technical queries

[filmguy]

hi guys

am a newbie and dont have much technical knowledge. i had a few technical queries i hope u'll cld help me with :

1) i'm planning to buy a sub and hv been told that bigger is better but i was wondering that if one calibrates the sub to ones fronts properly so that they blend together and are seamless then wont the extra capacity be wasted. for eg., if in calibration my bookshelves matches a 12" sub at its, say, 40% volume level then isnt the remaining 60% of the sub amp going wasted whereas if i went for the 8" or 10" sub where they were matched at the 60-75% level i'd theoretically get the same spl output. is this correct?

2)if i crossover to my subs at say 80hz then what is the use of a bigger bookshelf or a floorstander that goes down to 35-45 hz as from 80hz and below all the work will anyways be done by the sub. why waste the money on larger speakers if they are anyways going to do the work of a satellite ?

3)if my a/v reciever has a fixed crossover i've read that its better to use the subs high level connections and connect my fronts to the subs high level output. but in this case i'm using the sub's amp to drive my fronts and cldnt this sound possibly be inferior to my main a/v reciever?

thanx for the knowledge.

[Indy_Cornwall]

1) If you have to drive you amp in your smaller sub to 75% to get the same output as a larger sub at 40%, the smaller sub will be more susceptible to noise, etc. The harder you have to drive an amp, the more noise, etc. which leads to a "muddy" sound.

2) Most AVR receivers have settings for speaker sizes. Set to "large" and the full spectrum of sound will be set to the speakers, independent of the low frequency cross-over.

3) I have never heard that but I would not do it.

[DrWho]

1. A larger subwoofer driver means less frequency modulation distortion (aka doppler distortion). To create the same SPL (volume), a smaller driver needs to move back and forth further than a larger driver. This moving back and forth causes the same doppler effect that you might have heard when a train or ambulance goes by: the pitch changes as the source of the sound changes from moving towards you to moving away from you. You get the same effect with speakers as well, which is why many people around here are fans of hornloaded speakers (keeping it simple, horns reduce FMD).

Another advantage to using a larger subwoofer is that it can play lower. There is a general rule in audio that when you reduce size, you have to give up either efficiency or extension. Lower efficiency means you'll need a more powerful amp to drive the speaker as well as a driver capable of handling the extra power. Typically, manufactures find the thermal limits of the driver and then limit the extension to accomodate the size that they're trying to accomplish. This means that larger drivers generally can play lower notes. Extension down to 20Hz tends to be considered optimal.

I understand your analogy regarding the difference in volume levels, but the original idea leading to your conclusions isn't the best way to approach things. First off, every speaker has a sensitivity rating, which is defined as how loud the speaker is in dB when it's recieving 1 watt, measured at a distance of 1m. If you subwoofer driver is rated at 97dB sensitivity, then your sub will be playing at 97dB when your subwoofer amp is putting out 1 watt! Most every speaker system is running with under 5 watts of power. The reason the speakers can handle so much extra power is to be able to handle the peaks that can require hundreds of watts for a very short period of time (ie, explosions).

There is also the issue of power compression, but I'll save that and some other factors for later for the sake of brevity.

2. For starters, crossovers aren't brick walls where everything above the frequency goes one way and everything below goes the other way. The crossover frequency is defined as the point where both drivers are reduced to -3dB (which in theory results in a 0dB change because two drivers playing the same note results in a doubling of output. 3dB = a doubling of power). There is a gradual slope where the driver's response is attenuated more the further from the crossover point you get. Most recievers use a 12dB/octave slope. If you set it to 80Hz then your mains are going to be dropped -3dB at 80Hz. At 40Hz (one octave lower), the mains will be at -15dB. At about 35Hz, the mains will be at -20dB...a difference of 20dB is generally accepted as the minimum difference for masking to take effect (masking is the inability to hear something because other sounds are 20dB louder. In this case, the subwoofer will be 20dB louder at 35Hz). Basically your speakers need to be able to play flat down to 35Hz where the crossover will put them to -20dB in order to accomplish a perfect crossover transition. The other alternative is to use a steeper slope: A 24dB/octave slope means that your mains would need to play a bit below 45Hz with an 80Hz crossover. 36dB/octave would be like 60Hz.

