Verdant Audio Bambusa MG 1 Speaker Review

[witwald]

Speaker drivers, like speakers themselves are inevitably a compromise. The main draw for metal cones is their rigidity and no breakup modes up to relatively high frequencies. As discussed earlier, they will very much require some attention in the crossover, possibly a notch filter if need be, ... Of course, there is nothing keeping a driver designer from applying the same electrical design to other cone materials and possibly ending up with an about equally well-performing but less quirky unit.

It's clear, now even more so than in the past, that speaker drivers are difficult to design to get a smooth response. However, one needs to take a quick look at the published natural on-axis response curves of drivers such as the KEF B200 and B110 series from yesteryear to see that a smooth on axis behaviour can be obtained (decades ago). The following (translated) quote seems to be quite relevant and applicable in broad terms to the situation whereby the SEAS woofer might typically be chosen instead of other measurably better performing drivers:

"Membrane substances and their composition are sometimes reported as real wonders combined with mysterious backgrounds, but evaluable and scientific statements in the German-speaking world are avoided as much as possible, [...]."
From: Heinz Sahm, Arbeitsbuch für Lautsprecher-Systeme, 1987, p. 98.

Looking at the SEAS woofer and other drivers with significant high-Q break-up modes in their passband, typically those using aluminium and magnesium diaphragm materials, it would seem that they are falling into the very trap described by Sahm.

 

[tuga]

Using 4 additional inexpensive components, the second peak can be reduced to more than 40 dB down (although I don't think that's necessary).

Would this be adding a steeper low-pass second knee?

 

[tuga]

It's clear, now even more so than in the past, that speaker drivers are difficult to design to get a smooth response. However, one needs to take a quick look at the published natural on-axis response curves of drivers such as the KEF B200 and B110 series from yesteryear to see that a smooth on axis behaviour can be obtained (decades ago). The following (translated) quote seems to be quite relevant and applicable in broad terms to the situation whereby the SEAS woofer might typically be chosen instead of other measurably better performing drivers:

"Membrane substances and their composition are sometimes reported as real wonders combined with mysterious backgrounds, but evaluable and scientific statements in the German-speaking world are avoided as much as possible, [...]."
From: Heinz Sahm, Arbeitsbuch für Lautsprecher-Systeme, 1987, p. 98.

Looking at the SEAS woofer and other drivers with significant high-Q break-up modes in their passband, typically those using aluminium and magnesium diaphragm materials, it would seem that they are falling into the very trap described by Sahm.

Back in the early 90s Monitor Audio came up with the Studio series which sported a 1" aluminium dome tweeter and a 6.5" aluminium cone woofer with 2nd order filters if I'm not mistaken.
These speakers where highly praised by the press of the day, and yet I always found them very hard on the ear. I used to spend long ours at the distributor back then (last year of high school and early days at the university) and got very familiar with most models.
It was only years later that I came upon Stereophile's measurements of these speakers.


Monitor Audio Studio 6

source: https://www.stereophile.com/content/monitor-audio-studio-6-loudspeaker-measurements



Monitor Audio Studio 10

Woofer impulse response

source: https://www.stereophile.com/content/monitor-audio-studio-10-loudspeaker-measurements

 

[ctrl]

It's clear, now even more so than in the past, that speaker drivers are difficult to design to get a smooth response.

Not really. Even today there are still very inexpensive chassis that show practically no cone-breakup. The problem was and is that some listeners are of the opinion that the strong damping of such drivers is at the expense of sound quality.

https://www.tymphany.com/transducers/hds-p830874/

However, one needs to take a quick look at the published natural on-axis response curves of drivers such as the KEF B200 and B110 series from yesteryear to see that a smooth on axis behaviour can be obtained (decades ago).
...
Looking at the SEAS woofer and other drivers with significant high-Q break-up modes in their passband, typically those using aluminium and magnesium diaphragm materials, it would seem that they are falling into the very trap described by Sahm.

I'm afraid you have a very narrow view. Focusing on the smoothest possible axis frequency response of a chassis belongs to times long past.

