Buck Box Designs - Refreshed Thread

[Buck 5,000+ posts]

Ported box for a Focal K2 Power E 30 KX (12") going in a coupe trunk. These seem like really good SQ woofers.

 

[Buck 5,000+ posts]

 

[Buck 5,000+ posts]

I'm trying to understand the differences between half-bridge and full-bridge amps.

"Energy Flow – In linear amplifiers the energy flow is always from supply to the load, and in Full bridge Class D amplifiers this is also true. A half-bridge Class D amplifier however is different, as the energy flow can be bi-directional, which leads to the “Bus pumping” phenomena, which causes the bus capacitors to be charged up by the energy flow from the load back to the supply. This occurs mainly at the low audio frequencies i.e. below 100Hz."

"Similar to conventional Class AB amplifiers, Class D amplifiers can be categorized into two topologies, half-bridge and full-bridge configurations. Each topology has pros and cons. In brief, a half-bridge is potentially simpler, while a full-bridge is better in audio performance. The full-bridge topology requires two half-bridge amplifiers, and thus, more components. However, the differential output structure of the bridge topology inherently can cancel even the order of harmonic distortion components and DC offsets, as in Class AB amplifiers. A fullbridge topology allows of the use of a better PWM modulation scheme, such as the three level PWM which essentially has fewer errors due to quantization.

In the half-bridge topology, the power supply might suffer from the energy being pumped back from the amplifier, resulting in severe bus voltage fluctuations when the amplifier outputs low frequency audio signals to the load. This kickback energy to the power supply is a fundamental characteristic of Class D amplification. Complementary switching legs in the full-bridge tend to consume energy from the other side of the leg, so there is no energy being pumped back towards the power supply. Table 1 shows the summary of the comparison."

https://www.eetimes.com/how-class-d-audio-amplifiers-work/

"Class D Amplifier Terminology, and Differential vs. Single-Ended Versions

Figure 3 shows a differential implementation of the output transistors and LC filter in a Class D amplifier. This H-bridge has two half-bridge switching circuits that supply pulses of opposite polarity to the filter, which comprises two inductors, two capacitors, and the speaker. Each half-bridge contains two output transistors—a high-side transistor (MH) connected to the positive power supply, and a low-side transistor (ML) connected to the negative supply. The diagrams here show high-side pMOS transistors. High-side nMOS transistors are often used to reduce size and capacitance, but special gate-drive techniques are required to control them (Further Reading 1).


Full H-bridge circuits generally run from a single supply (VDD), with ground used for the negative supply terminal (VSS). For a given VDD and VSS, the differential nature of the bridge means that it can deliver twice the output signal and four times the output power of single-ended implementations. Half-bridge circuits can be powered from bipolar power supplies or a single supply, but the single-supply version imposes a potentially harmful dc bias voltage, VDD/2, across the speaker, unless a blocking capacitor is added.


The power supply voltage buses of half-bridge circuits can be “pumped” beyond their nominal values by large inductor currents from the LC filter. The dV/dt of the pumping transient can be limited by adding large decoupling capacitors between VDD and VSS. Full-bridge circuits do not suffer from bus pumping, because inductor current flowing into one of the half-bridges flows out of the other one, creating a local current loop that minimally disturbs the power supplies."

Class D Audio Amplifiers: What, Why, and How | Analog Devices

Class D amplifiers, first proposed in 1958, have become increasingly popular in recent years. Here’s some basic information.

www.analog.com

I think what could be going on, possibly, is that a half-bridge amp allows energy flow from changes of voltage from inside of the amp into your 12v power wires. It almost seems like a half-bridge amp makes your car's 12v electrical system part of the amplifier system. Full-bridge amps seems to only draw current from the 12v system, where it seems like a half-bridge amp can pulsate both + and - into your vehicle's 12v system. Half-bridge seems like your vehicle's batteries and everything now determine electrical factors for how the power from them interacts with your amp feeding power back into the 12v system. I think high charge/discharge capacitors or something like the lithium banks would really help dampen the the amp pulsations. They would possibly like a giant 12v + and - dampener for your entire system.

