Cabinet question (and yet another watt/ohm question)

[leechrimes]

If you are used to using 8x10s and don't like 4x10s, I think a 2x12 isn't going to make you happy.

this is the concern, more for my 45 year old back than anything

 

[leechrimes]

I would use a 410 cab on top of a powered subwoofer, and run the FX line out from the Digbeth to the sub. That should give the feel.

I've been thinking a hybrid setup - a 15" for the lows and a separate cab for the rest - so I'll give this some thought. Thanks

 

[leechrimes]

No. Knob position does not tell you how much headroom the amp has remaining.


A good rule of thumb is the speaker should be able to handle at least as much power as the amp will deliver. Use RMS power ratings.

AFAIK the DB500H does not have published specs rated power at 8 ohms Usually solid state amps make more power as the impedance goes lower. Available power at 8 ohms could be 250W or as much as 350W. So if you have one 8 ohm cab, you would want it to be able to handle at least 350W. Not problem if it can handle more.

The RMS power rating only tells you part of the story. Basically the RMS rating tells you have much power the voice coil can handle without burning up. More important for bass cabs can be the mechanical power limits below 100hz. The mechanical power handling relates to how far the driver can move without tearing itself apart. Unfortunately most companies don't post any information on their speaker's mechanical power handling. The Mesa Subway line is an exception.

I will try to explain the problem:

Let's use a large Eminence cab design for the 2512, which is rated 250W RMS.

If you chart the excursion plot for a woofer in a ported design it will have sort of an S-shape. See excursion plot below. As the frequency drops below 500hz, cone excursion will increase. Usually a bit below 100hz, the port will start to become resonant. This resonance suppresses cone excursion. The port is tuned so it becomes active at about the same frequency where the woofer starts to cut off. The idea is to use the port resonance to smoothly extend response a bit lower. At resonance (Fb), the port is making most of the sound and providing maximum suppression to cone excursion. Below Fb system response drops of quickly and the driver unloads and starts bouncing around.

Here are the response and excursion plots for the 2512 in a large cab. This is the second design in this doc: https://www.parts-express.com/pedocs/more-info/290-593--eminence-deltalite-2512-cabinet-design.pdf

View attachment 7197927
View attachment 7197926

The first thing to notice is the cab is mechanically limited to 100W and requires a steep HPF at 40. I will remind you here that the driver is rated 250W RMS.

Notice the S-shape of the excursion plot.

Fb is 50hz. Notice the dip in the excursion plot is centered at 50hz.

Max linear excursion (Xmax) for the 2512 is 4.9mm. With 100W excursion approaches 4.9mm at about 70hz and exceeds 4.9mm as the frequency dips below about 40hz.

The -3dB point (F3) for this design is 58.71hzf and response drops off quickly below that.

You could use EQ to extend LF response a bit, but EQ will not allow the design to produce more output or handle more power. EQ is only effective if you don't need much volume. If you look at the excursion plot, the design is capable of about 112dB at 48hz. At this point response is down about 6dB. With the right EQ curve and 6dB of boost, the design could have flat response to 48hz, but it will still only be capable of 112dB.

See, this is why I hope forums never go away, because this kind of deep dive is the good stuff we all need. Thank you for your time on all this, greatly appreciated

 

[leechrimes]

The first thing I think you need to accept is that it's not realistic for your rig to have flat response down to the fundamental of your lowest notes. It's possible to buy gear that will play this low, but it will be very expensive and also big and heavy.

The good thing is our ears trick us into thinking there is more fundamental than there is. As a minimum you need a speaker with strong response to the first overtone, which is the octave above the fundamental. The fundamental for A#0 is about 28hz, so you need strong response down to 56hz or lower. This is very doable.

In order to protect a ported design I suggest using a steep HPF (24dB per octave or better).

You can do the rice test to determine Fb, and then set the HPF at or slightly below Fb. The rice test is basically lay the speaker flat on it's back and put a few grains of rice in the cone. Then do a frequency sweep and note the frequency where the excursion dips. The rice is to help you see the dip. There are online tone generators you can use to do the frequency sweep.

Most people adjust the HPF to the point where it starts to thin out the sound, and then back it down a hair. Although it may seem counterintuitive, a properly adjusted HPF may actually fatten and focus the lows a bit.

Alternately you could spend a fortune and buy subs that will play as low as you want. Danley DTS10 has response down to 10hz. One weighs 285lbs, and you may need multiples.

DTS10 | Danley Sound Labs

The DTS10 theater subwoofer is the ideal subwoofer for home theatre and cinema use with a powerful low end sound.

www.danleysoundlabs.com

fine-tuning my HPF pedal is definitely something I need to spend more time with - I've noticed a positive change already but knowing the sweet spot should make a huge difference whatever I'm running out of.

 

[Pulverizor]

You should grab a train ticket to Andertons mate.

Take your amp and try out the lightweight Markbass 210, GK Neo 210, and Ampeg Venture 212. See if any of those will substitute for a fridge.

It's unrealistic to expect any >20kg cab to move as much air as a much larger cab, but if you've got the budget...

 

[6thplanet]

4/10 at the least, X2 would be best. Cone area is your friend in this situation.

 

[leechrimes]

You should grab a train ticket to Andertons mate.

Take your amp and try out the lightweight Markbass 210, GK Neo 210, and Ampeg Venture 212. See if any of those will substitute for a fridge.

It's unrealistic to expect any >20kg cab to move as much air as a much larger cab, but if you've got the budget...

Yeah, a good day spent in a decent space running my typical rig through actual cabs may be the only true way to figure this out