Fantastic, that looks to be more suitable to my level of experience and knowledge. I think I've found my solution.
Is there a graph showing how low the impedance is likely to fall with that xo combined with those drivers?
Is there a graph showing how low the impedance is likely to fall with that xo combined with those drivers?
The XO causes the impedance of the tweeter to get very large below the XO point and the impedance of the woofer to get very large above the XO.
A very large impedance in parallel with 8 ohms is 8 ohms.
dave
A very large impedance in parallel with 8 ohms is 8 ohms.
dave
Great, sounds as if my amp should be able to handle it easily then.
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Now that I have my drivers and crossover sorted. Is there a generic style of cabinet I can build to house them (bookshelf style), or is it really down to experimentation?
Edit:
Now that I have my drivers and crossover sorted. Is there a generic style of cabinet I can build to house them (bookshelf style), or is it really down to experimentation?
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Been looking through this thread and found some useful links which were offered to Matt when he was going through the same stage. I'll compile quotes here for convenience.
Just to give a better idea of what sort of space I have to work with, I've attached a picture showing my TV cabinet, I'm assuming that I am limited to a bookshelf design based on the height of the platform that the speakers are placed on.
Just to give a better idea of what sort of space I have to work with, I've attached a picture showing my TV cabinet, I'm assuming that I am limited to a bookshelf design based on the height of the platform that the speakers are placed on.
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The simple 1st order crossover wouldn't work with that MA combination as the tweeter has a highish Fs and would possibly shelve during the roll off so it would not be far down at Fs (I haven't modelled it but just a hunch). Tweeters need to be quite robust with a low Fs below 600Hz when using a 1st order crossover combined with a 6.5" woofer. The crossover that planet10 has posted is on the money on what is required. 1st order on the woofer with a zobel to tame the rising impedance and a 2nd order on the tweeter to help it drop fast. Planet10 may know if this crossover has been built and finalised or modelled only.... and of course what it sounds like.
Going by your listening needs, room etc I would suggest the 2-way using a 6.5" woofer is a better choice as smaller woofers are not going to fill up that room. You'd be looking for an F3 below 50Hz to get some satisfying bass happening.... wall loading will help the cause for sure. Even a 2-way with a 5" driver is going to be pushing it and a small FR isn't going to be up to the task (I've used the CHR-70 and FR125). The SB Acoustics does take a lot of crossover work and pushes the parts count upward.
From experience I have a DX25TG (or 27TDFC) / Peerless 830875 that I imagine would be similar to the MA 6.5" combo and can inform you that it can fill a room of that size. The smaller ones I have such as the P13 or W15LY001 based speakers would not do the job.
Planet10 I'm sure would be able to point you to some designs for the MA#6 and would suggest a vented to get decent bass out of a smallish box. I can't find details of this driver at MA..... anyone have a link?
I have a two systems with a similar setup and place the speakers so they are around 50mm-75mm from the from front edge of the cabinet and you'll have no issues with reflections and places the speakers forward of the TV screen which is another reflective surface. This allows the use of rear firing port that is placed in line with the tweeter. Trust me on that one as it works very well and controls a lot of the mid energy coming out of the port.
That might be a bit odd to look at considering the chest is over 500mm deep.
That sounds a bit more practical for my needs. So I take it that I am to install the port directly behind the tweeter then. I need to read up on what using a port actually achieves. I see a lot of you talking about "tuning the port" to different frequencies. "Mid energy" is also a term I'm not familiar with. I think I'm learning more from researching all these terms than what I learn in a lecture at uni, haha.
Good to know. I also had trouble finding the spec sheet for the woofer at MA, I found the tweeter easily. I believe there is a thread here somewhere that Mark from MA posted the details in.
Here it is http://www.diyaudio.com/forums/markaudio/154837-marks-proto-6-5-woofer-1-silk-tweet-combo.html
Sorry, but what does a ML-TL refer to?
Also, what size port should I be looking at roughly? I'm assuming that a bigger port would make the loud speaker act as if it was in a larger enclosure, meaning more bass?
Also, what size port should I be looking at roughly? I'm assuming that a bigger port would make the loud speaker act as if it was in a larger enclosure, meaning more bass?
Mass Loaded Transmission Line
http://www.diyaudio.com/forums/mark...woofer-1-silk-tweet-combo-12.html#post2208246
dave
http://www.diyaudio.com/forums/mark...woofer-1-silk-tweet-combo-12.html#post2208246
dave
Here are a couple quick design passes...
28 liter, 492 x 200 x 304mm HWD internal with a 230mm slot, 25 mm high with a 50mm wide port spacer down the middle of the port. F3 38 Hz, F10 28 Hz
15 liter sealed, F3 50 Hz, F10 31 Hz.
dave
28 liter, 492 x 200 x 304mm HWD internal with a 230mm slot, 25 mm high with a 50mm wide port spacer down the middle of the port. F3 38 Hz, F10 28 Hz
15 liter sealed, F3 50 Hz, F10 31 Hz.
dave
Thanks Dave.
