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Large vs small

Discussion in 'Configuration & Setup' started by bmwuk, Jul 8, 2018.

  1. bmwuk

    bmwuk Well-Known Member

    Yes I realize this may have been covered before but just asking from you guys on my setup.

    Currently I have a Yamaha TSR-7790. It seems like a good receiver for processing but the bass management seems weak. Unless I'm missing the feature, it only has a universal bass crossover for the sub. So I have a wonderful front sound stage with the Revel F206s for mains and the beast of a C208 for the center. I presently have the mains and center set to large.

    Thanks to @Dentman he helped me setup the phone app for Yamaha to send the bass to the sub and the the speakers set to large. However after watching Interstellar and reading some info about people messing up their speakers, I'm a bit concerned about messing up my speakers. I'm sure the mains and centers can handle below 80hz easily but that low end I'm not sure.

    So questions:

    1. Is this current setup okay for my speakers?
    2. Would I be better with the receiver to not have them drive full range? I feel the center and mains aren't being fully utilized in small. But then no way I can my bookshelf speakers handle lower than the 80hz.

    Thanks
     
  2. Flint

    Flint "Do you know who I am?" Superstar

    Unless you are blasting it (like consistrntly over 100dB SPL) , you should be fine.

    That said, the output below the tuning frequency of the cabinets for your mains and center will be out of phase with your subwoofer and will cancel each other ou TV in the range down to the tuning frequency of the sub cabinet.
     
  3. JeffMackwood

    JeffMackwood Maxi-Me

    Maybe it's because I've been drinking rather heavily for the last few hours, but me and my super duper decoder ring are having trouble figuring that one out.
     
  4. Flint

    Flint "Do you know who I am?" Superstar

    So... the main speakers have a tuning frequency of about 28Hz and reaches a peak phase inversion at about 18Hz (using Stereophile's measurements). His subwoofer (PSA 15V) is tuned to something like 20Hz, so if we assume after careful tuning of the crossover controls, the range between 28Hz down to about 19Hz puts the Revel mains in conflict with the PSA sub because the Revel mains swap phase starting at the 28Hz tuning frequency while the PSA sub doesn't do the same swap until you get down to about 20Hz, or so. While the output from the mains will also drop below the tuning frequency, that doesn't mean they are not generating appreciable air pressure until you get about 10dB down, which according to Stereophile's measurements is about 20Hz. So, in the range from about 20Hz to about 28Hz the mains and the sub are fighting each other because one is canceling out the other.

    I don't have the specs on the center, but I imagine it isn't much different.

    So, I would not be surprised that if the mains and center are set to LARGE and the bass from those channels is also being sent to the subwoofer that there is a clear and obvious lack of output in the bass below 30 Hz. The LFE channel should only be going to the subwoofer, so that should not be affected. Only the bass in the mains and center which is also being directed to the subwoofer will cancel each other out.
     
  5. Flint

    Flint "Do you know who I am?" Superstar

    By the way, this out of phase stuff can be dramatically reduced by plugging the ports on the mains and the center because the port is where the out of phase energy comes from. It will reduce the bass output a bit, but with a good subwoofer that shouldn't matter.
     
  6. Flint

    Flint "Do you know who I am?" Superstar

    Well.... all of my estimates on the tuning frequency of the Revel mains were wrong, I was looking at measurements of the F208, not the F206 which Bryan has.

    So, instead I will estimate the conflicting range between the F206 speakers and the Subwoofer is from about 30Hz to about 45hz. Because of this, I recommend both plugging the ports on the F206 and setting them to small. Even with a 80Hz crossover to the sub, it would significantly improve the performance of the sub in the room. It would also reduce the distortion of the output in the mains above 80Hz.
     
  7. JeffMackwood

    JeffMackwood Maxi-Me

    Pardon my remaining confusion but...

    I was not able to download a copy of the receiver in question's owner's manual, so I'm going entirely on previous posts / assumptions.

    If the mains (F R/L) and centre are set to large I assume that no bass management will take place with those channels. Since they represent the greatest likely presence of low(er) frequencies it seems that the sub will rarely, if ever, be in conflict with whatever signals are present / output from those channels. The LFE signal that is present (with no bass managed signal of any consequence) will likely be so low as to not conflict (phase-wise) with what's happening in the "mains."

