I agree, the tweeter could be improved and compared to the other drivers, it's more than justified to spend a bit more on it, the return is well worth it and compared to the rest of the speaker, just a fraction of the cost anyway.
If I where you and I want to make something with a ribbon-like radiating pattern at a medium budget I would do this:
When I want a smooth sound:
Tweeter:
-2: SB-Acoustics SB26STAC or SB26STCN
Midrange:
-2: SB-Acoustics SB17NRX2C35-8 or SB15NRXC30-8
Woofer:
-2: SB-Acoustics SB23NRXS45-8
When I want a fast, transparent and detailed sound:
Tweeter:
-2: Seas Prestige 27TBFC/G or 1: Seas Prestige 27TBCD-GB
Midrange:
-2: SB-Acoustics SB17NBAC35-8 or 2: SB-Acoustics SB15NBAC30-8
Woofer:
-2: SB-Acoustics SB23NBACS45-8
When I want detail and transparency yet naturality and a nice fullness (basically the best of both worlds):
Tweeter:
-2: Seas Prestige 27TBFC/G or 1: Seas Prestige 27TBCD-GB
Midrange:
-2: SB-Acoustics SB17NRX2C35-8 or SB15NRXC30-8
Woofer:
-2: SB-Acoustics SB23NRXS45-8
I would throw it in an entirely sealed enclosure (so also the woofers) wire every pair of drivers in parallel and actively try-amp them with a Hypex FA123. The 8 ohm versions of the SB-Acoustics woofers actually go quite a bit deeper. The SB23NRXS45-8 in simulation has a F3 of ~48 Hz in a sealed box of 35 L / driver which is actually quite low, especially for its size. With the help of the DSP you should be able to get them to go down to a F3 of about 22 Hz and still be able to play very loud, which is some very fun bass. And that depth with the speed and tightness of sealed enclosure.
This setup will give you the perfect radiating pattern, endless flexibility, the best bass one could get from the drivers, the best possible overall sound quality and it's very easy to put together compared to a passive system.
Yours for just €1.419,97 to €1.595,94 for the components.
When I want a smooth sound:
Tweeter:
-2: SB-Acoustics SB26STAC or SB26STCN
Midrange:
-2: SB-Acoustics SB17NRX2C35-8 or SB15NRXC30-8
Woofer:
-2: SB-Acoustics SB23NRXS45-8
When I want a fast, transparent and detailed sound:
Tweeter:
-2: Seas Prestige 27TBFC/G or 1: Seas Prestige 27TBCD-GB
Midrange:
-2: SB-Acoustics SB17NBAC35-8 or 2: SB-Acoustics SB15NBAC30-8
Woofer:
-2: SB-Acoustics SB23NBACS45-8
When I want detail and transparency yet naturality and a nice fullness (basically the best of both worlds):
Tweeter:
-2: Seas Prestige 27TBFC/G or 1: Seas Prestige 27TBCD-GB
Midrange:
-2: SB-Acoustics SB17NRX2C35-8 or SB15NRXC30-8
Woofer:
-2: SB-Acoustics SB23NRXS45-8
I would throw it in an entirely sealed enclosure (so also the woofers) wire every pair of drivers in parallel and actively try-amp them with a Hypex FA123. The 8 ohm versions of the SB-Acoustics woofers actually go quite a bit deeper. The SB23NRXS45-8 in simulation has a F3 of ~48 Hz in a sealed box of 35 L / driver which is actually quite low, especially for its size. With the help of the DSP you should be able to get them to go down to a F3 of about 22 Hz and still be able to play very loud, which is some very fun bass. And that depth with the speed and tightness of sealed enclosure.
This setup will give you the perfect radiating pattern, endless flexibility, the best bass one could get from the drivers, the best possible overall sound quality and it's very easy to put together compared to a passive system.
Yours for just €1.419,97 to €1.595,94 for the components.
You are right, that is very controversial. I know of the different sound of midrange of certain sizes. The linearity is given by the driver itself (which is excellent), the crossover and the baffle. In my experience, the surface matters and that's just logical, a bigger surface has to move less to reach the same sound level and the distortion rises with the excursion. With a xo frequency of 250Hz the excursion is already that low with two RS125, at HiFi levels you cannot improve it by adding 18% more SD, not measure it and it will not be audible either.
So what, besides the 18% more cone surface does the RS180 have to offer? The dispersion isn't better (rather the opposite), a lower maximum usable frequency, dispersion patter diverts much more, it needs a wider baffle (not relevant here though). It got higher losses than the RS125, a weaker motor in comparison, a worse much worse moving weight (17,8g vs. 5,7g), higher inductance (crosses the 5 Ohm at 1,5kHz vs. 4kHz or compare the plain Le), a lower spl and dynamic (it's almost the same as one RS125 in that range but there are TWO of them), higher distortion (sry, can't find the measurements again, got a k3 peak in the mid at 95dB), no advantage regarding the linearity and much more aggressive resonance peaks at the top end.
