Here is a little experiment I'm on with at the moment.
It is an open baffle design with a sub bolted to the base.
Drivers on the open baffle section are:
Goodmans Axiom 401 12 inch lower mid/upper bass
Fostex FE108EZ upper mid/tweeter
It fits very nicely into a small room.
Steve
It is an open baffle design with a sub bolted to the base.
Drivers on the open baffle section are:
Goodmans Axiom 401 12 inch lower mid/upper bass
Fostex FE108EZ upper mid/tweeter
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It fits very nicely into a small room.
Steve
Hi,
Neat idea, and the baffles/cabinets are simple yet elegant. The rounded tops do make the baffles look somewhat like gravemarkers though - to me at least!
So what kind of subs are you using, and where does the driver face? It looks like it's facing toward the side, where the blue stuff is. How much space is there? The driver needs some room to "breathe" otherwise there can be very clearly audible damping of the response.
If you had a yen to cut another hole in the baffle and move the sub right up to it, it would look rear mounted and integrate well into the aesthetics; in fact to me the sub showing would give the speakers a more poweful, "aggressive" look.
Just my 2c, but it's a nice speaker just as it is. How is the performance?
Neat idea, and the baffles/cabinets are simple yet elegant. The rounded tops do make the baffles look somewhat like gravemarkers though - to me at least!
So what kind of subs are you using, and where does the driver face? It looks like it's facing toward the side, where the blue stuff is. How much space is there? The driver needs some room to "breathe" otherwise there can be very clearly audible damping of the response.
If you had a yen to cut another hole in the baffle and move the sub right up to it, it would look rear mounted and integrate well into the aesthetics; in fact to me the sub showing would give the speakers a more poweful, "aggressive" look.
Just my 2c, but it's a nice speaker just as it is. How is the performance?
Hi
The driver in the sub actually fires downwards. There is a slot cut into the base of each wing to allow the bass to escape to the sides and of course the sub is free to vent to the rear.
The phase of the sub is arranged so that the bass is in phase with the rear baffle radiation and crosses over to the main array at around 75Hz. There is no direct radiation of the out of phase bass through the front of the baffle.
I have spent around six months working on trying to successfully marry monopole bass with a dipole mid and treble radiation pattern, Very difficult to do but I think I have achieved the objective.
The blue towel stuffed down the side of the sub is a temporary arrangement until I fit the board over the top to isolate the sub from the baffle above. All it does is damp out a slight cavity resonance at around 500Hz that would otherwise intrude with some programme.
As to the sound of this hybrid:
It is a very even tempered sound from top to bottom. The midrange is fast and clean, without a hint of shoutiness and the bottom end is quick and deep.
The subs are a pair of Ruark Vita 50 actives and are fed via their high level inputs from the speaker outputs of my 7W PX25 single ended valve amplifier.
As to their looks: my 23 year old daughter reckons I need to stencil R I P around the inside of the rounded tops But my wife likes the looks.
Steve
The driver in the sub actually fires downwards. There is a slot cut into the base of each wing to allow the bass to escape to the sides and of course the sub is free to vent to the rear.
The phase of the sub is arranged so that the bass is in phase with the rear baffle radiation and crosses over to the main array at around 75Hz. There is no direct radiation of the out of phase bass through the front of the baffle.
I have spent around six months working on trying to successfully marry monopole bass with a dipole mid and treble radiation pattern, Very difficult to do but I think I have achieved the objective.
The blue towel stuffed down the side of the sub is a temporary arrangement until I fit the board over the top to isolate the sub from the baffle above. All it does is damp out a slight cavity resonance at around 500Hz that would otherwise intrude with some programme.
As to the sound of this hybrid:
It is a very even tempered sound from top to bottom. The midrange is fast and clean, without a hint of shoutiness and the bottom end is quick and deep.
The subs are a pair of Ruark Vita 50 actives and are fed via their high level inputs from the speaker outputs of my 7W PX25 single ended valve amplifier.
As to their looks: my 23 year old daughter reckons I need to stencil R I P around the inside of the rounded tops
But my wife likes the looks.Steve
Ah - I noticed the slots in the side panels and that tipped me off, but I hadn't noticed the legs on the sub enclosure so at first it looked like it was resting directly on the bottom panel.
So, what sort of crossover design did you come up with, and how did you design it? Do you have a rough figure for the cost of the project?
So, what sort of crossover design did you come up with, and how did you design it? Do you have a rough figure for the cost of the project?
The design was evolved over a period of six months, starting with a cardboard mock- up. I'm not much of an acoustician, so it was a case of trial and error with the wing size until I got the sound balance I was after.
I was more into my comfort zone with the crossover. It is just a simple first order crossover with a 10uF polyproplylene motor run cap feeding the Fostex unit and a 4mH inductor in series with the Axiom 401. Crossover point is well clear of the critical 3khz region.
