To THX or to not THX

brody05

Hi all,
Wondering what people do with the setup in regards to the THX mode on most amps. With the full range frequencies recorded in soundtracks on all channels why would anyone want to cut out the <80hz from the fronts, center, rears and side channels and lose the beneifit these lower frequencies add to the home theater enviroment. Me personaly, I run a sub on each channel in the rear and when something happens in the rear with bass such as the circling Dragon in Dragonheart you really notice the difference, even without active speakers in the rear most HT rear speakers go down to the 35hz range so why send it all to the sub in the front (or wherever) and diminish the need for having anything other than 'satalite' type speakers?????
Thoughts please....

Dr. Spec

http://www.hometheaterhifi.com/volume_9_3/feature-article-multiple-crossovers-9-2002.html

mantis

Ok,
fist off I'm a supporter of THX and everything they did and still do for our hobby and industry.

THX is a helpfull tool if you own THX gear.My advise is to set up the system in THX then without and see/hear what sounds better.I perfer watching movies with THX active.

I own B&K which is THX ultra

Dan

brody05

OK, so that article says that it is easier for a sub to not have to do work above 80hz, regardless of THX mode or not how many people run a full range signal to their sub anyone, ie filtered or not and even if not, I dont know anyone that has the xover set at 150hz and regardless of THX or not, I still have mine set at 75 to 80 hz.
It also states that by sending nothing less to a speaker than 80hz the amp is not working as hard and niether is the speaker, well what is the point of having a big amp and full range speakers then? I would liken it to a Bose set up with little satelite speakers and one sub.
It also says when DD was coming onto the market place THX looked at a number of sound tracks..... Well sound tracks have come a long way since then, theres an extra 2 channels on the side and I have noticed more bass going to the rears in the last couple of years.
More consistency freq resp across channels.... Why? I would prefer an explosion in the rear or on the left front to sound like an explosion coming from that direction, not even an explosion but someting like the "race" in Starwars where the 'cars' come from behind 'chug, chug ,chug' you really feel the bass coming from behind you along with the mid and upper freq range rather than the bass from the front and the rest from the back.
At least the article does go into the fact that losing 'stereo' bass is a downside (even though it does get played down), well its true, it is a big downside, I too have THX gear (mostly) and I have tried many diff combinations and found that the THX mode is 'boring' and lacks impact, theres nothing like stereo bass and seperate active speakers in the rear, people that come around for a demo really notice it and like it, just a couple of weeks ago a mate came and heard and went home with a new sub and ..... lets just say he loves it.
Everyone has opinions and likes different setup, but have you actually tried running subs off preouts in different channels and noticed how much lower freq stuff gets through, try the center channel with a sub, I had a CS1000 and it amazed me, the difference it made, mens voices such as mel gibson and sean conery had a 'timber' to it, no longer sounded like a swarqk.
Center channel plays a huge part in movie soundtracks and why not bring it to life with some lower than 80hz signal.
I enjoy hearing a sub work when it has to with the lower freq stuff and hear each channel work when it gets the desired signal, but hey, thats just my opinion.
Love to hear from others that share my view too.
Brody

goingganzo

my take on thx stuff is that a pre amp is where thx can do sothing for you other stuuff may not have thx stamp on it but it proabley perfprms to the standard.

also you have to pay more for a thx product take the sunfire cinima grand and anthem 20 both sell for about the same price but anthem has thx and sunfire dues no. sunfire has some more ins and outs and has some features becues they are not thx but andthem has thx and a little less but still sounds good as the sunfire it is all in what you want.

dorokusai

THX isn't a life changing audio standard.

mantis

Allowing you system to be setup in small for movies has alot of advantages.Your missing the point with bass as well.

taking away bass from speakers even if they can extend behond 80hz(not many do it well or better then a good setup sub)will free up amp dynamic range.this allow sthe system to perform it's best and you as the listener enjoy the full potential of the movies soundtrack.
When a system is properly calibrated and tuned to the room,these things not matter.Small large what have you depends on the speakers ability.

Lets talk more about the system you own and we can get further with this.

Dan

brody05

OK.
Denon AVCA1se
Denon 2900 DVD
Polk RT2000i in the rear
Polk FX1000 in the side
Polk FX55i in the center

As far as the fronts go, I am in the process of changing but lets say SRT front left and right.
Also have an NAD 218 running another homemade sub that goes down to 10 hz.

