2 Way Speakers : 8 inch woofer directivity question.

[Hiten]

Hi,
in multiway speakers it is said that for mid range 3/4 inch driver are ideal. Larger than this size it will beam. I see lots of studio monitors with 7 to 8 inch driver. so...
1) how do these designs manage directivity ?

Compared to passive speakers, mostly I see the studio monitors have little bit more low end extension (even for 5 inch driver)
2) how do they do it ?
Thanks

 

[mdsimon2]

Hi,
in multiway speakers it is said that for mid range 3/4 inch driver are ideal. Larger than this size it will beam. I see lots of studio monitors with 7 to 8 inch driver. so...
1) how do these designs manage directivity ?

Compared to passive speakers, mostly I see the studio monitors have little bit more low end extension (even for 5 inch driver)
2) how do they do it ?
Thanks

1) Many studio monitors use a wave guide to match the tweeter directivity to the woofer (which will be beaming at the crossover frequency). Without the wave guide the tweeter will be much more omni directional than the woofer resulting in mismatched directivity.

2) Many active monitors use DSP to boost low end response.

Michael

 

[Tom C]

The lower the crossover frequency, the less the woofer will beam. Compression driver mated a waveguide or horn can help facilitate a lower crossover.

 

[AnalogSteph]

Yep, waveguides (which are also helping out the tweeter on the bottom end) + low XO is pretty much it. Up to 5" you can get by without a waveguide and still get decent directivity (see e.g. KRK RP5 G4 or Dynaudio LYD 5), but at 8" it's pretty much impossible otherwise.

 

[dfuller]

1) how do these designs manage directivity ?

Dispersion matching waveguides.

2) how do they do it ?

combination of EQ and active speakers being more efficient with use of amplifier power.

Up to 5" you can get by without a waveguide and still get decent directivity (see e.g. KRK RP5 G4 or Dynaudio LYD 5), but at 8" it's pretty much impossible otherwise.

I'd argue up to about 6.5", but definitely agree that flat baffle 1" + 8" is not going to work so hot. Even with a waveguide once you're getting that big I'd prefer a 3 way design because you're just asking for weird behavior at the top of the midwoofer's passband.

 

[Dj7675]

This seems quite amazing to me for a 1 inch tweeter/8 inch woofer, and in an outdoor speaker no less.

 

[digitalfrost]

Hi,
in multiway speakers it is said that for mid range 3/4 inch driver are ideal. Larger than this size it will beam. I see lots of studio monitors with 7 to 8 inch driver. so...
1) how do these designs manage directivity ?

You can't cheat physics. Speed of sound is 343m/s. If you insert any hz value (1/s) you can solve for distance and see where it will beam. For example a 5" woofer (which is roughly 13cm) corresponds to a wavelength of 343m/s / 0.13m = 2638hz. Since the baffle is larger than the chassis, it will starting beaming lower than that in practice. Incidentally this is a region where typical crossover points will be, so crossover design can be used to tweak directivity in that region.

The background is that a monopole speaker will radidate into 4pi space by default (i.e. in all directions), but if the wavelength is <= chassis/baffle size it cannot do that anymore and it will move to radiate into 2pi space (baffle step).

For constant directivity the only thing you can do is match the tweeter to the woofer/baffle size. If it is not controlled you get the typical christmas tree sonogram, since the wavelength at crossover point is large for the tweeter (i.e. wide directivity) but the woofer is already beaming (wavelength is small for the woofer).

 

[Hiten]

Thanks gentlemen.

For constant directivity the only thing you can do is match the tweeter to the woofer/baffle size. If it is not controlled you get the typical christmas tree sonogram, since the wavelength at crossover point is large for the tweeter (i.e. wide directivity) but the woofer is already beaming (wavelength is small for the woofer).

Newbie posting :
how about AMT tweeter, Narrow (Slim) baffle and two 5" woofer designed as 2.5 Way ? Need to study 2.5 way design's dispersion too; which has same mid/woofer drivers at different crossover points.

By the way I am not buying anything. Just reading for learning. Currently looked at Yamaha HS8 measurements on web. to see the difference as tweeter does not have much of a waveguide comparatively. and some measurements online does show little dispersion oddities.
regards

 

[KSTR]

how about AMT tweeter, Narrow (Slim) baffle and two 5" woofer designed as 2.5 Way ? Need to study 2.5 way design's dispersion too; which has same mid/woofer drivers at different crossover points.

Should be OK directivity-wise, for the mid/tweeter XO this reduces to a simple 2-way.
2.5-way speakers are seldom done right with woofer and midwoofer running strictly with coherent phase for a correct forward pointing main lobe of radiation. If it's not, and the woofer XO is high enough and the spacing large enough (like in a MW-T-W setup) you'll run into directivity issues quickly.

 

[Davide]

By chance in the shop I was able to listen to the Dali Opticon MK2 library (1 and 2). I was intrigued by their 29mm tweeter (larger than usual), which I didn't understand if it is combined with a waveguide.
It looks like a similar design to Dynaudio with its 28mm Cerotar.
The thing that intrigued me when comparing it to the Dynaudio specs is the crossover frequency.
Dali on the version with 6.5" woofer chooses 2khz, while Dynaudio chooses 3.8khz (very different).
What could this choice depend on? Is a tweeter that goes lower in freq better or worse?

 

[thewas]

With a 6.5" midwoofer a 28 mm tweeter without waveguide crossed so high will have a directivity mismatch at the crossover.

 

[Davide]

Honestly I can't understand if the tweeters of Dali / Dynaudio have a real waveguide. In any case, Dali sounded quite coherent, so I think their design choice is ok.

 

[jonfitch]

Dynaudio claims the little dip around their tweeter is a waveguide lol. The only Dynaudio I can see with a real "traditional" waveguide is the Confidence floorstander.