Question about driver range overlap.

[im_gumby]

Hi,
I was looking at the Philharmonic line of speakers.
In their BMR Monitor Speaker (https://philharmonicaudio.com/products/bmr-monitor?variant=44484954554612)

Its a three way w a tweeter, 2" BMR and then a woofer. (6" SB Accoustic)

I'm trying to understand why they have the BMR where the range of the tweeter and the woofer could potentially be enough.
This also seems true w the other speakers that they offer.

I guess it goes down to driver choices... but what's the advantage of a 3 way where the mid mostly overlaps the woofer and the tweeter.

 

[Vincent Kars]

where the mid mostly overlaps the woofer and the tweeter.

Does it?
Why should we use 2 drivers (woofer and tweeter) as there are full range drivers?
If you are able to understand that a full range driver is not able to cover full range, you understand why the audio range is split into 2 by using a tweeter and a woofer.
Lets assume the crossover is at 2300 Hz. This requires the woofer to climb up to 2300 (that ain't bass isn't it) and the tweeter to go as low as 2300.
What about handing the midrange e.g. 200-8000 over to a midrange driver. Now we can use a true woofer (bass only) and a true tweeter (treble only).

 

[im_gumby]

I understand that.
In these speakers the woofer is a midrange so lets say the xo is at 2.2kHz and the tweeter can go down to 1.8kHz and the mid/woofer goes up to 3kHz.
Why would you want the BMRs ?

I just picked this midrange from Madisound pretty much at random.

Morel TSCM634 6" Titanium Supreme Carbon-Fiber Midrange: Madisound Speaker Components, Inc.

Morel TSCM634 16cm Carbon Fiber Cone Midrange features an underhung 3" Hexatech voice coil on a titanium bobbin for ultra-quick transient response, a Uniflow chassis for reduced power compression, and a copper-sleeved pole piece for reduced inductance.

www.madisoundspeakerstore.com

It says "The 6" TSCM 634 midrange features a 4-ohm impedance and a unique, carbon fiber-Rohacell® composite cone offers flat frequency response from 49 Hz to 8,000 Hz on-axis. "
Note: This isn't a cheap driver ... nor is a good ribbon driver either.

So if the mid range / woofer can cover up to 4K and the Tweets can go down to 1.8K... why use a BMR?

Or maybe this is a bad example?

That the mid/woofer can go up in range but that its not flat, so you'd cut it to a point where it was flat, then use the BMR to be flat further up the range and then xo to the tweeter where its flat?

Is this what Philharmonics is doing with their speakers? So they can use less expensive parts? To provide that flat response?

 

[mcdn]

There are two reasons to use a midrange driver. One is to enable higher power handling, as tweeters often struggle to be efficient when crossed low to a woofer. The other is to avoid the narrowing of the woofer‘s output at the top of its range, giving wider more even dispersion overall. In the case of the Philharmonic BMR it’s mostly about the latter effect.

 

[im_gumby]

There are two reasons to use a midrange driver. One is to enable higher power handling, as tweeters often struggle to be efficient when crossed low to a woofer. The other is to avoid the narrowing of the woofer‘s output at the top of its range, giving wider more even dispersion overall. In the case of the Philharmonic BMR it’s mostly about the latter effect.

Ok, that makes sense.

I know its a retail speaker, but it seems like something one could match if they made good choices in drivers and cabinet design choices.

 

[MAB]

Hi,
I was looking at the Philharmonic line of speakers.
In their BMR Monitor Speaker (https://philharmonicaudio.com/products/bmr-monitor?variant=44484954554612)

Its a three way w a tweeter, 2" BMR and then a woofer. (6" SB Accoustic)

I'm trying to understand why they have the BMR where the range of the tweeter and the woofer could potentially be enough.
This also seems true w the other speakers that they offer.

I guess it goes down to driver choices... but what's the advantage of a 3 way where the mid mostly overlaps the woofer and the tweeter.

They allude to it in their marketing, and they are not making things up. Matching the dispersion of a tweeter to the woofer in a 2-way is almost always going to be a huge challenge.

Consider the Verdant Audio Bambusa MG-1:
It simple 2-way with top-shelf drivers from ~25 years ago, still good to this day. The tweeter is isn’t mounted in a wave-guide so you get the typical dispersion of a 1" dome. The woofer is magnesium allow and has great passband properties but has enormous breakup modes above 4kHz.

It has large directivity mismatch between the woofer and the tweeter at the crossover, which leads to a depression in the midrange response that will not readily respond to EQ.

The resulting in-room response will always have a dip, even if you use DSP to attempt to flatten the response.

The directivity mismatch manifests in many in-room artifacts:

Imaging, the often cited benefit of a 2-way, isn't good with these types of frequency and reflection inconsistencies...

I used these drivers for years, mostly in a DIY speaker called Thor, which make up for some of the issues but trade for a whole set of new issues...
I repurposed some into a very similar speaker to the Verdant (totally unknown to me!!!). My measurements with a DSP crossover show the same directivity mismatch as the Verdant.

Same in-room response error:

I have changed many things in the DSP crossover since then, and have much better directivity match, but am running the crossover very low, too low for anything but desktop/workstation speaker use where I only run at low power. I also adjusted the Q of the passive notch to flatten the huge out of band notch the woofer has, I now both tame the peak but also flatten the response. Here are overly-smoothed graphs of the woofer peak, and passive vs. DSP filter of the peak from my original post:

I am happy with the performance now, it's about as good as a small standard 2-way desktop can sound without some innovations that are beyond me!

I do have a floor standing 2-way that avoids this problem by using an acoustic lens and crossing over the woofer to the Compression Driver at 780Hz. But this is not the norm.

I have thought about updating the build-thread with new measurements, but hope you get the idea that the drivers' directivities depend on frequency and effective radiator size, and you usually will sacrifice some in-room performance if these are not matched. It turns out that 3-way allow much better directivity matching. And allow you to keep the individual drivers away from problematic resonant peaks. Of course, they are more difficult to design, build, and tweak. DSP filters really helps since passive crossovers in a 3-way do require way more understanding.

Some may not care about the tradeoffs in a 2-way, I have lots of 2-way speakers, some sound pretty good! But I find that speakers with poorly controlled directivity in my imperfect listening room really degrade imaging, and can make speakers very track-dependent on how they sound, while emphasizing parts and artifacts in recordings oddly.

Edit: typo; tweeter is NOT loaded in a waveguide!!!

 

[LTig]

There are two reasons to use a midrange driver. One is to enable higher power handling, as tweeters often struggle to be efficient when crossed low to a woofer. The other is to avoid the narrowing of the woofer‘s output at the top of its range, giving wider more even dispersion overall. In the case of the Philharmonic BMR it’s mostly about the latter effect.

The third reason is reduced IMD in the mid range.

 

[mcdn]

The third reason is reduced IMD in the mid range.

That is true, although I don’t think it’s really a reason for making the design choice, more a nice side benefit!

 

[LTig]

That is true, although I don’t think it’s really a reason for making the design choice, more a nice side benefit!

Well, it's one reason why my K&H O300D (and its successor, the Neumann KH310) is a 3-way. Both are famous for their clean mids.