In regards to the 'freeing up the dynamic range', amps have enough power to run speakers, changing the freq cut off to 80 hz really has little impact on available head room, it is true that doing things like bi amping ect can make changes in the quality of the sound but in a home theater enviroment where there can be so much happening in all channels at any given moment what is more noticable, slight improvement in 'quality' or full range running all around, I'm just saying that what I like best is full range, others may differ, but how many actually try? How many just take the fact that THX says this is the way they do it in an enviroment that is unlikely to look anything like most peoples lounges and with equipment that even less would have.

Also, what about the poor sub amp, how much can that handle? most average subs would have to be turned down to be able to handle the bass from the LFE and 7 other channels signals at once and stay tight and punchy without distortion, what happens to its 'dynamic' range?

The RT2000i have seperate amps to do the low stuff so have little impact on what the denon is doing, running THX with active speakers wastes the fact that there are active speakers at all.
Why is it that Polk (and others) make active speakers at all if they are not getting a signal less than 80 hz, my RT2000i go down to 20 hz and sound great, the Denon has no trouble running the rest.

I am just questioning the whole THX philophosy, trying to get people to think about the benefits of running full range and not just follow like 'lemmings', have you actually tried it yourself? or just plug and played THX without questioning.

jefft1314

Really deep bass can't be positioned by the human ear so why have explosions happening all around you? I think you may be seeing the affect of having multiple subwoofers in your room than anything else.

HBombToo

great processors but what about the AMP? before we comment inquiring minds want to know:D

twin

brody05

The AVCA1se is the amp, 7 x 175 watts at 8 ohms, the 230volt equivilant of the ?5800-

Although as you say 'deep bass cant be positioned by the human mind', one can tell extremes such as left and right, front and rear, honestly, can you say you couldn't tell if a single sub system has the sub in the front or the back of a room, I can certainly feel the bass from behind. The RT2000is are run of the channel as opposed to sub out so only reproduce the given signal of that channel, as opposed to multiple subs running of the sub out reproducing the 'same' signal as each other.

bokdaddy

Mantis mentioned dynamic range. Now, I am definitely not an expert by any means, but from what I can tell he is saying that by not using the amp to power the deep bass in the speakers, it allows power to run more cleanly for the rest of the receiver's frequency range. Now I hope I'm right or this rant is going to be pointless, but what I've been mulling over is the effects of an 80hz crossover compared to use of full range.

Now for example, my Denon AVR-1803 has a frequency range of 20-20,000hz. Obviously it would depend on the volume of the frequencies, but it looks to me like setting it to small instead of large would have a very insignificant effect. If the full range of frequencies were played at the same volume level, keeping the extra 60hz going to just the subwoofer would only free up .3% of work from the receivers load

20000 - 20 = 19980
60 / 19980 = .003003003...


But once again, I'm not an expert and that is an imprecise, simple piece of mathematics. I don't know the science of sound, but logic tells me that THX's suggestion of 80hz couldn't possibly make much of a difference.

brody05

Thanks for the input, I agree with what you say and appreciate the 'support'.
In regards to frequencies (and anything else home theater), nothing is as simple as it seems, an example is the lower the frequency the more the load on the amp so the lower stuff does make the amp work a bit harder than higher frequencies but your theory is right, I don't think a speaker that goes down to say 40hz is going to have a great deal of impact on an amp if the signal is suddenly cut to 80 hz, it would obviously have an impact on what your going to hear coming from said speaker.
I'm no expert either, got a lot to learn compared to others but being the curious little bugger I am I always ask questions like this, at the end of the day people will always like what they like but if it gets us all thinking and learning at the same time and just one or two people experiment with their setup and find something better then all the better.

goingganzo

actuley tou need more power to drive a sub than a the rest of the range. i have 1000 wats to 2 subs and i olny have 125 to the rest of the speakers but their limits are about the same in db so you free up alot more than 3%

bokdaddy

Originally posted by goingganzo
actuley tou need more power to drive a sub than a the rest of the range. i have 1000 wats to 2 subs and i olny have 125 to the rest of the speakers but their limits are about the same in db so you free up alot more than 3%

I think you misunderstood. We're talking about subs hooked up to the LFE out on the receiver and the effects of removing bass duty from the speakers so that the subs amp can take over for those frequencies. In this case the receiver isn't powering the sub.

