Top contenders in their class 15,18,21 inch drivers - Page 3

With the resources available today almost anyone willing to study a bit can get their head around a great deal of driver design. Nothing ventured nothing gained applies here.

Way back in the eighties it was a different story. You had the Loud Speaker Design Cook Book and all the references to the Journal of the Audio Engineering Society in there. It was and is still a goldmine.

Today man are there some smart people posting really usefull info. Most of them are posting in this thread. Some of the reasons why things are reccomended are the greatest points to remember and learn from.


Unfortunately there are also a lot of people posting smart sounding info. That's the hardest part to figure. And I guess it always has been.

Not directed at anyone posting in this thread. Just an observation in general about the internet.


I think you are pointing to a bandpass type idea?

It will boost the efficiency. But the bigger the boost the harder it is on the driver. Generally you need a driver with a heavy strong cone to survive these kinf of enclosures. There are a couple of possible combinations.

Mark

Again this goes back to looking at a single # like a normalized inductance figure. Especially if based off of a manufacturers 1khz spec. It does not represent what you really need to know to judge a sub drivers inductance relationship. There are so many variables involving vc position, frequency and drive level that need to be looked at to make a real judgement. It is the percentage of change that matters. Look at the impedance curve for the lmsr and consider that it is an lmt motor that is very linear and that is has shorting paths in the motor. Id say that it easily bests the w15gti as far as linearity and control is concerned even if the inductance isn't as low it should be well controlled.

We've already discussed the xxx many times. Your needs are not mine. It is a device optimized more for the 2 octaves 12.5-50hz than for 25-100hz. A true subwoofer. Don't use it like a woofer and it does not disappoint. Most of the info about them that is 3rd party comes from me anyway. I would never chose some of the drivers mentioned elsewhere in this thread to perform the same ht or extreme extension role. Different strokes. I just wish it didn't take a nuclear reactor to power it. They are dreadfully power hungry and a heavy load for an amplifier.


Subwoofer efficiency. Yes the enclosure size will limit your sensitivity, but there is more to it than that. You are always advocating for lower inductance which in big subwoofers is mostly indicative of how they will perform above 100hz which is outside of their main role, but then you say that the efficiency afforded by the stronger motors over this exact same range above 80hz doesn't matter?

First, thanks for shedding some light on different issues. I'm not quoting your whole post (which I think everyone on this thread should read, and then perhaps re-read) but I certainly learned a few things from it.

That said, one minor bone to pick. I don't think anyone thinks that the Auras have 75mm of xmax. More like 15-20mm. (Their current spec sheets say 18mm xmax; a presumably older one* says 25mm.)

*Madisound has had the same sheet up since they started carrying the NS18 years ago. Aurasound redesigned their website last year. So I assume the Aurasound-posted specifications are accurate. Also, the number is lower, so the aurasound.com data sheet is the more conservative guess for someone who hasn't put the driver on a Klippel.

True, as you mention their spec sheets play the game that Dynaudio plays (ditto Seas) of listing peak-peak throw as Xmax, as opposed to using the standard rest-peak number. (In fairness, all three of them add a "peak-peak" disclaimer to their specification.) But, like many pro driver venders, Aura lists two numbers: rated linear and rated maximum excursion.

I see such motor-limited xmax as a good thing, because in practical use it means the driver will sound bad when overdriven but parts won't smash into each other and possibly take the driver out of contention. By the same token, I could see how someone else might prefer a longer linear throw with a risk of damage, because such a driver will get louder cleaner.


I think the presumption is that the latest/greatest/highest-tech is going to be disproportionately expensive for the performance gain.


Along those lines, it's worth mentioning that to my knowledge still the reigning low-end SPL champion (to my knowledge, at least) is still Genelec's sub with 1kW powering four Peerless XLS12's.

Could you elaborate?

I don't see what any (real world) design can do to overcome a small box.

Mark, what's special about 128 W?

I'm guessing you mean it's where power compression starts being an issue for most designs, but that's painting with a pretty broad brush.

129 watts is the point where the largest gain in volume versus the power input. After 128 watts you have to crack 3 kilowatts before you see 21 db gain in loudness.

Mark

21dB more from 129w? I think you would need a whole more than 3,000 watts dissipated. More like >12,000w but maybe I missed a part of the conversation.

Is that all the drivers in that are?

128-256-512-1024-2048-4096-8192-16384

Where I came up with 3 kw???

That's the power progression for the next 21 db.

At least if I typed properly on my phone!

Mark

What phone? I can not get AVS to work properly on my Blackberry storm

Great thread.... some great posts in here - for some of us that are less then top of the heap.... Mark great reading... thanks for stopping in

Iphone, AVS has an app for that....

Its really quite nice....

yeah, I was hoping someone would say it works on BlackBerry now.

Iphone sucks for real work

Stopping in is fun with you guys.

