when you talk about your ideas what comes to mind are the Audio Physic systems like the Cardeas
[audio physic] - no loss of fine detail
or the smaller Scorpio
[audio physic] - no loss of fine detail
You could go MMT instead of MTM. Since you are using smaller mids (5") their excursion limitations will mean higher distortion so doubling the mids allows for lower distortion at the same SPL.
There are many 6" mid woofers (like the 18sound430 or Seas Nextel 16/18) that also are very good in the midrange (upto 3kHz). With such woofers you can go MT.
MTM's typically have a tighter but narrower sweet spot. I have built 3 (Focal 8N515 with Morel MDT 33, ScanSpeak 18W8546+9900 and Dynaudio Gemini) and all 3 exhibited this characteristic.
I like to cross my tweeters lower than 3500Hz. Partially to make offsets easier, and partially to remove the crossover from this critical region in our hearing. Not that there's anything wrong with crossing as you wish to, though.
Why fourth order? It would seem to do the job more effectively, but it adds complexity, and isn't strictly necessary.
A driver's response at its crossover is not only the result of the filter, but of the response (including phase) of the driver itself. You will want this combination to produce the desired rolloff.
This is why you'll often see what look like odd crossovers, like a first order high pass and a second order lowpass filter. The response combined with the drivers' response may well be fourth order.
Furthermore, a driver has a complex impedance which changes the effect of the filter and although an active setup gets around this, it won't get around the need to consider the response of the driver/filter as a combination.
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Good question. I have not, as yet, put any effort in learning the XO issues. So I just chosed what I believed would be the best option of the very little I "know".
As with everything else with this project, I will have to learn as I go by.
By the way, what are there for major differences between MMT and MTM, because regarding MTMs I've apparently misunderstood almost everything as I had the impression that you would get a wider vertical dispersal and approx. the same horizontal. The box build would be slightly easier with a MMT-solution.
I've also been told that with MTM you are supposed to XO low, he had XO at 1400 Hz, so is there a recommended range for MTM XOs?
Ther more I hear, the more confused I get. Is there some good sources for learning more about MTMs, or MMTs specifically? Briefly, what are the greatest differences between MTMs and MMTs, my books doesn't say that much on the subject.
Ther more I hear, the more confused I get. Is there some good sources for learning more about MTMs, or MMTs specifically? Briefly, what are the greatest differences between MTMs and MMTs, my books doesn't say that much on the subject.
Hi buggsson,
Here is one attempt to recommend how to choose an XO using the driver inter C-C distances for good M-T-M setups:
http://www.diyaudio.com/forums/multi-way/102936-mtm-behaviour-questions.html#post1225434
b
The MTM has a lot going for it but the crossover design will be critical. Without getting this right (or following a previous design), it will be no better (or worse) than a standard design. You'll need to appreciate the way the drivers' responses combine, their phasing etc.
an MMT is perhaps a little more straight forward. The upper mid-woofer is crossed normally to the tweeter, and the lower one is used to compensate for the baffle step (where the lower frequencies wrap around the cabinet and are less loud at the listening position). Designing a zobel for this lower mid-woofer and choosing an inductor, is a more straightforward and perhaps rewarding step in learning crossovers in my opinion. And what's to say you can't change the front baffle later?
an MMT is perhaps a little more straight forward. The upper mid-woofer is crossed normally to the tweeter, and the lower one is used to compensate for the baffle step (where the lower frequencies wrap around the cabinet and are less loud at the listening position). Designing a zobel for this lower mid-woofer and choosing an inductor, is a more straightforward and perhaps rewarding step in learning crossovers in my opinion. And what's to say you can't change the front baffle later?
however since Buggsson's system has a woofer, the woofer's output cna be used for BSC and hence the second 5" is only needed to extend the SPL capabilities of the system. This can be more easily accomplished by using a 6" which has good dispersion a la Fostex, Supravox, etc. or even the earlier mentioned 18sound or Seas midwoofer.
BTW what about Troel's DTQWT?
So, now I really don't know what to think. I've tried to calculate the XOs with the help of bjorno's image, and if I got it somewhat correct, it ended up in the excellent region, 0.5xlambda. The mids are 124mm and the Morel MDT40 I'm contemplating for tweeter is 54mm and then 1mm each side to create some "distance" between the drivers.
I feel very lost right now, but I guess I have to start simulating a bit to see if I can come up with something usable instead of just talking about it. MTM or MMT, thats the question for now I guess.
Regarding the XO for a MTM, would that be considered way above my head, super newbie as I am, or is it doable?
I also need suggestions as to how to connect the two boxes together, as the distance in between them will affect some other things. I have a few ideas, but nothing rock solid.
I feel very lost right now, but I guess I have to start simulating a bit to see if I can come up with something usable instead of just talking about it. MTM or MMT, thats the question for now I guess.
Regarding the XO for a MTM, would that be considered way above my head, super newbie as I am, or is it doable?