    And even if those speakers were set to "small" and assuming that this means a fixed crossover (bass management frequency) of 80 Hz, then again this will be well above anything frequency where phase will come into play. The LFE will be the same as with a "large" setting.

    Again (not having an owner's manual to consult) these seem to be the only two choices (for the mains.) It would therefore be really easy to change the settings, compare the two, and choose the one that sounds the best.

    If the same signal was present in both the mains and the sub, but out of phase, I can see where there would be a conflict. But in both cases considered above I don't see where there would ever be the same signal present. That is, after all, the whole purpose of proper bass management and a separate LFE channel - whether simple as assumed here, or more complex where different bass-management crossover frequencies can be selected.

    What am I missing?

    Jeff
     
  8. Flint

    Flint "Do you know who I am?" Superstar

    I was under the impression that Bryan found a way to let the mains and center and the sub operate in the same bass range.
     
    Dentman and bmwuk like this.
  9. JeffMackwood

    JeffMackwood Maxi-Me

    Ok. I understand - if that's the case.

    I assume that you mean a case of the classic "double bass" effect where one can choose to send the bass-managed frequencies to the sub (and exclude them, from the channels being bass-managed) or send them to the sub AND allow them to remain in the bass-managed channels (hence the double-bass effect.) In the latter case phase could / would be a potential issue.

    Some Outlaw products (like the Model 950 I think) gave the user that option.

    Jeff
     
  10. Xgm3

    Xgm3 Active Member

    What does plugging a port on a speaker do? And what would one use to plug the speaker port? The title of this thread and the plugging of ports can go a lot of different ways.:bouncygrin:
     
    Last edited: Jul 8, 2018
  11. Flint

    Flint "Do you know who I am?" Superstar

    Dude, this is a family forum..... lol

    So, plugging a port on a speaker will typically reduce the bass output significantly starting about an octave above the tuning frequency. It prevents the resonance of the tuned enclosure from existing and instead makes the speaker behave more like a closed box, though often a closed box larger than what would be ideal for a sealed acoustic suspension system. Since the port enhances the bass output be resonating at a specific frequency exactly out of phase with the woofer, plugging the port not only reduces the deeper bass, but it also stops the phase shift which occurs when the majority of the sound energy shifts from the woofer to the port. It also adds some restriction to the motion of the woofer at lower frequencies which will increase the power handling of most high quality woofers. The mechanical resistance of the sealed box also increases the electrical impedance at the lower frequencies and reduces the voltage feeding the voice coil from the amplifier.

    So, the net result is a speaker system with 1) less deep bass (which doesn't matter if the set the speaker to small and the speaker is designed to operate to frequencies lower than the receiver's "small" setting crossover frequency); 2) more power handling in the operating range; and 3) significantly less phase shift and group delay in the frequencies where the port used to operate. If you have a great subwoofer and the speaker is designed to operate about an octave lower than the subwoofer's crossover frequency, this is a often a good idea.

    As for how to plug the port, I usually use a wash cloth, hand towel, or dish towel folded and rolled very tight to make a good seal on the port. For a proper plug, you can sometimes find acoustic foam of the right cylindrical shape to plug the port.
     
    Xgm3 likes this.
  12. Flint

    Flint "Do you know who I am?" Superstar

    Here are some test results of a real world speaker, the classic Insignia 6.5" coax home theater speaker I modified for a project back in the S&V forum days. After all my modifications to the cabinet and crossover, I measured the performance with the front port open and with it plugged.

    First we have the frequency response:
    Insignia 6.5 Plugged & Not.jpg
    The blue response curve is for the open port, notice the higher output in the 60Hz to 160Hz range and the lower output in the octave centered at 600Hz. The output below 140Hz was reduced in the yellow (sealed port) curve because the port was no longer contributing to the output, and the dip at about 600Hz is from the hole in the front baffle not reinforcing the output from the woofer. I had recommended to people who made the modifications I made to plug the ports (which I did with a rolled up dish rag) if they were setting them to "small" and using a good sub with a crossover setting at 80Hz.

