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Title: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 03, 2014, 05:22:25 PM
Sorry I couldn't find this in a search....I tried, I really did :)

....but if I have a test signal @+ 4 dbu going into and coming out of each channel of a mixer's stereo input,
    what dbu or voltage should I read coming out of the mixer's summed mono output?

I'm getting about .9v from the summed mono output......which is LESS that the 1.23v I read from each channel of the stereo output. ??????

Thanks,  Mark
Title: Re: Mixer summed mono voltage?
Post by: Ivan Beaver on August 03, 2014, 08:11:48 PM
Sorry I couldn't find this in a search....I tried, I really did :)

....but if I have a test signal @+ 4 dbu going into and coming out of each channel of a mixer's stereo input,
    what dbu or voltage should I read coming out of the mixer's summed mono output?

I'm getting about .9v from the summed mono output......which is LESS that the 1.23v I read from each channel of the stereo output. ??????

Thanks,  Mark
It depends on the particular mixer and how much gain it has in that stage.

Telling what gear you are working with goes A LONG WAY to getting answers-since gear varies quite a bit.  There is no "standard" in terms of gain.
Title: Re: Mixer summed mono voltage?
Post by: Tim Padrick on August 03, 2014, 08:59:32 PM
1.23 from each driven one at a time, or both driven?  If the former, I'd consider that to be just fine.
Title: Re: Mixer summed mono voltage?
Post by: John Roberts {JR} on August 03, 2014, 09:20:40 PM
What Ivan said... the summed mono output is for convenience and not critical about calibration levels. Often has it's own gain trim on the back.

JR
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 04, 2014, 12:00:07 PM
What Ivan said... the summed mono output is for convenience and not critical about calibration levels. Often has it's own gain trim on the back.

JR

Thanks everybody.  The mixer is an Allen and Heath Xone 464, a better DJ mixer. 

John, if the summed mono is just for convenience and isn't calibrated, I don't want to use it. I have 4 Labhorns that I want to fully power and limit properly, and I'm trying to learn the science behind proper levels, xover, limiter, and amp settings. I was going to use the summed mono as a feed to the C input on a DCX2496, because I could control the level to the subs with a separate main fader ... the mixer has two main busses, either of which can be summed to a mono out.

I've started with trying to understand signal sources and mixer levels..

Ivan, I'm not sure what you mean by 'how much gain it has at that stage'...Its maximum output level is spec'd @+26dbu.
Tim, the same signal is going to both channels via a y cable. I've been using a 1kz +4dbu 1.23v sine wave.

The mixer's input level meter reads 0db; and with the main output fader and meter at 0db, each channels output voltage is right about 1.23v ...so all makes sense so far and seems to be pretty dang accurate.
But then I read the summed mono (which doesn't have a trim) and get only about .9v. .... this is what throws me....

It's not a big deal if the summed mono is just for convenience and wont give a true level.... I can get around that easy enough.
It's more about finally learning and understanding how this stuff works, and not blowing up my labhorns  ;D

Thanks for the generousity of your help,  Mark
Title: Re: Mixer summed mono voltage?
Post by: John Roberts {JR} on August 04, 2014, 01:14:15 PM
Thanks everybody.  The mixer is an Allen and Heath Xone 464, a better DJ mixer. 
;D
Quote
John, if the summed mono is just for convenience and isn't calibrated, I don't want to use it. I have 4 Labhorns that I want to fully power and limit properly, and I'm trying to learn the science behind proper levels, xover, limiter, and amp settings. I was going to use the summed mono as a feed to the C input on a DCX2496, because I could control the level to the subs with a separate main fader ... the mixer has two main busses, either of which can be summed to a mono out.

I've started with trying to understand signal sources and mixer levels..

Ivan, I'm not sure what you mean by 'how much gain it has at that stage'...Its maximum output level is spec'd @+26dbu.
Tim, the same signal is going to both channels via a y cable. I've been using a 1kz +4dbu 1.23v sine wave.

The mixer's input level meter reads 0db; and with the main output fader and meter at 0db, each channels output voltage is right about 1.23v ...so all makes sense so far and seems to be pretty dang accurate.
But then I read the summed mono (which doesn't have a trim) and get only about .9v. .... this is what throws me....

It's not a big deal if the summed mono is just for convenience and wont give a true level.... I can get around that easy enough.
It's more about finally learning and understanding how this stuff works, and not blowing up my labhorns  ;D

Thanks for the generousity of your help,  Mark
Did you try RTFM (read the fine manual).  According to the A/H user guide the mono output on the XLR is active balanced (both legs hot)  +4dBu, while the mono output on TRS is impedance balanced (one leg hot) -2dBu. It is pretty common to see the 6dB difference between one legged and two legged signals.

-2 dBu should be roughly 1/2 of the +4 dBu voltage or 0.61V

0.9V is too low from the mono XLR, and too high from the mono TRS.

If you are confident that your measurement is accurate contact A/H customer service for assistance

JR
Title: Re: Mixer summed mono voltage?
Post by: Tim McCulloch on August 04, 2014, 01:49:54 PM
Thanks everybody.  The mixer is an Allen and Heath Xone 464, a better DJ mixer. 

John, if the summed mono is just for convenience and isn't calibrated, I don't want to use it. I have 4 Labhorns that I want to fully power and limit properly, and I'm trying to learn the science behind proper levels, xover, limiter, and amp settings. I was going to use the summed mono as a feed to the C input on a DCX2496, because I could control the level to the subs with a separate main fader ... the mixer has two main busses, either of which can be summed to a mono out.

Why, oh why, would you give a DJ separate control over any segment of a system?  Unless you're the only person running the rig, I think this is a bad idea and don't care how Shorty used to do it (Systems by Shorty).

That said, NOTHING about this output being different in output level will keep you from running your subs to their full potential.  You can compensate at the processor input, or output.  Makes little difference.
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 04, 2014, 02:37:09 PM
;DDid you try RTFM (read the fine manual).  According to the A/H user guide the mono output on the XLR is active balanced (both legs hot)  +4dBu, while the mono output on TRS is impedance balanced (one leg hot) -2dBu. It is pretty common to see the 6dB difference between one legged and two legged signals.

-2 dBu should be roughly 1/2 of the +4 dBu voltage or 0.61V

0.9V is too low from the mono XLR, and too high from the mono TRS.

