Open Baffle Suggestions

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JamesD
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#76

Post by JamesD »

Lowther EX4 sensitivity 99.5db/1W/1M.

AER Mk.1 sensitivity 102.5dB/1W/1M

However in the Quasar the AER sensitivity is reduced due to the series crossover design and the Quasar is 98dB/1W/1M so it might appear a little less sensitive than the EX4.

In terms of how much support the bass helper can give the fullranger in the Quasar - the Supravox 285GMF is flat to 6KHz so both drivers can run together up to the Lowther peak if needed...

As an illustration of the typical Lowther response here is the EX3 http://www.troelsgravesen.dk/Lowther.htm

The Supravox and the baffle shape can be used to help fill in the response below 2KHz.

I'll try some modelling this weekend and see what we might be able to do...

James
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Paul Barker
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#77

Post by Paul Barker »

Is it possible to remove that modern gubbins off the back of the Lowther?
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Ray P
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#78

Post by Ray P »

Yes Paul it is; Google should reveal some info on 'how to'. Basically the module is stuck on with silicon glue, which you can slice through with a suitable blade. If you remove the back from an EX4 I believe you have a DX4.

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#79

Post by Ray P »

Here you go;

http://www.diyaudio.com/forums/full-ran ... r-ex4.html

I would go with post #4; Jon runs Lowther America and knows his stuff.

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#80

Post by Ray P »

And having mentioned Lowther America, these are the bass units specified for their large open baffle, partnered with PM5s as I recall.

http://www.ebay.co.uk/itm/Altec-Lansing ... 35c5278b18

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IslandPink
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#81

Post by IslandPink »

Quick question for James -
On the Quasar the shallow 'U' shape of the baffle lower down is helping to turn the bass into a 'cardoid' pattern to reduce room interaction , I think you have mentioned ?
Ok, so I assume this means it's tuned to be a null for the rear-wave at some bass frequency - and is this for a very low-end frequency like 40Hz, or somewhat higher-up ?
How does this transition from dipole to cardoid affect the phase of the response coming out of the front to the listener ?
Just wondering how this might best be done at a higher frequency eg. 65-70Hz , and how this would affect the crossover into the low-bass solution ( sub/tapped ) for the lowest octave.
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JamesD
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#82

Post by JamesD »

The best exposition of U-baffle theory on a single page is Linkwitz http://www.linkwitzlab.com/H-U%20woofer2.htm and he spends some time establishing the cardiod radiation pattern and how to tweak it...

Of course the Quasar isn't a simple U-Baffle as the sides are not straight and so the U-Baffle depth isn't constant depth but varies with every vertical element of the baffle height and this has two principle effects on the cardiod, one - it isn't as sharply defined as in the pure U-baffle case and, two - it extends over a much wider frequency reange than the classic case... in the Quasar case it runs from 40Hz up into the lower midrange...

It has no effect on the phase of the forward radiating acoustic wave at all - this is true around to at least +/- 60 degrees...

I guess you need to match the radiation pattern to the horn above and??? what from the tapped horn? At some frequency the tapped horn is going to be effectively omni-directional but is it at 65-70Hz - I don't know...I guess a first design would be cardiod from 65 to 700Hz?

Assuming you stay with first order crossovers then it has no additional effect on the crossover design...

Hope that helps a bit!

J
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#83

Post by IslandPink »

Thanks... to be honest it's a bit difficult to follow his poorly-annotated diagrams and the equivalent circuit is a bit of an abstract step up for me - I might get more from that page in the future .
I understand the 'blending' effect that comes from the slanted sides , that's OK .
I think I need to start from basics : and I'm struggling to see how the U-baffle makes much difference at low frequencies .
If we take 70Hz, then the wavelength is 4.8m, and 1/2 wave is 2.4m, 1/4 wave is 1.2m . How can side-panels that are eg. 50cm deep, have much effect at 70Hz ( or lower in the case of the Quasar ? ) .
Is it that the floor-gain starts to be dominant below 100Hz ?

In my case I don't really need to do too much up at 600-700Hz where it crosses to the horn . I suppose room nodes are becoming less important up there, anyway ?
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#84

Post by steve s »

JamesD wrote:Lowther EX4 sensitivity 99.5db/1W/1M.

AER Mk.1 sensitivity 102.5dB/1W/1M

However in the Quasar the AER sensitivity is reduced due to the series crossover design and the Quasar is 98dB/1W/1M so it might appear a little less sensitive than the EX4.

In terms of how much support the bass helper can give the fullranger in the Quasar - the Supravox 285GMF is flat to 6KHz so both drivers can run together up to the Lowther peak if needed...

As an illustration of the typical Lowther response here is the EX3 http://www.troelsgravesen.dk/Lowther.htm

The Supravox and the baffle shape can be used to help fill in the response below 2KHz.

I'll try some modelling this weekend and see what we might be able to do...

