Horns impact on 8 to 4 ohm driver swap in a Ampeg PR-15h

[fourty6an2]

I would like to put a 4 ohm speaker (of appropriate wattage) into the cab . Will the horn's ohm rating impact the overall load on the amp? Can I can just disconnect it to eliminate worry? I would like to keep it, but ill ditch it if it will cause an issue.

 

[agedhorse]

The horn doesn’t affect the load appreciably due to the crossover.

Changing the driver to 4 ohms may not increase the volume (and it may decrease) because most 4 ohm drivers actually have lower sensitivity than their & ohm counterparts.

The driver’s electro-mechanical properties also needs to match the cabinet (power handling is only one of about 10 parameters that impact performance) or you could end up with worse performance.

 

[Marko 1]

This is such a frequent question, I wonder if there should be a sticky,

not open to comments, but written by an engineer that addresses all the typical issues and facts involved in swapping out drivers in a cab.

Then instead of the typical few having to educate folks over and over and over, someone could just be referred to that sticky.

Just a (probably flawed) thought.

 

[Passinwind]

This is such a frequent question, I wonder if there should be a sticky,

not open to comments, but written by an engineer that addresses all the typical issues and facts involved in swapping out drivers in a cab.

Then instead of the typical few having to educate folks over and over and over, someone could just be referred to that sticky.

Just a (probably flawed) thought.

It's all been in the FAQs here for quite some time, but I doubt very many people at all ever read them. We all know how well "do a search" plays out on TB in any case.

 

[Marko 1]

It's all been in the FAQs here for quite some time, but I doubt very many people at all ever read them. We all know how well "do a search" plays out on TB in any case.

I never saw that... I mean, who the hell pays attention to stickys?!



Aha, I see your point!
.

 

[Wasnex]

I would like to put a 4 ohm speaker (of appropriate wattage) into the cab . Will the horn's ohm rating impact the overall load on the amp?

Others have addressed that you need to choose a driver that is compatible with the cab.

I will try to give you a bit more background specifically related to your question.

In the event that your cab has a full crossover, you can't change the woofer impedance without messing up the response of the woofer's LPF section.

Most bass cabs don't have of full crossover. Usually the woofers are run full range and the cab only has an HPF for the tweeter. If the woofers are run full range, then the tweeter doesn't have a significant impact on the impedance.

Ref: A Speaker Maker's Journey: Crossover Basics - Impedance (speakermakersjourney.blogspot.com)

Notice the impedance presented by the HPF and tweeter is high below the cutoff.

Another factor is the impedance of a woofer is not fixed at 4 or 8 ohms. Instead 4 or 8 ohms is the nominal impedance, and the actual impedance varies by frequency.

Here is the frequency response VS impedance plot for a 4 ohm Eminence Kappa 15C:

Notice the impedance rises above about 180hz. By 3.5kHz, where many tweeters are high passed, the actual impedance of this driver is over 20 ohms.

Additionally, the tuning of the cab will have a impact on the impedance at lower frequencies. Sealed cabs have one impedance peak, and ported cabs have two.

Here is the impedance plot of a large ported cab loaded with the Kappa 15C.

Here is a the plot for a small vented cab loaded with the 15C:

Here is the impedance of an 8 ohm Delta Pro 15A in a small sealed cab:

Ref:
290-459--eminence-kappa-15c-spec-sheet.pdf (parts-express.com)
Eminence Designer (parts-express.com)
290-512--eminence-delta-pro-15a-spec-sheet.pdf (parts-express.com)
Eminence Designer (parts-express.com)

 

[fourty6an2]

Thank you very much for your time. I really do appreciate it.