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The Goals for an "Ideal Loudspeaker"

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Can we add "home workshop capability independent" to the list of goals? :)

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And can approach your 120° and DI = 6 spec, as well:

http://www.jblpro.com/catalog/support/getf...&docid=1079

Though I'd argue against that.

The 120 degree wide looks pretty reasonable to me. d.i. is more like 8, but put DSP EQ on it and add a sub and you may be done.

We were trying to define listening windows for brochures at Snell and it seemed like, on a cursory listen, that when you fell about 2dB into a crossover hole it was pretty evident. So, if you define best response as no more than 2dB variation from on axis, you don't get a lot of listening window width. Even with a 120 degree wide waveguide you only have about +- 20 or so for -2dB, and even less for vertical shift.

David

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I've seen it stated many times that the ideal loudspeaker would be suitable for use across a wide range of reproduction applications -- two-channel music, multichannel, home theater, studio monitor, sound reinforcement, even.

Do we buy that as a goal?

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I've seen it stated many times that the ideal loudspeaker would be suitable for use across a wide range of reproduction applications -- two-channel music, multichannel, home theater, studio monitor, sound reinforcement, even.

Do we buy that as a goal?

Certainly WRT to two-channel, multichannel and home theater. I do that with mine and would expect it from any speaker that is supposedly better than what I have now. I don't know what special requirements a studio monitor or sound reinforcement speaker might have compared to a home speaker, and if meeting them would make the speaker more expensive, harder to move around, or visually unattractive, I'd prefer the speaker come in home and professional versions rather than a one-size-fits-all.

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Over the years, many designs have been made in both standard and "utility" models, among these, even the JBL Paragon.

In original large Advents, I have read that the vinyl-clad utility outsold the furniture-finish variant.... :)

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Over the years, many designs have been made in both standard and "utility" models, among these, even the JBL Paragon.

In original large Advents, I have read that the vinyl-clad utility outsold the furniture-finish variant.... :)

AR's were the unfinished pines; fine with me as long as they aren't the only choice, but what I was thinking about was more along the lines of 10000 watt power handling or the ability to survive being thrown off a truck. If the ideal speaker does everything I want it to do it won't bother me one bit if it has other capabilities, as long as they don't make it unnecessarily (to me) expensive or harder to use in a home.

Advents were marketed heavily at starving students; I think the ones who picked the vinyl boxes to save $30 a pair are the ones responsible for all that black stuff that I hate today.

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AR's were the unfinished pines; fine with me as long as they aren't the only choice, but what I was thinking about was more along the lines of 10000 watt power handling or the ability to survive being thrown off a truck. If the ideal speaker does everything I want it to do it won't bother me one bit if it has other capabilities, as long as they don't make it unnecessarily (to me) expensive or harder to use in a home.

Advents were marketed heavily at starving students; I think the ones who picked the vinyl boxes to save $30 a pair are the ones responsible for all that black stuff that I hate today.

In retrospect, it's absolutely astonishing that the difference in Advent's cabinet choices were only $14 (102-116), or that the 2ax difference was a mere $19.00 (109-128).

Couldn't be done today for anywhere near that little a difference.

Steve F.

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In retrospect, it's absolutely astonishing that the difference in Advent's cabinet choices were only $14 (102-116), or that the 2ax difference was a mere $19.00 (109-128).

Couldn't be done today for anywhere near that little a difference.

AR cabinets during the classic period were sourced from relatively small domestic suppliers and involved a fairly large amount of handwork, so the difference in cost between the finish options were primarily based on the materials. With today's automated/offshored high-volume

manufacturing methods, if "ideal speaker" is produced in any sizable quantity you'll probably have to pay more for an unfinished "utility" version.

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I've seen it stated many times that the ideal loudspeaker would be suitable for use across a wide range of reproduction applications -- two-channel music, multichannel, home theater, studio monitor, sound reinforcement, even.

Do we buy that as a goal?

I think the goals of accuracy would be similar for speakers of any intended use, but obviously sound reinforcement or studio use places extra demands and some compromises may be called for. Needs for higher SPL will always force some compromise. I put a lot of effort into getting KEF KM1's to play loud enough for studio use without degrading fidelity.

There have been some interesting papers that point out that studio people want higher directivity for studio use and wider directivity at home.

Coverage requirements are a specific PA need. I'm typically doing calculations of best height behind the screen and right CD horn to use, to balance out the level across a cinema audience. That isn't an issue for domestic systems.

