So, I have a pair of satellite speakers that have a sensitivity of about 94dB. I'm having trouble picking a subwoofer driver to go with them. This will be a self powered subwoofer with a plate amp. Do I choose a driver that is less, the same, or more sensitive than what I've got? If I choose a driver that is a lot less sensitive, won't the increased gain required to match the satellites cause a lot of distortion in the sub (I'm assuming the driver has the required power capacity)? If I use one that is more sensitive, how do I pad it down to match if it has it's own amp (maybe that's not a problem)?
It seems that all the subwoofers that go really low have very low sensitivity, which is a problem also, since the gain would have to be so high that I assume they'd have a lot of distortion.
I'm intending to build just a regular vented type of box for this.
It seems that all the subwoofers that go really low have very low sensitivity, which is a problem also, since the gain would have to be so high that I assume they'd have a lot of distortion.
I'm intending to build just a regular vented type of box for this.
OK. thanks.
Assuming the driver can handle the extra power, doesn't the distortion go up with greater cone displacement? Don't we want low distortion subwoofers, since we can hear all of the harmonics?
the sensitivity figures is just one part of three things you need to know. You figure out how much dynamic range you want then use the sensitivity to figure out how much power you need achieve that range.
example: 1w to your mains gives you 94db output. If you get a sub that has a sensitivity of 87db 1w/1m you need 6.6w going to the sub for it to match (94db). if you want 12db headroom over 94db the sub would need to handle 105.6w and a amp to supply that power. the mains would need 32w to hit the target 12db headroom (106db).
example: 1w to your mains gives you 94db output. If you get a sub that has a sensitivity of 87db 1w/1m you need 6.6w going to the sub for it to match (94db). if you want 12db headroom over 94db the sub would need to handle 105.6w and a amp to supply that power. the mains would need 32w to hit the target 12db headroom (106db).
distortion goes up if you exceed xmax, as long as you stay within the ratings of a driver the distortion is minimized.
Thank you very much. Interesting. How much headroom is considered a good value? How do you calculate this?
So, let's say I screw up and I make a sub that has 98 dB sensitivity and it's own amp. What do I do then?
You figure out... "hummm, how loud do i want this to go..."
that's it.
you're going to build your own driver? just kidding
the system dosent have a sensitivity rating, just the driver.
You match the driver with the amp and use design to make sure the driver and amp work together to make the type of sound you want plus about two dozen other things to consider with box design.
you might want to start here: WinISD Pro Tutorial and Download (A detailed guide on how to use WinISD Pro) - Home Theater Forum and Systems - HomeTheaterShack.com
or here: http://gonecatfishin.net/WINISD.htm
or here: http://gonecatfishin.net/WINISD.htm
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I've been using WinSpeakerz. Is this better? It looks like WinISD has more features.
You figure out... "hummm, how loud do i want this to go..."
that's it.
you're going to build your own driver? just kidding
the system dosent have a sensitivity rating, just the driver.
You match the driver with the amp and use design to make sure the driver and amp work together to make the type of sound you want plus about two dozen other things to consider with box design.
OK, thanks. I guess it becomes a system once an amp is connected to the speaker, so the sensitivity of the driver is only part of the picture.
I found this on another forum:
"The second factor we need to consider is how output is achieved. Sensitivity isn't what determines maximum output. Output is a function of air displacement. The maximum amount of linear displacement (Vd) you can achieve is limited by your cone area (Sd) and linear excursion (Xmax). As you increase the amount of displacement at your disposal, you increase the potential linear output you can achieve. Even though a driver may have a higher sensitivity, if it's maximum linear displacement (Vd) is less than that of a driver with a lower sensitivity, the lower sensitivity driver will have the potential for higher levels of output.
We also have to consider the effects of Power Compression (http://www.soundsolutionsaudio.com/forum/Understanding-Power-Compression-t7112.html) (and I again urge you to read the link). Consider the effects of power compression applied to our scenario. A higher sensitivity driver may, for example, begin to experience more power compression at a lower output level than a lower sensitivity driver. If this is the case, then as output is increased beyond that level the higher sensitivity driver would gain less output for each increase in power and experience more parameter shift."
