate the subwoofer signal in the mains and center, how is balancing accomplished.  What band-limited pink noise signal would you use?  On my Outlaw, you can balance the sub using its dedicated pink noise signal, but I don't see how you could get proper bass balance even if a receiver could play a bass signal through all the speakers.  You could set the output equally for each speaker, but wouldn't that sum to way more bass than the sub would provide alone?  In any event, I take it you're saying the only advantage to running the mains full range would be evening out bass modes.  You wouldn't be hearing any bass signals that you wouldn't hear if only the sub were used?

[satfrat]

With my Sunfire, I also have both options available, that is playing the sub while having the other speakers play small or large and I just don't like it myself. I play all my Lorelei's on small and plug the rear ports. I have my sub set at 80hz and even tho I can go as low as 40hz, I find by plugging up the ports and having the bass set at 80hz sounds the best for a full uninterupted sound. As for balancing out thew difference between playing the speakers either large or small, that's a good question. I'm sure there's a volume difference that's not being taken account for when balancing out the sub with the speakers on small but then playing the speakers at large. But just combining the large speaker setting with the sub on doesn't sound good to my ears. It's a preference decision for sure. I like a full range sound while at large but i think playing small allow for more power & emphasis to the midrange and a much clearer bass in my system. It's this combination of the two that's the reason for my decision go go small with the sub cutting in at 80hz.

I don't think you'll ind an answer to your power question here, that's better discovered in a lab i think. I actually just posted to support your dicision to go samll with a sub. I recently heard a Salk HT-3 w/Salk center system with 2 subs set at 80hz and this system simply rocked. The center simply disappeared as did the subs (front & rear) The multisound system, an Anthem processor that's set at All Stereo sounded better to me than just having the HT-3 playing stereo. BTW, I was totally impressed with the HT-3 and shocked at the incredible fullness of the sound stage when played at high volume. My friend does have cathedral ceilings which mades me wonder how overpowering this setup would be in a simular room with 7' ceilings(like my room). The HT-3 is one of the best loudspeakers I've ever hear for clarity at high volumes.


Cheers,
Robin

[DMurphy]

I'm glad you liked the HT3's at full cry.  That's the benefit of using low-distortion drivers with lots of power handling.  Of course, it does take a bit of power to make them cry full.  But there's no shortage of powerful amps.  Anyhow, we'll be asking for public comment on the actual difference in power demands with and without a sub, hopefully based on lab measurements.  But right now I'm just trying to get a handle on what kind of bass management is available in current receivers, and whether most receivers would be used in a configuration that would actually relieve the main amps from handling deep bass. 

[avahifi]

Hi Dennis, the following is an observation I made in another thread here that got overlooked.  I would like your comments if possible.

>>>Hey Jim, regarding amplifier measured frequency response and what we can hear, you may be overlooking one issue that most do.

Namely, although a human cannot hear much about 20K Hz, your equipment can!  Case in point, a few watts of 100K amp output will fry most tweeters.  Could you hear the 100K?  No.  Could your tweeters "hear it"?  Yes, and they melted.  Could you hear the result?  Sure, no tweeters any more.

The point is that it is critically important to investigate the performance of the electronics broad band to make sure that out of hearing range non-linearities are not disturbing equipment downstream and causing distortions you can indeed hear (or even smell in the case of the fried tweeters).

I would suggest to speaker designers that they design a top end low pass filter into their speaker system crossover to protect them from misbehaving drive electronics.  I suspect that in a double blind A-B test the speaker with the amplifier protection built in will "sound better" in most cases.

It would also suggest this might be a better experiment to try than debating the sound of the terminal jumpers.

Regards,

Frank Van Alstine<<<

Frank

[DMurphy]

I guess I would have to approach that question both as an economist and a crossover designer.  The threshold question is whether the actual incidence of tweeter failures due to miscreant 100K amp signals is great enough to justify insuring every speaker by adding the necessary components.  I suspect the expected value of the injury is not worth the cost of insurance, but I don't know for sure.  (For Jim's ribbons, the post-failure fix would be pretty cheap--a new ribbon element plus shipping and installation,  and a number of popular dome tweeters offer replacement voice coils).  From a design standpoint, the fix could be tricky.  100 k is only a smidge more than two octaves away from 20k, and you wouldn't want the protective circuitry to affect the response around 20k, or the phase relationships further down.  Most ribbons have an elevated response beginning around 15-18k.  I usually end up adding a little series inductor or a parallel capacitor to smooth that out.  This will add a little over 12 dB electrical attenuation at 100k.  I don't know whether that would be enough to provide useful protection or not.  If so, then a number of Jim's speakers already have some protection.  If the tweeter output is flat or starting to decline at 20 k, then I'm not sure what I would do in the way of topology.  I guess you would try and get a fairly steep slope beginning around 30k.  I would have to model that with a specific tweeter to tell whether it's feasible, and I don't think my software goes above 20k.

