Large vs small

[Flint]

I found Sound & Vision's test bench measurements of the Performa3 lineup, in this case the larger F208, and it seems clear to me that Revel intended all of the Performa3 speakers to be used in HT installations and always set to "Small" with a good subwoofer.

This graph shows the quasi-anechoic (employing close-miking of all woofers) frequency response of the F208 L/R (purple trace), B112 subwoofer (blue trace), C208 center channel (green trace), and M106 surround (red trace). All passive loudspeakers were measured with grilles at a distance of 1 meter with a 2.83-volt input and scaled for display purposes.
Read more at https://www.soundandvision.com/cont...speaker-system-test-bench#HV1qfwYIeXTEzkVH.99

 

[bmwuk]

Okay. Will make the changes tonight. Makes sense and thanks for talking me through it.

 

[bmwuk]

So definitely on the port plug? Seems to make sense based on what you showed. Have to dig them out of the boxes in my attic.

Btw I didn't understand all of the explanation when you mentioned octave.

 

[Flint]

So definitely on the port plug? Seems to make sense based on what you showed. Have to dig them out of the boxes in my attic.

Btw I didn't understand all of the explanation when you mentioned octave.

An Octave is a range on a musical instrument. The low E on a standard tuned Bass Guitar is about 41.5Hz if tuned to the common A440 pitch. The E above that is one octave higher, which is about 82Hz. So, when making relationships between the frequency response of a speaker as it pertains to music, we often use the term, "octave".

Our hearing range, 20-20,000Hz, is just under 10 octaves, but most of us don't really hear pitch above about 8,000Hz. So, our practical musical pitch hearing range is about 8 octave, or from 20Hz to about 6,000Hz (with many exceptions for certain instrument sounds and individual variation).

It isn't entirely perfect, though, as a bass guitar's root pitch at low E is 41.5Hz, what we here is mostly harmonics which are at higher frequencies. An upright jazz bass or classical double bass make a more pure 41.5Hz pitch when playing the low E, so they tend to resonate the bass in the room more than, say, a rock & roll Fender Precision bass playing the same notes.

But, when I consider the range of a standard 4 string electric bass guitar, which is approximately 40Hz to 200Hz (plus the harmonics commonly heard up to about 1,600Hz), when I think about blocking the bass from my main speakers below 80Hz, I am taking about one octave of bass guitar range out of the main speakers and putting it into the subwoofer - though all of the harmonics will likely come from the main speakers which will give the impression the mains are the source of the bass guitar sound.

Then, when considering a four way speaker system, with the subwoofer handling low bass, a set of woofers handling the mainstream bass, a midrange driver handling the mids, and a tweeter for the treble, you have the octaves divided sorta as follows:
Subwoofer: 2 octave (20 - 80Hz)
Woofers: 3 octaves (80 - 320Hz)
Midrange: 3 octaves (320 - 2,560Hz)
Tweeter: 3 octaves (2,560 - 20,480Hz)

So, that's how I like to relate speaker driver ranges to real world brain functions on how we hear music and pitch.

 

[PaulyT]

A simpler answer is that an "octave" is a factor of two in frequency; one octave up from 80Hz is 160Hz, one octave down from 2000Hz is 1000Hz. And yes this is the same thing as an octave in musical pitch.

 

[Flint]

A simpler answer is that an "octave" is a factor of two in frequency; one octave up from 80Hz is 160Hz, one octave down from 2000Hz is 1000Hz. And yes this is the same thing as an octave in musical pitch.

Absolutely correct.

I was explaining why I bother using terms like octave when I could just say "double..." or "half the frequency."

 

[PaulyT]

Yeah I know. It's all good info, thanks.

 

[Razz]

wow...
Good stuff Flint! Thanks

 

[bmwuk]

I always wonder if I'm doing too many questions because if I look at the posts in the audio section, it seems many of the posts show my avatar. I fully appreciate the responses. Now I shall reread the earlier posts now that I know what octave is. I don't pretend to be knowledgeable on music reading or looking at these graphs.

 

[Xgm3]

I always wonder if I'm doing too many questions because if I look at the posts in the audio section, it seems many of the posts show my avatar. I fully appreciate the responses. Now I shall reread the earlier posts now that I know what octave is. I don't pretend to be knowledgeable on music reading or looking at these graphs.

You won't know unless you ask.

 

[Flint]

This stuff is very rarely discussed. Anytime two speakers are operating at the same frequencies and are being fed the same signal, there will be frequency cancellation nulls and contributed modes which could really wreak havoc on the overall balance of the sound.

 

[bmwuk]

This stuff is very rarely discussed. Anytime two speakers are operating at the same frequencies and are being fed the same signal, there will be frequency cancellation nulls and contributed modes which could really wreak havoc on the overall balance of the sound.

Alright, I went back through the discussions and your answers. I understand now a little bit what you are saying .

