Open baffle or no baffle for nearfield full range monitors? Open baffle or no baffle for nearfield full range monitors? - diyAudio
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Open baffle or no baffle for nearfield full range monitors?
Open baffle or no baffle for nearfield full range monitors?
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Old 21st November 2015, 05:39 AM   #1
mdevelde is offline mdevelde  Netherlands
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Default Open baffle or no baffle for nearfield full range monitors?

Hello all,

I'm hoping to get a pair of Jordan Eikona 2 drivers from the groupbuy here on diyaudio: http://www.diyaudio.com/forums/group...group-buy.html
I wish to use them to make full range nearfield monitors. Going for a very pure sound, something in between headphones and normal speaker use is probably the best description.
Listening distance (ear to driver) will be 50 to 70 cm, drivers suspended in the air at ear height without any reflecting surfaces nearby (and wall behind the drivers is about 6 meters away), no box or porting etc, will make the frequency flat by high quality EQ on my computer.

Originally I thought I would do best to do away with any open baffle and simply use the drivers "naked" with some minimal suspension system (was thinking something based on mic stands with boom arm so I can position and angle the drivers any way I want).
But now I'm questioning if doing away with a baffle is a good design because of several reasons. First, will the surround of the driver cause edge diffraction which is a form of distortion and will create a new wavefront all around the edge making the "point source" a lot bigger?
And secondly, a driver is not a perfect dipole. I picked up a small full range driver and listened carefully from all angles and the back sounds completely different than the front, not only in the treble (of which there is about none in the back) but also in the mids. And from the side there isn't anything like perfect cancellation of frequencies.

Now my questions are the following:
Does anybody know if this "compromised" audio from the back can reach my ears at the front through methods like edge diffraction from the surround edge or any part of the driver construction at the back (perhaps combined with reflections at the back of the driver from parts of the driver construction / magnet system), or simply bend around the driver / surround by omnidirectional wave behavior at lower frequencies? (at which frequencies would this behavior start?)
Now a baffle with nice rounded edges will reduce or eliminate edge diffraction from the surround edge, but how large does it need to be to "block" for instance any audio from the back above let's say 500Hz?
And what I also don't understand yet is if and how the effect of baffle size changes with listening distance from the baffle.

Btw to make clear, I'm not looking at baffle use for EQ / Qt purposes. I will do all my EQ-ing of the driver on the computer.
Also, if I'll use a baffle I prefer it to be as small as required for sound quality purposes, and make it round with the driver in the middle, no need for me to smooth out the bass dropoff below baffle size with baffle design, a well defined point will only make EQ-ing easier it seems to me.

Many thanks for any insights anybody can share on this!
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Old 21st November 2015, 08:23 AM   #2
TNT is offline TNT  Sweden
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You will get no bass.

//
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Old 21st November 2015, 08:56 AM   #3
picowallspeaker is offline picowallspeaker  Italy
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Quote:
Originally Posted by mdevelde View Post
Now a baffle with nice rounded edges will reduce or eliminate edge diffraction from the surround edge, but how large does it need to be to "block" for instance any audio from the back above let's say 500Hz?
Infinite baffle completely separates frontal wave from back wave emission.
And the baffle needs to be solid, i.e. sound-proof

Once you EQ the driver to be linear, the distortion will rise because the driver excursion for reproducing the bass will modulate the motion for the mid and high frequencies, so it's better to use dedicated drivers if you fell you're going to surpass the extimated limit of the driver.
I guess that 10 W would be the maximum allowable for such driver in the (low) bass region.

*the speakers should be suspended with rubber bands and not just laid on something*
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Old 21st November 2015, 11:03 AM   #4
Scott L is offline Scott L  United States
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Open baffle or no baffle for nearfield full range monitors?
Default open baffle mania strikes again

Sir, that Jordan driver is designed to be used in an enclosure.

How in the world did all this "box phobia" start anyway ?
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Old 21st November 2015, 06:49 PM   #5
mdevelde is offline mdevelde  Netherlands
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Thanks for the replies!

But my thinking was that normal rules apply less because I'm listening at such a close distance.
50cm listening distance will give me 12db more volume than 2m listening distance, and 18db more volume than a somewhat normal 4m listening distance.
So if I have to EQ 18db extra in the bass at 50cm listening distance for a "naked" driver to be linear, the driver works just as hard as a very large ported speaker at 4m listening distance.
And I don't think I need to EQ 18db extra to get the bass linear with a "naked" driver, but less. So I would actually gain volume or less distortion and intermodulation distortion, including in the bass, relative to a big ported speaker at 4m listening distance.