I know some people with very large systems, with lithium ion banks, super caps, and they all run what seem to be half bridge amps. The loudest people that I actually know run a lot of extra electrical components in between the alternator 12v and the subwoofer amp. All of that extra equipment seems to act as a dampening system for both the alts and the amplifiers, which would theorectically translate to your subwoofers moving exactly like they're supposed to be at all frequencies. I could be a massive noob; I'm not sure.

Like, is the the Sundown Salt 8k a half-bridge amp (8000w)?: https://sundownaudio.com/lv/sa/amplifiers/salt-series/salt-8/

Here's the Sundown SFB 8000, labeled as a full bridge (8000w): https://sundownaudio.com/lv/sa/amplifiers/sfb-series/sfb-8000d/

The Salt 8 is literally about twice the size of the SFB 8000. That has to make the Salt sound much better. It seems like the not-full bridge car audio amps tend to have better musical performance over the full-bridge amps. It also seems like a lot of full-bridge amps have a lower dampening factor than the half-bridge. I can't find the dampening factor on some of the full-bridges. The Salt 8 has a dampening factor of 400<. That's pretty high, from what I've seen. The dampening factor seems to really play a role in the amplifier controlling the woofer across a relatively wide bandwidth of notes, for something like a ported box. I would really consider these things when you're setting up your audio system.

I think box design + overall quality of amplified signal into subs are wayyyyyyy more important than the type of sub you have.

 

[SlugButter]

I am running a full bridge and it seems ok. It’s a cheap Timpano, but it seems to be fine. I can’t tell a difference in audible sound between the Timpano and the JL G1700 I was running. The JL took a serious beating for years though. I bet I’m buying a new amp in a couple of years when this Timpano burns up. The speaker terminals are cheap and not sturdy, and the power and ground doesn’t even accept a 4 gauge without trimming it. It does seem to put out decent power though. I know it will do 1000 rms. I haven’t tried to get the 1400 rms like it says it will do, but I never planned on running 1400 rms when I bought it. 900-1000 watts was the plan. At 175$ I doubted I could even get 1000 watts honestly, but it does it.

 

[Buck 5,000+ posts]

I am running a full bridge and it seems ok. It’s a cheap Timpano, but it seems to be fine. I can’t tell a difference in audible sound between the Timpano and the JL G1700 I was running. The JL took a serious beating for years though. I bet I’m buying a new amp in a couple of years when this Timpano burns up. The speaker terminals are cheap and not sturdy, and the power and ground doesn’t even accept a 4 gauge without trimming it. It does seem to put out decent power though. I know it will do 1000 rms. I haven’t tried to get the 1400 rms like it says it will do, but I never planned on running 1400 rms when I bought it. 900-1000 watts was the plan. At 175$ I doubted I could even get 1000 watts honestly, but it does it.

I'm sure every amp should be judged by it's individual performance. I just can't help but notice that on the more extreme builds I do or people I talk to, that the full-bridge amps do not perform like the seemingly half-bridge amps do. I'm referring to musical boxes and high SPL at very low frequency playing boxes. I am not including higher bass SPL boxes in that amp comparison.

Since the wavelength of low notes is so long, the sub tries to push in and out for a longer duration. Each + and - peak lasts for longer, so to speak. So, the amp's ability to control the sub's cone movement during those potentially high xmax/long polarity duration situations can very greatly affect the overall sound. There's a difference between amps pushing/pulling a woofer cone vs "throwing" the woofer cone; the actual sound wave being produced by the sub can be distorted if the amp loses control of the woofer, say at a certain amount of woofer xmax.

 

[SlugButter]

I'm sure every amp should be judged by it's individual performance. I just can't help but notice that on the more extreme builds I do or people I talk to, that the full-bridge amps do not perform like the seemingly half-bridge amps do. I'm referring to musical boxes and high SPL at very low frequency playing boxes. I am not including higher bass SPL boxes in that amp comparison.

Since the wavelength of low notes is so long, the sub tries to push in and out for a longer duration. Each + and - peak lasts for longer, so to speak. So, the amp's ability to control the sub's cone movement during those potentially high xmax/long polarity duration situations can very greatly affect the overall sound. There's a difference between amps pushing/pulling a woofer cone vs "throwing" the woofer cone; the actual sound wave being produced by the sub can be distorted if the amp loses control of the woofer, say at a certain amount of woofer xmax.

