If you want to save space why not use a telescopic design? The round tube shape is a good one for speaker use. I'm also currently building a boombox with focus on bass grunt. I am also thinking of a bass peak in the 60-70Hz area. But instead of using a BR I've made my own slave bass from an old speaker. The benefit comes from the fact that the driver won't bottom out when suddenly playing a 45hz tune loud. Also the slave speaker takes up very little distance/space so you can achive a low tuning point in little space. I've made a slave bass for a Morel sc 12" and then the slave has fatboy rubber. It works extremely well in a very small box.
To make a slave driver you can just saw off the magnet and just add strength&weight by brushing on epoxy to the speaker cone. The slave should have atleast twice the piston abilty of the driver. (twice the speaker area or 2x better X-max. When you cut of the voice coil and remove the magnet a regular speaker gets suddenly good x-max!).
In practical terms you choose an enclosure that is large enough to play the frequency you wan't (a little less is also fine) and then you add the slave driver. When it's all mounted you play test tunes though it. Lets say 70 hertz from your phone (free tone generator app or pc) and you add more and more layers of epoxy (just to add weight to the cone. It got lighter if/when you cut off the voice coil..). If a sub woofer cone is used you might not need to add weight. But if you use a light cone you have to add weight. Sometimes I usally cut off some of the spider to make the cone travel more pliable. This will help to improve effiency.
The slave cone travel will start to increase until you hit the sweet spot for a chosen frequency. The only way to mess up the tuning is to add to much weight too fast and miss the sweet spot(max travel). If that happens the cone travel decreases, and you are loosing efficency and effectively lowering tuning frequency of the slave driver.) The tuning is very easy to get right if you don't apply to much glue each time.
When the slave is tuned properly to the 70hz it works like a bass reflex. And when playing too low frequencies the setup just works like a closed enclosure. Nothing spectacular happens
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If you go the BR route with a so high tuning point there is a large risk of bottoming out your speakers since most music extend into 45hz. At that frequency your speaker won't see any resistance from the BR and you might aswell have put it in an open baffle! This is usally what happens when people destroy their speakers when playing loud with different bass songs! They bottom out and destroy the voice coil..
In my project I'm aiming for mono sound since stereo doesn't work all that well in a small enclosure. The tpa3116 can be made into mono easily and delivers a lot of power in 2-3ohms. You can also find bluetooth receivers with the Apt-x standard for just 13usd on ebay. It also have line -in and works with a lot of voltage ranges.. Well worth looking into!
To make a slave driver you can just saw off the magnet and just add strength&weight by brushing on epoxy to the speaker cone. The slave should have atleast twice the piston abilty of the driver. (twice the speaker area or 2x better X-max. When you cut of the voice coil and remove the magnet a regular speaker gets suddenly good x-max!).
In practical terms you choose an enclosure that is large enough to play the frequency you wan't (a little less is also fine) and then you add the slave driver. When it's all mounted you play test tunes though it. Lets say 70 hertz from your phone (free tone generator app or pc) and you add more and more layers of epoxy (just to add weight to the cone. It got lighter if/when you cut off the voice coil..). If a sub woofer cone is used you might not need to add weight. But if you use a light cone you have to add weight. Sometimes I usally cut off some of the spider to make the cone travel more pliable. This will help to improve effiency.
The slave cone travel will start to increase until you hit the sweet spot for a chosen frequency. The only way to mess up the tuning is to add to much weight too fast and miss the sweet spot(max travel). If that happens the cone travel decreases, and you are loosing efficency and effectively lowering tuning frequency of the slave driver.) The tuning is very easy to get right if you don't apply to much glue each time.
When the slave is tuned properly to the 70hz it works like a bass reflex. And when playing too low frequencies the setup just works like a closed enclosure. Nothing spectacular happens
. If you go the BR route with a so high tuning point there is a large risk of bottoming out your speakers since most music extend into 45hz. At that frequency your speaker won't see any resistance from the BR and you might aswell have put it in an open baffle! This is usally what happens when people destroy their speakers when playing loud with different bass songs! They bottom out and destroy the voice coil..
