I loved a flat open baffle with a foam box around rear of driver.
Super clean mids, no boxy sound, no front to back nonlinearities in pressure.
Now I need higher waf.
I'm not looking for intoxicating dipole front wall bounce ambience.
What will a no backed box sound like with stuffing ?
I think a box 8" wide and 21.5" deep would look like an open baffle 47.5" wide.
47.5" wide would give a 6-10db dip at 285hz (front and back 180 degrees out of phase) then near 6db peak at 142hz (front and back 90 degrees out of phase thusly adding) and rolling off to oblivion.
I figure a driver will roll off at its mass corner (Fs / qts) regardless of how big the baffle is.
Then add the baffle rolloff to that.
Long ago I sawed off the back to a small yamaha 8" 3way. Mid and tweet were closed back.
Good sound, voice was better, but I heard a few resonances (bare walls inside), so I removed the sides.
Well, that was a mistake, probably rolling everything off below 1khz.............
Norman
Super clean mids, no boxy sound, no front to back nonlinearities in pressure.
Now I need higher waf.
I'm not looking for intoxicating dipole front wall bounce ambience.
What will a no backed box sound like with stuffing ?
I think a box 8" wide and 21.5" deep would look like an open baffle 47.5" wide.
47.5" wide would give a 6-10db dip at 285hz (front and back 180 degrees out of phase) then near 6db peak at 142hz (front and back 90 degrees out of phase thusly adding) and rolling off to oblivion.
I figure a driver will roll off at its mass corner (Fs / qts) regardless of how big the baffle is.
Then add the baffle rolloff to that.
Long ago I sawed off the back to a small yamaha 8" 3way. Mid and tweet were closed back.
Good sound, voice was better, but I heard a few resonances (bare walls inside), so I removed the sides.
Well, that was a mistake, probably rolling everything off below 1khz.............
Norman
Someone at work brought in a pair of very cheaply made speakers and asked me to upgrade the parts for him. They were old no names and sounded very boxy on first listen. Inside was a small super tweeter and a full range driver. I believe the cap on the super tweeter was 1uf and the main driver played full. Since there was no way to get to the drivers without cutting into the box I cut out the back to have a look inside. Then i played them without the back and they did not sound boxy at all. In fact, i compared them with the Pioneer B20 speakers i had on hand and the cheaper speaker without the back of the box sounded better overall! I was shocked as was my friend Tom. So we took off the backs of both and nothing but good sound came from them always. Secretly i wanted those drivers for myself but there was no way to dispute how good they sounded. He wanted them back without any changes. I helped him screw a fancy metal grill on the back and he brought them home, bought a sonic impact amp and has it all connected to his computer, tv, nintendo. He tells me all the time how much he enjoys his stereo and listening/watching sports. He says his daughter is always in there with her friends. What i am trying to say is that an open back speaker could sound really great and i think this type of cabinet is very well suited for many of the speakers we use on this forum.
Godzilla
Godzilla
This is similar to what you are looking for but I'm WAF is just about zero! 
An externally hosted image should be here but it was not working when we last tested it.
I've always been intrigued by the slatted-back, tunable design from this French company:
http://www.phy-hp.com/English/Communication_E/Communication_E.html
Has anyone tried the idea with more affordable drivers?
http://www.phy-hp.com/English/Communication_E/Communication_E.html
Has anyone tried the idea with more affordable drivers?
repen backed boxes, anyone?
Let me be the first guy to mention the Hartley "boffle" concept here. Hartley (he of the white coned drivers, including the legendary 220 full ranger) was for years a champion of what he called a boffle-- a large backless box with several curtain-like layers of cotton or foam to attenuate the rear wave. Never heard one myself, but there have been periodic mentions of them over at AudioAsylum, and the old timers who remember seem to like them.
--nosmok
pen backed boxes, anyone?Let me be the first guy to mention the Hartley "boffle" concept here. Hartley (he of the white coned drivers, including the legendary 220 full ranger) was for years a champion of what he called a boffle-- a large backless box with several curtain-like layers of cotton or foam to attenuate the rear wave. Never heard one myself, but there have been periodic mentions of them over at AudioAsylum, and the old timers who remember seem to like them.
--nosmok
FWIW, I've periodically mentioned that I 'voice' drivers in a foam box to get a feel for what they can do and not being a dipole fan, I've used them in conjunction with woofers to good effect, so pick a baffle size, add a slender frame for the sides, back (I use dowels) and wrap it with whatever works best for you. For a finished product you can cover it with an expanded knit or actual grill cloth.
GM
GM
yea, I'm all for absorbing the backwave.
Seems it may be tricky to balance box depth with how much, what and where the stuffing.
Like the old consoles, only fill with stuffing (and no amp inside).
To me a benefit you be golden ratio off set.
I'd been wrapping my mind around a 4' wide x 6' tall open baffle.
If the driver center is 18 1/3" from one side, it'd be 29 2/3" from the other, then place it 48" from the top.
That give a 1 : 1.618 ratio.
