Verdant Audio Bambusa MG 1 Speaker Review

[Deleted member 2944]

But won't those 10-dB or so resonances continue to ring and add their response to the sound even though they are attenuated below the crossover frequency? Would it not be even more sane to just not use this particular driver because of its fundamental vibroacoustic flaws?

No, not if you don't excite them they won't add their response.
You seem to be under the impression these drivers are flawed in a problematic way. Not so. These particular metal cone drivers are excellent in numerous aspects. But they need to have a proper crossover design.........as all speakers do.

Dave.

 

[andreasmaaan]

I agree with you @dreite, these drivers are difficult, but not impossible, to work with in a passive speaker.

Indeed, the same could be said of most Seas woofers IME.

I'm not sure why (other than looks and name) you'd choose to use a driver like this unless you were willing to put serious work into the enclosure and crossover.

 

[witwald]

But the filter design is typically going to be a 2nd-order or 3rd-order design. Those resonances are still little more than an octave above a nominal crossover frequency of 3 kHz. This means that they will get excited, all be it at a reduced level. But then, don't they have a peak level 10–15 dB above the nominal driver natural rolloff curve? That will leave a large high-Q resonance superimposed on the filtered response. Won't that be audible on some program material?

 

[witwald]

I agree with you @dreite, these drivers are difficult, but not impossible, to work with in a passive speaker.

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?

 

[andreasmaaan]

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?

I'd make a distinction between "difficult" and "flawed".

If the driver's resonance peak is nullified by the crossover, even if that takes a lot of work, where's the flaw?

Personally/practically though, I do tend to agree with you. This is not a driver I'd be likely to choose for a passive design in the first place.

 

[andreasmaaan]

But the filter design is typically going to be a 2nd-order or 3rd-order design. Those resonances are still little more than an octave above a nominal crossover frequency of 3 kHz. This means that they will get excited, all be it at a reduced level. But then, don't they have a peak level 10–15 dB above the nominal driver natural rolloff curve? That will leave a large high-Q resonance superimposed on the filtered response. Won't that be audible on some program material?

Options would include:

• lowering the crossover frequency (3kHz is very high for a 2-way in my view)
• increasing the filter slope to 4th order or higher
• using an LCR network to tame the resonance

As I said though, personally I would probably just start with a different woofer in the first place (also due to this woofer's TS parameters and what that means for enclosure size).

 

[MattHooper]

I'd make a distinction between "difficult" and "flawed".

If the driver's resonance peak is nullified by the crossover, even if that takes a lot of work, where's the flaw?

Personally/practically though, I do tend to agree with you. This is not a driver I'd be likely to choose for a passive design in the first place.

Makes sense to me.

I note the stereophile review of the Joseph speakers using the SEAS woofer mentions peaks that were well controlled by the crossover.
The designer must have known what he was doing in choosing those particular drivers because the results are fantastic - extended, tons of surprisingly low, punchy bass for the size, well balanced, and a combination of fantastic clarity that is smooth as silk.

 

[andreasmaaan]

Makes sense to me.

I note the stereophile review of the Joseph speakers using the SEAS woofer mentions peaks that were well controlled by the crossover.
The designer must have known what he was doing in choosing those particular drivers because the results are fantastic - extended, tons of surprisingly low, punchy bass for the size, well balanced, and a combination of fantastic clarity that is smooth as silk.

I'm not familiar with the particular speakers but I know Joseph generally uses very high-order crossover filters.

 

[Alice of Old Vincennes]

Sooo. I am sitting here in Vincennes, Indiana tonight with no electricity for third night in a row combined with social distancing. Drove 30 miles to find ice. Told my son these 2020 events would imprint on his brain cells like 1963, 1968 and 2001. I don't think he understood. He is young, I had this boy late in life. So did my father. Son's grandfather was born in 1910. I know this rant is irrelevant to this topic. Sorry. Good things happened. Son is torn away from computer by natural disaster. We went outside with Canon stabilizers to look at dark sky. He had never seen the Milky Way. This site is about sound. I liked the lack of light tonight.

