Isobaric back to back lowers sf up to 10 Hz ?

[Tangband]

Thinking back on it now, I just had a handful or so of fluff (either Polyfill or long-haired wool) in the isochamber, and it was clearly inadequate for absorbing the midrange energy off the back of the front cone, and off the front of the back cone. In retrospect a geometry more like Tiefenbrun's in the patent application, with a thick slab of high-quality foam in the isochamber and separating the two woofers, probably would have worked a lot better. Maybe THAT is what makes the Totem Mani successful, or is at least part of it.

Linn made an isobaric two-way called the SARA and so presumably they found a solution to the midrange issue that de-railed my efforts to do something similar.



Back in the 90's I tried to design a subwoofer "fast enough" to keep up with Maggies and Quads, my theory being that there would be a market for such (I was still an amateur at that stage, but with aspirations). I tried just about everything except horns, including an amp with circuitry which allowed adjustment of the effective driver electrical Q, and eventually gave up. Years later Earl Geddes taught me that the dominant issue regarding sound quality in the bass region was room interaction, and so I started using his ideas with his permission, manufacturing a commercial distributed mult-sub system (having crossed over to the "dark side" by then). NOT trying to dissuade you from your quest! Just relating my own experience.

Very interesting .
The constructor Dr. Rod Crawford at Legend acoustics who made the Linn Keltik, the newer version of Linn isobarik in the ninethies , and the Linn Sara II has come out with a new construction - named Legend ultimate isobaric.
He has overcome the difficulties in a two way isobaric with a 3-way dsp speaker.

He writes:

“Ultimate Isobaric”. That’s the tentative name of a new prototype loudspeaker I have just built. The ‘Ultimate’ part comes partly from being one of our Ultimate series that are DEQX-active loudspeakers but also because it aims to be as good a 3-way stand-mount loudspeaker as I can make without the silly money of some high-end loudspeakers.
And the “Isobaric” part comes from its bass driver configuration with a second driver in a small closed chamber behind the outer one. I first came across it while working at Linn in Glasgow when I redesigned crossovers for their Sara and DMS Isobarik speakers – and totally designed the DMS’s replacement, the Keltik. As described in an earlier post the term ‘isobaric’ (meaning equal pressure) is actually a misnomer and a better description is the 2 closely coupled bass drivers have double the mass so lowering their resonant frequency by 1/sqrt(2) or about 40%. However the term ‘isobaric’ remains entrenched in history!
Legend’s Ultimate Isobaric also has its roots in the Isobaric Small Red (ISR). It has a similar pyramidal shape that minimizes internal standing waves from the bass units with non-parallel sides – and minimizes the amount of baffle around each driver leading to lower diffraction effects.
However the bass driver is much improved being a true subwoofer driver. It has 8.5” rather than 6.5” diameter and a much longer throw with a dual magnet system so it can go much deeper and louder with lower distortion. As the attached graphs show the in-room frequency response at 3m goes down to 20 Hz.
I have also changed the mid driver - from 3” to 4” diameter and again with longer throw. This allows it to go louder with more ease to match the new bass drivers. The mid driver now has a sealed conical chamber behind it with no parallel walls so internal standing waves are further minimized,
Finally we have retained the beryllium tweeter from the ISR because it is one of the best available!
The Ultimate Isobaric is ‘DEQX-active’ ie each driver is connected directly to a separate power amplifier channel without intervening passive crossovers - so the speaker is very dynamic, both micro and macro, with great foot-tapping ability/PRAT and detail resolving. The crossovers of frequencies to the various drivers are performed very accurately in the digital domain before the power amplifiers by a DEQX processor that also keeps the drivers in time alignment and corrects for any of their frequency anomalies – so the overall response is very flat in both the frequency and time domains for superb tonal reproduction.
In summary the Ultimate Isobaric prototype is as good as I hoped it would be. It has superb dynamics and resolution plus a very accurate frequency and time response from around 20 Hz to over 30 kHz – what more could one want? Yes, it really does sound ‘like being there’!!”
——————

