Loudspeaker replacement

[Lou Albano]

I want to replace the current loudspeaker in a HK Premiere PRO 18" cabinet with a (presumably) better speaker. The cabinet is very solid, so SPL is no problem. The current transducer is a Eminence Delta Pro (600W/ 4ohm). I want to replace them with RCF`s LF18G401 (900W AEF/ 8 ohm). I plan to power these with the t.amp MK 2400 (650W/ 8 ohm). My question is: do I have to disconnect the built-in passive frequency divider (splits signal at 150 Hz), or can it handle the increase in power/resistance values?

[James Perrett]

Loudspeaker selection is more complex than just sticking it in a box and hoping it will work. The system will probably be tuned to the characteristics of the old speaker (things like resonant frequency and frequency range are the obvious ones) and a different speaker, even if it is supposed to be better, will actually sound worse.

If it is a power handling issue, you may find that the power rating of the existing unit is fine for use with the amp that you propose as the normal advice seems to be to use an amp with a rating of 1.5 - 2 times the speaker's continuous power rating. This is due to the fact that music isn't continuous and an amp that is driven into clipping is more likely to damage a speaker.

[Hugh Robjohns]

Loudspeaker selection is more complex than just sticking it in a box and hoping it will work. The system will probably be tuned to the characteristics of the old speaker (things like resonant frequency and frequency range are the obvious ones) and a different speaker, even if it is supposed to be better, will actually sound worse.

^That!

If you compare the specs and response plots for the two drivers you'll see they are significantly different in many key areas.

http://www.rcf.it/c/document_library/ge ... E-2218.pdf

http://www.eminence.com/speakers/speake ... ta_Pro_18C

Not only is the sensitivity very different -- meaning that the crossover matching

If you're using the cabinet's internal high-pass filter to drive top units, power handling shouldn't be an issue, but the different woofer impedance may well alter its crossover slope in an adverse way...

But even if it doesn't, the RCF woofer is roughly 4dB more sensitive, so the balance between sub and tops through the crossover region will be wrong.

Then there's the cabinet and port tuning to consider.

The RCF driver has a resonant frequency of 33Hz as opposed 27Hz for the Eminence. It may not sound a big change but it will probably have a substantial effect on the cabinet performance. The QTS figures are also well off with 0.29 for the RCF and and 0.32 for the Eminence. These are critical parameters when it comes to designing and optimising cabinets/drivers...

And then there's the actual response curves of the two woofers drivers. The RCF holds onto its low end a lot better than the Eminence, which is great... except that the cabinet design will have been optimised to give the best possible LF extension with the Eminence driver and so may well end up sounding quite bloated with the RCF.

I'm not sure a random change of driver -- especially one with substantially different specs -- is the best idea, especially when it's going to cost you £200+ for the new driver to find out!

Perhaps it would help if you explain why you're considering changing the bass driver, so those with the appropriate experience here can offer alternative solutions.

H

[Lou Albano]

Hugh and James!

Thank you so much for your sincere consideration of my unqualified projections!

The reason why I would want to try a different woofer, is that I already had the fortunate experience of using an Eminence Omega Pro 18A (800W / 8 ohm) in the HK cabinet. I just conjectured that the cabinet could handle an even stronger woofer. It never occured to me that I should also consider resonance and QTS (??) data.

Again, thanks!

[Hugh Robjohns]

If you compare the specs of the Delta Pro 18C (4 Ohm original) against the Omega Pro 18A (8 Ohm replacement) you'll see they are actually pretty similar.

http://www.soundonsound.com/forum/posti ... 26&t=55760

http://www.eminence.com/pdf/Delta_Pro_18C.pdf

While the sensitivity of the Omega Pro (8 Ohm) is about 3dB higher, the Fs is 27Hz vs 25Hz, and Qts is 0.32 against 0.31. Even the overall frequency response and bass extension are almost identical. So basically, the cabinet tuning would have barely changed with the replacement 8 Ohm sub, but the LF output would be a little more (assuming a more powerful amp to cope with the higher impedance).

So yeah, not surprised it worked... but that doesn't mean any old 18-inch woofer will work as well. As the Eminence Omega is cheaper than the RCF, and you had a good experience with it, why not go for that?

(There is C version of the Omega Pro with a 4 Ohm impedance, by the way...)

http://www.eminence.com/pdf/Omega_Pro_18C.pdf

H