Open-Baffle and Equalizer - why not :)

Bass loudness (not quality!) is a well known problem with OB implementation and to remediate this, large-ish woofers are required. But this morning I played around with foobar's equalizer and boost the lower frequecies to anything above +12db :D .... and it sounds good !

IMG_3290.jpg


I know there will be distortions due to signal change but honestly they were not audible. The OB + equalizer still sounded better than flat source + boxed speakers.

I wonder if it is reasonable to implement a 'bass correction' circuit such as low frequency parametric equalizer to compensate the bass.
 

ashok

Member
2002-06-06 4:43 am
3RS
Every OB design needs ( or not !) it's own equaliser for the bass , be it a passive crossover or an active one.
It's not too hard ( though it might involve work and time ) to design a crossover for the system.
The bass driver performance also matters a lot . Drivers with very high Q like the Eminence Alpha 15A's can work well without any bass lift. Balancing the upper frequency driver to the bass unit can be tricky . Lot's of info on this forum. Suggest you search for OB speakers on this forum. Too much to explain in a single post.:D
 

ttan98

Member
2006-04-04 11:24 am
Melb
my experience is that if your woofer has Qts<0.7 the bass will roll off very quickly,

you need,

1. equalizer, active or passive.

or

2. woofer house in U-frame cabinet

or

3. woofer house in H-frame cabinet

mine is housed in U frame the freq response improves dramatically, flat to 50 Hz. beware of resonance it generates. I use an elecronic x-over hence equalization is easy for me. I don't need it for mine.

if you want to build one then search the net lots of example around.
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
gainphile said:
But this morning I played around with foobar's equalizer and boost the lower frequecies

Yeah, I did the same thing to get a feel for what an active EQ might sound like. It worked very well and sounded nice. Just be sure you don't overdrive Foobar or the sound card. All that boost can lead to clipping. The EQ has an Autolevel feature that helps average things out a bit. Mostly it just lowers everything. :)

It's a fast and easy way to get an idea of the boost you need.
 
FYI, foobars built in equalizer may not behave like you think it does.

[IMGDEAD]http://www.michnicki.com/diy/eq/foobarsettings.jpg[/IMGDEAD]

[IMGDEAD]http://www.michnicki.com/diy/eq/foobaroutput.jpg[/IMGDEAD]

[IMGDEAD]http://www.michnicki.com/diy/eq/foobar0.9.1eq.jpg[/IMGDEAD]

[IMGDEAD]http://www.michnicki.com/diy/eq/foobar0.9.1eq-output.jpg[/IMGDEAD]

IMO, unusable.

Dan
 

Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
That's a pretty sharp EQ! Looks like real WYSIWYG EQ.

Thanks for the info.

If you get a chance, please try a gentle slope up to about +16 at 55Hz starting at 156Hz. That is what I was using.

Are you looping back into the sound card, or using some sort of internal routing?
 

DAMIC

Member
2006-01-30 1:14 pm
Beograd
ttan98 said:
.....

you need,

1. equalizer, active or passive.

or

2. woofer house in U-frame cabinet

or

3. woofer house in H-frame cabinet

.........

Hi,

Can anybody advise, wheteher U-frame or H-frame design is better for bass reproduction. Actually, I am in process to go for OB design with Eminence 12 inch and Gradient ribbon tweeter, from current bass reflex and want to have deeper response as much as possible.

Thanks
 

john k...

Member
2004-08-10 2:50 am
US
DAMIC said:
Can anybody advise, whether U-frame or H-frame design is better for bass reproduction. Actually, I am in process to go for OB design ... and want to have deeper response as much as possible.
If your equalising is done there is still the room to consider. How free are you in choosing your OB-to-front-wall distance? Have a look at two sims:

reflektion_90cm.gif


Red is the response of a driver on OB (working in principle like a H frame) without any front wall. Green is the same, but with a front wall at 90 cm distance. You "win" some efficiency between 40 and 130 Hz, but you loose below 40 Hz and will have to cross over at 100-150 Hz.

By varying the front wall distance you can "tailor" this response a bit:

reflektion_90_120cm.gif


Green line is the same as above, red line shows a front wall distance of 120 cm.