David

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I'm typically doing calculations of best height behind the screen and right CD horn to use, to balance out the level across a cinema audience. That isn't an issue for domestic systems.

Wouldn't they be similar, directivity-wise, for a domestic home theater, particularly a multi-row one?

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I think the goals of accuracy would be similar for speakers of any intended use, but obviously sound reinforcement or studio use places extra demands and some compromises may be called for. Needs for higher SPL will always force some compromise. I put a lot of effort into getting KEF KM1's to play loud enough for studio use without degrading fidelity.

David

Hi David,

What role did you play in the design of the KEF KM1? Was Laurie Fincham still there when it was designed?

For those not familiar with that design, it was (and is) a fine, no-compromise studio loudspeaker. It seemed capable of very high acoustic outputs (something like 120 dB SPL in the 60-20 kHz range at one meter). I don't have the impression that it was a commercial success as a studio monitor, but I always felt that it was "as good as it got" for such a speaker! Extremely heavy and extremely expensive!

--Tom Tyson

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Wouldn't they be similar, directivity-wise, for a domestic home theater, particularly a multi-row one?

The issue with cinemas is the large distances and greater depth involved. Typically the back row is 2 to 3 times the distance of the front row so you might have 6 to 9 dB drop of the direct sound. A well behaved horn at the right height can have the back row on axis, the front row sufficiently off axis to largely compensate for the level difference. I haven't seen a home theater with that depth. Usually they are set up for the "money seat"(he who pays the bills).

There have been some horns optimized for oblique coverage of an audience by JBL, Altec and EV.

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Hi David,

What role did you play in the design of the KEF KM1? Was Laurie Fincham still there when it was designed?

--Tom Tyson

I was hired by Laurie from JBL when the early prototypes of the KM1 were running. I was to turn it into a viable pro monitor. Ric Cicconi and I did the design work and then I was in charge of building and selling it to studios.

It wasn't a commerical success but was a good new-idea test bed. The biggest challenge was hitting the SPLs required without using horns and compression drivers. Besides the usual thermal issues we would have bextrene cones crack and fail from acceleration.

Initially we had power protection that injected a little DC through each voice coil and shut off the amps when the DCR rise indicated excessive temperature. That was replaced by an analog simulator that used two time constants for each driver. A fast time constant represented the voice coil temperature rise. A slow time constant represented the heating of the frame and magnet structure.

Over the top engineering in the usual KEF way.

David

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I was hired by Laurie from JBL when the early prototypes of the KM1 were running. I was to turn it into a viable pro monitor. Ric Cicconi and I did the design work and then I was in charge of building and selling it to studios.

It wasn't a commerical success but was a good new-idea test bed. The biggest challenge was hitting the SPLs required without using horns and compression drivers. Besides the usual thermal issues we would have bextrene cones crack and fail from acceleration.

Initially we had power protection that injected a little DC through each voice coil and shut off the amps when the DCR rise indicated excessive temperature. That was replaced by an analog simulator that used two time constants for each driver. A fast time constant represented the voice coil temperature rise. A slow time constant represented the heating of the frame and magnet structure.

Over the top engineering in the usual KEF way.

David

What became of the KM1? How many were produced, and how many years was it in production? I supect that replacement parts would be very difficult to source today. This speaker had a sort of AR-LST appearance, and the design goal was about the same: greater SPL while maintaining linearity and accuracy. Obviously, it was a very sophisticated design.

The KEF KM1 reminds me of the B&W 800, the large speaker designed for studios, but never particularly successful. I think that B&W took the design criteria and put it into the hugely successful 801 and the family of speakers that followed -- arguably the most successful of the "high-accuracy" monitors of that era.

--Tom Tyson

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What became of the KM1? How many were produced, and how many years was it in production? I supect that replacement parts would be very difficult to source today. This speaker had a sort of AR-LST appearance, and the design goal was about the same: greater SPL while maintaining linearity and accuracy. Obviously, it was a very sophisticated design.

We didn't make that many, either 50 units or 50 pair, I can't remember exactly. Some went to studios around the UK, such as the BBC Maida Vale facility. Others were bought by the rich including in Saudi Arabia and Hong Kong. I know a year or two after I left they tossed the central frames and a few cabinets that were still unbuilt. The woofer was stock B300, so it would have been available. The tweeter was stock T52 except for a better adhered rear damping ring and special braids. The mid was full custom, initially bextrene SP1052 derived, then became a custom polypro cone. Electronics were Quad 405 mkII output amp cards and proprietary input and EQ. Peter Baxandall did consulting on a special transformer balanced input stage (He was a brilliant engineer. I still have the long and lucid engineering reports he wrote.)