As others have already mentioned, cone-breakup doesn't matter with a correctly designed crossover. The only important thing, as has already been said, is that the distortion caused by the cone-breakup is also taken into account when choosing the crossover frequency - increased HD3 at 1000Hz will not disappear with a steep filter at 2kHz.

A low-midrange driver in which even the smallest driver resonance is suppressed by damping measures is not automatically a " top driver ".
Harmonic distortion, multitone distortion and radiation behaviour are equally important. Added to this are the different sound perceptions described above.

Another factor is the "different philosophy" of the chassis manufacturers. There are manufacturers who see a tonal advantage in hardly/not damping e.g. the surround resonances. Or try to keep the mechanical losses as low as possible (of course this has been done in the past too) - which in many cases does not allow for strong damping.

 

[Vuki]

17 years ago I made a br 2way with similar drivers (IIRC W17 002? and Millenium tweeter) and it didn't look and sound bad

On axis there was shallow dip around 5kHz from box edge diffraction that filled nicely when measured at ca. 30deg hor.

 

[Dennis Murphy]

Back in the early 90s Monitor Audio came up with the Studio series which sported a 1" aluminium dome tweeter and a 6.5" aluminium cone woofer with 2nd order filters if I'm not mistaken.
These speakers where highly praised by the press of the day, and yet I always found them very hard on the ear. I used to spend long ours at the distributor back then (last year of high school and early days at the university) and got very familiar with most models.
It was only years later that I came upon Stereophile's measurements of these speakers.


Monitor Audio Studio 6

source: https://www.stereophile.com/content/monitor-audio-studio-6-loudspeaker-measurements



Monitor Audio Studio 10

Woofer impulse response

source: https://www.stereophile.com/content/monitor-audio-studio-10-loudspeaker-measurements

Now those are bad crossovers. Good thing we've learned a few things since the early 90's.

 

[AnalogSteph]

Now those are bad crossovers. Good thing we've learned a few things since the early 90's.

Honestly it's not just the XOs. The Studio 10 may still be salvageable like that, but in the Studio 6 midwoofers breakup modes are so low in frequency that it's almost impossible to control them with the chosen crossover point. Today you would slap a waveguide on the tweeter and cross it over <2.5 kHz, and then you may still stand a chance. But at the time it would have been a real stretch for a 2-way.

 

[Dennis Murphy]

Honestly it's not just the XOs. The Studio 10 may still be salvageable like that, but in the Studio 6 midwoofers breakup modes are so low in frequency that it's almost impossible to control them with the chosen crossover point. Today you would slap a waveguide on the tweeter and cross it over <2.5 kHz, and then you may still stand a chance. But at the time it would have been a real stretch for a 2-way.

I'm not seeing much difference between the breakup modes of the 6 and 10, unless I need to clean my glasses. The main peak is between 5k and 6k on both speakers, and that's higher than the Excel W18. A trap circuit should work on the Monitors as well.

 

[peanuts]

apart from cone material, here is an example of the most recent evolution of seas. these drivers are the same, only difference is the shape of the cone. look at the breakup, much higher in frequency.
http://seas.no/index.php?option=com...6rnx&catid=44:utv-prestige-woofers&Itemid=461
http://seas.no/index.php?option=com...rnx3&catid=44:utv-prestige-woofers&Itemid=461

 

[Dennis Murphy]

apart from cone material, here is an example of the most recent evolution of seas. these drivers are the same, only difference is the shape of the cone. look at the breakup, much higher in frequency.
http://seas.no/index.php?option=com...6rnx&catid=44:utv-prestige-woofers&Itemid=461
http://seas.no/index.php?option=com...rnx3&catid=44:utv-prestige-woofers&Itemid=461

The Seas 16 series have been around for quite a while. They use the same chassis as the 5.5" drivers, but Seas manages to squeeze a 6" cone in. The sealed version of the aluminum L16 was developed for Sigfried Linkwitz for use in his plumbing fixture Pluto loudspeaker many years ago. The U16 uses a woven fabric cone and in various forms is used in the Ascend Sierra 2 and a souped up version of the Salk Song Tower. The Excel W16 is used in Salk Veracity Song Tower and has extraordinary bass capability. The breakup points aren't any higher than the 15 series Excels, But as a group they're terrific performers.

