Hi everybody,
I've come across a lot of threads which seem to like the open baffle aproach.
Thus, I got curious and started searching. I found a lot of pages (here and on Google), but the ones I found seemed to take the basics for granted. I really need some assistance on these basics to get me started. Any help appreciated...
Could someone please be so kind as to comment on me being right or wrong in the following?
1)
The way I understand it, an "open baffle" speaker has only the front panel (baffle) and maybe some small sides to give stiffness to it. No full sides, no rear to make a "real" enclosure.(?)
2)
What's so magical about these things? My guess would be that the drivers have "unlimited" air behind them, so they don't need to fight the preassure change in a cabinet - thus making the membranes move easier?
3)
This kind of speakers will have a bass problem. Low frequencies cause the Baffle Step Response in "ordinary" speakers. Won't this be the case with open baffles also? (sort of an accoutic short-circuit for low frequencies , if that term makes sense?)
If the lower frequency dependent on the baffle width, just like when calculating for baffle step?
Thanks-
Jennice
I've come across a lot of threads which seem to like the open baffle aproach.
Thus, I got curious and started searching. I found a lot of pages (here and on Google), but the ones I found seemed to take the basics for granted. I really need some assistance on these basics to get me started. Any help appreciated...
Could someone please be so kind as to comment on me being right or wrong in the following?
1)
The way I understand it, an "open baffle" speaker has only the front panel (baffle) and maybe some small sides to give stiffness to it. No full sides, no rear to make a "real" enclosure.(?)
2)
What's so magical about these things? My guess would be that the drivers have "unlimited" air behind them, so they don't need to fight the preassure change in a cabinet - thus making the membranes move easier?
3)
This kind of speakers will have a bass problem. Low frequencies cause the Baffle Step Response in "ordinary" speakers. Won't this be the case with open baffles also? (sort of an accoutic short-circuit for low frequencies , if that term makes sense?)
If the lower frequency dependent on the baffle width, just like when calculating for baffle step?
Thanks-
Jennice
I'm somewhat new here too, but I'm going to boldly jump in anyway with the expectation that some of the old-timers will appear to elaborate and correct me. 
1) Yes.
2) A big part of the magic has to do with the unique dispersion pattern of a dipole; as you surmised, there is cancellation involved but the cancellation approaches 100% to the sides of the speakers (imagine a figure 8), greatly reducing radiation to the sides and thus lessening troublesome reflections from the walls etc.
Dipole bass in particular also benefits from being based on velocity rather than pressure; since there is no sealed area containing the backwave, the air in your room isn't alternately compressed and rarified, instead being simply energized and pushed toward the listening position. This combined with the lack of side radiation does much to avoid exciting room nodes, and the net result is a sound much less troubled by peaks and nulls scattered around the room, and with a well thought-out design can sound startlingly more natural than typical box speakers.
3) Yes there will be cancellation; dipole designs often deal with this by using somewhat larger (wider) baffles and sometimes with active EQ. There are other ways around it with careful driver choice and consideration of the physics involved, but those are for more experienced and clever speaker designers than me to discuss.
Hope some of that is helpful.
1) Yes.
2) A big part of the magic has to do with the unique dispersion pattern of a dipole; as you surmised, there is cancellation involved but the cancellation approaches 100% to the sides of the speakers (imagine a figure 8), greatly reducing radiation to the sides and thus lessening troublesome reflections from the walls etc.
Dipole bass in particular also benefits from being based on velocity rather than pressure; since there is no sealed area containing the backwave, the air in your room isn't alternately compressed and rarified, instead being simply energized and pushed toward the listening position. This combined with the lack of side radiation does much to avoid exciting room nodes, and the net result is a sound much less troubled by peaks and nulls scattered around the room, and with a well thought-out design can sound startlingly more natural than typical box speakers.
3) Yes there will be cancellation; dipole designs often deal with this by using somewhat larger (wider) baffles and sometimes with active EQ. There are other ways around it with careful driver choice and consideration of the physics involved, but those are for more experienced and clever speaker designers than me to discuss.
Hope some of that is helpful.
Thanks for your answers
Yes, it sure is helpful. I'm mostly concerned about the cancellation issue of the sound. Is it comparable to the baffle step, so the baffle (in this case) should be fairly wide, compared to a normal box xpeaker, where a narrow baffle is desireable (as I understand it)?
Also, if these open baffle speakers become linear by the help of an equalizer, don't they end up being rather in-efficient?
