Frequency Response - A General Question - Page 3

Set your sub's setting to 120Hz as that's how the .1 channel is mixed.

C'mon gang, does anyone else recommend setting his speaker's crossovers to 120 Hz.,
Of course, set the LPF to 120 Hz but....

120hz would be a good setting for the poster.

Quantum,

1st keep in mind the OP is talking about speakers with 3" woofers or less in size. There is no way these should be run full range.

Mxing rooms are diferent animals and many crossover their speakers. However, they are different because they are only trying to get the sound correct for 1 position not multiple seating. I have been in many recording studios and watched engineers and artists change seats so they can be in the sweet spot. If I only have to worry about one seat being good that is a lot easier. I could go into a lot of differences between a recording studio and HT. But heare are some facts. There are over 100,000 recording studios worldwide and they are not acoustically identical by any means. So if we can't replicate the recording environment, how are we going to hear what the artist intended? By contrast there are less than 20 dubbing stages where the final mix of most movies are produced. They follow a set of acoustic standards and are very similar acoustically.

If we can set up our systems to replicate this acoustically, we will hear what was intended. The problem comes is that a dubbing stage is a large room. It is a theater with a mixing console in the middle of it. Our homes are small rooms. There are different obstacles to overcome in each environment.

One specifical problem in small rooms is standing waves or AKA room modes. These aren't problems in large rooms because the rooms are bigger than the wavelength of the lowest frequency we are likely to produce. That's why I said ~50 x 50. A 20hz wave is ~56 feet long.

Anyway, good bass response is a correlation of good seating placement and good speaker and sub placement. We place the seating and the sub in a location that gives us a good bass response. What happens to the bass response if we have the same low frequencies coming out of the center channel? The left channel? With combinations of channels and subs we could have hundreds of different bass response in the room dpending which channels are playing the low frequencies. What if the best location for the low freequencies doesn't sound good for the high frequencies? Highly likely! To solve this we send low frequencies to the subwoofer channel so our low frequency information comes from only one channel. We now have a controlled bass response.

Here are some good articles that discuss placement of subs and standing waves. For subwoofers Part 3 getting the bass right would be recommended.
http://www.harman.com/EN-US/OurCompany/Technologyleadership/Pages/WhitePapers.aspx?CategoryID=White papers

A calculator for figuring room modes.
http://www.harman.com/EN-US/OurCompany/Technologyleadership/Pages/Calculators.aspx?CategoryID=Calculators

What I'm looking at when I set the LPF to 120Hz is to prevent noise cancelling that's created when the mains reproduce <120Hz and conflict with the <120Hz content reproduced by the LFE channel. Couple this with an off axis listening position and a lot of content gets lost as the bass gets unnecessarily muddied.

I'm still learning about the <300Hz standing wave problems as I've gone over room calculator provided information and don't have a clue how to control the mess these standing waves create short of turning the lvrm into a sound studio with room treatments which neither the wife nor I have any intention of doing.

So far, the solutions I've come up with is rotate the speakers so the sound is divided up by the corner to mime furniture placement (help cancel standing waves) and have made plans to replace the subs with a pair of Martin Logan ESL series subs (Depth i) so as to evenly disburse the <120Hz material with one of the three 8" emitters in each sub positioned toward the middle point between the two seats so directionality of the 80-120Hz material is maintained from each main speaker.

There is an intentional flaw in the speaker placement as the center channel is square to the opposite wall as opposed to being rotated to the seating position but the opposite wall has two openings, one to the left and right of the wall allowing the sound waves to pass into the other room, acting as a baffle which helps eliminate the standing waves created by the less then ideal placement of the center channel. Also, we have a cathedral ceiling so the off angles of the pitched ceiling ameliorates ceiling caused standing wave problems.

For the purpose of analyzing the room, the main listening mic position is not the actual sitting position but is the position equidistant between the two listening positions. Room measures r16' x r22' with a cathedral pitched ceiling that peaks at r12'.

This is one of the links I used for homework purposes:

http://physics.info/waves-standing/

And this link is for the calculator I used to get a better understanding of what the frequency of the standing waves are that are standing around in the room.

http://www.marktaw.com/recording/Acoustics/RoomModeStandingWaveCalcu.html

BobL, are there any thoughts you can add to my above comments?

