Having done few OB prototypes I have few understanding how the drivers behave on them and really want to do one now that is full-range and most importantly: Low distortion.
The obvious answer is to build an Orion but it's so expensive. Even then the W22EX is being strained to 1500Hz according to SL himself due to him needing them to cover 150Hz zone, perhaps the H-frame woofer can only cover up to 150Hz due to cavity resonances.
So I have on hand now:
- 4x Eminence alpha 15A (2 are broken in)
- 2x Vifa P13WH midbass
- 2x Vifa TC20TD tweeters (cheapish)
The objective is to operate the drivers at their "pistonic" and non-beaming properties. I have experimented using Eminence up to 1kHz as CS2 but convinced that this is way beyond its ideal operating range and although it sounded "good" and "Live" perhaps distortion is at play here. I also have played with P13WH on OB and it did not sound good at the time when run at its well-known flat response 250-5kHz, so it has to be revisited.
According to SL the rule of thumb is to operate them at 1/2 wavelength of the cone diameter. This gives:
20 - 300Hz: use 4x eminence alpha
300 - 1500: use 2x P13WH
1500 - 20kHz use 2x TC20TD.
The tweeter is bad as it has Fs of 1400 so it will need to be replaced with better one. P13WH had been extensively measured and reviewed by SL and Lynn, and I have done plenty distortion measurement on the alphas.
All will be crossed using active 4th order filters and tri-amped. Baffle width will be 45cm x 120cm (or shorter). Flat.
Is this sane thinking and what are the pitfalls here?
The obvious answer is to build an Orion but it's so expensive. Even then the W22EX is being strained to 1500Hz according to SL himself due to him needing them to cover 150Hz zone, perhaps the H-frame woofer can only cover up to 150Hz due to cavity resonances.
So I have on hand now:
- 4x Eminence alpha 15A (2 are broken in)
- 2x Vifa P13WH midbass
- 2x Vifa TC20TD tweeters (cheapish)
The objective is to operate the drivers at their "pistonic" and non-beaming properties. I have experimented using Eminence up to 1kHz as CS2 but convinced that this is way beyond its ideal operating range and although it sounded "good" and "Live" perhaps distortion is at play here. I also have played with P13WH on OB and it did not sound good at the time when run at its well-known flat response 250-5kHz, so it has to be revisited.
According to SL the rule of thumb is to operate them at 1/2 wavelength of the cone diameter. This gives:
20 - 300Hz: use 4x eminence alpha
300 - 1500: use 2x P13WH
1500 - 20kHz use 2x TC20TD.
The tweeter is bad as it has Fs of 1400 so it will need to be replaced with better one. P13WH had been extensively measured and reviewed by SL and Lynn, and I have done plenty distortion measurement on the alphas.
All will be crossed using active 4th order filters and tri-amped. Baffle width will be 45cm x 120cm (or shorter). Flat.
Is this sane thinking and what are the pitfalls here?
The P13WH midrange selection. It is interesting that the 1/2 wavelength rule coincide with that bit of dip (breakup?) at 1500Hz. Perhaps ideally the upper freq. selection should be at 1kHz but then there will be no tweeters able to cover this (?)
The other option is perhaps lower at 1300-1400Hz. Orion ASP shows that the tweeters are crossed at 1440Hz. It seems this is as low as it would go (and they're excellent tweeters).
Being small this midrange came up excellent when SL tested it. His complain is it is audibly strained when tested, maybe because of the low frequency requirement. Hopefully by running only from 300Hz up, this defficiency would not show.
"The Vifa drivers 10 (PL14WJ) and 11 (P13WH) exhibited very good burst behavior, something one might have expected for the small cones. Unfortunately, they audibly strain even at the modest volume displacements of this test series." -SL
I hope the good burst behaviour will give the speakers good clarity in the midrange. Lynn seems to emphasize them although I read as well that the Vifa changed over the years.
"I first heard the 5.5" Vifa in the Lineaum LFX, and was impressed with the wonderfully transparent midrange. I was not so impressed with the thin bass. " -LO
Again, the bass is removed from the equation by running them 300Hz up. Hopefully this is logical thinking.