Considering the wave-length of lof frequencies, I have a hard time imagining a deep bass produced from such speakers. Should they be supplemented by more ordinary designed sub's, or is there a similar "open" approach to sub-woofers, which complement these open baffle speakers?
Jennice
Yes, it sure is helpful. I'm mostly concerned about the cancellation issue of the sound. Is it comparable to the baffle step, so the baffle (in this case) should be fairly wide, compared to a normal box xpeaker, where a narrow baffle is desireable (as I understand it)?
Also, if these open baffle speakers become linear by the help of an equalizer, don't they end up being rather in-efficient?
Considering the wave-length of lof frequencies, I have a hard time imagining a deep bass produced from such speakers. Should they be supplemented by more ordinary designed sub's, or is there a similar "open" approach to sub-woofers, which complement these open baffle speakers?
Jennice
Yes, dipole bass is inefficient, but you can't have your cake and eat it too.
What you _can_ do is use a dipole subwoofer to reproduce the frequencies below the ones which result in reverberant room behavior occurs (below 200Hz in many rooms, though the lower you cross the easier it is to integrate the subwoofer with your main speakers) - i.e. dipolar radiation in the frequencies that result in discrete room modes. Then, you can use a monopolar subwoofer starting below the frequencies whose wavelengths are twice as long as the longest dimension in the room (generally), as the modes disappear below this frequency.
Concerning one of your earlier questions, the small sidewalls are generally added to increase the effective path distance (to lessen the cancellation at lower frequencies). OBs don't need to be very stiff, as they store minimal amounts of energy. Unless you're talking about the pieces that brace the bottom of the baffle to the base, then yes, those are for added strength.
What you _can_ do is use a dipole subwoofer to reproduce the frequencies below the ones which result in reverberant room behavior occurs (below 200Hz in many rooms, though the lower you cross the easier it is to integrate the subwoofer with your main speakers) - i.e. dipolar radiation in the frequencies that result in discrete room modes. Then, you can use a monopolar subwoofer starting below the frequencies whose wavelengths are twice as long as the longest dimension in the room (generally), as the modes disappear below this frequency.
Concerning one of your earlier questions, the small sidewalls are generally added to increase the effective path distance (to lessen the cancellation at lower frequencies). OBs don't need to be very stiff, as they store minimal amounts of energy. Unless you're talking about the pieces that brace the bottom of the baffle to the base, then yes, those are for added strength.
Im in the same boat for open baffle too..
Living in an apartment I have VERY limited access to woodworking facilities, but I can easily cut round holes in boards.
My question is how do you fit a driver to your baffle ?
I found an app (forget the name) that allows you to simulate size & positioning of the driver, but no place to enter T/S parameters & thus see how they affect the overall performance.
does anyone have links to articles or open baffle simulation software?
And Jennice - Thanks for your Question!
Living in an apartment I have VERY limited access to woodworking facilities, but I can easily cut round holes in boards.
My question is how do you fit a driver to your baffle ?
I found an app (forget the name) that allows you to simulate size & positioning of the driver, but no place to enter T/S parameters & thus see how they affect the overall performance.
does anyone have links to articles or open baffle simulation software?
And Jennice - Thanks for your Question!
I discovered OB's, dipoles about 9 months ago. Just on a fluke I mounted a cheap driver on a piece of cardboard and was floored with the result. I would characterize the difference as being much more open and natural sounding. When was the last time you heard a singers voice coming out of a box? Never in real life.
I believe the open sound is created by the reflections and their timing from the back side of the cone and the natural sound results from the free air movement of the cone combined with the lack of reflected energy from inside the box back out to the cone.
The bass roll off resulting from wave cancellation is less than you'd think at only 6db per octave until you get down to a driver's Fs. Below Fs it combines with the driver's natural roll off and becomes an 18db roll off. With narrow baffles and/or low Qts drivers (which won't make OB bass without EQ), I characterize the sound as thin and it just takes a little help to attain a rich full sound for music.
One of the things I love about OB is that it's easy to experiment. Just put a driver on a piece of cardboard and you have an OB speaker. If you are lucky enough to have a relatively high Qts driver, then the improved sound is immediately apparent. If you have a sub, that helps with first impressions. Just run one channel with a boxed speaker and the other with your test OB. It's a real eye opener.
Then, once you can do bass in dipole at least down to 40-50hz to combine with the sweet dipole midrange and crystal clear vocals, you'll be able to compare dipole bass to muddy, in comparison, boxed bass. Instead of just a bass beat, you here the different notes and instruments creating that beat.