Phone is HTC Touch Pro 2

X-Max is defined as voicecoil winding height minus top plate thickness divided by 2.

Aura sound has more linear throw than their X-max spec as do any under hung or dual gap techniques.

We all need to do our home work.

Mark

I had thought the same, too. Prior to discovering the W15GTi the only "small box" sub that sounded remotely like music to me was the Peerless 830500 in a design similar to their Application note. (Box a smidge bigger, PR massed a smidge more.)

But a friend bought a W15GTi and wanted the smallest box for it that wouldn't sound terrible. So I put it in my test box (originally designed for a TC2+, so maybe 5 cubic feet) and we progressively stuffed chunks of wood into it, EQ'ed it, and listened.

I honestly couldn't hear any of the typical high-Q sub tells until under 2 cubic feet, at which point Qtc was through the roof. We ended up building him a 2.5 cubic foot box for the W15GTi...and smaller boxes for the supplemental Peerless SLS woofers I convinced him to buy. (I think they were 10's.)

Overall, very nice bass from just three (well-placed) woofers.

Power was a "1kW" Dayton rack amp for the W15GTi, and if memory serves the 240W plate amps from PE for the other two subs.

That led me to wonder if what I considered to be innate flaws of a high Qtc weren't in fact really thermal management issues, because that seems to be the one area where JBL put way more thought into the W15GTi than most other venders put into their woofers.


I wouldn't say "all," as the XLS12 was at the top of the heap when the Genelec sub came out, and it's still a darned good driver. Especially if one wants deep bass out of a small cube (with PR assistance).


Well, it depends. I like the definitions based on the smaller of BL and suspension linearity better than the geometric ones. And I don't like even top-flight venders such as Aura and Seas playing with the numbers. (I don't expect better from Dynaudio, who I don't hold in especially high regard.)

Hey DS-21

The true secret in what you are pointing out is valid only if the information is presented in a fair manner and the motor design is different from the standard pole piece top plate design.

The definition is by Richard Small. I'm not that smart!


What you have said here is one heck of a mouthfull. If a driver has a low power comression ratio then it can sound very good in a smaller enclosure. The problem is that there are very few consumer type drivers that are designed properly to have the lowest possible power compression. It happens in all loudspeakers. Pass enough current through a coil and it will heat up. The resistance goes higher and the amount of power that you can push into the coil is lessened as it heats up. This happens rather quickly.

Another neat thing that most people don't take into account in their quest for ultra low frequency response is that when you approach the drivers Fs or mechanical resonance the electrical impedance rises. 40 ohms is common. Some drivers do much higher.

So how much power can be pumped into a 40 ohm peak? One tenth of what you can pump into 4 ohms. So your Kilowatt monsters from hell can only push out 100 watts when a driver is being pushed hard away down low. Now to depress us a bit further I have measured peaks of 80 ohms. That is small signal mind you. Heat these puppies up a bit by actually using them and then measure them. I gets depressing and funny at the same time.

We are usually very happy listening to music at less then 10 watts input. The peaks need to much higher, but for most music we usually stay much below the 10 watts point. Unclipped we can use a heck of a lot. I was measureing some killer organ CD's a couple weeks back and found peaks of 52 db from loudest to quietest points. Do the math on that and you will just shake your head and say ouch! ( Unclipped it is an enormous number. And it is one of the reasons why I am now designing line arrays alla Don Keele and such. You have such a leg up on the ability to go loud and proud when called for. Actually leg up is not quite right. It's more like a scissor lift up! )

Ok now I make my case for higher efficiency enclosure designs.

In breif. CHECK THEM OUT!

There are real horn designs on this forum that incorporate real horn gain. Some to the tune of 8 to 9 db above free air efficiency. These designs will get you to 120 to 130 db with about 200 watts. That is in real rooms. Not cars. Some of them use one 12" driver to do this.

I have one, I think Ricci has finally nailed down his design. There are some really well thought out pieces of work out there.

Anyway enough rambling.

Mark

+1 #77.

All I can say is WOW, what an educating thread.....one of the main reasons this forum is great......no rambling detected.

I thought about starting a thread about impedance rise close to Fs relative to amp power.....but kept thinking I just missed the boat (or a thread) somewhere. So....my question is, does the impedance peak decrease by 4x if running a dvc in parallel (vs. series), therefore all the more reason to run the amp close to its lowest tolerable ohm value to help mitigate reduced output near Fs?

If an amp maxes out at 500 watts into 4 ohms, at 40 ohms it is only capable of 50 (voltage limited) watts?.....a depressing thought indeed.

"but kept thinking I just missed the boat (or a thread) somewhere."

you are on the right track. current is minimized when impedance is maximized. that has ramifications for distortion and power compression. not sure that i follow the second part of your question. in my estimation, this is a bigger factor than many consider it to be.

