A Great Day With Lots of Data

[toddalin]

On Friday, 9/28, Grumpy (Dave) came by loaded with an arsenal of testing equipment to get to the bottom of the "hole" issue of the depressed midrange of the 2235 and more specifically, 2205J recently recharged and reconed as a 2235 by Orange County Speaker (OCS).

Sitting drinking my morning coffee, I looked out the windows at about 9:00 a.m. and Dave is walking up the walk. We had talked about the date and time, and not hearing anything (Dave was out of town), I wasn't sure this was going to happen. But Dave was right on time and it did.

First order of business was load software onto my laptop for the test. Dave brought the Parts Express Woofer Tester 2 along with his Mac laptop with the necessary software to determine the differences and possible reason that I was getting a "suck-out" in the 600-900 Hz range. I'm sure that Dave will chime in and tell us exactly what was done, but I know that I needed a bunch of nickels to perform some of the testing.

What we found that was OCS used a legitmate JBL 2235 cone and all parameters supported the JBL tag that was still on it. But the BL, reportedly a measure of the magnetic strength in the gap, was down around 17-18 whereas the 2235 specs call for 20. Dave brought two real 2235s along and the measured BLs were 22-24.

This difference (~15% off spec) could account for some roll off, perhaps, and anyone is welcome to chime in here for an educated opinion. Has anyone had a 2205 recharged and measured the BL and if so, what were your results?

While woofer testing was typically performed in Dave's calibrated lap, all in cabinet testing was done with an L200 cabinet. Most tests were performed with one port blocked. Dave's graphics clearly showed the benefits of blocking one port, although at those frequencies the result is less audible than visual in the plots.

Replacing the Alnico-framed 2205/2235 with a new 2235 in the L200 cabinet did alter the response somewhat, but after many measurements and mic placement changes, we decided to move the speakers relative to the walls. Dave feels that sidewall reflections appear to be the main suckout culprit in the 500-900Hz octave. The real 2235 did exhibit a response similar, though not identical to the 2205/2235 and in these cabinets, in this environment, and using these crossovers did have the dreaded dip in response (that most people don't seem want to acknowledge ).

Scooting the systems closer (inches) to the rear wall helped smooth the response a bit elsewhere.

The day quickly passed and we headed off to Ruby's for lunch. We got back to the house and continued the tests going through various combinations of crossover settings, and slight movements of the speaker and mic placement, and after reinstalling the 2205/2235, testing the right and left speaker for similarity.

BTW, Dave's tests did prove what I asserted all along that a 16 ohm resistor in series with the woofer did smooth out the troublesome 600-900 area to a large extent! (Actually we used a 20 ohm in this case.) I know that many here said that this is strickly taboo (putting a resistor in series with the woofer), but there it is! The really weird thing is, it hardly had any effect on the woofer's volume! Dave has the plots.

When I reconnected the speaker to the amp, because the speaker had now been moved back to the wall (was pulled out) I couldn't see the wires and inadvertantly put the + on the red and - on the black (wrong for my system). I fired up "You're So Far Away" (on Brothers in Arms) and Dave instantly said "something's wrong". He instantly knew the polarity was wrong and the Yamaha's self test agreed.

Later when testing the speakers for similarity, we found differences in the plots because the right tweeter was out of phase. I phased them using a sound level meter looking for the louder volume for a tone near the crossover point. But that portion of the spectrum is suseptible to combing, so that small differences in frequency have large differences in volume. Anyway, Dave's plots clearly showed the difference and both speakers track extremely well together now both in volume and frequency.

According to Dave, the speakers are +/- 3dB from ~40-14KHz (albeit 1/3 octave) and that's still nothing to sneeze at. Some by-ear tweaking of levels for the listening position made the system pretty smooth to listen to (the point, after all). L-R matching for frequency response tracking is within 1/2dB almost throughout the useful bandwidth, according to Dave, in no small part due to my carefully measured speaker placement and fairly symmetrical room.