I also need suggestions as to how to connect the two boxes together, as the distance in between them will affect some other things. I have a few ideas, but nothing rock solid.
One thing about MTM is that it gets taller, as you need to have tweeters at listening height
With a normal MT listening heigth is lower, somewhere in between the two
Though somewhat depending on driver offset
MTM is mostly used when you really need two mids to get higher sensitivity
Though with MTM in 3way the upper mid is further apart from the woofer, which presents a problem
Which is why you often see the use of double woofers, making a WMTMW
And then it gets really tall
Listening distance is very important, to deside for the right design
One thing about MTM is that it gets taller, as you need to have tweeters at listening height
With a normal MT listening heigth is lower, somewhere in between the two
Though somewhat depending on driver offset
MTM is mostly used when you really need two mids to get higher sensitivity
Though with MTM in 3way the upper mid is further apart from the woofer, which presents a problem
Which is why you often see the use of double woofers, making a WMTMW
And then it gets really tall
Listening distance is very important, to deside for the right design
I think that height would not be a problem to me. I've done rough measurements and I can't see that they would become to tall, and the tweeter can be placed at ear level.
I don't know if I need higher sensitivity, I was thinking more in terms of less excursion and being able to cope with the dual 10"s for using two mids, but I guess that will show in simulations.
I never thought of the distance between the upper mid and the woofers, but I have to check that out again, but that would be the length of the wavelength at the lower XO? The CC between upper mid and upper woofer needs to be shorter than the wavelength?
The WMTMW is doable, but then my two-box scheme goes out the window and I guess that format has its own problems? And would it really change the height? The driver number is the same, and they all have the same diameter and I would lose two times 1" of BB between the two boxes plus the empty space. The box aught to be able to be lower??????
Start with your requirement.
What SPLs do you need?
How Low do you want the system to go?
What Room/Speaker placement issues do you need to compensate for?
From what I gather from your first post is that you want to go as low at 35Hz or so (-3db in room), produce about 110db peak from 40Hz-20kHz, and might end up placing the speaker close to the back wall so that they are better accepted by WAF.
2 10" in a sealed box having a Qtc or about 0.6 and calculated F3 of about 50-55Hz should get you in room F3 in the 30s. That is box 1.
For box 2 do consider larger (namely 6") mids that are usable/comfortable at 3kHz (SEAS W18NX/W16NX etc...) mated to a 1" dome (SEAS T25FC001 etc..) or even a ready solution like the Phlea ( Humble Homemade Hifi )
A larger mid will allow you higher SPLs without having to worry so much baout the c-c distance between the 2 mids.
but the tweeter must be at listening height (about 34-36" from floor) so adding a mid and a woofer above the tweeter might mean that your speaker be 52-54" tall.
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I've read that D'Appolito himself apparently has stopped using 1st order filtering, one of the reason as I understood it, among other would be the much more prolonged frequency range where two drivers share the same frequencies, that could be as wide as two octaves on either side of the XO. Apparently, that is not a concearn of yours, so I would appreciate if you could explain the advantages of 1st order compared to higher orders for MTM and hopefully, I will get a better understanding of this concept.
I tried a bit, but I wasn't that successful, but I will try again with another approach. I had? some problems with how to input what. I calculated my C-C to 180mm and Lambda/2 to 90, but I'll try some more I guess, because what I got looked really ugly.
For now, I will try to fill in some of my many knowledge gaps, and try to have a closer look at system level.
Right. Good analysis. I'm only dealing with moderate listening level gear, good for listening at home. If you put yourself in this arena, everything simplifies down. Let me explain. There are two different factors mutually reinforcing themselves.
First factor is that you don't need to use medium drivers larger than 10 centimeter (4 inch) : a moderate listening level, say at 500 Hz, is only commanding a moderate-sized voice coil and a moderate-sized membrane. As a consequence, using a 4 inch driver, the frequency response of such driver can be smooth without the membrane fractionning, until 7 kHz or even more if you are lucky. This means that even if you cut your driver low pass at 3.5 kHz, 1st order, your phase response will be smooth and consistent untill 7 kHz or so. It is only past 14 kHz that you will see an ugly phase response, because of the membrane fractionning. And this is not an issue : this will be masked by the output of the tweeter, being 15 dB above the medium, at 14 kHz.
Second factor is that, when you only need a moderate listening level, that the tweeter won't suffer (excursion issue) when receiving 3.5 kHz at -3dB, 1.75 kHz at -6 dB and 875 Hz at -12 dB. Those values are the ones when using a tweeter, high-pass filtered 1st order at 3.5 Khz.
My advise is thus : if you understand this, you will try a simple MTM 1st order filtered at 3.5 kHz. Always compare more elaborate designs with this starting point.
There is a third factor, hidden. You definitively know that you need to phase-align your tweeter with your medium. Therefore, most of the time, you need the small analog delay line in the tweeter, as described above. Avoid complicated loudspeaker faces, for avoiding diffraction. Keep the loudspeaker face in one plane, and compensate the tweeter depth using the small delay line.
