Blown speaker?

[Guiria]

I built the following center channel a few months ago:

http://www.eldamar.net/audio/RS150MTM/

Recently I've noticed one of the speakers is fuzzy at a certain frequency range of upper male speech. Fuzzy as in it sounds blown fuzzy but below that frequency range the speaker clears up again and sounds just fine.

The problem has me baffled. Do I replace the speaker? Is a crossover component bad? Is something else going on?

How would you troubleshoot the problem?

 

[highfigh]

I built the following center channel a few months ago:

http://www.eldamar.net/audio/RS150MTM/

Recently I've noticed one of the speakers is fuzzy at a certain frequency range of upper male speech. Fuzzy as in it sounds blown fuzzy but below that frequency range the speaker clears up again and sounds just fine.

The problem has me baffled. Do I replace the speaker? Is a crossover component bad? Is something else going on?

How would you troubleshoot the problem?

Press on the frame of the speakers, individually. Run your finger around the edge and make sure the flange isn't vibrating. Could be a deformed voice coil, could be a loose screw, a bad glue joint, etc. what's the volume control setting when it makes this noise, and are you using any equalization or tone control?

Isolate the driver that's making the noise and remove it from the cabinet. Does it still make this noise? If it's a woofer, don't crank it too loud- it needs the cabinet to dampen the cone's excursion.

 

[Guiria]

I pulled the driver out of the cabinet and left it connected to the crossover and played some content and it does still have the fuzzy sound. I disconnected the driver and pushed on the cone and the excursion is smooth but with a slight notch of resistance in the movement. After a few more pushes the notch is gone and it moves back and forth smoothly and pretty quiet although I can hear a faint scratching noise if you will uniformly throughout the motion.

Should the movement be totally quiet? If so then I think the voice coil is rubbing on something and is most likely toast.

 

[highfigh]

I pulled the driver out of the cabinet and left it connected to the crossover and played some content and it does still have the fuzzy sound. I disconnected the driver and pushed on the cone and the excursion is smooth but with a slight notch of resistance in the movement. After a few more pushes the notch is gone and it moves back and forth smoothly and pretty quiet although I can hear a faint scratching noise if you will uniformly throughout the motion.

Should the movement be totally quiet? If so then I think the voice coil is rubbing on something and is most likely toast.

It looks like the woofers have a stationary phase plug, not a dust cap. This means it's possible for debris to get into the gap. Turn the driver face down and see if anything comes out. Sniff the center of the speaker- if it smells like something burned, it probably is. If not, turn it face down and move the cone gently to see if something will fall out.

 

[Guiria]

No burnt smell but there is something definitely in the speaker. When I turn it upside down and move the cone then something falls into the voice coil or whatever is moving inside there and it makes the movement jagged and sticky in one spot but then if I turn right side up and move the cone the "something" falls out of the way and the movement returns to smooth.

I worked on getting something to fall out for a while last night but never had any luck.

I've tracked down some replacement drivers over on the parts-express forum and will hopefully just buy a replacement.

the driver that has this issue was in my garage for about 3 months uncovered and its very possible something got in between the phase plug and cone during that time.

 

[highfigh]

No burnt smell but there is something definitely in the speaker. When I turn it upside down and move the cone then something falls into the voice coil or whatever is moving inside there and it makes the movement jagged and sticky in one spot but then if I turn right side up and move the cone the "something" falls out of the way and the movement returns to smooth.

I worked on getting something to fall out for a while last night but never had any luck.

I've tracked down some replacement drivers over on the parts-express forum and will hopefully just buy a replacement.

the driver that has this issue was in my garage for about 3 months uncovered and its very possible something got in between the phase plug and cone during that time.

Might be bugs. I would bet that if you continue to play them, the crumbs will eventually be expelled. If they were facing up and uncovered, it could be grit from the shingles, if that's the kind of roof you have.

 

[TLS Guy]

No burnt smell but there is something definitely in the speaker. When I turn it upside down and move the cone then something falls into the voice coil or whatever is moving inside there and it makes the movement jagged and sticky in one spot but then if I turn right side up and move the cone the "something" falls out of the way and the movement returns to smooth.

I worked on getting something to fall out for a while last night but never had any luck.

I've tracked down some replacement drivers over on the parts-express forum and will hopefully just buy a replacement.

the driver that has this issue was in my garage for about 3 months uncovered and its very possible something got in between the phase plug and cone during that time.

The voice coil is becoming unraveled. I would bet it has dropped at least one turn.

The speaker needs reconing or replacement.

 

[Guiria]

Unfortunately for me the guy I wanted to buy the drivers from wants top dollar for the driver even though its used and discontinued. The replacement driver has a couple different parameters but PartsExpress tech support claims that they work as a direct replacement so I may buy one of the newer ones and hopefully it all sounds good still <cross fingers>.

 

[TLS Guy]

Unfortunately for me the guy I wanted to buy the drivers from wants top dollar for the driver even though its used and discontinued. The replacement driver has a couple different parameters but PartsExpress tech support claims that they work as a direct replacement so I may buy one of the newer ones and hopefully it all sounds good still <cross fingers>.

Are the parts available for that speaker, so you can recone it? Otherwise I would replace both drivers. What are the spec differences?

 

[Guiria]

Are the parts available for that speaker, so you can recone it? Otherwise I would replace both drivers. What are the spec differences?

Here are the specs garbeled together. I think the most significant differences are those listed in red although most of the T/S parameters are slightly different. I went for side by side comparison to easily see the spec differences...wish I could insert an html table to clean it up a bit.

