15” 4 ohm bass speaker

[elwaupo]

I need to replace a 15” bass speaker and was looking for a recommendation. My current speaker is a 4 ohm speaker, would an 8 ohm be better? I’m using a Gallien Kruiger cabinet through my Genz Benz 12.0. Thinking of upgrading my amp head but I’m happy with this for now.

 

[Wasnex]

The most important issue is to select a driver that will work in the cab. Usually the original driver is your best choice. If you want to use a different driver, you need to research potential candidates, and then model how they will perform in the cab. A driver may be totally unsuitable for a given cab or you may be able to modify the ports a bit to get the tuning into an acceptable range.

Regarding 4 VS 8 ohms. People often make this choice because their amp makes more power at 4 ohms than 8 ohms. Some considerations:
1. How much power will the driver actually be able to handle? For bass you need to be concerned more with mechanical power handling than the driver's RMS power rating. The RMS power rating basically tells you how much wattage the voice coil can dissipate. But with bass cabs you need to be concerned more with cone excursion below 100hz. Cone excursion is determined by driver characteristics as well as how the cab is tuned.
2. How much louder will the 4 ohm variant play. When drivers come in either 4 and 8 ohms, the 4 ohm variant is often 1-2dB less efficient. So even if your amp makes double the power at 4 ohms, you only gain 1 to 2dB...and this is assuming the driver can actually handle all of the extra power.
3. When you push a driver close to its limits, it tends to experience power compression. This means actuals gains will be less than the calculated gains.


FYI Eminence publishes cab design docs for many of their professional drivers. I sorted this page by Eminence, 4 ohms, and 15": Brand, Impedance, Nominal Diameter
There are two options. I suggest looking at the spec sheet and cab design doc for both drivers. To get these documents, select the driver and the scroll down about 1/3 page. There you will see a tabbed menu. Click Manuals and Resources and then scroll up a bit for links to the spec sheet and cab design doc.

One of the available 4 ohm drivers is an LF variant. These are usually not ideal for full-range bass. They are more like a subwoofer.

Good luck!

 

[agedhorse]

Since your amp is rated at 600 watts RMS into 4 ohms, and since there are very few 15” drivers rated for even 400 watts RMS mechanically, an 8 ohm driver would be (much) more appropriate. Another benefit is that most 8 ohm drivers have a higher sensitivity.

I suspect that a good part of the original driver failure was related to over-powering.

My suggestion is to contact GK and see if they have correct replacement driver in 8 ohms. Also mark the cabinet as 8 ohms if you do this.

 

[AK Bass Guy]

What @Wasnex and @agedhorse said above. They know their stuff. I trust them to speak from experience and not just what they read on a forum or saw in a YouTube video.

 

[retslock]

What @Wasnex and @agedhorse said above. They know their stuff. I trust them to speak from experience and not just what they read on a forum or saw in a YouTube video.

This exactly. Ignore their advice at your peril.

 

[sokolasty]

Another benefit is that most 8 ohm drivers have a higher sensitivity..

Can I take this as a rule of thumb and extrapolate it to 16 ohms and 32 ohms speakers?

 

[leonard]

2. How much louder will the 4 ohm variant play. When drivers come in either 4 and 8 ohms, the 4 ohm variant is often 1-2dB less efficient. So even if your amp makes double the power at 4 ohms, you only gain 1 to 2dB...and this is assuming the driver can actually handle all of the extra power.
3. When you push a driver close to its limits, it tends to experience power compression. This means actuals gains will be less than the calculated gains.

This is very useful information that is seldom articulated in as clear terms as here. Thanks!

So I conclude that having two 8 ohm speakers in parallel to make 4 ohms total is a louder and more efficient solution than having one 4 ohm speaker. Especially with a solid state amp where you get more watts to a 4 ohm load than to an 8 ohm load.

 

[Redbrangus]

Can I take this as a rule of thumb and extrapolate it to 16 ohms and 32 ohms speakers?

No

 

[murphy]

This is very useful information that is seldom articulated in as clear terms as here. Thanks!

So I conclude that having two 8 ohm speakers in parallel to make 4 ohms total is a louder and more efficient solution than having one 4 ohm speaker. Especially with a solid state amp where you get more watts to a 4 ohm load than to an 8 ohm load.

Two speaker cones of 8 ohms will be a louder and fuller solution that one 4ohm cone.

 

[RandomKaren]

Can I take this as a rule of thumb and extrapolate it to 16 ohms and 32 ohms speakers?

Most manufacturers publish technical info such as sensitivity on their websites, always best to check for any specific driver.

 

[jnewmark]

I need to replace a 15” bass speaker and was looking for a recommendation. My current speaker is a 4 ohm speaker, would an 8 ohm be better? I’m using a Gallien Kruiger cabinet through my Genz Benz 12.0. Thinking of upgrading my amp head but I’m happy with this for now.

I do the same thing myself, using a 4 ohm version of the Schroeder PL115, with a Shuttlemax 12.2. I do not play in loud bands and I have never really pushed the Shuttlemax to clipping. Not going to get into the 4 vs. 8 ohm cab discussion, I like what I like and to each his own. I would just get a GK replacement for it, and watch the volume.

 

[agedhorse]

Can I take this as a rule of thumb and extrapolate it to 16 ohms and 32 ohms speakers?

Good question. Yes and no, it depends on the number of turns that fit within the magnetic gap, the current in the wire, the flux density, the coil wire gauge, etc. It’s a complex balancing act, but for high powered 4 ohm drivers the wire gauge grows which reduces the number of turns which impacts the gap width but if you make the gap longer flux density falls without increasing magnetic strength…

This is very useful information that is seldom articulated in as clear terms as here. Thanks!

So I conclude that having two 8 ohm speakers in parallel to make 4 ohms total is a louder and more efficient solution than having one 4 ohm speaker. Especially with a solid state amp where you get more watts to a 4 ohm load than to an 8 ohm load.

Yes, in almost all cases I can think of.

Two speaker cones of 8 ohms will be a louder and fuller solution that one 4ohm cone.

Correct

Most manufacturers publish technical info such as sensitivity on their websites, always best to check for any specific driver.

Agreed, there can alway be exceptions to the general rules, and each driver has its own design parameters.