Andy, try it if you like but I'd want to at least have the theory right first. When I've built something against sound theory and logic, it has merely proven to make plan to my ears what I should have known already from a theoretical point of view. I think you'd get better results with a U frame.
Paul, it really wont be a waste of time either way. I'm building two .5cubic foot enclosures tuned to 35hz for my extremises and I'm going to set them back to back and wire out of phase, then I'll compare the response to a Hframe I'm making. Regardless of whether or not they sound good this way, or yeild better response, I still get the enclosures i was going to build, and at no expense.
I do think there is potential within this reflex dipole idea of mine. The backwaves are being utilized through the port resonance to gain efficency while at the same time the dipole effect will decrease the efficiency down lower. I think the gain from the ports might also have a different radiation pattern than a speaker would.
The increased distance between the front wave radiation and the reverse polarity "backwave" radiation might also cause different effects
I will try this idea not only with the enclosures back to back, but seperated at a few different distances to find what effect that has on the response.
I do think there is potential within this reflex dipole idea of mine. The backwaves are being utilized through the port resonance to gain efficency while at the same time the dipole effect will decrease the efficiency down lower. I think the gain from the ports might also have a different radiation pattern than a speaker would.
The increased distance between the front wave radiation and the reverse polarity "backwave" radiation might also cause different effects
I will try this idea not only with the enclosures back to back, but seperated at a few different distances to find what effect that has on the response.
Rudolf,
Do you think that curving the back would be of benefit. I can see that it would crete a loss in volume, but on the other hand I believe it would create less turbulance and a more coherent wave front. In the design I'm considering I would increase the height of the center space to make up for the volume loss. My other question regards the performance difference between 2 N baffles versus the reduced W, looks like you went with 2 -N. Can you make any comparisons? Thanks again.
Do you think that curving the back would be of benefit. I can see that it would crete a loss in volume, but on the other hand I believe it would create less turbulance and a more coherent wave front. In the design I'm considering I would increase the height of the center space to make up for the volume loss. My other question regards the performance difference between 2 N baffles versus the reduced W, looks like you went with 2 -N. Can you make any comparisons? Thanks again.
At 80 Hz wavelenght is more than 4 m, so adjusting 20 cm somewhere inside the ripole doesn´t change the wavefront coherency much IMHO. What should be considered is the TML function of the ripole enclosure. A cabinet with 90° sides emphazises the lambda/4 resonance peak most. You could try to "smear" that by tilting the front (or back) by 45°. Regarding the loss in volume: I´m not aware that dipoles need a specific volume like BR boxes. So you need not be overly accurate about it.Jazr said:
Actually I had the Linkwitz W baffle first and then split it to get two N baffles. The really significant difference was not between the W baffle and two N baffles, but between having the N baffles side by side in the middle between left and right satellite and then one N baffle under each satellite (still with the mono subwoofer signal). I didn´t use the stacked N baffles regularly. I just showed them to illustrate how small a dipole tower speaker could be built.
Hope this was of some help
Rudolf
Subwoofer
Rudolf,
I would ask your help for a particular project.
I take part in a no-profit association (Agorà - Onlus Lesina - Italy).
Among the various initiatives we have organized a Course of Electronic for children (8-12 years).
In this context we have recently planned to build an HiFi audio system to present to the Municipal Library. It is so structured:
- CD-player
- 300B tube amplifier
- Dipole speakers.
- Subwoofer
Our dipole speakers have a natural 6dB roll-off at about 150 Hz.
So, we need to integrate them with a subwoofer system.
Since we already have new-old RCF woofers (see parameters below), we'd like to use them for 2 subwoofers.
The questions I'd like to submit to you are the following:
1) Can we use two separate subwoofers (one for each channel) consisting of one woofer each (as in your post #365 )? ... or do you suggest to employ a 2-single central unit subwoofer ?
2) Can we utilize the RCF woofers for this project ?
3) If so which cabinet measurements and which filter we'd adopt ?
We'd be very grateful if you could help us.
-----------------------------------------------------------
RCF woofer parameters (the only available):
Continuos power: 100W
Musical power: 200W
Sensibility: 98.5 dB
Fs: 37 Hz
Frequency range: 37-4.000 Hz
Impedance: 8 ohm
Total flux: 3,890 mWb
Coil diameter: 75 mm
Diameter of the woofer: 387 mm
Weight: 9.5 Kg
Rudolf,
I would ask your help for a particular project.