VR3

Since my Preamp has no real built in crossover...

My fronts, (use to be center, and surrounds) ALL ran on larger. Personally, I wouldnt do it any other way. Not at all.

Sounds so much fuller when watching a movie than these squeaky sound effects flying over your heard.

Thats just my opinion. If you HAVE the speaker to do it, do it.

Dr. Spec

No, Bryan didn't misunderstand you.

He runs all his speaks on small and uses 125 watts x 7 to power them. He uses 1,000 watts to power his subwoofer, which handles redirected bass below 80 Hz and the LFE channel.

The bass frequencies require a huge amount of power to fill the room with adequate sound pressure, as compared to the mids and highs; Bokdaddy's logic is flawed (no offense).

And a speaker's low frequency capabilities have nothing to do with how much power the receiver sends them if all the speakers are set to large.

Say the source has a strong 15 Hz signal in the LFE channel. If the speaks are set to large, the amps in the AVR will be required to send a high power 15 Hz signal to the L/R fronts. Whether or not the speakers can actually play a signal that deep is a moot point; power will still be sucked from the AVR amps to send it.

The problem with self-powered "full range" speakers is that you feel compelled to run them all on large, regardless of whether they can actually do justice to all the bass in that channel. The RT2000, RT1000, and CS1000 are all in the same boat, to a greater or lesser extent. None of these speakers can do 25 Hz (or lower) clean and loud. If the source has a strong 25 Hz bass hit in the center channel, the CS1000 will ignore it, for example.

Also be aware that the distribution of bass varies on DVDs. Some DVDs use the LFE channel almost exclusively for bass, and some DVDs have full range bass in all channels. U-571 (DTS 5.1) and The Haunting (DTS-ES 6.1 Discrete) are good examples of DVDs that have full range signals in all channels extending down to below 20 Hz.

brody05

I think there are flaws in what most people are saying.

I am of the understanding that a speaker dictates how much power is drawn from a reciever or amp not the amp.

If an amp was run at high levels with no speakers connected at all, would it get hot? I dont think so, now plug in a couple of speakers and do the same, sould it get hot then, you bet. I can run the sub I have with 1200watts like it is getting now or with 350 wattts like it was before and the SPL levels changed by about 3DB, wattage is NOT an indicater of volume, a 75 watt amp will run a speaker to the same SPL as a 175 watt amp (give or take a few DB).
Also does that mean if I hooked up a tweeter only to a full range signal it wall draw as much power to run it as a large multidriver speaker? Your theory that the signal processing dictates the power would suggest so but that makes very little sense to me. I can agree that a full range signal does draw more power but the difference between full range and 80hz cut off is not that big of a deal, and most soundtracks dont go below mid 15hz anyway.
My amp can go from THX to non THX at the push of a button mid full noise and there little difference in the level of SPL or quality of sound, there is however a big difference in how much bass is coming out at certain times.

Subs require more power in part due to the lower freq but mostly due to the impedance, I have just spent 2 weeks getting my head around how to run the sub I have made and discovered the current is what has been the problem, ex, the HCA1000 has 350 W mono and 25 ampers per channel, couldnt run the sub at high levels and low freq without cutting out, the HCA1000a my cousin has is similar in wattage but has 45 ampers per channel, ran it without any problems, the NAD218 has 1200 watts at 4 ohm (or 780 W at 8) and will cut out before the HCA1000a due to not having as much ampers per channel.

There is obviously 2 different points of view on this subject but I am yet to hear one of those for the THX mode to actually say they have tried otherwise and didn't like it, there can be figures and theories (complicated jargon) thrown up to support or not support ones point of veiw but is that a veiw of experiance or just what has been read from 'experts'. I have listened to speakers reccomended by 'experts' and thought them to be rubbish, my personel tastes are just that, what I like may differ to others and some do agree, but at least I can say I have tried many different options and not taken for gospel the word of others.

I must say I am enjoying this thread and look forward to more input.

Dr. Spec

I am of the understanding that a speaker dictates how much power is drawn from a reciever or amp not the amp.

