Ask an Acoustic Engineer (me)

[Justin Zazzi]

So.... Just so I understand at a more "basic" level. :-)

- An amplifier with a "regulated" power supply will provide the same amount of power regardless of the speaker impedance.
- An amplifier with an "un-regulated" power supply will provide less power to speakers with higher impedance.

Are those two statements true?

Not quite.

The reason that I ask is because I'm still not clear why my JL XD600/6v2 (which does NOT have a RIPPS power supply) provides 100W RMS at 2 ohms, but 75W RMS at 4 ohms. Why is there such a small difference between the 2 and 4 ohm outputs? Don't most "un-regulated" amps provide twice the amount of power at 2 ohms (compared to 4 ohms)?

While the JL XD line of amps don't have the "RIPPS" power supplies, do they maybe have some "lesser" version of a regulated power supply instead? I honestly don't know if they are regulated or un-regulated.

Thanks - and sorry if this was already explained earlier - maybe I just didn't understand it.

I'm not sure how the XD amplifier from JL works. However, the regulated vs non-regulated power supply usually means the power output can vary when the battery voltage changes. Usually, as I understand it, this effect will not show up in the specs when you look at power ratings vs impedance so the non-regulated nature of the amplifier isn't responsible for the 100w@2Ω vs 75w@4Ω thing. I think. Again, I can't speak for the JL line of amps.

[JCsAudio]

In an amplifier with a non regulated power supply if the power doesn’t double when the impedance load gets cut in half then it’s because the power supply isn’t designed for this and runs out of current capacity before it can. This is how I understand it. In the interest of efficiency and amplifier size reduction, plus cost savings, many of today’s modern amplifiers have power supplies that are on the small side of things compared to the golden age of huge surfboard class AB amplifiers from years ago.

[jtrosky]

I guess I just assumed that a JL Audio XD amp wouldn't "skimp" on the power supply. I mean they are not "cheap" amps. Hell, I paid more $$$ for half the power (compared to an AudioControl LC-6.1200, for example). Kind of sucks that I only "gain" 25W going from 4 ohms to 2 ohms.

Looks like the AudioControl LC-6.1200 goes from 125W x 6 (4 ohms) to 200W x 6 (2 ohms). So I could have paid less $$$ and got twice the power (if running 2 ohms). Oh well... I do like the JL Audio XD amps otherwise - and it's not like I really need more volume - but I just think it would be nice to have a little more power for the midbass channels, which are the volume-limiting channels in my system.

Any thoughts on the JL XD series amp vs the AudioControl LC-series amps?

When trying to decide which amp to go with (JL X600/6v2 or AudioControl LC-6.1200), I decided on the JL Audio because of JL's reputation as well as the fact that the AudioControl had all kinds of features that I just didn't need since I was going to run fully active with a full DSP - and you couldn't bypass all of the high/low pass filters on all channels with the AudioControl. Not the end of the world, but I figured that the less "circuitry" the signal has to go through, the better chance of clean, noise-free output.

Thanks for all of the info!!

[Euphonic]

So.... Just so I understand at a more "basic" level. :-)

- An amplifier with a "regulated" power supply will provide the same amount of power regardless of the speaker impedance.

- An amplifier with an "un-regulated" power supply will provide less power to speakers with higher impedance.

Are those two statements true?

The reason that I ask is because I'm still not clear why my JL XD600/6v2 (which does NOT have a RIPPS power supply) provides 100W RMS at 2 ohms, but 75W RMS at 4 ohms. Why is there such a small difference between the 2 and 4 ohm outputs? Don't most "un-regulated" amps provide twice the amount of power at 2 ohms (compared to 4 ohms)?

While the JL XD line of amps don't have the "RIPPS" power supplies, do they maybe have some "lesser" version of a regulated power supply instead? I honestly don't know if they are regulated or un-regulated.

Thanks - and sorry if this was already explained earlier - maybe I just didn't understand it.

In the old days, an amplifier with a regulated power supply would produce the same amount of power at 12 volts as it would at 14 volts. It would just draw more current at the lower voltage. An amplifier with an unregulated power supply would produce more power at 14 volts than it would at 12 volts.

