Moondog55 said:
Dipole speakers are normally done with no enclosure
The energy coming from the rear of the driver is 180 degrees out of phase from the front. This causes figure 8 radiation With nulls on the sides of the cabinet.
People like to do Dipoles because it often sounds more lifelike especially for acoustic, spacial music.
Standard Dipole suffers from lack of power handling and less efficiency.
Dipole in an enclosure requires twice as many drivers, but has higher output capability.
http://www.linkwitzlab.com/ ...need I say more
He doesn't speak specifically about sealed Di-Poles but the theory is the same.
Antone-
There is obviously some confusion in my mind here; perhaps some-one could give me a definition of the difference between bi-polar radiation and bi-pole speakers ( Andy's "Blackwoods" "The Eathers" ) and di-poles where speakers are in sealed/vented enclosures and firing front and rear
Moondog55 said:
Technically I think Di and Bi have the same meaning.
But maybe Bi polar is used to describe sealed versions of Di-Poles???
Bi polars/Di Polars will have a + and - side.
It is simpler to build a Single open air Di-pole.
An enclosed di/bi-pole requires twice as many drivers. The + and - drivers are isolated acoustically from each other in the enclosure.
Another interesting side note. If you Delay the - (rear radiators) by the distance of the Front radiators. You get a cardioid speaker.
sumsound said:
Only when close to a dipole baffle or in relatively free space !
In a room you can be in line with the baffle plane and observe really deep bass just 6ft away.
Listening room boundaries seriously modify LF wave motion.
sumsound said:
Only for a small 'sweet spot' and for a very narrow range of frequencies after amplitude and phase correction has been applied to counter wall/room reflections.
And if you delay waveform to/from the rear drivers ? then what does this do for the timely addition for leading edge dynamic impules like kick drum and plucked bass ?
I'm not trying to pick on you Antone, its just that 'the room rules at LF' and can thus seriously modify output from a carefully considered design running the very best and most expensive of drivers.
Cheers ......... Graham.
Graham Maynard said:
I wasn't advocating Cardioid, just something I figured out when I was playing with Di-Pole designs in EVI Array Show.
I've never taken a TEF measurement of a cardioid speaker, perhaps you can tell me what it will do. The most important information for determinig the atack of percusion is not in the bass range that would be the treble.
If a rear firing tweeter is incorporated it would most likely arive as a late room reflection with greatly reduced amplitude relationship to the initial signal. I would call that reflected signal ambience.
From what I've read, Di-Pole configurations can significantly reduce problems with room modes Vs Mono pole (Until one gets into the low/sub range).
There is a lot of information about this on the Linkwitz Labs site.
I think the project in question has a budget that can afford the extra drivers. And He seems to want to have a tougher than usual load to drive. This would be a quick easy way to halve the impedance of the design. And some people think Di Pole is the cats Meow for acoustic music.
I've never personally built a Di-Pole. Is there any compelling reason to not go Di-Pole? If it reduces room modes problems I think its about as Viable as Di Apolito.
Re: Re: Re: Half space sensitivity
I would go for a significantly lower Qtc or LT it for an effective Qtc~0.6 to 0.7
with a Qtc (Qbox) up at 0.8 this could sound boomy.G.Kleinschmidt said:
I would go for a significantly lower Qtc or LT it for an effective Qtc~0.6 to 0.7
I would also go for the lowest box "Q" possible but it's easy to drive a woofer to it's maximum excursion with the bigger box.
I'm selling my B-139's on Ebay and I've just seen these;
http://cgi.ebay.com.au/ws/eBayISAPI...m=130247356349&ssPageName=STRK:MEWA:IT&ih=003
I know nothing about them but T/S parametres should be avaliable, I think these would be made by "Lorantz" but which model you would have to ask the vendor.
Regards Ted
http://cgi.ebay.com.au/ws/eBayISAPI...m=130247356349&ssPageName=STRK:MEWA:IT&ih=003
I know nothing about them but T/S parametres should be avaliable, I think these would be made by "Lorantz" but which model you would have to ask the vendor.
Regards Ted
Re: Re: Re: Re: Half space sensitivity
According to the Cookbook:
"High Qs in the vicinity of 1 tend to have a warm, if somewhat robust quality..."
"Lower values around 0.8 sound more detailed....and, by comparison, somewhat shallow."