The impedance of the speaker at the frequency in question will partially dictate the amount of power the amp delivers. Naturally, the relative signal strength also matters.

If an amp was run at high levels with no speakers connected at all, would it get hot?

No, and no one is suggesting otherwise. Do you think that simply because a speaker's frequency response trails off below a certain point that it no longer presents an impedance load to the amplifier?

I can run the sub I have with 1200watts like it is getting now or with 350 wattts like it was before and the SPL levels changed by about 3DB, wattage is NOT an indicater of volume, a 75 watt amp will run a speaker to the same SPL as a 175 watt amp (give or take a few DB).

Provided the speaker is still operating within its linear limits, a doubling of power will provide a 3 dB increase in volume.

Also does that mean if I hooked up a tweeter only to a full range signal it wall draw as much power to run it as a large multidriver speaker?

If you connect a tweeter (with no crossover network to protect it) to a full range signal, it will burn out almost immediately.

I can agree that a full range signal does draw more power but the difference between full range and 80hz cut off is not that big of a deal, and most soundtracks dont go below mid 15hz anyway.

Instead of assuming the difference in power draw between an 80 Hz 2nd order high pass and a full range signal is "not that big a deal", why don't you burn some sines, break out your DMM and SPL meter, and measure the power being delivered to the speaker with an 80 Hz sine @ 100 dB, and a 30 Hz sine @ 100 dB.

Subs require more power in part due to the lower freq but mostly due to the impedance, I have just spent 2 weeks getting my head around how to run the sub I have made and discovered the current is what has been the problem, ex, the HCA1000 has 350 W mono and 25 ampers per channel, couldnt run the sub at high levels and low freq without cutting out, the HCA1000a my cousin has is similar in wattage but has 45 ampers per channel, ran it without any problems

Gee, thanks for making the argument for high passing the speakers at 80 Hz. If you think the HCA1000 had troubles delivering the high current required for reproducing bass frequencies, into a low impedance load, how well do you think the typical AVR will handle the job?

If the source has high amplitude, low frequency content in all channels (like the depth charge scene in U-571 DTS), the amount of current the typical AVR can deliver to any given channel drops to about 4-5 amps; IOW totally inadequate. This type of signal will send the AVR amplifier into clipping almost immediately at moderate to high playback volumes. They simply lack the current capability to cleanly drive several full range signals simultaneously.

Polk does not make a loudspeaker which is capable of cleanly delivering clean, loud bass in the 15-25 Hz region. If you run your speakers on large, and there is a full range signal in that channel that extends down into the 15-25 Hz region, it will be ignored by the speaker and you won't hear it.

Furthermore, several sources of low bass in a single room are a nightmare for standing waves, cancellation, and an uneven bass frequency response at the key listening positions.

And the 80 Hz high pass is not a brick wall. The speakers are still allowed to produce bass below that frequency (albeit at a progressively diminishing rate). Since deep bass is truly non-directional, the audible cues on "where" a bass effect emanates from in the room do not require the use of a full range speaker. Any decent size speaker with an F3 of 50-60 Hz will get the job done just fine.

HT speakers (center channel, surrounds, etc.) are simply not designed to play full range signals. And even if you put so called "full range" speakers into service for EVERY channel (a PITA, impractical, and requires external amps), they STILL can't play deep bass as well as a dedicated quality subwoofer.

Can TRUE full range be properly done in each channel for HT? Sure: With proper room acoustics, bass traps, sophisticated equipment for measuring and equalizing the FR at the key listening positions, REAL full range speakers (i.e., NOT a powered tower with a 50 watt amp and an 8" woofer that rolls off at 35 Hz), and sufficient power/current capability for each channel. BIG $$.

For the rest of the world....buy the absolute best mids and highs you can afford, and high pass them to the best powered subwoofer you can afford and I guarantee it will provide better overall acoustics AND better deep bass performance than any "compromise" attempt at "full range" in all channels.

Doc

dorokusai

EDIT

bokdaddy

Originally posted by Dr. Spec
Bokdaddy's logic is flawed (no offense).

