For a little background, I'm building an active, multi-way speaker, and I'm using pro audio coaxial speakers for mids and highs.
I want to knock down the sensitivity of the horns. They have a sensitivity of 107db.
To this end I bought adjustable L-Pads from Parts Express (the 100watt version) to quickly gauge how much of a reduction I need. I decided -10db is the point where I stop noticing the amp hiss from the seating position. (It's still audible close to the speaker, but it's in the acceptable range.)
The adjustable L-pad is rated to -10dB and 8ohms. I measured resistance values and used an L-Pad reverse calculator to confirm that it was a reduction of 10dB.
Then I bought resistors for the same -10dB reduction @ 8ohms. That's 5.8ohms series and 3.7ohms parallel. I wired them up, but they don't give the same reduction as the adjustable L-Pad.
The adjustable L-Pad set to -10db is 8ohms series, 8 ohms parallel. So I used a combination of resistors to match the 8 ohms for parallel and series. But it still doesn't match the adjustable L-Pad. (I did measure the resistors individually, and they are correct.)
When the values of the adjustable L-pad and the resistors is the same, the adjustable is significantly quieter in terms of hiss. To make the adjustable match the resistors, I set it to what should be -7db.
I guess I'll leave it there. Any ideas about why the adjustable L-pad reduces hiss more than resistors of the same value? And how do I get the reduction of hiss I'm looking for without using the adjustable units? I don't want them to be adjustable in the finished speaker.
I want to knock down the sensitivity of the horns. They have a sensitivity of 107db.
To this end I bought adjustable L-Pads from Parts Express (the 100watt version) to quickly gauge how much of a reduction I need. I decided -10db is the point where I stop noticing the amp hiss from the seating position. (It's still audible close to the speaker, but it's in the acceptable range.)
The adjustable L-pad is rated to -10dB and 8ohms. I measured resistance values and used an L-Pad reverse calculator to confirm that it was a reduction of 10dB.
Then I bought resistors for the same -10dB reduction @ 8ohms. That's 5.8ohms series and 3.7ohms parallel. I wired them up, but they don't give the same reduction as the adjustable L-Pad.
The adjustable L-Pad set to -10db is 8ohms series, 8 ohms parallel. So I used a combination of resistors to match the 8 ohms for parallel and series. But it still doesn't match the adjustable L-Pad. (I did measure the resistors individually, and they are correct.)
When the values of the adjustable L-pad and the resistors is the same, the adjustable is significantly quieter in terms of hiss. To make the adjustable match the resistors, I set it to what should be -7db.
I guess I'll leave it there. Any ideas about why the adjustable L-pad reduces hiss more than resistors of the same value? And how do I get the reduction of hiss I'm looking for without using the adjustable units? I don't want them to be adjustable in the finished speaker.
I'd stick with the L-pads due to possible later-on changes in other parts of the system, and room location.
Besides, L-pads are not the same as using fixed resistors due to their varying impedence curves.
Besides, L-pads are not the same as using fixed resistors due to their varying impedence curves.
Fair point about adjusting things, but in this case I'm using an individual DSP channel for each driver (4 way design). So I want to do all the adjusting in DSP. But I can't reduce the horn sensitivity with DSP!
I thought the whole point of DSP was to eliminate crossover components.
You could get a low power, quiet amp for the tweeters.
However, sticking with what you have, what's wrong with keeping the L Pad?
If you want to use fixed resistors, check your wiring and measure results as post 4.
Or most amps would tolerate just a series resistor since that's how most bi-wired/bi amped passive speakers work.
You could get a low power, quiet amp for the tweeters.
However, sticking with what you have, what's wrong with keeping the L Pad?
If you want to use fixed resistors, check your wiring and measure results as post 4.
Or most amps would tolerate just a series resistor since that's how most bi-wired/bi amped passive speakers work.
I found my mistake. I was measuring the adjustable L-pad wrong. I was measuring from 3 to 2 and 3 to 1. But it should be measured 3 to 2 and 2 to 1.
I measured it wrong because for some reason I was convinced it would produce a -10db attenuation. And I believed -10db attenuation would be enough to make the noise go away.
Measured correctly, the setting I'm using is 8ohms series and 1 ohm parallel. -20db reduction.
What helped me get through my mental block is I combined all of my resistors to make a 36ohm series by 4.3ohm parallel filter. This calculates to ~22db drop on the calculator I was using, and the output roughly matched the adjustable L-pad.
Yes, I'm going with DSP because I don't know anything about passive crossovers! Can you tell? (And because I'm trying to be fancy with the woofers/ subwoofers.)
Do you know of a small, extremely low noise amplifier, preferrably in 1ru form factor, with XLR connectors? Something like 2x50watts? Affordably priced?