Click the image to open in full size.
Here is the frequency response of the Eikona 2 driver.
I'm assuming this was measured anechoic and with a "naked" driver?
If so, I would need to EQ around 10db at 50Hz (I'm fine with 50Hz don't need it to be linear any lower). So after EQ-ing I still have about an 8db advantage over a big ported speaker at 4m listening distance for 50Hz reproduction.
So I'm not going to exceed the designed limits of the driver at all it seems to me (also do not need ear shattering levels, moderate levels are fine).

Of course the driver itself acts as a baffle as well. But as by my original message, I was wondering if I'd do well to still make some kind of additional baffle for sound quality purposes. And what are the formulas for baffle size and it's influence on frequency? Also I'm very interested to learn if baffle size and distance are linked in some way to the baffle influence on frequency. I mean, a 50cm baffle at 50cm distance is relatively as big as a 3m baffle at 3m distance. Instinct tells me that distance should matter as well as baffle size regarding baffle frequency effects but maybe I'm wrong about this?
Could someone perhaps point me to a good website which explains all this in a somewhat understandable manner?
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Old 21st November 2015, 06:57 PM   #6
mdevelde is offline mdevelde  Netherlands
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Quote:
Originally Posted by picowallspeaker View Post
*the speakers should be suspended with rubber bands and not just laid on something*
Thanks! I hadn't thought of that yet. Rubber bands would be good, 2 at the frond and one supporting the magnet.
(btw, I wasn't planning to just lay them on something.)
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Old 21st November 2015, 07:15 PM   #7
hitsware is offline hitsware
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Old 21st November 2015, 07:49 PM   #8
sreten is offline sreten  United Kingdom
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Hi,

You don't understand that baffle loss throws away speaker excursion,
not just response. You have absolutely no hope of EQing it down to
50Hz if its mounted on a small baffle / no baffle, even at 0.5m.

The above response is certainly not a naked driver.
Its into half space on a very large open baffle.

Your looking at about 20dB baffle loss at 50Hz and very poor SPL.

I'd recommend a tallish, thin, well rounded box, very well built,
about 10L, fitted with a Peerless 830878 3-1/2" passive radiator,
then EQ away to your hearts content. Sealed is also possible, 5L.

rgds, sreten.

Last edited by sreten; 21st November 2015 at 07:57 PM.
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Old 21st November 2015, 10:22 PM   #9
mdevelde is offline mdevelde  Netherlands
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Quote:
Originally Posted by sreten View Post
Hi,

You don't understand that baffle loss throws away speaker excursion,
not just response. You have absolutely no hope of EQing it down to
50Hz if its mounted on a small baffle / no baffle, even at 0.5m.

The above response is certainly not a naked driver.
Its into half space on a very large open baffle.

Your looking at about 20dB baffle loss at 50Hz and very poor SPL.

I'd recommend a tallish, thin, well rounded box, very well built,
about 10L, fitted with a Peerless 830878 3-1/2" passive radiator,
then EQ away to your hearts content. Sealed is also possible, 5L.

rgds, sreten.
Aaah.. Thank you for that information!!
I was just beginning to suspect that. The open baffle math didn't make sense at all with the given frequency response of the Eikona 2. I was calculating the Eikona 2 as having a 15cm "baffle" as a naked driver, and indeed came to about 21db difference at 50Hz compared to a ~2m open baffle.
Ok, so that published frequency response is already open baffle.. That changes a lot.

That brings me to another question.
Baffle is half space. If you were to attach it to a tube (or horn) of 1m length, that would in a sense behave as a 2m baffle, except that the front wave doesn't see half space but nearly full space. Would that give 3db/oct instead of 6db/oct dropoff below true baffle size? (15cm in the case of the driver)
And I'm suspecting a simple tube would give a lot of resonance which would still be audible at listening position even when the end of the tube is 3 times as far away from the ear as the driver, so would a widening tube / horn fix that? (I was thinking making the angle such that it would be "hidden from sight" from the perspective of my ear)
I still really want to explore my options of getting away from a box.
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Old 21st November 2015, 10:45 PM   #10
planet10 is offline planet10  Canada
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Open baffle or no baffle for nearfield full range monitors?
Quote:
Originally Posted by Scott L View Post
How in the world did all this "box phobia" start anyway ?
Bad MDF boxes?

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