Don't worry Dr., no offense taken. It was just the simple logic of someone that hasn't studied how the equipment works. I knew there was a good chance I was wrong but wanted to post my thoughts anyway. I figured there's no better way to get to the truth than to lay our own thoughts out on the line. Thanks for correcting me. I just appreciate that you even took the time to read through my ramblings and give your own thoughts.

brody05

I couldn't be bothered doing sine wave sweeps in each channel just to check how much current is being drawed, it means nothing to me, I have full range going to my speakers and thats the way I like it, it sounds great, I like hearing bass (not LFE bass) from the rear when dictated my amp is handling things just fine.

We do not disagree on a lot of points, maybe just to the extent, it is true that as the freq drops it draws more but it is compounding and your talking about the really low stuff that is not in channel signals. When I was making reference to my sub running off the NAD amp, my cross over is set at 35 hz with a 12 DB drop per octive, thats the really hard stuff, a speaker doing between 40 and 80 hz is not quite the some comparison.

You said that 80hz is not a dead line, so if it is say even at 12DB drop per octive then just how much difference is selecting the THX mode really making? if the amp is still letting signal (albeit diminishing) through below that level.

My point is this: I would prefer to have a full range signal reproduced than not, in a movie enviroment crysal clear audiophile sound is not as important to me as being able to hear mens voices sound deep, a car door closing behind me sound like steel rather than tin in the area the rest of the sound is coming from. I dont think that running full range from my Denon as opposed to 80hz impacts to the point some think, sine waves are a constant sweep, movies values change all the time.

A person determines direction of sound by two mechanisms, 1: the time lag between the entry of sound into one ear and into the opposite ear and 2: the difference between the intensities of the sounds in the two ears, the first of the 2 methods works best at at frequencies below 3000 cycles per sec and the intensity mechanism operates best at higher freq because the head acts as a sound barrier at these freq.
The time lag mechanism works best out of the two because it does not depend on on extraneous factors but only on the exact interval of time between the acoustical signals.
Lower frequencies are harder to place because the lower stuff depends to a great extent of loudness, there are many variables but lets say an average adult relies on sound and vibration thresholds. Low freq soundwaves travel all the way up the basilar membrane as opposed to medium and high freq, brain neurons are are activated by specific sound freq and as low freq stimulate the entire basilar membrane at 200 cylcles per second it is difficult to differentiate between low sound freq betwwen 20 and 200 cycles. This however has no bearing on the first of the two theories only the second but it does not stop the brain from placing bass at 22hz or above, just limits one of the two mechanisms. At a level of 73.8 DB the vibration sensors are stimulated at 1 hz (prickling and tactile threshold).

In saying that at a moderate level of 72 DB and above I and others are more than capable of telling the difference where the sound is coming from to a certain degree regardless of the freq most speakers are able to reproduce right up to 10,000 cycles.

This is the reason I like the bass coming from where it was intended by the people that made the movie, not from one point in a room. You are obviously in favour of the THX mode but can you answer me this, have you tried otherwise and not liked it or just going of writing on a piece of paper?

I didn't start this thread with the expectation of it becoming such a 'depate' of complexities that would cause most to lose interest, just wanted to see if anyone else likes the 'unorthodox' way that I do.

PS. Polk rated the RT2000i at 20hz.

dorokusai

The specs are more than available, the test/groundwork are valid; and have made THX pretty much an industry standard....but THX certification should not drive gear purchase IMO.

Money is what what made THX.

brody05

THX is the industry standard for quality parts ect and the 'stamp of approval', the THX mode on an amp is purely a crossover function of sending signals to the sub, just like Dolby digital, Dolby prologic and DTS as well as EX and ES, all surround modes/parrameters. I am refering to the mode of THX, not its 'industry standard'. Just like someone may prefer 2 channel music and some may prefer DTS audio, or SACD.

I have said it before, but has anyone tried runnig full range to speakers and if so, what did they think???

There are obviously some pros and cons as above, but who prefers what?

cdubya

Lets not forget that thx is not solely about the 80hz cut-off. Thx also comprises of timbre matching of the channels and a reduction in high freqs for the home environment. We should all be thankful for thx granted, it is great imo. But harping back, how many have experimented with what brody has done? Personally im for thx but i havent heard full range on all channels.

TheReaper

Thunder definately sounds better on large speakers. The sound is noticably shallow without some lower frequency sound comming from the same place.

