Good driver for small volume cabinet

[AstroSonic]

Well, I've owned one of the two EV 15B speakers for many years and it has performed well in the past while mounted in a different cabinet, however, that cabinet was slightly over 5cf in volume.

Now I'm attempting to get the same speaker to sound as good in a 3.0cf compartment.

From the info Astrosonic provided, the Fs of the EV 15B is 43Hz, which is where I have the compartments tuned. Further reading about box tuning vs Fs of the speaker tells me there are situations where I would want to tune the box above or below Fs of the speaker (above, in this case?) to achieve more perceived low end by enhancing the second harmonic of 40Hz.

Since I don't currently have easy access to modeling software (dead PC, currently living on, but haven't found a modeling app for, iPad), I'm not running models on this cab with this specific speaker.

So, speaker has performed well in a larger box with Fb ~= Fs. Smaller box with the same speaker might benefit from Fb different from Fs, but the difference is yet to be determined. I wouldn't think I need to go to Fb = 2nd harmonic of "E" = 80Hz, but I'm not sure what value will help achieve a boost at ~80 Hz; perhaps Fb = 55-60 Hz?

Port length and ports are fairly easy to change, but it would be nice to get close on the first try....

The EV data sheet shows and discusses the response of the 15B in the TL-606, a 3.2cf reflex enclosure tunable to either 55 or 40 Hz. Tuning to 55Hz results in less than 1db of fall-off at 80Hz, and an F3 of 63Hz. EV recommends the 40Hz tuning for bass guitar 'to discourage speaker bottoming at the lowest bass guitar notes'. Response is down around 2.5db at 80 Hz. Note that the bass performance of the 15B in your current box (about 3cf) would be audibly almost indistinguishable from that in the TL-606.

There is a continuum of alignments (tunings), each offering a mix of advantages and compromises. Tuning high results in gradual peaking, while tuning low results in a gradual loss of mid and low bass. Where these extremes occur relative to Fs depends largely on the drivers Qts. Among other things, this means that tuning at the drivers Fs is not a good rule of thumb. However, one important characteristic of the tuning frequency (Fb) is that the driver is loaded in the region around the tuning frequency. In this frequency range, cone motion is minimized. Below this region, the driver is unloaded - driver excursion is high and the driver is easily driven into overload. Above the tuning frequency, the driver transitions into behaving as if it were in a closed/sealed box.

The driver is most easily overloaded (Xmax is exceeded) on the lower bass guitar notes. Therefore, EV recommended tuning near low E for bass guitar use. Tuning higher (like to 55Hz) results in more mid-bass output, but leaves the driver unloaded on the low notes. It is not necessary to tune to 41Hz. The frequency range of loading surrounds the tuning frequency. Tuning may be higher, as long as 41Hz is covered by the loading range (meaning that the driver is loaded by the enclosure resonance at 41Hz. Modeling suggests that the highest Fb that will cover 41Hz is 46 Hz. Fb of 55Hz loads down to about 48Hz. The work-around for this is a high pass filter set to decrease signal level (and power to the driver) in the range where the driver is unloaded.

Note that performance of the EV-15B in a 5cf box tuned to 41Hz yields response that is -3db at 78Hz, - 2.8db at 80Hz, -4db at 60Hz and -7.5db at 40Hz. The 15B's performance in a 5cf box is very similar to the Dayton PA380-8, Eminence Kappalite 3015 or Faital Pro 15PR400 in a 3cf box. The newer drivers allow a few db more spl at the lowest frequencies due to their greater Xmax.

 

[Remus_Redbone]

I think the descrepancy had to do with end correction factors, I'm getting more calculators to agree now or come very close.

For 50hz tuning...

Two 4" = 9.33" length. You'd need 14" internal depth to do that.

Two 3" = 5.24" length.

Your current 2", make them 7/8" shorter than they are now.

I went with 3" but stuck with 43Hz tuning and made them 6.9" long. Thought I'd try tuning back at Fs with the larger ports to see if that was the issue. I haven't had much of a chance to test yet, but it seems as though the bottom is going to be greatly improved.