Fully dipole for music isn't too difficult and doesn't have to be big. If you want flat extension and high output down in the 20's that's a whole other ball game.
I already have the drivers for my next project. $200 worth of $12.50 12" drivers (yes 16) and a pair of Selenium 15" coaxials that I got in day before yesterday (another $300 with shipping and duties). The bottom will consist of 8 12" drivers per side in a W baffle 28"H X 21"W X 22"D . The Seleniums will go on top with a small baffle.
Why so many drivers in the bottom? Because I want these speakers to have the same output at 20-25hz that the Seleniums have a 100hz. Fully dipole, no subwoofer necessary, even for HT.
I believe the open sound is created by the reflections and their timing from the back side of the cone and the natural sound results from the free air movement of the cone combined with the lack of reflected energy from inside the box back out to the cone.
The bass roll off resulting from wave cancellation is less than you'd think at only 6db per octave until you get down to a driver's Fs. Below Fs it combines with the driver's natural roll off and becomes an 18db roll off. With narrow baffles and/or low Qts drivers (which won't make OB bass without EQ), I characterize the sound as thin and it just takes a little help to attain a rich full sound for music.
One of the things I love about OB is that it's easy to experiment. Just put a driver on a piece of cardboard and you have an OB speaker. If you are lucky enough to have a relatively high Qts driver, then the improved sound is immediately apparent. If you have a sub, that helps with first impressions. Just run one channel with a boxed speaker and the other with your test OB. It's a real eye opener.
Then, once you can do bass in dipole at least down to 40-50hz to combine with the sweet dipole midrange and crystal clear vocals, you'll be able to compare dipole bass to muddy, in comparison, boxed bass. Instead of just a bass beat, you here the different notes and instruments creating that beat.
Fully dipole for music isn't too difficult and doesn't have to be big. If you want flat extension and high output down in the 20's that's a whole other ball game.
I already have the drivers for my next project. $200 worth of $12.50 12" drivers (yes 16) and a pair of Selenium 15" coaxials that I got in day before yesterday (another $300 with shipping and duties). The bottom will consist of 8 12" drivers per side in a W baffle 28"H X 21"W X 22"D . The Seleniums will go on top with a small baffle.
Why so many drivers in the bottom? Because I want these speakers to have the same output at 20-25hz that the Seleniums have a 100hz. Fully dipole, no subwoofer necessary, even for HT.
Everything you need to know about OB speakers...
is right here, free.
http://www.woodartistry.com/linkwitzlab/index.htm
is right here, free.
http://www.woodartistry.com/linkwitzlab/index.htm
It's hard to talk about the real efficiency of open baffle bass. Because of the low roll off the efficiency degrades towards the lower frequencys downwards 20 hz, but in the higher range at say 80 to 100 hz they are as efficient as a closed box speaker. And that's the range where a lot more of the music power is going to. (I presume you listen to music and not to test tones all day).
My open baffle woofers produce a sound pressure of 99dB/1w/1m at 100Hz while thy only produce about 80dB at 20 Hz. Are they only 80dB efficient then ? well no, the amplifier has to deliver only 1watt to achieve 99db output at 100Hz, about 10 watt for 99dB at 50Hz and about 20 watt for 99dB at 20Hz.
I would not worry about the efficency to much. When you are gonna make open baffle bass the only way to do it is going active anyway and powerfull amps are very common these days. I would worry more about the max SPl out of it. If you just be sure to use about four times as much moving area compared to what you would use for a close or vented box then you are playing safe in that area as well. Simply put, if you had a 10"driver in mind for a closed box, just use four of the same drivers for open baffle.
I am using two 15"drivers in a w-baffle wich can produce as much SPL as one 10"driver in a vented box. The w-baffle with the two 15"driver however is smaller in size then the vented box for the 10"and the open bafle goes down to 20Hz with ease while the 10"doesn't go any lower as 35Hz.
Don't expect to get deep bass from a 8"driver on a open baffle. It's just a little bit more than just removing the enclosure.
My open baffle woofers produce a sound pressure of 99dB/1w/1m at 100Hz while thy only produce about 80dB at 20 Hz. Are they only 80dB efficient then ? well no, the amplifier has to deliver only 1watt to achieve 99db output at 100Hz, about 10 watt for 99dB at 50Hz and about 20 watt for 99dB at 20Hz.
