Allison on Soundfields

[soundminded]

A "senior moment" my wife would say.

80 to 85Hz for the 901 resonance sounds plausible, more so than the 180 Hz quoted above. The 901 section of the forum links to some measurements of a series 2 EQ box. We did a fair amount of bass EQ at KEF with the KUBE series. Each one was done with a particular model in mind. It's particular fc and Q would be cancelled and a lower fc and Q would be dialed in. The power handling deficit (headroom loss from bass extension) depended on how small the speaker was and how low the extension but, very broadly, once you got past a danger zone of 40 to 50+ Hz you could extend quite low. Program material seemed to fall rapidly enough that the lowest frequencies didn't cause as much problem as the mid bass frequencies. It all ties into the statistics of music and, of course, there were always atypical exceptions.

David

"80 to 85Hz for the 901 resonance sounds plausible"

Which series and where they verified air tight? The putty on original 901 tended to dry out and crack causing air leaks which would cause lower Fc. By contrast, the putty on AR2a turned to glue. 85 hz directly contradicts Dr. Bose's design intent as stated in his white paper explaining the entire theory behind 901.

[Zilch]

Why is this hard?

Measure.

Post the impedance plot.

Done.

[speaker dave]

Why is this hard?

Measure.

Post the impedance plot.

Done.

Nooo, its way more fun to speculate and pontificate!!!

I don't have access to any 901s but here is an EQ curve lifted from and excellent post (in the 901 forum) by Mr T, Thiery Martin. We can infer that the 901's response is the inverse to this. Visualize the curve turned upside down and the response from 35 to 200 should be a close fit to the measured LF of a 901. At least that is what we lowly speaker engineers would strive for. Looks to me like a -3dB point of 95-100Hz.

Also note that the boost peaks at +17 from a midband level of -3, i.e. 20dB total boost at 35 Hz, so again, lets hope our program material doesn't have a lot going on at 35.

Regards,

David

[Robert_S]

A "senior moment" my wife would say.

A light interlude, on that selfsame subject:

'A True Senior Moment'

An elderly couple had dinner at another couple’s house, and after eating, the wives left the table and went into the kitchen.

The two elderly gentlemen were talking, and one said, ‘Last night we went out to a new restaurant, and it was really great. I'd recommend it very highly.’

The other man said, ‘What's the name of the restaurant?’

The first man thought and thought and finally said, ‘What's the name of that flower you give to someone you love? You know… the one that's red and has thorns.’

‘Do you mean a rose?’

‘Yes,’ the man said, then he turned toward the kitchen and yelled, ‘Rose, what’s the name of that restaurant we went to last night?

(Anonymous)

As you were!

[Zilch]

Also note that the boost peaks at +17 from a midband level of -3, i.e. 20dB total boost at 35 Hz, so again, lets hope our program material doesn't have a lot going on at 35.

We once had a noob on AK recommend a 901 "Super System" using three of those EQs in cascade configuration. Looking up the curve in the Bose patent revealed essentially the same curve, and a brouhaha ensued.

On his way out, he yelled, "FORGET the measurements, trust your EARS; it's the MUSIC, stupid!"

[That wasn't YOU, was it Soundminded? ]

[Pete B]

What is interesting is that we ought to step back and consider a valid comparision to a single woofer

driver. The total area is roughly the same as a 10" woofer; from memory the full mechanical Xmax is

about .25" one way, and the limit is reached with a crack against the back plate. The linear Xmax is about

1/8" from memory, a lot for the small 901 driver but rather low for a serious woofer. The total volume

displaced (VD) is not much and this is what sets the limit on low frequency max SPL. There is no magic here.

The midband efficiency is high since there is a broadband gain of 3 dB each time the number of drivers is

doubled for a total of 9 dB going from one to 8, not significantly more for the ninth.

Considering the total area of the 1" voice coils (VC) it would take a nine inch VC of the same length and wind

height to match them. This is why the power handling is so high.

A Linkwitz transform could be used to equalize the system to any new 2nd order transfer function in the bass.

Again, no magic and since the speaker and filters are minimum phase, the resulting small signal performance

will be identical to any other sealed box system with the same frequency response/transfer function.

