Not to beat a dead horse...

[jneutron]

Specific parameters of the flexure, mass, etc., are not available. But measurements of the transmitted resonance(s) demonstrate an excellent behaviour, relative to most other cabinets, on the N802/N801 design(same midrange module). And when I tried these, no perceptible sound was transmitted from the plastic enclosures, as was not the case with the thin plastic enclosures I have been exposed to.

Bet they coulda gone thinner with same results...

Thin plastic meaning Bose?, or comp speakers..

The subwoofer on the Acoustimass responds to frequencies that are too high, for a modulized system that sits several feet from the midrange radiators. I did not even mention the very high non-linear distortion that must be present[or can be traded or linear distortion, a.k.a. one-noted bass -- if that is decided by the engineering team], by using a single 6" subwoofer in a normal size room.

So, now you are introducing system nuances that the vast bulk of the human race do not know about or care about..how many people care that the module freq's climb into the localization regime?

High non-linear distortion that "must" be? Then, you've not listened for it, but are generalizing..

One note bass...I kinda think the Bose acoustimass module doesn't fall into that category..with two cavities, three different port sizes, and another active cone firing down into god knows what, they have kinda engineered the darn thing a little more than the car boom boxes..

But, for the cost, geeze, I would rather build something on my own...but, that's me..

Cheers, John

PS..I'll stop for coupla hours, we are interleaving..and I edited a post you responded to..

 

[WmAx]

I figured..it's very hard to guess thickness based on tapping..they do such weird things with plastic nowadays..

That is true, but in extreme examples, like computer speakers[and bose acoustimass satellites], it so thin, it's hard to think of how it would not have a negative impact.

A very thin plastic enclosure[that does not feature extensive internal support systems] will allow a great deal of sound to be transmitted in the form of high amplitude resonances, unless it is heavily mass loaded/damped[which is costly] or too pliable to be useful to resist pressure differences. Plastic has rather broad[low Q] resonance(s). Alternatively, a very highly resonant and very stiff material with high Q resonance(s)[such as metal] can be used, and the stiffness adjusted to mass, to push the resonant mode(s) into bands that are not likely to be [very] audible, since high Q resonances, especially at higher frequencies, are not as easily detectable to humans.

-Chris

Nah, they also consider sound quality..but not to the extreme that others do..

Right. Like Infinity; they obviously put lots of effort into the sound quality portion.

Cost is not a quality issue..unless, of course, the production line suffers lots of scrap..

But production cost relates to sound quality, when a company[such as Bose] takes it to the extreme, and cuts basic known corners that would yeild higher sound quality. That was my only point.

-Chris

 

[WmAx]

Bet they coulda gone thinner with same results...

I don't know if they could have gone thinner -- as the data to conclude this is not available. They may have already used the minimum thickness that was sufficient for the material used.

Thin plastic meaning Bose?, or comp speakers..

Meaning both. The Bose seem about as thick as the computer speakers of with which I was comparing them. On the computer speaker it was insufficient. But it's true, that I don't have an Acoustimass in order to analyze. But I don't have confidence in Bose, as they have not shown that they cared in other choices that effect sound quality.

So, now you are introducing system nuances that the vast bulk of the human race do not know about or care about..how many people care that the module freq's climb into the localization regime?

Well, this is true. But I was not responding or referring to sound quality in this thread from the perspective of the average person. The average person does not seem to care very much about fidelity of sound reproduction. If I have[up to this point] appeared to be speaking from this perspective, let it be known that this is not the case.

High non-linear distortion that "must" be? Then, you've not listened for it, but are generalizing..

Yes, I am generalizing, based on my knowledge/results of many drivers. Unless Bose is using a very sophisticated driver with extraordinary motor linearity(this would be costly -- so I can not assume they do this), then the device must produce high non-linear distortion at moderate to high SPL levels, unless they traded this for a highly resonant tuning[in which case linear distortion is high], or used a massive horn loaded bass design[the module is not massive, therefor this is not likely].

But, for the cost, geeze, I would rather build something on my own...but, that's me..

I agree.

-Chris

 

[jneutron]

For a speaker enclosure, the main thing is to make sure the walls don't resonate. With a woofer, all ya gotta do is make the walls stiff enough to raise the resonance freq to that above what the woof goes to..for mid cabs, that freq can be quite high..the good thing, is it's also small.

Next is actual movement..it's opposite the cone, so should be small as possible..

Both can be solved by internal side to side bracing..I've run turntables on top of 15 inch enclosures at 300wrms and 100 dbspl, 1/2 ply thickness with good internal bracing..

So it wouldn't suprise me if the plastic enclosures of bose had these thing taken into account..

As for system linearity/response peak and the such, don't forget..you, like I, would like the group delay to be less than a coupla hours...that missing factor in a bose system, most don't miss..

I expect my shirt to pop it's buttons with a kick drum...but, most people just wanna watch the mechanical dinosaurs with the laser beams...

Cheers, John

 

[WmAx]

For a speaker enclosure, the main thing is to make sure the walls don't resonate. With a woofer, all ya gotta do is make the walls stiff enough to raise the resonance freq to that above what the woof goes to..

