WEak alnico drivers, symptoms?

[krzys]

Hello guys, I have read a lot of this and other forums and made some research but the question remains: what are the symptoms of a weak alnico driver in both woofers and HF drivers?
Till now I understand that the HF driver will lose some high frequency capacity. How much? I can measure but don't have a reliable reference of a good driver (806A/511 combo) and therefore can't be sure.
The recharge of the drivers costs a bit when shipping is involved.
The question is important to me and many others I'm sure.
Chris

[speakerdave]

GT has said that with the advent of large solid state amps JBL began to notice a loss of about 1 dB sensitivity in the woofers with 4" voice coils. Woofers with smaller voice coils were much more sensitive. I'm not aware of any authoritative comments about compression drivers, but any Alnico device whose coil has been blown could have received a voltage jolt that would cause some loss. When having them reconed or rediaphragmed it is more or less standard procedure to have them regaussed.

On the other hand, one of our most prolific posters (and buyers of used drivers) has a magnetic field tester and has said he's never run across a driver that needed recharging.

So if you are using a system that sounds ok, I would suggest you stop worrying about it. If you are building a new system to an exacting standard, especially if it is for someone else, you want Alnico drivers that have been both reconed and regaussed. In the case of drivers whose original software (cone, etc) is no longer available, their overall condition is probably a reliable indicator. Woofers can be regaussed with the cone in place.

David

[tom1356]

.... Woofers can be regaussed with the cone in place.

David
Can coaxial drivers like the 604 be regaussed with the woofer cone and tweeter diaphragm in place?

[speakerdave]

I would think so, but ask Great Plains Audio, to be sure. They would be the ones I would have work on a 604. Speaker frame/motor assemblies are made before the magnets are charged.

David

[Robh3606]

Here read this

http://audioheritage.org/vbulletin/showthread.php?p=110522#post110522


Rob:)

[krzys]

Thanks everybody for the answers. From the last answer I conclude that there will eventually be a loss in efficiency. Makes sense.
What about the measurment of one of my 806 on a 511 horn. Is that the expected FR ? It drops quite fast in the highs arround - 10dB at 9 kHz.
Chris

[grumpy]

... on 811b. measured at horn face between vanes, & then backing off
to a similar distance (~.5m) ... uniform drop in amplitude (so I show
only one plot). 1KHz+ as I had an active crossover in place. -grumpy

[grumpy]

FWIW,
I'd be happy to run other plots, I have 511b's, but no other Altec drivers.
The 807's came free with the horns :). -grumpy

or K77's in K-horns, if that will float anyone's boat...

[krzys]

Thanks grumpy, that's exactly what I was looking for. Your result is very similar to mine: a 10 dB drop from 1 to 9-9.5 kHz.
If somebody else doesn't show other result I must conclude that it is the nature of the beast. Is that what can be called the vintage sound ?
Chris

[Zilch]

Without compensation, that looks like "Theater" sound to me, the "X" curve.

http://www.jblpro.com/pub/cinema/cinedsgn.pdf

See also Fig. 5 here:

http://www.jblpro.com/pub/technote/tn_v3n03.pdf

[grumpy]

Plot was indeed with no compensation, and should have been well within the
"beam" ... direct vert center, and either side of the center vane (both sides measured
identically, as one would expect). I can check out another 807-z and look at
a more extended response (lower and w/511) later. -grumpy

[krzys]

Thanks Zilch for your valuable post. The Altec drivers were created for theatres and therefore aimed at the voice reproduction.
My measured driver approaches the X cinema curve. I must then conclude that we are very far from the modern drivers HF extension and that for HI-Fi musical use the HF shall be or boosted and/or completed with a tweeter crossed at 3-4 kHz.
This seems strange to me since many members report a good sound from two way Altec systems!?
Some others FR measurements available from other members?
Chris

[Zilch]

Thanks Zilch for your valuable post. The Altec drivers were created for theatres and therefore aimed at the voice reproduction.
My measured driver approaches the X cinema curve. I must then conclude that we are very far from the modern drivers HF extension and that for HI-Fi musical use the HF shall be or boosted and/or completed with a tweeter crossed at 3-4 kHz.
This seems strange to me since many members report a good sound from two way Altec systems!?
Some others FR measurements available from other members?
ChrisWe are working on this in another thread, actually, and that's why I jumped in here. Read on through the end from here:

http://audioheritage.org/vbulletin/showthread.php?t=14690&page=6

There does not seem to be a lot of quantitative information on Altec performance available, surprisingly, but more is forthcoming. I recall one member asserting that VOTT did not translate well for home listing for the opposite reason, namely, that they were overly bright, intended to be used behind the screen, and EQ'd by it as shown in the second link I provided.