If you are confident that your measurement is accurate contact A/H customer service for assistance

JR


John, I've read the manual till my eyes have crossed...even downloaded the latest revision to see if it had a better explanation of things..

I've been taking all voltages across xlr pins 2 & 3 with a good meter...
I guess I'll probably will have A/H take a look at it, if and when something major goes wrong...

Thx,  Mark
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 04, 2014, 02:57:06 PM
Why, oh why, would you give a DJ separate control over any segment of a system?  Unless you're the only person running the rig, I think this is a bad idea and don't care how Shorty used to do it (Systems by Shorty).

That said, NOTHING about this output being different in output level will keep you from running your subs to their full potential.  You can compensate at the processor input, or output.  Makes little difference.

Hi Tim, you called it...I'm the only operator.  This is pure personal hobby...many decades of it.
And yes, its easy enough to compensate for elsewhere.

For playing a mix of recorded music, I have found I like having two sliders next to each other, one for the mains and one for the subs.  I know this messes with the crossover region acoustically, but it sure is handy, especially for balancing out perceived  highs vs lows across wide volume swings.  Any overpowering reason not to ?

Thx, Mark
Title: Re: Mixer summed mono voltage?
Post by: g'bye, Dick Rees on August 04, 2014, 03:26:20 PM
Just do it (LF boost) with the channel strip EQ.
Title: Re: Mixer summed mono voltage?
Post by: Ivan Beaver on August 04, 2014, 03:28:13 PM
Thanks everybody.  The mixer is an Allen and Heath Xone 464, a better DJ mixer. 

John, if the summed mono is just for convenience and isn't calibrated, I don't want to use it. I have 4 Labhorns that I want to fully power and limit properly, and I'm trying to learn the science behind proper levels, xover, limiter, and amp settings. I was going to use the summed mono as a feed to the C input on a DCX2496, because I could control the level to the subs with a separate main fader ... the mixer has two main busses, either of which can be summed to a mono out.

I've started with trying to understand signal sources and mixer levels..

Ivan, I'm not sure what you mean by 'how much gain it has at that stage'...Its maximum output level is spec'd @+26dbu.
Tim, the same signal is going to both channels via a y cable. I've been using a 1kz +4dbu 1.23v sine wave.


Max output and gain are very different things.  You can reach max output with just a little gain or a lot-it depends on the previous stages and devices.

"Calibrated" can mean very different things to different people.  Calibrated to "what"?  You don't calibrate gain.  It is what it is.  You can calibrate some meters-but you also have to consider at what point the meter is reading.

Some mixers have level controls after the stage that the meters are looking at-others do not.  The good ones will show the actual output level.

The limiting is done AFTER the mixer and the mixer gain has nothing to do with the limiting of the amplifier outputs.  Those are separate discussions with different outcomes.

And before we go down the same rabbit hole-the level controls on the amplifier have NOTHING to do with the output power capability of the amplifer.

You can turn them just about all the way down and the amp can still put out full power.

Just heading it off before we go there. ;)
Title: Re: Mixer summed mono voltage?
Post by: Tim McCulloch on August 04, 2014, 04:42:16 PM
Hi Tim, you called it...I'm the only operator.  This is pure personal hobby...many decades of it.
And yes, its easy enough to compensate for elsewhere.

For playing a mix of recorded music, I have found I like having two sliders next to each other, one for the mains and one for the subs.  I know this messes with the crossover region acoustically, but it sure is handy, especially for balancing out perceived  highs vs lows across wide volume swings.  Any overpowering reason not to ?

Thx, Mark

Just increase the level at the DSP input to make it match the L/R levels.  Your faders will then track together.
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 04, 2014, 05:11:34 PM
Just increase the level at the DSP input to make it match the L/R levels.  Your faders will then track together.

Yes, will do.  Just to learn, what should a summed mono voltage read, both stereo inputs with 1.23v?  Would it matter if the two input signals were identical?
Thanks again.
Title: Re: Mixer summed mono voltage?
Post by: John Roberts {JR} on August 04, 2014, 05:58:55 PM
Yes, will do.  Just to learn, what should a summed mono voltage read, both stereo inputs with 1.23v?  Would it matter if the two input signals were identical?
Thanks again.

The "nominal" output on the mono XLR is supposed to be the same 1.23V (according to their user advice).

That said when you combine a real stereo signal to mono, the answer is not so clear-cut because the left and right signals are not coherent. Are you using stereo program material and expecting some stable precise mono output level? 

Without looking at their schematic I can not predict accurately. I am not aware of any hard rules for how to handle mono outputs in a stereo world. Mono feeds are generally provided for less critical applications.

Summing two identical mono signals on L & R might combine 2x or might be normalized so each adds with 1/2 weight to sum to 1x.

You are the man with the meter,,, you tell us. (Your 0.9V measurement does not appear to agree with any of my hypotheticals).

JR

PS:  BTW have you tried asking A & H ? They are generally pretty responsive to customer service issues.
Title: Re: Mixer summed mono voltage?
Post by: Patrick Tracy on August 04, 2014, 07:16:12 PM
I'm getting about .9v from the summed mono output.

I may be off base here, but I'm wondering if it's an impedance balanced output and measuring hot to ground would be different from hot to cold.
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 04, 2014, 07:28:45 PM
The "nominal" output on the mono XLR is supposed to be the same 1.23V (according to their user advice).

That said when you combine a real stereo signal to mono, the answer is not so clear-cut because the left and right signals are not coherent. Are you using stereo program material and expecting some stable precise mono output level? 

Without looking at their schematic I can not predict accurately. I am not aware of any hard rules for how to handle mono outputs in a stereo world. Mono feeds are generally provided for less critical applications.

Summing two identical mono signals on L & R might combine 2x or might be normalized so each adds with 1/2 weight to sum to 1x.

You are the man with the meter,,, you tell us. (Your 0.9V measurement does not appear to agree with any of my hypotheticals).

JR

PS:  BTW have you tried asking A & H ? They are generally pretty responsive to customer service issues.

Thanks John, yes the .9v doesn't seem to agree with anything.....
I'll ask A&H..

Patrick, the mono out has a balanced xlr and impedance balanced trs...I'll compare the two..