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Edited by BeeMan458 - 8/27/12 at 12:22pm

My understanding, the SPL should be set with a SPL meter at 75dB while doing the pink noise test. If set at 93-95dB, you've burned up all your headroom and basically killed the dynamic range of the movie sound track.


Well, except for the part about going out and getting a SPL meter.

Responding to Bob L comment on big rooms...

My experience is that uncontrollable bass build up happens most in very large rooms, where the rooms are big enough to create "natural low-end room amplification" With big rooms, low bass "excites" the room to resonate. Even if the natural frequency of a big room is BELOW 20Hz - yes even far below - the harmonics kick in and fill the room with way to much bass and then long reverberation times exacerbate the issue. Often excess bass can never be controlled or absorbed in a big room.

Big square rooms, which you speak of, are a bass nightmare! For example, there's not enough EQ or absorption in the world to fix a gymnasium's low end or an arena! This bass resonance issue is addressed in theaters and auditoriums by having a narrow front and wide back so long spaces don't create a singular bass frequency amplifier, but a broad low and controlled environment.

Hence, your point that bass is controlled by a big sub in a medium or small room, simply is opposite acoustical dynamics. in a home theater environment, you can ENJOY bass from multiple directions without having the room join in and make too much extra bass. [/U][/U]

Second, your assertion that a recording studio can't be replicated in the home theater is also backwards. The whole point is to make the studio neutral so its product sounds great in most every environment. When a sound engineer sees a car crash on the left side of the screen and directs bass energy to the left side of the room, why would you take that bass and pump it out a single sub somewhere else? The purpose of Home Theater is NOT to replicate the recording studio or sound stage. The purpose of a home THEATER is to replicate the THEATER and its experience at home.

Your point on low frequency standing waves terrorizing small to medium rooms is just not true. The whole reason some people look for corners and other experimental positions is to find a "sweet spot" where the sub output can be enhanced. Why? Exactly because a small to medium room DOES NOT amplify low energy. The standing wave problems of small and medium rooms are much higher in the spectrum. They create interference, audible harmonics, multiple paths to the ear and generally degrade the perception of sound directionality. This is why anything you can do to enhance imaging and reduce phase distortion increases the listening experience of surround sound. BobL, you seem so well studied. I would encourage you to rethink this particular bass vs. room size philosophy.
Edited by Quantum Studio - 8/27/12 at 11:28am

I've been working in this for a long time my career started in 1983 with my engineering degree. What you are saying is true that excessive reverberation times are problems in big rooms. In fact we just corrected one of these problems in a church where the decay times were greater than 7 seconds. This is where I stated Large vs. small rooms have a different set of problems. Small rooms the bass is dominated by standing waves which isn't the problem in large spaces.

There have been many studios I have been in an measured that are from neutral. There are a LOT of studios around the world and they do not measure the same. Just think about how many put their monitors on the metering bridge and the acoustical problems it causes? Yes, the better studios typically use baffle mounted speakers or speakers on stands to solve this issue. The better studios place a greater emphasis on the room too. But, there is no standard. Some are lively others dead and anywhere in between.

The dubbing stage is a small theater where the final mix is created. TV dubbing stages are often smaller and more numerous, movie ones there are probably less than 20 worldwide. That is the area to replicate, not your local cineplex which can be varied between theaters. Here is what a good dubbing stage looks like. Click on the link for the Kurosawa Studio.
http://www.skysound.com/qtvr/qtvr_tour_mix_a.html

Here is a quote right from Dolby Labs

"In small studios with basic acoustic treatment and geometry, the frequency response of a speaker system below 100 Hz is dominated by the modal response of the room. Strong low frequency standing wave patterns can be observed in small rooms. Therefore, it is very difficult to achieve consistent low frequency response from multiple fullrange speakers in such limited space. One solution to this basic acoustical problem is to set-up the monitoring system using a Bass Management System. If the multichannel set-up uses small or mid sized monitors, then a subwoofer should be included in the system and by using active electronic filters and crossovers, one can extract the low frequency information from the main channels and route that information to a single subwoofer feed. The LF cut-off of the subwoofer in the room should be close to 20 Hz. Also, the crossover low-pass filter should be very steep so that midrange information is sufficiently attenuated. The ‘bass-managed’ low frequencies will then originate from one single source that can be placed in an optimum position in the room. Therefore, the Bass Management’s basic and main goal is to ensure that the entire audio bandwidth of all channels can be accurately monitored."

