Speaker cab desighns

[Rice]

It's not as simple added back pressure. The pressure in a speaker cab is a dynamic thing---even in a sealed box. Adding back pressure will help in one direction, but be a hindrance in the other direction. In other words---the added pressure will help propel the cone forward but limit its return. Your cab will go less loud and have less bass because you are hindering the rearward motion of the cone.
A few ways designers have dealt with this are adding a passive radiator or an aperiotic(sp? ) vent. These allow the speaker to behave like it's in a larger cab. There are tradeoffs and these designs don't work as well with bass cabs.
I'm using a different technology that allows the entire rear wave to be harvested and re-combined with front wave in phase. It works up to 4khz. It also does not unload as reflex cabs do. If I'm not mistaken, the Barefaced cabs are a variant of bass reflex design.

This is what EA does with there cabs and what attracted me to them in the first place. Size to power to weight to frequency spectrum, they were the best out there (at least on paper.) As such, once i actually got ahold of them, I was a believer. I can't pretend to know how the science and calculations work, but it seems EA and Mike A. are some of the few if only who have made this work.

 

[crazyBassClown]

It's not at all difficult to lower Qtc by a full point, say from 0.8 to 0.7. To some extent that emulates the effect of a larger box, but by no means does it duplicate it, as the lowered Qtc from stuffing also results in a loss of sensitivity, whereas the lower Qtc from a larger box is accompanied by increased sensitivity. More information on what stuffing does, and how it affects ported cabs, can be found at Data-Bass

And it has absolutely nothing to do with how acoustic suspension works.

Isn't a larger box with it's lower Q also less sensitive than a smaller box with higher Q?
See graph on Invalid Link Removed relating Q to efficiency.

 

[DukeLeJeune]

Isn't a larger box with it's lower Q also less sensitive than a smaller box with higher Q?
See graph on Invalid Link Removed relating Q to efficiency.

The chart at that link labelled "Frequency response of sealed enclosure system with different values of Qtc" does not include a very important piece of information when it comes to choosing box size: As the Qtc changes due to change in the box size, SO DOES THE Fs. (Specifically, Fs and Qtc both go down as box size increases, and vice-versa.)

The small box/high Qtc system is more efficient at the box tuning frequency, but the large box/lower Qtc system would have a correspondingly lower resonant frequency. As a result, the larger box's efficiency holds up well down to a lower frequency.

The chart is not incorrect, but it is ONLY showing the shape of the curve for different Qtc values, and NOT everything that happens in real life when the box size is changed.

If the only change you make is adding damping material, the Qtc is reduced but the Fs does not change by a corresponding amount (it changes very little).

 

[Rick James]

Duke is right. The problem with the Audio Judgement article is that their section about how stuffing works was copied and pasted, with slight alterations, from other sources that also didn't have it right. Adding stuffing doesn't translate into 15 % – 25 % volume increase, and it doesn't give up to 15% efficiency increase. They make no mention of Qa at all. Any discussion of Qtc and stuffing that doesn't include Qa is flawed from the get go.
Confusion about what stuffing does can be traced to an article about it back in the 90s by a speaker builder who stuffed some boxes and measured the results. He concluded that the stuffing made the cab act as if it was a larger box, because the -3dB frequency went down. Unfortunately he only measured the -3dB point, and left out all the other pertinent factors, especially impedance, which shows what's really going on. He didn't even get the -3dB frequency drop right, because stuffing doesn't lower the -3dB frequency, it just appears that way when the response hump caused by high Qtc is tamed by the lowering of Qtc. Other respected engineers, even Vance Dickason, took his results at face value without first making sure they were accurate. They weren't.

 

[BogeyBass]

So if a speaker sounds muffled from being over stuffed by means of friction between the fiber and sound waves ,
Does that suggest that a speaker needs the volume of space behind it for acustic reasons ? Or is it the actual systematic compression of air that make a speaker box efficient ?

Yes because of volume or the need for volume. To get a certain ripple response in a sealed enclosure or Qtc. Qtc being the total Q of the enclosure and all it's resistance. A Qtc of .707 is most common or sometimes consired the " ideal" response. Since .707 is considered to give the flatest frequency response.

Depending on the speakers electrical properties and mechanical properties. There is formulas to calculate what volume is needed to get whatever Qtc is desired.

A.N.Thiele and Richard H. Small devised methods to obtain loudspeaker data. And Thiele Small parameters are used to calculate system Q for sealed enclosures. Or used to align speakers to a filter response in a reflex or ported enclosure.

Eminence Speaker has a pretty good write up on TS parameters and makes for a good read

Understanding Loudspeaker Data | Eminence Speaker

 

[BogeyBass]

Isn't a larger box with it's lower Q also less sensitive than a smaller box with higher Q?
See graph on Invalid Link Removed relating Q to efficiency.

For the most part yes , making a sealed enclosure smaller will make a response peak. And that response peak will be higher in dB.

Depending on the speaker and it's parameters that response peak appears at only certain frequencies. Not across the whole bandwidth. So it's more sensitive at the peak. This could be the downfall to a bad sounding speaker enclosure. Or sometimes the designer uses a higher Q design intentionally.

For the most part larger boxes give you more bass response, but the trade off is less power handling.

Likewise a smaller box gives more power handling but the tradeoff is that response peak.

Often with some bass speaker designs, they are hoping for the most power handling they can get. And push the limit on how much system Q can be tolerated and make the box relatively small.