 

[ThisBass]

The EV data sheet shows and discusses the response of the 15B in the TL-606, a 3.2cf reflex enclosure tunable to either 55 or 40 Hz. Tuning to 55Hz results in less than 1db of fall-off at 80Hz, and an F3 of 63Hz. EV recommends the 40Hz tuning for bass guitar 'to discourage speaker bottoming at the lowest bass guitar notes'. Response is down around 2.5db at 80 Hz. Note that the bass performance of the 15B in your current box (about 3cf) would be audibly almost indistinguishable from that in the TL-606.

There is a continuum of alignments (tunings), each offering a mix of advantages and compromises. Tuning high results in gradual peaking, while tuning low results in a gradual loss of mid and low bass. Where these extremes occur relative to Fs depends largely on the drivers Qts. Among other things, this means that tuning at the drivers Fs is not a good rule of thumb. However, one important characteristic of the tuning frequency (Fb) is that the driver is loaded in the region around the tuning frequency. In this frequency range, cone motion is minimized. Below this region, the driver is unloaded - driver excursion is high and the driver is easily driven into overload. Above the tuning frequency, the driver transitions into behaving as if it were in a closed/sealed box.

The driver is most easily overloaded (Xmax is exceeded) on the lower bass guitar notes. Therefore, EV recommended tuning near low E for bass guitar use. Tuning higher (like to 55Hz) results in more mid-bass output, but leaves the driver unloaded on the low notes. It is not necessary to tune to 41Hz. The frequency range of loading surrounds the tuning frequency. Tuning may be higher, as long as 41Hz is covered by the loading range (meaning that the driver is loaded by the enclosure resonance at 41Hz. Modeling suggests that the highest Fb that will cover 41Hz is 46 Hz. Fb of 55Hz loads down to about 48Hz. The work-around for this is a high pass filter set to decrease signal level (and power to the driver) in the range where the driver is unloaded.

Note that performance of the EV-15B in a 5cf box tuned to 41Hz yields response that is -3db at 78Hz, - 2.8db at 80Hz, -4db at 60Hz and -7.5db at 40Hz. The 15B's performance in a 5cf box is very similar to the Dayton PA380-8, Eminence Kappalite 3015 or Faital Pro 15PR400 in a 3cf box. The newer drivers allow a few db more spl at the lowest frequencies due to their greater Xmax.

Totally agree.

But there is a very special incidence that can't be predicted.

Every players picking style is different, every players damping technique is different.

Different picking styles and damping techniques force different transient content of sub harmonics, but these transient sub harmonics occur below every "Fundamental" which is played on the fretboard.

 

[Remus_Redbone]

Well, I must divulge the outcome of this experiment.

After changing the length of the two, 2" ports in each compartment multiple times, and not realizing much difference between a 4" port and the ports completely removed from the baffle, I took Will33's suggestion to upsize to a minimum size of 3" ports (didn't have adequate depth or baffle area for 4" ports).

The difference is astounding. I won't be ordering any new speakers for this cabinet, the old EV 15B are more than adequate.

Here's the progression;
- Obtained cabinet and loaded the EV 15B's with the original shelf ports. Not terrible, but not really good. I think the ports were too open, allowing the speakers to perform as unloaded.

- Sealed the shelf ports and all other air leaks - actually not too bad, just a bit weak when standing back from the cabinet several feet. Very tight, clean lows, just not much of them. Good mids. Not an 810 SVT tone, but kin to it a little.

- Two, 2" round ports in each compartment; pretty much what you would expect of a poorly sealed cabinet. No low end. Lots of midrange.

- Two, 3" ports in each compartment the length to tune boxes to 43HZ (Fs of speakers); This is what I was looking for when I started. Plenty of low end, too much with a Gibson T-Bird, perfect for Jazz with TI flats, amazing with P-bass and Rotosound 66 SS.

