I posted this on the Home Theater Forum and the PE Tech Talk boards, but I know you guys know a lot about enclosures, so take a look at the part that asks about enclosure Q.
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I have a question about the Parts Express subwoofer amplifier. I am planning to build a 1.2 cubic-foot sealed subwoofer and I will be needing a bit of bass boost help from the amplifier. The 300-794 allows up to 5 dB of boost but my question is:
does anyone know the slope of the EQ in the 300-794? (e.g., 12dB/oct, etc...)
Also, will a Qts of about 5 destroy a sub driver with a good 25mm of mechanical Xmax? What should I be careful of if I pursue this? At only 270w (the 300-794's measured power into 4 ohms) am I better off with a Q of about .6?
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Wow, I'm talking about sealed subwoofers. I feel so esoteric right now.
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I have a question about the Parts Express subwoofer amplifier. I am planning to build a 1.2 cubic-foot sealed subwoofer and I will be needing a bit of bass boost help from the amplifier. The 300-794 allows up to 5 dB of boost but my question is:
does anyone know the slope of the EQ in the 300-794? (e.g., 12dB/oct, etc...)
Also, will a Qts of about 5 destroy a sub driver with a good 25mm of mechanical Xmax? What should I be careful of if I pursue this? At only 270w (the 300-794's measured power into 4 ohms) am I better off with a Q of about .6?
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Wow, I'm talking about sealed subwoofers. I feel so esoteric right now.
Why should it?
Not to be technical, but Qts, as generally written, refers to the driver when it is unenclosed-out of any box. Qtc. refers to the driver when it is put into a sealed box. Unless the volume of the box is several times the Vas of the driver, (which is rare), the driver in the sealed box will have a higher Qtc than a Qts. The smaller the box compared to the driver's Vas, the higher Fc and Qtc will be compared to Fs and Fs.
Example: A driver with a Qts of .5, an Fs of 30 and a Vas of 2 cubic feet is put into a sealed box of 2 cubic feet.
Both Qts and Fs will be raised 1.4 times. So Qtc = .7, Fc = 1.4. With the same driver.
So when you say "Qts" are you talking about the driver inside the box, or outside the box?
Not to be technical, but Qts, as generally written, refers to the driver when it is unenclosed-out of any box. Qtc. refers to the driver when it is put into a sealed box. Unless the volume of the box is several times the Vas of the driver, (which is rare), the driver in the sealed box will have a higher Qtc than a Qts. The smaller the box compared to the driver's Vas, the higher Fc and Qtc will be compared to Fs and Fs.
Example: A driver with a Qts of .5, an Fs of 30 and a Vas of 2 cubic feet is put into a sealed box of 2 cubic feet.
Both Qts and Fs will be raised 1.4 times. So Qtc = .7, Fc = 1.4. With the same driver.
So when you say "Qts" are you talking about the driver inside the box, or outside the box?
I meant Qtc.
The finished enclosure has a total Q of 0.52
That is, a Qtc of 0.52
in a 1-cubic-foot enclosure
With a woofer that has 12mm one-way RMS Xmax but it clearly can do more that that.
Here's what I wound up with, and I think this design is quite a discovery:
A 1-cubic-foot sealed box with a Qtc of .52 (with a Qtc of 0.5 being considered "Transient-Perfect"). But the box on its own has an F3 of 51 Hz. However, when this enclosure's response is plotted on the same page as the frequency response of the Parts Express 300-796 plate amp (with 6dB bass boost at 30 Hz) the enclosure's response plus the assist from the bass boost (I took the two curves and averaged them) yields a tremendous frequency response: Flat from 85 Hz (+/-1dB) or so down to 30 Hz, with a total system F3 of 25 Hz, which is the same as my current ported enclosure using this driver except that my current enclosure is actually sort of an EBS alignment with a big shelf from 40Hz down to 25Hz.
This design is sort of a cross between an Assisted Resonance System and an equalized system like the Bag End subwoofers.
So now I have found a transient-perfect subwoofer with 270 watts, flat response down to 25 Hz, and an enclosure that is only 1 cubic foot using a now-discontinued 10" subwoofer driver (replaced by the new version of the Blueprint 1001) that has long excursion and a max power handling of 350w. And I'm wondering if this will be causing me to bottom my driver out at moderate levels.
The finished enclosure has a total Q of 0.52
That is, a Qtc of 0.52
in a 1-cubic-foot enclosure
With a woofer that has 12mm one-way RMS Xmax but it clearly can do more that that.
Here's what I wound up with, and I think this design is quite a discovery:
A 1-cubic-foot sealed box with a Qtc of .52 (with a Qtc of 0.5 being considered "Transient-Perfect"). But the box on its own has an F3 of 51 Hz. However, when this enclosure's response is plotted on the same page as the frequency response of the Parts Express 300-796 plate amp (with 6dB bass boost at 30 Hz) the enclosure's response plus the assist from the bass boost (I took the two curves and averaged them) yields a tremendous frequency response: Flat from 85 Hz (+/-1dB) or so down to 30 Hz, with a total system F3 of 25 Hz, which is the same as my current ported enclosure using this driver except that my current enclosure is actually sort of an EBS alignment with a big shelf from 40Hz down to 25Hz.
