Upper limits of driver diameters?

[Godzilla]

I was just over at the Multi-Way speaker forum. I enjoy visiting. There were discussions on optimizing slotted cabs that’s very interesting to me and applicable to full/wide range drivers. But then I read about problems using soft dome mids, crossover optimization related issues, choosing caps and coils and frequency points to crossover… I felt bad. It’s so much easier and less audibly obtrusive crossing above 10k and below 200hz… if they only knew!

One thing that troubles me, and maybe someone can elaborate, is why so many have set ‘rules’ on how high in frequency specific diameter drivers can operate up to effectively… for example, a 12” can only be used up to 1,200hz, an 8” up to 2,000hz, etc… is it all about dispersion?

[Pano]

I think so, mostly. Beaming. And then there is cone break-up that tends to happen around the same point for similar size drivers.

I have a pair of Tang-Band 6.5" woofers that will play right up to 12Khz. They beam badly that high, tho.

[Godzilla]

Thanks Pano! But why obsess over beaming and break up modes when adding additional drivers potentially damages the sound further? I don’t enjoy debating driver limitations with individuals pointing to spec sheets when I know (and they don’t) larger diameter drivers sound good at higher frequencies. Why are we hearing ‘good highs’ with larger diameter drivers despite these limitations?

[Pano]

Whizzer cones?

[goody75]

Nobody beats the WIZ! Whizzer cones help with dispersion but I don't know if you can get aftermarket cones for speakers that were not designed with them in mind. Phase plugs are another option. Dave at Planet10 HiFi sells both finished plugs and blanks so you can make yours to size.

If you want to add a phase plug, the Planet 10's are well regarded and Dave is knowledgeable, helpful and makes regular posts on DIYAudio. I do have to say, though, that I have never used them.

[planet10]

Many of those dispersion arguments are based on theorectical data generated by simulating a flat rigid piston. This proves true with real drivers but the limits are much more fluid. Things get even more fluid if you abandon the idea that the ideal driver is rigid within its passband.

In a multiway the issue isn't the dispersion per sey, but the change at the crossover as you pass from a large driver that is starting to have limited dispersion to a smaller one that has wide dispersion. (ie off axis FR becomes undulating)

With a FR driver there may not be as high a level of dispersion at the top end, but there are no discontinuities with off-axis dispersion.

Most FR drivers also pay little head to the rigid piston idea, by introducing controlled flex the effective size of the driver can become smaller as frequency rises. This is a much greater engineering challenge than brute forcing a rigid piston. If this shrinking diameter can be done without a whizzer i think, in general, that is a good thing. Whizzers introduce a whole set of other issues. One of the reasons i tend to prefer 3-5" FRs. Bass is best served with dedicated woofers if you need a true FR system -- and you can XO down where the drivers are becoming essentially omni-directional avoiding the whole dispersion and interdriver issues inherent in XO discussions.

dave

dave

[crispycircuit]

Full range is great for 1 person doing some serious listening. It beams straight ahead and doesn't interact with the room boundries. You can adjust the high end by aiming the speakers on axis or slightly off axis. Now desperison is needed and wonderful if your using the system for home thearter or general listening. It's a person taste, room requirements, decor, cost, and experience with high end set-up. It's a journey we all have to travel. A young person is impressed with loud boomy bass. An old person is looking for something more accurate/real. In the end you assemble what is right for you and don't pay attention to hype.

[planet10]

Originally Posted by crispycircuit

Full range is great for 1 person doing some serious listening. It beams straight ahead and doesn't interact with the room boundries. You can adjust the high end by aiming the speakers on axis or slightly off axis. Now desperison is needed and wonderful if your using the system for home thearter or general listening. It's a person taste, room requirements, decor, cost, and experience with high end set-up. It's a journey we all have to travel. A young person is impressed with loud boomy bass. An old person is looking for something more accurate/real. In the end you assemble what is right for you and don't pay attention to hype.

Your generalizations are far to general. True in some cases, not in others.

dave

[pinkmouse]

As a multi-way addict, my reasoning is simple. I like proper bottom end, not something that gets very vague below about 100Hz, clean, undistorted treble, not some mess of cone breakup and resonances pretending, and a good, flat overall frequency response. If you can find me a single driver that does that then I might be converted.

[ultrakaz]

Originally Posted by Godzilla

I was just over at the Multi-Way speaker forum. I enjoy visiting. There were discussions on optimizing slotted cabs that’s very interesting to me and applicable to full/wide range drivers. But then I read about problems using soft dome mids, crossover optimization related issues, choosing caps and coils and frequency points to crossover… I felt bad. It’s so much easier and less audibly obtrusive crossing above 10k and below 200hz… if they only knew!

One thing that troubles me, and maybe someone can elaborate, is why so many have set ‘rules’ on how high in frequency specific diameter drivers can operate up to effectively… for example, a 12” can only be used up to 1,200hz, an 8” up to 2,000hz, etc… is it all about dispersion?

I suppose some of the rules are based on some type of acoustic physics. A typical 8" cone is probably starting to beam at around 1kHz or so and depending on the cone material, break-up is inevitable, so high end response is the sound of distortion. Break -up can be mitigated to some degree by damping the cone, but this can also lead to the deadening of the sound.

I think the rules follow that speakers with wide uniform power responses can sound pretty darn good with less distortion.

Single driver speakers are about purity, cohesiveness and simplicity. If the listener values these qualities over others then this is the gospel they follow. Adding additional drivers tends to lead to crossovers, complications and dilution of the above qualities. The solution is to have more than one speaker.

Having said the above my preference is for the 4" paper, unadulterated single driver speaker. I have found that this size is the best compromise between highs and lows and ultimate volume level, while keeping that cohesive presentation. No filtering allows the driver to directly couple to the amp, which seems to preserve the immediacy/aliveness of the music. If more spls are needed and/or more people are listening, I simply change the speaker.