Ivan, no worries...had no intention of going down that rabbit hole !  I actually think I understand at least several of the issues in that hole :)  A lot of you guys posts, and stuff like Meyer's Sound Design Reference have helped.  Their Speaker Sense ECU for the non-powered stuff explains a lot.  Do you know of a reasonably priced limiter or speaker management device that monitors and controls actual amp voltage output, peak and rms?

And while I have you :) ..... and assuming my attachment makes it into this post (it doesn't preview for some reason)...
please look at these SPL readings I just took from 4 labhorns.   I measured each one individually, then 2, then 4.  Used sine waves at 2.0v, 4 meters. Measured unweighted with supposedly good meter.
Labhorns were next to my house, firing down the length of a 2nd floor deck.  So I don't really know what space to say they were in...probably something effectively a little less than 1/2 space.

Anyway, the way the dip at 62 hz on 1 and 2 boxes disappeared with 4 boxes blew my mind.  I went back and tried 3 boxes, and found the dip gone there too.  I remember Tom saying the design was for a minimum of 6 boxes...wow, now I wish I had two more.  I sure wont use less than 3 together...unless I find these measurements to be bogus.  Your thoughts?  Thx. Hope it was ok to change subject here...sorry if I should have made new post on Labhorn forum...
Title: Re: Mixer summed mono voltage?
Post by: Ivan Beaver on August 04, 2014, 07:54:11 PM
Thanks John, yes the .9v doesn't seem to agree with anything.....
I'll ask A&H..

Patrick, the mono out has a balanced xlr and impedance balanced trs...I'll compare the two..

Ivan, no worries...had no intention of going down that rabbit hole !  I actually think I understand at least several of the issues in that hole :)  A lot of you guys posts, and stuff like Meyer's Sound Design Reference have helped.  Their Speaker Sense ECU for the non-powered stuff explains a lot.  Do you know of a reasonably priced limiter or speaker management device that monitors and controls actual amp voltage output, peak and rms?

And while I have you :) ..... and assuming my attachment makes it into this post (it doesn't preview for some reason)...
please look at these SPL readings I just took from 4 labhorns.   I measured each one individually, then 2, then 4.  Used sine waves at 2.0v, 4 meters. Measured unweighted with supposedly good meter.
Labhorns were next to my house, firing down the length of a 2nd floor deck.  So I don't really know what space to say they were in...probably something effectively a little less than 1/2 space.

Anyway, the way the dip at 62 hz on 1 and 2 boxes disappeared with 4 boxes blew my mind.  I went back and tried 3 boxes, and found the dip gone there too.  I remember Tom saying the design was for a minimum of 6 boxes...wow, now I wish I had two more.  I sure wont use less than 3 together...unless I find these measurements to be bogus.  Your thoughts?  Thx. Hope it was ok to change subject here...sorry if I should have made new post on Labhorn forum...
I am not aware of any stand alone limiter with monitoring-but that might be a good idea for a product.

Part of the problem trying to measure sub cabinets is that you REALLY have to far (think 50' at a minimum-depending on your measurement distance-speaker to mic) away from any reflective surface.

I see two problems with the way you were measuring the cabinets.  First you were close to your house (being on a deck) and second you were on a deck  on the second floor.

So you were getting cancelling reflections from both the house AND the ground.

Ideally you need to get in the middle of a large parking lot-but that is not always easy to do.

Title: Re: Mixer summed mono voltage?
Post by: Ivan Beaver on August 04, 2014, 08:23:22 PM
Yes, will do.  Just to learn, what should a summed mono voltage read, both stereo inputs with 1.23v?  Would it matter if the two input signals were identical?
Thanks again.
There is no way to say what it "should" read.

Let's take a look at what is ACTUALLY going on in a mixer.

You cannot simply combine 2 signals/voltages.  Like with a Y cable.  Yes you can-but then the output stage of each stage will load down the output of the other stage-resulting in a lowered voltage and possibly damaging the output device due to driving a lower impedance than it is looking for.

So in a mixer-each signal goes through a series "summing resistor" and then they get combined into the next stage.

There is loss across these resistors.

Then the "makeup gain" stage provides gain to make up for the loss across the resistors-and maybe more.

So let's assume a meter that is placed after the summing resistors.  Let's say you read 1V with one channel (let's say the left) on.  When you add the same signal to the right channel the voltage will double or be 2V.  This is a 6dB gain (doubling of voltage-NOT adding 1 volt).  The difference between0.5 and 1 V is also 6dB.

So as you can see the gain of the summing amp can make a difference in what you are reading on the voltmeter.

And as JR said-if the signals are not the exact same-then there is no way to guess how much addition there will be.

I'm not sure if that helps or hurts any-but should give you something to think about.
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 05, 2014, 09:46:44 AM
Thanks Ivan, I'm good with all the points you raised.  By what "should" the voltage read, I thought maybe there was some industry convention for final level after the summing resistors and "make up gain".


I just rechecked my measurements before asking A&H for help. With 1.23v out of each stereo output, the summed mono reads .94v for either the balanced +4 XLR or the impedance balanced -2 TRS.
.94v was the same whether sending a split mono 1kz sine through both channels, or sending a stereo signal ---- 1kz through left and 700hz through right.

If it's ok, I'm going to continue the labhorn discussion over in the labhorn forum...again, i apologize for switching topics...
Title: Re: Mixer summed mono voltage?
Post by: John Roberts {JR} on August 05, 2014, 10:33:28 AM
Thanks Ivan, I'm good with all the points you raised.  By what "should" the voltage read, I thought maybe there was some industry convention for final level after the summing resistors and "make up gain".


I just rechecked my measurements before asking A&H for help. With 1.23v out of each stereo output, the summed mono reads .94v for either the balanced +4 XLR or the impedance balanced -2 TRS.
This seems wrong, since there should be a 6dB difference between TRS output and XLR unless their user advice is incorrect.

Apparently mono output is post fader, and there is a rear panel selector switch to alternate between mix 1 or mix 2.

JR
Quote
.94v was the same whether sending a split mono 1kz sine through both channels, or sending a stereo signal ---- 1kz through left and 700hz through right.

If it's ok, I'm going to continue the labhorn discussion over in the labhorn forum...again, i apologize for switching topics...

