What about a second rear facing tweeter?
Implementing options are two:
a) redesign the Zaph crossover for 1/2 of the impedance. Easiest way would be to delete the paralel L-pad resistor and alter the value of the series resistor;
b) add the second one with it's own crossover in parallel with the front firing, this would also require altering the values of the L-pad in order to preserve the tonal balance.
I think that adding the second tweeter to the back of the baffle will not alter the overall emitted power in the high frequencies as it will be with reverse polarity, but this should be considered as well.
Implementing options are two:
a) redesign the Zaph crossover for 1/2 of the impedance. Easiest way would be to delete the paralel L-pad resistor and alter the value of the series resistor;
b) add the second one with it's own crossover in parallel with the front firing, this would also require altering the values of the L-pad in order to preserve the tonal balance.
I think that adding the second tweeter to the back of the baffle will not alter the overall emitted power in the high frequencies as it will be with reverse polarity, but this should be considered as well.
>>> loss of efficiency - you have to make up for the open baffle bass loss if you want good tonal balance.
That's why i use the sub amp for the woofers. This allows their volume level to be raised to match the more efficient main drivers on the baffle. 15" woofers can handle judicious amounts of power so amplifying them is not an issue in a home setup.
It's exciting to see an ambitious project like T101s turn out nicely and it shows how people think differently in their efforts to achieve similar goals.
The Jamo speaker (which was very well received in a Stereophile review) offers an elegant, attractive design that works great. Many 'clone' Sonus Fabers and Wilson designs along with their complicated boxes and crossovers, why not the exciting Jamo? Besides, Jamo was not the first and only one to do this. There are MANY OB designs that are similar dating back many years. The concepts are sound.
That's why i use the sub amp for the woofers. This allows their volume level to be raised to match the more efficient main drivers on the baffle. 15" woofers can handle judicious amounts of power so amplifying them is not an issue in a home setup.
It's exciting to see an ambitious project like T101s turn out nicely and it shows how people think differently in their efforts to achieve similar goals.
The Jamo speaker (which was very well received in a Stereophile review) offers an elegant, attractive design that works great. Many 'clone' Sonus Fabers and Wilson designs along with their complicated boxes and crossovers, why not the exciting Jamo? Besides, Jamo was not the first and only one to do this. There are MANY OB designs that are similar dating back many years. The concepts are sound.
Just an idea for dipole tweeter. Instead of buying a second tweeter, you could just mount it horizontally in a dipole waveguide and with a 40mm Ikea bowl sphere on top.
The L-pad in the Zaph crossover tells me that there is enough headroom for a series RC which gives rising towards the HF response. This is needed for compensating the directivity of the tweeter and the falling towards the HF overall emitted power.
The science behind this is here: http://www.diyaudio.com/forums/multi-way/199252-ikea-omni-bowl-speakers.html
P.S. I do not yet know how that sounds... Yet...
Best regards!
The L-pad in the Zaph crossover tells me that there is enough headroom for a series RC which gives rising towards the HF response. This is needed for compensating the directivity of the tweeter and the falling towards the HF overall emitted power.
The science behind this is here: http://www.diyaudio.com/forums/multi-way/199252-ikea-omni-bowl-speakers.html
P.S. I do not yet know how that sounds... Yet...
Best regards!
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Hi.
Regarding the treble end, if its good enough for a $10,000+ speaker then .....
IMO its simply not worth messing around with the excellent phase tracking
and polar response exhibited by Zaphs c/o, you'll just mess up a good thing.
Built properly there is no reason why the mid/treble would be not too far
behind the Jamo's. Its at the bass end where you'd need to spend more
money to really make them fly, so if going for a basic bass end, IMO
don't mess with the top end at all, KISS, and cost effective.
rgds, sreten.
A subwoofer plate amp for the bass end would work, if it has
a L/R 2nd order low pass, and can be set as high as 200Hz.
If it has a built in bass boost option, a lower Qts driver could
be used. Sensitivity would not be critical, so more really what
you want is more Xmax, still difficult to find the right drivers.
The offset c/o schema is critical to the arrangement. Its
this that allows the 6dB sensitivity difference to compensate
for 6dB of the baffle loss, a further 4dB is compensated by
the peaking Q of the bass drivers for about 10dB's worth
of overall baffle loss correction.
The GWs would add a further 3dB @ 30Hz over the GRS's.
Regarding the treble end, if its good enough for a $10,000+ speaker then .....