First part: Is the Fs impedance peak reduced by 4x on given sub if the dvc is connected in parallel vs. series?

Second part: Will take care of itself if the first part is true.....e.g., run a dvc d4 sub at 2 ohms, if the amp is capable, to increase output/headroom at Fs......if the amp is voltage limited.....couldn't this potentially increase the output capability at Fs (compared to dvc in series/8 ohms), more so than other frequencies?

Wow you guys are so close and yet are still missing the boat completely.

In a way HIL is not exactly right in the way it is normally interpreted. The enclosure volume does not completely squelch the efficiency advantage of a more powerful driver. Going back to this metric Im trying to figure out for driver efficiency or power. On one hand you have bl^2 /re and that has to be weighed against mms, suspension compliance and somehow involve sd as well. Im thinking of some sort of unit of motor force, minus resistance to movement, cm^2 of sd. I don't know its probably already represented by the simple 1w efficiency rating, or the n0.

Anyway if you take one driver and compare it to another that is much more efficient even in a tiny sealed enclosure. The more efficient driver will maintain the advantage over the vast majority of the bass range even down as low as below 10hz. This does not show up in a voltage sensitivity graph like used in the majority of modeling programs or measurements. It can be seen by looking at the voltage sensitivity plus the impedance graph, or a constant wattage graph. That 80ohm peak that is being lamented above? That is exactly what I want to see. A huge 200 ohm peak that keeps the average impedance much higher than the minimum or nominal is fine with me. The more efficient the system/driver the bigger these spikes will be and the easier the load will be on your amplifier and driver in the real world. Sure there is a limit to the amount of voltage an amp can swing into high impedances but when 50w is enough to crack 120db who cares? Depending on the driver parameters the technically less efficient driver may still have a range where it is more efficient (near the impedance peak) but the average over the entire bass range will favor the more efficient powerfully motored driver and with actual real content this matters.

Btw I'm posting from my droid x because my connection to ave at home is wack. It keeps timing out or having connection issues. It is the only site with this problem. Otherwise I would have illustrative graphics to go with the post above.

Ltd02,
remember when you were wondering how the sealed b&c's seemed so efficient to me but when you modeled them they didn't look any better than a lot of other designs? They are in the top 4 sub drivers I know of so far. There were 2 in that enclosure. Look at it again when you get a chance.

"Wow you guys are so close and yet are still missing the boat completely."

shucks. :-(

"remember when you were wondering how the sealed b&c's seemed so efficient to me but when you modeled them they didn't look any better than a lot of other designs? They are in the top 4 sub drivers I know of so far. There were 2 in that enclosure. Look at it again when you get a chance."

maybe it is a little late and i'm not following...what are you saying?

Use 2nd paragraph of post #82 to investigate 2nd paragraph of post #83.

What size box houses the driver in BFM's horn?

The battle occurs after the box, not in the box. Placing a huge horn in front of the box or increasing the size of the box or adding slave diaphragms or a pipe all focus on what happens in free air.

I've posted various versions of the in-room response at the LP with no post EQ and no smoothing, but it bears repeating for this discussion:


I've also created many spectrographs by taking the direct analog signal from the players SW output jack into SL and comparing those to the same screen capture from a mic at the LP.


As you can fairly easily gather, the discrepancy in the reproduction by the subs at the LP is around 70Hz and has absolutely nothing to do with box size, heat, Le or most of the things that are agonized over in these discussions.

Mild use of 3 PEQ filters will rectify the dip at 70Hz, so I ask (again and again and again...), what exactly is there to overcome that is caused by small boxes?

When I've used very large boxes of various alignment with various drivers the result at the LP has been wildly less successful with huge loss of BW and, quite frankly, untamable FR non linearity.

But, I keep hearing from virtually everyone that the smart money for me would be to abandon my results and use some latest design, huge contraption
and suffer the consequences. Assuring everyone that I am sincerely trying to not be facetious when I say this; the whole affair is and has always been quite baffling to me.

Bosso

Doubling any given power gives 3 dB more. Aren't 128 W and 21 dB arbitrary?

DS-21, interesting analysis about small boxes sounding bad because the VC overheats and Q rises more from that than smaller volume.

But you never got to the LT part; bass will still be rolled off and need EQ, no?


Josh beat me to it. The impedance peak reflects higher back EMF which is due to the mechanical resonance.

This is free energy and is to be celebrated, not lamented.

In case anyone sees resonance as a red flag of potential sloppiness, if there’s not a bump in the freq response, it’s not. The same back EMF, ultimately reflected in Qe/Qt, will keep cone motion in check.

“I don't see what any (real world) design can do to overcome a small box.”


Re LT I meant that for sealed boxes.

I got that. Isn't the THT driver in a sealed box?

Bosso

Yes. It is a front loaded horn design.