 

[Gringoaudio1]

This review really makes me wonder about the audio business and the types of people that get into it. Wouldn't you , as a speaker designer have a blend of several core speaker-specific competencies? None of them seem to be embodied in the designer of this speaker. Harsh but sorry its true. If you're going to farm the crossover design out, which to me is bizarre, that seems to be the heart of being a speaker designer, but if you're farming that out then perhaps you are a talented Industrial Designer that is offering a statement that only Industrial Design can bring to the table. But no that gift is missing in these pleasant but nothing special boxes. Maybe you're a talented woodworker with a passion for joinery and you just need a vehicle for your woodworking skills. But no this is being farmed out and the joinery is nothing special.

 

[Gringoaudio1]

That all being said ... I think voicing speakers by ear in conjunction with measurements is part of the 'art' of speaker design. So I don't begrudge the designer for designing by ear and not depending on measurements. But that means understanding crossover design and theory and through years of experience knowing what the addition of an L-pad to drop the output of a driver or playing with the value of a capacitor or coil in the crossover will do to the sound. How can you be a speaker designer and not be tuning and tweaking the design often for months until it sounds right? And yes I know that is subjective. But we all know when a system sounds good or not. And a flat FR doesn't always sound good.

 

[Rick Sykora]

Tell her there are worse addictions that you could have.

Thanks Rick, but have used that one for a while.

Am thinking of switching it up a bit, more like “I have to have at least one vice”

 

[Ericglo]

The Bliesma T34 might be a better tweeter to match with this woofer.

 

[Ericglo]

Just to follow on to my previous post. I haven't seen a lot of use out of the Bliesma, but Troels used it in a two way and crossed at IIRC 1600. HIficompass used it in their Pharoah and crossed around the same IIRC.


One thing I am curious about from the owner, why use these drivers that have been used before? Try some of the new drivers that are coming out and provide something different and unique. If your current designer doesn't have any ideas then ask Rick or Dennis. I am not sure if Rick has played with the Bliesma or not, but there are others out there. SB has a new driver line with Textreme. I don't believe anyone has done anything with that yet. Lots of possibilities. Heck I doubt anyone would have given a lot of thought about using the BMR driver that Dennis used.

 

[ctrl]

I haven't seen a lot of use out of the Bliesma,

Because the Bliesma tweeter has a "difficult radiation pattern". Due to the special construction of the diaphragm, the tweeter, despite its 34mm (1.3'') voice coil, has the dispersion characteristics of a 19mm (0.75'') dome.
Most tweeters use a tiny wave-guide to support the radiation in the upper frequency range, the Bliesma tweeter does not.

In a German loudspeaker forum about 1.5 years ago I did some simulations of baffles to support a DIY project which uses a Bliesma tweeter- my simulations start with Post#60.

After many simulations it was clear that an even sound dispersion would not work without the help of a very flat wave-guide.

Here some examples from the thread:

A simple baffle like the one used here in the thread:
The baffle and the horizontal sonogram normalized to the axis frequency response and FR.



Complex baffle, but still without wave-guide:
The baffle and the horizontal sonogram normalized to the axis frequency response and FR.



The final result after many simulations. Full speaker simulation with an eighth-order LR crossover:
The baffle and the horizontal and vertical sonograms normalized to the axis frequency response.

 

[Ericglo]

Because the Bliesma tweeter has a "difficult radiation pattern". Due to the special construction of the diaphragm, the tweeter, despite its 34mm (1.3'') voice coil, has the dispersion characteristics of a 19mm (0.75'') dome.
Most tweeters use a tiny wave-guide to support the radiation in the upper frequency range, the Bliesma tweeter does not.

In a German loudspeaker forum about 1.5 years ago I did some simulations of baffles to support a DIY project which uses a Bliesma tweeter- my simulations start with Post#60.

