Amps for Passive Subs: Avoid Class D? Huh?

[ryanosaur]

This does not make sense. You can not drive a speaker in a vented box below its Fs. That Eminence driver is high sensitivity, low Qts, with an Fs of 29 Hz. So F3 vented will be considerably higher than Fs. So F3 will be around 50 Hz what ever you do. There is a direct inverse relationship between high sensitivity and bass extension. You can not fight that. So the only acoustic solution to pulling up the bass is a massive bass horn. It will be so big, that it will be impractical domestically because of the driver diameter.

The T/S parameters are not amenable to over drive in a sealed enclosure.

And that's part of the conundrum I experience. The fact is these drivers do perform to infrasonic output. Even with an Fs in the mid to high 30s.

I'm a Midwesterner by birth, and come from a notoriously stubborn state. I need to see it to believe it. Show me!

Modeled behavior for some Devastators indicate substantial output down to 16Hz at 2000w using the 21" Eminence NSW. Substantial? Over 120dB. That same design utilizing the 21" La Voce and B&C mentioned earlier is around 115Db. Similar measurements are being claimed in Marty Cabinets.

PSA Subs are claiming 14Hz anechoic using a 15" Pro Driver in a 24"d x 17"w x 25"h ported enclosure with a 4" flared port. The 18" ipal is in a slightly larger cabinet with a 4" port and sports the same measurement claims of 14Hz anechoic.

What needs to be accepted, potentially, is there is a design revolution taking place, a sea change if you will. Designers are taking these Pro Drivers and pushing them in a way I learned is not possible. But when I see measurements that are contrary to that learning, I am going to ask why and how!

 

[Verdinut]

And that's part of the conundrum I experience. The fact is these drivers do perform to infrasonic output. Even with an Fs in the mid to high 30s.

I'm a Midwesterner by birth, and come from a notoriously stubborn state. I need to see it to believe it. Show me!

Modeled behavior for some Devastators indicate substantial output down to 16Hz at 2000w using the 21" Eminence NSW. Substantial? Over 120dB. That same design utilizing the 21" La Voce and B&C mentioned earlier is around 115Db. Similar measurements are being claimed in Marty Cabinets.

PSA Subs are claiming 14Hz anechoic using a 15" Pro Driver in a 24"d x 17"w x 25"h ported enclosure with a 4" flared port. The 18" ipal is in a slightly larger cabinet with a 4" port and sports the same measurement claims of 14Hz anechoic.

What needs to be accepted, potentially, is there is a design revolution taking place, a sea change if you will. Designers are taking these Pro Drivers and pushing them in a way I learned is not possible. But when I see measurements that are contrary to that learning, I am going to ask why and how!

No, that's inexact. There's nothing new. There can be new designs but you cannot change the laws of physics and they cannot change over time. The speakers will abide by them no matter what you do.

 

[ryanosaur]

Well, I’m not the one making these designs. I do want to understand what’s going on.
I don’t think there is anything inexact there.

Beyond that, we’ll have to see. I will build a devastator down the road a bit once I get these SI Drivers up and running, at least through a test phase.

 

[lovinthehd]

Well, I’m not the one making these designs.

Who is and where are the measurements?

 

[ryanosaur]

Who is and where are the measurements?

Devastators variants and their models are indexed here. There are some measurements interspersed among that thread and here where the Dev thread began.
Have fun sorting through the 200 ages of posts and other links to build threads and what not!

The ones that have been measured do match up to the models pretty well.

When I have a chance to get back to the other thread I started to discuss Devs and Martys and such, I'll see what data I can pull together.

 

[TLS Guy]

And that's part of the conundrum I experience. The fact is these drivers do perform to infrasonic output. Even with an Fs in the mid to high 30s.

I'm a Midwesterner by birth, and come from a notoriously stubborn state. I need to see it to believe it. Show me!

Modeled behavior for some Devastators indicate substantial output down to 16Hz at 2000w using the 21" Eminence NSW. Substantial? Over 120dB. That same design utilizing the 21" La Voce and B&C mentioned earlier is around 115Db. Similar measurements are being claimed in Marty Cabinets.

PSA Subs are claiming 14Hz anechoic using a 15" Pro Driver in a 24"d x 17"w x 25"h ported enclosure with a 4" flared port. The 18" ipal is in a slightly larger cabinet with a 4" port and sports the same measurement claims of 14Hz anechoic.