Old Driver New Driver Units
RS150S-8 RS150-8
Imp. 8 Imp. 8 Ohms
Re 6 Re 6.13 Ohms
Le .76 Le .59 mH @ 1 kHz
Fs 53.8 Fs 47.8 Hz
Qms 2.52 Qms 2.15
Qes .56 Qes .49
Qts .46 Qts .40
Mms 7.38 Mms 7.5 g
Cms 1.18 Cms 1.48 mm/N
Sd 84.9 Sd 84.9 cm^2
Bl 5.43 Bl 5.8 cm^3
Vas 12.0 Vas 15.0 liters
Xmax 4 Xmax 4 mm
VC diam 25 VC diam 25.9 mm
SPL 88 SPL 87.1 dB@1W/1m
RMS 40 RMS 40 Watts
Freq 50-3.5K Freq 48-4.2K Hz

 

[TLS Guy]

Here are the specs garbeled together. I think the most significant differences are those listed in red although most of the T/S parameters are slightly different. I went for side by side comparison to easily see the spec differences...wish I could insert an html table to clean it up a bit.

Old Driver New Driver Units
RS150S-8 RS150-8
Imp. 8 Imp. 8 Ohms
Re 6 Re 6.13 Ohms
Le .76 Le .59 mH @ 1 kHz
Fs 53.8 Fs 47.8 Hz
Qms 2.52 Qms 2.15
Qes .56 Qes .49
Qts .46 Qts .40
Mms 7.38 Mms 7.5 g
Cms 1.18 Cms 1.48 mm/N
Sd 84.9 Sd 84.9 cm^2
Bl 5.43 Bl 5.8 cm^3
Vas 12.0 Vas 15.0 liters
Xmax 4 Xmax 4 mm
VC diam 25 VC diam 25.9 mm
SPL 88 SPL 87.1 dB@1W/1m
RMS 40 RMS 40 Watts
Freq 50-3.5K Freq 48-4.2K Hz

They are very close. I would replace both drivers, and you need to pad the tweeter down another down another db as these woofers are 1db less sensitive.

 

[Guiria]

They are very close. I would replace both drivers, and you need to pad the tweeter down another down another db as these woofers are 1db less sensitive.

If one driver is rated at 87.1 db 1W/1m then two drivers would be rated 90.1 db's, is that right? If that's the case then the tweeter needs no padding as it is rated at 88 db 1W/1m.

When building/designing a crossover do you pay attention to the single driver sensitivity rating or the combined driver sensitivity rating?

Or maybe more specifically, when building a crossover for an MTM which sensitivity should you pay attention to?

 

[TLS Guy]

If one driver is rated at 87.1 db 1W/1m then two drivers would be rated 90.1 db's, is that right? If that's the case then the tweeter needs no padding as it is rated at 88 db 1W/1m.

When building/designing a crossover do you pay attention to the single driver sensitivity rating or the combined driver sensitivity rating?

Or maybe more specifically, when building a crossover for an MTM which sensitivity should you pay attention to?

Always the combined.

However the combination of two new drivers will be down 1 db so the speaker would end up a little brighter.

 

[Guiria]

Always the combined.

However the combination of two new drivers will be down 1 db so the speaker would end up a little brighter.

Yes, and the speaker is mounted in wall and was a little bright to begin with so I think bringing it down 1 db is definitely the way to go with the new drivers.

 

[Guiria]

After running manual calculations for the RS28A tweeter to pad it down 1 db I've come up with the following values:

Parallel resistor: 32.78 ohms
Series resistor: .435 ohms

Anyone with software that could double check that for me? I was using calculations based out of Speaker Building 201 - pg. 78 Tweeter Attenuation

 

[TLS Guy]

After running manual calculations for the RS28A tweeter to pad it down 1 db I've come up with the following values:

Parallel resistor: 32.78 ohms
Series resistor: .435 ohms

Anyone with software that could double check that for me? I was using calculations based out of Speaker Building 201 - pg. 78 Tweeter Attenuation

Just put a 0.5 ohm resistor in series with the tweeter and you will be fine.

 

[Guiria]

Just put a 0.5 ohm resistor in series with the tweeter and you will be fine.

That's easy enough. Would you mind explaining the reason for a single resistor vs. The textbook version of both a series and parallel resistor?

 

[highfigh]

That's easy enough. Would you mind explaining the reason for a single resistor vs. The textbook version of both a series and parallel resistor?

It's not a large enough resistance value to cause problems with the crossover if you use the .5 Ohm alone. As soon as the value increases past a certain point, the crossover's -3dB point drops into an unacceptable range and will be too close to the tweeter's Fs.

 

[Guiria]

It's not a large enough resistance value to cause problems with the crossover if you use the .5 Ohm alone. As soon as the value increases past a certain point, the crossover's -3dB point drops into an unacceptable range and will be too close to the tweeter's Fs.

I assume the value that will start to lower the crossover's -3dB point can be calculated.

I'm not saying I'm going to calculate it, I'll stick to TLS recommendation of the .5 ohm resistor, in fact I have a .51 ohm resistor already so when the drivers come in I'll be good to go.

 

[TLS Guy]

I assume the value that will start to lower the crossover's -3dB point can be calculated.

I'm not saying I'm going to calculate it, I'll stick to TLS recommendation of the .5 ohm resistor, in fact I have a .51 ohm resistor already so when the drivers come in I'll be good to go.

Yes, that will be fine.

It is a matter of being more nearly correct, than precisely wrong.

The crossover will see a small increase in impedance, but it won't affect the crossover point significantly. The .5 ohm resistor, actually drops you 1.3 db, when I use your tweeter specs. However the 0.3 db is again is significant.

0.5 ohm resistors are plentiful and for a value that small in series, it is not worth shunting the tweeter with a resistance to correct the impedance. You will not know the difference.