 

[witwald]

The driver for the BBC LS5/9 loudspeaker is a difficult driver, as are most bass-mid woofers when it comes to integrating them into a two-way loudspeaker system with a 25–34 mm tweeter. Here is the response of a 1983 BBC-designed 200 mm woofer (Source: BBC RD Report 1983-10):

This is from way back in 1983, which is quite a long time ago now in loudspeaker driver design technology. The SEAS driver is vibroacoustically inferior to the BBC driver (some might label the design of the SEAS driver as being intrinsically flawed, as compared to an example from over 30 years ago). I am left wondering as to whether or not the SEAS driver's visually striking aesthetic played a large part in its being chosen.

The fact that it is difficult to control the 8 kHz resonance problem in the SEAS woofer is clearly shown in the Stereophile measurement that is shown reproduced below of a loudspeaker that uses the SEAS woofer (Source: Joseph Audio Perspective measurements). There really is no sign that the resonance problems (the peaks at 6.5 kHz and 9 kHz) are being controlled in a meaningful way; they are still there, imprinted on the low-pass response function The high-pass and low-pass responses shown here are definitely not complementary.

 

[MattHooper]

The driver for the BBC LS5/9 loudspeaker is a difficult driver, as are most bass-mid woofers when it comes to integrating them into a two-way loudspeaker system with a 25–34 mm tweeter. Here is the response of a 1983 BBC-designed 200 mm woofer (Source: BBC RD Report 1983-10):
View attachment 58213
This is from way back in 1983, which is quite a long time ago now in loudspeaker driver design technology. The SEAS driver is vibroacoustically inferior to the BBC driver (some might label the design of the SEAS driver as being intrinsically flawed, as compared to an example from over 30 years ago). I am left wondering as to whether or not the SEAS driver's visually striking aesthetic played a large part in its being chosen.

The fact that it is difficult to control the 8 kHz resonance problem in the SEAS woofer is clearly shown in the Stereophile measurement that is shown reproduced below of a loudspeaker that uses the SEAS woofer (Source: Joseph Audio Perspective measurements). There really is no sign that the resonance problems (the peaks at 6.5 kHz and 9 kHz) are being controlled in a meaningful way; they are still there, imprinted on the low-pass response function The high-pass and low-pass responses shown here are definitely not complementary.
View attachment 58212

Proofs in the pudding I think: how does it sound? How well has the designer balanced out the problems and benefits in his design?
In the case of the Joseph Speakers I understand Jeff Joseph likes to make "smaller speakers that sound big" - so domestically non-dominating size but with surprisingly full, big sound. Clearly he's chosen drivers that suit that goal (I think they are fairly long-throw for producing good bass in a smaller driver?). And his speakers hit that goal out of the park. The remark you hear over and over from listeners/reviewers/owners is how BIG the sound is coming from small looking speakers (e.g. the Pulsars give the impression of a bigger floorstander, the Perspectives sound like a much bigger floorstanding speaker than they look. I'm constantly amazed how life-sized the sound is from my Perspectives - similar to much larger speakers I've owned). And the speakers manage it with outstanding balance, clarity and smoothness. I notice the Joseph speakers through the years have garnered more than usual positive consensus among people who've spent time listening to them, from DIYers even to other manufacturers.

These are the reasons I ultimately go with what I hear from a speaker, vs being swayed too much by someone on a forum saying "look, this can't work, this can't be good!" (Because you can find detractors of almost every speaker design in some aspect).

 

[andreasmaaan]

But won't those 10-dB or so resonances continue to ring and add their response to the sound even though they are attenuated below the crossover frequency? Would it not be even more sane to just not use this particular driver because of its fundamental vibroacoustic flaws?

I mentioned the idea of using an LCR notch filter in my previous post.

You might be interested to see how this can work, in this case with another Seas driver that has a similar very strong resonance at a similar frequency.

The red trace on the left is the raw woofer response. The red trace on the right is woofer + low-pass filter. The blue trace on the right is woofer + low-pass filter + notch filter:

Or you may be interested in this speaker from Joseph Audio, where a similar resonance is largely avoided by use of a very high ("infinite") slope filter (FWIW I'm not saying this is a perfect design in every other way, of course):

 

[tuga]

Edit: @andreasmaaan beat me to it.

But won't those 10-dB or so resonances continue to ring and add their response to the sound even though they are attenuated below the crossover frequency? Would it not be even more sane to just not use this particular driver because of its fundamental vibroacoustic flaws?