I've taken classes at both these places (THX and Dolby) as well as many others. Bass management is always emphasized and even exists in larger theater spaces. But, in the larger spaces it is more about capability then solving standing waves. Like many surrounds can't play full range in many theaters, they often only go down to ~50-70hz.

You are obviously educated but need a little more understanding of small room acoustics. The links I provided before would be a great start. I would encourage you to look at bass problems in small acoustical spaces:)

I will study the standing waves in smaller spaces a bit more. Thanks.

I did a gym reverb / bass management job in our church about 4 years ago. We made great progress with intelligibility, dropping the long reverb times, and the bass build up multiplied by reverb. However, with parallel cement walls - which were quite unmovable - we found the harmonics from sub-audible standing waves a huge generator of pesky bass resonances. We improved things. But it was a bear. My hats off to you on that one.
Edited by Quantum Studio - 8/28/12 at 2:21pm

Ahh. . . all this talk of sub woofers, standing waves, etc. Wow! It makes me want to just pull out my vintage Utah WD-60 high end speakers and 15 watt/ch. vacuum tube amp from Olson Electronics. I think it was rated at no more than 1 or 2 % THD@1KHz. With that kind of power and fidelity I had no problems with standing waves.

Ahh. . . the good old days!


Seriously, very interesting posts and good reference for future consideration when I finish our lower level family entertainment area. Lot's of long flat walls down there.
Edited by Phase700B - 8/28/12 at 2:57pm

Most sub woofers aren't really sub woofers because most speakers today don't have real woofers. Subs are a cheapo substitute for real drivers in great full range mains. Most speaker manufacturers are either incapable of building real mains that pull down to 20 Hz, or they're laughing behind your back as they've figured out a way to sell you one woofer to go with mid-range performing mains that have omitted a pair of real drivers. So, enjoy your sub woofers: fake drivers that create all sorts of problems in most rooms - such as a shallow, narrow sound stage. Meanwhile, I'll continue to enjoy my ancient Altec/JBL hybrids: Altec horns, JBL mid-ranges and drivers in a 5.0 setup each the size of a dishwasher perfectly matched with a center and surrounds. What I like about this set-up is it works incredibly well at medium listening and low levels: crank it up and you better call a priest.

wow. what 'modern' subwoofers have you heard?
You aren't using one now, right? with your , um, how old speakers? How many subs have you heard lately?
What are you using to drive your 'full range' speakers that go all the way down to 20 hz ?
Have you measured that? Or are you basing that on the manufacture's specs from .. how many years ago??

You really joined this forum today just to post that?? Thanks for the input, and I'm sure everyone reading it will give it exactly the weight it deserves.

reminds me of a certain audiophile driving his speakers from a boombox...

I like to think myself a reasonable man, so I always deferred to experts with regards to speaker crossovers. In general, I cross my surrounds at 120Hz just because I know they can't handle the frequencies. I cross my fronts and subs at 80Hz, and I don't use a center speaker. Many people said I was a fool and should cross my fronts at 120Hz. Did that and I never thought it sounded better; certainly not any tighter bass IMO. So I went back to 80Hz and was happy.

Then I got Audissey XT32 and let it do all my thinking for me. Thanks Audissey! Ignorance is bliss!

The suspense is killing me!!!

Fwiw, I can't argue with Bill's reasoning if you have speakers with a single 3" LF driver for mains, but I would definitely consider Audyssey's settings if it recommends lower than that...That said, if you have capable mains there is no way I would set the crossover as high as 120 Hz. in a Home Theater situation.

Audyssey doesn't determine the crossover settings, the receiver does. Audyssey reports its findings to the receiver but it is up to the receiver to determine the crossover based on those findings. Some use the information well and others don't, some just set a standard 80hz. Most 3 inch drivers are not capable of having a crossover at 80hz and not having a gap in the frequency range.

A note about crossovers. First a crossover is not a cut off point. If you have an 80hz crossover you speakers will still receive 40hz information just at a lower volume. How much lower depends on the slope, higher end processors have adjustable slopes to be more finely tuned. Crossovers should be set by the acoustics of the room unless the speakers are not capable. Then a higher than ideal crossover might be used. From measuring lots of rooms and systems most average rooms the crossover would fall between 80-100hz. On occasion you might have a crossover in the 60-75hz region. All because speakers can go lower doesn't mean you should set the crossover lower. However, if speakers can't go lower setting then higher is a necessity so the whole frequency range is audible.

