[nicoch]

Equalization extends the frequency range of the system/driver, but it doesn't increase the power demand to create a desired excursion.

wrong ! if you need more db at 40hz ,you must push more watt with EQ

[nicoch]

This is why small-box sealed sub-woofers require so darn much power.
Dave.

only low efficiency speaker ie low qts low vas low fs big mass

[Davey]

wrong ! if you need more db at 40hz ,you must push more watt with EQ

The same would apply to a sealed box.  But you need more power for a boxed system.....all other things being equal.

Here's an experiment for you:  Install Driver X in an open-baffle and push it to Xmax at various frequencies.  Then install Driver X in a 1.0 cubic foot sealed box and do the same thing.

See which setup requires more power. 

Dave.

[JohnR]

What does a proper enclosure do to the native response of a driver in free air ?

Simplest thing is to use a simulation program like Unibox and enter the parameters of a woofer of interest.

So, my question is, is this a result of what is required, or, rather is this a result of what is yielded ?

Most amps are limited by voltage swing... not sure if that's what you mean.

[nicoch]

sure dave, but I will not put a 0.5< qts sealed speaker in OB...

[Davey]

sure dave, but I will not put a 0.5< qts sealed speaker in OB...

You could.  It would work fine.
You'd be applying 6db/octave dipole EQ anyway, so a bit more to achieve Q=0.5 is straightforward.

The vast majority of available drivers (some excellent) are specified with QTS < 0.5.  So, if you eliminate all those from consideration you've narrowed your choices greatly.

Dave.

[nicoch]

my driver are >0,8   I'm in OB from 2006

[Davey]

2006?  Ah, a newbie. 

I had my first open-baffle system (with conventional drivers) back in 1979....maybe it was 1980....I can't remember for sure. 

Cheers,

Dave.

[nicoch]

all that time with wrong qts ? 

[Davey]

I muddled through somehow. 
Back then many of the drivers were higher Qts.  Only in the last twenty/thirty years have we seen the migration to drivers with huge motors on the back.  A lot of vented-box systems are being produced nowadays. 

The first open-baffle system I ever heard was a DIY design with a Lowther PM4 (I think) driver mounted in the center of a rectangular piece of plywood (about 1' x 2') playing Nat King Cole.  Awesome!

Dave.

[Scott L]

Simplest thing is to use a simulation program like Unibox and enter the parameters of a woofer of interest.

Most amps are limited by voltage swing... not sure if that's what you mean.

John, you edited my post, which makes it appear out of context:

Okay, so taking this further.....
What does a proper enclosure do to the native response of a driver in free air ?
As I understand it, it raises the frequency of resonance, but at the same time, it lowers it's amplitude quite a bit.

Thus, open baffled drivers have a higher amplitude of resonance, as witnessed by the higher impedance peak.
If power is determined by the impedance of a system, and voltage squared over the impedance yields power, I can see where an amplifier is
yielding less power due to the restriction. For example 2.83 volts squared, over an eight ohm impedance, yields 1 watt
                                                               However, 2.83 volts squared, over an impedance of 50 ohms ( just as an example) equals .160178 watts
So, my question is, is this a result of what is required, or, rather is this a result of what is yielded ?

[Scott L]

Power is limited:

The relative high impedance peak of an open baffle woofer limits the available power to be delivered by the amplifier. Well, at least in terms
of a transistor amp. I will have consult my tube amp guru friend further on this topic.

This is just another reason why open baffles have such poor bass response. But it's not a reason unto itself. Most of the complications stem from the front-to-back
acoustical short circuit.

[JohnR]

Sorry... I did not edit your post, but I don't understand your question and don't agree with your followup assertion either... perhaps if you take my suggestion and model some woofers (change the box volume to a very large value for the open baffle case) it will become clearer? Amongst others, use a woofer with a free-air Qts of 0.71.

[Davey]

Scott doesn't appear to be a fan of open-baffle systems anyway. 

Dave.