Troels Gravesen designed a speaker using the W15CY001 Excell midwoofer and the W22EX001 Excell woofer:

Paper, when done right, can provide a speedy, transient sound and usually the break-up of the paper cones is of an ear-friendly kind. The sound simply gets muddled when the speakers are driven too loud. Not necessarily so with the hard-cones. These EXCEL drivers use magnesium membrane material, which is extremely hard and work as a piston in the range where the driver is intended to perform, but outside this area, they break-up and produce some very nasty peaks that has to be carefully removed in the filter.

For those interested, the individual response of drivers with no crossover. Please notice the humongous peak (cone break-up) from the bass driver at around 5 kHz. This is some 15 dB above average level! However, crossing over at 350 Hz can be done 2nd order without further fine-tuning.The W15 is doing great here, flat from 200 Hz to 4.5 kHz. Peaks are well above intended point of crossover to the tweeter. 27TFFC really is a sensitive tweeter. 93 dB/2.8V is no problem and it makes it suitable for the C17 construction where an overall level of 95 dB sensitivity is achieved.

source: http://www.troelsgravesen.dk/PMS-EXCEL.htm

 

[AnalogSteph]

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, but chances are they'd be well-behaved around crossover frequency and below which is appreciated.
They must also have low intrinsic electrical distortion (B*l / inductance nonlinearity) or else the peak from breakup will cause severe distortion spikes (particularly around fpeak/3), as electrical distortion is filtered through raw frequency response and accented correspondingly. This poses some challenges in driver design but if achieved, would result in low IMD levels above the excursion-limited range as a welcome side effect. I consider it quite possible that you could thus "accidentally" end up with an excellent driver even without fully understanding this relationship, assuming the distortion peaks irked you which seems likely.

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.

Regarding the previous general discussion on waveguides, one reason they are so popular is that in evening out the dispersion, they bring on-axis frequency response more in line with energy response, and that means gain towards the lower end and thus better level handling. A bare tweeter that measures flat on axis but has an uneven radiation pattern (and they all widen up below a certain frequency) inevitably cannot have a flat energy response. By focusing these lower-frequency components that would otherwise be spread out over a very large angle, on-axis response is brought up there, so levels and excursion can be reduced. So not only is tweeter dispersion more even to begin with, you also get a chance to cross over lower to boot for further benefits!
In the olden days, a 1" tweeter crossed over at only 2 kHz would have been exotic for multiple reasons and 3.5 kHz would have been a far more common choice. No longer so today. Can't do that without a high-order XO and waveguide.

 

[DSJR]

Because they are way past where sane people would crossover to a tweeter.

That peak will still not be very far down in a typical passive crossover. Maybe indeed it doesn't matter, but I'd still rather it wasn't there, especially now this unit is over twenty years old!

 

[Dennis Murphy]

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 are a few points that haven't been adequately addressed in this discussion. First, most woofers and mid-woofers, irrespective of cone material, have prominent break-up modes that have to be dealt with. Just take a look at the ceramic woofer used by Revel in their PerformaBe M126Be:
https://www.madisoundspeakerstore.c...coustics-sb17cac35-8-6-ceramic-woofer-8-ohms/
or a ScanSpeak fiberglass woofer: https://www.madisoundspeakerstore.c...eak-discovery-18w/4434g-00-7-midwoofer-4-ohm/ or see the attached raw measurement of the paper cone woofer used in my Affordable Accuracy monitor. Although the peaks on the Seas Excel woofers certainly look a little frightening because of their height, they are very high Q (narrow), and actually easier to deal with than the more chaotic and wider band breakup modes of many other woofers. Looking at the W18 in particular, since I believe this is the woofer used on the MG-1, It takes only 3 components to virtually eliminate the peak and suppress the second peak by by
30 dB. 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). So it simply isn't true that heroic measures are needed to tame the Excel drivers. I wish all of the drivers I work with were as easy. It took 6 components to get the AA woofer peak down 30 dB.

There is one criticism leveled at the W18 that at least has a theoretical basis. Unless the woofer is crossed below 1600 Hz (and that would be difficult in a 2-way), any third order distortion product generated at that frequency will excite the cone resonance no matter how steep the low pass slope is. That's because the 3rd harmonic at 1600 Hz is 3200 + 1600 = 4800 Hz, which is exactly the center of the W18's breakup peak. The crossover won't suppress the 1600 Hz signal, and so that resonant peak will intensify whatever 3rd order distortion is present at 4800 Hz. Fortunately, the W18's upper midrange distortion is very low, due to the well engineered motor and perhaps the stiff cone, and you can see from the Klippel distortion test that the MG-1 in fact has admirably low distortion across the treble band. The bottom line is that the Excel drivers are excellent and easy to implement. I've literally lost track of how many speakers I've designed using them.