    The more interesting measurement was the THD measurement for a 74Hz test tone at 10W:
    Insignia 6.5 10W 74Hz THD Ported Plugged.jpg
    It is clear that the midrange is significantly cleaner with the port sealed.
     
    Last edited: Jul 8, 2018
    Xgm3 likes this.
  13. Flint

    Flint "Do you know who I am?" Superstar

    And here's another example using the old SVS MBS-01 bookshelf speaker (which I still use in my family room system).

    The response with the speaker vented versus plugged is not a HUGE difference, but the bass is reduced when the port is plugged:
    MBS01_Ground_Plane_Resp.png

    But, if the look at the dynamic response of the speaker with the vent open versus closed, you can see the more dynamically accurate performance comes from the system with the port plugged.

    Dynamic response for the vented MBS-01:
    MBS01_Bass_Dynamic_Output_Vented.png

    Dynamic response for the MBS-01 with a plugged port:
    MBS01_Bass_Dynamic_Output_Plugged.png
     
    Xgm3 likes this.
  14. Xgm3

    Xgm3 Active Member

    Thanks for the info! Unfortunately I don't have True RTA to test my speakers.
     
  15. bmwuk

    bmwuk Well-Known Member

    Wow. The wealth of information. The F206s had plugs for the ports provided but I currently am not using them. The C208 is sealed already.
     
  16. bmwuk

    bmwuk Well-Known Member

    Okay so to recap, continue to keep the speakers on large, plug the ports on the F206s and continue with the bass plus which sends the low frequency to mains, center and sub?

    Is that what i read correctly?
     
  17. Flint

    Flint "Do you know who I am?" Superstar

    If it were me, I would not do the "bass plus" thing. The issue with ports being out if phase is only one of many problems you encounter when two or more mismatched speakers placed in different locations are producing the same signal. Basically, you only want identical speakers producing the same frequency range or there will be inherent acoustical signal cancellations in the room which are not addressable unless you start using a complex DSP to apply phase correction. Also, room placement even with identical speakers at low frequencies plays a huge role in how well they will work together. The mains need to be placed for ideal stereo imaging so you dr ont have the flexibility to move them around to work better for bass in conjunction with a separate sub.
     
  18. bmwuk

    bmwuk Well-Known Member

    The sub does not play if speakers are set to large, without the bass plus. So is the suggestion then to go "small" on the speakers ? I wish I could crossover the speakers individually.
     
  19. Flint

    Flint "Do you know who I am?" Superstar

    Since those speakers don't play all that low (42Hz), why are you set on having them set to large? With a 80Hz crossover you are sacrificing one octave of bass which your sub can easily handle. The woofers would still be operating from about 80hz to 275Hz, which is approximately 2.5 octaves of sound - not bad at all.

    I found the extremely reliable NRC measurements for your speakers.

    Here's the listening window frequency response:
    [​IMG]
    Notice the bass dramatically drops off below 100Hz... these speakers were not really intended for use as serious bass output machines.

    Here's a handy measurement of the THD at a average to slightly loud listening level (about 88dB SPL):
    [​IMG]
    Look closely at the distortion (bottom curve). It is pretty high below 100Hz.

    You can also consider your sub's and mains' overall mechanical ability to produce deeper bass - the cone area of your 15" subwoofer is about 820 cm2 where the combined cone area of the four 6.5" woofers in your mains is about 530 cm2 - the sub's cone area is nearly 55% greater, making the addition of those 5 main woofers not terribly impactful in terms of added output power in the room.
    Given your limited options and the fact the vast majority of your listening is surround sound soundtrack content (and not critical two channel listening), at least on paper, my advice is to plug the ports and set the speakers to small and enjoy the results. Keep in mind, low bass is the hardest frequency range to get right as it involves complex room issues, fragile speaker limitations, and so on. Your mains and center will play significantly cleaner & louder and with more dynamic punch if they are not being forced to produce the deeper bass.
     
  20. Flint

    Flint "Do you know who I am?" Superstar

    I will add, the center has plenty of bass output (-10dB at 34Hz in a sealed enclosure) and it is extremely rare that any soundtrack engineer would put deep bass into the center channel signal, so you could set it to "large" and turn off the "bass plus" for the center channel. That should work very well.
     

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