Noob question about speaker sensitivity

If I were you I'd just be shopping for a pair of speakers with the kind of voicing you want. Plenty of choices out there, and if what you want is punchy midbass, you can find that faster than you can create it. Not to discourage speaker building, but since you mentioned that as a specific parameter, there IS a way to get that in ready-to-play form.

But not with the FST mids
 
Important to note a few things about coupling/mutual summation. It's anything but broad band, and is very dependent on driver proximity and spacing. Even driver size plays a role.
Do you mean the drivers should be placed as close as possible to each other for best result? Is it more likely to work with smaller woofers than larger? What do you mean with driver proximity?
It's more likely than not when dealing with larger tandem woofers, acoustic coupling/summation gains will roll off below XO, sometimes well below..
Meaning if the two 90dB drivers are effectively 93dB at crossover point, say at 400Hz, the 3dB gain can be more or less gone at 200Hz or 100Hz unless the drivers in question have unusual specs?
 
One last question

In principle, will two bass drivers behave the same in one shared 100 litre cabinet as in a separate 50 litre cabinet for each? (Don't have the exact volume yet, so this is just an example) Will I have to calculate new reflex port tubes or would the ones used in the separate original 50 litre cabinets work in the 100 litre home made cabinet?
 
What do you mean with driver proximity?
The drivers' location relative to each other when not mounted on a common baffle in the same plane. A unity horn for example.

Do you mean the drivers should be placed as close as possible to each other for best result?
Generally, yes. But, any given design may use driver spacing to fine tune the range over which the drivers couple. It really is up to the engineer of the speaker system. I can drive a train, but an engineer i ain't. ;)

Meaning if the two 90dB drivers are effectively 93dB at crossover point, say at 400Hz, the 3dB gain can be more or less gone at 200Hz or 100Hz unless the drivers in question have unusual specs?
Simply meaning that any mutual summation of woofers in a multi-way system will roll off as frequency rises toward the XO point. It's not going to be a smooth linear 3db across their working range. But, we're only talking about the acoustic gain via summation/coupling, not the 3db of electrical gain from paralleling drivers.

In principle, will two bass drivers behave the same in one shared 100 litre cabinet as in a separate 50 litre cabinet for each?
The same.
 
The drivers' location relative to each other when not mounted on a common baffle in the same plane. A unity horn for example.

Generally, yes. But, any given design may use driver spacing to fine tune the range over which the drivers couple. It really is up to the engineer of the speaker system. I can drive a train, but an engineer i ain't. ;)

I see. Thanks for expanding on this

Simply meaning that any mutual summation of woofers in a multi-way system will roll off as frequency rises toward the XO point. It's not going to be a smooth linear 3db across their working range. But, we're only talking about the acoustic gain via summation/coupling, not the 3db of electrical gain from paralleling drivers.

Not sure I understand. So in theory it will be 3dB electrical gain, but in real life acoustics some of those 3dB will not show across the full working range of the bass, espesially in the upper working frequencies near the crossover point? The drivers in question are two of the same, and they will both receive the same signal, so they should be paralell all the time while playing, mounted on a common baffle.
You mean if there's a big difference between the placement/depth of the bass and mid drive that there could be some canceling in the range where the overlap in frequency over the xo roll off? I've been thinking about ways of aligning/pulling the midrange and tweeter back a bit to where they allign. As I understand it, the most important place for things to line up, both dB wise and with phase, is at the crossover points, because that's where errors are most noticable. But you're not talking about phase cancellation in the frequency range where the midrange and bass driver overlap when you point to the problem being in the upper frequencies approaching crossover point?

The same.

So they will behave the same. Cool. Less math for my brain to grasp. For the same reason I was hoping I could just snag the reflex ports from the original speakers as well, and put them in the 100 litre cabinets so I wouldn't have to calculate and make new ones. (There is originally one port in each 50 litre cabinet) Would this be the same as well, whether the ports are placed in one 50 litre cabinet each or both in a shared 100 litre cabinet?

Thanks again for the help. It means a lot. I think the math side of things is what's holding a lot of amatuers back from trying out DIY experiments that could possibly turn out quite interesting.
 
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If you need to - you can build an L-pad out of two resistors for the woofer. Its usually not a great solution to do this for the bass however as it is getting a lot more power from the amplifier to run it. Its usually better to pad the mid and/or tweeter as the are getting less power to run the. So that means padding the woofer will require some fairly large wattage resistors - or, you are better selecting another woofer with closer SPL. 3dB may not be an issue - it will be noticeable but given the woofer will have most of its range rolled off, it may not be an issue.

3dB is audible. Below 2 dB may not be audible for most.

Adding impedance to a woofer affects the damping factor. Remember, the speaker is a current generator as it contains a coil of wire in a magnetic field. In consequence, as the cone returns to its rest position a back EMF is generated. The amplifier absorbs this current. But when impedance is added to the path the damping ability of the amplifier is impaired. This issue is less significant for the smaller drivers as less current is generated.

A superior solution is to simply (a) use an equalizer or (b) adjust the amplifier's (if integrated) or preamplifier's (if component) bass control to balance the levels. One could, of course, build a simple filter to attenuate bass for the desired frequency band and place it at the input to the amplifier and thus pre-adjust, exactly as an equalizer would, the frequencies in question. Several speakers companies did such adjustment to increase the bass. The Bose 901, because it was unable to properly reproduce bass on the midrange drivers, or the Electro-Voice Interface speaker series.

Fixing the problem at the woofer driver will, at best, waste power and, at worst, alter the sound.

Edit: fixed typo and added increase for Bose and E-V.
 
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So they will behave the same. Cool. Less math for my brain to grasp. For the same reason I was hoping I could just snag the reflex ports from the original speakers as well, and put them in the 100 litre cabinets so I wouldn't have to calculate and make new ones. (There is originally one port in each 50 litre cabinet) Would this be the same as well, whether the ports are placed in one 50 litre cabinet each or both in a shared 100 litre cabinet?

Thanks again for the help. It means a lot. I think the math side of things is what's holding a lot of amatuers back from trying out DIY experiments that could possibly turn out quite interesting.

If each 50-L speaker had its own port, you can combine them into a single 100L cabinet but it would require both ports. Or one larger port to replace two smaller ones. Basically, with bass reflex cabinets, if you double the number of drivers you double the volume and ports too.
 
If each 50-L speaker had its own port, you can combine them into a single 100L cabinet but it would require both ports. Or one larger port to replace two smaller ones. Basically, with bass reflex cabinets, if you double the number of drivers you double the volume and ports too.

Thanks for clearing that up!
 
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