I've been lurking on on the forum for about 12 months and thought it was about time I posted something. I've become a bit obsessed with the idea of a full range open baffle ever since first reading about dipole speakers. I liked the idea of full ranger partly because of what people said about them but secondly because I didn't have the expertise to get into crossover design... I promptly bought a some full range drivers and began experimenting. I quickly became hooked on the openness of the sound and have since become pretty much obsessed the idea of designing a practically sized full range open baffle speaker that produces enough bass.
After numerous (Failed) protypes and quiet a bit of reading I've finally arrived at a design concept which I''m hopeful about and I'm interested to know what the minds greater than mine think of the concept.
The idea is to use 2 drivers... one in an open baffle back to back with one placed in a horn. The horn would have the driver firing inwards and would be wired out of phase. The idea is that the back driver would effectivley cancellout the back waves from the open baffle adn great a kind of 'dead zone' behind the baffle. hopefully this would reduce baffle step issues as well has ensure there are no back reflections to the front driver.
As the back driver fires into a quarter wavelength horn it would also extend the bass to something closer to full-range.
Anyway, I've greated some a crude 'sketchup'; to illustrate the idea... I still need to work out the specifics of the horn path but it should be enough to give an idea of my thinking...I'm just wondering if anyone had any thoughts' or had perhaps seen anything like this done before.
Any Thoughts?
After numerous (Failed) protypes and quiet a bit of reading I've finally arrived at a design concept which I''m hopeful about and I'm interested to know what the minds greater than mine think of the concept.
The idea is to use 2 drivers... one in an open baffle back to back with one placed in a horn. The horn would have the driver firing inwards and would be wired out of phase. The idea is that the back driver would effectivley cancellout the back waves from the open baffle adn great a kind of 'dead zone' behind the baffle. hopefully this would reduce baffle step issues as well has ensure there are no back reflections to the front driver.
As the back driver fires into a quarter wavelength horn it would also extend the bass to something closer to full-range.
Anyway, I've greated some a crude 'sketchup'; to illustrate the idea... I still need to work out the specifics of the horn path but it should be enough to give an idea of my thinking...I'm just wondering if anyone had any thoughts' or had perhaps seen anything like this done before.
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
Any Thoughts?
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Joined 2009
would this not just work like a leaky isobaric setup, only not as well?
surely you're still going to get colouration etc from the 2nd driver in the T/L enclosure, so negates the point in using open baffle? and because the 2 opposing drivers aren't sealed up, they're not really going to perfectly cancel each other out, so you'll get odd noise from there too?
surely you're still going to get colouration etc from the 2nd driver in the T/L enclosure, so negates the point in using open baffle? and because the 2 opposing drivers aren't sealed up, they're not really going to perfectly cancel each other out, so you'll get odd noise from there too?
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Joined 2009
Paid Member
very inventive !
Here's my thoughts - from a non-expert mind.
The OB with a single driver didn't have enough bass. You believe the biggest issue is the cancellation of the front wave by the wave emitted from the back of the driver. So, it's clear that the back wave from the driver has a big impact on the sound. And so the quality of the sound depends on the properties of the back wave.
So unless you cancel the back wave accurately, the 'error' will contaminate the sound even if you improve the bass. I assume that the 2nd driver will not behave like the front driver because it is loaded with a TL. This means its output will be different from the front driver so it can't accurately cancel the back wave of the front driver. The TL has a terminus, any sound emitted from it will also wrap around to the front. It will be time-shifted by it's travel down the TL and it's bandwidth with also be limited. This will also contaminate the sound.
But it might work just great - only way to find out is to try it out !
fyi - I recently came across a design that has drivers on the front and on the back and a TL between them. The two sets of drivers shared the TL. http://www.troelsgravesen.dk/JA8008_DTQWT.htm
Here's my thoughts - from a non-expert mind.
The OB with a single driver didn't have enough bass. You believe the biggest issue is the cancellation of the front wave by the wave emitted from the back of the driver. So, it's clear that the back wave from the driver has a big impact on the sound. And so the quality of the sound depends on the properties of the back wave.
So unless you cancel the back wave accurately, the 'error' will contaminate the sound even if you improve the bass. I assume that the 2nd driver will not behave like the front driver because it is loaded with a TL. This means its output will be different from the front driver so it can't accurately cancel the back wave of the front driver. The TL has a terminus, any sound emitted from it will also wrap around to the front. It will be time-shifted by it's travel down the TL and it's bandwidth with also be limited. This will also contaminate the sound.
But it might work just great - only way to find out is to try it out !
fyi - I recently came across a design that has drivers on the front and on the back and a TL between them. The two sets of drivers shared the TL. http://www.troelsgravesen.dk/JA8008_DTQWT.htm
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Thanks for the feedback guys... All food for thought.
To try and maximise the 'cancelling' properties of the second driver i'd make sure the physical layout of the middle space was symetrical. As bigun says you'd still get the colloration from the back driver. In my head i'm thinking that the sound you would hear within that back space would almost all be the colloration in fact butmy hope is that much less of this will make it to the listening position though i realise whether this will be the case or not will depend on the frequencies at which the horn collartion occurs.
By the way... It's not on the design but i'd also add felt wadding to the internal surfaces as well as well as some kind of interior baffle to prevent direct waves from each driver hitting each other.... I'm thinking this could be incorporated into some kind of brace between the drivers.
Chrisb-i understand your comment about the spl from the open baffle would be low but would the spl of the whole system but not comparible to astandard single driver TL?
At the end of the day I might just have to build it and see.