The other option is perhaps lower at 1300-1400Hz. Orion ASP shows that the tweeters are crossed at 1440Hz. It seems this is as low as it would go (and they're excellent tweeters).
Being small this midrange came up excellent when SL tested it. His complain is it is audibly strained when tested, maybe because of the low frequency requirement. Hopefully by running only from 300Hz up, this defficiency would not show.
"The Vifa drivers 10 (PL14WJ) and 11 (P13WH) exhibited very good burst behavior, something one might have expected for the small cones. Unfortunately, they audibly strain even at the modest volume displacements of this test series." -SL
I hope the good burst behaviour will give the speakers good clarity in the midrange. Lynn seems to emphasize them although I read as well that the Vifa changed over the years.
"I first heard the 5.5" Vifa in the Lineaum LFX, and was impressed with the wonderfully transparent midrange. I was not so impressed with the thin bass. " -LO
Again, the bass is removed from the equation by running them 300Hz up. Hopefully this is logical thinking.
You might want to consider that if you're using 2 drivers the directivity of the pair will be different than that of a single driver. Thus if you use SL's rule of thumb for 2 tightly spaced 15s you have to (roughly) half the upper cutoff frequency to get a maximum of 150 Hz. In the long dimension the situation is actually worse than a single 30" driver though because more cone area is away from center, so if you want wide directivity you need to lower the cutoff even more.
That is very interesting. I have no experience with multiple drivers on same frequency space. I did read that SL is against 2x P13 instead of one W22 albeit the strain -- on the ground of polar response problem exhibited by multiple drivers.
Is this what's called "Lobing" ?
Halving the upper cutoff frequency to 150Hz will be problematic with the mid driver and quickly will need SL's compromise of using 8" drivers.
The other option is just use one 15" alpha per channel and compromise the extreme lows.
Is this what's called "Lobing" ?
Halving the upper cutoff frequency to 150Hz will be problematic with the mid driver and quickly will need SL's compromise of using 8" drivers.
The other option is just use one 15" alpha per channel and compromise the extreme lows.
TC20 , 2 of ???? and at 1500.. gulp !!!!
(I assume one front and one at the rear ??)
You are right about them needing replacement
Try the DX25, its got plenty and you can probably cross it anywhere from 1k up..... with a steep enough filter from a digital x-o.
And if you are concerned at running the 15" drivers one above the other, you could always run one front and one back, but still open baffle. Any PA 15" is more than comfortable reaching way above 300, in fact, most are often used as vocal rather than bass drivers, particularly ones like the Eminence alpha and beta range.
ps, and you are right about the P13WH, much better to cross it 2.5k or below than to use its full range.
(I assume one front and one at the rear ??)
You are right about them needing replacement
Try the DX25, its got plenty and you can probably cross it anywhere from 1k up..... with a steep enough filter from a digital x-o.
And if you are concerned at running the 15" drivers one above the other, you could always run one front and one back, but still open baffle. Any PA 15" is more than comfortable reaching way above 300, in fact, most are often used as vocal rather than bass drivers, particularly ones like the Eminence alpha and beta range.
ps, and you are right about the P13WH, much better to cross it 2.5k or below than to use its full range.
Thanks for the tips on DX25 Andy. Price is very reasonable, the only gripes is they only stock the 4 ohms ones at speakerbits.com
The woofer:
This should be the simpler part of the design. I have sucessfully used the alpha 15s up to 1kHz with appropriate notches. They are at 2kHz and 400+ Hz. It's really curious that the 1/2 wavelength rule coincide in this driver's frequency range as well. Hopefully crossing at 300Hz 4th order will need no more notch at 400Hz. Definitely not at 2kHz.
Shelving lowpass will be needed to compensate dipole losses and with 45cm baffle it starts around 200Hz down to high 30s. A second SLP can also be implemented to raise the frequency even more but that's pushing it. Furthermore linkwitz transform can be investigated to exploit the high Qts of the woofer.
