What is the difference to play 80Hz SINE signal with 80 dBZ SPL between Large and Small speaker？

[Sokel]

You're kinda just calculating a circle between the mounting holes of a driver, not the actual area of the driver that moves.

Yes I thought of that,also the depth must change by the same ratio so you're right (that's what I put the "more" in the parenthesis).

 

[DonH56]

If my calc is right a 10" has 3.5 times (or more) the area of a 5",so the travel is 3.5 times more.

Dude, a 5" driver has like 70 cm² surface area (SATORI 5" MW13TX-4 ), a 10" driver around 350 cm² (Scan-Speak 26W/4558T00 ), a factor of ~5, not 2.

Too old really to be a "dude" but you are both right, brain fart, had diameter in mind but output (and excursion) scales with area and not diameter.

A = pi*r^2, at least I remember that one, so twice the diameter is four times the area.

And of course 5" and 10" driver sizes are usually inclusive of the surround and sometimes mounting ring, so not exactly double, but the idea was a simple calculation for the OP.

 

[MengW]

Piston Excursion calculator

www.baudline.com

There is one Xmax calculator of the different size loudspeaker and I did paste the Xmax result of the large and small loudspeaker at same SPL @ 1 meter to play the 80Hz.
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I think what I am interested in is, based on the principles of room acoustics and speaker acoustics, what is the difference between a large speaker and a small speaker to play the easy and simple sine signal with the same sound pressure level at the listening position?

 

[dasdoing]

the famous pizza trap. many would accapt two 8" instead of the 16" and loose money

 

[thulle]

Too old really to be a "dude"

I guess the influence of the language use in forums where I'm among the older participants shines through, I'm using dude more as a age-less and even gender-less word to interject/bring attention to something, basically like a "hey".

but you are both right, brain fart, had diameter in mind but output (and excursion) scales with area and not diameter.

Yeah, SPL is relative to the air volume swept by the driver. And as surround width increases the area that moves less increases (simplified: one side of the surround moves as much as the cone, the other side moves nothing, the average of the surround movement thus is ½ the cone movement) which makes for another inefficiency in using a small driver.

 

[thulle]

Piston Excursion calculator

www.baudline.com

There is one Xmax calculator of the different size loudspeaker and I did paste the Xmax result of the large and small loudspeaker at same SPL @ 1 meter to play the 80Hz.
--
I think what I am interested in is, based on the principles of room acoustics and speaker acoustics, what is the difference between a large speaker and a small speaker to play the easy and simple sine signal with the same sound pressure level at the listening position?

It becomes physically impossible for the small driver to play a low frequency signal at the same sound pressure as a large driver. See sound pressure as moving water with a bucket, and frequency how often you get to empty the bucket. With a small bucket you just can't move as much water as with a large bucket, you would have to move it more times per second, but that isn't allowed since it would be playing another frequency.

 

[DonH56]

Piston Excursion calculator

www.baudline.com

There is one Xmax calculator of the different size loudspeaker and I did paste the Xmax result of the large and small loudspeaker at same SPL @ 1 meter to play the 80Hz.
--
I think what I am interested in is, based on the principles of room acoustics and speaker acoustics, what is the difference between a large speaker and a small speaker to play the easy and simple sine signal with the same sound pressure level at the listening position?

You seem to be going in circles. If the large speaker and small speaker can output the same level with the same distortion then their size does not matter. The room does not really matter except in a bigger room you may be further away thus need higher SPL. The problem is not one of basic acoustics, like the wave equations, but the practical problem of making a small speaker that can deliver the required output. Physics matters for more than acoustics.

 

[Deleted member 48726]

You seem to be going in circles. If the large speaker and small speaker can output the same level with the same distortion then their size does not matter. The room does not really matter except in a bigger room you may be further away thus need higher SPL. The problem is not one of basic acoustics, like the wave equations, but the practical problem of making a small speaker that can deliver the required output. Physics matters for more than acoustics.

Also the smaller driver are physically limited to how large a voicecoil can be fitted and thus in general are limited in how much power and heat it can dissipate before it starts to smell funny.

 

[MengW]

You seem to be going in circles. If the large speaker and small speaker can output the same level with the same distortion then their size does not matter. The room does not really matter except in a bigger room you may be further away thus need higher SPL. The problem is not one of basic acoustics, like the wave equations, but the practical problem of making a small speaker that can deliver the required output. Physics matters for more than acoustics.

If the large speaker and small speaker can output the same level with the same distortion, there are still some different between the large and small speakers.
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For example,
- the low frequency directivity performance
- group delay perfermance
- "Large speaker is closer to SURFACE sound sources, and small speakers are closer to POINT sources."
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These differences are real, but I don't know how much of the impact.
--
Also is there some performance difference like this type?

 

[BDWoody]

See sound pressure as moving water with a bucket, and frequency how often you get to empty the bucket. With a small bucket you just can't move as much water as with a large bucket

It's more like a shallow bucket vs a deep bucket.

The excursion would be the depth of the bucket.

 

[thulle]

It's more like a shallow bucket vs a deep bucket.

The excursion would be the depth of the bucket.

I think of a small bucket as low volume bucket, a large bucket as a larger volum bucket. A bucket with disproportionally low depth isn't a bucket, it's more like a tray
But it's volume that matters, not shape, so I'm not sure why you're bringing it into this

 

[MengW]

It's more like a shallow bucket vs a deep bucket.