The cost is a bit vague at the moment. The subs were second hand acquisitions at £100 each the wood was £50 the Fostex FE108EZs were £70 each. The missing links are the Axiom 401s which are on loan at the moment from a fellow DIY enthusiast. There's no way I can avoid buying them from him now I've heard them (but then he probably knew that would happen when he lent them to me...crafty bugger) The 401s with the Fostexes are a match made in heaven and it would be tragic to break up the partnership
I would give a rough estimate of around $600 the pair.
Steve
I was more into my comfort zone with the crossover. It is just a simple first order crossover with a 10uF polyproplylene motor run cap feeding the Fostex unit and a 4mH inductor in series with the Axiom 401. Crossover point is well clear of the critical 3khz region.
The cost is a bit vague at the moment. The subs were second hand acquisitions at £100 each the wood was £50 the Fostex FE108EZs were £70 each. The missing links are the Axiom 401s which are on loan at the moment from a fellow DIY enthusiast. There's no way I can avoid buying them from him now I've heard them (but then he probably knew that would happen when he lent them to me...crafty bugger) The 401s with the Fostexes are a match made in heaven and it would be tragic to break up the partnership
I would give a rough estimate of around $600 the pair.
Steve
Steve Cresswell said:
From intuition I would have said: Let the sub radiate to the front and in phase with the mid front. So the omnipolar radiation pattern of the sub might have merged with the dipole pattern of the midwoofer to some sort of cardioid - at least where both are running parallel. Obviously you found it better the other way round. But did you ever try to run the sub in reverse phase? If yes, how would you describe the difference?
Hi Rudolf,
The sub is in reverse phase to the front radiation ie in phase with the rear radiation. Trying the sub in phase with the front whilst it was mounted behind the baffle resulted in an uneven bass response with audible peaks and suckouts everywhere as it fought with the out of phase signal coming from the rear of the baffle. Also there was a weird discontinuity between the two radiation patterns that was audible from the listening position.
I've heard a few panels where attempts have been made to merge a forward firing cone bass driver with a panel. Without exception the results were not exactly encouraging. Only a pair of Martin Logans came anywhere near succeeding and even then there was still a feeling that the bass was somehow detached from the rest of the spectrum.
Alas I have no measuring equipment to measure the response in-room. Therefore I can't prove that what I'm hearing is any more than self-deception. The point is that it works beautifully and is the most realistic and musical sound I've had in 35 years of playing around with this hobby.
Of course that is not much good for those wanting to reproduce the design in a different environment. I'm not exactly scientific in my approach to speaker design
Steve
The sub is in reverse phase to the front radiation ie in phase with the rear radiation. Trying the sub in phase with the front whilst it was mounted behind the baffle resulted in an uneven bass response with audible peaks and suckouts everywhere as it fought with the out of phase signal coming from the rear of the baffle. Also there was a weird discontinuity between the two radiation patterns that was audible from the listening position.
I've heard a few panels where attempts have been made to merge a forward firing cone bass driver with a panel. Without exception the results were not exactly encouraging. Only a pair of Martin Logans came anywhere near succeeding and even then there was still a feeling that the bass was somehow detached from the rest of the spectrum.
Alas I have no measuring equipment to measure the response in-room. Therefore I can't prove that what I'm hearing is any more than self-deception. The point is that it works beautifully and is the most realistic and musical sound I've had in 35 years of playing around with this hobby.
Of course that is not much good for those wanting to reproduce the design in a different environment. I'm not exactly scientific in my approach to speaker design
Steve
How about this:
Making the sub in phase with the FRONT of the woofer, and lifting the whole baffle for a gap to floor -- thus you may get a polar response similar to cardioid -- double up in the front and cancelling at the back.
From the picture, there's a gap (to floor) on the side. And the sub is out of phase with the front of woofer. So it should be major cancelling here. Also, the OB woofer has cancelling on both sides of baffle already, so I guess it's almost silent around the gap now.
Making the sub in phase with the FRONT of the woofer, and lifting the whole baffle for a gap to floor -- thus you may get a polar response similar to cardioid -- double up in the front and cancelling at the back.
From the picture, there's a gap (to floor) on the side. And the sub is out of phase with the front of woofer. So it should be major cancelling here. Also, the OB woofer has cancelling on both sides of baffle already, so I guess it's almost silent around the gap now.
tinitus said:
Yes, you would have thought so. But in the small room 12' x 12' that is not the case, in fact to my ears. The midrange is well balanced with the rest of the spectrum. The crossover arrangement I have is based on Gilbert Briggs' work in the late 1950s. The dip in the mids If I had measuring gear would correspond to the classic "BBC dip" that was deliberately engineered into classic British speakers such as the LS3 5A.
With these "faults" deliberately engineered in I don't think this speaker, if it were a commercial design would have a hope in hell of selling if demonstrated against a three humped response " boom squawk and tizz" speaker in a showroom. It would simply not be exciting enough. However over the longer term, in a real room rather than an anechoic chamber, the speaker sounds well balanced with an even response from top to bottom.
A lot of the more modern designers armed with measuring microphones and Thiel Small parameters aim for a flat response at the listening position then wonder why they get a forward shouty presentation. Flat across the midrange to me equals squawk and shriek.
