Well yes obviously, if you push a driver beyond its capabilities then you'll get compression and high levels of distortion, but this has nothing to do with driver sensitivity.
If you're satellites are 94dB then that's how loud they will get with say 1 watt. The sub might give 91dB with 1 watt, so you'd need to give the sub twice the amount of power as the satellites to match their SPLs, so 2 watts.
What's important however is how loud you listen.
In my system the bass driver is 88dB, whereas the midrange is 96dB. At the volume levels I listen at the midrange gets 0.05 watts on average and the bass driver gets 1 watt. Quite clearly neither of the drivers is struggling to provide this.
If however I looked at it from another angle, say the midrange is 96dB and it can handle 128 watts. Well the maximum SPL it will generate is 120dB. This is ridiculously loud and the bass driver would be blown to bits if I wanted it to get loud enough to match the mid. This doesn't matter though because I don't want to listen to it anywhere near that loud and for all the listening levels that I choose to listen at, the bass driver is more then capable.
Well, don't we want both the sub and the satellites to have the same dynamic headroom? We don't listen to sine waves, we listen to dynamic music that varies a lot between soft and loud. So, in your case, it appears that your sub does not have the same or more dynamic headroom of the satellites. Given that we are not as sensitive to bass frequencies, shouldn't that fact play into how loud the sub should be able to play?
Does anyone know of a chart showing Vd, which is the product of Sd and Xmax, for a variety of drivers?
I'm liking the B&C 18PS100 more and more now. For a vented box of 7.5 cu ft tuned to 30Hz gives a nice curve down to a -3dB point of 32Hz. The box is about 39" tall, 24" wide, and 15" deep, so basically slightly taller than a kitchen base cabinet. Plus, it costs about $240, not much more than the Dayton 12" or 15" subwoofer drivers. Driver sensitivity is about 95dB also, same as my satellites. I'm just not used to the idea of even handling an 18" driver. The term "whoa!" comes to mind....
I would prefer to use something like the 15PS100, but I can only get it to go down to about 45Hz in a vented box. The Qts is too low I think.
I would prefer to use something like the 15PS100, but I can only get it to go down to about 45Hz in a vented box. The Qts is too low I think.
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Is this going to be used for just music? tuning that high tends to make a muddy subwoofer Group delay is too high in the noticeable Frequency range 25hz and up, i try to keep group delay below 20-25ms until below 25hz in a ported design. Ya get a little less output but much cleaner sound.
what i do... mostly, use at your desecration, no refunds, beer donations accepted 🙂 . Choose a box volume slightly above Vas and tune to ~16hz which makes a kind of hybrid between a sealed box and bass reflex, best of both in my opinion.
what i do... mostly, use at your desecration, no refunds, beer donations accepted 🙂 . Choose a box volume slightly above Vas and tune to ~16hz which makes a kind of hybrid between a sealed box and bass reflex, best of both in my opinion.
Group delay for the 18PS100 in the box I picked maxes out at 20ms @ ~27Hz. Thanks for the heads up on that.
No, this is not how it's done. Typically you look at what max SPL and to what frequency extremes you want a system to achieve and then design it to be able to go that loud.
As an example you may be designing a two way loudspeaker with a 6.5" mid/bass and a 1" dome tweeter. The mid bass has a rising distortion profile above 1kHz and the lower you can cross over to the tweeter the better. The tweeter has a very well designed motor and doesn't show rising distortion till under about 1200Hz under test, nevertheless it still has a limited amount of linear excursion and you want to remain within this at all times. If your maximum listening level were 80dB you might get away with an xover @ 1500hz, however if you like to crank it to 95dB you would have to use an xover at say 2000hz.
It is exactly the same with a sub or a bass driver. Bass is generally the hard thing to do, if you want deep bass at loud levels then you need a large box and a large driver. You can then decide I want a small box with a large driver as you cannot fit in a large box. This reduces how deep the bass will go, but the driver has a lot of linear excursion, so to get around the loss of deep bass you use active equalisation to extend the response. This takes more amplifier power, but you've got plenty of that so that isn't a concern, but as you have to drive the sub harder for a given bass frequency you hit its linear excursion faster then if the box was bigger for a given SPL. Obviously this limits the maximum SPL that the system can achieve, however if it goes loud enough for your requirements then there is no problem.