All that said, 20dB is a bit extreme and you can probably get away with 10dB if you've never heard the difference.

3. Running your sub off the high level output from your reciever is only a feasible option when listening in stereo. If you plan on listening to anything with surround sound, then you will want to hook your sub to the LFE output on your reciever. When watching movies, there are two ways your sub is being used. First off, there is a dedicated LFE channel (the ".1" in "5.1") that gets sent only to the subwoofer. The LFE will not get sent to the sub unless it is connected to the LFE output of yoru reciever. Secondly, there is the "bass management" features on your reciever that allow you to route low frequency information that would otherwise be sent to the satellites. The human ear has a hard time localizing sounds below 80Hz so sending low frequency information to the sub is a trick that can be done to put less strain on the other speakers that weren't designed to play that low.

I hope you find this helpful and feel free to ask more questions. You've scratched the surface of a lot of different topics that are all very much interrelated, which makes it hard to give short and sweet answers.

[johnyholiday]

#2 if your avr has dsp your sub might not be running all the time ,ie true stereo vs another setting,ie dolby dts movie setting or a dsp setting creating a concert hall or jazz club,same goes,for center channel speaker, you will noitce it is not on all the time, vs the avr dsp settings

[sivadselim]

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On 3/6/2005 12:50:41 AM DrWho wrote:

3. Running your sub off the high level output from your reciever is only a feasible option when listening in stereo. If you plan on listening to anything with surround sound, then you will want to hook your sub to the LFE output on your reciever. When watching movies, there are two ways your sub is being used. First off, there is a dedicated LFE channel (the ".1" in "5.1") that gets sent only to the subwoofer. The LFE will not get sent to the sub unless it is connected to the LFE output of yoru reciever. Secondly, there is the "bass management" features on your reciever that allow you to route low frequency information that would otherwise be sent to the satellites. The human ear has a hard time localizing sounds below 80Hz so sending low frequency information to the sub is a trick that can be done to put less strain on the other speakers that weren't designed to play that low.

I hope you find this helpful and feel free to ask more questions. You've scratched the surface of a lot of different topics that are all very much interrelated, which makes it hard to give short and sweet answers.

----------------

that is just not true. if a receiver is setup with NO SUB, then the LFE will definitely be sent to the front speaker high level AND pre-amp level outputs (if you have them). so if you connect a sub to the high level front speaker outputs in this instance, you WILL definitely get LFE into it (or is that out of it?) and most likely into your front speakers, depending upon what crossover setting you use on the sub. the bass, INCLUDING THE LFE when present, will be "smeared" across and shared by both the front speakers and the sub. in some instances, this IS a solution for people who have a receiver with a fixed xover that they feel is at too high a setting. you then use the subwoofer's variable crossover to adjust to a lower setting. the receiver will, of course, "force" you to set your fronts to LARGE in a NO SUB setup. as far as any speakers set to SMALL are concerned in this instance, such as your center and/or your surrounds, the receiver's fixed crossover will still come into play and will control which frequencies are sent where. again, any bass that would normally be destined for those speakers that are set to SMALL, and that is below the receiver's xover, will be "smeared" across and shared by the front speakers and the subwoofer.

[sivadselim]

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On 3/5/2005 12:14:21 PM filmguy wrote:

hi guys

am a newbie and dont have much technical knowledge. i had a few technical queries i hope u'll cld help me with :

1) i'm planning to buy a sub and hv been told that bigger is better but i was wondering that if one calibrates the sub to ones fronts properly so that they blend together and are seamless then wont the extra capacity be wasted. for eg., if in calibration my bookshelves matches a 12" sub at its, say, 40% volume level then isnt the remaining 60% of the sub amp going wasted whereas if i went for the 8" or 10" sub where they were matched at the 60-75% level i'd theoretically get the same spl output. is this correct?

