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Old 6th January 2011, 06:54 PM   #31
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This definition of power handling has been used, I know. For me, saying you have increased power handling because you can operate at decreased bottom end extension at same input voltage levels and with greater resonance effects pushed up higher in frequency doesn't mean you have a higher power handling speaker.

Technically, it Will handle more power, it just doesn't normally do anything nice with it. It's like saying a sealed back midrange handle more power than the same driver with a vented basket. Depends on the drive frequency, and what you mean by "handle".
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Old 6th January 2011, 10:21 PM   #32
sreten is offline sreten  United Kingdom
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Hi,

Yes it does when your talking excursion limited rather than thermal power handling.

You can trade more needed power with EQ for box size, that is the point
and is also the way most compact high power subwoofers are designed.

Fact is though a driver say ideally used in 60L with 50W might be able
to be used in a 20L box with EQ and 200W. Max SPL for the two cases
will be no different, being excursion limited, the latter needs more power.

Of course it does not mean the higher the amplifier power the louder it
goes for a particular driver, that is my whole point, and the way its done.

Modern subs are shrunk and EQed such that the thermal limits and the
excursion limits are very similar, what is any other point < 80 Hz ?

rgds, sreten.
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Old 7th January 2011, 02:01 AM   #33
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Quote:
Originally Posted by chris661 View Post
You're using the Linkwitz Transform on a subwoofer, so it won't see the higher frequencies, because it'll be crossed over. For excursion calculations, they can be safely ignored.
Yes Chris, The higher frequencies mean the higher frequencies that come into subwoofer band range. say if BPF is 30Hz - 150Hz. then I was talking of 150Hz.

Well, a few words what made me think of equalized subwoofer. I had listened BoneyM, ABBA at school age. Then I had made stereo sealed enclosure speakers at the age of 12 ( not designed. technically that might be a wrong enclosure design). I used graphic equalizer to listen them. The bass was always good. I used it only for home listening. Now as i grew up old I got time and money to have my basic system. its JBL. but this subwoofer being Vented I always miss that clean deep bass. but yes I always doubt vented goes good for movie and Sealed for music.As you are living with sealed EQed subwoofer, I would like to hear from you on this.

I have delebrately selected woofer that should have been used with Vented. The Xmax given by Mfg is 6.75 mm. So this should help me to be enough safe when its excursion limit.

In my next post I will put TS of the driver selected. And also experiments using WINISD. So that the discussion here can go more practical.

This thread participants has given me and other readers lot of new information, It has also made me think of different aspects which I had missed. thanks to you all. keep it alive.
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Last edited by Aucosticraft; 7th January 2011 at 02:18 AM.
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Old 7th January 2011, 03:25 AM   #34
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I have uploaded the design PDF. I had to cut it into individual pages to limit file size. Pl. give your valuable comment on it.
Attached Files
File Type: pdf The Design_Page1.pdf (56.3 KB, 28 views)
File Type: pdf The Design_Page2.pdf (129.9 KB, 18 views)
File Type: pdf The Design_Page3.pdf (121.1 KB, 17 views)
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Old 7th January 2011, 07:19 AM   #35
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I've been advised to not to aim for 0.707 directly, but to start with something like 0.6 or 0.65 and to aim to finish at 0.707 if that is your goal. Stuffing the box will "make it seem" larger than it is, and if you go for 0.707 directly in your design, you might in the end land on something larger than Q=0.707.
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Old 7th January 2011, 07:33 AM   #36
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Originally Posted by buggsson View Post
I've been advised to not to aim for 0.707 directly, but to start with something like 0.6 or 0.65 and to aim to finish at 0.707 if that is your goal. Stuffing the box will "make it seem" larger than it is, and if you go for 0.707 directly in your design, you might in the end land on something larger than Q=0.707.
You gave me a point to think over...
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Old 7th January 2011, 09:01 AM   #37
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Originally Posted by chris661 View Post
Henry, I currently (well, up until very recently, where I removed the amp's PSU) ran a LT circuit on a pair of 8" drivers in a 40 litre cabinet. There was around 14dB of gain to get the f3 down to 28Hz.

At low levels (up to comfortable listening, maybe 80-85dB in a small room), the subwoofer worked fine. Turn it up a little, excursion became visible, but it was still a passable performance. Remember, this is in a small room. Turned up, the drivers quickly hit the stops when any sub 40Hz bass came along. In larger rooms, the cone excursion to fill a room at normal listening levels got kind of silly. Almost a passable performance, but given anything sub 40Hz, there were loud mechanical noises.
Having lived with said subwoofer for nearly two years now, I know it's limits. It won't do movies without a high pass filter to stop the drivers bottoming out. This is not a low and rumbly subwoofer, it was reasonably tuneful, reasonably deep, with reasonable output. Fine for music in a small room, but at ~3mm Xmax per driver, distortion got out of hand when really turned up.
In conclusion, yes, you can get away with a (relatively) small driver and plenty of eq. But you must get used to the limits of the system. I wouldn't try to take an 8" past 40Hz without a specialist subwoofer driver with plenty of linear(!) Xmax, and sufficient amplifier headroom to get there.