Might be a touch big, or would something of that height still be suitable to be placed on my TV cabinet?
Otherwise 15 litres sounds more on the money, I don't suppose you have dimensions for that one, would placing a port in a 15 litre box do anything beneficial?
Might be a touch big, or would something of that height still be suitable to be placed on my TV cabinet?
Otherwise 15 litres sounds more on the money, I don't suppose you have dimensions for that one, would placing a port in a 15 litre box do anything beneficial?
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I left the 15 litre sealed because at that volume it is how i'd go... as to dimensions a sealed box is pretty tolerant of aspect raio (and also exact volume, too small you can increase damping to get back some apparent volume, if too big --- well it has to get a whole lot bigger to make a big difference)
As long as internal measurements aren't integer multiples you are usually fine. I try to use irrational numbers to determine box dimensions.
Here are a couple examples:
1/ Golden ratio box. 15 litres = 15,000 cm^3. Cube root of 15,000 = 24.7 cm, 24.7 * 1.618 = 40 cm, 24.7 / 1.618 = 15.3 cm -- box with internal 153x247x400mm
The #6 would just fit on the narrow side -- perhaps a bit tight, on the wide side no problem (the latter is the Classic GR config)
2/ let's do one where the narrow side is a bit wider. We can't just use sqrt(2) in the same way, because when squared we get the long side 2x the narrow side. So lets use sqrt(2) and the golden number (phi).
xyz=15,000 = sqrt(2)*phi*x^3, x = 18.7, y = 26.5, z = 30.3
using 15mm material you end up with a box with external 333x217x295mm external.
You can use the 2nd method and any 2 irrational numbers to generate a trial starting point.
dave
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I'd suggest 15 litre vented as would give half an octave lower extension than sealed. It would provide more kick and thump but depends on your tastes. That way you could plug the port and try it as sealed to see which you prefer. It's harder to go the other way.... sealed to vented as you need to add in a port and that volume would come off the actual available.
With 15 litres I had it tuned to 44Hz (51mm port) giving F3=47Hz. I modelled this with software I generally don't use as my LspCad is on another computer. I'll run it through in the next couple of days and generally gives a lower F3 than shown above as well as a more accurate port size.
You could use the drawing in post #112 as a guide and alter the driver centres (leave the tweeter position as is) etc to suit. Add 22mm to the height (use H=392mm) to get the extra litre to make up the 15 litres. The actual internal volume is larger than 15 litres as it has to allow for bracing, drivers, port which take up internal volume. The 15 litres is the air space left in the box. Increasing up to 20 litres will give lower extension and 15 litres is what I would consider minimum to achieve F3<50Hz.
Kit in Australia post #112
Reading from there will give you other information on damping etc to help with the build.
With 15 litres I had it tuned to 44Hz (51mm port) giving F3=47Hz. I modelled this with software I generally don't use as my LspCad is on another computer. I'll run it through in the next couple of days and generally gives a lower F3 than shown above as well as a more accurate port size.
You could use the drawing in post #112 as a guide and alter the driver centres (leave the tweeter position as is) etc to suit. Add 22mm to the height (use H=392mm) to get the extra litre to make up the 15 litres. The actual internal volume is larger than 15 litres as it has to allow for bracing, drivers, port which take up internal volume. The 15 litres is the air space left in the box. Increasing up to 20 litres will give lower extension and 15 litres is what I would consider minimum to achieve F3<50Hz.
Kit in Australia post #112
Reading from there will give you other information on damping etc to help with the build.
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Thanks for the advice people.
I think I like the idea of porting, gives me something else to do in the build and I can plug it if I want to.
So I take it that I really need to know the internal volume of my speaker box before I can decide on what size port to use? I downloaded WinISD but it doesn't list the MA woofer in the list.
Once I have decided on port size, I'll be ready to purchase. I'm very excited, haha.
I know that sizing a port obviously has a lot of calculations behind it, but could I just purchase something like a 60mm x 125mm port assuming that it would have to give a lower F3 frequency than not having a port at all?
I think I like the idea of porting, gives me something else to do in the build and I can plug it if I want to.
So I take it that I really need to know the internal volume of my speaker box before I can decide on what size port to use? I downloaded WinISD but it doesn't list the MA woofer in the list.
Once I have decided on port size, I'll be ready to purchase. I'm very excited, haha.
I know that sizing a port obviously has a lot of calculations behind it, but could I just purchase something like a 60mm x 125mm port assuming that it would have to give a lower F3 frequency than not having a port at all?