What needs to be accepted, potentially, is there is a design revolution taking place, a sea change if you will. Designers are taking these Pro Drivers and pushing them in a way I learned is not possible. But when I see measurements that are contrary to that learning, I am going to ask why and how!

Well it may have output at 16 Hz, but what is its level with reference to the output at 50 or 60Hz. And another issue is the distortion. Trying to push a driver in a ported enclosure will result in enormous distortion. Sure you could seal the driver and equalize the hell out of it. Then you have given up the sensitivity advantage and have an extremely wasteful design. Fighting the laws of physics is never a good design plan, but working with them and making use of them will always win. Elegant solutions will always win over brute force. I have never used brute force solution, but always sought the elegant road ahead. That is the best advice I can give you.

 

[ryanosaur]

Well it may have output at 16 Hz, but what is its level with reference to the output at 50 or 60Hz. And another issue is the distortion. Trying to push a driver in a ported enclosure will result in enormous distortion. Sure you could seal the driver and equalize the hell out of it. Then you have given up the sensitivity advantage and have an extremely wasteful design. Fighting the laws of physics is never a good design plan, but working with them and making use of them will always win. Elegant solutions will always win over brute force. I have never used brute force solution, but always sought the elegant road ahead. That is the best advice I can give you.

This I agree with, wholly and completely.
It still doesn't change the aspect of conversation about the use of Pro Drivers in Subwoofers with Infrasonic capabilities. Believe me, half of me still screams at the thought of it, but now that I've talked to enough people that have worked with them... well, there's something going on there that I want to figure out and understand.
As for my comments regarding PSA: I still feel strongly that we need to see Third Party measurements of at least one of his designs. Even though I have opened my mind to the possibility of this working, I still haven't seen evidence that tells me its everything it is said to be.
Hence why I'm willing to try this. I may be able to sell a Dev if its not what I want or doesn't do what everybody using them swears they do. Or, I can strip the driver out and resell that and only be out the cost of wood and labor. (Surprisingly, I have talked to a couple guys that build and sell Devs, almost as a side hustle. Who knew!? )

All I can say is please stay tuned. I'm hoping to get back to the other thread I had to abandon due to time constraints. When I do, I plan on detailing much more information about what I've learned about the Devastators and sharing my build and attempts to measure them.
I will likely be including links to the Sealed and Ported builds I'm going to try with the SI Drivers I mentioned above. And hopefully a surprise that may be right up your ally, Mark!

 

[ryanosaur]

Getting back to the Amp question:

I talked to a guy at SpeakerPower today. I'm not going to pretend to grok everything we discussed, but I did learn some good stuff about their gear that wasn't readily apparent to me from reading their site. I definitely enjoyed and appreciated the time he took for me: they have moved up on my long-game list of possible Sub Amp purchases.

Now, what got more interesting is something he mentioned about how they use power from the wall vs how other designs use it. This is something @PENG might be able to shed some light on if he is willing to come out and play. (Please see the first post about the guy that gives an unsubstantiated claim about Class D Amps not being suitable for Subs.)
Anyway, what this gentleman at Speaker Power basically described is that a lot of Class D Amps route power through various stages en route to the Cap Bank. I queried at some point if this is the SMPS that he's referring to and he seemed to agree that most power supply scenarios aren't strong enough to support sustained bass in a power hungry Subwoofer application.
Effectively, he said it is not uncommon for many of the bigger drivers to drain the available power out very quickly which will result in a (he had a name for it, but effectively a rolloff in SPL due to lack of power available to sustain a pronged frequency). He suggested that most Amps can sustain for about 4-6 seconds before the power reserve stored in the Caps is depleted and this attenuation begins, at which point the transformer/power stages need a little time to replenish the Cap Bank.
In their design, he says they bypass all the various stages referenced above and route the power much more directly to the Caps. What this results in is the claim that their Amps can Sustain for as long as 10 seconds before depleting and also that the recharge cycle is faster.
Again, this is a layman (me ) reporting on a conversation I had this morning with a guy in Sales. I wasn't expecting all this but this what came of it.

Thoughts, comments, questions?

I'm still intrigued by the impetus of this thread and want to know more!

 

[Verdinut]

I just wouldn't believe if I heard from a manufacturer that does not build Class D amplifiers, when he tells me that most of them are not adequate to drive subwoofers, or of any other fault with them.
One thing for sure is that the DCA series of QSC Cinema amps use a SMPS power supply, and they're adequate to drive subwoofers without a hitch. They are used in cinemas worldwide, and they are also built in the US. They have been so good that the whole series has not been modified since their release in 1998.