This design is sort of a cross between an Assisted Resonance System and an equalized system like the Bag End subwoofers.
So now I have found a transient-perfect subwoofer with 270 watts, flat response down to 25 Hz, and an enclosure that is only 1 cubic foot using a now-discontinued 10" subwoofer driver (replaced by the new version of the Blueprint 1001) that has long excursion and a max power handling of 350w. And I'm wondering if this will be causing me to bottom my driver out at moderate levels.
Power restrictions
I can't use a Linkwitz transform circuit because my power is limited. And I can't get more power because my budget is limited (and how much my parents will let me get away with is also limited). But if I have this particular situation that I previously described (Which is NOT an LT, just ordinary bass boost), how can I estimate cone excursion so I don't have it flopping wildly and bottoming?
I can't use a Linkwitz transform circuit because my power is limited. And I can't get more power because my budget is limited (and how much my parents will let me get away with is also limited). But if I have this particular situation that I previously described (Which is NOT an LT, just ordinary bass boost), how can I estimate cone excursion so I don't have it flopping wildly and bottoming?
Please note the chart I posted at the following thread:
http://www.diyaudio.com/forums/showthread.php?threadid=8071
A box with a Qtc of .5 is 6 dB down at resonance, (Fc). We can see from the cahart that the F3 down point is 1.5 the resonance of the box. So 51 is 1.5 the Fc. Therefore, Fc equals 34.
We can also see from the chart that when a speaker with a Qtc of .5 rolls off 8 dB in the octave below Fc. 25 Hz is .45 of an octave below 34, so it is about 3.6 dB below the level of Fc.
If you set your 6 dB boost to 34 Hz, or near it, you will in fact be about 3 dB down at 25. So the numbers do work out-with a 6 dB boost, you are 3 dB down approximately at 25 Hz.
http://www.diyaudio.com/forums/showthread.php?threadid=8071
A box with a Qtc of .5 is 6 dB down at resonance, (Fc). We can see from the cahart that the F3 down point is 1.5 the resonance of the box. So 51 is 1.5 the Fc. Therefore, Fc equals 34.
We can also see from the chart that when a speaker with a Qtc of .5 rolls off 8 dB in the octave below Fc. 25 Hz is .45 of an octave below 34, so it is about 3.6 dB below the level of Fc.
If you set your 6 dB boost to 34 Hz, or near it, you will in fact be about 3 dB down at 25. So the numbers do work out-with a 6 dB boost, you are 3 dB down approximately at 25 Hz.
However, the boost comes with a price. When you use up 3/4 of your power to boost a certain narrow range, you don't have that much to spare when a loud, low note comes through. You still only have 270 watts to pump into the speaker at 25 or 30 Hz, regardless of boost.
If your speaker's midpoint is 90 dB @ 1Watt/1Meter, then you will still only achieve about 106 dB at 25 Hz. That is at the full power of 270 watts going to the speaker, boost or not. That is not counting room gain, however.
If your speaker's midpoint is 90 dB @ 1Watt/1Meter, then you will still only achieve about 106 dB at 25 Hz. That is at the full power of 270 watts going to the speaker, boost or not. That is not counting room gain, however.
From the chart I posted on the following thread, which gives the amount of air moved to produce a certain SPL at a certain frequency, we see that we need a little under 64 cubic inches of air moved to produce 106 dB at 25 Hz in an average room.
http://www.diyaudio.com/forums/showthread.php?threadid=5668&highlight=SPL+displacement+chart
You said that you have a 10" driver. 10" drivers routinely have approximately 56 square inches of cone surface. So you would need about 1" of one way excursion to produce that output. If your mechanical limit is twice the 12 mm linear limit, you should just barely make it. You are in danger of bottoming out if you do not have a mechanical excursion of at least one inch, one way.
If, however, your speaker is rated at 87 dB @ 1Watt/1Meter, then you would need only 3/4 that excursion, and you would be safe.
What is the SPL @ 1Watt/1Meter of your speaker?
http://www.diyaudio.com/forums/showthread.php?threadid=5668&highlight=SPL+displacement+chart
You said that you have a 10" driver. 10" drivers routinely have approximately 56 square inches of cone surface. So you would need about 1" of one way excursion to produce that output. If your mechanical limit is twice the 12 mm linear limit, you should just barely make it. You are in danger of bottoming out if you do not have a mechanical excursion of at least one inch, one way.
If, however, your speaker is rated at 87 dB @ 1Watt/1Meter, then you would need only 3/4 that excursion, and you would be safe.
What is the SPL @ 1Watt/1Meter of your speaker?