There are not many people knowing that factor 1, 2 and 3 need to be understood and done for getting the best results. "Best results" did I wrote ? Yes ! The big bonus is that when you complete this, you get a horizontal, linear phase from 200 Hz to 12 kHz. No other system can deliver this. Even if you design a Linkwitz time-aligned crossover, 3rd order, you'll get a 270 degree phase shift from 200 Hz to 12 kHz. This, even if using the exact same transducers. The 270 degree phase discontinuity will be centered on 3.5 kHz, the frequency where your ear has the greatest physical sensitivity.
Do you get me now ? Do you understand why the MTM 1st order, time aligned, is the best crossover, if you put yourself in the home audio listening levels market ?
The reason why this is never used by companies, only reserved to the DIY audio world is the small extra cost (delay line coils, delay line capacitors) and the fact that the coils are non-standard, compared to filtering coils. Depending on your tweeter depth, depending on your tweeter impedance above 3.5 kHz, depending on the accuracy of the delay line (linear phase), you'll need coils in the range of 20 µH to 100 µH. You need to do simulations using LTspiceIV, as shown above.
There are so many enthusiasts, making their own loudspeakers, measuring the amplitude and the phase, and still having a big doubt about what they've done when they read the phase curve 100 Hz to 10 kHz. They can't believe the ear is insensitive to phase distorsion.
Make a linear phase system if you can, if there is no hidden penalty. This is my final advice.
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Yes, thank you, due to this very explanatory reply, I think I actually can say I understand your way of thinking. It's just so many aspects of audio and somuch to learn of every aspect, but I'm strugling on.
What can be considered moderate listening levels, just as an approx. reference level?
The delay line, must it be analog?
I've just started out trying to understand the different effects of the various filters, it feels like a very steep learning curve is ahead of me.
For the two mids, shall I go for separate boxes or one, and why?
Does a 1st order electrical crossover offer adequate protection to the tweeter? Unless you are considering tweeter with very low Fs (500hz or so) and high power handling (like the Morel MDT33/Dynaudio D28af etc..) my guess is most tweetes night need more protection than a 1st order electrical crossover might be able to provide.
1) Moderate listening level is a 120 Hz to 20 kHz MTM fitted with two 87dB/watt medium drivers (and a tweeter), fed by a 30 Watt RMS amp. If you manage to get a 35 Hz to 120 Hz subwoofer that copes with this, you'll get a "sufficient" sound level by home audio standards. 2) Yes, I advise you to time-align the tweeter using an analog delay line. You may not like this but that's part of the deal. 3) For the two mids you put them in a common box, this is the simple normal way to do a MTM.
I've choosen the Morel MDT40 as tweeter, it has a Fs of 750 Hz and a nominal power handling of 120W, which I do hope will suffice.
Vas test box size
I've been trying to figure out a suitable test box size for the Monacor mids. In the Testing Loudspeakers book, it says that if you know the drivers Vas it is a simple task of choosing the box size. Yes, I do know the drivers Vas. He has also posted a table from Dickasons Cookbook, that indicates that 3.6 liters will be a good approximation for 4-5" drivers. I also tried to calculate the Fct value for the driver in a box with a volume that will raise the free air value with at least 50% with the formula given for Fct in the Testing Loudspeakers book, ((Vas/Vb)+1)^1/2. I then landed on a Vb of 2.1 liter for a raise of just over 50%.
So, the table given suggests 3.6 liters,
Vas is given as 2.7 liters (Fs as 95 Hz)
my calculations gives 2.1 liters
My math is not very good, so I can have done wrong when trying out the formula, but what gives? How does one decide on test box volume, the above have got me to think it's not that clear, and where comes the known Vas into the equation? The volume in itself is not that important I know, but if one needs to raise the in-box resonanse frequency by more than 50% of the free-air value, then one needs to know how to go about it.
I've been trying to figure out a suitable test box size for the Monacor mids. In the Testing Loudspeakers book, it says that if you know the drivers Vas it is a simple task of choosing the box size. Yes, I do know the drivers Vas. He has also posted a table from Dickasons Cookbook, that indicates that 3.6 liters will be a good approximation for 4-5" drivers. I also tried to calculate the Fct value for the driver in a box with a volume that will raise the free air value with at least 50% with the formula given for Fct in the Testing Loudspeakers book, ((Vas/Vb)+1)^1/2. I then landed on a Vb of 2.1 liter for a raise of just over 50%.
So, the table given suggests 3.6 liters,
Vas is given as 2.7 liters (Fs as 95 Hz)
my calculations gives 2.1 liters
My math is not very good, so I can have done wrong when trying out the formula, but what gives? How does one decide on test box volume, the above have got me to think it's not that clear, and where comes the known Vas into the equation? The volume in itself is not that important I know, but if one needs to raise the in-box resonanse frequency by more than 50% of the free-air value, then one needs to know how to go about it.
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