The lows are now abundant, perhaps a little on the distorted side, but just 15" speaker tone, not Big Muff. Driven with a clean SS amp, the cabinet is very loud, punchy, with tons of mids and plenty lows. I can't imagine not being able to hear it over loud drums & guitar. It will be what I use outdoors with perhaps some sub reinforcement from a second rig.

Driven with 200 watt tube amp; 1969 - 1971 bass tone & some of you may recognize the years as an album title (GFR). Very thick low mids. Smooth, warm, round tone (tubes & 15's!!). It's what I will use in small to mid-size indoor gigs.

Thanks for the help and education.

 

[will33]

I went with 3" but stuck with 43Hz tuning and made them 6.9" long. Thought I'd try tuning back at Fs with the larger ports to see if that was the issue. I haven't had much of a chance to test yet, but it seems as though the bottom is going to be greatly improved.

One problem with small, constricted ports is that they won't contribute as much to the overall output as they should. Port output is out of phase with cone output. At the tuning frequency, the cone is almost at a standstill, fully loaded. It just barely vibrates just enough to "excite" the cabinet resonance (port tuning frequency). At that point, the LF output is coming almost solely from the ports...small ones don't put out enough and LF performance suffers.

In other words, moving to more proper size ports from really small ones will improve LF output even though the box, driver and actual tuning frequency haven't changed.

Anyway, yup, you should notice an improvement. Shortening them will bring up the 80-150 response even more if you wish. Go to far though and it'll unload below the tuning frequency and/or just get more boomy, indestinct. Extremes can lose definition and even sense of pitch if you really overdo it....plenty of wiggle room there though that can still sound like different flavors of good.

 

[AstroSonic]

I am afraid that I completely missed the post where you mentioned the ports being 2" diameter. Fortunately Will33 caught that, and you now have a very functional cab. For high output bass cabs, always use multiple 3-6 inch diameter ports.

Just for future reference, small diameter ports have higher air velocities. In theory, the higher velocities make up for the smaller radiating area. However, the frictional/turbulence losses are relatively high. These damp the cab resonance, making it less efficient, and producing less output. A further complication in your case was the tuning frequency, which was actually around 35Hz (for the 3.1 inch length). This further reduced output in the 50-100Hz range. These two issues combined to really suck the life out of these cabs (which you very clearly heard).

To make sense out of disparities between various online port calculators use the 'rice' test.

Glad it all worked out.

 

[beate_r]

I'll second the Kappalite 3015 in small cab... I replaced the EVM15L in a "stock" TL606 cab, and the 3015 is outstanding!

I'm also using a pair of 3015s in a sealed cab (similar in size to JohnK's DIY 215, but sealed, and as much as 10% smaller). It too sounds fab!

The 3015 is truly a killer speaker!

I do not like the 3015 with such low tunings. After a lot of experimenting i ended up with a tuning of around 57-60 Hz, similar to 12"-chassis with a free air resonance and VAS in a similar range (like the Emi Beta and Delta 12). But with such a tuning it is really outstanding. Even in direct comparison with the 2515 (at an estimated tuning of 57 Hz).

 

[AstroSonic]

I do not like the 3015 with such low tunings. After a lot of experimenting i ended up with a tuning of around 57-60 Hz, similar to 12"-chassis with a free air resonance and VAS in a similar range (like the Emi Beta and Delta 12). But with such a tuning it is really outstanding. Even in direct comparison with the 2515 (at an estimated tuning of 57 Hz).

Not trying to be skeptical, or questioning your opinion, but a little more information would add value to what you have said. What is it about the sound that you don't like with the low tunings, and what is it about the sound that you like about the higher tunings? What kind of music are you playing? How loud? Are you using a high pass filter?

 

[beate_r]

With the low tunings the boxes the 3015 simply lacks bass and is mid emphasized.

No, i do not (yet) use a high pass filter, but low powered tube amps instead, usually old tube amps (e.g. a 50 W Dynacord Bassking), and need the sensitivity of the 2x115 to compensate for the relatively low power.
I would not give these speakers more than, say, 100 Watts (each) without a low pass.