IMO its simply not worth messing around with the excellent phase tracking
and polar response exhibited by Zaphs c/o, you'll just mess up a good thing.
Built properly there is no reason why the mid/treble would be not too far
behind the Jamo's. Its at the bass end where you'd need to spend more
money to really make them fly, so if going for a basic bass end, IMO
don't mess with the top end at all, KISS, and cost effective.
rgds, sreten.
A subwoofer plate amp for the bass end would work, if it has
a L/R 2nd order low pass, and can be set as high as 200Hz.
If it has a built in bass boost option, a lower Qts driver could
be used. Sensitivity would not be critical, so more really what
you want is more Xmax, still difficult to find the right drivers.
The offset c/o schema is critical to the arrangement. Its
this that allows the 6dB sensitivity difference to compensate
for 6dB of the baffle loss, a further 4dB is compensated by
the peaking Q of the bass drivers for about 10dB's worth
of overall baffle loss correction.
The GWs would add a further 3dB @ 30Hz over the GRS's.
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Hi T101,
You have to use an open backed ribbon or two dome, rear one wired out of phase to approximate the output of the backwave of the cone drivers.
Your suggestion here is just a broad dispersion flooder.
This concept can only give you flawed, broken up omni radiation, the baffle will make it act like a poor bipole. The treble will be the same phase in both directions.
Effectively there is no rear output from a regular dome tweeter as it is damped and ultimately blocked by the motor structure so you only hear the forward wave. Hence you need two units wired different phase.
You could use the rear output from open backed ribbons if you want dipole operation.
Hi All,
Adding a rear tweeter is a good point, the rear tweeter is no do a perfect radiation dipole but add more headroom in the treble. You have a deeper image.
About Jamo design, technically I see at least three flaws for the price : 12000$ !
1. The 5" in the middle of the panel makes a big hole centred at 1000Hz.
See here :
Jamo Reference R 907 loudspeaker Measurements | Stereophile.com
TITLE
But I think Jamo's designers have some aesthetic constraints.
2. The crossover frequency 250-2000Hz : i never use a 5" so low in frequency, even if it is a high end driver. Sure we should heard sound compression at high level. But the 15" should be push to 400Hz, a higher limit for them. I think a 7" for midrange is a better choice.
Comment of S. Linkwitz : Design of Loudspeakers
3. It misses a rear tweeter ...
In conclusion, i think like a lot of people, it is a good thing to have this commercial design. There are no much such designs. It is a source of inspiration and discussion for us
Cheers.
Adding a rear tweeter is a good point, the rear tweeter is no do a perfect radiation dipole but add more headroom in the treble. You have a deeper image.
About Jamo design, technically I see at least three flaws for the price : 12000$ !
1. The 5" in the middle of the panel makes a big hole centred at 1000Hz.
See here :
Jamo Reference R 907 loudspeaker Measurements | Stereophile.com
TITLE
But I think Jamo's designers have some aesthetic constraints.
2. The crossover frequency 250-2000Hz : i never use a 5" so low in frequency, even if it is a high end driver. Sure we should heard sound compression at high level. But the 15" should be push to 400Hz, a higher limit for them. I think a 7" for midrange is a better choice.
Comment of S. Linkwitz : Design of Loudspeakers
3. It misses a rear tweeter ...
In conclusion, i think like a lot of people, it is a good thing to have this commercial design. There are no much such designs. It is a source of inspiration and discussion for us
Cheers.
Hi All,
Adding a rear tweeter is a good point, the rear tweeter is no do a perfect radiation dipole but add more headroom in the treble. You have a deeper image.
About Jamo design, technically I see at least three flaws for the price : 12000$ !
1. The 5" in the middle of the panel makes a big hole centred at 1000Hz.
See here :
Jamo Reference R 907 loudspeaker Measurements | Stereophile.com
TITLE
But I think Jamo's designers have some aesthetic constraints.
2. The crossover frequency 250-2000Hz : i never use a 5" so low in frequency, even if it is a high end driver. Sure we should heard sound compression at high level. But the 15" should be push to 400Hz, a higher limit for them. I think a 7" for midrange is a better choice.
Comment of S. Linkwitz : Design of Loudspeakers
3. It misses a rear tweeter ...
In conclusion, i think like a lot of people, it is a good thing to have this commercial design.
There are no much such designs. It is a source of inspiration and discussion for us
Cheers.
Hi.
In this case with a 4 ohm tweeter adding the same rear tweeter is a
bad idea IMO. Of course you always can but your not fixing anything.
