Just being playing with some numbers for a sub for my up and coming system and one particular driver in the Jaycar catalogue, an 8" double magnet bizzo http://www1.jaycar.com.au/productVi...xxx&pageNumber=&priceMin=&priceMax=&SUBCATID= seems to give extraordinarily good results when I run a simulated box using WinISD Beta. I mean really, is 16 Hz to 82 Hz +/- 0.5 dB believable?? Especially the 16Hz part. 
Opinions please!
GP.
P.S. I uploaded the pic as a GIF, not a JPG. Notice how much clearer it is. Smaller file size too.
Opinions please!GP.
P.S. I uploaded the pic as a GIF, not a JPG. Notice how much clearer it is. Smaller file size too.
Attachments
looks good on paper (or simulation in this case) but...
I think winisd assumes a perfectly flat acoustic response for the speaker. So if you want the real respone of the speaker you would need to use its response data as well. I went to the website and they has a "graph" that looked like it might be response graph, it was real fuzzy (intersting that the blow up picture of the driver worked just fine). It didn't even look like it was on log scale to me. I give no credit to this graph. If the speakers response drops with the frequency (every driver i have seen) then the winisd graph needs to be lowered by this amount. So how good will the speaker work, I have no idea at all - just not enough information.
I think winisd assumes a perfectly flat acoustic response for the speaker. So if you want the real respone of the speaker you would need to use its response data as well. I went to the website and they has a "graph" that looked like it might be response graph, it was real fuzzy (intersting that the blow up picture of the driver worked just fine). It didn't even look like it was on log scale to me. I give no credit to this graph. If the speakers response drops with the frequency (every driver i have seen) then the winisd graph needs to be lowered by this amount. So how good will the speaker work, I have no idea at all - just not enough information.
The problem with this design is not only what Lligior mentioned, but the fact that you're now getting an efficiency of -5db from your starting values (which could be QUITE low, considering this is an 8" driver with an Fs of 35.71hz!).
In the end, you'd probably get only 80dB efficiency, with a max power handling of only 100w. Not to mention you have a relatively large (4 cu ft) box, and have to pay for some decent ports.
In the end, you'd probably get only 80dB efficiency, with a max power handling of only 100w. Not to mention you have a relatively large (4 cu ft) box, and have to pay for some decent ports.
Circlotron,
6th order boxes sound very slooowww, ok for subs for HT, when they are just doing explosions and stuff, but rubbish for music.
From just a quick glance at your numbers, your best bet for music at normal volumes may be a sealed box with a Linkwitz correction circuit, see the ESP site for details.
6th order boxes sound very slooowww, ok for subs for HT, when they are just doing explosions and stuff, but rubbish for music.
From just a quick glance at your numbers, your best bet for music at normal volumes may be a sealed box with a Linkwitz correction circuit, see the ESP site for details.
I mean really, is 16 Hz to 82 Hz +/- 0.5 dB believable??
I can't even find the fact that you asked the question believable....
In real life the room nodes will give you about ten or twenty times that amount of variation. Sorry for the reality check. I think it has something to do with the closeness of midterm elections here.
http://www.silcom.com/~aludwig/Room_acoustics.html
http://philsaudio.stryke.com/getting.htm
http://www.kbacoustics.com/visualears/index.html
pest-HH er... I mean... post-HH
I can't even find the fact that you asked the question believable....
In real life the room nodes will give you about ten or twenty times that amount of variation. Sorry for the reality check. I think it has something to do with the closeness of midterm elections here.
http://www.silcom.com/~aludwig/Room_acoustics.html
http://philsaudio.stryke.com/getting.htm
http://www.kbacoustics.com/visualears/index.html
pest-HH er... I mean... post-HH
C'mon Fred, no speaker can take room nodes into account-that 's the luck of the draw! All anyone can do is make something with good response into half space or quarter space-what happens in your actual room is pure luck. That's why we move subs around the room, to try to minimize the room node factor as much as we can.