The link in there no longer works.
So, there is a formula, which I could derive myself I suppose, for maximum Vd, which would be a useful method of comparing drivers.
I am not familiar with power compression.
I am not familiar with winspeakers, so i can't say if one is better than the other. I'd guess they are about the same as all design software for speakers is similar.
for a ported system power compression isn't really something to worry about, you'll need to watch excursion, as it is generally the limiting factor in a bass reflex enclosure.
power compression occurs when a driver is driven to it's limits of power handling and the VC heats up too much and cannot dissipate heat faster than the input power is heating it.
for a ported system power compression isn't really something to worry about, you'll need to watch excursion, as it is generally the limiting factor in a bass reflex enclosure.
power compression occurs when a driver is driven to it's limits of power handling and the VC heats up too much and cannot dissipate heat faster than the input power is heating it.
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this is a good general guide to choosing a driver : The Subwoofer DIY Page v1.1 - Choosing a Driver
Ah, ok, thanks. WinSpeakerz has calculated excursion based on power input, so I check that of course. I don't think this software is very professional, but it's good enough for me right now. I guess power compression would be more of an issue with a low sensitivity driver, since more power would be required of the amp to match the satellites. My current choice is a Dayton 12" titanic in a 3 cu ft vented box tuned to 22 Hz. With 100 watts into it, driver excursion is a problem down around 12 Hz. The software says SPL output @ 100 watts is 109dB. The -3dB point is about 22Hz in this box. I'm trying to make one of the B&C drivers work but have only found the 18PS100 suitable so far.
Thanks. Been there, downloaded the pages, read through them pretty good while on vacation. Maybe this isn't so complicated after all.
One thing I figured out is that a driver with a Qts of around 0.4 makes for a good vented box response in simulation.
OK, thank you. I modeled the RSS315HF-4 is a sealed box, 2.5 cu ft, -3dB is 37Hz. You can put in 300 watts and not exceed the driver's excursion limit. Output in the flat part of the band is almost 111 dB at that input level. It looks like a pretty good choice. I don't know if 37Hz is low enough though. I read that room gain can create problems if the cut off frequency is much below 30Hz. Do you have any experience with that? I'm intending to put this in a corner, with a trapezoidal shaped box with 45 degree sides.
If you've got a plate amp then there's nothing to worry about at all. The gain setting on the sub will allow you to turn it up or down to match the level of the satellites.
Edit - lol. I'm replying to the first post, it seems the question has been more then answered by the time I actually got around to replying
Edit - lol. I'm replying to the first post, it seems the question has been more then answered by the time I actually got around to replying
If you've got a plate amp then there's nothing to worry about at all. The gain setting on the sub will allow you to turn it up or down to match the level of the satellites.
Edit - lol. I'm replying to the first post, it seems the question has been more then answered by the time I actually got around to replying
Well, I suspect there is more to the story than that. To minimize distortion, don't we also want to minimize driver excursion?
"When most persons talk about audible distortion in a working (as opposed to faulty) subwoofer, they're usually referring to the gross levels of distortion that appear when the driver (or amplifier) has reached its limits. In other words, they're talking about VERY audible distortion.
However, distortion actually starts occurring at much lower output levels. In fact if you see the driver's cone moving, it is likely also producing distortion along with the source signal that it's attempting to reproduce. This distortion may be at too low a level to be distinctly audible, or it might be high enough in level to appear to be a subtle but noticeable change in the tonal response of the subwoofer.
...
Fortunately, we are not that sensitive to distortion at very low frequencies (if we were, most speakers and subwoofers would sound like garbage). When it's present, we usually interpret it as a change in tonality rather than an unwanted addition to the signal that the subwoofer is trying to produce. However, in a side-by-side comparison, it's usually not that difficult to distinguish between a subwoofer that exhibits very low distortion compared to one that has a somewhat higher level, particularly at higher levels."
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