Title: Sub Measurements
Post by: Art Welter on August 05, 2014, 02:30:01 PM
1) Do you know of a reasonably priced limiter or speaker management device that monitors and controls actual amp voltage output, peak and rms?
2)Anyway, the way the dip at 62 hz on 1 and 2 boxes disappeared with 4 boxes blew my mind.  I went back and tried 3 boxes, and found the dip gone there too.  I remember Tom saying the design was for a minimum of 6 boxes...wow, now I wish I had two more.  I sure wont use less than 3 together...unless I find these measurements to be bogus.  Your thoughts?
Mark,

1) Eminence markets a unit called D-fend that is put between amp and speaker that controls the voltage output, peak and average. It can be (must be) set for the specific parameters of the speakers used, but once set is virtually bulletproof.
2) Looks like the 2 box output at 62 Hz is simply a typo (I have done the same more than once..), most of your other readings average around a +6 dB per doubling of cabinets and power as is normal, though from 2-4 is generally a bit less, perhaps due to amplifier current limiting. As Ivan points out, your test conditions are responsible for some of the frequency response you measured, the dip at 60 Hz is larger than the usual Lab Sub response deviation.

As far as how many cabinets you use, that should simply be determined by the SPL level you require for the gig. Every room (or partial room like your deck measurements) requires it's own EQ to deal with room modes and proximity to boundaries, so the relatively small differences in EQ required between 1 and 4 cabinets are just another variation to deal with.

Art
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 05, 2014, 05:09:09 PM
Mark,

1) Eminence markets a unit called D-fend that is put between amp and speaker that controls the voltage output, peak and average. It can be (must be) set for the specific parameters of the speakers used, but once set is virtually bulletproof.
2) Looks like the 2 box output at 62 Hz is simply a typo (I have done the same more than once..), most of your other readings average around a +6 dB per doubling of cabinets and power as is normal, though from 2-4 is generally a bit less, perhaps due to amplifier current limiting. As Ivan points out, your test conditions are responsible for some of the frequency response you measured, the dip at 60 Hz is larger than the usual Lab Sub response deviation.

As far as how many cabinets you use, that should simply be determined by the SPL level you require for the gig. Every room (or partial room like your deck measurements) requires it's own EQ to deal with room modes and proximity to boundaries, so the relatively small differences in EQ required between 1 and 4 cabinets are just another variation to deal with.

Art

Art,
1)  Yes, I've been looking for user reports on the d-fend...doesn't seem to have sold too well and seems to be sold out everywhere except Amazon Home and Garden Shop...really !
Should I give it a try?
2) Yes thanks, typo...should have been 94.3
3) As you and Ivan point out, boundaries and reflections make the kind of measurements I'm trying perilous.... but I did get lucky and figure out the crazy dip at 63 hz for 1 and 2 labs as per yesterday's chart...

I knew the dip couldn't be a reflection cancellation because the suckout was everywhere I walked around and listened to.  I am using steady sine waves with time to roam around and listen.
(the freakin reflections are what made me give up trying to learn Smaart indoors about 10 years ago lol )

It turns out, there must be a passive radiator suckout from the adjoining Labs that aren't being driven.
The middle two in my bank of 4 get sucked out at 63hz, either singly or as a pair when the others aren't driven.
With subs numbered 1-4 left to right, yesterday I chose (by bad luck :)  #2 as typical for one sub, and 2 & 3 together as typical for 2 subs.
Today I remeasured pairs and quickly found the only 2 sub combo that would dip at 63hz was 2 & 3.
So I removed 1 and 4 from the bank, from physical proximity, and bingo...no dip for the pair, or singly!

Here's the results of today's test .. #4 is closest to house, hence the gradual increase in levels with tests that lean towards the higher combos.
Sorry for the false alarm on the subs...the novice learns...

Oh, and John...waiting to hear from A&H....
Title: Re: Sub Measurements
Post by: Ivan Beaver on August 05, 2014, 05:16:15 PM


It turns out, there must be a passive radiator suckout from the adjoining Labs that aren't being driven.
.
Any time you have woofers nearby that are not hooked up-they will cause notches (suckouts) in the response.

Shorting the speaker terminals helps-but the best thing is to move them a long distance away-at least relative to the distance to the mic position.

I have spent quite a bit of time with the D fend circuit.  It works quite well-when programmed properly-that usually requires careful measurement of the speaker.  They do have a guideline that is a good start.  However there are some maximum input levels that can damage it when exceeded.
Title: Re: Sub Measurements
Post by: Art Welter on August 06, 2014, 01:44:03 PM
Art,
1)  Yes, I've been looking for user reports on the d-fend...doesn't seem to have sold too well and seems to be sold out everywhere except Amazon Home and Garden Shop...really !
Should I give it a try?
Today I remeasured pairs and quickly found the only 2 sub combo that would dip at 63hz was 2 & 3.
So I removed 1 and 4 from the bank, from physical proximity, and bingo...no dip for the pair, or singly!
Mark,

I have not actually tried the D-fend yet, but have an earlier model available if you are interested.
Proper settings of limiters would be more cost effective since you are running multiple amp channels, but for  safeguarding a cabinet against people that like to see red, D-fend seems perfect.

Since you seem to enjoy testing, another interesting test would be to compare the response of a pair of your subs with a pair of shorted cabinets flanking on either side, so the front of the stack is 135" wide by 45" tall. You will probably find about a 4 dB increase in level over the single pair, if you measure away from boundaries.

The "cool" thing about that +4 dB gain is it requires no additional power, therefore no thermal compression, which is a weak point on the Lab 12 in a small compression chamber.

Art
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 06, 2014, 05:16:18 PM
Mark,

I have not actually tried the D-fend yet, but have an earlier model available if you are interested.
Proper settings of limiters would be more cost effective since you are running multiple amp channels, but for  safeguarding a cabinet against people that like to see red, D-fend seems perfect.

Since you seem to enjoy testing, another interesting test would be to compare the response of a pair of your subs with a pair of shorted cabinets flanking on either side, so the front of the stack is 135" wide by 45" tall. You will probably find about a 4 dB increase in level over the single pair, if you measure away from boundaries.

The "cool" thing about that +4 dB gain is it requires no additional power, therefore no thermal compression, which is a weak point on the Lab 12 in a small compression chamber.

Art

Thanks Art,

I went ahead and ordered a D-Fend to see how it works.