Again, there is no magic here.

[soundminded]

What is interesting is that we ought to step back and consider a valid comparision to a single woofer

driver. The total area is roughly the same as a 10" woofer; from memory the full mechanical Xmax is

about .25" one way, and the limit is reached with a crack against the back plate. The linear Xmax is about

1/8" from memory, a lot for the small 901 driver but rather low for a serious woofer. The total volume

displaced (VD) is not much and this is what sets the limit on low frequency max SPL. There is no magic here.

The midband efficiency is high since there is a broadband gain of 3 dB each time the number of drivers is

doubled for a total of 9 dB going from one to 8, not significantly more for the ninth.

Considering the total area of the 1" voice coils (VC) it would take a nine inch VC of the same length and wind

height to match them. This is why the power handling is so high.

A Linkwitz transform could be used to equalize the system to any new 2nd order transfer function in the bass.

Again, no magic and since the speaker and filters are minimum phase, the resulting small signal performance

will be identical to any other sealed box system with the same frequency response/transfer function.

Again, there is no magic here.

I was going to post a similar thought about the equivalent aggregate area of the cones. I measured the effective diameter of the cones and they are exactly 3". This makes the total aggregate 20 pi square inches. By comparison, an AR 12" woofer has an area of 16 pi square inches. I compute the aggregate to be equivalent to a 14" driver. Tom Tyson posted that Xmax is 6 mm, about 1/4 inch. The internal volume appears to be no more than 1800 cubic inches or about 1.0 cubic feet. Each Bose 901 can therefore displace 15 cubic inches of air. Assuming an AR 12" driver's maximum excursion is 12 mm or about 1/2 inch it can move 25 cubic inches of air.

Zilch, I was not the one who posted on AK. As I have said, there is no amout of electrical power that could overcome the inertial mass of those midwoofers to make them into effective tweeters and their 4" diameter means that the front radiation of high frequencies even if it could would be only on axis. Considering how important high frequencies are to directional perception and how the front driver is credited with this due to what is commonly called "the precedence effect" it is small wonder that Bose 901 as sold does not usually exhibit the pinpoint source location of direct firing speakers. It should also be noted though of direct firing speakers that as soon as you move away from a point midway between them, the stereo effect and perceived location of the sources changes radically, much less so with Bose 901 optimally installed.

[Zilch]

This means that any statements you make about how speakers sound involve speculation and not much else.

I don't make statements about how speakers sound.

That is YOUR territory, Howard, and you are apparently well practiced in the high art of subjectivist blather....

[Zilch]

What kind of audio expert does not make "statements" about how speakers sound?

I think there are plenty of audio buffs out there who would like to know if Zilch has a CLUE about how good (or even bad) speakers sound in a good room, and one way to do that is to to have some actual information about his primary listening room. Photos are welcome.

Proof of the validity of what I do may be found in the enjoyment of those hundreds of individuals now practicing its insights, not in a photo of my listening space. Go ridicule Linkwitz's listening space. There are videos even....

[speaker dave]

As I have said, there is no amout of electrical power that could overcome the inertial mass of those midwoofers to make them into effective tweeters and their 4" diameter means that the front radiation of high frequencies even if it could would be only on axis.

Apparently, based on the EQ curve, 15dB extra power is sufficient. This is slightly less than the required bass boost. Their high directivity remains but for the rear units this doesn't matter: they are splayed on the back of the cabinet and the reflecting surfaces behind should give them dispersion (or diffusion). For the front unit, consider the level (see below).

Considering how important high frequencies are to directional perception and how the front driver is credited with this due to what is commonly called "the precedence effect" it is small wonder that Bose 901 as sold does not usually exhibit the pinpoint source location of direct firing speakers. It should also be noted though of direct firing speakers that as soon as you move away from a point midway between them, the stereo effect and perceived location of the sources changes radically, much less so with Bose 901 optimally installed.

With 8/9ths of the power radiating backwards, the Directivity Index of the system is (roughly) minus 9.5dB. That means that the direct front-firing component is 9.5dB less than that of an omnidirectional source radiating the same power. If a typical front firing system has a D.I. of (plus) 3 to 6, then its direct sound component would be 12 to 15 dB louder than that of a 901, again when the same radiated power levels are set.