Alpha's distortion is acceptable down to 30Hz. At 20Hz it's not. If a 20Hz tone is fed to them, they give out loud 60Hz tone. There is alot of debate about the audibility of these harmonics though and there is no harm to try to equalise them to low 20s.
30Hz:
20Hz:
The woofer:
This should be the simpler part of the design. I have sucessfully used the alpha 15s up to 1kHz with appropriate notches. They are at 2kHz and 400+ Hz. It's really curious that the 1/2 wavelength rule coincide in this driver's frequency range as well. Hopefully crossing at 300Hz 4th order will need no more notch at 400Hz. Definitely not at 2kHz.
Shelving lowpass will be needed to compensate dipole losses and with 45cm baffle it starts around 200Hz down to high 30s. A second SLP can also be implemented to raise the frequency even more but that's pushing it. Furthermore linkwitz transform can be investigated to exploit the high Qts of the woofer.
An externally hosted image should be here but it was not working when we last tested it.
Alpha's distortion is acceptable down to 30Hz. At 20Hz it's not. If a 20Hz tone is fed to them, they give out loud 60Hz tone. There is alot of debate about the audibility of these harmonics though and there is no harm to try to equalise them to low 20s.
30Hz:
An externally hosted image should be here but it was not working when we last tested it.
20Hz:
An externally hosted image should be here but it was not working when we last tested it.
gainphile and terry j,
There is really just one extremely general idea here. Suppose you have two points that are each emanating a wave (of any kind). If you are the same distance from the two they add constructively to form a wave with twice the amplitude. If you are a different distance from the two sources, they won't add perfectly because they aren't in phase- there is a phase offset from the difference in path lengths to the two sources. You might have a look at the wikipedia article:
http://en.wikipedia.org/wiki/Interference
In the case of a speaker, as you go off-axis you are closer to one side of the cone and further away from the other. At low frequencies this doesn't matter because the path length difference this creates is small compared to a wavelength and hence doesn't create much phase shift. At high frequencies this makes the speaker become more directive because the phase shift from the path length difference makes the sound coming from the near and far parts of the cone add destructively. "Lobes" occur when you get high enough in frequency where at some angle(s) off-axis you get near perfect cancelation. The drawing below illustrates the directivity of a piston (decent approximation to a speaker) at various frequencies.
Note a wider piston will become directional at lower frequencies because going the same angle off-axis creates a larger path length difference. This is the same reason why two drivers mounted on the same baffle will have greater directivity than 1. If they are arrayed vertically, the horizontal directivity will be the same, but the vertical directivity will be higher. The reason why it won't be simply the same as that of a piston of twice the diameter in the vertical dimension is that more of the radiating surface area of the pair of drivers is off-center than in the case of a piston, so going off-axis creates more cancelation.
Does that clear things up?
There is really just one extremely general idea here. Suppose you have two points that are each emanating a wave (of any kind). If you are the same distance from the two they add constructively to form a wave with twice the amplitude. If you are a different distance from the two sources, they won't add perfectly because they aren't in phase- there is a phase offset from the difference in path lengths to the two sources. You might have a look at the wikipedia article:
http://en.wikipedia.org/wiki/Interference
In the case of a speaker, as you go off-axis you are closer to one side of the cone and further away from the other. At low frequencies this doesn't matter because the path length difference this creates is small compared to a wavelength and hence doesn't create much phase shift. At high frequencies this makes the speaker become more directive because the phase shift from the path length difference makes the sound coming from the near and far parts of the cone add destructively. "Lobes" occur when you get high enough in frequency where at some angle(s) off-axis you get near perfect cancelation. The drawing below illustrates the directivity of a piston (decent approximation to a speaker) at various frequencies.
An externally hosted image should be here but it was not working when we last tested it.
Note a wider piston will become directional at lower frequencies because going the same angle off-axis creates a larger path length difference. This is the same reason why two drivers mounted on the same baffle will have greater directivity than 1. If they are arrayed vertically, the horizontal directivity will be the same, but the vertical directivity will be higher. The reason why it won't be simply the same as that of a piston of twice the diameter in the vertical dimension is that more of the radiating surface area of the pair of drivers is off-center than in the case of a piston, so going off-axis creates more cancelation.