Now some questions without me sounding too uneducated...oops too late

1. As for the plugging of the ports, if the port frequency is at 42hz and I plug it, bumping it up an octave of 84hz and I have bass xover at 80hz, is there not a small frequency gap in the sound? Hope that makes sense...
2. I believe if I run any speakers at large on this receiver, the bass does not get sent to the sub. It would be getting back to doing the bass plus and then center and sub cancelling out each other, what range I don't remember the logic. (20-80hz?) So I think I HAVE to run the center on small as well

 

[bmwuk]

To add, my receiver will probably be happy not trying to drive 3 speakers at full range

 

[Towen7]

I may have missed this but ... can you not set the RCVR to “small” and adjust the crossover to something like 60Hz?

 

[Flint]

Alright, I went back through the discussions and your answers. I understand now a little bit what you are saying .

Now some questions without me sounding too uneducated...oops too late

1. As for the plugging of the ports, if the port frequency is at 42hz and I plug it, bumping it up an octave of 84hz and I have bass xover at 80hz, is there not a small frequency gap in the sound? Hope that makes sense...
2. I believe if I run any speakers at large on this receiver, the bass does not get sent to the sub. It would be getting back to doing the bass plus and then center and sub cancelling out each other, what range I don't remember the logic. (20-80hz?) So I think I HAVE to run the center on small as well

1) No, it doesn't exactly work that way. The plugged port won't necessarily raise the low frequency cutoff an entire octave, it should raise it a bit, like to 60Hz, and then give the bass a slower roll-off rate than with the open port. Sealing the port could actually result in a bass limit (-10dB point) lower than the open port option. Also, the crossover isn't a brick wall. Most are 12dB per octave or 18dB per octave roll-off slopes which start slightly above the stated frequency (80Hz) and at the stated frequency it is 3dB lower than the passband frequencies. So, a little dip on a speaker which is already acting wildly due to placement and room issues shouldn't be a problem. Even with the potential of maybe having a slight reduction of the SPL at 80Hz, the other benefits of lower distortion, smoother acoustic phase response (to blend with the subwoofer - you should retune the crossover settings after plugging the ports) and higher power handling will be preferred.




2) I have no idea how "bass plus" works. But, if you run the center as large it should be able to handle everything in the center channel signal completely on its own without any assistance from the subwoofer. I base this opinion on the measurements, specs, and design. So, if you set it to large and turn off Bass Plus, the center will take the entire center channel signal by itself, but I assume the bass for the stereo front and the surround channels, plus the LFE, will still go to the subwoofer??? If so, set the center to "large", all the rest of the speakers to "small" and turn off "bass plus".

 

[Flint]

To add, my receiver will probably be happy not trying to drive 3 speakers at full range

Technically, correct. Although, based on your listening levels and the size of your room, I seriously doubt your receiver is barely breaking a sweat anyway.

 

[bmwuk]

1) No, it doesn't exactly work that way. The plugged port won't necessarily raise the low frequency cutoff an entire octave, it should raise it a bit, like to 60Hz, and then give the bass a slower roll-off rate than with the open port. Sealing the port could actually result in a bass limit (-10dB point) lower than the open port option. Also, the crossover isn't a brick wall. Most are 12dB per octave or 18dB per octave roll-off slopes which start slightly above the stated frequency (80Hz) and at the stated frequency it is 3dB lower than the passband frequencies. So, a little dip on a speaker which is already acting wildly due to placement and room issues shouldn't be a problem. Even with the potential of maybe having a slight reduction of the SPL at 80Hz, the other benefits of lower distortion, smoother acoustic phase response (to blend with the subwoofer - you should retune the crossover settings after plugging the ports) and higher power handling will be preferred.




2) I have no idea how "bass plus" works. But, if you run the center as large it should be able to handle everything in the center channel signal completely on its own without any assistance from the subwoofer. I base this opinion on the measurements, specs, and design. So, if you set it to large and turn off Bass Plus, the center will take the entire center channel signal by itself, but I assume the bass for the stereo front and the surround channels, plus the LFE, will still go to the subwoofer??? If so, set the center to "large", all the rest of the speakers to "small" and turn off "bass plus".

Okay. I will double check on the receiver. Hoping that it was only the mains that drove that issue with bass not playing on the sub.

So I believe you are still in the "plug" camp, correct?

 

[Flint]

Okay. I will double check on the receiver. Hoping that it was only the mains that drove that issue with bass not playing on the sub.

So I believe you are still in the "plug" camp, correct?

Yes...

See, here's the deal, even with an 80Hz crossover frequency, the mains are still putting out sound below 80Hz where when the ports are open there will be extreme phase shifts in the output. As such, plugging the ports and retuning the subwoofer to sound as perfect as possible will result in a flatter, cleaner, more pure bass sound.

 

[PaulyT]

I always wonder if I'm doing too many questions

Never worry about that! Good to have audio being discussed on the AUDIO Annex!

 

[Dentman]

Great thread.