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betty boop

How Much Power Do I Need ?

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That's right, one might own a racing car of enormous power but there is generally little need to use that capability to go to the local shop, so it is with high power amplifiers and small rooms.

C.M

My race car can get to the shops and back, plus allow me time to eat my hamburger, faster than you can get out of your driveway. Like audio it's not about top speed (loudness) it's about acceleration (response).

Cheers

Gary

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My race car can get to the shops and back, plus allow me time to eat my hamburger, faster than you can get out of your driveway. Like audio it's not about top speed (loudness) it's about acceleration (response).

Cheers

Gary

No, audio is not about top speed (loundess) or acceleration (response), it is about how good your system sounds to your ears.

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My race car can get to the shops and back, plus allow me time to eat my hamburger, faster than you can get out of your driveway. Like audio it's not about top speed (loudness) it's about acceleration (response).

Cheers

Gary

When all is said and done it all comes down to the transparency and the dynamics of the speakers you are using. Over the years I have built and designed many speakers and finally resolved the best sounding speaker design of them all, at least to my ears, and that is a properly designed Open Baffle loudspeaker.

Anything in a box sounds like something in a box regardless of the quality of the drivers. The transparency and the dynamics exhibited by drivers freed from an enclosure and working under a properly designed crossover for the purpose will convince you, there is something much, much better than the boxed counterpart.

What's more it can be done relatively cheaply too. OB speakers are much more musical and exhilarating, in my experience.

C.M

Edited by Tweet

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No, audio is not about top speed (loundess) or acceleration (response), it is about how good your system sounds to your ears.

To my ears if it's not responsive (dynamic, punch, slam, grunt etc) then it doesn't sound good.

Cheers

Gary

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On 31/12/2007 at 12:37 AM, norpus said:

The THX Home Cinema certification calls for a flat power response from the subwoofer down to 20Hz with an SPL of at least 105dB

http://www.subwoofer-builder.com/SPL-comparison.htm

Note, doing 20Hz takes twice as much power (and more excursion) as doing the 40Hz (where most smaller box subs are happy at.)

I recall JA measuring my front IB at nearly 130dB at the throat (no room gain) so I think I have the THX spec covered :)

It's really unlikely that you've got a 20 hz frequency happening. Also the power required to produce a certain frequency is related to the impedance at that frequency.

If your room isn't sealed you have tp be ay the quarter wave of the frequency which fot 20 hz is 16.4 meters. 

 

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On 02/01/2018 at 10:50 PM, magical said:

It's really unlikely that you've got a 20 hz frequency happening. Also the power required to produce a certain frequency is related to the impedance at that frequency.

If your room isn't sealed you have tp be ay the quarter wave of the frequency which fot 20 hz is 16.4 meters. 

 

that old chestnut - producing low bass in a room that isn't sealed doesn't require a big room IME.

 

I ran a whole bunch of tests, generating low bass in different sized rooms, from an open deck to three different sized rooms reducing in size down to toilet sized (literally), both as sealed as I could get them, and windows and doors open.

The measured bass in all cases was much lower than the lowest mode based on room dimensions.

The measurements didn't change that much between "as sealed as I could get" and "all windows and doors open" - at least regarding how low the bass got to.

On 02/01/2018 at 10:50 PM, magical said:

quarter wave of the frequency which fot 20 hz is 16.4 meters.

The lowest mode generated in a room is the longest room dimension = wavelength/2, not wavelength/4 - but this is just where modal support stops, not how low you can generate bass - room sealed or unsealed.

 

In any room, below the lowest modal frequency, you just need drivers with enough cone radiating area/excursion (and amp power) to generate pressure change in the room - which does not require the room to be sealed.

 

Smaller systems may require the bass boost of modes and room gain to hit SPL targets at lower frequencies - a smaller system may be able to generate 20Hz "in room" but only get down to 50Hz outdoors.

 

A speaker able to generate 20Hz outdoors will easily generate 20Hz "in room", regardless of the size of the room.

 

A great thought experiment put forward by @davewantsmoore on the ability for small rooms to have low bass:

"You have a speaker generating 20Hz outdoors - now wrap a room around it - the bass hasn't gone..."

 

cheers

Mike

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On 02/01/2018 at 11:50 PM, magical said:

If your room isn't sealed you have tp be ay the quarter wave of the frequency which fot 20 hz is 16.4 meters. 

I'm not quite sure I can understand exactly what you mean here .... but it seems to be wrong.

 

You can make 20Hz in any sized room... and you can hear 20Hz, when you are any distance from a sound source.

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On 18/09/2018 at 7:11 PM, davewantsmoore said:

I'm not quite sure I can understand exactly what you mean here .... but it seems to be wrong.

