Sweet thanks heaps, ill have a look at it later. Better than WINisd?
No one has quite answered my question about the box size effecting efficiency yet. Not sure if that is because Its a dumb question, it's obvious or maybe I've just missed the answer but ill phase it again. If my driver reaches Xmax at 150W input in a 1.5 ft^3 box, does this mean the efficiency has increased and I should only supply <150W to this driver?
Much better than WinISD. It's the program generating all the graphs I've posted.
Your question has been answered but let me be more clear. If your driver reaches xmax with 150 watts input, if you give it more than 150 it will exceed xmax at some frequencies. If you give it a lot more you will hit xmech (you can't exceed xmech, it's the damage point). At frequencies where xmax is not exceeded you could boost quite a bit (until you exceed the thermal capacity) and still not hit xmax.
As far as efficiency, efficiency spikes at a frequency close to the box impedance peak.
Here's a look at impedance and efficiency.
Left top - 14 liter box impedance
Right top - 14 liter box efficiency
Left bottom - IB impedance
Right bottom - IB efficiency
As you can see, impedance and efficiency are tied together and both vary with frequency.
An externally hosted image should be here but it was not working when we last tested it.
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The way those efficiency graphs are scaled is misleading. Here's an overlay which uses the same scale.
The 1/2 cu ft box does provide a lot of efficiency at higher frequencies where you really don't need it while the IB provides a very modest amount of efficiency at lower frequencies where it is more needed.
The top end in all 3 box sizes I've shown is already too much - there's rising frequency response (room gain won't be enough to correct for any of the smaller boxes so the top end will have to be eq'ed down or the low end eq'ed up) and a high pass filter will be applied. This will dramatically cut down the power consumed by higher frequencies so there's no need at all to have your efficiency spike as high as the small box has.
An externally hosted image should be here but it was not working when we last tested it.
The 1/2 cu ft box does provide a lot of efficiency at higher frequencies where you really don't need it while the IB provides a very modest amount of efficiency at lower frequencies where it is more needed.
The top end in all 3 box sizes I've shown is already too much - there's rising frequency response (room gain won't be enough to correct for any of the smaller boxes so the top end will have to be eq'ed down or the low end eq'ed up) and a high pass filter will be applied. This will dramatically cut down the power consumed by higher frequencies so there's no need at all to have your efficiency spike as high as the small box has.
Right, so the overall efficiency isn't necessarily better but it is at the low frequencies where it counts? Do others disagree with this? I really don't have room for IB so is a 1.5 ft^3 box a good in between? Do I then only need a 150W amp?
Also, As i understand most subwoofer amps have an adjustable hi pass filter? but how does one 'Eq' the sub?
Thanks!
Myles
Look, the particular ridiculously argumentative "guy" who wants to argue the merits of an IB vs. a 14 liter box is losing sight of your goal. I don't agree with his method or conclusions concerning IB for this woofer, power compression, thermal vs. mechanical failure tradeoffs, etc.... Anyone wanting max SPL at 30Hz would not choose this woofer, let alone this woofer in an IB, the whole argument is specious blather I won't waste any more time on.
As I said MUCH earlier in this thread, using a simple formula any high schooler could do, this woofer (using published specs) gives a Qtc of 0.707 with a ~1.3 Cubic foot box. You could go 1, or 1.5 and things wouldn't change hardly at all. As to how you EQ it, what is your goal?
My goal is to get as lower frequencies as possible in a simple to build, relatively small box that will produce quality sound at a reasonable but not ridiculous volume. I have not yet decided on this driver and chose to consider it merely off price, reviews and looks as I knew nothing about what would make a driver appropriate for a particular purpose. I know a little more now but the range of drivers easily available to me here in Aus is very limited, Dayton Audio seems to be the most common available and the RSS265HF-4 10" Reference HF seemed to fit my purpose the best. If you think it isn't the right driver for achieving my goals please let me know. This thread was as much about finding out about how well this driver would perform as it was about the enclosure. But anyway, back to Eq. How does it work? 🙂
Cheers!
I'd guess at ±5% by volume to be a top limit and only just being audible.
I built a 72litre tall floor stander a while back. When I came to test the final build I decided there was too much volume in the box. After some further testing using blocks of MDF inside, I decided to saw 5" off the bottom and reseal.
