[mor2bz]

I recently received a form letter sent to those on his mailing list describing the
situation.  Unfortunately many people made commercial designs without cutting
Martin in for the pittance he asked.  And very few DIY types were buying his
program.  Those who had bought in remain allowed, but no new subscribers
will be able to buy.

I now join the ranks of those who enjoyed the benefit of his programs and posts
in this forum, and even built one of the projects he gave for anyone to build
(the eminence alpha15/fostex 103 openbaffle), but never became a paid subscriber
for his work.  Although he never tested this
design, it worked very well!   I do very much regret not ponying up his fee
and helping him to keep going. 

I thank Martin for this very large and accurate modeling work of loudspeakers.
He saved people many hours, trees,  and dollars.  I believe that the use of his
programs would get people very close to what was needed for a final design,
with a minimum of tweaking.

I call on this community to chime in and give thanks.   

[ejfud]

1

[ejfud]

2

[ejfud]

A real shame. He's  guy more than willing to help all. His work sheets are a thing of beauty and tons of work on his part I'm dure. A real shame it is.

[panomaniac]

I have enjoyed Martin's work, his contributions to the art and his worksheets.  I guess that I was in the small majority that paid for his work.

I can say, however, that the time limited licence did NOT make me happy.  The datasheets were far too slow to get much use from, so I felt that my money was a bit wasted.  When I buy software, I expect it to use it for as long as I like - not just one year.  But those were Martin's terms, so I stuck to them.

Photoshop is a much, much more expensive (and bigger) program. But if I use it to make an image, I do not expect to pay Adobe for the rights to sell that image. And they do not ask me to.  Ditto MS Word and others.  Nothing against Martin, just his software licencing policy.  My 2 cents.

[tubesguy2]

Well, I'd just say that it's too bad that Martin didn't give some advance warning of his plan to limit access.  I'd held off because Mathcad and the worksheets were a little intimidating, but I'd likely have ponied up the money to buy if there was an upcoming deadline, with a plan to learn what I needed to learn in the future.

On the other hand, if the problem was with folks benefiting without compensation to Martin, I suppose he handled it correctly - boom, you and others of your ilk are cut off at the knees.

[Badwater]

I plan to build two systems and would appreciate any comments.  I have all the drivers in hand.

System 1

Alpha 15A in H frame powered using a Parts Express plate amp
Electrovoice SP12B running full range.  Should I add a low pass filter?
Electrovoice T35 tweeter with 1st order high pass using a 2uf cap.

System 2 - passive solution

Alpha 15A in H frame with 125 hz low pass filter as suggested by MJK
Fostex FE166ES-R with 200 HZ high pass filter and 6 olms of series resistance to address the mismatch in driver efficiency. I also plan to add an L-pad to allow it to be fine tuned.

Using a plate amp for Fostex system didn't seem to make sense since the Fostex would not go low enough on the baffle to mate with the Alpha 15A when using the available low pass filter on the amp.

The H frame would be interchangeable. The top baffle would sit on top of the H frame.

I am a noob so please keep it simple. 

Thanks for the help.

Bill

[tubamark]

I plan to build two systems and would appreciate any comments.  I have all the drivers in hand.

System 1

Alpha 15A in H frame powered using a Parts Express plate amp
Electrovoice SP12B running full range.  Should I add a low pass filter?
Electrovoice T35 tweeter with 1st order high pass using a 2uf cap.

System 2 - passive solution

Alpha 15A in H frame with 125 hz low pass filter as suggested by MJK
Fostex FE166ES-R with 200 HZ high pass filter and 6 olms of series resistance to address the mismatch in driver efficiency. I also plan to add an L-pad to allow it to be fine tuned.

Using a plate amp for Fostex system didn't seem to make sense since the Fostex would not go low enough on the baffle to mate with the Alpha 15A when using the available low pass filter on the amp.

The H frame would be interchangeable. The top baffle would sit on top of the H frame.

I am a noob so please keep it simple. 

Thanks for the help.

Bill

Bill:

What is the attenuation slope on the PE plate amps?  The reason I ask, is that MJK's designs derive their success in part due to 12db slope on the bass units to perfectly counter driver response rise AND dipole roll-off at the same time, with the result being moderate effective roll-off in the 200-400 range.  This isn't possible with the higher-order XO of most plate amps.

I also have gone with the plate-amp approach, BUT by using a pair MCM electronics (very affordable) plate amps, which have a "mere" 2nd order rolloff, plus constant variable phase adjustment. http://www.mcmelectronics.com/product/50-6272   or   http://www.mcmelectronics.com/product/50-6262.  The 100 watt version is plenty adequate.  My pair have been great.  THey go on sale now and then, got mine for only $59 each!  Serious value for decent quality

This enables the ease of driver integration of Martin's passive (and more recently active) 2-way designs, without the hassles of either driver level matching (passive case) or hi-tech signal processing units (the Goldwood active case).   High pass can still be done passive (try line-level passive XO) . . .

My guess is that Martin might have gone the plate amp route, but had the hi-tech processor and extra amplification already on-hand.
These plate amps give perhaps the most cost-effective path to bi-amping that still enable you you to stick with Martin's design approach.