I always liked my old half bridge sub amps for sure. I’ve been running full range class D amps on my front speakers for a long time, all the way back to the old Xtant 1.1 amps. My experience has always been with daily music setups also, so I’ve never ran over 2000 watts rms in my vehicles. I competed a little, but not at the high power level you’re talking about. My highest metered system was a precision power pc2350 running the subs and xtant 1.1 amps on my front speakers, so I went full assbackwards running class AB amp on my sub and class D on my fronts.

 

[Buck 5,000+ posts]

I always liked my old half bridge sub amps for sure. I’ve been running full range class D amps on my front speakers for a long time, all the way back to the old Xtant 1.1 amps. My experience has always been with daily music setups also, so I’ve never ran over 2000 watts rms in my vehicles. I competed a little, but not at the high power level you’re talking about. My highest metered system was a precision power pc2350 running the subs and xtant 1.1 amps on my front speakers, so I went full assbackwards running class AB amp on my sub and class D on my fronts.

The systems I'm thinking of are mostly walls. These systems all have somewhere between 8-30kw. It would still apply to everything; it all works the same. The stress levels on equipment in some of these walls is very high. When you're pushing stuff to the limits, every small thing that's wrong or "less better" than another product can affect the quality of the system. I mean, some of these subs are doing high 150's in the 20's on quite a good bit of over-powering. The nightshades are really good at this; so are the higher level DC's. But they travel a lot, and the more distance the coil travels, the more feedback the motor puts into the amp. That stresses the amp a lot and can cause voltage issues. Many factors change how the sub moves; a bunch of them can.

Idk, it's fun for me to learn this and it helps me design. Amps are interesting. The electricity in your speaker wires moves just like your woofer (hopefully lol).

 

[Buck 5,000+ posts]

@Coolhand20th

 

[Buck 5,000+ posts]

2 Skar EVL 8's ported going in a sedan trunk

 

[Firewalker]

Sawwwwwwwwwweeet! Looks awesome Buck!

 

[Bobbytwonames 5,000+ posts]

Both of those have relatively low xmax's and fairly high Fs's. I'm not sure if I'm believing the frequency response listed down to 20 hz, lol. I've never heard them before; the way the info sheets are presented reminds me of American Bass.

I've heard them and they get low. These two were underpowered but they were pretty impressive.

 

[Bobbytwonames 5,000+ posts]

@Buck, I would've mentioned these, but I know that people don't like AB so much. ABHD8'S. 24 pounds/each.

 

[Buck 5,000+ posts]

@Buck, I would've mentioned these, but I know that people don't like AB so much. ABHD8'S. 24 pounds/each.

View attachment 32399View attachment 32400

I like AB.

 

[Buck 5,000+ posts]

I just don't know if they'll get as low as an 8 with a ~32 hz Fs and 15mm of xmax.

The t/s parameters on the F8L look so good to me. Here they are (from SSA's site):

Dual 4 ohm Specifications:

• Fs: 32.1hz
• Re: 4ohm
• Qms: 4.31
• Qes: 0.27
• Qts: 0.25
• Rms: 6.7 kg/s
• Cms: 0.17 mm/N
• Mms: 143.5 gr
• Bl: 20.8 N/A
• SPL: 82.6 db
• Vas: 9.7 L
• Rp: 57.0 ohm
• Lp: 70.0 mH
• Cp: 496.4 uF
• Le: 3.16 mH
• Sd: 201.93cm²
• Xmax: 15mm

 

[Buck 5,000+ posts]

My very first 4th order design was for myself for a pair of Elemental Designs 8's when I was 17. They were 200-300w RMS. I didn't understand 4th order tuning, so I had a 4" aero as the port tuned to 40 hz. Those eD 8's were playing low 20's in that 4th order, not even joking. It wasn't very loud, being that they were only on like 400w RMS, but they were definitely playing a very low bandwidth with as much authority as 400w RMS can have in the 20 hz range lol.