2)if i crossover to my subs at say 80hz then what is the use of a bigger bookshelf or a floorstander that goes down to 35-45 hz as from 80hz and below all the work will anyways be done by the sub. why waste the money on larger speakers if they are anyways going to do the work of a satellite ?

3)if my a/v reciever has a fixed crossover i've read that its better to use the subs high level connections and connect my fronts to the subs high level output. but in this case i'm using the sub's amp to drive my fronts and cldnt this sound possibly be inferior to my main a/v reciever?

thanx for the knowledge.

----------------

1. think of the defensive lineman who takes ballet lessons to improve his FINESSE.

2. this point can draw a good argument. i assume you mean if you run your fronts as SMALL. i'm sorta in your camp, and run bookshelves, however many people DO run large floorstanders as SMALL with an 80Hz crossover with great success. running the speakers as SMALL is less taxing on your receiver's amp(s) and relieves your speakers' woofers from having to produce the low-end stuff, thereby allowing them to more accurately reproduce those frequencies above the crossover setting. again, FINESSE.

3. when you connect a sub that way the sub's amp does NOT drive the front speakers, only the sub. the receiver's power is still "passed" through the sub and that's what powers the front speakers.

[DrWho]

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On 3/6/2005 3:19:33 AM sivadselim wrote:

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On 3/6/2005 12:50:41 AM DrWho wrote:

3. Running your sub off the high level output from your reciever is only a feasible option when listening in stereo. If you plan on listening to anything with surround sound, then you will want to hook your sub to the LFE output on your reciever. When watching movies, there are two ways your sub is being used. First off, there is a dedicated LFE channel (the ".1" in "5.1") that gets sent only to the subwoofer. The LFE will not get sent to the sub unless it is connected to the LFE output of yoru reciever. Secondly, there is the "bass management" features on your reciever that allow you to route low frequency information that would otherwise be sent to the satellites. The human ear has a hard time localizing sounds below 80Hz so sending low frequency information to the sub is a trick that can be done to put less strain on the other speakers that weren't designed to play that low.

I hope you find this helpful and feel free to ask more questions. You've scratched the surface of a lot of different topics that are all very much interrelated, which makes it hard to give short and sweet answers.

----------------

that is just not true. if a receiver is setup with NO SUB, then the LFE will definitely be sent to the front speaker high level AND pre-amp level outputs (if you have them). so if you connect a sub to the high level front speaker outputs in this instance, you WILL definitely get LFE into it (or is that out of it?) and most likely into your front speakers, depending upon what crossover setting you use on the sub. the bass, INCLUDING THE LFE when present, will be "smeared" across and shared by both the front speakers and the sub. in some instances, this IS a solution for people who have a receiver with a fixed xover that they feel is at too high a setting. you then use the subwoofer's variable crossover to adjust to a lower setting. the receiver will, of course, "force" you to set your fronts to LARGE in a NO SUB setup. as far as any speakers set to SMALL are concerned in this instance, such as your center and/or your surrounds, the receiver's fixed crossover will still come into play and will control which frequencies are sent where. again, any bass that would normally be destined for those speakers that are set to SMALL, and that is below the receiver's xover, will be "smeared" across and shared by the front speakers and the subwoofer.

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I'm not so sure that's true for every reciever. I have the Denon 1803 and when I added a pair of Chorus II's to my system, I moved the previous Marantz 940 mains into subwoofer duty driven by a crown xls 402. For those not familiar with the speaker, it's a 4 way design using a 12" woofer and it gets good output down to 20Hz. There are also volume knobs for all the drivers so I've got them all off except the woofer. Once I got them hooked up as a dedicated LFE, there were definetly new sounds never present when I was previously running the 940's as mains with no sub (i had the reciever set up properly as well).

I also have a sony str-502 driving my computer setup and there is no way to get the LFE signal into the mains. In fact, the only way to get a crossover below 200Hz is to use the multi-channel inputs (which of course would never allow the LFE to get sent to the mains either).

All that said, a good reciever should let you send the LFE to the mains, but a good reciever is also going to have better crossover options as well.