Chris
Getting back to the original question, if we use the above setup, which is already a compromise, reducing the box to 20L (and applying more boost from the ltx for the same F3 will result in even less output. If the box is made 80L, less boost is needed for the same F3 and more output will be available. If you must use a small box, you have to select a driver with more linear xmax, say at least 10mm, higher sens, at lower Fs or t/s params that yield a lower box Res.

As i said the above setup is already a compromise, with 2 8" drivers, xmax of 3mm, as far a using an LTX cct.

Heres my guidelines to properly implement an LTX system
These are MINIMUM requirements
Unless you can afford expensive smaller drivers, use 10"
Unless you can afford expensive 10" driver with large xmax (10mm+), use two 10"
These drivers xmax should be 6mm+
Select drivers that will yield a low box Res (max 50Hz) this means low Fs drivers <25Hz
Driver sens 90dB+
The box should be as large as you can allow to yield a low Q/Res. A bigger box means less boost for the same system F3
Do not LTX below one octave of the box Res
The usual box requirements stand,with very strong build, 2 or more shelf braces, damping etc.

However, and most importantly, before you start you must be able to correctly measure the q/Res to the box to be ltx'd. Without this correct data, the ltx response is wrong, thus the overall system response is wrong, leading to poor results.
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Old 7th January 2011, 09:11 AM   #38
Calvin is online now Calvin  Germany
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Hi,

on first glance the Linkwitz transform comes handy to reduce cabinet size and still have extended lowfreq-response. But I donīt use it. If equalization of low frequencies is needed I do this with a variable Highpass-filter/Subsonic. Why if? Well, the Linkwitz transformation does not take into account the room gain, which adds considerably and increasing at 12dB/oct with decreasing frequency to the SPL. In other words, a falling amplitude response of the box may lead to a linear in-room response. A linear response may sound boomy or too much. The LW-Transform is also fixed in its parameters and a additional subsonic filter is strongly recommended.
Instead I rather use a notch-filter on the resonance frequency to cope with the elevated Q of teh resonance. If the crossover frequency is low enough You might even omit with the notch-filter.
The variable Subsonic then allows You to tune the amplitude response so that it gives a linear in-room response. Calculation and implementation of the filters is easier and handling and setup of the bass is more flexible.

jauu
Calvin
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Old 7th January 2011, 03:51 PM   #39
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Quote:
Originally Posted by Henry8 View Post
Getting back to the original question, if we use the above setup, which is already a compromise, reducing the box to 20L (and applying more boost from the ltx for the same F3 will result in even less output. If the box is made 80L, less boost is needed for the same F3 and more output will be available. If you must use a small box, you have to select a driver with more linear xmax, say at least 10mm, higher sens, at lower Fs or t/s params that yield a lower box Res.

As i said the above setup is already a compromise, with 2 8" drivers, xmax of 3mm, as far a using an LTX cct.

Heres my guidelines to properly implement an LTX system
These are MINIMUM requirements
Unless you can afford expensive smaller drivers, use 10"
Unless you can afford expensive 10" driver with large xmax (10mm+), use two 10"
These drivers xmax should be 6mm+
Select drivers that will yield a low box Res (max 50Hz) this means low Fs drivers <25Hz
Driver sens 90dB+
The box should be as large as you can allow to yield a low Q/Res. A bigger box means less boost for the same system F3
Do not LTX below one octave of the box Res
The usual box requirements stand,with very strong build, 2 or more shelf braces, damping etc.

However, and most importantly, before you start you must be able to correctly measure the q/Res to the box to be ltx'd. Without this correct data, the ltx response is wrong, thus the overall system response is wrong, leading to poor results.
Two boxes, one smaller than the other but each containing the same driver, with the same eq'd response will have the same output, until power ratings are reached. Sure, one won't require as much power, but that's irrelevant when the drivers would pass linear travel on much less than their power ratings. It took me a while to realise this. A larger sealed box won't give more output, but it will reduce the power needed to get there (ie, increasing LF efficiency).
I'd tend to agree with your guide lines, but of course they will be room dependant. For a bedroom system, a couple of 8" woofers is plenty. Hard and fast rules are rarely relevant. For small rooms, a decent 8" is enough, for medium rooms, a couple of 10"s, for large rooms, maybe a few distributed 15" subwoofers...
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Old 7th January 2011, 04:00 PM   #40
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Quote:
Originally Posted by Aucosticraft View Post
I have uploaded the design PDF. I had to cut it into individual pages to limit file size. Pl. give your valuable comment on it.
It's going to be experimental, though I'm not sure if you'll be satisfied with the amount of volume available when the really low frequencies come along. Flat to 20Hz simmed might be boosted by your room. However, rooms are fickle things and can also put huge notches in the response, so I wouldn't take it for granted, just be prepared to modify the circuit to integrate the subwoofer into the room to give a nice, flat response.

I'm not sure if the output at 20Hz will be loud enough to be audible - it comes to ~84dB, assuming the excursion plot shown is at 1 watt input. I think I'd sacrifice those last 10-15Hz of excursion and make use of what the driver will be able to do.

Chris
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