"Qtc = 0.5 is usually regarded as excessively taut and overdamped."
"Qtc greater than 1.2 or so, however, should be considered undesirable".
For “orchestral and organ music” an Fc of <50Hz and a Qtc<1.1 is recommended.
A Qtc of 0.8 corresponds to an amplitude peak above a flat (critically damped) magnitude of only 0.213dB. This should still produce pretty "tight" bass, without being "excessively taut".
Cheers,
Glen
AndrewT said:
Moondog55 said:
According to the Cookbook:
"High Qs in the vicinity of 1 tend to have a warm, if somewhat robust quality..."
"Lower values around 0.8 sound more detailed....and, by comparison, somewhat shallow."
"Qtc = 0.5 is usually regarded as excessively taut and overdamped."
"Qtc greater than 1.2 or so, however, should be considered undesirable".
For “orchestral and organ music” an Fc of <50Hz and a Qtc<1.1 is recommended.
A Qtc of 0.8 corresponds to an amplitude peak above a flat (critically damped) magnitude of only 0.213dB. This should still produce pretty "tight" bass, without being "excessively taut".
Cheers,
Glen
bass boom
Could the reason for lack of bass be due to placing well away from corners (attempts to avoid the boom of corner reinforcement) and thus the omission of BSC results in a bass light presentation.
With a Qtc above 0.7 the speakers can become very room placement sensitive.
Most small commercial speakers are deliberately high Qed to produce the extra apparent bass frequencies from small cabinets and use second harmonic distortion to fool the ear/brain into believing that real bass is being heard.
A big cabinet and multiple drivers does not need this "trick" to produce apparent bass, particularly if BSC is used to create a really flat frequency response. I cannot recommend any Q above 0.7 for a big cabinet.
shallow? Could this mean lacking in deep bass?G.Kleinschmidt said:
Could the reason for lack of bass be due to placing well away from corners (attempts to avoid the boom of corner reinforcement) and thus the omission of BSC results in a bass light presentation.
With a Qtc above 0.7 the speakers can become very room placement sensitive.
Most small commercial speakers are deliberately high Qed to produce the extra apparent bass frequencies from small cabinets and use second harmonic distortion to fool the ear/brain into believing that real bass is being heard.
A big cabinet and multiple drivers does not need this "trick" to produce apparent bass, particularly if BSC is used to create a really flat frequency response. I cannot recommend any Q above 0.7 for a big cabinet.
Agreed but it's a personal preference of mine for the extra depth in the bass, and for organ music I would have said FC lower than 30; IF POSSIBLE.
Re: bass boom
Like it says - "detailed". Shallow as in not artificial, I guess.
But 0.8 isn't "high Q'ed". A Qtc of 1.2 or greater is "high Q'ed".
The relationship isn't linear either. There is a much bigger difference between 0.8 and 0.9 than between 0.7 and 0.8, for example.
Organ and pipe music requires well damped bass (low Qtc). Richard Small recommended a Qtc<1.1 for this application in 1969, with big closed-box cabinets (that's how they made them back them).
Anyway, this is all academic because I haven't decided on an absolute value of Qtc at this stage. I just posted that Shiva-X sim to show how it performs in a relatively modest enclosure.
I will most likely build a prototype sub box for a single woofer before anything, to experiment with Qtc for my own subjective assessment.
Cheers,
Glen
AndrewT said:
Like it says - "detailed". Shallow as in not artificial, I guess.
AndrewT said:
But 0.8 isn't "high Q'ed". A Qtc of 1.2 or greater is "high Q'ed".
The relationship isn't linear either. There is a much bigger difference between 0.8 and 0.9 than between 0.7 and 0.8, for example.
Organ and pipe music requires well damped bass (low Qtc). Richard Small recommended a Qtc<1.1 for this application in 1969, with big closed-box cabinets (that's how they made them back them).
Anyway, this is all academic because I haven't decided on an absolute value of Qtc at this stage. I just posted that Shiva-X sim to show how it performs in a relatively modest enclosure.
I will most likely build a prototype sub box for a single woofer before anything, to experiment with Qtc for my own subjective assessment.