I take part in a no-profit association (Agorà - Onlus Lesina - Italy).
Among the various initiatives we have organized a Course of Electronic for children (8-12 years).
In this context we have recently planned to build an HiFi audio system to present to the Municipal Library. It is so structured:
- CD-player
- 300B tube amplifier
- Dipole speakers.
- Subwoofer
Our dipole speakers have a natural 6dB roll-off at about 150 Hz.
So, we need to integrate them with a subwoofer system.
Since we already have new-old RCF woofers (see parameters below), we'd like to use them for 2 subwoofers.
The questions I'd like to submit to you are the following:
1) Can we use two separate subwoofers (one for each channel) consisting of one woofer each (as in your post #365 )? ... or do you suggest to employ a 2-single central unit subwoofer ?
2) Can we utilize the RCF woofers for this project ?
3) If so which cabinet measurements and which filter we'd adopt ?
We'd be very grateful if you could help us.
-----------------------------------------------------------
RCF woofer parameters (the only available):
Continuos power: 100W
Musical power: 200W
Sensibility: 98.5 dB
Fs: 37 Hz
Frequency range: 37-4.000 Hz
Impedance: 8 ohm
Total flux: 3,890 mWb
Coil diameter: 75 mm
Diameter of the woofer: 387 mm
Weight: 9.5 Kg
Attachments
Re: Subwoofer
@1) The main advantages of a W baffle with two drivers over a N baffle would be impulse compensation (because both drivers work diametrically opposed) and some compensation of harmonic distortion (if you arrange the drivers in Linkwitz style). These advantages are needed most when playing LOUD.
Since your system is fed by a tube amp and situated in a public library I believe it is intended as an audiophile system and NOT a party rocker. So high power impulse and distortion compensation are not a main demand.
If your dipole speakers roll-off at about 150 Hz (as stated) you really should consider to do one subwoofer per channel, because musical content above 100 Hz becomes increasingly locatable.
@2) One 15" woofer per side seems quite sufficent for the purpose. I don´t see any problems regarding SPL there. Whether your RCL woofer is suitable for a dipole can´t be decided with the given parameters. Two hints: You will need a bit more excursion (Xmax) than for a closed box or bass reflex. And you will prefer a Qts>0,5.
If you could state the exact type of your woofers, chances are we could retrieve those parameters from the internet.
@3) A W or N dipole cabinet should just fit the driver. There is not much sense in making it taller or deeper than the driver demands. Regarding the width of the chambers in front and back of the cone: If you make them smaller, the lambda/4 resonance peak will rise and the resonance frequency of the driver will drop. If width of the dipole sub is no issue, I would stick with the values Linkwitz recommends.
Regarding a filter: There is no way to decide on component values before you have built the actual cabinets. AFAIK both Linkwitz and Ridthaler state that system resonance isn´t just determined by the depth of the baffle. Different drivers in the same size W baffle lead to different resonance frequencies. So you need to actually measure the resonance somehow. I would strongly recommend that you look for someone near you to help with the actual construction.
Best luck for your interesting project
Rudolf
Antonio,Antonio Tucci said:
@1) The main advantages of a W baffle with two drivers over a N baffle would be impulse compensation (because both drivers work diametrically opposed) and some compensation of harmonic distortion (if you arrange the drivers in Linkwitz style). These advantages are needed most when playing LOUD.
Since your system is fed by a tube amp and situated in a public library I believe it is intended as an audiophile system and NOT a party rocker. So high power impulse and distortion compensation are not a main demand.
If your dipole speakers roll-off at about 150 Hz (as stated) you really should consider to do one subwoofer per channel, because musical content above 100 Hz becomes increasingly locatable.
@2) One 15" woofer per side seems quite sufficent for the purpose. I don´t see any problems regarding SPL there. Whether your RCL woofer is suitable for a dipole can´t be decided with the given parameters. Two hints: You will need a bit more excursion (Xmax) than for a closed box or bass reflex. And you will prefer a Qts>0,5.