I'm concerned about the midterm elections too, but let's not lash out at the world audio community.
There is nothing wrong with trying to make a good smooth graph.
However, there are two problems I see with this. I have never built a bandpass sub, but I have read extensively on them.
A) As has been pointed out before, bandpass subs can extend low frequency while lowering the midpoint efficiency at the same time. It is good to be -3 dB at 16 Hz or whatever, but if that is -3 dB from a midpoint of 82, it 's going to take a lot of power to get hearable bass out of this sub.
B) Although the port greatly augments the output of the speaker in ported and bandpass enclosures, you still have to move a lot of air to have hearable bass at 16 Hz. For instance, it takes four-yes, four-times the air moved to generate a tone of 50 Hz as it does to generate a tone of 100 Hz. So by the time you get down to 16 Hz, the air volume required gets enormous. An 8 inch speaker does not have those air moving capabilities.
Let me illustrate.
I have put up some graphs which show how much air needs to be moved by a closed box speaker with no help from a port. We will deal with how the port helps in a moment.
Take a look at the chart I provided here. You might want to hit F11:
http://www.diyaudio.com/forums/showthread.php?threadid=5668&highlight=displacement+spl There are two charts-one for normal measurement and one for metric.
As you can see, it requires something like 250 cu in of air to be moved, without port augmentation, to produce a 112 dB note at 16 Hz.
One of your chambers is tuned to 17 Hz. Good, that is almost right at the 16 Hz frequency you are trying to reproduce. Port augmentation will be near a maximum at 16 Hz.
If you take a look at the theoretical excursion chart for ported systems, they show that at the tuning frequency, the cone has to move almost not at all to produce great volumes of air moved.
In practice, the cone has to move about one fourth of the amount a closed box speaker must to produce the same volume. The port cuts the need to move air by 4. Half an octave above the tuning frequency, it cuts the requirement by 2. An octave above the tuning frequency, there is generally no help from the port.
Okay, so what is the air moving capability of your speaker? An 8 inch speaker generally has a cone surface of 32 square inches. What is it's excursion? Usually about (+ or - ) 1/4 inch-but let's be generous and give it (+ or -) 1/2 inch, making it one of the longest excursions on the market.
That means your 8 inch can move 16 cubic inches of air.
At the port tuning frequency, we multiply that by 4.
So at 16 Hz in a ported or bandpass sub tuned near 16 Hz, the 8 inch can move the equivalent of 64 cubic inches.
Checking the SPL chart, we see that 64 cubic inches will produce about 98 or 99 dB at 16 Hz. That is unlikely to be hearable. And that is giving the 8" speaker one of the longest excursions on the market, which it probably does not have.
Even if the port augmentaion at the tuning frequency is greater with the bandpass than with the ported-even if it is greater than 4 to 1-once you move away from the tuning frequency a little it most likely will quickly resemble the ported box's characteristic.
I hope I haven't gone overlong on this. I will be happy to clarify.
In short, an 8 inch in a bandpass box wil not produce hearable bass at 16 Hz, no matter what the curve looks like.
I'm concerned about the midterm elections too, but let's not lash out at the world audio community.
There is nothing wrong with trying to make a good smooth graph.
However, there are two problems I see with this. I have never built a bandpass sub, but I have read extensively on them.
A) As has been pointed out before, bandpass subs can extend low frequency while lowering the midpoint efficiency at the same time. It is good to be -3 dB at 16 Hz or whatever, but if that is -3 dB from a midpoint of 82, it 's going to take a lot of power to get hearable bass out of this sub.
B) Although the port greatly augments the output of the speaker in ported and bandpass enclosures, you still have to move a lot of air to have hearable bass at 16 Hz. For instance, it takes four-yes, four-times the air moved to generate a tone of 50 Hz as it does to generate a tone of 100 Hz. So by the time you get down to 16 Hz, the air volume required gets enormous. An 8 inch speaker does not have those air moving capabilities.