Does that clear things up?
Thanks Ryb. That clears a lot of things. I think I'm sold to using 1 woofer per channel first and only if needed, try the second one later. I got massive bass already with 1 woofer anyway. The other issue with using 2 alphas is the tweeter axis will not be at ear height.
But, considering that horizontal directivity is less affected and normally people don't change height when listening, in practice how acceptable are these vertical lobing?
But, considering that horizontal directivity is less affected and normally people don't change height when listening, in practice how acceptable are these vertical lobing?
The issue isn't the direct sound. The issues are that (1) you have reflections (for example ceiling and floor) arriving with holes in the response and (2) that the power response (reverberent field) will be uneven. These effect the overall tonality of the system and aren't correctable with EQ upstream.
The hard part is determining the relative importance of these effects. I don't have any hard numbers for you but I think it's safe to say vertical directivity does matter but isn't as important as horizontal directivity.
Now that I think about it, I guess I never really consider the trade off you're talking about- the extra dynamics and max SPL of the 2 woofer setup for the cost of narrowed vertical directivity. I only consider setups with well-behaved directivity (in that frequency range at least) and design within that realm for the output I need. I think it's just not necessary to make that comprimise... you can use a more efficient driver and/or a different enclosure to boost the efficiency and power handling of the device. I guess I consider directivity to be non-negotiable in this case. That might not be a very useful reply but that's how I think of it.
In most speakers I do end up making a dynamics vs. directivity trade-off in the mid to high transition because at the crossover the center to center spacing of the mid and HF driver is big enough where there is a little vertical pinching if crossed where the tweeter is comfortable and a lot of stress on the tweeter if crossed low enough where the vertical directivity is smooth through the transition. The increased vertical directivity is mainly from the center to center spacing and only a little bit from the size of the mid's cone. A partial solution (what I do) to this problem is to minimize the frequency range this occurs over by using steep filters.
Enough rambling... I like the idea of starting with 1 15 and seeing if that will provide enough output. If that isn't sufficient, go from there.
The hard part is determining the relative importance of these effects. I don't have any hard numbers for you but I think it's safe to say vertical directivity does matter but isn't as important as horizontal directivity.
Now that I think about it, I guess I never really consider the trade off you're talking about- the extra dynamics and max SPL of the 2 woofer setup for the cost of narrowed vertical directivity. I only consider setups with well-behaved directivity (in that frequency range at least) and design within that realm for the output I need. I think it's just not necessary to make that comprimise... you can use a more efficient driver and/or a different enclosure to boost the efficiency and power handling of the device. I guess I consider directivity to be non-negotiable in this case. That might not be a very useful reply but that's how I think of it.
In most speakers I do end up making a dynamics vs. directivity trade-off in the mid to high transition because at the crossover the center to center spacing of the mid and HF driver is big enough where there is a little vertical pinching if crossed where the tweeter is comfortable and a lot of stress on the tweeter if crossed low enough where the vertical directivity is smooth through the transition. The increased vertical directivity is mainly from the center to center spacing and only a little bit from the size of the mid's cone. A partial solution (what I do) to this problem is to minimize the frequency range this occurs over by using steep filters.
Enough rambling... I like the idea of starting with 1 15 and seeing if that will provide enough output. If that isn't sufficient, go from there.
gainphile,
if low-distortion is what you want you will at least need a H frame for one alpha - or two alphas on an OB.
Two alphas will have the same horizontal directivity as one. Vertical directivity will be ok up to 300 Hz. IMHO two drivers will help to make at least the ceiling reflection less pronounced than a single driver. I really don´t see any lobing that could force you to "half the upper cutoff frequency to get a maximum of 150 Hz".
And please DON´T try to force a dipole to work down into low 20 Hz. You may be able to measure those 20 Hz in the near field, but it will all be sucked up by the acoustic shortcut at normal listening distances.
if low-distortion is what you want you will at least need a H frame for one alpha - or two alphas on an OB.