--TubaMark

[panomaniac]

Using a plate amp for Fostex system didn't seem to make sense since the Fostex would not go low enough on the baffle to mate with the Alpha 15A when using the available low pass filter on the amp

You might be surprised.  Depending on your baffle and driver, the rising response may be tamed just right with the low pass of the plate amp - even if it's set "too low."  The Alpha is a bit different, with its high Qts, but I've heard other OB rigs with plate amps crossed as low as 60~40Hz that mated well with the mid that falls off under 200Hz. Sometimes an inductor is also called for after the plate amp to make a 3rd order LP.

Why?  Because that low frequency LP filter actually flattens out the rising response of the woofer on open baffle.  It took me a looooong time to understand this, even when it was told to me over and over.  Of course you have to boost the gain on the plate amp to make up, but that's what the volume knob is there for, right?

Edit: Mark, we were posting at he same time.  The forum software warned me, but I posted anyway. =)
AFAIK, the PE amps are 2nd order LP.

[Badwater]

Thanks for the info it is much appreciated. 

Parts Express has a couple options available:


1)  70  watt 4 ohm with a variable low pass 2nd order from 60-200 hz for $53 plus free shipping.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-784

2) 100 watt 4 ohm with a variable 4th order low pass from 60-180 hz for $109 plus free shipping

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-802

3) 240 watt 4 ohm with a variable 4th order low pass form 60-180 hz for the same price as the 100 watt unit

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-804

The MCM amp has a 2nd order low pass from 50 -120 hz for $80 plus shipping.

Another much more expensive option is the MnK 250 subwoofer amp offered by Apex Jr. This amp has 2nd order 40-180 hz crossover. I can't tell from the literature what the slope of the crossover is for the 150 watt MnK amps.

http://www.apexjr.com/MnKAmp.htm

From the above it looks like that either the 70 watt PE amp or the MCM amp would be the ticket. Based upon the modeling work I did using MJK's worksheets the Alpha doesn't need all that much power to produce reasonable sound levels.  Using 15 watts the model indicates 95 db sound levels, which is more than enough for what I want. The PE amp would appear to be a good inexpensive choice or should I consider one of the more expensive options?

Again thanks for the help.

Bill

[panomaniac]

I've used 2 (stereo) of the small PE plate amps and had no trouble on OB - 8ohms

[Telstar]

I wonder why I cant find a MONO plate amp

[panomaniac]

Hmmmm???? 

[Telstar]

Hmmmm???? 

one plate amp for each speaker, w/o waste of connections and power.

[panomaniac]

Sorry, I still don't follow....

All the plate amps I've seen are mono.  They do have 2 connections, tho - to mix left & right.  Is that what you mean?
You just use one for mono - works fine.  I've run one for each speaker before, no problems.

[tubamark]

Hmmmm???? 

one plate amp for each speaker, w/o waste of connections and power.

You can run dual basses in mono . . . But when running >100 Hz with gentler effective slopes, you'll sacrifice stereo seperation to some extent - in the MJK alignements, there is significant driver overlap and the basses are not limited-range "subwoofers".
I would only consider it a "waste of power" if the plate amps (or whatever amp) are larger than needed.  That's why I advocated the use of 2 inexpensive plate amps (those PE 70 watt-ers would be fine) that total in cost to less than a typical boom-maker plate amp.  Cost of extra connections is negligible, unless one chooses esoteric line-level connectors.  Any connector that lets the electrons do their thing is sufficient for this case.

--Tubamark

[Telstar]

Sorry, I still don't follow....

All the plate amps I've seen are mono.  They do have 2 connections, tho - to mix left & right.  Is that what you mean?
You just use one for mono - works fine.  I've run one for each speaker before, no problems.

Yep, it was that

[Telstar]

I would only consider it a "waste of power" if the plate amps (or whatever amp) are larger than needed.  That's why I advocated the use of 2 inexpensive plate amps (those PE 70 watt-ers would be fine) that total in cost to less than a typical boom-maker plate amp.  Cost of extra connections is negligible, unless one chooses esoteric line-level connectors.  Any connector that lets the electrons do their thing is sufficient for this case.

--Tubamark

This is what I plan to do. Not sure about wattage. Anyway, I'm in europe and i'll shop there.
I'll have a 15" Hawthorne Augie to drive with each plate amp. I wont use esoteric cables for <100hz, altough I'll go with affordable diy silver litz that I found preferable to copper for low frequencies.

[panomaniac]

Cool -  I think that some of the Augie users are running their plate amps pretty low, like 40~50Hz.  Then boost it a lot.  You might try that.  Worked well for me with my Selenium 15s on OB.

[Telstar]

Cool -  I think that some of the Augie users are running their plate amps pretty low, like 40~50Hz.  Then boost it a lot.  You might try that.  Worked well for me with my Selenium 15s on OB.

Hmmm... I cannot boost much: I have room resonances at weird points from 40 to 110hz. No boost for me.
One of the reasons I'm going dipole for bass is the reduced creation of resonances from open baffles.