Let me illustrate.
I have put up some graphs which show how much air needs to be moved by a closed box speaker with no help from a port. We will deal with how the port helps in a moment.
Take a look at the chart I provided here. You might want to hit F11:
http://www.diyaudio.com/forums/showthread.php?threadid=5668&highlight=displacement+spl There are two charts-one for normal measurement and one for metric.
As you can see, it requires something like 250 cu in of air to be moved, without port augmentation, to produce a 112 dB note at 16 Hz.
One of your chambers is tuned to 17 Hz. Good, that is almost right at the 16 Hz frequency you are trying to reproduce. Port augmentation will be near a maximum at 16 Hz.
If you take a look at the theoretical excursion chart for ported systems, they show that at the tuning frequency, the cone has to move almost not at all to produce great volumes of air moved.
In practice, the cone has to move about one fourth of the amount a closed box speaker must to produce the same volume. The port cuts the need to move air by 4. Half an octave above the tuning frequency, it cuts the requirement by 2. An octave above the tuning frequency, there is generally no help from the port.
Okay, so what is the air moving capability of your speaker? An 8 inch speaker generally has a cone surface of 32 square inches. What is it's excursion? Usually about (+ or - ) 1/4 inch-but let's be generous and give it (+ or -) 1/2 inch, making it one of the longest excursions on the market.
That means your 8 inch can move 16 cubic inches of air.
At the port tuning frequency, we multiply that by 4.
So at 16 Hz in a ported or bandpass sub tuned near 16 Hz, the 8 inch can move the equivalent of 64 cubic inches.
Checking the SPL chart, we see that 64 cubic inches will produce about 98 or 99 dB at 16 Hz. That is unlikely to be hearable. And that is giving the 8" speaker one of the longest excursions on the market, which it probably does not have.
Even if the port augmentaion at the tuning frequency is greater with the bandpass than with the ported-even if it is greater than 4 to 1-once you move away from the tuning frequency a little it most likely will quickly resemble the ported box's characteristic.
I hope I haven't gone overlong on this. I will be happy to clarify.
In short, an 8 inch in a bandpass box wil not produce hearable bass at 16 Hz, no matter what the curve looks like.
There is nothing wrong with trying to make a good smooth graph.
Agreed..... Other than small fact that YOU CAN"T LISTEN TO A GRAPH!
"I can't even find the fact that you asked the question believable...."
Let me remove any implications of a personal affront and just look at it from the absurdity of the idea from the perspective of the real world. It was a poor way to make my point, which is that you absolutely cannot consider a loudspeaker without the influence of the room it is located in. That is possibly THE MOST IMPORTANT FACTOR IN SPEAKER DESIGN!
Can I get an AMEN brothers and sisters?
Fred
Agreed..... Other than small fact that YOU CAN"T LISTEN TO A GRAPH!
"I can't even find the fact that you asked the question believable...."
Let me remove any implications of a personal affront and just look at it from the absurdity of the idea from the perspective of the real world. It was a poor way to make my point, which is that you absolutely cannot consider a loudspeaker without the influence of the room it is located in. That is possibly THE MOST IMPORTANT FACTOR IN SPEAKER DESIGN!
Can I get an AMEN brothers and sisters?
Fred
No amen from me, brother.
Designing a speakers response to correct for room problems is conceptually no different that designing a pre-amp to correct for room problems. Pre-amps, amps and speakers ought to be flat. If the room is a problem, speaker placement is the first line of defense. Follow up with room treatment, if necessary.
Designing a speakers response to correct for room problems is conceptually no different that designing a pre-amp to correct for room problems. Pre-amps, amps and speakers ought to be flat. If the room is a problem, speaker placement is the first line of defense. Follow up with room treatment, if necessary.
speakers ought to be flat
Hell.... I can throw one liners like that around too. How about:
All men are created equal.