The flanking subs setup sounds incredible !  Do the 2 "flankers" have mouths pointing away from, or into the active pair?  And where do they position to the active pair?  ie even with the fronts, or mid, or backs?  Is the +4 db gain across the whole sub range?
 
I know what corner stacking the Labs can do above and beyond the 1/4 space gain...can't wait to try this..
Title: Re: Mixer summed mono voltage?
Post by: Mark Wilkinson on August 08, 2014, 02:40:19 PM
This seems wrong, since there should be a 6dB difference between TRS output and XLR unless their user advice is incorrect.

Apparently mono output is post fader, and there is a rear panel selector switch to alternate between mix 1 or mix 2.

JR

A&H says they don't know what the XLR output should be under the conditions I give without a unit to test, but that there should definitely be a 6db difference between TRS and XLR.
And yes, the mono out is post fader and with a switch to choose mix 1 or mix2.......my switch is wired backwards....may be indicative of further wiring issues...?
Probably wont get service though...too many workarounds and everything else appears to work great
best, mark
Title: Re: Sub Measurements
Post by: Ivan Beaver on August 08, 2014, 08:05:26 PM
Thanks Art,

I went ahead and ordered a D-Fend to see how it works.

The flanking subs setup sounds incredible !  Do the 2 "flankers" have mouths pointing away from, or into the active pair?  And where do they position to the active pair?  ie even with the fronts, or mid, or backs?  Is the +4 db gain across the whole sub range?
 
I know what corner stacking the Labs can do above and beyond the 1/4 space gain...can't wait to try this..
The mouths should be positioned so that the whole thing looks like a big horn.  The exits should "flare" towards the outsides-so the "narrower part" should be towards the center.

What this does is to help change the acoustic impedance that the drivers see with respect to the air.  The cabinets help each other.  This can increase the gain and smooth out the response.
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 09, 2014, 08:29:35 AM
The mouths should be positioned so that the whole thing looks like a big horn.  The exits should "flare" towards the outsides-so the "narrower part" should be towards the center.

What this does is to help change the acoustic impedance that the drivers see with respect to the air.  The cabinets help each other.  This can increase the gain and smooth out the response.

Thank you Ivan,

Looking down on the subs, does the little diagram below picture what you mean?  If so, best angle  to use?  Could you just add plywood flares?

Also, I remember you said you spent a good deal of time with the D-Fend... Any advice/ comments for the settings below for a single Labsub with a bridged QSC capable of at least 3400 watts into 4 ohms...ie plx 3402, pl 340, etc
Double thanks !!!
Title: Re: Sub Measurements
Post by: Ivan Beaver on August 09, 2014, 12:41:32 PM
Thank you Ivan,

Looking down on the subs, does the little diagram below picture what you mean?  If so, best angle  to use?  Could you just add plywood flares?

Also, I remember you said you spent a good deal of time with the D-Fend... Any advice/ comments for the settings below for a single Labsub with a bridged QSC capable of at least 3400 watts into 4 ohms...ie plx 3402, pl 340, etc
Double thanks !!!
If using 4 subs I would stack them up 2 over 2-laying with the large flat sides down.  So the whole block would be 90wide x45tall.

Yes I have spent a lot of time with the Dfend.

The first thing I do is to determine the real parameters of the speaker they are to be used with.

Things such as measuring distortion per freq (to determine the point of the excursion limiting), measuring the point of power compression and so forth.

Without having real data-I am hesitant to suggest something-because if something should "go wrong", then I could be blamed for "Well Ivan said to do this" type of thing.

To even determine the voltage based on rated power requires an actual impedance measurement (NOT DC resistance) to put into the calculation.

But my "gut feeling is that your voltage are to high-based on the "simple numbers" and not measurement.

The attach and release times on the all pass are to short.

When I was considering it, I spent a lot of time measuring the actual speaker under consideration.

I came up with some pretty good settings that amazed people (myself included) with what I could do to a loudspeaker and it not tear up.  Including taking a 300 watt 8" full range speaker-driven by a 4000 watt amp into full clip (ie the clip light never went off) with music-then add a 8KHz sine wave (to simulate feedback) that was a high enough level to drive the amp to full clip and then add a 15dB boost down at 40Hz to try to overexcursion it.

It could run like this for hours with no damage.  Now I did not say it sounded good-but rather that I could not find a way to tear it up.
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 10, 2014, 06:21:29 PM
If using 4 subs I would stack them up 2 over 2-laying with the large flat sides down.  So the whole block would be 90wide x45tall.

Yes I have spent a lot of time with the Dfend.

The first thing I do is to determine the real parameters of the speaker they are to be used with.

Things such as measuring distortion per freq (to determine the point of the excursion limiting), measuring the point of power compression and so forth.

Without having real data-I am hesitant to suggest something-because if something should "go wrong", then I could be blamed for "Well Ivan said to do this" type of thing.

To even determine the voltage based on rated power requires an actual impedance measurement (NOT DC resistance) to put into the calculation.

But my "gut feeling is that your voltage are to high-based on the "simple numbers" and not measurement.

The attach and release times on the all pass are to short.

When I was considering it, I spent a lot of time measuring the actual speaker under consideration.

I came up with some pretty good settings that amazed people (myself included) with what I could do to a loudspeaker and it not tear up.  Including taking a 300 watt 8" full range speaker-driven by a 4000 watt amp into full clip (ie the clip light never went off) with music-then add a 8KHz sine wave (to simulate feedback) that was a high enough level to drive the amp to full clip and then add a 15dB boost down at 40Hz to try to overexcursion it.

It could run like this for hours with no damage.  Now I did not say it sounded good-but rather that I could not find a way to tear it up.

Thanks for the continuing help. I'm gathering there is a need to find the real world edges to protect what I'm hearing or smelling haha ....and then making D-Fend (or limiter) settings based on measuring those edges ....

But to try know where to look for the edges, I've been running impedance sweeps on single boxes.  And then on 2, 3, and 4 boxes in series, to see how acoustic coupling effects their impedance.
Also ran it on 4 in series / parallel just to check vs readings vs 4 boxes in series, average per box
   
The lowest dip I could get on any one box was 2.6 ohms at 42hz, but my tester is 1/3 octave so it could sure be a little lower for a 42hz sine wave. 2 boxes gained .3 ohm and 4 boxes took it 3.1 ohms.  I was happy to see any rise.
I mean, I'm gonna get in thermal trouble where current is highest, right?