[sivadselim]

very few, if any, receivers will NOT reroute the LFE properly when setup with NO SUB. for most basic and usual setups, what i described is a perfectly viable solution. running a setup in "pure direct" or other special modes like that can be problematic with that sort of setup. but for most basic setups it can work quite well. in some other situations, of course, it isn't an option. such as when running analog multichannel inputs from a player to a receiver, because most, if not all multichannel players, will NOT reroute the LFE the way that a receiver will. it is just lost if a multichannel player (not the receiver) is setup with NO SUB.

but often times, in the NO SUB setup, running the fronts off of a sub which is connected by the speaker-level (high level) outputs can be quite beneficial, actually, in that the sub's continuously variable "crossover" (of course, it's really just a low-pass filter on most subs, and speakers connected this way will still receive a full-range signal) can be dialed in more perfectly to match the front speakers' natural roll-off instead of being locked in to one or even one of several different fixed crossover points by the receiver.

even though i do use my receiver's crossover, i do wish i could adjust the slopes of both it's high and low pass filters to taste, as i've dicovered, as many others have too, that the fixed slopes of most ht receivers are not absolutely ideal for music listening, which is what i do the most. the continuously variable low-pass filter of many subs is often of a different slope than the recommended ht slopes that most receivers have, and can actually be better suited for music listening when the fronts are run full-range.

[filmguy]

thnx guys.. very well put

[JohnA]

This actually is a case of bigger is better.

If the bigger sub is loafing, it will produce less distortion.

As to the amount of power and/or capability you would be using normally, you've forgotten one of the HT sub's main purposes, sound effects, or effectively explosions. You can expect those to demand at LEAST 20 dB louder sounds than average. 20 dB is 100 times the power. Even a big sub operating at 40% of its capability, on average, will not be able to reproduce that car crash without massive distortion. You should be thinking in a different scale.

[John S]

Hi Mike,

You sound pretty sharp on this stuff, so I thought I'd ask you . I have been running a pair of Cornwalls off of an old Kenwood KA 7100 that is over 20 years old. Everybody is telling me to get a MacIntosh and pump in some big power to get these speakers doing all they can do. Do you have any suggestions? Mac's seem pretty pricy and I know I'd need a power amp and pre amp to do this.. I looked at a 2105. I'd appreciate your advice. Thanks!

[DrWho]

Wow, pulling old threads outta the grave.

What all do you have in the rest of your setup? Mac's are fine, but like you said, expensive. Also, what kind of music do you listen to?

[John S]

Mike,

I'm 52, so have a lot of 70's rock and jazz, Kansas, Boston, Dobbies, Bob James, Stanley Clarke, also like Billy Joel, Elton, but new favorite is Dream Theatre - these guys are technically the best. I like realistic sound, not thumpy rap and stuff.

I don't have a surround sound system, just old school stereo, Technic turntable still running. My old Kenwood is dying, so I need to think about fresh power. Thanks!

[John S]

Mike,

Didn't realize this thread was so old!! Just came on the site and signed up, found you from a search and found a guy with very similar question. Good you're still around

[DrWho]

I would probably recommend finding yourself an old 70's Harmon
Kardon - like an HK 430, 630, 730, or 930 (they're all "twin powered").
They're a forum favorite since they usually go for under $200 on E-Bay
and mate very well with Klipsch speakers. They also have a really good
phono section, which would mate up real nice with your turntable. The
only concern would be worn out caps.

You might also look into the modern HK 3485, which a lot of forum members have been impressed with as well:

http://www.harmankardon.com/product_detail.aspx?Region=USA&Country=US&Language=ENG&cat=REC∏=HK%203485&sType=C

It won't be up to par with the Mac, but it'll be a whole heck of a lot cheaper.

Another popular forum favorite is Outlaw Audio:

http://www.outlawaudio.com/products/rr2150.html

I've never heard this receiver, but I would imagine that it would come close to the Mac.

Btw, are you strictly running a turntable, or do you do CD's too?

You might trying starting a new thread in the 2-Channel section on the forum as you'll get a lot more replies than just my own.
I'm more into the world of sending digital output from a CD Player into
an active crossover and then bi-/tri-amping my speakers.