Right. Easy for woofers.

for mid cabs, that freq can be quite high..the good thing, is it's also small.

Not so easy when using such thin plastics. Tapping on the side of an acoustimass reveals the resonant frequency is located in the [critical] midrange. True, that this is not quantitive, but it seems rather extreme effect on this product. Unless the internal volume is double-chambered(cabinet in a cabinet, and one mechanically decoupled from the other), the effect is going to probaby have a significant negative impact on sound quality.

As for system linearity/response peak and the such, don't forget..you, like I, would like the group delay to be less than a coupla hours...that missing factor in a bose system, most don't miss..

Being as most people seem perfectly happy with the recording quality of the average popular music selection today -- I suspect it would require rather extreme negative quality in any parameter, to get many people upset or notice!

-Chris

 

[Steve1000]

What I find most interesting is that the Bose Acoustimass 3 and Acoustimass 5 tested as tied for the most accurate speakers in the most recent consumer reports test at 94 out of 100, tied with a Cambridge Soundworks Newton something or other. Whatever the shortcomings of CR's test regimen, it is hard for me to believe that Bose has done just an awful job and still achieved this level of apparent performance. Fequencey response curves published by CR of the acoustimass systems over the years have shown a very smooth and balanced and generally superior frequency response, with no obvious areas of resonance in the midrange apparent from the graphs. Now as matters of audio go, I am barely a novice. But still, these are facts not easily explained away by general criticisms of CR and Bose, IMHO.

 

[WmAx]

What I find most interesting is that the Bose Acoustimass 3 and Acoustimass 5 tested as tied for the most accurate speakers in the most recent consumer reports test at 94 out of 100, tied with a Cambridge Soundworks Newton something or other. Whatever the shortcomings of CR's test regimen, it is hard for me to believe that Bose has done just an awful job and still achieved this level of apparent performance. Fequencey response curves published by CR of the acoustimass systems over the years have shown a very smooth and balanced and generally superior frequency response, with no obvious areas of resonance in the midrange apparent from the graphs. Now as matters of audio go, I am barely a novice. But still, these are facts not easily explained away by general criticisms of CR and Bose, IMHO.

Steve, you'll have to share some of these CR measurements, and the procedures used to make them. From what I have read in the past, CR does not adhere to a methodology or measurement set that would reveal real issues, but instead, uses a very coarse windowed off axis averaging technique[appropropriate only in specific contexts]. Please correct me if is not the case today.

BTW, here is a 3rd party on-axis measurement of a Bose Acoustimass. I have seen several like this on the internet over the years:

This response example denotes severe resonances. This is evidently a smoothed measurement -- which removes/hides problems, yet so many problems are still evident. Single condition response graphs don't tell much in the context of speakers, but in this example, it is evident that the driver is farily resonant.

It would be nice if thorough measurements existed, but alas, they do not[of which I'm aware].

-Chris

 

[furrycute]

So it wouldn't suprise me if the plastic enclosures of bose had these thing taken into account..

Cheers, John

A properly braced cabinet has CONSIDERABLE weight. Plus, when you knock on a properly braced cabinet, you seldom hear the high frequency resonances you usually hear with poorly braced cabinets.

Those tiny feather weight Bose cubes are braced?!

 

[jneutron]

This response example denotes severe resonances. This is obviosly a smoothed measurement -- which removes/hides problems, yet so many problems are still evident. Single condition response graphs don't tell much in the context of speakers, but in this example, it is evident that the driver is farily resonant.
Chris

The graphs show something..I wonder if it's the room stuff, though. It's rather difficult getting meaningful measurements with that darn room in the way..

Anyone done anechoic tests?

John

 

[Steve1000]

Let me thank jneutron, resident loser and wmax for a fascinating and spirited debate between folks who know a ton more than I do! I really appreciate it and it's great reading.

Thanks. I would not be surprised to learn there were significant resonances; nor, however, would I be surprised to learn there were not severe resonances. I've simply not seen enough evidence.

The CR curves of the acoustimass 3 and 5 systems are smooth as silk, and stand in stark contrast to the curves of many other speakers that CR measures. There's a touch of a mid-bass emphasis, but relatively the high degree of accuracy and impressive tonal balance compared to the other speakers they test, as they measure them, is obvious. The gap between the bass and midrange is not present in the CR curves, and the FR extends out smoothly out to at or near 20 khz, IIRC, and extends quite low. This is even for the Acoustimass 3s!

I do not doubt that localization of upper bass frequencies (to about 200 hz) is a problem that Bose just decided wasn't worth the trade-off and that CR doesn't think is that significant for their purposes.

I'll see what I can do about maybe scanning an old FR curve from an old CR magazine I have at home and sending it to you. I don't doubt that their measuremnts are not world class, as they do not build speakers or review audio in an expert way; nor, however, do I beleive their measurements to be worthless.

Not all of the Bose products fare so well in the CR tests, BTW.