Clearly, very little direct sound is available to create a virtual centered image in front of the speakers, hence little change as you shift across the mid plane between the speakers. The speaker and the room should make a nicely diffuse sound field, but, as pointed out by a number of reviewers at the time, would fail at generating focused images or in replicating solo insturments with low apparent source width.

Regards,

David

[soundminded]

Apparently, based on the EQ curve, 15dB extra power is sufficient. This is slightly less than the required bass boost. Their high directivity remains but for the rear units this doesn't matter: they are splayed on the back of the cabinet and the reflecting surfaces behind should give them dispersion (or diffusion). For the front unit, consider the level (see below).

With 8/9ths of the power radiating backwards, the Directivity Index of the system is (roughly) minus 9.5dB. That means that the direct front-firing component is 9.5dB less than that of an omnidirectional source radiating the same power. If a typical front firing system has a D.I. of (plus) 3 to 6, then its direct sound component would be 12 to 15 dB louder than that of a 901, again when the same radiated power levels are set.

Clearly, very little direct sound is available to create a virtual centered image in front of the speakers, hence little change as you shift across the mid plane between the speakers. The speaker and the room should make a nicely diffuse sound field, but, as pointed out by a number of reviewers at the time, would fail at generating focused images or in replicating solo insturments with low apparent source width.

Regards,

David

While I hear what you say, experience shows otherwise. First of all, regardless of what the measurements say, Bose 901 sounds to my critical ears to have a dull high end that lacks the clarity and sharp transient attack characteristic of even lower pitched instruments such as the attack of a bow on a cello string or the timbre of a kettle drum. Higher pitched instruments just don't sound right ever. This includes violins especially, cymbals, bells, triangles, xylophones. Instruments in the middle range don't have the overtones that give them clarity, distinctiveness and presence. This includes all brass and woodwind intstruments. Reproduction of a piano is out of the question, especially a brilliant one like a Steinway or a Baldwin particularly in its top three octaves. The upper bass peak intrudes on everything. Deep bass is usually not evident unless the speaker is driven to very loud levels. This was true for the original and series II as well as series VI, the only ones I heard but I expect it is true for all of them. While the human ear is not particularly sensitive to high frequencies, from my experience the brain makes enormous use of this sound and small changes have a big impact in the way overall sound is perceived.

Re-engineering Bose 901 changed all of that. the radiated indirect to direct sound above 9khz is around 15:1, much higher than even the 8:1 ratio of the mid and lower frequencies. What's more, that ratio of generated sound actually increases with increasing frequency by virtue of the fact that the front firing driver is equalized differently than the others. The last piece to be added was realization of the importance of reflecting high frequencies off the ceiling.

Enhancing higher frequencies not only makes it possible to correct the inaccuracies in timbre in Bose 901, it improves what people call "imagaging which I have said is usually of little concern to me. However, experiments with LVR of a Steinway piano and a similarly enhanced pair of AR9s shows that even when the timbre of the sound reproduced through the speakers matches the real piano, radical differences in the shape and directional components of the sound field between the two sources makes it impossible for a direct firing speaker to sound like the huge source of a grand piano in the same room. It's became clear no direct firing speaker could ever match that magnificent room filling sound of a grand piano except perhaps in a very large room at considerable distance, but I'm not even sure of that.

It never ceases to amaze me how audiophiles and even audio engineers treat music as some sort of abstraction. You rarely hear them talk about actual music and musical instruments yet for me, having experienced real music and recordings all of my life, live music is very real and divorcing it from the sound of recordings seems absurd. It is the only audible standard I base my judgements of audio equipment on. Here are some exercises you can try to see how good your listening is, how much you know. Play a recording of an ensemble, say a symphony orchestra, the largest and most varied music ensemble. Can you hear the difference between violins and violas? It isn't always very easy, they sound much alike especially where their ranges overlap. How about the difference between an English horn and an oboe? That can be very hard, the instruments are nearly identical. What about the difference between a trombone and a French horn...or a trumpet? A soprano saxophone and a clarinet? Listen to another recording and see if you can hear the differences between the way the same insturments sound on that one and the previous one. Now go hear a live performance and see how they sound different still. Then go back and listen to your recordings again. How do they sound different from the live instruments? What can you do about it? If you want a recording that will demonstrate the different sounds of different instruments, Benjamin Britten's "Young Person's Guide to the Orchestra" is a good choice. You will hear an entire orchestra, each of the four sections individually, and individual instruments of each section play variations of the same melody by Henry Purcell. One I have on DG is narrated by Lorin Maazel who explains at length each instrument and group. It's a good start.

