Bijou 170 Light THT

[Ostoja]

Guten Abend!


Es tut mir leid, aber ich spreche kein Deutsch, also muss ich auf Englisch wechseln...


I am from Serbia, 40 years old and finally started my HiFi journey. Glad to meet you all here

Since I don't have much money to spare for this "project", I thought of doing one of Visaton kits as they are documented very good. Looks are secondary, sound quality is the primary goal to achieve (with a limited budget). I dont have carpenter skills or can pay a specialised carpenter but I can order MDF processed on CNC and glue it myself. I will probably end up with unpainted MDF with best sound quality possible, I don't mind.

I live in a rented apartment, so wall drilling is forbidden. I can do bookshelf + stands but then special care is needed as I have a kid who can tip them over, so the situation, more or less, requires a floorstander. Room is 20m2, 3,5x5,5 with a big carpet, 2 sofas and 2 big book shelves.

Alas, I was unable to find much 8 Ohm designs, and I dont know why are they a thing of the past. It is much easier to drive by any amplifier or receiver, wires leading from amplifier can be longer for same surface, etc. etc. So I started a blank design in BoxSim, and this is what I simulated. Can you, please, take a look and comment is this feasible, or, in other words, "is it going to fly"?

I chose W170S as I found opinions that it is very well behaved woofer, and SC10N as that's a rare one that fits my budget. DT94 measures best but I was told to avoid it as sound is not the best, and G20/G25 are a big stretch in the budget. Crossover coils I can have made locally with thick wire and +-1% precission, for capacitors I can source some MKP of solid quality (again, talking budget here). All of the drivers have been recessed in simulation so that speaker sits "flush" with front side of speaker box.

So, finally, the design:
95cm tall floorstander with MTM configuration. Bass reflex design, front port (for easier placement), ~38L box volume (minus bracing, drivers, port should get ~36L). As it is going to be listened to from mid-field (2m+ distance) slight vertical off-axis is counted on.

Can you, please, take a look and find some obvious flaws, as I dont have experience with this, this is my first project?


Danke!

[Ostoja]

May be easier to attach the BoxSim file, so here it is.

[blindrabbit]

Hi Ostoja,

This looks pretty good. It uses the drivers at the edge of their capabilities. The only thing I noticed is the hump in the energy response around 5000 Hz. This can lead to some harshness and overemphasis of sibilants.
In the attached file I have tried to smooth out the energy response. However, this may push the SC10 over the edge and only gives a slight improvement. Still, i think it may be worth a try if the sound is too harsh.

In any case you may want to place the tweeter off center, as I did in the simulation. This will improve lateral directivity.

[Ostoja]

Thank you for the feedback, appreciate it very much!

I will play with tweeter offset and baffle width to find the sweet spot, I thought symmetric was the way to go as i can point them to a middle of sofa and still have right and left seat "covered"
.
Seems taht, with these modifications, they will end up remotely looking to Dali 104 (a really good old speaker I heard somewhere).

Can you, please, explain me what is the energy response in relation to frequency response, as I was aiming to have frequency response near flat, but i cannot seem to "tame" the energy response in this MTM setup, there is always a hump in SC10N 4-7Khz energy region no matter what I try. It looks somewhat better with "classic" M(id) T(weeter) setup, but then I lose efficiency and power handling. I have a 15db headroom amplifier (35W) so would like to be over 85dB with speaker efficiency if possible.

As I said, I was counting on slight vertical angle (+5 degree) from listening spot and BoxSim shows slight (1-2dB) recession in 2-6Khz region, centered at 3.5kHz (-2dB), but now this energy response that you mentioned is spoiling my happiness. You think that angle "trick" will not be enough and some vocals will be "hissing"?

I saw that you have slanted edges (1cm, 45 degree I guess), I cannot do this as I have planned speaker cloth to protect the drivers (10mm MDF grid + cloth). Does it affect the sound much?

Also, simulations in BoxSim are somewhat of an approximation, since I dont have measuring equipment, how "true" can I expect the end result to be in comparison to simulation? It is a very good tool (thank you Uwe), just wondering on what to expect...

I initially tweaked the crossover to have very good phase tracking between W170S and SC10N in crossover region, and predicted a large "dip" if polarity is reversed. These modifications suggested somewhat change that phase tracking, will that be "hearable"?

Again, thank you very much!

[blindrabbit]

Can you, please, explain me what is the energy response in relation to frequency response, as I was aiming to have frequency response near flat, but i cannot seem to "tame" the energy response in this MTM setup, there is always a hump in SC10N 4-7Khz energy region no matter what I try. It looks somewhat better with "classic" M(id) T(weeter) setup, but then I lose efficiency and power handling. I have a 15db headroom amplifier (35W) so would like to be over 85dB with speaker efficiency if possible.