Two alphas will have the same horizontal directivity as one. Vertical directivity will be ok up to 300 Hz. IMHO two drivers will help to make at least the ceiling reflection less pronounced than a single driver. I really don´t see any lobing that could force you to "half the upper cutoff frequency to get a maximum of 150 Hz".
And please DON´T try to force a dipole to work down into low 20 Hz. You may be able to measure those 20 Hz in the near field, but it will all be sucked up by the acoustic shortcut at normal listening distances.
gainphile said:
You are almost certainly going to have to pad it to bring its level down to meet the dual P13's. so you could just add resistance in series if the 4 ohm impedance bothers you. You would only need one of them on the front.
If you are planning on one on the front and one on the back, you would probably need to wire the back one with variable padding of some sort, so again, not a problem.
How were you planning to wire those dual P13's.. in parallel they would give 4 ohm mids. Seems to me that that things match up nicely.
Hi Gainphile,
I'm interested in the results you get with your new take on the P-13 as a midrange.
Please keep us informed as you progress.
Are you using single or dual p-13s in this build?? as I took note of your comments on the earlier use of them and I'm plannung on using 2 in each baffles for power-handling and efficiency but they can cross higher than 1500, looking at your first baffle I think you need to get the P-13 a bit closer to one edge of the baffle and don't forget to mirror image baffles.
I'm interested in the results you get with your new take on the P-13 as a midrange.
Please keep us informed as you progress.
Are you using single or dual p-13s in this build?? as I took note of your comments on the earlier use of them and I'm plannung on using 2 in each baffles for power-handling and efficiency but they can cross higher than 1500, looking at your first baffle I think you need to get the P-13 a bit closer to one edge of the baffle and don't forget to mirror image baffles.
Thanks for all the insights! Few sketches:
This is my current prototype and I've lived with it for about 1 month, simply an alpha actively crossed at 1kHz 24db to TD20 (yes, yuck!). I primarily focus on the vocal component and quite surprisingly they are ok although both drivers are strained. Quite surprised with the high extension of the alphas though, at one stage I used them full-range. I played around with the bass with few variants of SLP filters and actually had to tone them down, so bass is plentiful.
This is what I'm designing to build now. Similiar treatment to the alphas but operating all drivers at their best ranges. Played with P13 before but passive. Hopefully going active and new frequency range will get them sound correct. I have few reservation about their rear sound radiation before when operated fullrange ("cuppy?"). The P13WH is make-or-break in this design. Lower space is reserved for second pair of alphas (in case) but I don't like the tweeters being about 15cm higher than ear level.
If the above is successful, then perhaps add another pair of alphas. I don't see the need of assistance from 40Hz upwards, so the other thinking is to use them to complement 20-35Hz. This will also remove concerns about lobing (?). But then I need another pair of amps and the system become quad-amped (or use really big inductor?). Not too much concern with gainclones.
Come to think of it, they look like an active JAMO.
This is my current prototype and I've lived with it for about 1 month, simply an alpha actively crossed at 1kHz 24db to TD20 (yes, yuck!). I primarily focus on the vocal component and quite surprisingly they are ok although both drivers are strained. Quite surprised with the high extension of the alphas though, at one stage I used them full-range. I played around with the bass with few variants of SLP filters and actually had to tone them down, so bass is plentiful.
This is what I'm designing to build now. Similiar treatment to the alphas but operating all drivers at their best ranges. Played with P13 before but passive. Hopefully going active and new frequency range will get them sound correct. I have few reservation about their rear sound radiation before when operated fullrange ("cuppy?"). The P13WH is make-or-break in this design. Lower space is reserved for second pair of alphas (in case) but I don't like the tweeters being about 15cm higher than ear level.
If the above is successful, then perhaps add another pair of alphas. I don't see the need of assistance from 40Hz upwards, so the other thinking is to use them to complement 20-35Hz. This will also remove concerns about lobing (?). But then I need another pair of amps and the system become quad-amped (or use really big inductor?). Not too much concern with gainclones.
