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Is my amp the problem?

I recently decided to bi-amp my speakers so I purchased a crown xls 1002. (225w 8 ohm). I am driving a 10 woofer. It sounds horrible. I can't seem to get it to put out much power despite its rating even when I make all the right adjustments. Its a class D amp. Is that my problem? It just doesn't seem to have any Ba**s. Lol. Advice is appreciated.
jimbones
jimbones OP
256 posts
 
Wow lots of great suggestions THANK YOU ALL!! very, very, kind.

I am using the 0.775 input setting on the crown. The minidsp is a 2x4 HD. Speakers are DIY. Woofer is sealed and midrange is OB.  I removed the passive XO from the woofer cabinet. Aux, I can reinsert the passive XO external to the cabinet and not use the mini: Good suggestion. Note: I was able to get some improvement volume wise by adjusting the gain to +6db on the mini. That helped. regarding the 30 ohms impedance on the woofer, I could put in a zobel to tame that right?   Now it seems to be a qualitative issue, bass is blah.

Lots of great suggestions.I can't thank everyone enough.
Question: exchanging the crown for another similar amp (QSC) would not yield an improvement correct? also, more power wouldn't help right? I think the Emotiva or used A/B amp with a good supply would yield better results.


jimbones OP
256 posts
 
BTW, I am only using the LP crossover in the mini @ 225 hz. I would not even consider using the HP to the Modwright. The Modwright is a wonderful piece of equipment and Dan is a great gut to work with.
erik_squires
16,063 posts
 
Based on that, I'd say your biggest problem is lack of measurements.

Don't change any hardware. Get Room EQ Wizard and a Dayton imm6 microphone ($25, calibrated) first.


auxinput
2,920 posts
 

Agreed, if you are using active crossover, especially with two different types of amps, you really need to get actual speaker response measurements. This does become more difficult in your own home, unless you build some sort of sound absorbing tunnel (or do something outside aiming the speaker up with an infinite baffle type of area. You’ll need some sort of gain adjustment if you use different amps, or you will have to put in some sort of level adjustment in the passive crossover.  Generally, people who bi-amp will use the exact same amp for highs/lows, but it may be a waste of expense to buy a second Modwright amp. I guess the pro audio amps are good because they do come with a gain adjustment.

You could change to a QSC amp if you wanted to if you look for a Class A/AB.  Pro audio amplifiers are designed to work in extreme environments, push a lot of -general- power to speakers that are extremely efficient (i.e. 98db/watt) and be as efficient with the A/C power as possible. Hence, more Class D/H/I style amps with switching power supplies and fans.  What you want is more of a linear power supply with huge amounts of power supply capacitance and lots of output transistor devices. Usually, this does mean looking for an amp that has a lot more watts (since you need that bigger power supply to be able to push the watts), but it does not mean you have to use all the power. It just means that you have enough brute force from the power supply to drive speakers with low or radical impedance curves.

I have used a Crown CTS600 and a Crown CTS2000. The CTS 600 was a Class AB amp. The sound quality was okay, but somewhat dry. The CTS2000 was definitely stronger and better for woofers, but it was a Class I (Class D variation) and it definitely had some tube-like overtones/colorations in the sound. The Emotiva XPA-1 monoblock was significantly better than either of these Crown amps. Emotiva was totally stronger than either and just sounded better overall. Much more current on tap.

As far as I remember, a Zobel will not change the basic impedance of the speaker. It will still be 4 ohms. A Zobel is to control the rising impedence as the woofer tracks towards the higher frequencies. It’s good to put in a Zobel for the woofer anyways. See this:

https://trueaudio.com/st_zobel.htm

The Modwright is an excellent amp. My suggestions of the Emotiva XPA-1/1L and the Parasound A21 was to try to get a good enough amp to match the resolution/fidelity of the Modwright for the lower woofer registers. You don’t have to spend as much if you don’t want to. You could even go with a single Emotiva XPA-2 (2 channel), or other alternative. In the end, you get what you pay for. Actually, the Parasound A21 has a gain adjustment on the back, so it may work well unless the internal gain of the Modwright is so much higher.

almarg's avatar
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almarg
9,670 posts
 
OK. The 2x4HD has a rated maximum output of 2 volts, which should be fine relative to the 0.775 volt sensitivity the Crown is set for.

However the 2x4HD’s input impedance of 10K is still fairly low. And if I’m correct in understanding that you have been connecting the LS100 to both the miniDSP and the Modwright amp, the LS100’s output stage is most likely seeing the combined parallel impedances of the miniDSP (10K) and the Modwright amp (23K). That combined impedance would be (23K x 10K)/(23K + 10K) = 6.97K, which again could very well be too low for the LS100 to drive without significant rolloff in the deep bass region. And with adverse effects perhaps resulting at higher frequencies as well, that are handled by the Modwright amp and the mid/hi drivers.

That would most likely be the case regardless of whether you have been using the LS100’s XLR output or its second RCA output to drive the Modwright amp, because its XLR output is described as being driven with a single-ended signal. Which I would feel very confident means that the same output stage (and output coupling capacitor) is driving both of the RCA connectors AND the XLR connector.

So that’s one more reason why eliminating the mini may very well be helpful.

Regarding your question about a Zobel network, as Auxinput indicated I believe what that would make possible is just a reduction or elimination of the impedance rise of the woofer that occurs at midrange and treble frequencies, as a result of its inductance. I don’t think, though, that a Zobel would allow you to reduce the relatively narrow impedance peak I referred to that occurs in the vicinity of 30 Hz. But that peak may very well not be an issue anyway, its only significance perhaps being that the maximum power capability of the amp at frequencies in that vicinity would be a good deal less than its 8 ohm rating.

Good luck. Regards,
-- Al

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