My thoughts on THX:

The main-stream market wants smaller speakers, both for cost and ease of placement. A THX specification that didn't take into acount the main-stream market, would never generate enough license fees to be worth anything.

Dr. Spec

You are obviously in favour of the THX mode but can you answer me this, have you tried otherwise and not liked it or just going of writing on a piece of paper?

Yes, I tried all my speakers on large. The increase in intermodulation distortion was quite noticeable (manifesting itself as a marked decrease in midrange clarity), since all of them are either 2-way or 2.5 way.

IM distortion is of more consequence (and much easier to hear) when a quasi full-range two-way speakers (like say the RT800i which has an internal xo of 2.5 kHz on the dual mid-range drivers) is asked to simultaneously produce a loud 40 Hz tone (low E on a bass guitar) and a bunch of signal content in the 1,500-2,500 Hz region. The high excursion required by the midrange driver to produce a 40 Hz signal will significantly modulate those upper frequencies to a greater and more audible extent than will a subwoofer producing a 28 Hz and a 50 Hz signal at the same time.

Furthermore, none of my speakers can play bass with any authority below 50 Hz, including my RT800i. I actually measured the FR of the RT800i, and it starts to die just under 50 Hz and is about 6 dB down by 40 Hz. It cannot even do justice to low E on a bass guitar.

The CS400i and the FX1000's are even worse. And forget about the CS245i's pulling anything reasonable below 60 Hz.

The number of people who overestimate the bass capabilities of their speakers never ceases to amaze me. If you took the time to actually measure the FR of the RT2000i - not at 70 dB but at real playback volumes - you would note it starts to nosedive at about 38 Hz.

The roll-off of a vented woofer below the tune point is 24 dB/octave. As the woofer and the vent start to decouple, they start to operate out of phase and cone excursion rises dramatically because woofer motion is no longer being damped by the vent. To prevent overexcursion and bottoming below the tune point, Polk almost assuredly installed a steep high pass filter at 35 Hz.

Next comes dynamic compression. Start running FR sweeps at progressively increasing volume and watch the curve start to compress in the lower octaves. It's easy to have a nice looking FR curve at 70 dB. At realistic playback volumes, the "real" FR of the loudspeaker will quickly become apparent as dynamic compression starts to set in.

The THD the speaker generates at a given frequency must also be considered. The industry standard for "clean" bass is 10% THD or less. You would be surprised at how low of a sound pressure the RT2000i hits 10% THD at common bass frequencies (like 25-35 Hz). The deeper you go, the harder it is for a speaker to maintain low distortion.

If you ran the RT2000i through the objective measurements ringer, you would discover its legitimate clean bass limit at realistic HT playback volumes is 38 Hz. Below that, you will observe a very quick rise in THD, and a very steep roll-off - probably 6th order when dynamic compression and the HPF are factored in.

My typical response to exaggerated claims of deep bass capabilities like "my subwoofer goes to 10 Hz" or "my towers are rated to 20 Hz" is two words: Prove It.

Regarding the THX recommended xo of 80 Hz: In the day, THX recommended an 80 Hz xo and the 2nd order high pass and 4th order low pass filter rates because THX certified surround speakers were sealed units with a natural 2nd order roll-off and an F3 of about 75 Hz.

The combined effect of a 2nd order high pass filter at 80 Hz, and a 2nd order natural speaker roll-off at 80 Hz, resulted in a 4th order roll-off - not coincidentally the same as the low pass filter rate imposed on the subwoofer. The final result: a 4th order high pass and 4th order low pass filter rate at the selected xo of 80 Hz and a nice neat crossover.

Unfortunately, nearly all surround speakers these days are vented, and imposing a 2nd order filter above the tune point will result in a 2nd order roll-off. Below the tune point, the combined roll-off suddenly steepens to 6th order.

With an 80 Hz xo, the use of vented surround speakers with an F3 of 50 Hz will likely result in an emphasis in the 90-50 Hz region because the vented speaker has not yet begun to naturally roll-off, and is only being artificially filtered at a 2nd order rate.

People desiring better bass management have turned to external BM units with adjustable filter points and filter rates for each channel, including the LFE channel. Or they use variable phase controls and PEQs to achieve a flat response at the crossover bandwidth.