 

You can make 20Hz in any sized room... and you can hear 20Hz, when you are any distance from a sound source.

 

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I'm not going to engage in this conversation as you clearly have no idea about physics. You can pm me if you want to know facts. 

 

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6 hours ago, magical said:

you clearly have no idea about physics

As I said, perhaps I didn't understand your post correctly.   I've sent a PM.

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On 02/01/2018 at 11:50 PM, magical said:

It's really unlikely that you've got a 20 hz frequency happening.

I didn't actually see this comment previously....

 

What would you assume that?    It's possible he may not (lots of things are possible) .... but it is not difficult (hence not "unlikely") to do (ie. make 20Hz), and trivial to confirm whether energy exists at 20Hz (or not) and the level.

 

10 hours ago, magical said:

I'm not going to engage in this conversation as you clearly have no idea about physics.

Just let me also say that comments like this are particularly unhelpful  as they cast vague conjecture over everything which is being said, and leave people who know no better none the wiser - and then they typically (and very incorrectly) conclude that "nobody agrees on/understands these things".

 

If I am wrong, then lay that out.... and help (me and) everyone.     If I understand why you think I'm wrong, I can counter, or I can clear up whatever misunderstanding there is between us (much more likely outcome).

 

If you have been involved in any type of collaborative science at any level, you would understand this quite well.

 

FWIW.   I only took the first 2 years (out of 3) of physics in my undergraduate science degree - as I majored in other things.... but I remain a keen student.  So please be quite specific.

 

 

 

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On 18/09/2018 at 7:11 PM, davewantsmoore said:

I'm not quite sure I can understand exactly what you mean here .... but it seems to be wrong.

 

You can make 20Hz in any sized room... and you can hear 20Hz, when you are any distance from a sound source.

 

Right.   I think I can see where the misunderstanding is now, and it is somewhat my fault.

 

The above bolded text ... assumes that 20Hz is located around or below the lowest eigenmode in the room.     ie. it assumes a room which is not enormous (or not so open, that it is really a much larger room).    

 

If there were a mode operating at 20Hz, then it would be possible to sit in a null (and not hear 20Hz due to the cancellation) .... and this is likely where the comment below comes from.

Quote

If your room isn't sealed you have tp be ay the quarter wave of the frequency which fot 20 hz is 16.4 meters. 

 

If the assumption is that there is a significant modal behaviour at 20Hz .... I think is a poor one, because:

 

  • It requires a room >> 60 cubic meters  (which would place the low mode close enough to 20Hz to have an effect)
  • Rooms which are "leaky" do not display significant modal behaviour below the (0,0,0) mode you would predict from the dimensions

 

This means that it is a safe assumption in a home sized room, that for 20Hz, it doesn't matter where you sit as are outside the frequency range where the modes are causing significant peaks and cancellations.

 

Even if the room did have modes around 20Hz ....   then the above statement need clarification.... "be at the quarter wave point" for what?    To be able to hear 20Hz at all?   No.

 

 

 

Edited by davewantsmoore

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On 02/01/2018 at 10:50 PM, magical said:

It's really unlikely that you've got a 20 hz frequency happening. Also the power required to produce a certain frequency is related to the impedance at that frequency.

If your room isn't sealed you have tp be ay the quarter wave of the frequency which fot 20 hz is 16.4 meters. 

 

based on some poorly phrased passages in respected texts (eg Everest) I had a misguided view that you couldn't produce bass below the lowest mode in the room unless the room was sealed.

I struggled to reconcile measuring 15 - 20Hz in various sized rooms well below the lowest mode based on room dimensions, both as sealed as I could get (windows/doors closed), and unsealed (windows/doors open).

My understanding of the physics was incorrect.

 

Below the lowest mode in the room (longest dimension = wavelength /2) there are no room related resonances occurring, but that doesn't mean sound can't exist in the room below the lowest mode, just that you don't get room related peaks and troughs...

Of course in a lightly constructed room you may still get modal peaks/troughs below the lowest mode based on room dimensions, as there may be more rigid boundaries outside the room contributing to modal behavior...

 

...if you consider a room of any typical construction without any rigid boundaries outside it, then you won't get modal behavior (room resonance) below the longest dimension = wavelength/2.

Below this frequency/wavelength you can still generate/hear/feel/measure frequencies if your speakers can generate it at sufficient SPL - IME regardless of whether the room is sealed or unsealed.

 

cheers

Mike

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On 25/12/2007 at 9:22 PM, betty boop said:

we're not talking the 1000w pmpo that you've seen on the chingwa htib at cash converters.

Gotta love it. Plastic watts

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As my first boss in Hifi used to say:  "They're called Amplifiers, not Wattifiers.

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