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Old 16th June 2012, 08:50 PM   #11
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... 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.
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Old 17th June 2012, 02:38 PM   #12
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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.
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Old 17th June 2012, 06:18 PM   #13
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Quote:
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.
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Old 18th June 2012, 01:03 PM   #14
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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.
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Old 18th June 2012, 03:53 PM   #15
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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,
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.
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Old 18th June 2012, 05:44 PM   #16
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This picture may be of some interest:

Click the image to open in full size.

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 - TH-Micro - a 6,5" tapped horn - 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
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Old 18th June 2012, 06:48 PM   #17
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Quote:
Originally Posted by midrange View Post
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.
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.
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Old 8th August 2012, 09:38 AM   #18
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Quote:
Originally Posted by skorpion View Post
This picture may be of some interest:

Click the image to open in full size.

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' - My 'Volks-OB' Mission Accomplished played together with Anders' small 6.5" TH - TH-Micro - a 6,5" tapped horn - 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
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
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Old 12th August 2012, 03:25 AM   #19
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Location: Willamette Valley
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
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Old 12th August 2012, 07:55 AM   #20
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Hi TY,

If you follow my link for the diy-Audio thread and then further to Martinsson's blog I think you will find the complete plans. Perhaps not really a sub but very competent bass down to 40 Hz. Very direct, open, musical and joyful presentation.

/Erling
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