After many simulations it was clear that an even sound dispersion would not work without the help of a very flat wave-guide.

Here some examples from the thread:

A simple baffle like the one used here in the thread:
The baffle and the horizontal sonogram and FR normalized to the axis frequency response.
View attachment 59847 View attachment 59848 View attachment 59849


Complex baffle, but still without wave-guide:
The baffle and the horizontal sonogram and FR normalized to the axis frequency response.
View attachment 59850 View attachment 59851View attachment 59852


The final result after many simulations. Full speaker simulation with an eighth-order LR crossover:
The baffle and the horizontal and vertical sonograms normalized to the axis frequency response.
View attachment 59843 View attachment 59845 View attachment 59846

That is interesting. I haven't seen any DIYers use this tweeter. It is good to get some more data points.

 

[alexman]

But why spend so much time and effort overcoming the fundamental vibroacoustic flaws in such drivers when better behaved drivers exist, no doubt at a similar price/quality point? And the best that can be done is still having a flawed response, compared to the known design criteria already well covered in BBC design information. Wouldn't choosing a vibroacoustically well-behaved driver be much more possible to do, rather than attempting a fix that is not impossible, but ostensibly quite difficult and flawed from an engineering point of view?

The main benefit of this kind of driver is to postpone the membrane breakup(s)/fragmentation far over its utile bandwidth.
The CSD measurement is very relevant to highlight the difference between smooth and stiff membrane.

SEAS U18 (polypropylene)

SEAL L18 (aluminium), cleanest up to the breakup.

Same measurement condition + almost the same driver... apart from the membrane material.

 

[witwald]

The main benefit of this kind of driver is to postpone the membrane breakup(s)/fragmentation far over its utile bandwidth.
The CSD measurement is very relevant to highlight the difference between smooth and stiff membrane.

SEAS U18 (polypropylene)

SEAL L18 (aluminium), cleanest up to the breakup.

Same measurement condition + almost the same driver... apart from the membrane material.

@alexman Thank you for posting the CSD plots.

Looking at the CSD measurements doesn't really offer any significant new information above and beyond what we can determine from the frequency response plot. Although it can be instructive the first time to have a view of the decaying behaviour of sharp, high-Q resonances, the resonant behaviours displayed by the CSD plots are intrinsically contained within the frequency response plot. A decay curve for one sharp resonance is just the same as the decay curve for another sharp resonance. The use of CSD plots just complicates interpretation of the important facts. If the frequency and Q of resonances in two drivers are the same, then those resonances will decay away at the same rate.

Below are the frequency response plots for the two drivers you mentioned. Without all the distracting decay curves, it is immediately clear that the L18RNX/P aluminum cone is a very poor choice as a loudspeaker driver. I think that the erstwhile BBC engineers of old would be quite shocked if they saw it. They knew that sharp, high-Q resonances should be avoided, and they worked hard to avoid them. The U18RNX/P has a much better controlled response, and will be easier to work with in any loudspeaker design.

SEAS Prestige L18RNX/P (H1224) 7" Aluminum Cone Woofer

SEAS Prestige U18RNX/P (H1571) 7" Curv Cone Woofer

 

[alexman]

It's always interesting to get different point of views from HIFI enthusiast based on technical facts. For some people the SEAS L18 would be a poor choice because of these high Q resonances at hight frequencies, and for other (like me ) the SEAS U18 would be a poor choice because of the membrane fragmentations who appear in the medium band (for two ways setup I precise).

The membrane fragmentation or breakup of the U18 apprears from about 800Hz, its also visible on its impedance curve.

I agree the overall response of the U18 looks friendly to use, but the waterfall shows that its membrane have a inferior behaviour especially in the medium band compared to the L18.

I've tested both of these speakers in the two way setup. SEAS tweeter was used (H1212), for each setup (L18 or U18) I used the emulator function of LSPCad that allows to switch from one and other setup instantanelly. Beside the L18, the U18 has always given a medium band "muffled" or "felted" even with flat response curve.

I humbly recommend this kind of experiment.