Since a U frame´s back wave is less pronounced it will have less influence on the end result.

PS: The simulations have been done with a now out-of-date version of MJKs worksheets. The trend will nevertheless still be valid.
 
Hi Rudolf, thanks for response. My room is 4m x 6m, average height 3m, but unfortunately due to side doors I can placed front baffle max at 65 cm from the wall. This is exactly the place where, for years, I am keeping my Apogee Centaurus Minor’s, also dipole speakers. Recommended distance for almost all Apogees is between 90 and 120cm, but even 65cm gives me excellent performance.

Recently, I made 2-way reflex box with 12 inch Eminence ME12-2008 driver what seems to be older version of later Eminence Delta 12 and Eminence Delta-12A. The tweeter is German ribbon Gradient GRT 195. Box, net volume 109 liter, tuned to 47Hz, with F3 about 45Hz. The sound is surprisingly good and with flat tone controls there is enough bass in the room. I must point that only one box is made.

Last 2 weeks I found myself more to listen the Eminence than my regular setup. There is something catchy in that efficient paper cone speaker.

Now, reading all that posts about OB, I wish to try this design with same components. I know that OB will further decrease the bass, but also noticed that variations with wings, U or H frame gave better low response. In fact, I would be satisfied if I could provide the amount of bass from two speakers OB like I have with present one reflex box.

Rudolf, thanks for the graphs, again. Anyway, I am going to try U frame.

Regards,
 

SamL

Member
2004-06-11 4:47 am
Wgtn
ttan98 said:
mine is housed in U frame the freq response improves dramatically, flat to 50 Hz. beware of resonance it generates. I use an elecronic x-over hence equalization is easy for me. I don't need it for mine.


Sorry to drag this out.

Hi ttan98,

What size woofer are you using in the U-frame? What is the high pass crossover point? Well, reading John K note, he mention 150Hz for U-frame, which is a bit low for the list of mid I have in mind.


Thanks :D
 

Rewind

Member
2009-01-18 7:42 pm
Oslo
I am using a 12" JBL cone which is a nice midbass speaker in open baffle U frame, the dimensions of a 50L Marshall guitar cabinet. Sounds more open and less distorted than in the same cabinet but sealed. It is pretty powerful and very sensitive (100+dB). According to JBL is a compromise if you don't have room for a bigger bass driver.

I did a simple test in minidsp 4x10hd to put a low shelf on the midbass channel (which reaches approx 50Hz), then lowering the shelf for the high freq lower than the low shelf. Then I raised the volume of the whole bass channel more than usual and instant Doof, doof!
 
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Pano

Administrator
Paid Member
2004-10-07 6:05 am
Panama
Ah, an old thread come back to life!

Since 2007 I've found that I don't much like the sound of typical bass EQ (like a shelf) on OB. I just can't get it to sound right, and don't know why. What does work great is a very low frequency Low Pass filter. Sometimes as low as 60Hz or lower. It can be 1st order, or near 2nd order, but it works. It will make the woofers sound natural and true. And it will put the -3dB or -6dB point right were they need to be for the midrange driver.

It seems a strange way of doing it, but it works great.
 

Rewind

Member
2009-01-18 7:42 pm
Oslo
I am doing it for my single U-formed open baffle now with a BW18dB high pass at 150Hz and I can't hear a difference. At 200Hz I start to hear it. The JBL 2204H has a Fs of 35Hz! Hm.
The JBL 2204H is supposed be a high powered low frequency speaker, but in open baffle it does little below 200Hz. But open baffle gave me cleaner midrange.
 

john k...

Member
2004-08-10 2:50 am
US
Ah, an old thread come back to life!

Since 2007 I've found that I don't much like the sound of typical bass EQ (like a shelf) on OB. I just can't get it to sound right, and don't know why. What does work great is a very low frequency Low Pass filter. Sometimes as low as 60Hz or lower. It can be 1st order, or near 2nd order, but it works. It will make the woofers sound natural and true. And it will put the -3dB or -6dB point right were they need to be for the midrange driver.

It seems a strange way of doing it, but it works great.

There is more to eqing a dipole woofer than just adding an LP shelf...

Gradient woofer equalization