A wider baffle 'supports' at lower frequencies, the baffle step goes down in frequency, you gain spl there. And that's what you know as 'more authority' of the bigger drivers, they are tied to a wider baffle. If the SD, spl, needed excursion and frequency range is comparable, it's the baffle width which makes the difference in the midrange. Yes, there is a difference but you haven't compared the drivers, you've found a wider baffle gives more 'grunt'.
YW.
If a design is good, it's good, no matter if I disagree in other things.If the back chamber is big enough and can absorb enough erergy to not radiate through the membrane (like at some paper cones (not all though)) or create resonances, there will be no audible or measurable difference. The soundstage is determined by the sound the speaker radiates.
Does it provide with theoretical and practical advantages? Yes.
Does it add clarity? Yes (can be achieved by other principles or geometry too though).
Does it improve the details? Yes (in most cases).
Does it change the sound stage? Uhm, no, the dispersion is not changed.
Well, if nothing comes out in the midrange, the beneficial effect will be very low too. I mean, if nothing comes out, it can't change anything.
No, that's not the way to go. The DSN25Ti-4 got one distinctive advantage: It's small. It's only 72,2mm in diameter. If you use a ribbon etc with a longer diaphragm, the outer dimensions will increase too and the mid drivers will start lobing much, much sooner. That means it can get much worse with reflections and energy bilance in the room in the mids. There are a lot of speakers which got a MTM arrangement with a ribbon with quite high distances between the mid drivers and while that can sound excellent, it's not ideal for the vertical dispersion. That ofcourse depends on the room and its properties (furniture, ceiling, carpet etc) and if the reflections in the highs are more critical than in the midrange. To my experience, mid reflections are most of the time worse since they aren't absorbed as quickly as high frequencies and the dispersion patter is usually much wider there (remember the lobes?).
As always, "it depends". As absorbers for the high frequencies, often it's enough to put a fabric over something (courtains i.e.). In the mids though, you usually need 'real' absorbers - which the wife won't be very happy about.
For the type of tweeter: AMTs provide often much more dynamic than ribbons or planars because (compared to them) they can do excursion. I personally strongly prefer AMTs but that's most likely a matter of personal taste though.
For MTM or MTTM layouts the Monacor DT-25N are excellent, they got a high spl and very small outer dimensions. I know there are others to, I don't remember them exactly. TangBand got such small tweeters too but I think they were not that great.
Well I don't know everything either. Then if a single tweeter is better after all, I think the Seas Prestige 27TBCD/GB is a very good option. It is quite expensive in comparison with the other single tweeters and but it is a very good tweeter and with it's waveguide narrowing it's dispersion just a bit I think it has a great radiating pattern for this system. And the waveguide does have other advantages like the better impedance matching and lower distortion.
That's a very good tweeter. However, the WG only helps in the lower range. While the spl there is impressively high (95dB), it drops down to 86dB@12kHz. Since the woofers come to 92-93dB, that's a lot too low.
Wow, that is a lot of information to process and unfortunately, you guys don't agree on much which makes it more of a challenge for me...lol.
I'll look through the driver recommendations. Specifically for the tweeter, I found that the DSN25Ti to have a very flat response which is why I picked it. I didn't like how the Reference Series tweeter faded in the higher frequencies.
Ok, still the big question remains. How the heck do you compensate for baffle step?!? I feel like this is the same thing as "turf toe" in sports...everyone talks about it, but nobody can tell you exactly what it is.
So, using this formula --> f3 = 380 / WB, I get f3 = 445 Hz. What does that mean (especially if I am only compensating for 3dB of loss)? Is that the frequency where I should start rolling off, halfway of my rolloff, or the end of my rolloff.
Here are two graphs of the PSB Imagine T2 Towers, the first is the anechoic response and the 2nd is the woofers measured nearfield and the mids/tweeters measured in farfield.
Based on this, I calculated the F3 is 545 Hz. In looking at the graphs, it looks like the bass peaks around 80 Hz and drops until around the F3 point of 545 Hz. Looking at that in a perfect anechoic setup that results in a pretty flat response.
Obviously, my speakers will not be in an ideal scenario from a room standpoint, so I am at a loss on how to properly account for the baffle step. I am using Vituix to model my frequency response and it does have a baffle compensation tool, but I am having a hard time knowing if the info I am putting in is correct and trying to interpret the results.
Any help is greatly appreciated. Once I get a better understanding of baffle step, I can concentrate on driver selection and box design again.