That took off ~14% from the internal volume. It was very definitely different sounding.
It certainly measured differently.
Hi Myles,
As Ron posted, a 1.3 Cubic foot box is what this woofer wants to be in. Deviate from that and you will muck up the damping and possibly even end up with "one note bass" if you reduce the volume too much. Going larger will drop the system Q to a lower value giving you early roll-off and less bass. Aiming for a system Q of 0.7071 (if you like decimals) will produce the flattest response and lowest bass extension within a 3dB window. 10dB if you want to rate it so the numbers look fantastic. On top of this, the size of your room will have the final say.
If you don't like the numbers with that woofer, try another woofer and so on. In the end, you will have something that suits you the best. Don't forget to allow for the speaker, bracing and port (if used).
-Chris
As Ron posted, a 1.3 Cubic foot box is what this woofer wants to be in. Deviate from that and you will muck up the damping and possibly even end up with "one note bass" if you reduce the volume too much. Going larger will drop the system Q to a lower value giving you early roll-off and less bass. Aiming for a system Q of 0.7071 (if you like decimals) will produce the flattest response and lowest bass extension within a 3dB window. 10dB if you want to rate it so the numbers look fantastic. On top of this, the size of your room will have the final say.
If you don't like the numbers with that woofer, try another woofer and so on. In the end, you will have something that suits you the best. Don't forget to allow for the speaker, bracing and port (if used).
-Chris
All this has been answered in detail but let me make it a lot more simple.
A 1.3 cu ft box is a nice compromise as I said previously. Small changes don't matter much, so a 1, 1.5 or 2 cu ft box is also a nice compromise. 0.5 cu ft is too small, it requires too much power to reach excursion limits. IB would perform marginally better than the 1.3 cu ft box from the power perspective (given a demanding signal at high power) but since small size is a stated goal and you haven't expressed any interest in cutting into your house IB is obviously not an option for you. A true IB is well past the point of diminishing returns anyway so no need to go that large.
In the 1.3 cu ft box a 150 watt amp will allow you to reach xmax so you don't need a larger amp than 150 watts.
Most plate amps have an adjustable high pass, most other types of amps don't. A unit like the mini dsp will allow you to high pass and eq all in one unit for about $100.
This particular example is pretty benign but let's consider the logical extension. Data-bass regularly puts 18 inch drivers into 4 cu ft boxes and dumps 5000 watts into them. Here's a laundry list of problems with that type of small box approach.
1. The 5000 watts does cause severe thermal issues, notably power compression, which is measured and looks really bad (significant losses and different frequency response).
2. An amp that can put out 5000 watts into very low frequencies for any sustained duration of time is EXTREMELY expensive, not many can do it.
3. Qtc is CRAZY high, this can be seen with all the measured drivers having massive "inductance humps" which are actually caused by high qtc. The lossy inductance of that type of driver also exacerbates the issue by cutting down the apparent motor strength which results in an even higher than expected qtc.
4. As data-bass shows, the box air spring is not a reliable safety feature. The amp used for testing is capable of pushing the drivers well past xmax and the test needs to be stopped when things start to sound very bad before xmech is reached.
5. Running a single 18 with 5000 watts is flirting with the ragged edge of destruction. The amp is running hot, the driver is both hot and at it's excursion limits and the safety factor provided by the air spring might not be enough to save the driver if the user doesn't turn it down when it sounds bad.
There's more points I would like to add but I have to get to work.
The point here is that in the world of high performance small box size is a limiting factor, it's the difference between 500 or 5000 watts required to reach max spl, and max spl is higher in the large low powered box because of power compression issues.
Bigger is almost always better from a performance perspective. But since small size is often a priority some compromises must be made.
Okay done. I'm putting this in a 1.3 ft^3 box with a 150W amp. I think a lot of my confusion has come from this IB disagreement. I know I asked about the amp way too much but I was wanting a yes or no answere. I couldn't be sure I understood the detailed explanation enough to make my own conclusion.
Thanks everyone for your help 🙂 Its very much appreciated. Ill let you know how it all goes and I'm sure ill have more questions soon.
Cheers!
Myles
Thanks everyone for your help 🙂 Its very much appreciated. Ill let you know how it all goes and I'm sure ill have more questions soon.
