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Room size to match wavelength and bass quality?


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#1 of 39 OFFLINE   ChrisBee

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Posted June 13 2006 - 09:14 AM

Does anyone subscribe to the idea that a room has to be large enough to allow a half or even a full wavelength to exist for best bass sound quality?

Or is pressurisation of a smaller space just as good with regards to sound quality in the bass?

I am more interested in hearing opinions on quality rather than quantity. Posted Image

#2 of 39 OFFLINE   Geoff Gunnell

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Posted June 13 2006 - 09:36 AM

You've heard live music performed in different acoustic spaces -- lets at least agree the sound is 'different'.

Now look at recording studios -- size? monitors? headphones? define 'best' in this context...

The 'best' orchestral music I've heard is in small auditoriums reinforced with Altec speakers but that's just my taste...

#3 of 39 OFFLINE   John Garcia

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Posted June 13 2006 - 09:41 AM

I'd have to say half wavelength is a good thing for reducing cancellation, but that is already a very large room. I've experienced this first hand - small rooms, especially closer to square, are not good for bass and long, large rooms can actually enhance it (at least certain frequencies) oddly enough.
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#4 of 39 OFFLINE   ChrisWiggles

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Posted June 13 2006 - 11:33 AM

Quote:
Does anyone subscribe to the idea that a room has to be large enough to allow a half or even a full wavelength to exist for best bass sound quality?

No. There's this thing called physics. It tells you that that's nonsense.

#5 of 39 OFFLINE   Kevin C Brown

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Posted June 13 2006 - 12:35 PM

I agree with Chris W. But there *are* room dimensions that are bad for bass.

8x8x8 is bad. 8x16x24 is bad. Basically, repeating dimensions, or multiples are bad. You get too much constructive interference at very specific frequencies.
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#6 of 39 OFFLINE   Nathan W.

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Posted June 13 2006 - 03:59 PM

If this were true then all headphones would sound like tweeters, but they don't. Some have excellent deep bass, although you don't get the tactile effect on your skin or through the furniture as you could with a good sub throwin' out some deep notes.

#7 of 39 OFFLINE   ChrisWiggles

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Posted June 13 2006 - 04:59 PM

Quote:
Originally Posted by Kevin C Brown
I agree with Chris W. But there *are* room dimensions that are bad for bass.

8x8x8 is bad. 8x16x24 is bad. Basically, repeating dimensions, or multiples are bad. You get too much constructive interference at very specific frequencies.

Yes. One does not preclude the other. But you'll find people saying that there is a "lowest frequency that a room can support" which is nonsense. Yes there is a lowest frequency mode that depends on dimension size, but that does not mean that frequencies below that are nonexistant in the room. Rather, they just won't be subject to modal reinforcement or "room gain" one might say.

#8 of 39 OFFLINE   ChrisBee

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Posted June 13 2006 - 08:29 PM

So there is no change in the waveform below the half-wave minimum boundary dimension?

Is there no increase in harmonic distortion where a half wave cannot physically exist between boundaries?

A skipping rope cannot reproduce a specific half wavelength where the distance between the rope swingers is too short. Posted Image

#9 of 39 OFFLINE   Mark Seaton

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Posted June 14 2006 - 01:57 AM

Hi Chris,

There are changes below where a 1/2 wavelength won't "fit" in the room, usually defined by the longest dimension, top-to-bottom of opposite corners.

Below this point you no longer see modal behavior, problems, or variations. What you do see is a gain in LF output for a given subwoofer output. So in fact the result is the opposite: More output, less distortion.

In simplest terms you transition to a mode of pressure modulation, where you are basically modulating the pressure in the entire room. Remember that our ears react to air pressure modulations and it doesn't matter what causes the level of modulation, since the observer (us in this case) is exposed to the same changes in pressure as if they were outdoors.
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#10 of 39 OFFLINE   John Garcia

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Posted June 14 2006 - 01:58 AM

I agree with ChrisWiggles that there isn't really a limit to the lowest frequencies within a room, but as Geoff also said, the sound can vary considerably with the shape and size of the room. The specific modes created by the size of the room will most definitely affect the resulting bass.
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#11 of 39 OFFLINE   Arthur S

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Posted June 14 2006 - 02:25 AM

Besides headphones, it may be useful to think about how much bass can be reproduced in a car, let alone a relatively small room in your home.

#12 of 39 OFFLINE   Geoff Gunnell

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Posted June 14 2006 - 04:31 AM

Chris, the unfortunate thing is that typical residential room dimensions DO lead to the nodal pattern mentioned by others -- in other words it depends where you sit Posted Image how even the bass frequency response will be. The larger the space the less this occurs -- but by larger, I'm sure you've walked through bass nodes in small clubs -- I mean Much larger, as in 5 wavelengths or more.

I suppose one could go the other way and make the room much smaller than the wavelengths -- move your speakers into your bathroom Posted Image -- hmmm one could solve two pressurization problems at once Posted Image

#13 of 39 OFFLINE   Kevin C Brown

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Posted June 14 2006 - 12:50 PM

Maybe that's why we all sound so good ... singing in the shower. Posted Image
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#14 of 39 OFFLINE   ChrisBee

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Posted June 15 2006 - 10:20 AM

Thankyou for your interesting responses.