Problem is you'd want the driver in the middle so you'd have 24" min distance to cabinet edge.
here seems to be a golden ratio offset open baffle.
http://pic4.picturetrail.com/VOL706/2663514/5325320/97442407.jpg
But what if you could put a box right next to your tv?
The speaker driver would be next to the middle of the tv.
The open baffle could be L-shaped (the drive at the edge).
It could be 29" wide and a wall going straight back (18 1/3").
There was an open baffle test showing nulls and such but I can't find it now.
"There are surprisingly little knowledge in the issue, I think. Harry Olsens "elements of acoustical engineering" , D. Van Nostrand Co; 2d ed edition (1947) is most the most recent reading I have found in the issue. He for example discusses of open-back boxes as a loud speaker type. Basically, adding wings behind the baffle causes similar effect, only in smaller scale. You have a peak in the response, whichs "fS" is baffles width. The deeper the wings, the higher the peak. rectangular base gives highest amplification in "fS". Twisting -or folding- another- or both- of the wings reduces effect. Look at the Auditorium23:s site for some really interesting baffle and folded baffle ideas, meant for PHY:s, but will of course work with any OB driver as well. Folding the baffle does anyway not affect to the baffles lower limit, compared to the same width of straight baffle. the only effect is that peak(s) in response in upper frequencies. The major advantage is higher WAF, I think. Or, one can have advantage of that peaking effect in compensating defects of the baffle and driver.
http://auditorium23.de/PHY/Plaene.html
then, "weitere bauworschläge". Only auf deutch. BTW; some really, really nice TT's also there."
http://members.myactv.net/~je205d/monob.htm
Boffle, neat stuff
http://homepage.mac.com/planet10/TLS/downloads/hartleybrochure.pdf
"As I remember, the original Boffle was an open-back cabinet with curtains of felt hanging inside. Later, the cabinet was stuffed with a layer of felt and fiberglass that were rolled up in the manner of a jellyroll..............H A Hartley’s intent was to minimize the audibility of the back wave, and to mimic, as far as possible, a baffle of infinite size. He was quite opposed to ports, horns, etc."
Norman
Seems it may be tricky to balance box depth with how much, what and where the stuffing.
Like the old consoles, only fill with stuffing (and no amp inside).
To me a benefit you be golden ratio off set.
I'd been wrapping my mind around a 4' wide x 6' tall open baffle.
If the driver center is 18 1/3" from one side, it'd be 29 2/3" from the other, then place it 48" from the top.
That give a 1 : 1.618 ratio.
Problem is you'd want the driver in the middle so you'd have 24" min distance to cabinet edge.
here seems to be a golden ratio offset open baffle.
http://pic4.picturetrail.com/VOL706/2663514/5325320/97442407.jpg
But what if you could put a box right next to your tv?
The speaker driver would be next to the middle of the tv.
The open baffle could be L-shaped (the drive at the edge).
It could be 29" wide and a wall going straight back (18 1/3").
There was an open baffle test showing nulls and such but I can't find it now.
"There are surprisingly little knowledge in the issue, I think. Harry Olsens "elements of acoustical engineering" , D. Van Nostrand Co; 2d ed edition (1947) is most the most recent reading I have found in the issue. He for example discusses of open-back boxes as a loud speaker type. Basically, adding wings behind the baffle causes similar effect, only in smaller scale. You have a peak in the response, whichs "fS" is baffles width. The deeper the wings, the higher the peak. rectangular base gives highest amplification in "fS". Twisting -or folding- another- or both- of the wings reduces effect. Look at the Auditorium23:s site for some really interesting baffle and folded baffle ideas, meant for PHY:s, but will of course work with any OB driver as well. Folding the baffle does anyway not affect to the baffles lower limit, compared to the same width of straight baffle. the only effect is that peak(s) in response in upper frequencies. The major advantage is higher WAF, I think. Or, one can have advantage of that peaking effect in compensating defects of the baffle and driver.
http://auditorium23.de/PHY/Plaene.html
then, "weitere bauworschläge". Only auf deutch. BTW; some really, really nice TT's also there."
http://members.myactv.net/~je205d/monob.htm
Boffle, neat stuff
http://homepage.mac.com/planet10/TLS/downloads/hartleybrochure.pdf
"As I remember, the original Boffle was an open-back cabinet with curtains of felt hanging inside. Later, the cabinet was stuffed with a layer of felt and fiberglass that were rolled up in the manner of a jellyroll..............H A Hartley’s intent was to minimize the audibility of the back wave, and to mimic, as far as possible, a baffle of infinite size. He was quite opposed to ports, horns, etc."
Norman
FWIW, it should be able to ~model an open-back cabinet design using Martin King's H-frame MathCAD worksheet. Just reduce the length of the front cavity to 0.001in. It'll be a bit of a fudge, as it still assumes the entire front of the box is the forward radiating area, but better than nothing & probably more accurate than the U-frame sheet which doesn't account for the top.
Unless I misunderstood MJK's Figure 2 (pg. 4) in his "Comparison of the Bass Performance of Passive Open Baffle, U Frame, and H Frame Speakers" paper (http://www.quarter-wave.com/OBs/U_and_H_Frames.pdf) his U Frame MathCad model does account for the top. Yes?