So shouldn't I set RMS limiting based on a 3 ohm load, and play with raising it till I measure compression or distortion  ....particularly in the low 40's hz?

And for 4 boxes, I'm willing to call them 5 ohm nominal....graph below....
I'm thinking of using the 5 ohms for initially choosing/calculating peak voltage settings? Not sure how to really tell when to limit peak till I tear something up....
Peak is about mechanical failure, right?

Is mechanical distortion more likely to be audible at a particular frequency based on impedance, (or other criteria)?

Art, thx for your reply in the subwoofer forum.  I'm trying to reconcile the number of people who have reported using bridged amps on single labs (when in a bank), with wattage typically in the 3000 @ 4 ohm category. 
Maybe they just never got hammered with low 40 hz music? ... assuming I'm thinking straight....
Title: Re: Sub Measurements
Post by: Art Welter on August 16, 2014, 06:36:49 PM
1)I mean, I'm gonna get in thermal trouble where current is highest, right?
2)So shouldn't I set RMS limiting based on a 3 ohm load, and play with raising it till I measure compression or distortion  ....particularly in the low 40's hz?
3)Peak is about mechanical failure, right?
4)Is mechanical distortion more likely to be audible at a particular frequency based on impedance, (or other criteria)?
5) I'm trying to reconcile the number of people who have reported using bridged amps on single labs (when in a bank), with wattage typically in the 3000 @ 4 ohm category. 
Maybe they just never got hammered with low 40 hz music?
1)The worst point for thermal is at Fc, where excursion and impedance are lowest.
2) The impedance drops below 3 ohms at Fc, closer to 2 ohms.
3) Or to limit distortion, hard to tear up a Lab 12.
4) If the horn is driven below Fc, distortion goes through the roof, exceeding 100% without much power at all.
5) 3000 watt peaks for a pair of drivers, no problem. Sustained 38 volt sine wave, and you can smell the adhesives cooking  within a few seconds.

Although this is about a tapped horn, rather than a FLH, there is some useful info about the Lab 12s in it:

http://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html

As far as the flanking cabinets, they could be pieces of plywood and have the same effect, the SPL  increase due to the boundary is what I was suggesting you measure.
Title: Re: Sub Measurements
Post by: Ivan Beaver on August 17, 2014, 10:02:07 AM

As far as the flanking cabinets, they could be pieces of plywood and have the same effect, the SPL  increase due to the boundary is what I was suggesting you measure.
Yet another "'ol timers thing" that works quite well.

We used to call them "barn doors".

Forward directivity is a GOOD thing.  It increases the level out front-reduces the level in the rear and is cheap. 

Acoustic issues are better addressed physically-rather than electrically. Yes today we can do all sorts of "steering" and such-but still the better SONIC result is done physically.  Every thing from less drivers with less interaction-to physical pattern control-to sub cabinets with directivity etc.

But I admit that is not always possible due to some restraints.
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 19, 2014, 11:14:51 AM
1)The worst point for thermal is at Fc, where excursion and impedance are lowest.
2) The impedance drops below 3 ohms at Fc, closer to 2 ohms.
3) Or to limit distortion, hard to tear up a Lab 12.
4) If the horn is driven below Fc, distortion goes through the roof, exceeding 100% without much power at all.
5) 3000 watt peaks for a pair of drivers, no problem. Sustained 38 volt sine wave, and you can smell the adhesives cooking  within a few seconds.

Although this is about a tapped horn, rather than a FLH, there is some useful info about the Lab 12s in it:

http://www.diyaudio.com/forums/subwoofers/185588-keystone-sub-using-18-15-12-inch-speakers.html

As far as the flanking cabinets, they could be pieces of plywood and have the same effect, the SPL  increase due to the boundary is what I was suggesting you measure.

Art, thanks for your answers .... and the keystone threads are very interesting.

My deck is only 10 ft wide where it is most reflection free. .....
So I've focused on understanding impedance and power handling for now, until I figure out an easy, relatively reflection-free way to try measure different arrangements and baffles.

I've checked impedance using a rackmount Audio Tool Box to generate constant level sine waves, and have the amps deliver 1.0v  to the speakers. And then measure actual current being drawn at each freq.
The lowest impedance i can measure is 2.71 ohms at 39 hz, with readings below 3 ohms from 37 -41 hz. This is measuring 1 box in a bank of 3, all three driven the same.
Is the 2.2 ohm minimum you use, from the keystone or labhorns?
Just trying to make sure my impedance measurement technique is valid...

And I plain don't get how impedance can fall below the voice coils resistance.... pls help !

But I get what happens below Fc....

It seems from digging in old posts, that you guys have found that heat dissipation, particularly when trying to bump up the labhorns response at 40hz, is the labhorn's achilles heel.
I've put some temperature probes on a driver and hope to play around a little with em today.

Based on 38 volts frying,  I think I'll try 30 volts at  39hz and watch the temp....I get that should put about 5.5 amps on the coil...
Another I don't get........ how coils take all the current with their thin wiring.....  I know it comes down to how long do they have to take it, but still.......

I've ended up running each driver off parallel amp channels, to keep loads above 4 ohms.   Seems to sound the same as running drivers in parallel and amps in bridge mode, at low volume levels. But when pushed, the channel per driver seems to stay cleaner longer.  Maybe I'm giving up a little power, but clean trumps IMO. (Using a plx 3402 or equiv per box.)

I like the idea of Wayne Parham's cooling plug http://www.audioroundtable.com/PiSpeakers/messages/17999.html 
But I don't see how much heat it would remove since labhorn cover plates always end up abutting each other unless you separate them...   
Hey can we put baffles between labhorns to any good acoustic effect, and give the plates space to dissipate heat?
Title: Re: Sub Measurements
Post by: Ivan Beaver on August 19, 2014, 12:52:55 PM
Art, thanks for your answers .... and the keystone threads are very interesting.

My deck is only 10 ft wide where it is most reflection free. .....
So I've focused on understanding impedance and power handling for now, until I figure out an easy, relatively reflection-free way to try measure different arrangements and baffles.