If you could state the exact type of your woofers, chances are we could retrieve those parameters from the internet.
@3) A W or N dipole cabinet should just fit the driver. There is not much sense in making it taller or deeper than the driver demands. Regarding the width of the chambers in front and back of the cone: If you make them smaller, the lambda/4 resonance peak will rise and the resonance frequency of the driver will drop. If width of the dipole sub is no issue, I would stick with the values Linkwitz recommends.
Regarding a filter: There is no way to decide on component values before you have built the actual cabinets. AFAIK both Linkwitz and Ridthaler state that system resonance isn´t just determined by the depth of the baffle. Different drivers in the same size W baffle lead to different resonance frequencies. So you need to actually measure the resonance somehow. I would strongly recommend that you look for someone near you to help with the actual construction.
Best luck for your interesting project
Rudolf
Rudolf,
Thank you very much for your replay.
Only some further precisations.
1) In the case we decide to employ the Vifa 30 WN 380/8ohm ... Is the filter you reported in the Post #4 the correct filter ? .
2) In the case of Vifa ...which are the dimensions of the cabinet (in particular ... the anterior chamber)?
3) IMPORTANT: Do we have to arrange the two subwoofers in a mono-configuration or in a stereo-configuration ?
4) Which amplifier do you suggest for the ripoles ? What do you think about this DIY one (http://sound.westhost.com/project101.htm)?
5) Which is the best seller in Europe (... or in Italy) for the Vifa woofers ? (...where we can buy the woofers at a low cost ?).
Thanks again
Thank you very much for your replay.
Only some further precisations.
1) In the case we decide to employ the Vifa 30 WN 380/8ohm ... Is the filter you reported in the Post #4 the correct filter ? .
2) In the case of Vifa ...which are the dimensions of the cabinet (in particular ... the anterior chamber)?
3) IMPORTANT: Do we have to arrange the two subwoofers in a mono-configuration or in a stereo-configuration ?
4) Which amplifier do you suggest for the ripoles ? What do you think about this DIY one (http://sound.westhost.com/project101.htm)?
5) Which is the best seller in Europe (... or in Italy) for the Vifa woofers ? (...where we can buy the woofers at a low cost ?).
Thanks again
Attachments
Hej Bjørn,
the point is to make both drivers see the same "Strahlungswiderstand" (I don´t know the proper translation - something like radiaton resistance) as each single driver sees in its own box. My guess (but I don´t really know): 20-30% less gap area than the added ones for single drivers.
Rudolf
the point is to make both drivers see the same "Strahlungswiderstand" (I don´t know the proper translation - something like radiaton resistance) as each single driver sees in its own box. My guess (but I don´t really know): 20-30% less gap area than the added ones for single drivers.
Rudolf
BassAwdyO said:
You have to remember that with these N-Baffles or Ripoles is that the back wave of the driver is fully open just like the front wave is. They do not react to the baffle as say a sealed or ported enclosure. The baffles are not tuned to any given freq.
Doing two ported enclosures 180* out of phase from one another is totally void. For one, you have the back wave sealed off from the front, then tuned to a certain freq. The drivers will act like they are in sealed enclosures until they reach down to the tuning freq, then after that they will act like being in free-air. It's a totally different situation that I believe will not be very eventfull.
BassAwdyO,
most people who turn to dipoles or open baffles are attracted by two different aspects:
1. the dipole radiation as derived by Linkwitz from the model of two drivers radiating 180° out of phase.
2. the absence of a sealed/ported enclosure with its sound deteriorating aspects.
You just should be aware that your concept will only achieve the advantages of aspect 1. I´m under the impression, that many people building dipoles regard the advantages of aspect 2 as more important for them.
Find out for yourself.
most people who turn to dipoles or open baffles are attracted by two different aspects:
1. the dipole radiation as derived by Linkwitz from the model of two drivers radiating 180° out of phase.
2. the absence of a sealed/ported enclosure with its sound deteriorating aspects.
You just should be aware that your concept will only achieve the advantages of aspect 1. I´m under the impression, that many people building dipoles regard the advantages of aspect 2 as more important for them.
Find out for yourself.
And no, I don't think I'm wrong either.