From an Elk's point of view
Scottmoose,
You are somewhat unlucky, I think ! Do you like music and above all live music ? If so am I sure you would like OB.
With regard to 'Topless-U' as I have coined winged OBs with bottom and two sides and no top, MJK's models will give a good prediction if you calculate the corresponding flat OB baffle size.
With regard to the U- and H-baffle models they are very versatile. Both will allow for user determined terminus size and user determined stuffing of damping. The H-baffle besides also will allow for any placement of the main baffle in the H, thus at the extremes converging to traditional U or having all the H in front to an front U OB.
/Erling
Scottmoose,
You are somewhat unlucky, I think ! Do you like music and above all live music ? If so am I sure you would like OB.
With regard to 'Topless-U' as I have coined winged OBs with bottom and two sides and no top, MJK's models will give a good prediction if you calculate the corresponding flat OB baffle size.
With regard to the U- and H-baffle models they are very versatile. Both will allow for user determined terminus size and user determined stuffing of damping. The H-baffle besides also will allow for any placement of the main baffle in the H, thus at the extremes converging to traditional U or having all the H in front to an front U OB.
/Erling
Norman -
Thanks for the link to auditorium23.de BTW - They do have an "English language option on their home page - interesting stuff! http://www.auditorium-23.de/Welcome/Contents.html
Thanks for the link to auditorium23.de BTW - They do have an "English language option on their home page - interesting stuff! http://www.auditorium-23.de/Welcome/Contents.html
Re: From an Elk's point of view
Not unlucky at all. I've heard plenty of OBs & designed a few as well. They all sound decent enough, but I just happen to prefer monopoles. As for using the regular flat fronted mathCAD worksheet to model an open topped U frame rather than an open backed cabinet, forgive me if I have reservations. It doesn't account for potential standing waves / resonances in the rear cavity for a start, or any other performance related departures from a purely flat baffle.
skorpion said:
Not unlucky at all. I've heard plenty of OBs & designed a few as well. They all sound decent enough, but I just happen to prefer monopoles. As for using the regular flat fronted mathCAD worksheet to model an open topped U frame rather than an open backed cabinet, forgive me if I have reservations. It doesn't account for potential standing waves / resonances in the rear cavity for a start, or any other performance related departures from a purely flat baffle.
Scottmoose,
I think in fact a bit unlucky because you miss some excitment. Otherwise I am glad you could stand the ironic undertone.
My stating 'From an Elks point of view' was also a paraphrase pointing to E.S.T's 'From Gagarings point of view'. I have heard E.S.T live on several occasions and I am glad to play their records over my OB speakers. Tragically Esbjörn Svensson died in a diver accident this summer. He was in fact one of this worlds really renewing jazz/rock personalties, producing all over enchanting jazz performances/records.
The argument about standing waves, resonances etc in 'Topless-U's has been covered by MJK (with argument) and myself (with measurement) in some threads over at the Audio Circle. The short story is: no problems.
/Erling
I think in fact a bit unlucky because you miss some excitment. Otherwise I am glad you could stand the ironic undertone.
My stating 'From an Elks point of view' was also a paraphrase pointing to E.S.T's 'From Gagarings point of view'. I have heard E.S.T live on several occasions and I am glad to play their records over my OB speakers. Tragically Esbjörn Svensson died in a diver accident this summer. He was in fact one of this worlds really renewing jazz/rock personalties, producing all over enchanting jazz performances/records.
The argument about standing waves, resonances etc in 'Topless-U's has been covered by MJK (with argument) and myself (with measurement) in some threads over at the Audio Circle. The short story is: no problems.
/Erling
Actually, that's one of the reasons I don't like baffles all that much: I've yet to hear one that gives me any real sense of excitement sonically, with the exception of my mate Ed's electrostatics. They just don't give me what I happen to value.
Re the other, I'll maintain my reservations if Martin will forgive me. That will likely be a design-dependant issue, particularly WRT the size shape & depth of the side pieces. Given that several such bent (hinged actually) baffles I've heard suffered from a variety of colourations / resonant issues which vanished the second they were straightened out (no preconceptions either as the subject of modelling them was not in question at the time), I regard the notion that you can simply treat all of them as flat baffles & expect no differences of any kind with deep suspicion.
Either way, my opinion, for what it's worth (nothing) is moot, because, as I say, I'm simply not very interested in OBs.
Re the other, I'll maintain my reservations if Martin will forgive me. That will likely be a design-dependant issue, particularly WRT the size shape & depth of the side pieces. Given that several such bent (hinged actually) baffles I've heard suffered from a variety of colourations / resonant issues which vanished the second they were straightened out (no preconceptions either as the subject of modelling them was not in question at the time), I regard the notion that you can simply treat all of them as flat baffles & expect no differences of any kind with deep suspicion.
Either way, my opinion, for what it's worth (nothing) is moot, because, as I say, I'm simply not very interested in OBs.
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