Come to think of it, they look like an active JAMO.
Speakerbits still have a few Vifa D-27-45-06s which are considered by some to be the best sonic match, and the ones I've bought for my system, also perhaps a decent peerless tweeter, consider also that a rear firing tweeter is recommended by SL in the "Orion" pages
Thanks for the additional information on tweeters. I have done few reading on various tests and conclude that the focus would be on:
- cutoff frequency of 1.5kHz (this eliminates XT25 unfortunately)
- distortion measurement
- frequency response.
- about $50-$65 (this eliminates peerles HDS, seas, SS)
This tweeter topic is more challenging than I initially thought so I will do more reading later. Fortunately there is a wealth of information on the web.
Block diagram:
I drew up a block diagram of the system. Quite curious why Orion ASP's tweeter feed is taken from post-lowpass of the midrange. Wouldnt' that add more distortion? I simply feed it from the buffer after 5Hz HP.
I am also not sure wheter feeding the mid and tweeters from *before* 5Hz HP would yield different phase compared to the woofer.
- cutoff frequency of 1.5kHz (this eliminates XT25 unfortunately)
- distortion measurement
- frequency response.
- about $50-$65 (this eliminates peerles HDS, seas, SS)
This tweeter topic is more challenging than I initially thought so I will do more reading later. Fortunately there is a wealth of information on the web.
Block diagram:
I drew up a block diagram of the system. Quite curious why Orion ASP's tweeter feed is taken from post-lowpass of the midrange. Wouldnt' that add more distortion? I simply feed it from the buffer after 5Hz HP.
I am also not sure wheter feeding the mid and tweeters from *before* 5Hz HP would yield different phase compared to the woofer.
I don't know if you ever saw this thread about playing the Alpha full range? I know it's not relevant to this project, but thought you might be interested anyway...
http://www.audiocircle.com/circles/index.php?PHPSESSID=nrnb2v1gesmpjgt05160htgja4&topic=56536.0
http://www.audiocircle.com/circles/index.php?PHPSESSID=nrnb2v1gesmpjgt05160htgja4&topic=56536.0
Thanks for that link. I was active at the "sister thread" which was CS2 clone thread. The guys gave up and run them fullrange instead.
I built a prototype running alpha as fullrange (with passive filters and active shelvings+notches) and only needed 1 amp. But it's sonically much better crossing them at 1kHz.
I built a prototype running alpha as fullrange (with passive filters and active shelvings+notches) and only needed 1 amp. But it's sonically much better crossing them at 1kHz.
It's time to do bit of shopping and implement the circuits.
I have the components for the Shelving filters and notches for Alphas. Hopefully the P13WH would not need any. The time correction would only be able to be calculated after measuring the mounting offset, and any peaks would need to be measured first.
The values were first chosen for the critical 1.5kHz. It then uses the same C for Woofer-Mid filter. If I'm in luck Jaycar would have 40 pieces of them and I can finish before the fireworks tonight 😎
Interesting enough, the whole XO can become Orion XO just by changing 8k2 with 15k. Now If only I have spare $2k for the drivers 🙂
Op-amp uses the trusty TL072. I will investigate later wheter it's worth changing them to OPA2134 or LM 4562.
Values:
High-pass filters
Low-pass filters
!HAPPY NEW YEAR TO ALL !!
I have the components for the Shelving filters and notches for Alphas. Hopefully the P13WH would not need any. The time correction would only be able to be calculated after measuring the mounting offset, and any peaks would need to be measured first.
The values were first chosen for the critical 1.5kHz. It then uses the same C for Woofer-Mid filter. If I'm in luck Jaycar would have 40 pieces of them and I can finish before the fireworks tonight 😎
Interesting enough, the whole XO can become Orion XO just by changing 8k2 with 15k. Now If only I have spare $2k for the drivers 🙂
Op-amp uses the trusty TL072. I will investigate later wheter it's worth changing them to OPA2134 or LM 4562.
Values:
High-pass filters
Low-pass filters
!HAPPY NEW YEAR TO ALL !!
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