[JCsAudio]

Jtrosky, JL Audio amplifiers dyno really well so I think you’re getting more than what’s rated by a good margin plus there are things about amplifiers that are as important or more important than just the total power output. https://youtu.be/UsLUeO33DgE

[ckirocz28]

I guess I just assumed that a JL Audio XD amp wouldn't "skimp" on the power supply. I mean they are not "cheap" amps. Hell, I paid more $$$ for half the power (compared to an AudioControl LC-6.1200, for example). Kind of sucks that I only "gain" 25W going from 4 ohms to 2 ohms.

Looks like the AudioControl LC-6.1200 goes from 125W x 6 (4 ohms) to 200W x 6 (2 ohms). So I could have paid less $$$ and got twice the power (if running 2 ohms). Oh well... I do like the JL Audio XD amps otherwise - and it's not like I really need more volume - but I just think it would be nice to have a little more power for the midbass channels, which are the volume-limiting channels in my system.

Any thoughts on the JL XD series amp vs the AudioControl LC-series amps?

When trying to decide which amp to go with (JL X600/6v2 or AudioControl LC-6.1200), I decided on the JL Audio because of JL's reputation as well as the fact that the AudioControl had all kinds of features that I just didn't need since I was going to run fully active with a full DSP - and you couldn't bypass all of the high/low pass filters on all channels with the AudioControl. Not the end of the world, but I figured that the less "circuitry" the signal has to go through, the better chance of clean, noise-free output.

Thanks for all of the info!!

I believe the "regulated" power supply is only regulating the power input, the "RIPS" was an output side regulation. I'm quite fond of the XD series, I've got two of the 400/4's. But I agree they're a little low on power for midbass duty, that's why I have 2 channels bridged on each mid.

[Bnlcmbcar]

Hey Justin or any acoustic engineers,

I would like to hear more discussion or breakdown on stereo stages involving a 3rd center channel. Yes we know the standard 2 channel R and L stereo creates a proper center image when properly aligned. We know that when introducing a mono sum center R+L, the stage width will severely collapse due to the same R and L information coming from both the center and the sides speakers.




But with stronger DSP options becoming available I wanted to hear more about what the shortcomings of the following center channel schemes would present to listeners when compared to the standard 2 channel stereo scheme. We know the 1st scheme collapses the stereo stage width, but what can be generally expected from the last 3 schemes? I could be wrong but I believe the 2nd scheme is what Audiocontrol used to implement for their discontinued ESP-3 center channel processor. The last 2 schemes are assuming the center channel is derived via an up-mixer with an algorithm to steer only common information in both R and L to the C channel (like Logic 7, Pro Logic 2, or Helix RealCenter).



*For comparison sake, let’s assume the listener is in central listening position and all 3 speakers are the same.

[Justin Zazzi]

Hey Justin or any acoustic engineers,

I would like to hear more discussion or breakdown on stereo stages involving a 3rd center channel.

Those are some good questions but they are beyond me for now. I recommend looking at the original Dolby Pro Logic circuits wince they are well documented and heavily discussed. There are also a lot of psychoacoustic studies done and published in the AES E-Journal that would be fun to read. If you find a couple papers that you'd like to read, let me know and I'll see if I can get them. Pro tip: the AES wants you to pay for the papers but you can contact the authors directly and if you ask nicely, they will send you a copy for free (I've done this a few times and made some good friends!).

I would like to learn more about this too.
Andy Wehmeyer has a lot more center-channel knowledge and he would be a good person to ask!

[geolemon]

When playing a high-output burst the voice coil heats up which changes the impedance of the system, which changes the resonant frequency, and on and on. I met a competitor once who mapped this temperature rise and performance change vs time and then created a burp track that started at some frequency (maybe 52hz) and changed frequency over time to match the change in the performance of the system as it heats up over a very short time. This way the frequency of the tone is always matched to the instantaneous resonant frequency of the system for maximum output not just when it starts, but as the system continues pounding over time. This stuff is crazy!