I would not worry about the efficency to much. When you are gonna make open baffle bass the only way to do it is going active anyway and powerfull amps are very common these days. I would worry more about the max SPl out of it. If you just be sure to use about four times as much moving area compared to what you would use for a close or vented box then you are playing safe in that area as well. Simply put, if you had a 10"driver in mind for a closed box, just use four of the same drivers for open baffle.
I am using two 15"drivers in a w-baffle wich can produce as much SPL as one 10"driver in a vented box. The w-baffle with the two 15"driver however is smaller in size then the vented box for the 10"and the open bafle goes down to 20Hz with ease while the 10"doesn't go any lower as 35Hz.
Don't expect to get deep bass from a 8"driver on a open baffle. It's just a little bit more than just removing the enclosure.
johninCR said:
John,
Is there a website describing the 12" drivers you are buying for so cheap? I'd like to check them out.
I have a pair of the 12CO1P Selenium coaxials. I think these are an outstanding quality driver for this amount of money. I used them in a large front loading horn for my HT as well as for music. I wanted very high efficiency. One thing I'd like to do is pull one and try it just to hear in a standard BR box of around 4 cubic feet.
RCAVictim,
They're just some cheap Nippon America woofers that are available locally here in Costa Rica. About the only info I have on them is 235watts 8ohms. What I do is just go and listen to cheap stuff that's available. I listen for the quality of the sound at low power, both using their demo box and free air. I buy whatever shows the best potential at the cheapest price.
These particular woofers don't do bad in an isobarik alignment. 4 of them in Decware's Housewrecker, a 6th order bandpass enclosure with the sealed center chamber, works amazingly well for $50 in drivers plus a piece of plywood. It's a club type in your face bass presentation that works pretty well for HT, but calls attention to itself too much for my musical taste.
The driver has a highish Q which I haven't bothered to measure and an Fs of 27hz.
They're just some cheap Nippon America woofers that are available locally here in Costa Rica. About the only info I have on them is 235watts 8ohms. What I do is just go and listen to cheap stuff that's available. I listen for the quality of the sound at low power, both using their demo box and free air. I buy whatever shows the best potential at the cheapest price.
These particular woofers don't do bad in an isobarik alignment. 4 of them in Decware's Housewrecker, a 6th order bandpass enclosure with the sealed center chamber, works amazingly well for $50 in drivers plus a piece of plywood. It's a club type in your face bass presentation that works pretty well for HT, but calls attention to itself too much for my musical taste.
The driver has a highish Q which I haven't bothered to measure and an Fs of 27hz.
John,
Thanx for the description. With a highish Q and that low an Fs they sound well suited to your OB idea. Any chance of posting pics of this driver? I'd like to try and track them down. BTW, how large is the magnet, what ius the VC diameter and what kind of surround foam, rubber, corrugated paper, corrugared cloth , treated corrugated, other? Sorry for all the questions. The price is about my speed right now.
Thanx for the description. With a highish Q and that low an Fs they sound well suited to your OB idea. Any chance of posting pics of this driver? I'd like to try and track them down. BTW, how large is the magnet, what ius the VC diameter and what kind of surround foam, rubber, corrugated paper, corrugared cloth , treated corrugated, other? Sorry for all the questions. The price is about my speed right now.
I am using the JBL 2205H (16 ohm Alnico version) wich is the predessor of the 2226 and can be find pretty cheap second hand. They have a Fs of 31Hz wich is lowered due to the compression in the W-baffle to 16Hz (measured that). The Qts is pretty low at 0.31 but it's not a problem. You will need a lot of active eq for them (about 20dB) but they can handle that as long as the amplifier keeps them under tight control. At the moment I'm still running them with an old NAD 2200PE amp (more than enough power), will try a class D amp soon.
rcavictim said:John,
Thanx for the description. With a highish Q and that low an Fs they sound well suited to your OB idea. Any chance of posting pics of this driver? I'd like to try and track them down. BTW, how large is the magnet, what ius the VC diameter and what kind of surround foam, rubber, corrugated paper, corrugared cloth , treated corrugated, other? Sorry for all the questions. The price is about my speed right now.
I found the model#. It's Nippon America NWX-1277. It has a treated paper cone, foam surround, and a 1way xmax of 8mm. It looks like a 1" voice coil. The magnet is smallish, but not overly small like some extremely high Qts woofers have. I haven't measured the other T/S parameters because I don't need to know them for the way I use them.