I looked at the watch and it was now 4:00 p.m. Time for Dave to head back to the family. A lot of data was obtained and there may be some suggestions out of this to make the "keeper" crossovers work even better to fill the hole.

What a great day! Thanks for stopping by Dave!

[boputnam]

Interesing afternoon...

But, I'm confused:

...to determine the ... reason that I was getting a "suck-out" in the 600-900 Hz range.

and

...a 16 ohm resistor in series with the woofer did smooth out the troublesome 600-900 area to a large extent!

You had both a "suck-out" (I guess that means acoustic cancellation...?) and a "troublesome" character to the frequency response from 600-900Hz...? Maybe I'm lost - I don't understand the resistor remedy. Did it smooth the measurement or the sound or what?

wrt the latter, how did the "troublesome" character to the frequency response from 600-900Hz manifest before the remedy? Was it audible and/or merely in Dave's measurements?

Thanks.

[Steve Schell]

Hi Toddalin,

By putting the 20 ohm resistor in series with the woofer you have effectively lowered the amplifier damping. There will be an efficiency loss from the power dissipated in the resistance, but the lower bass will increase relative to the midband due to the loosening of the amp's grip on the woofer.

Since the advent of solid state amps we have been sold on the supposed virtues of high damping factors. I regard this as another case of "If you can't fix it, feature it." A high damping factor works okay with low efficiency floppy cone drivers, but can be detrimental with high efficiency speakers; the amp grips the speaker so tightly that the low end response is rolled off. We have all gotten used to that super tight, heavily damped sound, but there are other ways of looking at the amp/speaker relationship.

The best article I have seen on this subject was written in the mid 1950s by D.J. Tomcik, chief electronics engineer at Electo-Voice. Here is a link:

http://www.paulspeltz.com/tomcik/index.html

I have often used resistors in the speaker line to try to come closer to what Mr. Tomcik refers to as "critical damping." I also use fine gauge magnet wire for speaker cables, which helps in this regard. I have heard through a first hand account that Jim Lansing used to advocate placing resistors in the speaker line until the bass sounded best.

It does make sense that a driver with lower BL will be missing some of its top end. Lowering BL has the effect of moving the mass break point, above which the reponse rolls off at 6dB per octave, lower in frequency. Response below the break point is pretty much unaffected, or at least it appears so in simulations.

[toddalin]

Interesing afternoon...

But, I'm confused:



and



You had both a "suck-out" (I guess that means acoustic cancellation...?) and a "troublesome" character to the frequency response from 600-900Hz...? Maybe I'm lost - I don't understand the resistor remedy. Did it smooth the measurement or the sound or what?

wrt the latter, how did the "troublesome" character to the frequency response from 600-900Hz manifest before the remedy? Was it audible and/or merely in Dave's measurements?

Thanks.

A "suck-out" meaning a big, fairly broad dip in frequency response. "Troublesome" also referring to the dip area and its irregularities. Perhaps Dave will post some of the curves and you'll be able to see what I mean.

Yes it manifests itself audibly, to my ear as a muffling or reduction in intelligibility of the male voice. Putting the resistor inline brightens the voice up and increases intelligibility.

Steve, another possible effect of the resistor in series with the woofer is in raising the crossover frequency that is obviously dependant on the woofer impedience. This may be why these crossovers work so well with the 12 ohm load of the W##GTI series too.

[4313B]

The real 2235 did exhibit a response similar, though not identical to the 2205/2235 and in these cabinets, in this environment, and using these crossovers did have the dreaded dip in response (that most people don't seem want to acknowledge ).

The lack of acknowledgement is probably based on most people's experiences. Your experience might be unique. Some people have trouble getting 2235H's to do what they want them to do, most people do not.

BTW, Dave's tests did prove what I asserted all along that a 16 ohm resistor in series with the woofer did smooth out the troublesome 600-900 area to a large extent! (Actually we used a 20 ohm in this case.) I know that many here said that this is strickly taboo (putting a resistor in series with the woofer), but there it is! The really weird thing is, it hardly had any effect on the woofer's volume! Dave has the plots.