[genek]

It never ceases to amaze me how audiophiles and even audio engineers treat music as some sort of abstraction.

Doesn't surprise me at all. Most people fall into one of three groups. The first doesn't have a baseline of live, unamplified listening to base a comparison on; the second is basing their comparison on a "live" baseline of mostly amplified sound; and the third knows that making too much of a quest for perfect reproduction will either result in a lifetime of excessive spending on home audio systems that will never satisfy them (if they're consumers), or an admission of failure that may impact their livelihood (if they're professionals). The only people who can do otherwise are those with unlimited amounts of time and money to devote to home audio, either as consumers or professionals.

[soundminded]

Doesn't surprise me at all. Most people fall into one of three groups. The first doesn't have a baseline of live, unamplified listening to base a comparison on; the second is basing their comparison on a "live" baseline of mostly amplified sound; and the third knows that making too much of a quest for perfect reproduction will either result in a lifetime of excessive spending on home audio systems that will never satisfy them (if they're consumers), or an admission of failure that may impact their livelihood (if they're professionals). The only people who can do otherwise are those with unlimited amounts of time and money to devote to home audio, either as consumers or professionals.

"The only people who can do otherwise are those with unlimited amounts of time and money to devote to home audio, either as consumers or professionals"

It doesn't seem that way to me. The problem isn't lack of money but of knowledge. No matter how much money you throw at a fatally flawed idea, it can't be made to work. I think that's the state of high fidelity sound reproduction today. Accurate reproduction of acoustic musical instruments is simply beyond the state of the art. What a shame so few people will ever get to experience just how beautiful that sound can be.

Zilch, have you ever tried to directly compare the sound from your Geddes inspired speakers with a grand piano? How did it fare? BTW, the fundamental frequency of the lowest note on a piano I think is around 27.5 hz. Most speakers start fallling off far above that, often an octave or more. How can they produce that lowest octave? Perhaps they should just restrict themselves to recordings of music that isn't written for those notes

[genek]

It doesn't seem that way to me. The problem isn't lack of money but of knowledge.

I was referring to the quest for perfect reproduction, not to the achievement of it.

[Zilch]

Zilch, have you ever tried to directly compare the sound from your Geddes inspired speakers with a grand piano? How did it fare? BTW, the fundamental frequency of the lowest note on a piano I think is around 27.5 hz. Most speakers start fallling off far above that, often an octave or more. How can they produce that lowest octave? Perhaps they should just restrict themselves to recordings of music that isn't written for those notes

I have not. I am one of those realists who recognizes and acknowledges the futility, and it doesn't have to be a piano; it's obvious bowing one note on a cello, or plucking one on a guitar. I have no desire, and certainly not the requisite expertise, to reinvent music reproduction from end to end. Far more comprehensive resources than any I could conceivably muster have not accomplished it successfully, and bottom line, I don't care; it's all I can do just to understand and manage the trivial....

[soundminded]

I have not. I am one of those realists who recognizes and acknowledges the futility, and it doesn't have to be a piano; it's obvious bowing one note on a cello, or plucking one on a guitar. I have no desire, and certainly not the requisite expertise, to reinvent music reproduction from end to end. Far more comprehensive resources than any I could conceivably muster have not accomplished it successfully, and bottom line, I don't care; it's all I can do just to understand and manage the trivial....

"Far more comprehensive resources than any I could conceivably muster have not accomplished it successfully, and bottom line, I don't care; it's all I can do just to understand and manage the trivial.... "

That is the frankest and most honest statement you have made IMO and more so than most others. I on the other hand continue to choose to bang my head against that brick wall. It provides and endless source of amusement and frustration those with lesser ambitions in this endeavour can hardly appreciate.