[Scott L]

Sorry... I did not edit your post, but I don't understand your question and don't agree with your followup assertion either... perhaps if you take my suggestion and model some woofers (change the box volume to a very large value for the open baffle case) it will become clearer? Amongst others, use a woofer with a free-air Qts of 0.71.

It's just basic operating principles of loudspeakers. A speaker driver in free air yields some kind of crazy wild resonance. This is measurable. This has been further clarified by Thiel/Small in the 1970's.
You can observe any woofer type raw driver and see (as example: Eminence Kappa-Lite 3015LF) a free air resonance at 44 Hz/95 ohms. A proper enclosure will tame this resonance down to a lower value impedance peak, but it will raise it's frequency, dependent upon the air load [enclosure size, type].

Modeling a high Qts woofer in a very large enclosure is simply not the same thing as what will happen in an open baffle because it's takes away the acoustic short circuit. Qts is simply a determinant of action at/or near resonance. It will not totally mitigate the front-to-back sound wave cancellation. Again, this is why open baffle speakers are such poor performers of bass frequencies.

This thread started on the asking to see the baffle roll-off chart. Yes, this does mean that cancellation plays a definite part in this "design" but my observations have been that this fact is largely held in denial by the many OB fans. I admire all the optimism, but I'm sorry-- I simply don't share it.

http://hyperphysics.phy-astr.gsu.edu/hbase/Class/PhSciLab/speakerres.html

https://en.wikipedia.org/wiki/Loudspeaker_enclosure

https://www.eminence.com/support/understanding-loudspeaker-data/

https://courses.physics.illinois.edu/phys406/Student_Projects/Spring16/Thomas_Jerome_Physics_406_Final_Report_Sp16.pdf

[AJinFLA]

A speaker driver in free air yields some kind of crazy wild resonance. This is measurable.

Right, the magnitude of the impedance peak is higher. So??

Modeling a high Qts woofer in a very large enclosure is simply not the same thing as what will happen in an open baffle because it's takes away the acoustic short circuit.

Which dipole model program doesn't account for that??

Yes, this does mean that cancellation plays a definite part in this "design" but my observations have been that this fact is largely held in denial by the many OB fans. I admire all the optimism, but I'm sorry-- I simply don't share it.

Don't share what? Perhaps you could use some of the freely shared programs and see what you are missing?

Again, this is why open baffle speakers are such poor performers of bass frequencies.

Below Fequal, they are less efficient than boxes, above they are more efficient. Do you understand this?
They also radiate 6db less power into the room, which means 6db less maximum excitement and decay of modes that your boxes. Not all of us want rock concert sound. Pitch, definition and clarity with instruments like acoustic bass can be important to some. Could you explain how 6db more power exciting all modes and decay is helpful here?
Oh, if you have evidence that contradicts the studies finding gradient bass superior, please present, thanks https://secure.aes.org/forum/pubs/conferences/?elib=17270

[JohnR]

This thread started on the asking to see the baffle roll-off chart. Yes, this does mean that cancellation plays a definite part in this "design" but my observations have been that this fact is largely held in denial by the many OB fans. I admire all the optimism, but I'm sorry-- I simply don't share it.

OB speakers do work very well, optimism is not required. Just some design and engineering/acoustics knowledge, or willingness to acquire it.

[JohnR]

Which dipole model program doesn't account for that??

I suggested he use Unibox to see for himself that the impedance peak is not causing his claimed loss of output. He won't, but has jumped on the horse he thought I gave him and ridden it straight off the cliff.

[Scott L]

Is there di-pole modeling in Uni-box?

Do I have the correct unibox program ?

http://audio.claub.net/software/kougaard/ubmodel.html

[Scott L]

For any of you who are following this thread, and wish further clarification on loudspeaker basics,

here is a place to start :

Un-enclosed loudspeakers

An un-enclosed loudspeaker radiates sound as an acoustic "dipole". This gives rise to a poor l.f. response (since sound from the back of the diaphragm cancels sound from the front) and highly directional radiation.

(click the link and scroll down to see the section where i cut from and highlighted in bold)

http://www.mh-audio.nl/LoudspeakerBasics.asp