That doesn't appear to be the case, however. Model 19 provided the compensation you suggest is necessary, but even there, it seems insufficient; the requisite sensitivity differential between woofer and mid/high compression driver not being available to accomplish the task with those components.

Another major element in this is the nature of the horns used. All compression drivers require compensation above mass breakpoint. JBL exponential horns do it "automatically" by narrowing the beamwidth with increasing frequency. Altec 511 and 811 are apparently radial (rotated exponential profile) horns requiring some compensation. Constant directivity horns, which includes MantaRay (presumably; I've never worked with one,) require full compensation for the compression driver rolloff to achieve flat frequency response.

[Tom Brennan]

This seems strange to me since many members report a good sound from two way Altec systems!

Well I think it's fair to say that some of us like many Altecs despite the high frequency response not because of it. The Nineteens are much better though and I would guess that the other "Teens" are also.

Makes me think about building Jeff Markwart's compensated crossovers for my 605As which look like they'll be sticking around. Right now I'm simply using them with the treble knobs on the old PAS-3 turned up. :)

[Mr. Widget]

Altec 511 and 811 are apparently radial (rotated exponential profile) horns requiring some compensation....or the correct driver. Take a look at this curve of the 511 horn with a TAD 2001 driver on it. This is a curve taken of cyclotronguy's system that is pictured in the EV Tweeter thread. The time windowing or sampling frequency reducing the usability of this plot on the lower mids on down, but as you can see, that 1" Be diaphragm does make it all the way out to 19KHz with no EQ or compensation and is still quite usable to 23KHz.


Well I think it's fair to say that some of us like many Altecs despite the high frequency response not because of it.That is an interesting observation, you might give the little TADs a go and see if they improve your experience.


Widget

[scott fitlin]

Well I think it's fair to say that some of us like many Altecs despite the high frequency response not because of it. :)I dont know.

I have Altec 288,s JBL 2441,s and TAD 4002,s.

Now, I happen to like the 2441,s on my lenses, and I like the 288-16G,s on an appropriate horn, alot.

I put the TAD 4002,s on my lens horns, and there was a very noticeable increase in higher frequency energy, its definitely audible. After a while, it irritated the heck out of me. Ill give TAD their due, their drivers resolve the most microscopic details in recordings I have ever heard out of any compression driver that I have heard or used, but, for whatever reason, I find they arent sweet sounding.

But, I can say for sure, one of the things that really bothered me WAS the increased HF energy.

[Mr. Widget]

But, I can say for sure, one of the things that really bothered me WAS the increased HF energy.Two points here...

A). You are running these in a PA application, not a studio monitor or home situation.

B). You are also running these with tweeters up top, so you aren't really talking about the driver's UHF extension per se.


Widget

[scott fitlin]

Two points here...

A). You are running these in a PA application, not a studio monitor or home situation.

B). You are also running these with tweeters up top, so you aren't really talking about the driver's UHF extension per se.


WidgetYes, I know, but, even with the 4002 rolling off at 7k, 18db, where the tweeter cuts in there was audibly more sound in the high frequencies, not VHF. Even the RTA showed increased response around xover region, up to 9.5k.

When I put the 2441,s back on, everything I wasnt liking went away.

At the time I put the 4002,s on, I was closed, took time to adjust system, used an RTA to show me what is going on, and listened to real music at moderate levels, as well as dance music PUMPING! When I first heard the 4002,s at the AES show, the speakers they demoed were of the commercial SR kind, NOT home hI fi, or studio monitors. And they had studio monitors, TAD 1601A and 4001 loaded with the TAD TH-4001 horn, and I didnt like these as much as the SR speakers. So, I dont really think that was the problem. Besides, the TAD-4002 IS marketed as a proffesional compression driver for both studio monitor applications and proffesional SR and any other type of sound requiring high quality. So, it is not a driver intended for `just` monitoring or home use.

I`ve tried them several times more, using a variety of different amps and xovers, got them to be more towards what I like, but, I still dont like them as much as some other drivers. But, I will concede, that of all the drivers i`ve used and heard, they resolved the most intricate and minute details in recordings. Vocals seem to have an almost holographic quality to them, but, brass sounds crisper and sweeter through the JBL 2441,s, to me. The 2441 has a more liquid sound.