That actually makes me think of a certain manufacturer (coughDDcough) who disclaimers their specifications saying that they don't accurately represent how "their" drivers behave on power.
It's a different thing, but definitely in the same vein as "the deeper you dive, the more complex it gets":

Part of me wants to agree with them - I was lucky enough to get to personally visit DLC Labs to meet Dave Clark in person and have some of my prototype subs tested on their DUMAX machine - specifically because it actually manipulates the driver using vacuum across the whole excursion range, to not only provide small-signal specs at the "at rest" position, but also across the entire range, so you can see linearity. We were licensing XBL^2 back in the mid 90's, specifically for that linearity, and I wanted to see if the suspensions that I chose were a good match for a motor design we already settled on. We wanted to design a subwoofer that was linear - so the specs on that sheet WERE good, at least until you got to Xmax - which we wanted to be way out there.

Essentially, DD's statement is basically saying "our subs aren't linear", which - I mean, fine. I had a 9915 back in the day, and it literally had a stack of glued-together spiders to control all that moving mass that an SPL sub needs to have, on the power that they expect an SPL sub to be burped at... and no one cares about linearity in the lanes. You want BL... that basically means ALL the coils in the gap at rest!

And ironically in a different way, in a different DD "tech talk" post, they DO advocate breaking in a sub - which, while that wouldn't fix linearity issues, it would at least somewhat resolve the initial "at rest" vs "in motion" point that they are actually making. I wish there was a comment thread below their blog, for people to say "Just break in your subs, THEN measure the official specs!" ...but clearly I'm no fan of gluing together stacks of spiders - that's not how a "multi-layer spider" is supposed to be IMO.

Now, your comment does make me think though - even using a DUMAX machine, it's still small signal analysis - so, to your point - no heat.
I'm past my sub engineering days (IT consulting pays better), but it makes me wonder - if we did a second DUMAX run after running the sub at rated RMS power for 15 minutes or so to bring the temperature up to the rated maximum, and then measured it - how far would the parameters shift?

Great point - and I'd expect those SPL nutcases to take those measurements after heat rise. It's actually the geek-level stuff that can make SPL fun. Well - to me.

[geolemon]

Hey Justin or any acoustic engineers,

I would like to hear more discussion or breakdown on stereo stages involving a 3rd center channel...

But with stronger DSP options becoming available I wanted to hear more about what the shortcomings of the following center channel schemes would present to listeners...

I would like to learn more about this too.

I would as well - and I'd also advocate Bnlcmbcar to do some searching some of the DIY audio forums that have home theater sections.

From the diagrams that you posted, I'd be concerned as you are (especially in a car) that you'd narrow the image, because you are pulling some of the L and R content into the center - which, most troublingly - brings some of the L content to your R side, if you are in the driver's seat. Conversely, for a passenger, brings some of the R content to the L of them. Eek.

What I'd like to see in a center channel for a car, would be "(L+R)-(L-R)". That way, it's only bringing the content from both speakers to the center, and even if there's a little content that's on both channels but simply louder on one than the other, it still mitigates that by attenuating that sound at the center channel. I'd believe that would at least help keep the stage width - hopefully as wide as with just a stereo pair.

But I think really, in a car, the KISS rule applies... there's already glass, and absorbant upholstery, and plastic, all pointing different directions - you could have ONE speaker in a car and end up with a nightmare of multiple pathlength distances, direct and reflected (with each of those having a 180 degree shift - plus pathlength difference offset!) creating anything but a flat response as it arrives at your ears.

So I subscribe to the "the fewer speakers the better" theory for car audio. There's exceptions - for example, three way components where you actually aim the mid and tweeter - can provide better imaging. But my default recommendation is simplicity over complexity, for those pathlength reasons.

I'm really interested in this myself, but in no way for creating a center channel (IMO, there's already enough direct and reflected pathlength sounds wreaking havoc on image-killing phase interactions as they all ultimately arrive at the listening position)...
I want to make a "L-(L+R)" channel and a "R-(L+R)" channel to add some rear fill (something I otherwise also don't believe in, for those same image-killing phase interaction reasons) plus some additional delay, so I'm going to be researching this soon myself. My DSP will only help with delay and passband. I'd be interested if you find any good threads.