To try and maximise the 'cancelling' properties of the second driver i'd make sure the physical layout of the middle space was symetrical. As bigun says you'd still get the colloration from the back driver. In my head i'm thinking that the sound you would hear within that back space would almost all be the colloration in fact butmy hope is that much less of this will make it to the listening position though i realise whether this will be the case or not will depend on the frequencies at which the horn collartion occurs.
By the way... It's not on the design but i'd also add felt wadding to the internal surfaces as well as well as some kind of interior baffle to prevent direct waves from each driver hitting each other.... I'm thinking this could be incorporated into some kind of brace between the drivers.
Chrisb-i understand your comment about the spl from the open baffle would be low but would the spl of the whole system but not comparible to astandard single driver TL?
At the end of the day I might just have to build it and see.
... Incidentally, i'm curious if it's possible to tune one of the folds like a bass reflex port? if so does it have to be at the mouth or is it feasible to do this along the horn path. Like i say i'm a relative noob to this so it might be stupid idea but nevertheless it's a question that i've been unable to find an answer to. I understand that bass reflex ports can muddy the sound somewhat but (assuming this would even work) i'm wondering if it would have detrimental effects on the sound outside the resonant frequency.
I have tried the cancellation idea with an OB speaker in front of a closed box speaker. I had difficulty making it work as I hoped. One thing to think about is whether the front and rear speaker baffles should be parallel or tilted in relation to each other. My suspicion is that if they are parallel, where the separation equals half a wavelength there will be a reinforced standing wave, rather than a cancellation.
Would you not get another standing wave from the second driver too that was the exact inverse?
Anyway, so curiosity got the better of me so i knocked up a couple of back to back open baffles and just to see what happened, mounted a heavilly damped sealed box over the back one with the driver firing into it.
First impressions are that there's definately seems to be a 'dead space' between the baffles though the does seem to be some higher frequencies coming from there. It's hard to say how much cancelation is happening but there does seem to be something going on.
I hope you keep on with it. I think that the cancellation works when the speakers are moving in sync. But at the half wavelength separation by the time the pressure wave from the front driver has reached the back, the back driver will have completed half a cycle and will be moving in opposition thus reinforcing the pressure wave. However at 3" separation for example this will occur above 2000Hz, and even a thin layer of sound absorbent on each face of the baffles in the gap, will reduce it a lot. It might be an idea to do this anyway since it will cut down the high frequency leakage.
I see what you're getting at... I hadn't thought about the effect of the distance between back of the drivers. Like you say though standing waves and these kinds of frequencies should be easier to tame. I've got some felt on the inside of the baffles to try and prevent reflections between the baffles but I'm starting to think that it's the actual higher frequencies eminating from the back of the drivers that is at least partly resposible for some of the 'open baffleness' and the increased soundstage that goes with it...I jsut need to allow these to escape into space without boucing around too much in the back cavity.
Anyway. I'm going to listen to it for a few days and then decide where to go from there.
This picture may be of some interest:
It is from an experiment that I and Anders Martinsson (of THAM Tapped Horn fame - see Subwoofer section) conducted. The Monacor SP-130/X8 fullranger from my 'Volks-OB' - http://www.audiocircle.com/index.php?topic=46951.0 played together with Anders' small 6.5" TH - http://www.diyaudio.com/forums/subwoofers/164199-th-micro-6-5-tapped-horn.html - to the right in the picture. The combination was played active with crossover tested from 180 - 300 Hz. The sound was in fact sensational given the units, very musical and joyful. No apparent phase issues. In fact Anders brought the combo to Hi-Fi Forum's DIY show 2010 in Gothenburg with great succsess. Anders' big THAM15 horn played too powerful to successfully integrate with the 5" fullranger.
/Erling
An externally hosted image should be here but it was not working when we last tested it.
It is from an experiment that I and Anders Martinsson (of THAM Tapped Horn fame - see Subwoofer section) conducted. The Monacor SP-130/X8 fullranger from my 'Volks-OB' - http://www.audiocircle.com/index.php?topic=46951.0 played together with Anders' small 6.5" TH - http://www.diyaudio.com/forums/subwoofers/164199-th-micro-6-5-tapped-horn.html - to the right in the picture. The combination was played active with crossover tested from 180 - 300 Hz. The sound was in fact sensational given the units, very musical and joyful. No apparent phase issues. In fact Anders brought the combo to Hi-Fi Forum's DIY show 2010 in Gothenburg with great succsess. Anders' big THAM15 horn played too powerful to successfully integrate with the 5" fullranger.
/Erling
would the impedance curves not have to match exactly to get perfect cancellation, providing both the drivers themselves are identical manufactured? i was reading around about things like this today, and from what i think i understand is, you'd get a combfilter type thing going on where you'd have reduction of some frequencies but an amplifcation of others. this high frequency ring or scream seemed to be quite common in certain styles of sealed isobaric when the distance between the drivers was quite large.
please correct where wrong, i'm learning.
Hello,this tapped horn sub in extreme right of the image seems to be the smallest TH sub, Can you guide me to the link for the plans.
TY
I built something like this except it has a TL configuration and less of an ob arrangement up front. I had an idea that an isobaric-ish doubling of the bass-mid without any pressure behind the front driver might be a good thing. A little bit stasis like, can I say that around here? I thought if the driver facing the room had no load on the back of the cone it would act as if it was lower mass or something. Very cool to see someone else putting this out. I didn't like my first listen to my box but that may have been because it wasn't boxy. Thanks for the presentation.
Edit: not like the TH
Edit: not like the TH
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