If you want the story behind them, the BBC was on strike one summer. The non-union people were still at work with nothing to do so they invited Laurie to come in and give a talk on speakers and sound reproduction. During that talk somebody challenged him to make a "really good sounding" studio monitor. The goal was to take the KEF 105 and "add 12dB". Four woofers would achieve that at LF but we needed two mids and one tweet to make a sensible array, in dispersion terms. We used 8 Quad amp cards running with 4 ohm loads: 150 watts each or a total of 1200 watts. There were only 7 drivers so the tweeter got 2! It was our first use of ferrofuid and we worried about the fluid boiling (turns to sludge) hence the special thermal protection. The cabinet looks a bit like 4 105 cabinets turned sideways and stacked. It was also good for dispersion and response. Ric told me he took the central midrange cabinet and put some hinged wings on it. The response was best when the wings were folded back to the angle in your photo.

The KEF KM1 reminds me of the B&W 800, the large speaker designed for studios, but never particularly successful. I think that B&W took the design criteria and put it into the hugely successful 801 and the family of speakers that followed -- arguably the most successful of the "high-accuracy" monitors of that era.

--Tom Tyson

I remember an 808 also, or are we thinking of the same model?. I believe the 801 came first and then they wanted to make something with a more useful form factor for studio use. I remember seeing them at Abbey Road (name dropper!)

Regards,

David

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I think the goals of accuracy would be similar for speakers of any intended use, but obviously sound reinforcement or studio use places extra demands and some compromises may be called for. Needs for higher SPL will always force some compromise.

The home theater DIYers demand that the mains meet THX spec, which they calc as implying 115dB max continuous SPL for mains. Sounds like studios want similar capabilities, which would also be compatible with many SR applications.

One formula for getting there is high-efficiency (read "Pro audio") woofers, compression driver horns/waveguides, and multiple subs. That little 8" AC18 specs at 116dB, and the dual-woofer variant AC28 at 120dB:

http://www.jblpro.com/catalog/support/getf...&docid=1083

If KM1 had similar SPL capability, then as a goal, multi-use may not be unrealistic.... :)

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We didn't make that many, either 50 units or 50 pair, I can't remember exactly. Some went to studios around the UK, such as the BBC Maida Vale facility. Others were bought by the rich including in Saudi Arabia and Hong Kong. I know a year or two after I left they tossed the central frames and a few cabinets that were still unbuilt. The woofer was stock B300, so it would have been available. The tweeter was stock T52 except for a better adhered rear damping ring and special braids. The mid was full custom, initially bextrene SP1052 derived, then became a custom polypro cone. Electronics were Quad 405 mkII output amp cards and proprietary input and EQ. Peter Baxandall did consulting on a special transformer balanced input stage (He was a brilliant engineer. I still have the long and lucid engineering reports he wrote.)

If you want the story behind them, the BBC was on strike one summer. The non-union people were still at work with nothing to do so they invited Laurie to come in and give a talk on speakers and sound reproduction. During that talk somebody challenged him to make a "really good sounding" studio monitor. The goal was to take the KEF 105 and "add 12dB". Four woofers would achieve that at LF but we needed two mids and one tweet to make a sensible array, in dispersion terms. We used 8 Quad amp cards running with 4 ohm loads: 150 watts each or a total of 1200 watts. There were only 7 drivers so the tweeter got 2! It was our first use of ferrofuid and we worried about the fluid boiling (turns to sludge) hence the special thermal protection. The cabinet looks a bit like 4 105 cabinets turned sideways and stacked. It was also good for dispersion and response. Ric told me he took the central midrange cabinet and put some hinged wings on it. The response was best when the wings were folded back to the angle in your photo.

I remember an 808 also, or are we thinking of the same model?. I believe the 801 came first and then they wanted to make something with a more useful form factor for studio use. I remember seeing them at Abbey Road (name dropper!)

Regards,

David

David,

Thanks for that update! Yes, you are right, the B&W version (introduced at the 1984 CES by John Bowers, I believe) was indeed the 808. It also was an excellent, high-power monitor speaker. I recall that it was fairly successful in recording studios, but the 801-series was considered sufficient and sold in large numbers, and only a wealthy few people bought the 808 for home use. Nevertheless, both the KM1 and the 808 demonstrated the technological accomplishments from KEF and B&W!