Using MJK's c/o pushes the electrical c/o point for the mid to 500Hz,
and the acoustic point to 400Hz, (200Hz electrical on the bass),
the 5" will be absolutely fine here, a bigger unit is not a good idea,
and you might lose the sensitivity matching needed for MJK's c/o.
Regarding the baffle, you can make it as thick as you like, use
a bracing pattern on the rear, incorporate a rear brace like
the Jamo's. Just stick to the 20" width, or a little more.
Two layers of 1cm / 1/2" ply joined with a contact adhesive layer
as a restrained damping layer should work very well. It would
also ease the cutouts for the bass units and chamfering for
the mid units. Any 2 layer restrained arrangement IMO.
The idea is something simple that will work, it will not be wrong.
There is no point complicating it, for nebulous conjectural gains.
rgds, sreten.
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Well said, so many people over think audio chasing subtle changes (not always improvements) based on some flawed understanding of the physics. It does not have to be rocket science to sound great. Simple can sound very good, it may not be the perfect solution but it can be good enough to be really enjoyable. Spending more money or going for something more complex is heading down the road of diminishing returns very quickly.
Martin
I don't know whether it could be considered as a beer budget -thing, nor a Jamo replica, but I've been cooking something with double 15" basses for almost a year now. It's still in a constantly evolving stage.
I built a pair of MJK open baffles a couple of years ago. They were very nice indeed (cheers MJK!). Although I used the Fostex FE108ESigma instead of the cheaper alternative. Nevertheless I thought the bass didn't integrate well with the original design. It was kind of wobbling along, while the Fostex tried keeping up pace. I first ditched the original crossover, in favor of a 2nd order Bessel series filter. This made the speaker a little more coherent, but substituting the Alpha with a Beta 15A made it even better.
At some point I ended up with a pair of Beta 10CX's. They were first intended as closed boxes for my bedroom. However I made the mistake of connecting them to my Fostex-baffles. The sound was - although very coloured with the simple one cap filter between the CX and the compression driver - very promising. There was a sense of ease and effortlessness to the sound I had been missing with the 4" fullranges.
I made the decision on embarking on what would be an almost neverending fiddling with the crossover trying to tame the 10" coaxial.
What I have now, is a 62cm wide, 130cm tall baffle with 2 15" Beta's, the 10" coaxials with ASD1001 drivers. The crossover has currently evolved to a version with only 1st order Solen Splits between the drivers at 120 and 1800Hz.
The sound would best be described as overall effortless. They do pack quite a punch, and have zero tolerance for second quality amplification. And yes, they do prefer tubes. With sandboxes the treble tends to get a bit hissy. With tubes it's cleaner and more natural. I've been listening to rock, metal (including the more underground genres of black metal), acoustic stuff and classical with them. The work is starting to pay off at last, since they are quite enjoyable with all I've been throwing at them. A little more air and intimacy would still be on the wishlist, but otherwise they sound surprisingly natural, given the cheap eminence drivers. Driver cost per speaker is a little over 200 euros here in Finland. And I'm considering spending more money on the crossover components...
I built a pair of MJK open baffles a couple of years ago. They were very nice indeed (cheers MJK!). Although I used the Fostex FE108ESigma instead of the cheaper alternative. Nevertheless I thought the bass didn't integrate well with the original design. It was kind of wobbling along, while the Fostex tried keeping up pace. I first ditched the original crossover, in favor of a 2nd order Bessel series filter. This made the speaker a little more coherent, but substituting the Alpha with a Beta 15A made it even better.
At some point I ended up with a pair of Beta 10CX's. They were first intended as closed boxes for my bedroom. However I made the mistake of connecting them to my Fostex-baffles. The sound was - although very coloured with the simple one cap filter between the CX and the compression driver - very promising. There was a sense of ease and effortlessness to the sound I had been missing with the 4" fullranges.
I made the decision on embarking on what would be an almost neverending fiddling with the crossover trying to tame the 10" coaxial.
What I have now, is a 62cm wide, 130cm tall baffle with 2 15" Beta's, the 10" coaxials with ASD1001 drivers. The crossover has currently evolved to a version with only 1st order Solen Splits between the drivers at 120 and 1800Hz.
The sound would best be described as overall effortless. They do pack quite a punch, and have zero tolerance for second quality amplification. And yes, they do prefer tubes. With sandboxes the treble tends to get a bit hissy. With tubes it's cleaner and more natural. I've been listening to rock, metal (including the more underground genres of black metal), acoustic stuff and classical with them. The work is starting to pay off at last, since they are quite enjoyable with all I've been throwing at them. A little more air and intimacy would still be on the wishlist, but otherwise they sound surprisingly natural, given the cheap eminence drivers. Driver cost per speaker is a little over 200 euros here in Finland. And I'm considering spending more money on the crossover components...
