What spl do I need?

I want to build one or two small subs to augment my full range drivers. I understand some of the trade offs, including that small implies sealed, and that if I want small with a deep response, I must accept reduced sensitivity. I’ve also learned that the limitation on output level at the lowest frequencies are limited by cone area and Xmax. But how much level should I target for my system? Can I simply target a matching level to my system or should I go higher to account for lower hearing perception at low frequencies?

Right now my system is two drivers with 89.7db/W sensitivity being driven by a 7W amp. If I crank it (I don’t really) that would put at about 96db for spl. Would it be reasonable to target a similar value for the subs at the lowest frequency of interest?
 
I’d like to get down into the 35hz range for a -3db without boosting, perhaps into the 20s with EQ if possible but I want stay reasonable. Everyone says they want to hit 20hz but I doubt the music I listen to has much energy that low. Linearity is more important. The mains get down to around 50hz (maybe lower) but I’m trying to unburden them below, say, 80 hz to improve clarity at higher volumes. I will high pass them appropriately.

So, shoot for 105 dB at like 30hz for a starting target? Sounds right. I’ll pick a driver and run the numbers tomorrow. Thanks.
 
I’m a bit out of my depth on driver selection so just going by what’s on Madisound and recommended for small enclosures it seems that getting to 105db at the sizes I had in mind is not possible.

For example, the SB Acoustics SB23MFCL45-4 looks like it can hit 98db at 30hz. The SB Acoustics SW26DBAC76-4 is better at 101.6 but I can’t find any “hifi” testimonials. There’s a very pricey ScanSpeak 23W/4557T-02 that only hits 93.5 and needs twice the enclosure volume for a typical alignment.

However, I have a cheap ported sub hooked up (that’s how I realized I wanted to go this direction) so I’ll take some measurements while it’s cranked to see what kind of levels are appealing. It’ll have to wait until my minidsp shows up as moving my computer is a bit of a project.
 
What i do with a similar driver is using a 10" subwoofer driver of 89db with a 6" FR of 88db. But if the sub is too efficient, you need to attenuate it and that is a lot of watts lossed in heat in stead of sound with a passive crossover. 1 or 2dB more is good because of the losses in the crossover.

But I think you will use an active, and then it does not matter that much as each driver has it's own amp. As long as your sub can get the same volume or more than your FR full open you're good. The end volume will be set in the preamp and the balance between the two drivers in the crossover (be it dsp or analog).
 
Thanks, waxx. You’re the one who put me on this new track with your comments over on the Altec thread. :)

So your advice is to target similar efficiencies between sub and main driver. This is good as it is more in line with the SPLs that simulations indicate. And yes, I will be crossing actively and and amping the subs separately. I have a 2x75W amp here that has no other commitments. It may be just enough depending on the driver I end up using. Thanks again.
 
So, at this point the best driver of the ones I know is the SB23MFCL45-4. It’s efficiency is very similar to my current drivers, and is the most efficient of the three I mentioned above. It also has the smallest enclosure for a sealed .707 alignment and plenty of linear excursion for modest EQing at the low end. It helps that they are also the cheapest (of the three, certainly not cheap in absolute terms).

Unless someone points out a pitfall I’ll probably buy a pair and throw some boxes together. I hear it doesn’t make that much difference in practice but I’m leaning towards a lower Q to extend the frequency response a bit more.
 
Can't be answered without reference to music genre. A women's chorus will have immense but very brief peaks. So you need real tweeter power, no kidding. Pop recordings have no peaks like that. All cooked away.

If everybody is dancing and jolly and the music is distorted, all you want is a speaker that doesn't fry even if sounding terrible.

A tricky question. Like with a car you can have top speed or time to pass another car at 60 MPH.

Anyway, I don't think you can make much of the the imaginative specs provided.
 

sumotan

Member
2013-10-16 4:18 pm
Very timely, I was about to ask the same question. What if my mains are 98db sensitive,
how does one find a sub that matches it ? I'm also looking at F3 of 35-40 hz.
Never play with Subs before so am a real noob. Going with huge PA woofers are a no no for me due to space constrain.

Many thanks
 
Very timely, I was about to ask the same question. What if my mains are 98db sensitive,
how does one find a sub that matches it ? I'm also looking at F3 of 35-40 hz.
Never play with Subs before so am a real noob. Going with huge PA woofers are a no no for me due to space constrain.

Many thanks

With a passive crossover, there is no other option than big pro woofers, as no small woofer will be that efficient and go low.

Active, you need to count for each 3db less efficient, you need to double the wattage to get roughly the same volume as the FR. And best is to keep 50% headroom on the woofer, so the amp and speaker never gets too much stressed

So a 90dB efficient 10" Dayton Audio RSS265HO-44 can be tuned to 35hz in a ported box and can handle 600w, and should be fit for such a FR of 98db, as long as the power of your amp for the woofer is at least 4x the power of the amp for the FR. Then you set the balance of the signal in the crossover (woofer 4x as loud as the FR) to get an flat frequencyrange.
 

sumotan

Member
2013-10-16 4:18 pm
Thks Waxx, I'm beginning to think if I've made the wrong choice in going with PA stuff for my diy speaker build. Adding subs would clutter up space with additional boxes. Btw think I've read somewhere that none horn loaded subs don't gel well with front horn loaded speakers, is there any truth to this ?
 
You need to watch the aliging, and with a hornloaded top and a direct radiator as sub, you need to put a delay on the sub driver so everything is in phase. Otherwise you will have phase issues wich can mess up the sound.

You can also make a hornloaded sub, but that will be a big box as the hornpath must be long to load the sub frequencies. So if space is an issue, use a ported box with a 10" sub driver with it's own amp (like the one i mentioned) and set in the crossover (i suppose it's a dsp) the delay for the sub right so it's as long as the horn of your topdriver. (how to do that is a whole other subject, but much documentation is found online). Then it should not be an issue. Most if not all mismatches between direct radiators and horns are due to bad time aligning of the speakers.