I was really trying to get at the difference in the bass sound quality between small room compression and a larger space able to support the half wave.
My fuzzy logic suggests that a large room should offer better quality bass.
(I'm not discussing room modes here. Just the distortion levels at the same low frequencies in both rooms from the same subwoofer)

Has anyone here actually measured the distortion levels of exactly the same subwoofer in both large and small rooms? Just to confirm if there is a measurable difference. One way or the other. Posted Image

#15 of 39 OFFLINE   Kevin C Brown

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Posted June 15 2006 - 12:32 PM

What would be causing that distortion?
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#16 of 39 OFFLINE   Jack Gilvey

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Posted June 15 2006 - 02:33 PM

Quote:
Originally Posted by ChrisBee
(I'm not discussing room modes here. Just the distortion levels at the same low frequencies in both rooms from the same subwoofer)


Room modes are distortion, in regards to ringing and frequency response.

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#17 of 39 OFFLINE   Geoff Gunnell

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Posted June 15 2006 - 03:46 PM

Chris, you are proposing that the room influences the cone or port radiation?

You are certainly correct that a lot of how we hear bass is due to the room -- but I think the sound being directly radiated from the speaker and port remains the same regardless of the surroundings. The room affects the sound only after it has left the speaker.

We could set up a 'perfect storm' scenario. Suppose a ported sub has a slight enclosure resonance at 40Hz, and you put the sub at a point in a room where 40Hz is reinforced. In this specific case the room would be contributing to a speaker distortion component.

But a general case eludes me...

#18 of 39 OFFLINE   ChrisBee

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Posted June 15 2006 - 07:17 PM

No. Of course I'm not suggesting the subwoofer itself is affected. Only its measured distortion performance in a particular room.

My basic question keeps nagging me: Can a room affect subwoofer distortion levels depending only on the dimensions of that room?

Your logic suggests that it doesn't. My logic suggests that it must.

I am just going to have to take my SVS cylinder down to the smallest room in the house along with my trusty SPL meter and try listening.
I'll report back if I survive the experience. My wife may kill me first! Posted Image

I suppose that room gain or even room modes would increase the in-room SPLs of a sub without extra effort from the subwoofer itself. But this would be so frequency dependent that any reduction in distortion (as a result of the free extra dBs) would be rather hit and miss.

If large room gain could be optimised to maximise the subs low end then that would be a free way of reducing distortion at those particular frequencies. The bottom end is where distortion rises rapidly with increasing output.... Hmm? Have I now answered my own question? Posted Image

#19 of 39 OFFLINE   LanceJ

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Posted June 15 2006 - 07:53 PM

This isn't exactly a scientific observation but I've tried out several pairs of speakers in my bedroom stereo system & my HT rig in the living room. Bedroom measures 14ft X 11.5ft, living room 19ft X 16ft with two @6 foot openings on the same long wall leading to the rest of the house.

> I am aware that final bass quality from two bass sources will be different than from a single one.

Speakers used: Boston Acoustics CR9s with a rear-ported 8" woofer (+/-3dB point at 42Hz), Pioneer CS-99A with a 15" woofer in a sealed 2.0cu/ft cabinet (25Hz-22kHz, no +/- range given*) and Infinity SL-30s with a 6.5" front-dual-ported woofer (manual w/spec page is long gone - 55Hz IIRC) and Radio Shack "Minimus" die-cast aluminum speakers with rear-ported 5.25" woofer (80Hz-20kHz is only spec provided) and Pioneer S-H253 bookshelf with front-ported 8" woofer (45Hz-35kHz is only spec provided, but these do seem to go nearly as low as the Bostons but lack their definition).

Findings: the quality of bass - the lowest that is feelable to its upper ranges - is always much better in the larger room. To use a food analogy Posted Image : bedroom bass is a burger from McDonalds; living room bass is one of those Big Mouth burgers from Chili's.

It's much less boomy so in turn is more defined sounding. Very lowest bass notes *are* less noticeable in the larger room, but they are definitely still present. The only speaker that really sounds good in the bedroom system is the Minimus speaker.....which I'm sure is due to the fact that it produces so little low bass (I figure this little guy gives up below 100Hz).

* detailed frequency graphs in the CS-99A's manual indicates frequency drops off quickly below 100Hz (100Hz when measured at speaker's average 95dB/SPL rating): 50Hz @82dB/SPL; 30Hz @70dB/SPL; 20Hz@66dB/SPL. In contrast, the much smaller Bostons have MUCH more low/"rumbly" bass & sound much better with movies that include such bass effects. But they cannot start to touch the CS-99As where music is concerned: bass guitars but especially drums (though not so much the bass drum) are nearly in the room with me, reproduced with incredible authority and definition at stupidly loud levels. The receiver powering them while they do this is a 23 year old Pioneer SX-6 with 45W/channel (at 8 ohms with .01%THD, 20Hz-20kHz)

#20 of 39 OFFLINE   Jack Gilvey

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Posted June 16 2006 - 01:05 AM

Quote:
Originally Posted by ChrisBee
No. Of course I'm not suggesting the subwoofer itself is affected. Only its measured distortion performance in a particular room.

My basic question keeps nagging me: Can a room affect subwoofer distortion levels depending only on the dimensions of that room?

Your logic suggests that it doesn't. My logic suggests that it must...


...If large room gain could be optimised to maximise the subs low end then that would be a free way of reducing distortion at those particular frequencies. The bottom end is where distortion rises rapidly with increasing output.... Hmm? Have I now answered my own question? Posted Image

Room modes and room gain are different. Room gain can lower distortion only inasmuch as it may allow you to turn down the subwoofer's level to achieve a given SPL. So, yes, turning down the sub lowers distortion.
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