Once again, your experience sounds unique. Most people don't go around sticking 16 to 20 ohm resistors in series with their 2235H's. If that's what you have to do to get your stuff to work then who are we to argue. Do what you have to do.

This may be why these crossovers work so well with the 12 ohm load of the W##GTI series too.

It sounds to me like you need to dump the 2235H's and go with the W##GTI series. You need to run an impedance curve of the 2235 with that conjugate you are using and compare it to an impedance run of a W##GTI with that same conjugate. Looking back in other threads I think that conjugate is a 33 uF capacitor and 7 ohm resistor.

[boputnam]

...but the lower bass will increase relative to the midband due to the loosening of the amp's grip on the woofer.

This change should be readily measurable in Dave's work - i.e., pre and post.

The real 2235 did exhibit a response similar, though not identical to the 2205/2235 and in these cabinets, in this environment, and using these crossovers did have the dreaded dip in response (that most people don't seem want to acknowledge ).

What you are describing would seem to be EQ'able.

Two questions?

1. What EQ / room measurements had you done beforehand, to optimize/minimize the room's influence on the output? If none, then Dave's work would be truly a step forward.

2. What "necessary software" was Dave using other than Woofer Tester?

[toddalin]

This change should be readily measurable in Dave's work - i.e., pre and post.

What you are describing would seem to be EQ'able.

Two questions?

1. What EQ / room measurements had you done beforehand, to optimize/minimize the room's influence on the output? If none, then Dave's work would be truly a step forward.

2. What "necessary software" was Dave using other than Woofer Tester?

The Yamaha RX-Z9 ($4,500) has it's own self eq that is not user adjustable once set (though you have some control over what band range you consider most critical). You can defeat it and use the graphic eq, but not both. Even so, I still hear the dropout effect.

Dave will have to describe the software.

[boputnam]

The Yamaha RX-Z9 ($4,500) has it's own self eq that is not user adjustable once set (though you have some control over what band range you consider most critical). You can defeat it and use the graphic eq, but not both. Even so, I still hear the dropout effect.

Holy-moly, that is some pricy unit. Surprised I don't know it...

So, help me out - it does some sort of room response measurement and auto-EQ's to that reading? The "YPAO" (Yamaha Parametric Room Acoustic Optimizer)? How do it know?

The noise on the website sez the YPAO "..checks the speaker connections and phase of each speaker." But, you said one of your cabinets was still out of phase? So...?

And, then: "...it sends out tones which are captured by the microphone to analyze the room acoustics and sets a variety of parameters, such as the speaker size, the distance of the speakers and even the sound pressure level, etc. Until it achieves the best sound conditions for your room and you don't have to do anything!"

Just curious - where is this little mic? Imbedded in the unit, or movable into the listening area?

Yammie makes some powerful pro gear, for damned sure, but I am (personally) not a fan of their consumer stuff.

[speakerdave]

. . . . the depressed midrange of the 2235 and more specifically, 2205J recently recharged and reconed as a 2235 by Orange County Speaker . . . .

I'm confused by the terminology. The 2235H is a 2nd generation ferrite motor. A 2205J would also be a ferrite motor, so it would not need recharging. Do you really mean a 2205B which would be Alnico?

You may have a room problem with reflection, etc, causing a null in that frequency range, though I would think it would not be huge.

I do not believe the ferrite 2235H has a depressed midrange, although I have not listened to it extensively. I have had a remagged Alnico core (2135) reconed with the 2235 kit and do not believe it can be expected to perform exactly the same as the ferrite 2235, although I have not been able to measure either.

David

[toddalin]

Holy-moly, that is some pricy unit. Surprised I don't know it...

So, help me out - it does some sort of room response measurement and auto-EQ's to that reading? The "YPAO" (Yamaha Parametric Room Acoustic Optimizer)? How do it know?