--Tom Tyson

Image 1: B&W 808 in Rosewood

Image 2: B&W 808 Cutaway Drawing

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I presume the 808's were sold as mirror image pairs?

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I presume the 808's were sold as mirror image pairs?

Carl,

Yes, I believe that the B&W 808s were available only as "mirror-image" pairs, but I think most all of the KEF and B&W high-end speakers were made as left-right pairs, and only sold in this fashion. For example, I don't believe you could buy just one B&W 801 unless it was a special-order item, and the onwer's guide contained performance data (such as fr and distortion curves) for the specific pair of speakers. Both KEF and B&W also kept records on each specific speaker sold, and the companies (at one point in history) maintained replacement drivers that would closely match the batch that were installed in each speaker.

By the way, the front of the 808 was massive, but the midrange-tweeter array (MTM) was at least placed close to the left or right side of the front baffle, and the side then was trancated and slanted back away from the front, so the diffraction was probably minimized.

--Tom Tyson

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Both KEF and B&W also kept records on each specific speaker sold, and the companies (at one point in history) maintained replacement drivers that would closely match the batch that were installed in each speaker.

--Tom Tyson

I remember once asking Andy Kotsatos during a factory tour about BA's QC (which was pretty tight, since they made all their own drivers and had very good process control) and how it compared to Snell's, B&W's, et al., companies that hand-tweaked specific x-overs to specific drivers.

He derisively waved his hand and muttered that such a practice was a tribute to poor driver QC, and was not necessary if the drivers themselves were within a tight response window to begin with (BA's were routinely cookie-cutter identical), especially if the x-o components were +/- 5% or less.

Ironically, a few years later, BA bought Snell, and each company continued their respective practices.

Ya never know.

Steve F.

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I remember once asking Andy Kotsatos during a factory tour about BA's QC (which was pretty tight, since they made all their own drivers and had very good process control) and how it compared to Snell's, B&W's, et al., companies that hand-tweaked specific x-overs to specific drivers.

He derisively waved his hand and muttered that such a practice was a tribute to poor driver QC, and was not necessary if the drivers themselves were within a tight response window to begin with (BA's were routinely cookie-cutter identical), especially if the x-o components were +/- 5% or less.

Ironically, a few years later, BA bought Snell, and each company continued their respective practices.

Ya never know.

Steve F.

Hi Steve,

Well, that's a damned-good answer from an outspoken man who was fast on his feet! What else was he going to say? I would think, however, that those companies had excellent quality control, and I believe both companies built many of their drivers in-house. That is interesting about Snell, however. Thanks, Steve!

--Tom Tyson

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I remember once asking Andy Kotsatos during a factory tour about BA's QC (which was pretty tight, since they made all their own drivers and had very good process control) and how it compared to Snell's, B&W's, et al., companies that hand-tweaked specific x-overs to specific drivers.

He derisively waved his hand and muttered that such a practice was a tribute to poor driver QC, and was not necessary if the drivers themselves were within a tight response window to begin with (BA's were routinely cookie-cutter identical), especially if the x-o components were +/- 5% or less.

Ironically, a few years later, BA bought Snell, and each company continued their respective practices.

Ya never know.

Steve F.

I got pressure from Andy to discontinue the practice but I managed to evade it while I was there. It was part of the Snell DNA, hence a marketing tool as well as a quality objective, I argued.

BA consistency was pretty good but I think there was a little bit of fooling themselves as well. For example, they would argue that they wanted +- 2 (on sensitivity and broad errors) and the measuring system had and inherent +-1dB uncertainty, so they would allow +-3 for a pass. I argued that was backwards: if you want +- 2, and the measurements give you +- 1 as a potential error, you would have to reject outside of +-1 to be sure of achieving your desired tolerance.

I didn't expect to win that arguement but the underlying notion is correct.

The Snell approach was brute force and I think a sorting approach could have done about as well.

At KEF, Reference series was built in batches of 96 and the computer would sort them into best pairs. Woofer pairs and tweeter pairs of the same sensitivity were then linked together. With crossovers, capacitors would be sorted into tolerance bands and inductors would be wound and linked to each cap group in a compensatory way. It was all very clever but a bit too cumbersome to really be practical. I wonder how the Chinese factory is handling it today??

David

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