There is absolutely nothing special or magical about wiring two identical ported enclosures out of phase. All you get is a big NOTHING. And it doesn't matter which direction you have the ports facing.
And the reason it won't work is because you are trying to do this with two mono-pole subwoofers. Those ports on your subs are only there to reinforce the bass output ONLY when the sound coming out of it is IN PHASE with the front wave of the exposed driver surface which only occurs right around the tuning freqency.
So don't get your hopes up about your little project because you fail to completely understand the concept of a mono-pole design.
I'm not trying to be an A-hole or start an argument, but it just won't work, period.
There is absolutely nothing special or magical about wiring two identical ported enclosures out of phase. All you get is a big NOTHING. And it doesn't matter which direction you have the ports facing.
And the reason it won't work is because you are trying to do this with two mono-pole subwoofers. Those ports on your subs are only there to reinforce the bass output ONLY when the sound coming out of it is IN PHASE with the front wave of the exposed driver surface which only occurs right around the tuning freqency.
So don't get your hopes up about your little project because you fail to completely understand the concept of a mono-pole design.
I'm not trying to be an A-hole or start an argument, but it just won't work, period.
Planet and Cal,
shame , shame, moderators. We both know that a Monopole subwoofer (which is what we are talking about) radiates sound omni-directionally. Whether ported or sealed. Does not matter. A monopole IS an omnipole at low frequencies - lets not split hairs.
BassO, fell free to do your experiments. Thats what DIY is all about. I'm not going to say what conepts you do or don't understand, but yes, one of the main reasons (and the only one IMHO) to go dipole is NOT to have a box. Not ported. Not sealed. You can mimmick a dipole radiation pattern using your "concept". But you will not get open baffle (dipole) benefits. Here is a link to someone who has already done something similar - though not ported.
http://www.musicanddesign.com/craw.html
btw, Planet (you would be proud) I just picked up a pair of these
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=264-452
a phase plug and OB and I'm in business. For $18. Frugalphility?
Cheers,
AJ
shame , shame, moderators. We both know that a Monopole subwoofer (which is what we are talking about) radiates sound omni-directionally. Whether ported or sealed. Does not matter. A monopole IS an omnipole at low frequencies - lets not split hairs.
BassO, fell free to do your experiments. Thats what DIY is all about. I'm not going to say what conepts you do or don't understand, but yes, one of the main reasons (and the only one IMHO) to go dipole is NOT to have a box. Not ported. Not sealed. You can mimmick a dipole radiation pattern using your "concept". But you will not get open baffle (dipole) benefits. Here is a link to someone who has already done something similar - though not ported.
http://www.musicanddesign.com/craw.html
btw, Planet (you would be proud) I just picked up a pair of these
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=264-452
a phase plug and OB and I'm in business. For $18.
Frugalphility?Cheers,
AJ
Here you go BassAwdyO
Ported version. Sound very nice for an outdoor rig. Chest crushing @ close range.
http://www.meyersound.com/products/concertseries/psw-6/
Ported version. Sound very nice for an outdoor rig. Chest crushing @ close range.
http://www.meyersound.com/products/concertseries/psw-6/
An externally hosted image should be here but it was not working when we last tested it.
AJinFLA said:
Hairs that need splitting every-once-in-awhile. I see far to many references that suggest that becasue it is a monopole it radiates in only one direction. An omnipole is not a monopole. One of the reason that a lot of people get confused with baffle step, because the same speaker transitions from being a monopole to being an omnipole.
If people would be a bit more precise (and i'm as guilty as the next) -- even Linkwitz -- terminology then perhaps we would have less confusion.
btw, Planet (you would be proud) I just picked up a pair of these
http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=264-452
a phase plug and OB and I'm in business. For $18.
Cool... the very high Q means a little more care tuning the baffle roll-off, but i bet they can be really musical...
Back to the original question, where 2 bass reflex boxes wired out of phase start to roll off is pretty much determined by how they are arranged. The spacing of the 2 sources complicates things somewhat, but if you put one on one side of a sheet of plywood, and another on the other side, roll-off should look pretty much like a driver with the same Q & Fs mounted in that 4x8 sheet (except of course won't suffer from all those nasties BR boxes tend to have). As you shrink the size of the "baffle" calculations become a bit more complex.
dave
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