How To Test Drivers On The Bench

[jviss]

I wonder how folks test drivers on the bench, tweeters, woofers, etc., safely and surely?

I'd like to test my tweeters when I open the cabs.  I don't want to blow them!  I have a signal generator, etc.  Wondering if anyone here has knowledge and experience in this area.

Thanks,

jv

 

[RoyC]

The easiest way to test them is to simply play some music at low level through each driver with the level controls/crossover disconnected. The woofers will be fine, but be cautious with the tweeters. Be especially careful if using signal generator.

[DavidR]

I use my stereo receiver and put a 4uF capacitor on the plus side wire that would go to the appropriate driver terminal. It should filter out any low frequencies.

[RoyC]

4 hours ago, DavidR said:

I use my stereo receiver and put a 4uF (or even a 3uF) capacitor on the plus side wire that would go to the appropriate driver terminal. It should filter out any low frequencies.

The use of a cap is very prudent advice. Assuming jviss is referring to his 4x project discussed in his other threads, a 20uf cap could even safely be used. The crossover cap for the 4x tweeter is 20uf.

Disconnecting the tweeters from those nasty old pots to test their functionality should be one of the first things on the agenda.

[genek]

Signal generator apps are readily availalble for both iphone and android. The advantage over music is that you are sending the actual tone you want to know whether the driver is outputting without the distraction of every other tone in a bit of music. Especially important once you get into the range above 10kHz.

[RoyC]

On 12/22/2023 at 4:12 PM, genek said:

Signal generator apps are readily availalble for both iphone and android. The advantage over music is that you are sending the actual tone you want to know whether the driver is outputting without the distraction of every other tone in a bit of music. Especially important once you get into the range above 10kHz.

Agreed...and certainly extremely helpful when identifying possible response issues.

Imo, however, determining whether or not the drivers are even functional separate from the typically compromised level controls is the first item to check with the old beasts. We conducted some measurements of AR high frequency drivers some years ago and found them to vary despite not exhibiting obvious subjective anomalies. To complicate matters, it is not easy to find perfect used original tweeters. And in the case of 4x tweeters it is very hard to find any functional used originals at all.

[jviss]

On 12/22/2023 at 4:39 PM, RoyC said:

And in the case of 4x tweeters it is very hard to find any functional used originals at all.

Oh, wow, is that so?  You mean, used originals that have been pulled form cabinets?  I have at least two functional ones, maybe four, depending on whether the tweeters or crossovers are at fault in two cabs.  

 

[RoyC]

5 hours ago, jviss said:

Oh, wow, is that so?  You mean, used originals that have been pulled form cabinets?  I have at least two functional ones, maybe four, depending on whether the tweeters or crossovers are at fault in two cabs.  

 

Yes, and yes. You most likely have 4 functional tweeters. The pots/level controls are the usual culprits.

[jviss]

17 hours ago, RoyC said:

Yes, and yes. You most likely have 4 functional tweeters. The pots/level controls are the usual culprits.

Thank you!  And Merry Christmas to you and to all the forum members.

I'm listening now, two pair of AR 4x speakers going at once, driven by my recently resurrected Pioneer SX-424 receiver.  I think that long neglected speakers "loosen up" with exercise. 

 

[ReliaBill Engineer]

I usually remove the drivers from the circuit, then test the drivers using a DMM set to 200 ohms. This tells me if the VC has continuity and at what DC resistance. The DC resistance tells me what impedence range the driver is in, 2/4/6/8 ohms nominal. All necessary to repair or replace the driver. 

[RoyC]

16 hours ago, ReliaBill Engineer said:

I usually remove the drivers from the circuit, then test the drivers using a DMM set to 200 ohms. This tells me if the VC has continuity and at what DC resistance. The DC resistance tells me what impedence range the driver is in, 2/4/6/8 ohms nominal. All necessary to repair or replace the driver. 

It is not unusual for the DC resistance of AR drivers to measure appropriately, yet subjectively exhibit distortion due to mechanical degradation.

[jviss]

43 minutes ago, RoyC said:

It is not unusual for the DC resistance of AR drivers to measure appropriately, yet subjectively exhibit distortion due to mechanical degradation.

That makes sense.  

Has anyone ever done a mechanical restoration of an AR driver?  

[RoyC]

5 hours ago, jviss said:

That makes sense.  

Has anyone ever done a mechanical restoration of an AR driver?  

At least a few of us are rebuilding various tweeters, mids, and woofers.

Roy

[jviss]

11 hours ago, RoyC said:

At least a few of us are rebuilding various tweeters, mids, and woofers.

Roy

Cool.  I'm curious as to the defects you find and how you address them.  

[RoyC]

6 hours ago, jviss said:

Cool.  I'm curious as to the defects you find and how you address them.  

Some tweeters and mids have degraded suspension and under-dome damping material due to issues with the old foam, and some require voice coil replacement (and associated suspension foam). A number of woofer parts can be replaced as well. Much of my work along these lines is done for "Vintage_AR" and forum members.

4x tweeters are not being rebuilt.

[ReliaBill Engineer]

On 12/27/2023 at 2:22 PM, RoyC said:

It is not unusual for the DC resistance of AR drivers to measure appropriately, yet subjectively exhibit distortion due to mechanical degradation.

True. But it’s difficult to address distortion from mechanical degradation issues when the VC windings are bad, reading discontinuity from being fried or severed. Mechanical degradation becomes secondary to a bad voice coil.

This mid driver read “open circuit”:

 

 

 

[RoyC]

8 hours ago, ReliaBill Engineer said:

True. But it’s difficult to address distortion from mechanical degradation issues when the VC windings are bad, reading discontinuity from being fried or severed. Mechanical degradation becomes secondary to a bad voice coil.

This mid driver read “open circuit”:

Obviously....but many posters and readers of this forum do not have meters (of any type). Simply testing for functionality is the first step.

Roy

[twinsig]

Ok. I often wondered if bench testing would reveal anomalies, and given the semi-fuzzy sounds i get from my 2ax mids I'll give that a try.

Lag-27 for source & drive with a sx 636. Yes?

 

[twinsig]

I tested both 2ax's after replacing the mids-pots w/ new Jkent units and concluded ONE of the mids is Buzzy. 

I have never disassembled one of these but i want to look for any type of cone separation? 

Or has this old thing just had enough?

 

[RoyC]

Remove the metal screen and try it again, as a loose screen can sometimes cause this issue. Of course, also inspect the cone for any obvious problems.