I've checked impedance using a rackmount Audio Tool Box to generate constant level sine waves, and have the amps deliver 1.0v  to the speakers. And then measure actual current being drawn at each freq.
The lowest impedance i can measure is 2.71 ohms at 39 hz, with readings below 3 ohms from 37 -41 hz. This is measuring 1 box in a bank of 3, all three driven the same.
Is the 2.2 ohm minimum you use, from the keystone or labhorns?
Just trying to make sure my impedance measurement technique is valid...

And I plain don't get how impedance can fall below the voice coils resistance.... pls help !

But I get what happens below Fc....

It seems from digging in old posts, that you guys have found that heat dissipation, particularly when trying to bump up the labhorns response at 40hz, is the labhorn's achilles heel.
I've put some temperature probes on a driver and hope to play around a little with em today.

Based on 38 volts frying,  I think I'll try 30 volts at  39hz and watch the temp....I get that should put about 5.5 amps on the coil...
Another I don't get........ how coils take all the current with their thin wiring.....  I know it comes down to how long do they have to take it, but still.......

I've ended up running each driver off parallel amp channels, to keep loads above 4 ohms.   Seems to sound the same as running drivers in parallel and amps in bridge mode, at low volume levels. But when pushed, the channel per driver seems to stay cleaner longer.  Maybe I'm giving up a little power, but clean trumps IMO. (Using a plx 3402 or equiv per box.)

I like the idea of Wayne Parham's cooling plug http://www.audioroundtable.com/PiSpeakers/messages/17999.html 
But I don't see how much heat it would remove since labhorn cover plates always end up abutting each other unless you separate them...   
Hey can we put baffles between labhorns to any good acoustic effect, and give the plates space to dissipate heat?

Since you have an audio toolbox-why not just use the impedance sweep to get the impedance.  That way it is faster-you get more steps etc

I have found it to be pretty accurate-at least accurate enough for most uses.

How are you putting the temp probes on?  Remember that the rear chamber has to remain SEALED or else the impedance/tuning etc will change.

Also remember that it takes time to heat up the magnet assembly and the voice coil could die long before the magnet gets hot.

Yes any boundary will help give directivity to low freq.
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 19, 2014, 03:33:39 PM
Since you have an audio toolbox-why not just use the impedance sweep to get the impedance.  That way it is faster-you get more steps etc

I have found it to be pretty accurate-at least accurate enough for most uses.

How are you putting the temp probes on?  Remember that the rear chamber has to remain SEALED or else the impedance/tuning etc will change.

Also remember that it takes time to heat up the magnet assembly and the voice coil could die long before the magnet gets hot.

Yes any boundary will help give directivity to low freq.

I ran individual sine waves because I wanted to get as accurate as possible, and compare manual measurements to the sweep function's 1/3 or 1/12 octave averaging.
Plus, making manual measurements has helped restore a bit of needed familiarity with ohms law and other basic audio math....which my rusty mellon sorely needs :)

I ran the temp probe leads through one of the cover plate bolt holes and sealed it up with silicone.

Yep, I've already seen that the magnets heat too slowly and that the coil will die long before I read much of a temp change. Gonna relocate a probe as deep in the vent hole as i can, but still think it will lag way to much for determining imminent danger.

This has me rethinking that what I really want to find is the onset of thermal compression. I mean, my really interest is how loud can i get and maintain linearity, not where they smoke...
I'm thinking to try incrementally higher voltages and watch for when amperage from the amp starts to drop from coil heating..... looking for a drop within 1 minute as a first stab.. ......??

Have you used the ATB's distortion meter?  Accurate enough for general purposes, like with the impedance sweep?

Thx,   Mark
Title: Re: Sub Measurements
Post by: Art Welter on August 19, 2014, 06:28:11 PM
Art, thanks for your answers .... and the keystone threads are very interesting.

1)Is the 2.2 ohm minimum you use, from the keystone or labhorns?
2)And I plain don't get how impedance can fall below the voice coils resistance.... pls help !
3)It seems from digging in old posts, that you guys have found that heat dissipation, particularly when trying to bump up the labhorns response at 40hz, is the labhorn's achilles heel.
4)Another I don't get........ how coils take all the current with their thin wiring.....  I know it comes down to how long do they have to take it, but still.......
5)But when pushed, the channel per driver seems to stay cleaner longer.  Maybe I'm giving up a little power, but clean trumps IMO. (Using a plx 3402 or equiv per box.)
6)Hey can we put baffles between labhorns to any good acoustic effect, and give the plates space to dissipate heat?
1)From all the sims and measurements I've seen, whether TH, FLH, or BR, the impedance minima is usually near DCR.
http://forums.prosoundweb.com/index.php/topic,134223.0.html
Silas Pradetto said he measured LabHorn dips at certain frequencies that are at about 2 ohms, actually they probably about half the Lab 12 DCR of 4.29 since two drivers are in parallel. 2.2 ohms is "close enough for rock and roll", depending on the current limiting scheme in the amp you use.
2) It does not.
3) The Lab 12 is definitely not good at getting rid of heat compared to many modern drivers, and when closed up in a tiny compression chamber, that heat is contained.
4) But still, with most music (that I like...) the average heat is 1/10th of the peak power or less, the thin wire can take it when it is moving and can wick to the magnet structure. Once the magnet structure and the box air heats up, the voice coil temp rises faster.
Even with the magnets exposed, with the Speakerpower SP4000 running pink noise (12 dB crest factor) the Lab 12s lost headroom in minutes.
5) Start using an amp that does not current limit like the PLX and you will hear the thermal compression faster :^).
6) You could, but the thermal dissipation capability still won't be what it would be with larger voice coils designed with better thermal dissipation capability. Wayne's thermal device is kind of like hot rodding a Model T engine, when there are 426 Hemis available.

As far as the Audio Toolbox distortion readings, I found them quite limited compared to the DIY approach outlined in the Keystone (and other) threads. That said, there are free programs now that do a good job of THD measurement without the bother, but they would require using a PC rather than Mac, which leaves me out.

Art
Title: Re: Sub Measurements
Post by: Ivan Beaver on August 19, 2014, 08:10:01 PM

This has me rethinking that what I really want to find is the onset of thermal compression. I mean, my really interest is how loud can i get and maintain linearity, not where they smoke...

Thermal compression and how loud can often be very different things.  It really depends on the dynamic range of the material-the duration etc.