Bass is a different matter and really ought to be measured in-room to be correct, but an experienced ear can get pretty close to the desired effect. I agree that deliberately putting the bass out of phase via a subwoofer is counter intuitive, yet it works in my room For a larger room the bass, could be gradually put into phase with the front via the phase control until a pleasing balance is achieved.
In my earlier experiments I tried lifting the baffle off the floor and all sorts of shenanigans with the sub, but the result was too bass heavy. However on the phase front 90 degrees out of phase is very good too in the smaller room and is almost on a par with 180 degrees. In fact i'm currently listening to both phase setups trying to see which I prefer.
From bitter experience with commercial speakers, most speakers with hi-fi pretensions I have had in there sound awful. Over the years, I have come to detest the three hump response speaker, which is virtually all you can buy these days, unless you are prepared to spend thousands of pounds. And along with the loudness wars on CD mastering, I have despaired of ever getting a decent sound in that room.
To get good realistic presentation, that sounds like real music I have had to plough a furrow that has been left mostly unexplored since the 50s. The result has been frankly spectacular.
Thanks Rudolf
Tinitus,
Just a bit more on my reasons for choosing such strange crossover values.
As I said earlier, the crossover is based on the one Briggs used in his SF3 open baffle design, however there is a bit more to it than that.
The 4mH inductance in series with the 8R bass/lower mid driver will start the roll off at around 400Hz. Looking at the cap value to the tweeter, it indeed seems that there will be a huge hole in the midrange. That would be true if a conventional 12 inch bass driver was being used, in fact the system response would be similar to a three way with the midrange driver disconnected! Not good.
However the Goodmans Axiom 401 driver has a 4 inch whizzer cone incorporated into its design, which alters things drastically. For example if I wanted to cross to the upper mid tweeter at 1200Hz and 6dB/octave I would, in theory and if I was using a conventional bass/mid driver, need a 16uF cap to the tweeter and a 1mH inductor to the bass driver. Using something like a 12 inch Eminence Alpha driver, that is indeed what I would have used. No doubt after a bit of tweakery of values we would get a nice balanced sound.
BUT..... the whizzer on the Axiom 401 boosts the mid and top of the driver by about 3dB through the presence region. Using that theoretically "correct" crossover with the Axiom driver and adding its high efficiency into the equation, would almost certainly result in a lovely big midrange hump right where it would do the most damage, resulting in the most awful shout. Impressive in the short term but we would be seriously limited in the type of music that could be played before we had to hide behind the sofa in terror.
The crossover values chosen for this speaker allow the mechanical characteristics of both the Fostex and the Goodmans units to work with each other and "fill in" the hole left in the midrange. They don't quite do it, which is a good thing really as it produces a slight dip through the presence region giving a sound that is musical and livable with in the long term.
Steve
Tinitus,
Just a bit more on my reasons for choosing such strange crossover values.
As I said earlier, the crossover is based on the one Briggs used in his SF3 open baffle design, however there is a bit more to it than that.
The 4mH inductance in series with the 8R bass/lower mid driver will start the roll off at around 400Hz. Looking at the cap value to the tweeter, it indeed seems that there will be a huge hole in the midrange. That would be true if a conventional 12 inch bass driver was being used, in fact the system response would be similar to a three way with the midrange driver disconnected! Not good.
However the Goodmans Axiom 401 driver has a 4 inch whizzer cone incorporated into its design, which alters things drastically. For example if I wanted to cross to the upper mid tweeter at 1200Hz and 6dB/octave I would, in theory and if I was using a conventional bass/mid driver, need a 16uF cap to the tweeter and a 1mH inductor to the bass driver. Using something like a 12 inch Eminence Alpha driver, that is indeed what I would have used. No doubt after a bit of tweakery of values we would get a nice balanced sound.
BUT..... the whizzer on the Axiom 401 boosts the mid and top of the driver by about 3dB through the presence region. Using that theoretically "correct" crossover with the Axiom driver and adding its high efficiency into the equation, would almost certainly result in a lovely big midrange hump right where it would do the most damage, resulting in the most awful shout. Impressive in the short term but we would be seriously limited in the type of music that could be played before we had to hide behind the sofa in terror.
The crossover values chosen for this speaker allow the mechanical characteristics of both the Fostex and the Goodmans units to work with each other and "fill in" the hole left in the midrange. They don't quite do it, which is a good thing really as it produces a slight dip through the presence region giving a sound that is musical and livable with in the long term.
Steve
I have previously seen the published frequency response of the Rogers LS3/5a and from my recollection it is very flat without the classic BBC dip. Are you sure that the BBC dip was introduced in the LS3/5a?
I used to have many pairs of Rogers monitors. When comparing to most other speakers they sounded quite polite and I suspect that they have the BBC dip. Even the LS3/5a sounds polite to me but I just did not find the BBC dip in the FR graph I saw.
I am just curious.
Regards,
Bill
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