[Zilch]

That is the frankest and most honest statement you have made IMO and more so than most others.

Thank you.

It's a corollary of the pragmatist dictum, "Know when a bad wank is at hand...."

[genek]

I on the other hand continue to choose to bang my head against that brick wall. It provides and endless source of amusement and frustration those with lesser ambitions in this endeavour can hardly appreciate.

I bought my first reasonably "hifi" system while I was in college. Spent $2500 on it, which was a fair amount of change to put into a turntable, amplifier, tape deck and one pair of speakers in 1970 (my online inflation calculator claims that's almost $14000 in today's money). Shortly after that I went to my first hifi show, heard a $5,000 system and realized that it didn't sound anywhere near "twice as good" as my new system, and that was enough to prevent me from banging my head into that brick wall. Maybe I've leaned against it once or twice since then, but no bruises. If I heard something I considered "better enough" to justify the purchase I could now easily spend 10x what I put into that first system, but considering that I'm still using many of its components nearly 40 years later, you can probably guess that I still haven't heard it.

Don't think that nobody appreciates all the brick wall headbanging just because we don't join in. Even if we don't experience frustration about the current state of the art in audio, we are often endlessly amused by other peoples'.

[Zilch]

Certainly, somebody out there has been to Zilch's place. Will they please speak up and give us a clue about this guy's domain.

My domain comprises hundreds of listeners on four continents thus far, Howard.

There's little point in concerning yourself, however, as this is the realm of the venturesome; you'd be decidedly out of place here....

[Zilch]

If you had a decent listening space you would not waste a New York minute at putting a picture of it out for all your fans to admire. After all, you just bragged about your fans "on four continents." So don't try to be witty and dodge the issue about your listening space. You are painfully aware that if you posted a picture for your panting followers to look over you would be marginalized ASAP.

O.K. Howard, how bad is this?

[Carlspeak]

O.K. Howard, how bad is this?

C'mon Zilch. This site thrives on honesty, not tomfoolery. That's Siegfried's L's room, not yours.

[Zilch]

C'mon Zilch. This site thrives on honesty, not tomfoolery. That's Siegfried's L's room, not yours.

SPOILER!

Just giving Howard opportunity to trash more loudspeaker gurus' listening spaces here.

He's already summarily dismissed Toole's as that of an obvious quack....

[Zilch]

Looking REAL closely, I'm betting even YOU could find the "Edit" button, Howard....

[soundminded]

Hmmm. Well, you are indeed a trickster and a con artist, Zilch. If we cannot trust you to give us a valid photo of your listening space (swiping one from somebody else), how can we or anybody else trust you to give us valid information about speaker performance?

Toole isn't a quack. He is just a man with an agenda that excludes a whole raft of speaker designs that do not fit into his paradigm. That fits you, too, but at least Toole has a decent listening room and of course had access to decent rooms when he was with both the NRC and Harman. And he actually has listened to ultra-wide-dispersion main-channel speakers (at least that is what he indicated to me), but he simply ignored them when he wrote his book, probably because they skewed the paradigm.

Howard Ferstler

I don't know what you're crowing about Howard. Your listening rooms don't look like Boston Symphony Hall, Concertgebouw, or Musikverein to me, they just look like ordinary rooms in houses. And because that's what they are, they can't produce the acoustical effect that would turn a recording of a symphony orchestra into something that resembles the sound of beautiful music. On the other hand, perhaps with careful adjustment, your equipment could be made to sound like one or a few instruments as they might be heard if they were in your room. That's still a very tough problem.

Toole may not be a quack but he is a fraud. He has scientific training but he is a marketer or market researcher masquerading as a scientist. Every one of his papers starts off paying lip service to reporducing the sound of music accurately and then veers off into the realm of what he has discovered people like. It appears that it will start out as science but he quickly gets away from that. Like all others who have studied this problem and published, his analysis is inaccurate, incomplete, and badly flawed. His products reflect the limits and limitations of his understanding.

[Zilch]

His products reflect the limits and limitations of his understanding.

And your products reflect what?