[fsimms]

The HT-3 is one of the best loudspeakers I've ever hear for clarity at high volumes

Interesting point.  I have a HT1 with a sub.   Even though I cross it over to my sub at 80Hz it does sound strained at very high volumes.  Does the 400Hz crossover in the HT3 allow it to play much louder cleanly?  Does the above crossover to the sub allow the HT3's woofer to play much louder?

If so, then would that be a good reason to use a sub with HT3's?

[randybessinger]

Thanks.  If you choose to duplicate the subwoofer signal in the mains and center, how is balancing accomplished.  What band-limited pink noise signal would you use?  On my Outlaw, you can balance the sub using its dedicated pink noise signal, but I don't see how you could get proper bass balance even if a receiver could play a bass signal through all the speakers.  You could set the output equally for each speaker, but wouldn't that sum to way more bass than the sub would provide alone?  In any event, I take it you're saying the only advantage to running the mains full range would be evening out bass modes.  You wouldn't be hearing any bass signals that you wouldn't hear if only the sub were used?

Dennis I never use that mode that duplicates the bass so I am not sure how it is applied.  Yes, on the bass mode thing as you are not be hearing any bass signals that the sub wouldn't play already.  Some receivers allow "strero bass" through the subs.  The lexicon did and so does the new Yamaha flagship reciever.  I know that is a controversial subject and I am not qualifed to address it, but Dr. Greisinger (spelling) founder of Lexicon has a whtie paper on it somewhere (I think) on Lexicon's site.  I woulld assume that if there is such a thing as stereo bass and you don't have two subs, running a speaker (like the HT3) full range would be advantageous  I assume this would affect the amp power needed.  One thing I would suggest Dennis, is to post your query on the amp ratings on the Theory section of the AVS.  There is some very experienced and knowledgeable people over there and the forum would be a good place to get some responses.

[avahifi]

Dennis, my concern is out of band garbage causing speaker nonlinearities long before actual failure such as coil saturation, etc. That is the reason I suggest a top end low pass filter.  I know the garbage I see on the scope while making torture tests of various amps, preamps and DACs.  I suspect speakers (and the music) would fare better if protected and I don't think that has ever been tried.

Regards,

Frank

[DMurphy]

That could be.  I suspect, however, that it would be much more efficient and practical to implement the filter actively before the speaker level. 

[BrianM]

Meaning, at the amplifier level?

[DMurphy]

Well, preamp. 

[idiotec]

This question reminds me why I decided to put my focus back into 2-channel audio.   

[BrianM]

Well, preamp. 

Isn't Frank's point that a lot of people don't do this?

[DMurphy]

If by "a lot of people" you mean preamp and reciever designers, then I think that's the point.  My point is that it probably isn't efficient for speaker designers to try and fix what could be implemented much more cheaply and effectively in active circuitry. 

[avahifi]

But Dennis, speaker builders have to live with whatever electronics are used ahead of the speaker, for better or for worse.

It seems to me that it would make sense to at least try the experiment of a "protection from nasty amplifier" low pass circuit in the crossover design.

The speaker designer likely does not know just how nasty amplifiers and preamps with out of hearing range signals can be.  The amplifier specs do not test for this.  An example, those doing CD players without switching frequency filters. They exist, and some people seem to actually love lots of 44K Hz and more into their systems.  Geeze.

My suggesting is try it, see how much difference it might actually make with more amplifiers than you would expect without looking at all the bad things that are really happening.

I would suggest that 1 percent distortion, for example, should more properly be considered as 100 percent distortion 1 percent of the time. But that is another story.

Please give this some serious thought.  It should not be all that difficult or costly to design into speaker crossover unless I am way off base.

What if it gave the speaker builder a huge market advantage by designing in the filters?  I think this is an idea worth testing.  I have seen too much high frequency garbage on the test bench, and I know it is going right into many many speakers.  The source can be cartridge mistracking, DAC, preamp, and or amplifiers doing ugly things, and even RFI pickup anywhere ahead of the speakers. The audio world is full of out of band garbage, protection from it at the speaker level seems pretty sensible.

Regards,

Frank Van Alstine

[konut]

This may be a brain fart, but didn't Empire Speakers of the '50s and '60s use high and low pass filters at 20 and 20,000hz?