In my project I'm aiming for mono sound since stereo doesn't work all that well in a small enclosure. The tpa3116 can be made into mono easily and delivers a lot of power in 2-3ohms. You can also find bluetooth receivers with the Apt-x standard for just 13usd on ebay. It also have line -in and works with a lot of voltage ranges.. Well worth looking into!
A slave bass design (like any other tuned cabinet design) requires a completely sealed airtight enclosure which rules out both telescopic and modularly assembled designs.
Sorry guys. It just does not work.
In principle you could make a telescopic BR design but the funny thing is that you'd need to seal the port when the cabinet is the largest otherwise the tuning won't work and then you have gained nothing.
Sorry guys. It just does not work.
In principle you could make a telescopic BR design but the funny thing is that you'd need to seal the port when the cabinet is the largest otherwise the tuning won't work and then you have gained nothing.
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I meant that the speaker enclosure could be telescopic with a driver and slave in each end..
You could use drainage pipes and put 2 o-rings on the inner tube. Apply grease on the rings and put the rings in place on the inner tube. Put the the tube upright and and smear/pour glue on top of each ring. Heat the epoxy so it becomes water like in viscosity. Then it will flow around like solder
After it has cured you to the same on the other side of the pipe. When thats cured you can take of the O-rings and change them when they become worn. The glue won't adhere to the rubber because of the grease. So what you are left with is to tracks for the rings to sit in. I would put 3-4cm between the o-rings. An you make a tightening mechanism to lock the two tubes together. The friction from the o-rings might be high enough so you don't even have to build that Also some tubes comes with o-rings btw.
Or you could just use Macgyver tape (or clear tape) around the seam every time you use it Then obviously you don't need the o-rings either
You could use drainage pipes and put 2 o-rings on the inner tube. Apply grease on the rings and put the rings in place on the inner tube. Put the the tube upright and and smear/pour glue on top of each ring. Heat the epoxy so it becomes water like in viscosity. Then it will flow around like solder
After it has cured you to the same on the other side of the pipe. When thats cured you can take of the O-rings and change them when they become worn. The glue won't adhere to the rubber because of the grease. So what you are left with is to tracks for the rings to sit in. I would put 3-4cm between the o-rings. An you make a tightening mechanism to lock the two tubes together. The friction from the o-rings might be high enough so you don't even have to build that
Also some tubes comes with o-rings btw. Or you could just use Macgyver tape (or clear tape) around the seam every time you use it
Then obviously you don't need the o-rings either
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Please consider that expanding (or contracting) the closed and sealed volume of air will absolutely certainly damage either the woofer or the slave or both permanently the first time you do this. The trapped air has no place to go beyond pushing the drivers used beyond their mechanical limits. Do I also need to remind you that it is the volume of air that is important. So expanding (or contracting) a sealed tube will only make the air pressure lower (or higher), the volume of air will be the same so the tuning will be exactly the same.
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It will.
Edit: Maybe I'm not get through clearly enough here. Me saying it won't work is not a warning from an ill-advised perspective, it's simply because I have been down both roads and explored all possibilities in trying to shrink designs that way. It does not work.
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Finally somebody who helps me
You need to explain the last part I guess :/
Is it enought to use 1 BR Pipe?
10L tuned to 75Hz also looks good to me, somewhat better damped too. Depends on what kind of sound one wants to get in the end. The two drivers in one chamber won't be problematic with one low-passed, they'll both be active in the bass region.
Finally somebody who helps me
You need to explain the last part I guess :/
Is it enought to use 1 BR Pipe?
Yes, one vent is enough. For the 10L enclosure, a 3" diameter pipe would need to be 7.375" long if that can fit the box, or 2" diameter at 2.75" in length.
Are you familiar with baffle-step? This is where the wavelengths emitted by the speaker become larger than the baffle and "wraps around" the enclosure, radiating in full-space instead of half-space (forward radiation only). You "lose" up to 6dB SPL under the baffle-step. A rough evaluation of the baffle step frequency is 343 / baffle width in meters / 3. A first-order low-pass on one of the two drivers around this frequency will compensate for this as you'll have an extra 6dB voltage sensitivity under the baffle-step due to two drivers being active (+3dB) and their parallel impedance being halved and drawing 2x the current from the amp (+3dB). This is often referred to as a 1.5-way speaker, where the .5 is the bass-only driver.
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