 

[ryanosaur]

This isn’t an advertisement for anybody. And just because a saleperson said so doesn't make it gospel. That said, they do have some good info up on their site under "technical" and "technology" => "comparative performance."

 

[mtrycrafts]

Getting back to the Amp question:

I talked to a guy at SpeakerPower today. I'm not going to pretend to grok everything we discussed, but I did learn some good stuff about their gear that wasn't readily apparent to me from reading their site. I definitely enjoyed and appreciated the time he took for me: they have moved up on my long-game list of possible Sub Amp purchases.

Now, what got more interesting is something he mentioned about how they use power from the wall vs how other designs use it. This is something @PENG might be able to shed some light on if he is willing to come out and play. (Please see the first post about the guy that gives an unsubstantiated claim about Class D Amps not being suitable for Subs.)
Anyway, what this gentleman at Speaker Power basically described is that a lot of Class D Amps route power through various stages en route to the Cap Bank. I queried at some point if this is the SMPS that he's referring to and he seemed to agree that most power supply scenarios aren't strong enough to support sustained bass in a power hungry Subwoofer application.
Effectively, he said it is not uncommon for many of the bigger drivers to drain the available power out very quickly which will result in a (he had a name for it, but effectively a rolloff in SPL due to lack of power available to sustain a pronged frequency). He suggested that most Amps can sustain for about 4-6 seconds before the power reserve stored in the Caps is depleted and this attenuation begins, at which point the transformer/power stages need a little time to replenish the Cap Bank.
In their design, he says they bypass all the various stages referenced above and route the power much more directly to the Caps. What this results in is the claim that their Amps can Sustain for as long as 10 seconds before depleting and also that the recharge cycle is faster.
Again, this is a layman (me ) reporting on a conversation I had this morning with a guy in Sales. I wasn't expecting all this but this what came of it.

Thoughts, comments, questions?

I'm still intrigued by the impetus of this thread and want to know more!

When an amps is rated for X Watts average continuous power it means that it will sustain that power for a long duration. That 10 sec, is not even in the test protoco for that power rating.
Peaks are different and short. So, one would need an sub amp of the power the driver needs for continuous rating it will withstand.

 

[Verdinut]

Peaks are different and short. So, one would need an sub amp of the power the driver needs for continuous rating it will withstand.

The continuous power rating a driver would withstand usually varies between 40 and 60% of its stated maximum power input.

 

[mtrycrafts]

The continuous power rating a driver would withstand usually varies between 40 and 60% of its stated maximum power input.

Then the rest will be taken care of by the amps peaks that is the peak power which is E-peak and I-peak which is 2x of amps continuous power rating.
Then the question is how much of the signal is in that peak range. If it is infrequent, not an issue. If frequently, need better driver and amp.

 

[Verdinut]

Then the rest will be taken care of by the amps peaks that is the peak power which is E-peak and I-peak which is 2x of amps continuous power rating.
Then the question is how much of the signal is in that peak range. If it is infrequent, not an issue. If frequently, need better driver and amp.

Then, if the amp clips with the peaks, it begins to be more risky for the tweeters.

 

[mtrycrafts]

Then, if the amp clips with the peaks, it begins to be more risky for the tweeters.

Oh, but we are talking about sub amps, no?

 

[Verdinut]

Oh, but we are talking about sub amps, no?

Oh yeah! Not as much risky but one should not drive a sub beyond its maximum power rating in any case, if he wants to keep it in good working condition for years.

 

[panteragstk]

Crown is actually considered high-end in the PA market. I'd absolutely do a Crown class D to drive a speaker that is only tasked to push about 200Hz of frequency range and not need to be especially detailed, just not distorted.

Crown has lines from dirt cheap up to very high end. I don't think the "Crown" name is associated with high end so much as quality and durability. Same with QSC. Both companies make low end amps and ultra high end.

I've never purchased anything from Behringer just because I know how much their specs are inflated most of the time. However, with some of their newer stuff that's been reviewed it looks like they may be getting it together. I still prefer Crown for my own preference, but I wouldn't throw away a Behringer amp if I could use it for something.

If I'm talking about non-consumer amps Crown and QSC are both at the top of my list.