Technical. You should try them crossed over at a higher setting 140-150 hz. This way they become much fuller in sound. As others have already stated, a 3" driver is way too small for an 80 hz setting. I'm dealing with 2 1/4" drivers in one of my systems. The satellite with one of these smaller drivers sounds fuller at 200 hz and the other satellite that contains two drivers sound better at 150 hz. Albeit, localization starts to really rear it's ugly head over 100 hz. That's why using more than one Sub helps in this situation, set very close to the front speakers. There are positives and negatives to using/implementing less than 5" midbass drivers because they just can't handle bass frequencies very well.

Output at the maximum linear excursion into full space for various representative drivers at 3 feet is as follows at 120, 80, 40, and 20Hz. Many drivers have less excursion and lower output. Subtract 3-5dB for living room dimensions and more for a larger space for the SPL at your listening position

Size Driver Sd (cm^2) x xmax (mm) 120Hz 80Hz 40Hz 20Hz
4 1/2" Seas W12CY001 50 x 3 89dB 82dB 70dB 58dB
5 1/4" Peerless 830873 88 x 3.5 95dB 88dB 76dB 64dB
6 1/4" Seas L16RN-SL 104 x 6 101dB 94dB 82dB 70dB
7" Seas W18EX001 126 x 5 102dB 95dB 83dB 71dB
8.5" Seas W22EX001 220 x 5 106dB 99dB 87dB 75dB
10" Peerless 830452 352 x 12.5 118dB 111dB 99dB 87dB

Good jazz recordings reaching the listener at a pleasant 85dBC SPL average can have 107dB peaks at the speaker. Reference level home theater can get you to 110dB. With dialog at a conversational volume (60dB, -14dB volume setting with dialnorm enabled on a calibrated THX receiver or proessor) and no dynamic compression aka midnight mode peaks may hit 96dB. It's logarithmic - 102dB takes 10X the displacement as 82dB.

After years of owning more than a dozen or so speaker systems in both stereo and surround configurations, I have discovered some, interesting, if not totally technical generalizations .In the last 3 homes we have lived in with living rooms approx. 12' x15' to our current 15' x 24' ( with an adjacent "open" plan dining/kitchen area); I have found that mid sized tower speaker systems (32" to 34" tall) with a pair of 7" to 8" bass/mid bass drivers and a good quality tweeter work the best. For added fullness and especially for LFE while watching movies, a pair of 10" to 12" subs work very nicely. Currently I have a pair of vintage B&W DM603 S2 for front mains, but I also have used some others in about the same size. As I said, this is a generalization, but it does makes sense from a technical standpoint.

For years my systems always included the usual 3-way 10" to 15" woofer-mid-tweeter in rather low but large boxy cabinets. These included the garden variety speakers from Advent, JBL, Infinity, Klipsch and more, and also some brief trials with friends high end "boutique" speaker systems. They all had their good attributes but also some trade-offs. Since then I've owned or auditioned quite a few mid tower designs from Polk, Altec Lansing, NHT, B&W and several more. I believe that the 7" to 8" mid bass/woofer configuration along with a properly matched tweeter and decent crossover network matches the average living room load and acoustics better than a 3 way system with a 4" or 5" mid range and very large woofer. Also, the speaker height of 32" to 34" is an ideal height allowing more ease in positioning the speakers while seated in the listening area. A tower system seems to provide a much better sound stage, less localization even in difficult rooms, and better definition and detail for both music and movies.

Obviously there is much more to choosing a sound system than what I have generalized, but again and again I have found that speakers that fit this general driver size and cabinet size along with a pair of carefully chosen sub woofers really works well in an average living room. I could go on into why a 7" or 8" driver may work better than a larger driver as well as other technical details, but I'm sure it has been covered in another thread. So when it comes to speaker size biggest is not always best.

Lastly, the WAF ( wife approval factor) often is better with a less obtrusive speaker cabinet like a mid sized tower and sub woofers can usually be included with a little imagination.
Edited by Phase700B - 8/30/12 at 6:59pm

The answer is, there is no way to know. Those frequency response specs have no relation to the sound quality. You must listen to the speakers.