Kittle,
Could you please let me know what software you found?
Sjef,
Could you please show a pic (or simple drawing) of this W configuration of tyour bass?
General question:
Is it correctly understood that there's no open baffle design without EQ'ing to compensate for the accoustic short-circuit of low frequencies?
If so, hat's the math, and what's the relation to bafle size (I suppose that the shortest length/width dimension of the baffle influences the low frequenfy roll-off)?
Jennice
Could you please let me know what software you found?
Sjef,
Could you please show a pic (or simple drawing) of this W configuration of tyour bass?
General question:
Is it correctly understood that there's no open baffle design without EQ'ing to compensate for the accoustic short-circuit of low frequencies?
If so, hat's the math, and what's the relation to bafle size (I suppose that the shortest length/width dimension of the baffle influences the low frequenfy roll-off)?
Jennice
Jennice,
search for Tolvan and for Xlbaffle.xls on this forum and you will get some tools to calculate baffle size and baffle roll-off compensation for OBs.
If you really dare to look into HEAVY math, try to get a copy of Juha Backman "A Model of Open-Baffle Loudspeakers".
It has all been discussed in this forum - so searching and reading for some weeks will give you almost any answer you need.
Rudolf
search for Tolvan and for Xlbaffle.xls on this forum and you will get some tools to calculate baffle size and baffle roll-off compensation for OBs.
If you really dare to look into HEAVY math, try to get a copy of Juha Backman "A Model of Open-Baffle Loudspeakers".
It has all been discussed in this forum - so searching and reading for some weeks will give you almost any answer you need.
Rudolf
Jennice,
Here's a graph for baffle width vs frequency of rolloff.
http://www.angelfire.com/electronic/DIY/OB-Speaker-concept-1b.html
Keep in mind that it's only a 6db/octave rolloff until you get down to Fs.
No, it's not the shortest distance. It's more complex and a combination of all the different distances including the floor which is an infinite baffle width.
EQ is not mandatory, just one of the shortcuts if your drivers have the capacity to move enough air without over exerting. Big baffles is another way, but folding them like in a W shape makes them unobtrusive. I prefer a third way and that is excess capacity. Use enough driver capacity to get what you want down low and then do a first order low pass down very low just above Fs, so you end up with a flat net response.
To bad dipole doesn't get room gain. It would be much easier to acheive a flat dipole bass response in room.
Here's a graph for baffle width vs frequency of rolloff.
http://www.angelfire.com/electronic/DIY/OB-Speaker-concept-1b.html
Keep in mind that it's only a 6db/octave rolloff until you get down to Fs.
No, it's not the shortest distance. It's more complex and a combination of all the different distances including the floor which is an infinite baffle width.
EQ is not mandatory, just one of the shortcuts if your drivers have the capacity to move enough air without over exerting. Big baffles is another way, but folding them like in a W shape makes them unobtrusive. I prefer a third way and that is excess capacity. Use enough driver capacity to get what you want down low and then do a first order low pass down very low just above Fs, so you end up with a flat net response.
To bad dipole doesn't get room gain. It would be much easier to acheive a flat dipole bass response in room.
Hi Jennice,
here is a picture of my speakers. As you can see, there is still work in progress, they sound better than they look.
The W-baffle woofer design was taken from the website of Siegfried Linkwitz (thanks again Siegfried for this idea)
www.linkwitzlab.com
here is a picture of my speakers. As you can see, there is still work in progress, they sound better than they look.
The W-baffle woofer design was taken from the website of Siegfried Linkwitz (thanks again Siegfried for this idea)
www.linkwitzlab.com
Attachments
Let's just say I'd call the look "interesting" (My main concern would probably be the stiffness of the baffle, but I trust you have thought about that?
Regarding the W-shape... I suppose it is made to make a physically longer path between the front and rear of the speaker membrane, yet keeping both sides open to room air (not in a complete enclosure), thus making a very large baffle, but foldes up to take up less room space...?
How big is the clear part of your baffle (approximately)? It's hard to judge by the picture.
Jennice
(My main concern would probably be the stiffness of the baffle, but I trust you have thought about that?Regarding the W-shape... I suppose it is made to make a physically longer path between the front and rear of the speaker membrane, yet keeping both sides open to room air (not in a complete enclosure), thus making a very large baffle, but foldes up to take up less room space...?
How big is the clear part of your baffle (approximately)? It's hard to judge by the picture.
Jennice
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.