There is no such thing as a free lunch.
A little knowledge is a dangerous thing.
Measured where? The boundry conditions of a particular room are what determine a speakers reponse at low frequencies.
Stop talking about about that old useless catch all phase "room problems" and start talking about how a room and loudspeaker interact at low frequencies. Oh that life were as simple as everyone would like.....
Designing a speakers response to correct for room problems is conceptually no different that designing a pre-amp to correct for room problems.
YES! And what's the problem with that? There are many low frequency alignments using equalization. It is not a sin. It will not make you a bad person. As Malcom X said " By any means neccessary.
I will include one more link and resist the impulse to start a battle of wits with the unarmed.*
http://www.linkwitzlab.com/
BeGones,
Fred
*My thanks to G Gordon Liddy for that one.
Hell.... I can throw one liners like that around too. How about:
All men are created equal.
There is no such thing as a free lunch.
A little knowledge is a dangerous thing.
Measured where? The boundry conditions of a particular room are what determine a speakers reponse at low frequencies.
Stop talking about about that old useless catch all phase "room problems" and start talking about how a room and loudspeaker interact at low frequencies. Oh that life were as simple as everyone would like.....
Designing a speakers response to correct for room problems is conceptually no different that designing a pre-amp to correct for room problems.
YES! And what's the problem with that? There are many low frequency alignments using equalization. It is not a sin. It will not make you a bad person. As Malcom X said " By any means neccessary.
I will include one more link and resist the impulse to start a battle of wits with the unarmed.*
http://www.linkwitzlab.com/
BeGones,
Fred
*My thanks to G Gordon Liddy for that one.
Matching loudspeaker to room
How about a bass horn where the fc coincides with the point at which the wavelength starts becoming significant compared to the room dimensions (which should give you 2nd order roll off when smoothed?, and not mentioning the boundary loading to make such a device fit in a room SAF issues aside). Same applies to some of the mad-scientist IB subs methinks as well (doesn’t Grey own such a doomsday device with ungodly output at 10 Hz?)
How about a bass horn where the fc coincides with the point at which the wavelength starts becoming significant compared to the room dimensions (which should give you 2nd order roll off when smoothed?, and not mentioning the boundary loading to make such a device fit in a room SAF issues aside). Same applies to some of the mad-scientist IB subs methinks as well (doesn’t Grey own such a doomsday device with ungodly output at 10 Hz?)
Wasn't the 901 EQ'd externally at line level? If so, that doesn't count. Anyway, I believe the EQ was to make up for the speakers shortcomings and wasn't meant to be a solution to room problems. Thoughts about room modes didn't come to the fore until much, much later.
I think the corner horn is a special case.
Really, can anyone make a case for a non-flat speaker? I'm not talking about external bass contouring electronics or equalizers. I'm talking about the speaker system itself.
I think the corner horn is a special case.
Really, can anyone make a case for a non-flat speaker? I'm not talking about external bass contouring electronics or equalizers. I'm talking about the speaker system itself.
You cannot tailor the response to a single room unless you have the means and expertise to make a room response curve. Even then, there are so many jagged peaks and valleys that it would be hard to imagine anyone tailoring a speaker and enclosure to account for them.
Of course, the response would change if you move the speakers in the room, or change the position you are sitting in.
A few years ago, I read that George Augsburger was in the business of building rooms specifically for stereo listening. I can just imagine the expense.
The reason most speakers are built to sound "flat" in half space or quarter space is that the ups and downs of every room are largely unknowable, so you might as well aim for a median, and adjust from there.
I imagine speaker projects have built where a room response curve was taken, suitable equalizers obtained, and speakers specially built to compensate.
I doubt every speaker builder is interested in undertaking such an involved and expensive process.
Of course, the response would change if you move the speakers in the room, or change the position you are sitting in.