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Oops, doing that to late at night. Went back to run Rabbitz numbers, the above is vented tuned to 32 Hz (30mm diameter/117mm long)
Sealed is F3 62 Hz, F10 35 Hz.
Rabbitz is F3 48 Hz F10 35 Hz, but with a much bigger hump (2 dB) than i'd consider.
Given that in room F10 is usually more indicative, i'm guessing i'd end up closer to sealed than vented, but a vent does give options.
dave
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Haha, I've got a long way to go before I can interpret such a graph. I can also see that I was way off target with my initial port dimensions.
Just for fun I'm going to post what I imagine it represents, feel free to ignore me, correct me if you can be bothered.
I'm going to take a wild guess here and say that the yellow lines are modelling the impedance of different speaker enclosures.
The black lines represents the db level over the frequency range, I can spot the 2db peak you are speaking of. What would that actually be like to listen to though, would that small range of frequency be noticeably louder than the rest? I find this incredibly interesting, I had no idea that speakers behaved in this manner.
The red lines represent the movement of the speaker cone? I'm guessing there is a safe limit so as to not damage the woofer. That's another aspect of speaker building I had no idea about.
The blue lines make no sense to me at all.
Can any of you suggest any good Loudspeaker design books that you have read that helped you along the way?
Also, I'm guessing that F10 refers to the frequency that is 10db below the 0 point. If you don't mind explaining, what is the significance of the F10 frequency?
On a side note, just in case my appreciation and enthusiasm isn't coming through in my posts to all that are contributing, it is currently 2:43 in the morning here and I have a programming lecture not too long from now, yet I can't sleep because all I can think about is building my first set of speakers. Building my gainclone had the same effect on me, most rewarding project I have completed in ages.
Just for fun I'm going to post what I imagine it represents, feel free to ignore me, correct me if you can be bothered.
I'm going to take a wild guess here and say that the yellow lines are modelling the impedance of different speaker enclosures.
The black lines represents the db level over the frequency range, I can spot the 2db peak you are speaking of. What would that actually be like to listen to though, would that small range of frequency be noticeably louder than the rest? I find this incredibly interesting, I had no idea that speakers behaved in this manner.
The red lines represent the movement of the speaker cone? I'm guessing there is a safe limit so as to not damage the woofer. That's another aspect of speaker building I had no idea about.
The blue lines make no sense to me at all.
Can any of you suggest any good Loudspeaker design books that you have read that helped you along the way?
Also, I'm guessing that F10 refers to the frequency that is 10db below the 0 point. If you don't mind explaining, what is the significance of the F10 frequency?
On a side note, just in case my appreciation and enthusiasm isn't coming through in my posts to all that are contributing, it is currently 2:43 in the morning here and I have a programming lecture not too long from now, yet I can't sleep because all I can think about is building my first set of speakers. Building my gainclone had the same effect on me, most rewarding project I have completed in ages.
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Right on
Group delay. A measure of the phase rotation as the box rolls off.
It is the level at which the bass is half as loud. These curves are aperiodic, and do not take room gain into consideration. All too often, an early, slow roll-off gives flatter end results because of the lift caused by room gain.
F3 is 3 dB done, and its use comes primarily from filter theory and is used extensively. Toole shows that it has no correlation with percieved bass response.
dave
PS: the curves, from left to right at the -1 dB level are 28 litre, 15 litre Rabbitz alignment, 15 litre my alignment, 15 litre sealed,
Ok, I think I understand the benefits of the 28 litre box. It has lower F10 and F3 values and stays fairly flat along the frequency range.
Your 15 litre box is the one with the 30mm diameter/117mm long port? I think I like that option more than the sealed box. It looks to have the same shape curve (not sure if that is the correct term), but it manges lower F3 and F10 values than what the 15 litre sealed unit does.
Room gain is another new term for me. To give a better idea, my room is carpeted, I have 2 small windows of ~ 1m x 1.5m HW, they both have heavy curtains on them (I'm a light sleeper, I like curtains that block out every trace of sunlight) and my walls are plastered. There is not really a lot of free open space. I'm guessing my room gain would not as high as an empty room with nothing to absorb the sound.
Do you mean flatter on the graph (the black line) or flatter as in lifeless sound?
Your 15 litre box is the one with the 30mm diameter/117mm long port? I think I like that option more than the sealed box. It looks to have the same shape curve (not sure if that is the correct term), but it manges lower F3 and F10 values than what the 15 litre sealed unit does.
Room gain is another new term for me. To give a better idea, my room is carpeted, I have 2 small windows of ~ 1m x 1.5m HW, they both have heavy curtains on them (I'm a light sleeper, I like curtains that block out every trace of sunlight) and my walls are plastered. There is not really a lot of free open space. I'm guessing my room gain would not as high as an empty room with nothing to absorb the sound.
Do you mean flatter on the graph (the black line) or flatter as in lifeless sound?
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