I try to summarize what I know:
The energy response is the integral of sound energy radiated by the speaker into it's surrounding. The directivity (Bündelung in Boxsim) is the difference between frequency response on axis and the energy response (in dB). The effect on the listening experience very much depends on the room. If there are many reflections from the side walls, floor and ceiling, the effect is significant, in a sound dead room the effect is nil.
You can see the energy response as noise. It can camouflage the on axis signal that you actually want to hear. On the other hand, reflections could as well add up to the on axis signal and amplify a certain frequency range. So if there is a low directivity in a certain frequency range, chances are good that your ear will notice. This is what the hump in the energy response means. As said before, the effect depends on the room, the position of the speakers and listening position in the room and the frequency range in question.
Generally you can say that a high directivety makes the sound clearer and the listening experience less dependent on the room. A smooth and steady energy response (or steady directivity) avoids, that certain frequency ranges stand out.

Your speaker design has a high directivity in the mid range due to the d'appo setup. Obviously, this is good for clarity in the mid range. The directivity is lower in the high frequency range (still ok, >6dB). This is determined purely by the SC10, so there is not much you can do and it is well possible that you don't have to.

What I tried, is to smoothen the directivity curve and the energy response in order to not have the high frequency range stand out too much (Reduced the valley in the crossover range and the hump in the high frequency range a bit). This comes with disadvantages in the phase tracking between W170 and SC10, also the frequency response on axis is a little less flat. The difference is not too big, so I guess chances are good that it will not create a problem. Nevertheless it is not a preferrable solution as the perfect phase tracking that you had is a good thing to have. However, if you find some harshness in your speakers it might improve things a bit. Another opportunity would be to just reduce the level of the SC10.

Best would probably be to use a tweeter in a waveguide. Unfortunately as far as I know there is no WG for the SC10.

Still, overall you found a pretty good solution.

[blindrabbit]

I saw that you have slanted edges (1cm, 45 degree I guess), I cannot do this as I have planned speaker cloth to protect the drivers (10mm MDF grid + cloth). Does it affect the sound much?

Also, simulations in BoxSim are somewhat of an approximation, since I dont have measuring equipment, how "true" can I expect the end result to be in comparison to simulation? It is a very good tool (thank you Uwe), just wondering on what to expect...

Slanted edges reduce the edge diffraction and the resulting waviness of the frequency response in the high frequency range. Boxsim simulates that. I think the effect was neglegible so you would not need to have it.

In my (limited) experience, the results of boxsim are close to reality. However I also found deviations with very slim baffles. Also, things can go wrong in building the crossover. So it is good to have basic measurement equipment in order to identify flaws.

[Ostoja]

Dankeschon!

I know it wasn't going to be easy, or everyone would be building their own speakers . It's just that there are not many 8 Ohm kits available today, so I had to do that "trickery" with woofers in series to get the impedance up but with somewhat high efficiency at the same time, which one woofer can't really do. So 2 woofers, 1 tweeter seemed the way to go, and I got what I got. Not without flaws as you explained to me.
I was also looking at Clou kit as it is really good documented and seems easy to build, but, alas, also 4 Ohm. My amplifier is declared for 4 Ohm's but its always easier to drive an 8 Ohm speaker, and I don't know why 4 Ohm now prevail in home usage. 4 Ohm should be where there is limited supply voltage (like in cars or similar)...

Box was foreseen to have 3 internal braces binding front, back and sides, with uneven spacing between them to break resonances into smaller ones with different frequencies, so the box shouldn't ring (much). I also thought of adding a 3-4l sand compartment at the bottom, by making a box slightly taller and "deeper". Primarily to move center of gravity near ground , so they cant be easily tipped over by people or pets...

Managed to slightly change the output by lowering the coil on woofer to 1.5mH and 2x1.5uF in front of SC10N instead of 3.3uF, but it still looks "peaky" although phase tracking still looks good. Going to need to sleep over this and tweak some more...

Is the 45Hz tuning too high? I saw on other projects that people usually go lower than this in comparable projects but in Boxsim then it looks a little "thin" in bass for this project....

[blindrabbit]

Is the 45Hz tuning too high? I saw on other projects that people usually go lower than this in comparable projects but in Boxsim then it looks a little "thin" in bass for this project....

This question should go the the real experts I guess.
All I can say is that I have also made the bass thinner in my speakers via low tuning frequency. My speakers stand back to wall which amplifies the range below 200Hz. I was aiming for -3dB @ 100Hz and I am happy with the result.
If your speakers are far enough away from the back wall (0,5 - 1m ?), your tuning is probably best. Also, it will save you from trouble with room modes (~30Hz and ~50Hz in your room) and gives the best max. output level.