The excursion would be the depth of the bucket.

I prefer to imagine big and small hand fans. Use the same frequency, fan out the same air volume.

 

[puppet]

The large loudspeaker is 15 inches, the small loudspeaker is 8 inches, and they have the good performance to play the 80Hz with -0dB.



IF the listen distance is same, for example 2.5 meter,
Why can't I use small speakers in a large room？
Why can't I use large speakers in a small room？



Thanks a lot.

As the volume of the room increases so does the need to overcome the spl losses at the listening position. The acoustic radiation is like a balloon ... not a straight line. The larger room has more internal volume to fill vs the smaller space. A smaller loudspeaker will require more power in a large room than a larger loudspeaker will. The increased Sd of the drivers in the larger loudspeaker win out over the smaller loudspeakers drivers.

 

[DonH56]

If the large speaker and small speaker can output the same level with the same distortion, there are still some different between the large and small speakers.
--
For example,
- the low frequency directivity performance
- group delay perfermance
- "Large speaker is closer to SURFACE sound sources, and small speakers are closer to POINT sources."
--
These differences are real, but I don't know how much of the impact.
--
Also is there some performance difference like this type?

Why do you keep asking if you already know the answer?

At 80 Hz the smaller and larger speakers in your examples are effectively point sources so dispersion is irrelevant. As frequencies increase to where their wavelength approaches the diameter of the speaker then dispersion becomes a factor and they will transition to directional sources. That has already been mentioned in this thread.

At higher frequencies a larger cone is harder to move (inertia) and keep from flexing (modal distortion). There are a lot of reasons different sized speakers are used for different frequencies. May be time to get a book (or class) or two and go beyond trying to learn it all on the 'net.

AFAIK physical speakers are minimum-phase; group delay in speaker systems usually arises from the crossover and not the drivers except for physical position in the box.

I think I've chased my tail as much as I can; hopefully others can better help answer your questions.

 

[audiofooled]

I'll try one more time. Read the notes on the Piston Excursion calculator. Try a free software like WinISD, take a smaller driver and a larger one and model a simple closed box. Take a look at drivers TS parameters just to see how many of them there are and that drivers are different, period. Observe how different will a small and large driver behave in different plots that the software has to offer. Then imagine a real situation where you put them in a box and in a room. They will sound different. Maybe similar in that 80 Hz, 80 db sinewave, but lower in frequency and higher in SPL, for the smaller driver you'll need a ported box, and/or DSP, if it can handle additional power. Ported box is another can of worms in terms of driver behavior and frequency response. DSP will basically demand more excursion and more power for the given frequency, so if the smaller driver can handle it, ok, but if not, distortion would sky rocket.
Yes, you could probably level match smaller and larger driver at a single frequency in the same room and hear no difference. Then lower the frequency just a bit and already the smaller driver will be more quiet, so you'd have to give it more power to level match again. What's the point?

 

[MengW]

Why do you keep asking if you already know the answer?

At 80 Hz the smaller and larger speakers in your examples are effectively point sources so dispersion is irrelevant. As frequencies increase to where their wavelength approaches the diameter of the speaker then dispersion becomes a factor and they will transition to directional sources. That has already been mentioned in this thread.

At higher frequencies a larger cone is harder to move (inertia) and keep from flexing (modal distortion). There are a lot of reasons different sized speakers are used for different frequencies. May be time to get a book (or class) or two and go beyond trying to learn it all on the 'net.

AFAIK physical speakers are minimum-phase; group delay in speaker systems usually arises from the crossover and not the drivers except for physical position in the box.

I think I've chased my tail as much as I can; hopefully others can better help answer your questions.

Thanks a lot.

I did set these conditions with the 80Hz sine signal, 80 dBZ SPL, 2.5 meter listening distance, aim to eliminate the difference what I know between the big and the small speaker at frequency, SPL, Xmax, distortion and timbre.

In the past, I have struggled to find these differences (the bigger size layout, directivity, group delay and "surface/point sources" ) , but I don't think which is the key reason for "big room need big speaker". So I hope to find more reasons here.

Perhaps the key reason is still just listening distance, SPL, distortion and low frequency performance, because the sentence "big room need big speaker" was not designed for complex problems.

 

[MengW]

As the volume of the room increases so does the need to overcome the spl losses at the listening position. The acoustic radiation is like a balloon ... not a straight line. The larger room has more internal volume to fill vs the smaller space. A smaller loudspeaker will require more power in a large room than a larger loudspeaker will. The increased Sd of the drivers in the larger loudspeaker win out over the smaller loudspeakers drivers.

Great!

Could you tell me the full name of the "Sd" in the last sentence?

Thanks.

 

[dc655321]

Great!

Could you tell me the full name of the "Sd" in the last sentence?

Thanks.

Sd is the surface area of the driver. The notation is from the Thiele-Small formulation. I think…

 

[Chrispy]

Curious, what is the point of this exercise, to determine the smallest possible speaker to "fill" the room to the OP's satisfaction?

 

[MengW]

Curious, what is the point of this exercise, to determine the smallest possible speaker to "fill" the room to the OP's satisfaction?

Great question.

Perhaps the purpose is a little naive, a little silly~~~

Try to use some technical language or logic to explain the subjective feeling and common sense.

What is the “fill”？
Why the small speakers can't fill the big room?