84.75dB 1w/1m
As it happens, this driver is rated at 84.75 dB 1w/1m. I have been talking with Dan Saraceno of Bag End to find out how he gets his ELF subwoofers to work in that small sealed box with 12dB/oct of EQ. He said that driver displacement becomes even more important when you get into EQ'd subwoofers, and though a small sealed box exerts more control over the woofer, the woofer cone still does a good deal of excurison. (The Bag End S10E-I single 10" ELF subwoofer only handles 200W of power so I have more power than that, though I do not know whether that is thermal-limited or limited by available excursion. The 250w amplifier I am using is actually measured at 272W into 4 ohms, which is the impedance of my driver.
As it happens, this driver is rated at 84.75 dB 1w/1m. I have been talking with Dan Saraceno of Bag End to find out how he gets his ELF subwoofers to work in that small sealed box with 12dB/oct of EQ. He said that driver displacement becomes even more important when you get into EQ'd subwoofers, and though a small sealed box exerts more control over the woofer, the woofer cone still does a good deal of excurison. (The Bag End S10E-I single 10" ELF subwoofer only handles 200W of power so I have more power than that, though I do not know whether that is thermal-limited or limited by available excursion. The 250w amplifier I am using is actually measured at 272W into 4 ohms, which is the impedance of my driver.
Comprehensive T/S Parameters - Blueprint 1001
I thought I would do well to give you the full T/S parameters of my driver.
Qts: .265
Qms: 3.710
Qes: .285
Vas: 2.839 ft^3
Fs: 18.78Hz
SPL: 84.75 dB 1w/1m
Re: 3.2 Ohm
PE: 350W
BL: 12.64
Xmax: 12mm
Dd: 7.80 in.
Sd: 47.82 in^2
Z: 4 ohms
The Blueprint 1001 borrows T/S parameters from both the 10" Peerless XLS and the first-generation Dayton Titanic 1000. You can tell by listening to it that it has a heavier Mms than a non-high-excursion driver but I'm asking it to turn on a dime, and that is the real purpose of the small sealed box and large amount of power. The Bass Boost is intended to make the frequency response graph at least equal to that of my current vented subwoofer enclosure (f3 at 25 Hz) and with the sealed box and plate amp boost I have actually managed to achieve a flatter response than in my current ported box.
I thought I would do well to give you the full T/S parameters of my driver.
Qts: .265
Qms: 3.710
Qes: .285
Vas: 2.839 ft^3
Fs: 18.78Hz
SPL: 84.75 dB 1w/1m
Re: 3.2 Ohm
PE: 350W
BL: 12.64
Xmax: 12mm
Dd: 7.80 in.
Sd: 47.82 in^2
Z: 4 ohms
The Blueprint 1001 borrows T/S parameters from both the 10" Peerless XLS and the first-generation Dayton Titanic 1000. You can tell by listening to it that it has a heavier Mms than a non-high-excursion driver but I'm asking it to turn on a dime, and that is the real purpose of the small sealed box and large amount of power. The Bass Boost is intended to make the frequency response graph at least equal to that of my current vented subwoofer enclosure (f3 at 25 Hz) and with the sealed box and plate amp boost I have actually managed to achieve a flatter response than in my current ported box.
84.75 dB? You should be safe.
I have two further questions.
A) Is that 84.75 dB rating for 2.83 Volts @ 1 Meter or for 1 Watt at 1 Meter? This is an important consideration if your speaker is rated 4 ohms or less.
B) Can you give me the Thiele-Small parameters for the speaker? At the very least the parameters I need would be:
Qts, Vas, Fs. Qes and Qms would be nice as well.
One of our very own members here, F4ier, has developed Subwoofer Simulator, a program that plots excursion and response, as well as phase and a whole bunch of things. It allows you to enable or disable them so you can get as many or as few plots as you wish. It is freeware. I would like to run your Thiele-Small parameters through it.
http://www.geocities.com/f4ier/speaker.htm
Like I said, I think you are safe. With the rating approximately 6 dB less than the 90 dB I was estimating, the cone excursion would be about half. So it should only slightly exceed the half inch linear excursion. Since you can count on mechanical excursion to be 1.5 to 2 tmes the linear, you should be in range. But I would like to run Subwoofer Simulator anyway.
I have two further questions.
A) Is that 84.75 dB rating for 2.83 Volts @ 1 Meter or for 1 Watt at 1 Meter? This is an important consideration if your speaker is rated 4 ohms or less.
B) Can you give me the Thiele-Small parameters for the speaker? At the very least the parameters I need would be:
Qts, Vas, Fs. Qes and Qms would be nice as well.
One of our very own members here, F4ier, has developed Subwoofer Simulator, a program that plots excursion and response, as well as phase and a whole bunch of things. It allows you to enable or disable them so you can get as many or as few plots as you wish. It is freeware. I would like to run your Thiele-Small parameters through it.
http://www.geocities.com/f4ier/speaker.htm
Like I said, I think you are safe. With the rating approximately 6 dB less than the 90 dB I was estimating, the cone excursion would be about half. So it should only slightly exceed the half inch linear excursion. Since you can count on mechanical excursion to be 1.5 to 2 tmes the linear, you should be in range. But I would like to run Subwoofer Simulator anyway.
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