Efficient 8 inch speakers for a Pignose Hog 30?

[Wasnex]

I have.
You might be right...I hope your confidence in my skills is merited!

We’ve thought about that before but aren’t I doing the opposite of a HPF by adding bass frequencies when I turn the ultra low button on?

The HPF is used to attenuate frequencies that are below a speakers intended pass band.

Here is (approximately) how a ported cab works. As the frequency drops below about 500hz the excursion of the driver will start to increase (see attached charts below). At frequencies well above the port tuning frequency (Fb) the cab behaves pretty much like a sealed design. At some frequency, the output of the driver will begin to roll off. The port is tuned to start becoming active at this frequency range. The idea is the port fills-in and extends the cab's low frequency response.

An interesting side effect of the port resonance is it limits cone excursion. So at some point, as the frequency approaches Fb driver excursion will begin to decrease. At Fb the port is making most of the sound and driver excursion is highly suppressed.

Below Fb, the output of the cab drops of extremely fast and the excursion of the driver increases exponentially. An important observation should be made, although the driver is jumping around like crazy it is not making sound very efficiently...so the motion and power is not only being wasted, you are putting the driver at risk of being damaged.

As an example, here is the Cone Displacement graph of a cab design for the Deltalite II 2512

This design is limited to 100W with a steep HPF set to 40hz. The chart shows the driver hits Xmax of 4.9mm just about 40hz with 100W applied. This is where the trace turns from black to gray.

Fb for this design is 50hz. Notice excursion increases to about 70hz then begins to decrease as the port becomes active. The excursion reaches a minimum at Fb (50hz) and then starts to increase very quickly as the frequency dips below Fb. If you were to hit the driver with 100W at 20hz, excursion would be about 15mm...hopefully it's clear that this is a major problem since the driver's Xmax is only 4.9mm.

Here is the frequency response chart and maximum acoustic output chart for this design.

F3 is 58.71hz. This is the point where output is down 3dB. Note that at 20hz the response is down by about -30dB. So there is really no point in feeding the driver any power at this frequency because you won't hear it.

Note that acoustic power drops off fairly quickly below about 100hz, and then drops off even faster below Fb (50hz). There really is no benefit to feeding the cab a lot of power very much below the port tuning frequency (Fb)

The Cube Street Ex is a ported design. Fb will most likely be a bit higher than this example. If you limit the power you send to the Cube Street below its Fb, it's likely to be able to play above Fb louder with out farting out. Since the speaker is not working efficiently below Fb, you won't notice a loss of lows if you have the HPF adjusted properly. In fact you are likely to have the impression that the low end is fuller and more controlled.

I believe @brianrost uses an HPF with his Cube Street EX. Perhaps he will comment.

 

[brianrost]

I use the crossover in a Zoom B3 pedal as a HPF. I set the crossover at 125hZ with the lows dialed down to 0 so only the higher frequencies pass. I use a limiter after the crossover to keep peaks under control. I keep the amp's own EQ at 12:00 and use the "fliptop" amp model in the B3 with bass at 10:00 lows, mids at 800hZ and 3:00, treble at 12:00, with the Ampeg-style "ultra lo" EQ curve off.

I do not try to get a deep tone at all, why bother when the amp is incapable of delivering it? Busking on the street with a small amp, a clanky, snarly midrange tone works better.

BTW, a Hog 30 is easy to open up, disconnect the internal speaker and jury-rig a cable to use a larger speaker cabinet that will be both louder and deeper sounding. I imagine chopping the Hog's own cabinet to make it just a head would be easy enough.

Let me know if you have other questions.

 

[Aaron Houts]

@Wasnex @brianrost
Thank you both so much.
I know I’ll have questions.
I just need some time to research and digest this information.
Plus, I’ll move to a new thread instead of cowboying this one!

 

[rickwick7600]

I'm still considering changing out the speaker in my Hog30, but there's something that's confusing me within this thread. Looking at the schematic supplied by one of the posts, along with what others have stated here, it would seem that the driver should have an impedance of 4 ohms. However, after opening up the enclosure and looking over the
speaker, it clearly has 8 ohms printed on the side of the magnet area. Does this mean I have to get another 8ohm speaker, or should I consider replacing it with a 4 ohm. Thoughts?

 

[Wasnex]

I'm still considering changing out the speaker in my Hog30, but there's something that's confusing me within this thread. Looking at the schematic supplied by one of the posts, along with what others have stated here, it would seem that the driver should have an impedance of 4 ohms. However, after opening up the enclosure and looking over the speaker, it clearly has 8 ohms printed on the side of the magnet area. Does this mean I have to get another 8ohm speaker, or should I consider replacing it with a 4 ohm. Thoughts?

You would need to confirm the amp matches the schematic. The schematic says 4 ohms, but that speaker is clearly made specifically for a Hog 30.

Something to keep in mind. Running the amp at 4 ohms will cause/allow it to generate more power, but that is not necessarily a benefit. Running at a lower impedance is harder on the amp because it generates more heat.

Also, often 4 ohm speakers are slightly less efficient than their 8 ohm counterparts. In order to know if there is any real benefit to running at 4 ohms, you need to know how much power the amp makes at 4 ohms and 8 ohms, then you need the sensitivity rating of the each speaker so you can do the math. In most cases the difference is so small that it's not worth worrying about.

 

[AlanSanJoseBass]

I was in your same situation. I bought a Hog 30 and wasn't impressed with the sound. I found a schematic on the web that said the speaker was 4 ohms, so I purchased a 4 ohm 10 inch Jensen Mod 10 speaker which is supposedly good for bass. I even called Pignose whose tech guy said it was 4 ohms. When I took the original speaker out I noticed that it had 8 ohms printed on the side just like your picture. Anyway, I made a new front for the amp that would accommodate a 10 inch speaker and installed it. I would say it works a little better but not near anything that I was expecting. Someone told me (i don't know if it is true) that using a 4 ohm speaker with a 8 ohm amp will cause more distortion. It seems that setting the volume of the amp at 1/4 and the master at 1/2 seems to work the best. Beyond that produces too much distortion for my taste. I noticed the biggest improvement in the sound was by putting fiberglass insulation inside of the cabinet. Even one of the guys that I play with noticed the improvement even though I had not told him about the insulation. You can buy small pieces of fiberglass insulation at Home Depot for under $10. Anyway, here is a picture of my current modified amp. I use it to play with acoustic musicians where electricity is not always available.

 

[Wasnex]

Someone told me (i don't know if it is true) that using a 4 ohm speaker with a 8 ohm amp will cause more distortion.

When running a 4 ohm speaker on an 8 ohm solid state amp, there is significant risk that the amp will be damaged.