Another freind of mine has TAD 4001,s, and I went to his house to listen to his system, the 4001 I like better than the 4002, but, again, I found the TAD drivers just have a higher pitched sound, gives the music a different timbre and pitch register, some love this, I didnt. And, this guys system doesnt have tweeters, the horn goes all the way up, Ill tell you this, I like tweeters. I dont care for using a 2in all the way up. I LIKE TWEETERS.

Apples or oranges, which do you prefer?

[Mr. Widget]

I found the TAD drivers just have a higher pitched sound, gives the music a different timbre and pitch register, some love this, I didnt.I actually have never heard the 4002s... they are the lower priced TADs that were designed especially for PA/SR work... maybe they do tilt up to cut through the noise that is frequently present at live shows, I have no idea. My point was that your application is quite different from the one we were discussing. That's all. ...and as we have all said, many, many times... if you are happy, then it is the right choice for you.

I brought up the TAD 2001s because one of our fellow forum members uses them on 511 horns and quite likes them.


Widget

[scott fitlin]

...and as we have all said, many, many times... if you are happy, then it is the right choice for you.

I brought up the TAD 2001s because one of our fellow forum members uses them on 511 horns and quite likes them.


WidgetI understand, just let me say, dont take me the wrong way. I am in no way inferring what anyone should or should not like, or whats right or wrong.

I always say that " If YOU like something, then its RIGHT for you ".

The original point of what I was talking about was in response to Tom Brennans statement that some like Altec comp drivers despite their lack of response in the upper frequncies, not because of it.

I found I DO like Altec and older JBL comp drivers BECAUSE of their deficiencies up higher. Or, are they really deficiencies? Or were they deliberately made that way?

:)

[Mr. Widget]

Another freind of mine has TAD 4001,s, and I went to his house to listen to his system, the 4001 I like better than the 4002, but, again, I found the TAD drivers just have a higher pitched sound, gives the music a different timbre and pitch register...Not to belabor this, but yes, it would seem that you prefer a relaxed sound in the treble range.

Here is a plot made by JBL comparing the 2440, the 2441 and the TAD 4001. All three drivers were mounted on the same JBL 2350 horn. In this comparison, it is easy to see the 2440 has a rising up upper register, the 2441 while extended is a bit down in the treble range, and the TAD is quite flat. It also shows how the 2440 and the TAD have a nasty resonance which the 2441 has dampened with JBL's diamond surround technology. This resonance would be quite audible in the 4350 as the driver is allowed to play out with no low pass filter. The TAD's resonance was audible to me even though it was at a frequency that is beyond my ability to hear sine waves. However if you use a crossover and a tweeter this problem is solved.

Anyway, the long and the short of it is that as individuals we do have different flavors of preference and fortunately for us, there are many flavors available. Some like the very forward sound of some of these speakers, it would appear you prefer a slight dip in the upper treble, and I like the flatter more detailed sound the TAD 4003s offer. (The TAD 4003s are even flatter in response than the 4001 shown here.)


Widget

[Steve Schell]

To get back to krzys's original question, the loss of h.f. response is the main symptom (and result) of reduced flux density in the gap. The extent of the loss is dependent on the reduction of gap flux, or loss of motor strength.

A driver/horn combination will generally have a region or "plateau" of relatively flat response. On the low end it will generally roll off due to unloading of the horn below cutoff. On the high end there will be a "mass break point" above which the moving mass begins being a burden to the motor, and the power response falls at roughly 6dB/octave above that point. A loss of gap flux will move the mass break point downward, and all frequencies above this point will show a similar loss compared to a driver with a stronger magnet.

Measuring the frequency response of a driver may provide some indication, but the only reliable indicator of magnet charge is to measure the flux density in the voice coil gap with a gaussmeter. Fully equipped repair facilities such as Great Plains Audio can do this and place the driver in a magnet charger and bring the driver up to spec if necessary.

[krzys]

Thanks a lot, this is a clear and well written wrap-up. This was my conclusion from this and many others threads. I concluded that if in a doubt (not original diaphragms) recharge for your own peace of mind, in other circumstances just sit down and listen to the music.

Steve, one more question. What about symptoms for a woofer ?

Chris

[Steve Schell]

Hi Chris,

Basically the same thing happens with a woofer, loss of response on the top end as the motor becomes weaker. You can hear this when varying the voltage fed to the field coil of an electrodynamic woofer. As the voltage falls the high end dies away, the overall sound gets a little sloppier, then eventually the overall level falls off. In some cases the weaker motor may sound better, if the cone was breaking up and "crying" in the midrange. Usually though, and always with the horn loaded systems I play with, the stronger motor sounds mo' better.