”This is a brief follow-up of a couple of posts ago on Legend’s "Ultimate Isobaric” prototype. It is a DEQX-active speaker that is an upgrade to the Isobaric Small Red with a larger, longer throw sub-woofer type bass driver and a slightly larger midrange unit in a cone-shaped back enclosure - but the same beryllium dome tweeter.
Having listened to it almost exclusively over the past couple of months I continue to be amazed at how good it is! One of the main changes is its greater sense of scale with a wider range of dynamics that is particularly important when listening to orchestral music. But in addition to this increased macro-dynamics it maintains all the micro-dynamics & ability of resolve fine detail and to separate instruments during complex passages. Bass is unusually clear and the textures of bass instruments well resolved rather than the normal dull thud.
I think this sound character (or rather lack of it) is closely related to the Ultimate Isobaric's low distortion over a very wide range of frequencies as the attached graph shows. Even down to 80Hz it is below 0.3% - and around 0.1% for much of the mid-band and treble.
For the measurement purists it should be noted that the measurements were made at 25 cm - to get the signal to noise ratio up sufficiently to measure these low distortions - so the scale on the SPL axis is not normal. Measured at the standard 1 m the actual SPL at 1 kHz was 92 dB. Also the measurements were made midway between the mid and tweeter so the bass unit was significantly further away and its measured SPL is therefore smaller – but still has significant output down to 30 Hz!”

 

[mmi]

The constructor Dr. Rod Crawford at Legend acoustics who made the Linn Keltik, the newer version of Linn isobarik in the ninethies , and the Linn Sara II has come out with a new construction - named Legend ultimate isobaric.
He has overcome the difficulties in a two way isobaric with a 3-way dsp speaker.

More on isobaric over here from him: https://www.facebook.com/legendspea...ersion-of-legends-tripos-lo/2901909516789650/ but with slightly different outcome:

"One small surprise is that the bass sounded slightly less loud. However there is a good reason for this. In the non-isobaric configuration the bass is slightly underdamped giving rise to a small rise in bass response– this is almost inevitable with relatively small enclosures of book-shelf speakers and subjectively can sound ‘fuller’. The double magnets of isobaric loading gives higher damping that both reduces the height of this bass peak and also makes the bass stop and start more quickly."

 

[Jaxx1138]

Isobaric requires half the air volume. Lowers second harmonic distortion. Extends low frequencies a bit. It also lowers overall group delay in the lowest frequencies. It appears that many people do not like cleaner bass, with lower distortion and extended deeper low frequency response.. They seem to prefer louder bass, with more distortion and higher group delay. I guess they are not really audiophiles after all.

 

[Jaxx1138]

You don't get "more bass," you get "a different frequency response curve" combined with less bass output compared to a normal deployment of the two woofers because you're tossing the volume displacement of one away.

Basically this is an obsolete way of doing things. Best practices now - use a driver with tons of motor and EQ it to your target response.

If by "more bass" you mean SPL in terms of doubling the displacement this is true. But you get a lower FS so you do get more bass extension into the lower frequencies with half of the sealed box space normally required. So if you need a smaller box for space saving while still achieving lower bass extension, then it would not be obsolete. It all depends on you your requirements for your particular application.

 

[jhaider]

If by "more bass" you mean SPL in terms of doubling the displacement this is true.

To be clear, you lose bass by wasting a woofer.

But you get a lower FS so you do get more bass extension into the lower frequencies with half of the sealed box space normally required.

Which is basically saying you’re doing inflexible mechanical EQ. IMO that’s archaic and dumb.

So if you need a smaller box for space saving while still achieving lower bass extension,

Or just use more suitable drive units.

 

[Jaxx1138]

To be clear, you lose bass by wasting a woofer.


Which is basically saying you’re doing inflexible mechanical EQ. IMO that’s archaic and dumb.



Or just use more suitable drive units.

Your responses do not add much to this conversation. IMO.