It'd have to be a Class D, and a good Class D at that. Gene at audioholics showed measurements for a new Class D amp that had something like 120dB signal to noise at 1 watt (I believe it was the 1 watt metric). My emotiva is 86dB @ 1 watt, and that's pretty good for an class A/B amp.
I have looked around a little for a small amp to drive the horns. Nothing jumped out at me. I'm open to suggestions, but at the same time, using the right filter is a pretty cheap fix.
That's an attenuator, not a filter. Even if it reduces the noise, it also reduces everything else.
Not sure you tried it but check if the noise goes away if you short the amp's inputs. It could be the active crossover noise being amplified by the amp, not the amp. Although 107 is very efficient, so it could be the amp. At 107, I'm not sure you need 50, 5 may be enough. I think 5 would put out around 114db.
Active crossovers have unity gain, so it is unlikely to audibly increase the input noise level.
If it does, there are real design problems.
If it does, there are real design problems.
I use a behringer and it wants "professional" levels, so it can be a problem. I use an attenuator after to dcx.
Describe your system (amp models etc) and your budget.
It may help others advise on how to improve.
There may even be tweaks to the amps you have to reduce gain and noise.
It may help others advise on how to improve.
There may even be tweaks to the amps you have to reduce gain and noise.
I am pretty settled on using the correct L-pad, but for the sake of those looking on and those who may find this in the future... Starting from the beginning, the speaker hiss is significant! I measured it with an SPL meter inside the throat of the horn, because this was repeatable and reduces the influence of ambient noise.
With no attenuation, I measured 70dB when placing the SPL meter in the throat of the horn. This is clearly unacceptable. The hiss dissappears into the noise floor around 50dB, which is the -20dB attenuation I mentioned above.
The source is a mac mini, connected to my TV via Toslink, then Toslink to Emotiva XDA-2 DAC. Then I'm using XLR outs into splitter cables, into the 4 inputs on the Peavy VSX 48e Processor. And XLR from the processor to the amplifier.
(Before I added the horns, I had XLRs running from the Peavey processor to my M-Audio M3-8 monitor speakers. And the monitors didn't exhibit any noise except the self-noise they always have.)
I have tried 2 amplifiers. Both were noisy, and the noise of each was completely different. I started with the Art SLA-4, and the noise sounded like pink noise. Now I have the Emotiva XPA amp, and the noise is white noise.
I expect to keep the emotiva amp, since the subwoofer section of my speaker clearly benefits from the extra power. I configured the Emotiva amp to have 6 high power channels and 1 low power/ stereo channel for the horn.
A super quiet Class D amp would be nice, but I expect the cost will be prohibitive. I was recommended a D-Sonic amp, but it's 4x what I originally planned to spend, and their website says up to 7 channels. I need 8 channels. And they don't have a low power stereo amp.
So I plan to use a correctly designed L-Pad. If I shoot for -18 or -19dB, the 65amp stereo channels on the amp will be enough. With a -20dB L-pad, the horn would only see 0.6 watts of the 65. But -19dB puts that up to 1.1watt, which is enough to match the other drivers in the system.
I'll throw one other idea out there. A headphone amp that can drive 8 ohms. 107 is just crazy efficient. That is 20dB over a fairly typical 87dB driver. Most amps have a gain of around 26-30dB. You almost don't need any gain after the dsp for these drivers.
You should really learn about passive crossovers they are easy to learn to design and build and your speakers will like you , and if you have a horn with lots of hiss a 12 to 18 decible per octave passive butterworth crossover will tame that horn with an l pad , the passive xovers really make the speakers sound so much better .
Saying that passive crossovers are better is like saying vinyl sounds better. It just isn't true! But you are free prefer whatever you want, on the sole condition that you extend the same freedom to everyone else!
In fact you can't say one is simply better than the other as passive outperforms active in some areas, and active outperforms passive in others. You have to identify the criteria that matter for a comparison to be made. Active crossover is by its nature noisier for instance (if implemented in analog), and considerably more expensive typically due to the need for multiple power amplifiers (and hence lower reliability too). However active has many advantages too.
One key strength of passive crossovers is the simplicity of interface between amp and speaker. For instance you can swap different speakers and compare them, but with active crossovers you have to swap the speaker and matching crossover together, more error-prone and cumbersome...
One key strength of passive crossovers is the simplicity of interface between amp and speaker. For instance you can swap different speakers and compare them, but with active crossovers you have to swap the speaker and matching crossover together, more error-prone and cumbersome...
LOl! Yes, a passive crossover performs best in a passive speaker, and an active crossover works best in an active loudspeaker. So a person who is building an active speaker should use active crossovers, right? (Rhetorical. I don't care if you disagree.)
And BTW, this is a very old thread about L-Pads, not crossovers....
And BTW, this is a very old thread about L-Pads, not crossovers....