Cheers!
Myles
Hi Myles,
Good luck. I think it will turn out fine. As a rough guide, internal space taken up with bracing and speaker might run to 15%. Do add it up so you have some kind of idea what size of box you really have there.
-Chris
Good luck. I think it will turn out fine. As a rough guide, internal space taken up with bracing and speaker might run to 15%. Do add it up so you have some kind of idea what size of box you really have there.
-Chris
After read all posts here
I will using sealed for car only
And non-sealed for indoor and outdoor only
Thanks guys, you are helpfull so much
I will using sealed for car only
And non-sealed for indoor and outdoor only
Thanks guys, you are helpfull so much
That tone lasted about 1 second and somebody mentioned they smelled it after. That's extreme abuse, not an exception.
I just want to point out that the tests at Data-Bass of the passive sealed cabs are to evaluate how the driver itself performs in a very simple, common sized sealed cab, similar in size to what many end users would use and to use that information to help design a finished system design using the driver. Those tests themselves aren't indicative of a finished design, which would in all but 1 case, use drastically less amplifier than a bridged K20, different cabinet alignment or volume etc...
Max SPL being higher in a larger box or IB is not necessarily true. Higher deep bass efficiency, lower deep bass distortion and smoother response, most assuredly, but for sealed / IB the driver excursion limits are typically the limiting factor in the deep stuff. The air-spring can be used to control driver excursion quite successfully in a relatively small sealed enclosure if done right, so that a larger amplifier can be used which will allow higher upper bass headroom. There is a tradeoff with increased distortion, thermal heating, response shape, etc...Technically the IB will be capable of just as much headroom, but as a practical matter no one should allow the amplifier to be capable of voltages which easily mechanically damage the drivers in the deep bass. This limits the IB setup to much lower amplifier voltages available per driver than when in the smaller sealed cab and thus limits the maximum upper bass headroom a bit lower as well. As usual there are multiple tradeoffs involved in many areas.
Anyway I just want to point out for those reading along that the passive cab tests at DB do NOT indicate the performance of a finished system using an appropriate amplifier with the driver used. This is a common misconception I see made, as a lot of people do not understand that you need to be looking at: The impedance curves, voltages input into both the long term sweeps and the short term bursts, distortion levels and output compression, all taken together. This information would be used to help determine what an actual "safe" operating level, amplifier size and enclosure would be using the particular driver.
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Good notes, just a couple of comments.
Sure, like I said, max spl in a sealed box at the lowest frequencies is simply a function of how far the cone moves. If you can get it to it's excursion limits that's the most spl you will get regardless of the box size.
The only difference between the 14 liter sealed box and IB wrt max spl would be limits imposed on the small box like power compression. You might not be able to dump enough power into the small box for an extended period to get the cone to it's full excursion without power compression and possible thermal failure.
Interesting, more comments about the air spring.
The only thing the air spring does is prevent overexcursion (assuming the amp is sized appropriately).
I've been running a tapped horn in my home since 2009 without a high pass filter. And it doesn't have an air spring, it unloads completely below tuning. I've never had a problem with it, I turn it down when it sounds bad and I don't go crazy with media like movies that I know have strong deep bass below my tuning frequency.
The amp that's running the tapped horn is capable of pushing excursion to several times the driver's mechanical limits. It's a Behringer EP4000 pushing a single 6.5 inch Tang Band - this amp could launch the cone into space at low frequencies.
To recap - no air spring, unloads completely below tuning, no high pass filter, amp capable of absolutely destroying driver below tuning = no problem at all.
All it takes is a bit of caution and common sense and you will never damage your drivers regardless of the potential for damage.
As you said the box sizes you use to test are right in line with the box sizes people are using. So common in fact that diysoundgroup and by extension parts express are selling similar size flat packs. It is so ubiquitous that there is a conception now that these 3 - 4 cu ft boxes are optimum sizes when in fact they are the bare minimum size that will work.
When I do these small box vs IB comparisons I'm simply pointing out that the small box needs a lot more power to reach excursion limits. Not everyone can accommodate IB in their homes, that is not the point. I'm simply pointing out that bigger is usually better from a performance perspective if you can handle the space required.
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