>>> I've been listening to rock, metal (including the more underground genres of black metal), acoustic stuff and classical with them.
>>> they sound surprisingly natural, given the cheap eminence drivers.
I love the Eminence drivers i have. They sound different than the Fostex and TBs but not really better or worse, just different. You can absolutely listen to rock thru them as well as acoustic, classical and anything else... something i cannot say about the other brands i also own and enjoy. Funny how you crossover at 1800khz and i cross at 10khz. I think that 'cheap' tweeter they make sounds excellent!
>>> they sound surprisingly natural, given the cheap eminence drivers.
I love the Eminence drivers i have. They sound different than the Fostex and TBs but not really better or worse, just different. You can absolutely listen to rock thru them as well as acoustic, classical and anything else... something i cannot say about the other brands i also own and enjoy. Funny how you crossover at 1800khz and i cross at 10khz. I think that 'cheap' tweeter they make sounds excellent!
Funny I was musing about stiffening the panels back in post 39, also soft mounting the drivers.
Martin you have put a lot of thought and effort into modeling the peaks and dips in the response curve of the Open Baffle design discussed here. If I recall reading correctly this design was more a thought exercise and the OB that you built used different drivers on a larger panel.
For the project that you built what did you learn in regard to the point of demising returns for panel stiffness and driver mounting?
For a play thing I mounted coaxial Vifa A10CC-07’s on ¾” 15 X 21 Baltic Birch plywood panels with no picture frame reinforcement or rubber gasket rubber grommet soft mounting, kind of a desktop 2 ½ way system. I was surprised in a negative way by how much vibration I felt with my finger tips in the wood panels. I was impressed by the degree of vibration attenuation from adding a few cleats to the panel perimeter, support feet and closed cell foam neoprene plus rubber mounting grommets for the driver.
DT
A paper exercise is not a real exercise... Never forget we hear speaker before saying it is good or not.
I have made a lot of real exercises This is the reason I try to contribute as possible to this post. It could give some clues for who want do an open baffle, a jamo clone .
About rear tweeter, studies have been made here. And I don't think it is so marginal. It is not so expensive to do. I know i cannot build an open baffle without this !
The solution of a FAST could be good, as Pano have shown
Totally agree
More, I don't listen a lot the "best" drivers, the more expensive I have. I prefer the sound of some of my cheaper drivers.
I have made a lot of real exercises
This is the reason I try to contribute as possible to this post. It could give some clues for who want do an open baffle, a jamo clone .About rear tweeter, studies have been made here. And I don't think it is so marginal. It is not so expensive to do. I know i cannot build an open baffle without this !
The solution of a FAST could be good, as Pano have shown
Totally agree
More, I don't listen a lot the "best" drivers, the more expensive I have. I prefer the sound of some of my cheaper drivers.
I built an OB speaker that matched the design in my study.
Project 9 : Eminence Alpha 15A Experimental Open Baffle Design
You can see the bracing I used in one of the pictures, it is a simple window frame type of arrangement that doubled the thickness of the baffle around the edges and across the panel in a couple of locations. Seemed to work well, I have not observed significant panel vibrations but I do not check for them very often.
The only difference in the build was I used my active crossover to dial in the response for each of the small full range drivers in my collection. I have tried the Fostex FE83En, FE103En, FE108ESigma, FF85K, FF85WK, FF105WK, along with the Alpiar 6 and CHR70. For woofers I have tried the Eminence Alpha 15A and the AE Dipole 15.
The only driver I did not like was the CHR70, it did not have the sparkle of the others. The Alpair 6 worked very well. My favorite so far is still the FE108ESigma.
All the others worked very well in my opinion, the differences were subtle. I think that the larger diameter Fostex drivers integrated a little better than the smaller diameter Fostex drivers. The crossover technique was similar to what I described in the article but I did adjust the high pass frequency for a couple of the drivers and of course the bass boost when needed to match the woofer to the full range driver.
I am using only SS amps. I found that my tube amp did not mate well with this type of speaker when a passive crossover was used, I have also heard this observation from other builders. So I stopped using the tube amp and it is sitting in the corner.
All drivers are hard mounted to the baffle, I am not a fan of magnet mounting woofers or soft mounting drivers.
Martin
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