In the end, if you like the sound running all your speakers on large, all the more power to you. After all, it's your system. Just don't kid yourself into thinking your speakers at each channel can truly reproduce all the deep bass that may be present in those channels (again depending on the particular DVD).

scottvamp

Ya, what Doc said.......... Thanks - that really sumed up most of my logic.

brody05

I Dont want to be offensive to anyone but I dont know about most however I can say this, I listen to movies at well above 70DB, the reference level of 00 on the amp quite easily exceeds that number and it would surprise me to learn that anyone else watches a movie at below 70DB, to be honest my TV does 70 DB without even turning it up much past normal listening levels (just did it then with a kids show, took the volume all the way from 20 to 24.

I really am growing tired of this now, you might as well have called me a liar with my claims, maybe you should write to Polk and tell them to change the specs on their speakers, in particular the RT2000i. As to proving my sub goes to 10hz, well polk made SRT subs to go to 16hz and they have a low pass cut off in the SRT controller (I know this cause I tried), I made a sub the same and when I ran a setup disc through it couldnt beleive a 10hz sine was producing noise - if you would like to fly to NZ I would gladly show you, as I'm sure you know the depth of a sub is aquired by design and port ect so 10hz is not hard to reach, most manufacturers would cut that out as it puts too much of a load on an amp and sub, me, I love it, I am a bass head and I like it loud, I love the way my voice rattles like talking into a fan, I love the way my jeans flap against my leg, newcomers are amazed when they hear it. You may not like it like this and I am not putting you down for it. This is a movie enviroment, when it comes to music I run two channel pure direct and back the bass off, but hey thats music and a completely different ball game where a bit of 'distortion' is not as acceptable as in a movie.

I agree in a lot you have said, where I haven't agreed I have made my 'argument' but the degree to which can be heard by us in a movie enviroment is where I disagree with you, when you tried full range you didn't like it, but about from having RT800is what else are you running and with what power? and thats great anyway, YOU dont like it, others obviously do regardless of how 'innapropriate' some may think.

So what if (as you say) the RT2000i start to drop off at 38hz, much better than 80 ey, turn the bass dial up a bit more and it will keep up for longer, your RT800i lose 6db at between 50 to 40hz, big deal, I have the LFE and mains going to my sub so theres no dip in xover between my subs and speakers, and theres a big difference in some sounds between 80 and 40-50hz, the center channel has a lot of signal going to it where that will make a noticable difference.

Quote from the book "Parameters - Large speaker setting for speakers that can fully reproduce sounds below 80hz. Small when using speakers that cannot produce sounds below 80hz at sufficient volume."....Kinda sums up what I am saying, and again I say, I am happy to sacrifice the 'audiophile' sound for a full range signal and I dont think I am the only one. You can through all the stats and techno stuff in the world at me but it wont change what I like. I am not kidding myself about my (or other tower speakers) producing all the deep bass in that channel, they are however doing a hell of a lot more than 80 hz and even you said so yourself.

I know of your 'expertise' on this forum and admire your knowledge, to be honest some of what you have said I have had to read a couple of times to understand, you have even made points in my favour but at the end of the day, the extent of 'distortion' will vary from amp to amp and speaker to speaker, I happily sacrifice a bit of the quality for a more spatial and full range effect. In 99 when Lucas films came up with THX things were different, we've come a long way in 5 years and it is easy to tell by comparing the sond tracks in DVDS from then and now, I mean the latest Star wars is a great example, he's got lower than 80hz going to the rear channels, wonder why he bothered.

Anyway, got stuff to do. Brody;)

Dr. Spec

Hi Brody:

What I meant about the "70 dB" reference was that there is no industry standard for manufacturer's to measure the frequency response of their speakers and subwoofers.

It is common for manufacturers to run FR sweeps at very low volumes (like 70 dB) because it results in nicer looking curves; and you are right - no body listens that quiet! :eek:

If the same speaker were run at say 105 dB (appropriate to gauge Refererence Level playback capabilities), the FR often looks considerably different. Dynamic compression sets in, and the low bass capabilities are significantly reduced by thermal, mechanical, and port flow limitations.

And the infamous "overall" frequency response usually doesn't have a +/- dB limit attached to it. It is generally assumed to be -10 dB, but no one really knows for sure. :rolleyes:

Manufacturers also don't list the distortion levels the speaker produces at the FR test volume; what good is 30 Hz at 105 dB if total harmonic distortion is 60% at that point?