If your main speakers/satellites happen to be way more sensitive then the sub it doesn't matter. If the sub can go loud enough for your needs then you're doing fine.
As mentioned above find out what requirements you have for a sub and then design around that. If you're into HT and want solid extension down to 20hz at a THX spec of 105dB in room then you'll need to design to that specification. Remember that a sub driver will radiate omnidirectionally so you'll lose 6dB off of the sensitivity figure, however if you place the sub on the ground and in a corner/next to a wall you will get boundary reinforcement that will cancel that out +maybe more. You're also going to get some room gain happening below a certain frequency too.
in a perfect world... yes
but... if your mids go to 125db and the sub only goes to 112db it's ok because going to 125db is unnecessary (and dangerous). you have headroom you can't use. kinda like a really fast car on a public road... as long as it'll go 80 mph you're good.
edit: dang... sniped by 5th
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I can't see how could be true.
A given driver in a sealed box will always (so long as power limits aren't exceeded) have the same maximum SPL, no matter how large the box is.
The size of the box dictates how much power you need to use to move the cone.
Chris
You are indeed correct, I don't have a background in engineering so I just assumed. The maximum SPL is the same regardless of box size, only it takes a lot more power for you to get there.
See attached picture, the target cone excursion and frequency are the same for the first three and second three sets of graphs. The only difference is the required gain to push the driver into the end response. The first three being a box of around 10 litres and the second a box of 1.
Attachments
and if it takes more power to get there, then there will be much more distortion, both from the amp and from the driver. So, it seems a worthy goal for low distortion is to have a high efficiency subwoofer that doesn't require very much power to produce the desired SPL.
I'm liking this 18PS100 more and more... even if I never need 120dB...
It wont result in more distortion from the driver at all. As you can see from my graphs the driver excursion is identical for a tiny box and a large box. Non linearities from the motor should be similar.
The trouble here is that the driver will literally explode. In the large box it requires ~30 watts @ 20hz. For the small box it needs 2000 watts by 20hz....
I agree with your opinion that it's better to have more headroom then less, but certainly you have to accept that there is a point where having any more headroom will net you close to zero increase in sound quality. If you want to play it safe then spec your sub to 75% of its xmax for your required SPL.
I thought I'd just add in, that when completed my 4 subs will net me 105dB @ 20hz in room. This is strictly for explosions and stuff in films. Most of the time I don't watch films or listen at high levels, so in 95%+ of situations none of the drivers in the system will be working anywhere near their limits. You could do a similar thing, spec the system to be able to do something that you will call on it to provide only rarely. That way it will be able to satisfy your occasional extreme demands, but when under normal listening will have plenty of headroom.
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I found this statement on the DIY subwoofer page:
"In most rooms, the room itself provides additional gain at frequencies below approximately 30 Hz. There's a slight risk of creating a boomy system if you create a design that on paper has a cutoff point much below 30 Hz."
Anyone have any thoughts on this idea? The system I am considering building has a -3dB of 32 Hz. I don't know what the response would be like in a room.
"In most rooms, the room itself provides additional gain at frequencies below approximately 30 Hz. There's a slight risk of creating a boomy system if you create a design that on paper has a cutoff point much below 30 Hz."
Anyone have any thoughts on this idea? The system I am considering building has a -3dB of 32 Hz. I don't know what the response would be like in a room.
It depends on the size of the room as to where room gain will come in. I don't know if the BASH amp has a built in highpass for limiting excursion at really low (read 5hz etc) frequencies, but if it does you could modify it to roll off higher if this was a concern. What we class as boomy bass though isn't normally created as low as around 20-40hz and any extra output in that area could actually be beneficial toward ones perception of the sound. A bit more bass then 'flat' never tends to offend anyone, rather it's quite pleasing, what we dislike is 'one note' bass where room modes create severe dips and peaks. It the peaks that create the 'one note' effect by playing certain frequencies far louder then others and thus making it sound like the other notes aren't there.
Yes, it has a frequency selectable subsonic filter and a parametric equalizer too. The LP filter is 24dB/octave as well. The specs are some of the best I've seen for a subwoofer plate amp. That stuff from PE seems to be mostly unacceptable to me.
I haven't looked too closely at the BASH amplifiers but everyone seems to praise them incredibly highly.
The BASH system is just a type of efficient amplifier. The quality of performance is up to the designer. There are good BASH amps and crap BASH amps.
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