With bass speakers people describe some boxes as being " bloomy" or " boomy" as your playing some notes that are not in that ripple response. Then in a scale or progression you hit a note on that high Q response peak. The note seems to " Bloom" out.

 

[Honkey tonk]

With bass speakers people describe some boxes as being " bloomy" or " boomy" as your playing some notes that are not in that ripple response. Then in a scale or progression you hit a note on that high Q response peak. The note seems to " Bloom" out.

would a small box eliminate the cabinets resonant viability
Example , going back to putting an impact pad on a gong and running it through a guitars amp .

Say a gong is tuned say at 440 and when wired with an impact pad running through a signal of 440
The gong presents its natural 440, its resonance so to speak. The gong is in its perfect environment and
Will be at its absolute loudest at 440 , now put a signal at 880 the gong is not as loud as the 440 but
Much louder than say most any other frequency.

So if a speaker box has a resonant frequency of say 440 and the speaker is used primarily for bass

Would it make sense to try and use the smallest enclosure so the resonance and the range of frequency dont match within it's set of multiples

 

[Honkey tonk]

In theory couldn't you slap the side of a cabnet to figure out the resonance .

 

[Rick James]

You're on the wrong track, totally. You need to start at square one. When you understand everything here Invalid Link Removed
things will be much more clear.

 

[Honkey tonk]

You're on the wrong track, totally. You need to start at square one. When you understand everything here Invalid Link Removed
things will be much more clear.

Im not quite Not sure what you think I don't understand ?

 

[DukeLeJeune]

Would it make sense to try and use the smallest enclosure so the resonance and the range of frequency dont match within it's set of multiples

It is possible to make a loudspeaker using "acoustically small enclosures", with one driver for each frequency range, each mounted in its own enclosure whose internal (and ideally external) dimensions are small relative to the smallest wavelengths that driver reproduces. Doing so is probably not practical in a gig-worthy bass cab, but it has been tried in high-end home audio.

Imo "what makes sense" is to start out by deciding fairly specifically "where the goal posts are", and then figuring out the best way to get there given your constraints. (This implies sorting out which problems matter most and giving them priority). Imo there are simply too many different permutations of "what if we try this?" for it to be an efficient approach.

 

[crazyBassClown]

In theory couldn't you slap the side of a cabnet to figure out the resonance .

What is meant by the cabinet resonance is the resonance of the speaker in the cab, not the cab itself.

 

[JimChjones]

In theory couldn't you slap the side of a cabnet to figure out the resonance .

There are lots of resonances. Each panel of the cab has a resonance, the air in the cab has a resonance, the ports have resonances and so on. Worse still they all affect each other. My head started hurting when I discovered that the physical cab design affects the electrical impedance, and that's just the start before the maths gets involved...

 

[Honkey tonk]

There are lots of resonances. Each panel of the cab has a resonance, the air in the cab has a resonance, the ports have resonances and so on. Worse still they all affect each other. My head started hurting when I discovered that the physical cab design affects the electrical impedance, and that's just the start before the maths gets involved...

Yeah I'm not much into math honestly , your right about the many variables just to many to figure out .

 

[agedhorse]

Speaker design revolves around math, physics and electronics. Without understanding the principles, arguing this stuff is pretty futile imo.

 

[BogeyBass]

Would it make sense to try and use the smallest enclosure so the resonance and the range of frequency dont match within it's set of multiples

In some ways yes

Any type of cabinet panel resonance is considered a loss. The speaker is vibrating the cabinet and not air. So we have losses to the final output.

Technically yes less surface is less likely to vibrate or in actuality will vibrate at a higher frequency than the speaker itself.

Then again no, depending on bandwidth and especially in bass frequencies. The goal of the designer is usually to make the box as large as possibly. With of course consideration to trade offs, like portability/ power handling etc etc.

But for the most part you are correct when it comes to increasing frequency of the cabinet. Rather large or small this is pretty much what bracing does to cabinet panels. Raises the resonant frequency.

So yes eventually if we want a system that has a 50 or 40hz f3 system response. Your looking at 3 to 4 cubic feet of volume. Or 85 to 110 liters of volume.

That box has to be big, but again as you assumed yes we want the cabinets resonate frequency to be high. But this is obtained by adding bracing or using thicker cabinet panels.

As far as raising the impedance curve of the actual speaker. Or raising the reflex point. No
For the most part with bass frequencies we are trying to keep those low as possible.

So yes cabinet resonance should be high to reduce losses. But no it's not always necessary to make it small to achieve that. You were on the right track, but just basic panel bracing or cabinet construction methods can improve the system

 

[Honkey tonk]

Speaker design revolves around math, physics and electronics. Without understanding the principles, arguing this stuff is pretty futile imo.

I agree , and apologize for my lack of not fully understanding the design of speaker and cabinet,
That's kinda why I asked, clearly there's way more informed people such as yourself and others who have
Have chimed in , thank you I'm not trying to affend any one with my lack of knowledge,
If any thing I hope my questions help make something great ,
we could just all walk away and say
We are done the perfect speaker cab already exists...

 

[seamonkey]

We are done the perfect speaker cab already exists...

The ideal cab will come right after the ideal driver is created

 

[Honkey tonk]

The ideal cab will come right after the ideal driver is created

So true !

 

[agedhorse]

Understanding the math and principles helps understand why things are as they are.