Steve, you'll have to share some of these CR measurements, and the procedures used to make them. From what I have read in the past, CR does not adhere to proper methodology, but instead, uses a very coarse windowed off axis averaging technique. Please correct me if is not the case today.

BTW, here is a 3rd party on-axis measurement of a Bose Acoustimass. I have seen several like this on the internet over the years:

This response example denotes severe resonances.

It would be nice if thorough measurements existed, but alas, they do not[of which I'm aware].

-Chris

 

[WmAx]

The graphs show something..I wonder if it's the room stuff, though. It's rather difficult getting meaningful measurements with that darn room in the way..

Anyone done anechoic tests?

John

These are either gated mid-field, or near-field response graphs or some sort of anechoic measurement. Otherwise, lower frequency bands of the graph would be just as erratic[or more] as the higher frequency bands.

-Chris

 

[jneutron]

A properly braced cabinet has CONSIDERABLE weight. Plus, when you knock on a properly braced cabinet, you seldom hear the high frequency resonances you usually hear with poorly braced cabinets.

No. a properly braced cabinet does not have to be heavy. That is what the compressive modulus/stiffness is all about. If you don't want to engineer it, but just toss wood at it, yes it will be heavy..but it doesn't have to be.

You are confusing a dampened surface with a stiff one. If the wall has been treated to absorb the energy, it will have a dull thud. But if it is thin but very stiff, it can have resonance when you hit it..but don't forget, the woofer does not have those frequencies with which to hit the sides..so, it is of no concern, the walls cannot be excited into resonance.

Those tiny feather weight Bose cubes are braced?!

Why not? They could be molded in..but, only if it were necessary to move the resonance frequency out of the driver realm.

Cheers, John

 

[WmAx]

These are either gated mid-field, or near-field response graphs or some sort of anechoic measurement. Otherwise, lower frequency bands of the graph would be just as erratic[or more] as the higher frequency bands.

-Chris

Okay, these measurements were anechoic measurements sourced from Sound & Vision magazine.

http://www.intellexual.net/bose.html

Note: I do not present the link for any other reason than to show the source of the graph. The other information that may be presented at this link is not a reference.

-Chris

 

[jneutron]

Okay, these measurements were anechoic measurements sourced from Sound & Vision magazine.

Thanks..
Anechoic...I've no idea what that means for the bass module..nor, typical setup recommendations..nor, what the stimulus waveform was..

Cheers, John

 

[WmAx]

Thanks..
Anechoic...I've no idea what that means for the bass module..nor, typical setup recommendations..nor, what the stimulus waveform was..

Cheers, John

Right. That's why I stated that thorough measurements are needed in a prior post. I point to this graph as only evidence of the midrange/treble response problems, that indicate [significant] resonances.

-Chris

 

[Steve1000]

CR has never tested any of the Bose surround systems. I consider Sound & Vision measurements to be credible and expert, so it's a point well taken. I've noticed the Bose cubes get smaller as they get more expensive. CR takes measurements in an anechoic chamber as well, IIRC. Might it be that the larger cubes CR is testing are better-performing (and indeed less expensive) in terms of smoothness of response, resonance, and reach into the mid-bass region?

 

[jneutron]

How does one test a 4 or five satellite with sub system in an anechoic chamber??

Power up all five, and the mike to transducers spacing is gonna raise holy heck with the summed response of the sats....use only one satellite, and the sub isn't gonna play very nice..

I guess ya hafta just power one sat at a time?? Then, the sub in eighth space?

If it's setup in the final room, and ears are used, it's gonna play much differently from an A-chamber..

If I had to choose, I'd actually try the systems in a real room..I'm not sure the Bose systems can be measured in a way that reflects what we hear in the final application..luckily, my criteria for an HT system is not that high..(I like being the cheap date )

Cheers, John

 

[WmAx]

How does one test a 4 or five satellite with sub system in an anechoic chamber??

The only sensible way that they could have tested these in an anechoic chamber, is to measure each one individually. What they actually did, only they know, since this specific information is not available.

If it's setup in the final room, and ears are used, it's gonna play much differently from an A-chamber..

If I had to choose, I'd actually try the systems in a real room..I'm not sure the Bose systems can be measured in a way that reflects what we hear in the final application

True, that this single perspective measurement does not say much about it, so far as polar response, etc.. However, certain artifacts[such as severe resonances] can show up as erratic, high-amplitude frequency response spikes.....exactly what is evident on these plots. Anechoic response[or simulate anechoic response using gated MLS signals], btw, is the only way to accurately measure what is actually happening, so far as polar response[you have to measure many different horiztonal/vertical angles]. It's also the only way to get useful data on resonances, etc.. Far field sine wave sweep in a real room is useful, for certain limited purposes[like an idea of final tonal balance and low frequency room response], but it masks all sorts of critical performance issues.

-Chris

 

[WmAx]

Might it be that the larger cubes CR is testing are better-performing (and indeed less expensive) in terms of smoothness of response, resonance, and reach into the mid-bass region?

I don't know.

-Chris

 

[Audioholics]

This horse is beat dead, believe me...