Cheers,
Glen
It is possible. The easiest way (that I know of) in a 3 way design is to cross the woofer over at 80 hz or so. Put the correct woofer in "big" box such that its Qtc ends up at .5 or so. Then you can use your crossover to compensate for much higher F3 frequency.
But there are many compromises to doing it this way -- for any given woofer, you end up with a speaker with overall lower sensitivity. You need larger midranges -- like 6 1/2 inches in diameter. ( I prefer 3,4,or maybe 5.5 inch midranges).
There are probably other crossover tricks you can use to do it, but I think it would involve using big capacitors.
JJ
Re: Re: Re: Half space sensitivity
Okay Pete, I have just read through you post again and you are indeed correct. A pair of 12” Shiva-X woofers will indeed have a 2.83V sensitivity of 93.4dB
Now, I’ll proceed with an outline of the current plan 🙂
A pair of XBL motored 12” Shiva-X sub woofers will be used for the bass, all coils in parallel for a 2 ohm nominal impedance:
http://www.audiomarketplace.com.au/...acturer_id,0/option,com_virtuemart/Itemid,49/
The 2.83V sensitivity of the bass section will be 93.4dB
The enclosure will be 0.4m wide.
The baffle step is at ~280Hz. This relaxes the mid-range driver gain somewhat.
A compromised baffle step correction of 3-4dB sounds reasonable, making a mid-range driver with a 2.83V sensitivity of 90dB (1W/1m) ideal.
The lower crossover can be at 250Hz.
The Seas H1262 8-ohm mid-range driver would be ideal here:
http://www.seas.co.uk/pdf/h1262.pdf
It is a high quality mid-range driver with a 2.83V sensitivity of 90dB (1W/1m) as well as a recommended lower crossover of 250Hz. It also has quite substantial power handling on top of already good linearity.
The recommenced upper frequency crossover frequency is 3.5kHz.
The perfect tweeter for the top end would be the Visaton MHT-12:
http://www.soundlabsgroup.com.au/p/V-1080-MHT12/MHT+12+-+8+Ohm
It is an 8-ohm high power handling ribbon unit with a 2.83V sensitivity of 91dB (just perfect)
It is recommended for applications 3kHz and up. This would go nicely with the Seas H1262 3.5kHz recommended crossover.
What do you reckon? Sounds good?
Cheers,
Glen
G.Kleinschmidt said:
Okay Pete, I have just read through you post again and you are indeed correct. A pair of 12” Shiva-X woofers will indeed have a 2.83V sensitivity of 93.4dB
Now, I’ll proceed with an outline of the current plan 🙂
A pair of XBL motored 12” Shiva-X sub woofers will be used for the bass, all coils in parallel for a 2 ohm nominal impedance:
http://www.audiomarketplace.com.au/...acturer_id,0/option,com_virtuemart/Itemid,49/
The 2.83V sensitivity of the bass section will be 93.4dB
The enclosure will be 0.4m wide.
The baffle step is at ~280Hz. This relaxes the mid-range driver gain somewhat.
A compromised baffle step correction of 3-4dB sounds reasonable, making a mid-range driver with a 2.83V sensitivity of 90dB (1W/1m) ideal.
The lower crossover can be at 250Hz.
The Seas H1262 8-ohm mid-range driver would be ideal here:
http://www.seas.co.uk/pdf/h1262.pdf
It is a high quality mid-range driver with a 2.83V sensitivity of 90dB (1W/1m) as well as a recommended lower crossover of 250Hz. It also has quite substantial power handling on top of already good linearity.
The recommenced upper frequency crossover frequency is 3.5kHz.
The perfect tweeter for the top end would be the Visaton MHT-12:
http://www.soundlabsgroup.com.au/p/V-1080-MHT12/MHT+12+-+8+Ohm
It is an 8-ohm high power handling ribbon unit with a 2.83V sensitivity of 91dB (just perfect)
It is recommended for applications 3kHz and up. This would go nicely with the Seas H1262 3.5kHz recommended crossover.
What do you reckon? Sounds good?
Cheers,
Glen
jupiterjune said:
Hi JJ
The Shiva-X 12" woofer I intend to use will do 30Hz in a 115L closed box with a critically damped Qtc of 0.707 😀
And this is a device with absolutely massive power handling
capability and a linear excursion of 54mm peak-peak.
The inductance is so low than you can cross it over at a couple of hundred Hz no problem.