James
Thats interesting james, when i have had my amps on your speakers they always gave less volume than the lowther, there is something going on, i've seen measurements that show the aer mk i less efficient than that, not aer measurements i should add, just cant remember where..
That troelgravesen link is the one to batter lowthers owners with.. I have measured one of my ex4 and achieved a very similar result along with slight distortion in the sound, so i cant dispute it..
But I would like to add that my measurements where on a brand new driver, and it was compared directly to a well run in driver with was much smoother and clean and sweet, i m sure the well run in sound is the one that Ray knows

http://www.quarter-wave.com/Project04/DX4_Data.html
This response is much the same as i measured and was surprised to find a 30 deg off axis response which supported my experience.
I have alway wondered why a driver that is very close to a lowther and according to independent measures is very close , can sound so different at our meets with the volume turned up
i also don't quite understand the reference to the voice coil length / air gap height in the aer blurb they use it as a selling point. but i can think of something they may have done to achieve the effects or difference to the lowther
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#85

Post by chris661 »

IslandPink wrote:Thanks... to be honest it's a bit difficult to follow his poorly-annotated diagrams and the equivalent circuit is a bit of an abstract step up for me - I might get more from that page in the future .
I understand the 'blending' effect that comes from the slanted sides , that's OK .
I think I need to start from basics : and I'm struggling to see how the U-baffle makes much difference at low frequencies .
If we take 70Hz, then the wavelength is 4.8m, and 1/2 wave is 2.4m, 1/4 wave is 1.2m . How can side-panels that are eg. 50cm deep, have much effect at 70Hz ( or lower in the case of the Quasar ? ) .
Yep, Linkwitz's diagrams aren't the easiest to follow.

Apart from altering the polar plots (Linkwitz uses slightly unrealistic dimensions - a 0.6m deep U-frame? No thanks....), you effectively make the baffle wider.
Wider baffles mean you start your dipole losses off at a lower frequency - dimensions are bigger, so wavelengths need to be longer to wrap around and interfere.
Then you take the usual -6dB/octave dipole loses and you're doing much better than a flat baffle the same frontal size as the U-frame.
At very low frequencies, I think its fair to say all that matters is the path length: even Linkwitz's polar plots were looking rather dipole.

HTH
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Ray P
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#86

Post by Ray P »

steve s wrote:...i m sure the well run in sound is the one that Ray knows
Quite so Steve, I worked them hard on an old solid state amp for a while when I first got them. I love the sounds they deliver and my criticism of my current speakers would be around the bottom end where the horn is running things, it just doesn't match up to the direct radiation from the lowther, hence my interest with this thread.

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IslandPink
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#87

Post by IslandPink »

Thanks Chris . I see what you mean about the U-baffle being like a wider baffle as you have to 'go around' it all . I think I need to dig into Linkwitz's site more to understand his nomenclature for the diagrams . Are they all theoretical diags though, or are some 'measured' ?
You say the response becomes more dipole at low frequencies, but diagram 4 shows it still pretty-much cardoid at 30Hz ..?

Meanwhile, 'nicoch' posted an interesting link on the other thread . May be of interest , although I suppose Fs is likely to be too high ? :
http://wgs4.com/content/g15a
http://wgs4.com/content/g15c
No data on the alnico one, maybe similar to the ceramic .
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#88

Post by Scottmoose »

steve s wrote: I have alway wondered why a driver that is very close to a lowther and according to independent measures is very close , can sound so different at our meets with the volume turned up
i also don't quite understand the reference to the voice coil length / air gap height in the aer blurb they use it as a selling point. but i can think of something they may have done to achieve the effects or difference to the lowther
Lots of possible reasons, but the air-gap height & VC length mentioned contain, or at least cover, a few. For example, take the B*L factor. It's not necessarily a constant; it's a curve. Magnetic flux density in the VC gap varies depending on the details of the motor design; usually toward the ends it becomes weaker; how much & to what extent it's countered of course also varies with this. This changes the distortion behaviour of the driver, amongst other things.
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#89

Post by JamesD »

And in terms of the similarity to a Lowther the AER is only superficially the same i.e. physical dimensions and very high level design. The chassis design is different, the motor design is different the cone design is different and uses different paper, the voice coil and gap designs are different, etc. etc. In other words the engineering is totally different - if it wasn't you can bet that Lowther would have sued - so no wonder it sounds different but with some of the same characteristics -

Its interesting that Lowther have a whole family of drivers, as do AER, as do Voxativ... that all sound different from one another but all have a family sound too...

And its interesting that there are a whole raft of other twin cone drivers that sound nothing like any of these!

J
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#90

Post by chris661 »

IslandPink wrote:Thanks Chris . I see what you mean about the U-baffle being like a wider baffle as you have to 'go around' it all . I think I need to dig into Linkwitz's site more to understand his nomenclature for the diagrams . Are they all theoretical diags though, or are some 'measured' ?
You say the response becomes more dipole at low frequencies, but diagram 4 shows it still pretty-much cardoid at 30Hz ..?

Meanwhile, 'nicoch' posted an interesting link on the other thread . May be of interest , although I suppose Fs is likely to be too high ? :
http://wgs4.com/content/g15a
http://wgs4.com/content/g15c
No data on the alnico one, maybe similar to the ceramic .
The Zw=1000 suggests to me that he's effectively absorbed most of the back-wave. Lots of different ways to do this, though translating between density of stuffing and the impedance there is beyond me.

That said, if you put a pillow in the back of a u-frame, the response should start looking more cardoid at LF. Without any absorption, however, I can't see how the response would become anything other than dipole...

Chris
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