The noise on the website sez the YPAO "..checks the speaker connections and phase of each speaker." But, you said one of your cabinets was still out of phase? So...?

And, then: "...it sends out tones which are captured by the microphone to analyze the room acoustics and sets a variety of parameters, such as the speaker size, the distance of the speakers and even the sound pressure level, etc. Until it achieves the best sound conditions for your room and you don't have to do anything!"

Just curious - where is this little mic? Imbedded in the unit, or movable into the listening area?

Yammie makes some powerful pro gear, for damned sure, but I am (personally) not a fan of their consumer stuff.

Yes, its the YPAO system and autoeqs the room based on pulses and tones.

After we replaced the woofer in the box, and I reconnected it to the stereo system, it was moved back to the wall so this was done largely by feel (50% chance). It was connected correctly previous to the tests.

The Yamaha wouldn't be expected to give an out of phase report for an out of phase tweeter so long and the woofer and mid were correct.

Mic is on a long cord and I put it at the center of the listening location (couch) on a tripod. (One leg extended over floor and two legs on the couch with mic over exact center of couch cushion.

But the tests performed by Dave were at ~1 and 2 meters at the tweeter level with no eq at all. The speaker was totally disconnected from the Yamaha and Dave brought over a dedicated JBL amp and interface for his Mac computer. That guy was prepared!

This is Yamaha's top home unit and carries a 5 year (rather than the usual 2-3 year) warrantee. It's been in for warrentee work a few times and I expect to send it in again before the warrantee expires next Feb for the rotary volume knob.

[toddalin]

I'm confused by the terminology. The 2235H is a 2nd generation ferrite motor. A 2205J would also be a ferrite motor, so it would not need recharging. Do you really mean a 2205B which would be Alnico?

You may have a room problem with reflection, etc, causing a null in that frequency range, though I would think it would not be huge.

I do not believe the ferrite 2235H has a depressed midrange, although I have not listened to it extensively. I have had a remagged Alnico core (2135) reconed with the 2235 kit and do not believe it can be expected to perform exactly the same as the ferrite 2235, although I have not been able to measure either.

David

Was the 16 ohm version of an Alnico 2205.

[4313B]

I took a little time to review other posts about your woes with these 2235H's and it seems this has been going on for quite awhile. You've posted your dissatisfaction with them several times. Rather than beat a dead horse you should probably just go with better stuff from the get-go and that means no 2370's or 2425's either. Perhaps some 800 Arrays or 1000 Arrays would balance with your $5,000 Yamaha. To be blunt, I think you are throwing good money after bad.

[boputnam]

The Yamaha wouldn't be expected to give an out of phase report for an out of phase tweeter so long and the woofer and mid were correct.

Yea, I wondered about that, too. I suppose it was intended for detecting basic cross-wiring to the cabinet.

Still interested in some before/after plots, if you've got 'em.

[toddalin]

Yea, I wondered about that, too. I suppose it was intended for detecting basic cross-wiring to the cabinet.

Still interested in some before/after plots, if you've got 'em.

There was a lot of data and Dave said it would take a few days to crunch the numbers.

[subwoof]

I was buying a LOT of JBL frames during the intial ferrite crossover and the first gen 2205"H" frames used a gray magnet that was bolted thru the frame to the magnet assembly's back plate and *that* one had a different design than the later black magnet 2225H ( which also had a longer voice coil ).

I wonder if the BI loss you had / have ( even with recharging ) is because they used the *current* ferrite recharge procedure rather than the old...?

There is a tech report on the ferrite mag that I read somewhere that is slightly different than the one posted in the "technical reference" forum. It might of been a "not for release" memo or something since at the time I had access to the reps entire JBL paperwork stash...closest thing to the internet was his floor / filing cabinet.

I have a fewf shifted / cracked 2225 (35 ) frames to look at but no longer have any gray magnets. I will look around and see if I can find one since I might acquire a pair of 2231H's in about a month and this issue might creep up here..

I agree with giskard - spend the money in a more modern direction if the '35 isn't doing it for you.

sub