I'll look through the driver recommendations. Specifically for the tweeter, I found that the DSN25Ti to have a very flat response which is why I picked it. I didn't like how the Reference Series tweeter faded in the higher frequencies.
Ok, still the big question remains. How the heck do you compensate for baffle step?!? I feel like this is the same thing as "turf toe" in sports...everyone talks about it, but nobody can tell you exactly what it is.
So, using this formula --> f3 = 380 / WB, I get f3 = 445 Hz. What does that mean (especially if I am only compensating for 3dB of loss)? Is that the frequency where I should start rolling off, halfway of my rolloff, or the end of my rolloff.
Here are two graphs of the PSB Imagine T2 Towers, the first is the anechoic response and the 2nd is the woofers measured nearfield and the mids/tweeters measured in farfield.
An externally hosted image should be here but it was not working when we last tested it.
Based on this, I calculated the F3 is 545 Hz. In looking at the graphs, it looks like the bass peaks around 80 Hz and drops until around the F3 point of 545 Hz. Looking at that in a perfect anechoic setup that results in a pretty flat response.
Obviously, my speakers will not be in an ideal scenario from a room standpoint, so I am at a loss on how to properly account for the baffle step. I am using Vituix to model my frequency response and it does have a baffle compensation tool, but I am having a hard time knowing if the info I am putting in is correct and trying to interpret the results.
Any help is greatly appreciated. Once I get a better understanding of baffle step, I can concentrate on driver selection and box design again.
Well, that's the thing, nobody can take that off of you.
There are more ways than just one to get to the goal of a good speaker. But every decision in audio, every alternative brings compromises. You have to decide which of them is the best for you. Which parts of the listening experience is the most important for you, ie.An example: Some folks have a special listening position chair/sofa and don't move around much while listening to jazz or singer/songwriter with much emphasis on the room/stage, the homogenous sound being important but maybe the linearity or precise tonal match is not that important. For that scenario a medium to big wide band speaker might be the dream speaker. Or maybe horns.
A different example: Someone loves rap, house, dub or techno. That fullrange speaker is then probably the opposite of what he wants, deep bass, more loudness, dances to it or moves around. The fullrange may be a great speaker but it doesn't fit in the least on the needed profile.
Yet another example: Someone got a small room and the speakers have to stand close to the wall or even corner. The room got modes, frequencies on which the room adds a lot of gain (-> roomgain). For that situation a bump in the bass or even a linear, deep tuning is often completely wrong because the room makes the bass then completely boomy, squishy, unprecise. In such cases a sealed enclosure with relatively early but very slow decline can be much better because with the room gain it gets more or less linear and it still goes very deep because the slope is in a much less steep angle than for a BR speaker below the tuning.
I try to shed light on the outcome of some ideas, I always try to see the positive and the negative parts of it and I always try to implement the ideas or important things to the one who wants to build the speaker. I will not be angry if you take another route than my suggested one, it's your speaker, it's your decision and it's your money, I have no right to decide for you. You seemed to have a clear, well defined impression what you want to do and many choices/plans you've made at the start fit quite well together, most things were quite realistic to realize them. I tried to keep close to the MTM concept and layed out what advantages and disadvantages come with it.
There are mistakes you could do which should be avoided but many things are depending on what is the most important thing for you. There is no ultimate right or wrong for a lot of things. To make it easier, you could tell what kind of music you mostly listen to, how big the room is, how the speakers will be placed, what's the listening distance etc.
The fading isn't nice, that's true, especally because it gets worse under angles. The linear on axis response is what most ppl aim for but they forget that the tonal balance strongly depends on the energy radiated in the room, that adds to the percieved response too. That means that angle measurements are often more important than the on axis. If a tweeter drops at the top end on axis, it won't be better on other angles but more important, with a passive speaker you can't get any level 'back', you could only reduce the rest in level, that's why I would check at first if the tweeter actually can do at least the same spl as the woofer because to pad it down or equalize it a bit is always possible.
Well, passive you can only reduce the level of the drivers (not the woofer in the bass though). I've written so much in the past days, I'm a bit tired and exhausted. But maybe this can help you a bit:
Diffraction from baffle edges
YouTube
Loudspeaker Diffraction Loss and Baffle Step Compensation Circuits
I should mention you would greatly benefit if you could measure your speaker yourself too and not only rely on simulations, sometimes just to verify it. The simulations nowadays are often amazingly accurate but sometimes they don't tell everything or the underlaying data diverts from the actual drivers. That is often the case if you compare measurements made from different manufacturers, everyone measures very differently, scaling of the graphs and smoothing greatly divert.
I will answer more tomorrow, sorry.
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