I started doing a dual FFT measurement for power compression long before it got popular-back around 2000  (and is now part of an AES standard-but I didn't get an credit for it :(  ).

This allows you to find exactly the point of power compression at any  dB reduction you want.  3dB is "kinda standard".

Think of  heating of the voice coil like this-it is  like a candle flame.  You can hold your hand over it for quite awhile-if it is a long distance away and the closer you get it-the shorter that time becomes.

It is heat over time that kills most speakers.  So a lot for a little while or a little for a long while and everything inbetween.

There is NO easy or correct answer.

If you set your limits for the point of power compression- you are going to need a lot more rig to do the gig-because you will be missing the peaks.

As a "general rule" if you are doing bass intensive work (EDM-Dance-rap etc) then setting a slow attach (2 or 3 seconds) limiter at about 1/2 of the continuous rating of the speaker is a good starting point.  Sine waves can quickly kill a loudspeaker.

It is not a bad idea to have another limiter around the voltage of the continuous rating (with an attack time of maybe 20-30ms) and then a fast attack limiter at the peak rating (or 4 times the power or twice the voltage) of the continuous rating.

But you still have low freq excursion issues to deal with-so a freq selective limiter (as a side chain) is not a bad idea.

For example you can drive it really low if you don't drive it hard.  The harder you drive it, the less low freq you can get out of it.

An RTA (at least 1/6th octave) and a sine wave generator is a good setup to look at the distortion of the lower freq.  Put in a sine wave  (let's say 30Hz) and look at it on the RTA.  Look for the levels of the distortion components (60-90-120Hz) and see how quickly they rise as you increase the level of the fundamental tone.
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 20, 2014, 12:48:40 PM
1)From all the sims and measurements I've seen, whether TH, FLH, or BR, the impedance minima is usually near DCR.
http://forums.prosoundweb.com/index.php/topic,134223.0.html
Silas Pradetto said he measured LabHorn dips at certain frequencies that are at about 2 ohms, actually they probably about half the Lab 12 DCR of 4.29 since two drivers are in parallel. 2.2 ohms is "close enough for rock and roll", depending on the current limiting scheme in the amp you use.
2) It does not.
5) Start using an amp that does not current limit like the PLX and you will hear the thermal compression faster :^).
6) You could, but the thermal dissipation capability still won't be what it would be with larger voice coils designed with better thermal dissipation capability. Wayne's thermal device is kind of like hot rodding a Model T engine, when there are 426 Hemis available.

As far as the Audio Toolbox distortion readings, I found them quite limited compared to the DIY approach outlined in the Keystone (and other) threads. That said, there are free programs now that do a good job of THD measurement without the bother, but they would require using a PC rather than Mac, which leaves me out.

Art

1&2.  Sorry, I went brain dead in even wondering if it were possible for impedance to drop below dcr..

5. What are some amps that don't current limit so quick as plx's ?  I looked at the speakerpower stuff, but not available to non oems....
      (I have 2 plx 3402, a RMX4050HD, and a PL340...I've been thinking they are all about the same animal having very close sensitivity, and +32gain to +36.)

6 & toolbox comment.  Yea, the keystone thread is letting me see how much has happened since labs came out....
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 20, 2014, 12:56:58 PM
Thermal compression and how loud can often be very different things.  It really depends on the dynamic range of the material-the duration etc.

I started doing a dual FFT measurement for power compression long before it got popular-back around 2000  (and is now part of an AES standard-but I didn't get an credit for it :(  ).

This allows you to find exactly the point of power compression at any  dB reduction you want.  3dB is "kinda standard".

Think of  heating of the voice coil like this-it is  like a candle flame.  You can hold your hand over it for quite awhile-if it is a long distance away and the closer you get it-the shorter that time becomes.

It is heat over time that kills most speakers.  So a lot for a little while or a little for a long while and everything inbetween.

There is NO easy or correct answer.

If you set your limits for the point of power compression- you are going to need a lot more rig to do the gig-because you will be missing the peaks.

As a "general rule" if you are doing bass intensive work (EDM-Dance-rap etc) then setting a slow attach (2 or 3 seconds) limiter at about 1/2 of the continuous rating of the speaker is a good starting point.  Sine waves can quickly kill a loudspeaker.

It is not a bad idea to have another limiter around the voltage of the continuous rating (with an attack time of maybe 20-30ms) and then a fast attack limiter at the peak rating (or 4 times the power or twice the voltage) of the continuous rating.

But you still have low freq excursion issues to deal with-so a freq selective limiter (as a side chain) is not a bad idea.

For example you can drive it really low if you don't drive it hard.  The harder you drive it, the less low freq you can get out of it.

An RTA (at least 1/6th octave) and a sine wave generator is a good setup to look at the distortion of the lower freq.  Put in a sine wave  (let's say 30Hz) and look at it on the RTA.  Look for the levels of the distortion components (60-90-120Hz) and see how quickly they rise as you increase the level of the fundamental tone.

Thx Ivan, good clear useful info.   I'm gonna turn attention to measuring compression and distortion now.....
Title: Re: Sub Measurements
Post by: Art Welter on August 20, 2014, 08:59:39 PM
5. What are some amps that don't current limit so quick as plx's ?  I looked at the speakerpower stuff, but not available to non oems....
      (I have 2 plx 3402, a RMX4050HD, and a PL340...I've been thinking they are all about the same animal having very close sensitivity, and +32gain to +36.)
The Speakerpower SP4000 is great, and is available to individuals. It is only the Speakerpower DSP units that require a large purchase.

If you actually measure the musical SPL output of subs driven by the different amps you have, you will probably find they are different animals, even if their output ratings are the same.

http://www.diyaudio.com/forums/subwoofers/187472-speakerpower-torpedo-sp1-4000-plate-amp-review.html
Title: Re: Sub Measurements
Post by: Mark Wilkinson on August 21, 2014, 05:39:42 PM
The Speakerpower SP4000 is great, and is available to individuals. It is only the Speakerpower DSP units that require a large purchase.

If you actually measure the musical SPL output of subs driven by the different amps you have, you will probably find they are different animals, even if their output ratings are the same.

http://www.diyaudio.com/forums/subwoofers/187472-speakerpower-torpedo-sp1-4000-plate-amp-review.html

Ah, yes...didn't read the DSP qualification close enough....

My bet is the 4050 is the pick of the litter....