A few years ago, I read that George Augsburger was in the business of building rooms specifically for stereo listening. I can just imagine the expense.
The reason most speakers are built to sound "flat" in half space or quarter space is that the ups and downs of every room are largely unknowable, so you might as well aim for a median, and adjust from there.
I imagine speaker projects have built where a room response curve was taken, suitable equalizers obtained, and speakers specially built to compensate.
I doubt every speaker builder is interested in undertaking such an involved and expensive process.
Re: acerbic and tactless
Hey guys, lets keep the testy bit down... (moderator hat on)
(smiley used in its role as a moderater symbol)
(Now i'll just put my just another guy hat on)
A smart speaker designer -- especially one designing a single system for a know room (ie us) -- always considers the room (just as a good amp design considers the speaker it is going to drive). The room-speaker interface/interaction is one of the most complex and daunting areas of making a hifi work right. Not everyone can build a room designed to work well with speakers so those who can't can only fall back on designing the speaker to the room. Things like low Q roll-offs where the speaker's roll-off gets countered by the roon lift.
Big peaks (ie the floor-to-ceiling resonance common in rectangular rooms) & nulls are not really something it is practical to design against (other than separating the bass enclosure from the rest, so that room placement can be used to ameriolate as much as possible). These things require a fix further up-stream -- most often in the filters in the active XO.
Commercial speaker manufacturers, who have no idea what room their kit will end up in, have to make some descision on what compromise to make to best taylor their product to their market. We are actually seeing some designs coming to market that have an amount of flexibility built-in to allow for tuning the bass to the room -- Infinity for instance (RABOS?), and many plate amps.
dave
Hey guys, lets keep the testy bit down... (moderator hat on)
(smiley used in its role as a moderater symbol)(Now i'll just put my just another guy hat on)
A smart speaker designer -- especially one designing a single system for a know room (ie us) -- always considers the room (just as a good amp design considers the speaker it is going to drive). The room-speaker interface/interaction is one of the most complex and daunting areas of making a hifi work right. Not everyone can build a room designed to work well with speakers so those who can't can only fall back on designing the speaker to the room. Things like low Q roll-offs where the speaker's roll-off gets countered by the roon lift.
Big peaks (ie the floor-to-ceiling resonance common in rectangular rooms) & nulls are not really something it is practical to design against (other than separating the bass enclosure from the rest, so that room placement can be used to ameriolate as much as possible). These things require a fix further up-stream -- most often in the filters in the active XO.
Commercial speaker manufacturers, who have no idea what room their kit will end up in, have to make some descision on what compromise to make to best taylor their product to their market. We are actually seeing some designs coming to market that have an amount of flexibility built-in to allow for tuning the bass to the room -- Infinity for instance (RABOS?), and many plate amps.
dave
iteratively adjusting room repsonse and speaker response
Bill,
i fully second Dave's point and would like to report what Jean-Michel LeCleac'h reported of his own fancy vented woofer.
He intiially designed it for a Q_ts of 0.39 and was not happy with the actual result. HE tweaked the room, was not happy with the result, then started to tweak vent alingment, then tweaked the room, then the vent and so on until his bass unit had a Q_ts of 0.55.
BTW, he heartily agreed with my preference for using innocent looking and only-65%-filled book/record shelves carefuly placed. Room treatment with 100% WAF
Dave,
what are plate amps?
Bill,
i fully second Dave's point and would like to report what Jean-Michel LeCleac'h reported of his own fancy vented woofer.
He intiially designed it for a Q_ts of 0.39 and was not happy with the actual result. HE tweaked the room, was not happy with the result, then started to tweak vent alingment, then tweaked the room, then the vent and so on until his bass unit had a Q_ts of 0.55.
BTW, he heartily agreed with my preference for using innocent looking and only-65%-filled book/record shelves carefuly placed. Room treatment with 100% WAF
Dave,
what are plate amps?
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