Horn Driver Hiss Noise at idle

[nmunro]

Hi All,<br><br>I am trying to solve something that has come up during the build of my Tri-Amped JBL driver system. I have recently completed a DIY speaker build utilising JBL 2446J mid horn drivers. (stated 16 ohm but metered at nearer 8 )<br><br>The system comprises of 3 Rotel power amps (2 x 130 W for the bass and midrange and a 1 x 70W for the tweeters). The issue that has become apparent is a lot of audible hiss on the horn drivers<br><br>I have done some troubleshooting and I have found that with the amp disconnected from the rest of the system and sitting idle (switched-on) the hiss is intrusive to any listening. I have gone through the Ground loop investigation. I have swapped amps and interconnect cables to no avail. Nothing affects it. I have had to install a couple of L-Pads to reduce the noise but that of course changes dynamics of the midrange overall and requires gain during any playback.&nbsp;<br><br>I am coming to the conclusion that the 2446J drivers are sensitive enough that they are picking low level amp noise. It is a low level staticky type of hiss not hum. It is apparent in both channels so I assume that eliminates the possibility of any diaphragm issues<br><br>Just wondering if anyone has any thoughts on a fix. Obviously I may need to try another brand of amp (not available) but I was wondering if there was anything else I could try or do etc.<br><br>

[engineerjoe]

try turning the amp's input dials to 7 (or even 5, if equipped). Do you have an active crossover? If you have something else in the chain to the drivers turned down, reset the whole chain with less amp dialed up.
Some amps make even the hiss louder.
I don't think the ohm reading makes it an 8 ohm diaphragm. That's what 16 ohm ones read.

[short_circutz2]

A ground loop isn't going to cause hiss, it causes a low frequency hum.

Do some research into gain structure. This is important particularly for analog setups. Proper gain structure will reduce hiss and increase s/n (signal to noise) ratio.

[Robh3606]

What do you have in series with the 2446's?? You should have a protection capacitor and a fixed resistor attenuator pad. Depending on the woofer/midrange sensitivity you could probably drop a 10dB pad and not have any issues.

Rob

[Mr. Widget]

I may need to try another brand of amp (not available) but I was wondering if there was anything else I could try or do etc.

It sounds like your system is operating properly for the design.

A ground problem causes a 60Hz hum, an impedance issue is only an issue if you are working with passive crossovers, and as you noted... a higher quality amplifier with a lower noise floor will help, but as Rob and the others have pointed out you need to work with your gain structure. As was pointed out, if your Rotel amp that is on the 2446s has an input control, turn it down. If you don't have that available, you will need to lower the sensitivity of the 2446s by padding them down.

Below is a simple fixed value L-Pad set to -10dB for a 16 ohm driver. (Your drivers have a 16 ohm AC impedance, you likely measured the DC resistance)

This will not eliminate the hiss, but will cut it down by 10dB and will likely satisfy you. You can also try more padding if desired. Also, note that you should get close to these values, but you do not need to be spot on. I would use 11 ohms and 7.5 ohms which should be easy enough to hit.


Widget

[nmunro]

Wow thanks for the great feedback and the pad resistor details. I will certainly take this as a next step and advise on progress. I take it that -10db will not require any kind of heatsink ? The resistors can be strung across the driver terminals ?

It sounds like your system is operating properly for the design.

A ground problem causes a 60Hz hum, an impedance issue is only an issue if you are working with passive crossovers, and as you noted... a higher quality amplifier with a lower noise floor will help, but as Rob and the others have pointed out you need to work with your gain structure. As was pointed out, if your Rotel amp that is on the 2446s has an input control, turn it down. If you don't have that available, you will need to lower the sensitivity of the 2446s by padding them down.

Below is a simple fixed value L-Pad set to -10dB for a 16 ohm driver. (Your drivers have a 16 ohm AC impedance, you likely measured the DC resistance)

This will not eliminate the hiss, but will cut it down by 10dB and will likely satisfy you. You can also try more padding if desired. Also, note that you should get close to these values, but you do not need to be spot on. I would use 11 ohms and 7.5 ohms which should be easy enough to hit.


Widget

[nmunro]

What do you have in series with the 2446's?? You should have a protection capacitor and a fixed resistor attenuator pad. Depending on the woofer/midrange sensitivity you could probably drop a 10dB pad and not have any issues.

Rob

Thanks Rob !

[speakerdave]

To the above suggestions, which I agree with, I would add only a general observation: It is fairly common for people setting up their first speaker system with a horn and compression driver to have the horns set way too hot. If you do not have input sensitivity control on your tweeter amp, you may not have enough attenuation range on your crossover to set the horns properly. In that case you will need to add an L-pad in front of the horn (after the amp) as Widget suggests.

[Ian Mackenzie]

Hi All,<br><br>I am trying to solve something that has come up during the build of my Tri-Amped JBL driver system. I have recently completed a DIY speaker build utilising JBL 2446J mid horn drivers. (stated 16 ohm but metered at nearer 8 )<br><br>The system comprises of 3 Rotel power amps (2 x 130 W for the bass and midrange and a 1 x 70W for the tweeters). The issue that has become apparent is a lot of audible hiss on the horn drivers<br><br>I have done some troubleshooting and I have found that with the amp disconnected from the rest of the system and sitting idle (switched-on) the hiss is intrusive to any listening. I have gone through the Ground loop investigation. I have swapped amps and interconnect cables to no avail. Nothing affects it. I have had to install a couple of L-Pads to reduce the noise but that of course changes dynamics of the midrange overall and requires gain during any playback.&nbsp;<br><br>I am coming to the conclusion that the 2446J drivers are sensitive enough that they are picking low level amp noise. It is a low level staticky type of hiss not hum. It is apparent in both channels so I assume that eliminates the possibility of any diaphragm issues<br><br>Just wondering if anyone has any thoughts on a fix. Obviously I may need to try another brand of amp (not available) but I was wondering if there was anything else I could try or do etc.<br><br>

In addition to the fixed L pad you may not have the best SN (signal to noise ratio) with the input of the Rotel amplifier disconnected.

To be more specific an amplifier with an unbalanced or balanced input needs a low impedance source to provide the best SN. Left disconnected then there is virtually no common mode noise rejection by the input stage of the amplifier. The noise could be 40-60 db higher than it should be. This is particularly a problem if you disconnect the power amp signal cable at the preamp output socket.

I suggest you either connect the output of the active crossover (turned on with its input connected to your preamp and listen for noise with the preamp volume turned down to zero.

This will give you a true indication of the residual noise from the active crossover and your power amps.

The horn with the driver attached with has be an input sensitivity of between 107-111 db. This equates to an amplification of any noise 15-20db more than your direct radiator woofers. Add to this a noisy unterminated input and you have a very noisy horn.

I hope this is of some help.

Ian