 

[Selah Audio]

The are a few points that haven't been adequately addressed in this discussion. First, most woofers and mid-woofers, irrespective of cone material, have prominent break-up modes that have to be dealt with. Just take a look at the ceramic woofer used by Revel in their PerformaBe M126Be:
https://www.madisoundspeakerstore.c...coustics-sb17cac35-8-6-ceramic-woofer-8-ohms/
or a ScanSpeak fiberglass woofer: https://www.madisoundspeakerstore.c...eak-discovery-18w/4434g-00-7-midwoofer-4-ohm/ or see the attached raw measurement of the paper cone woofer used in my Affordable Accuracy monitor. Although the peaks on the Seas Excel woofers certainly look a little frightening because of their height, they are very high Q (narrow), and actually easier to deal with than the more chaotic and wider band breakup modes of many other woofers. Looking at the W18 in particular, since I believe this is the woofer used on the MG-1, It takes only 3 components to virtually eliminate the peak and suppress the second peak by by
30 dB. 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). So it simply isn't true that heroic measures are needed to tame the Excel drivers. I wish all of the drivers I work with were as easy. It took 6 components to get the AA woofer peak down 30 dB.

There is one criticism leveled at the W18 that at least has a theoretical basis. Unless the woofer is crossed below 1600 Hz (and that would be difficult in a 2-way), any third order distortion product generated at that frequency will excite the cone resonance no matter how steep the low pass slope is. That's because the 3rd harmonic at 1600 Hz is 3200 + 1600 = 4800 Hz, which is exactly the center of the W18's breakup peak. The crossover won't suppress the 1600 Hz signal, and so that resonant peak will intensify whatever 3rd order distortion is present at 4800 Hz. Fortunately, the W18's upper midrange distortion is very low, due to the well engineered motor and perhaps the stiff cone, and you can see from the Klippel distortion test that the MG-1 in fact has admirably low distortion across the treble band. The bottom line is that the Excel drivers are excellent and easy to implement. I've literally lost track of how many speakers I've designed using them.

The Revel actually uses a Chinese woofer from another manufacturer, not SB Acoustics. I totally agree on the Excel woofers except they don't fare well in humid environments. The new graphene-coated versions apparently avoid the disintegration of the cone.

 

[jhaider]

The Revel actually uses a Chinese woofer from another manufacturer, not SB Acoustics. I totally agree on the Excel woofers except they don't fare well in humid environments. The new graphene-coated versions apparently avoid the disintegration of the cone.

That’s true of M126Be, but I believe the older series used SB Acoustics drivers. Some may have been made by them or a related company too. I saw a set of M105s labeled Made in Indonesia.

 

[Dennis Murphy]

The Revel actually uses a Chinese woofer from another manufacturer, not SB Acoustics. I totally agree on the Excel woofers except they don't fare well in humid environments. The new graphene-coated versions apparently avoid the disintegration of the cone.

The Revel actually uses a Chinese woofer from another manufacturer, not SB Acoustics. I totally agree on the Excel woofers except they don't fare well in humid environments. The new graphene-coated versions apparently avoid the disintegration of the cone.

The Revel actually uses a Chinese woofer from another manufacturer, not SB Acoustics. I totally agree on the Excel woofers except they don't fare well in humid environments. The new graphene-coated versions apparently avoid the disintegration of the cone.

Well, if that's the case someone is ripping someone off. Care to disclose who's the ripper and who's the rippee? In any event, the 5" SB Ceramic is an amazing woofer. If Revel's not using the 6" version, perhaps they should be.

 

[Selah Audio]

Well, if that's the case someone is ripping someone off. Care to disclose who's the ripper and who's the rippee? In any event, the 5" SB Ceramic is an amazing woofer. If Revel's not using the 6" version, perhaps they should be.

I agree, the SB 5" is great as well as the other drivers in that series. The driver generation before the current line was made by SB. I heard from a good source which manufacturer is probably is making them now and that they copied the SB design. Since there are always two sides to a story I can only speculate.