A nice industry standard for speaker manufacturers to adhere to would be "something" like:

35-20,000 Hz +/- 3 dB @ 2 meters @ 105 dB @ <10% THD.

Think that's ever gonna happen?

So no, I wasn't calling you a liar (or even Polk, because all manufacturers are guilty of it); I was criticizing the method (or lack thereof) by which speakers are rated for FR.

Sorry you went from "enjoying this thread and looking forward to more input" to "I'm really growing tired of this now"; that was not my intention. I thought you were looking for discussion/debate and information exchange on the subject. And you'll note the last half of my previous post was a big negative against running vented speakers on small with a 2nd order high pass (which almost every AVR BM circuit still employs as a dated carry over from the THX standard).

Regarding the 10 Hz sine - sure, any vented subwoofer with the high pass filter removed from the loop will respond to a 10 Hz sine. If you have big enough driver(s), the sub will even move some air (as you noted). But if you can hear a 10 Hz sine, what you are hearing is the 2nd order (20 Hz) and the 3rd order (30 Hz) distortion harmonics that the woofers are producing. Unless the sub is actually tuned that low (and very few subs are), the actual SPL it can produce at 10 Hz before hitting 10% THD will be very low.

In fact, I've measured >100% THD (at pretty low volumes too) from subs at frequencies well below their tune points. At that point, the distortion harmonics are actually louder than the fundamental.

brody05

Hi 'Doc'

First let me start by saying the reason I 'grew tired' of this was I got defensive over the comment you made;

"My typical response to exaggerated claims of deep bass capabilities like "my subwoofer goes to 10 Hz" or "my towers are rated to 20 Hz" is two words: Prove It"

It felt just a tad 'personel', I was and am looking forward to more input but from others as well, a little less technical jargon and a little more open discussion about what peoples likes and dislikes are, I have not come accross many that experiment as much as I and know few who have bass in the rear (running of pre outs or fuller range signal), it is something I love and will never change, had a play around and discovered something totally awesome.

I do enjoy dicsussing/debating, it is a great way to open ones eyes and see what else is out there and an interesting way to learn. We both made valid points for and against but is was going over the same ol ground, just more stats. I will hapilly admit you know a lot more than I do (except maybe for the hearing thing as that is more my area of proffession), I haven't in the past got too caught up in statistics ect, I rely heavily on my ears, what they like is what mades my decision in set up, for ex I have my centers turned up higher than the other channels (by about 4 -5 DB from an SPL meter) but thats how I like it, unorthodox it may be but I am the one listening to it, much the same theory as the full range signal thing, without getting complex, I notice very minimal change in the speakers ability/quality of sound to handel a full range signal, I do notice a big difference in the 'lower' (<80hz) freq those speakers are producing, I guess it comes down to equipment and personel preference.

I am actually thinking of running some comparisons over the next few days as it has been a while and with being in the throws of a system change due for a good test.

The statistic you mentioned would be a great industry standard for information, would love to see something like that happen.

I don't know what the SRT subs are tuned to, they are rated by Polk at 16 hz with 300watts (theres that rating thing again), the home grown sub has original SRT drivers and virtually identical porting and cabinet ect (to within a couple of ml) and with the NAD 218 bridged are getting about 1200watts at 4 ohms (book doesnt actually offer this conversion but it does state 780W at 8 ohm so...), drivers are run in series. I am unsure of the THD but I can say this, it sounds and feels great. Drivers seem to be holding up as is the amp (after upgrading amps). There most likely is distortion at that level but I cant tell, it's too low for me to distinguish.

The towers in the rear, well anyone that owns a pair will know that the active subs in them produce a lot good tight bass, may not be the 20hz indicated by Polk but it is certainly noticible in movies when they make some noise.

I, as do others on this forum have a real passion for home theater and Polk Audio, it all started for me back in the days of Dolby Prologic (others most likely go back further, say silent movies haha), I was hooked then, when DD came out, wow, then DTS cool, THX and now EX and ES just too much fun, I love it and always will, we all have different tastes and preferences, it would be a boring world if we didn't.
I am a recent edition to this forum and do and will continue to enjoy using it. Thanks for the smilie faces.
Brody:D