To the best of my knowledge there isn't anything else out there that compares.
Cheers,
Glen
Attachments
G.Kleinschmidt said:
Hmmm......
Putting my WinISD simulations aside, I'm starting to wonder just how good the high frequency performance of the Shiva-X is now.
An unfortunate thing is that the manufacturer is only targeting the subwoofer builders and they do not publish any specs at all for performance at the higher end.
Other 12", Hifi-marketed woofers that I've looked at that have 4-ohm coils with similar inductance have recommended upper crossovers of ~200Hz.
The Shiva-X may very well be the perfect candidate for my 250Hz application, but without the manufacturer data to confirm if this is so, the purchase would be a gamble.
I might be better going with a high quality 12" 4-ohm woofer marketed for HiFi, whose performance capabilities can be verified.
😕
Cheers,
Glen
sumsound said:
A dipole has the rear wave 180 deg. out-of-phase. A bipole has both sides in phase. I believe that the term bipole was first used by Energy for a speaker system, I read a comment by someone there that they wished that they'd registered it's use. It's now a generic term.
A dipole does not require more than one driver, though it can be created that way. A bipole cannot be created with a single driver.
If you're interested at all in dipoles and cardioids, this is the place to learn about them:
John K's Dipole Pages - Music and Design
Dave
Did the manufacturer list any recommended frequency range or response graphs? In my experience, buying any driver is a gamble. Some of it just comes down to personal taste.
I did download the spec. sheet for that sub -- I intend on loading the specs into Crossover pro later on today. (for the past month or so, I have been working on a design simular to what you intend, just not with low impedence--the Shiva might work for me).
My comments about getting an Fcb and f3 down to 30Hz or so in a closed box were in reference to using smaller drivers (8" or so). Of course a driver like the Shiva will do it.
JJ
Re: Re: Re: Re: Half space sensitivity
Okkayyyyy!!!!!!
Here is the deal now, just before I got to bed to dream about speakers.........
I have an excellent 90dB SPL (2.83V) midrange driver for 250Hz-3.5kHz.
I have an excellent 91dB SPL (2.83V) ribbon tweeter for 3.5kHz-20kHz.
Both are 8 ohm and have rather high power handling - exactly what I need.
I want to compensate for ~4dB of baffle step gain in the actual speaker.
That means I need a bass driver with a sensitivity of 94dB!!
This is a next to impossible task for a single driver with a sufficently low fs.
Consequently, I will need two identical 12" bass drivers in parallel.
My amplifier is up to the task.
The bass driver must have a nominal impedance of 4-ohms and a power handing capability of ~200W (80V peak-peak drive)
It must have a 2V sensitivity of 94db-6db-3db = 85dB
It must be able to be crossed over at 250Hz, but have a low as possible fs but a not too low Qes.
For the best closed box performance fs/Qes should be not too much greater than 50.
Help!
Cheers,
Glen
G.Kleinschmidt said:
Okkayyyyy!!!!!!
Here is the deal now, just before I got to bed to dream about speakers.........
I have an excellent 90dB SPL (2.83V) midrange driver for 250Hz-3.5kHz.
I have an excellent 91dB SPL (2.83V) ribbon tweeter for 3.5kHz-20kHz.
Both are 8 ohm and have rather high power handling - exactly what I need.
I want to compensate for ~4dB of baffle step gain in the actual speaker.
That means I need a bass driver with a sensitivity of 94dB!!
This is a next to impossible task for a single driver with a sufficently low fs.
Consequently, I will need two identical 12" bass drivers in parallel.
My amplifier is up to the task.
The bass driver must have a nominal impedance of 4-ohms and a power handing capability of ~200W (80V peak-peak drive)
It must have a 2V sensitivity of 94db-6db-3db = 85dB
It must be able to be crossed over at 250Hz, but have a low as possible fs but a not too low Qes.
For the best closed box performance fs/Qes should be not too much greater than 50.
Help!
Cheers,
Glen
jupiterjune said:
I have not been able to find any at all. All I found was that specification .pdf and that applications note .pdf. The application note only discusses sub woofer box construction and does not mention upper cut off frequencies.
I'm not sure just how well the upper frequency response can be predicted from the driver parameters (coil inductance, etc).
Cheers,
Glen
- Status
- Not open for further replies.