atmosphere I did confirm polarity is correct.
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.
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Uh- all good suggestions, but before you do anything else, check to see that the woofers are in phase. That is to say, if the red connection on the back of the amp is connected to the plus terminal of the speaker, that such is also the case with the other channel. This way both speakers are pushing and pulling in unison. Otherwise they are fighting each other, and you would have some pretty 'blah' bass! |
One thing one thing to mention ,the amplifier is nothing special to begin within for sure invest in a known product such as Wyred 4 sound ,Pass labs 1st watt evrn Nad ,or tons of other proven companies. iwith your speakers who built them and how to know if they knew about proper speaker building Xovers very important and not easy to get right .usjng a online computer program Essential . I have bought from little companies before I won't name ,that had no clue ,no matter what cable or amp,preamp upgrade it was not seamless I tried my own Xover upgrading since I have modded caps, resistors,inductors for years f the design is flawed yiu can hear it . with the price of new Elac products ,and evrn lower priced excellent JL audio subs for under $1k you can build a great starter system for under $2-3 k for Everything including digital and cables. Just advise I have had single drivers and passive is not always so a inductor or resistors change the driver in some fashion.seek local Audiophiles many would love to help including myself . where are you located? Myself New England.If you don't know Ask I have been doing this for 40 years and still learning . No one knows everything !! |
Good comments by Auxinput. I just noticed something further about the Modwright amp. I had stated its input impedance as being 23K, because the impedance is indicated on its webpage as "Min. 15K 50Khz; 23K 1Khz," and I considered the 50 kHz impedance to be irrelevant. Although I wondered a little why he would bother specifying a 50 kHz impedance. However I now see that its manual (in contrast to the webpage) indicates an input impedance of "Min. 15K at 50Hz [not kHz]; 23K at 1Khz." So that makes it all the more important to avoid requiring the LS100 to drive a low input impedance device in addition to the Modwright amp. My suggestion at this point is that you communicate with Dan and ask him what minimum load impedance he would recommend be used with the LS100. While you're at it, also ask him to clarify if the amp's specified input impedance applies to its balanced input or its unbalanced input or both. Regards, -- Al |
Actually, looking at the Crown XLS 1002, it has a built-in low pass crossover as part of its DSP. You can setup a Linkwitz-Riley 24dB/octave low-pass crossover point anywhere from 30 Hz and 3,000 Hz. See page 8-9 of the manual. It does not publish the input impedance, but it -might- be better than using the miniDSP. |
Taking almarg’s comments... Emotiva XPA-1 unbalanced input impedance: 23.5k ohms -- means (23k x 23.5k) / (23k + 23.5k) = 11.6k ohms combined. Parasound A21 unbalanced input impedance: 33k ohms -- means (23k x 33k) / (23k + 33k) = 13.5k ohms combined. So, comparitively speaking, the increase of impedance when using these amps directly instead of using the miniDSP for low-end will significantely improve the impedance load on the Modwright preamp. That and the fact that these amps are just stronger in controlling the woofer in general would lead me to think that it’s better just to drop the miniDSP out of the mix. I would just use the passive crossovers in the speakers unless you wanted to use something like the Bryston 10B to do BOTH the high and low amplifiers. |
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 |
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. |
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. |
Regarding A/D, DSP and D/A. I have done comparisons on a high-end device. The Bryston SP3 has very high end power supply, audio stages, and A/D, DSP and D/A. Even on this device, when comparing audio using Bryston complete pass-through (just going through it's discrete Class A audio stages) and the Bryston DSP (using A/D, DSP, and then D/A). When using the A/D - DSP - D/A, the sound became much brighter and I did lose some midbass/midrange body - probably lost detail in areas as well. I suspect it will be far worse with a product like miniDSP. |
Erik, I have no experience with miniDSP products. But for example if the OP is using the 2x4 model or the 2x4HD model I would be skeptical that a product incorporating two channels of A/D conversion, four channels of D/A conversion, sophisticated digital signal processing, as well as USB and Toslink digital audio interfaces in the case of the 2x4HD, while selling for list prices of $105 and $205 respectively, would not significantly compromise the sonics of Modwright electronics. So I don’t find Auxinput’s comments about it to be surprising. But yes, measurements would most likely be necessary to properly match the mid/high and low frequency gains and sensitivities. Best regards, -- Al |
@almarg - You are totally correct. I didn't even think about the miniDSP. In addition to the input impedance issue, all the miniDSP devices will convert the analog input to digital before doing the crossover processing - then converting back to analog. These conversion steps as well as the very poor power supply section of the miniDSP will just kill any sound quality benefit you would be getting from the Modwright preamp or audio source. You would do better to look for an analog-only crossover. There are a couple of Bryston 10B crossovers for sale on Audiogon. They have input impedance of 15k ohms, much better than miniDSP. Also, completely analog and much superior power supply. That being said, I did think of one more thing. You should consider any built-in passive crossover inside your speaker. Are you using a manufactured speaker? Or something you built yourself (DIY). The internal crossovers of the speaker will conflict with any active crossover. While you could potentially set the active crossover above/below the internal crossover points, you are just wasting a step. If you do have internal crossovers in your speakers, you are just better off using a Y-splitter cable to go to two separate amps and take the active crossover out of the system completely. On a 2-way speaker, you could potentially just bypass any crossover wiring internally and wire directly to the speakers. If it is a 3-way (or higher), this becomes more complicated because you'll need to have some sort of internal speaker crossover to separate between mid/tweeter. The internal crossover will have this, but it will also have a high-pass section to rolloff the woofer frequencies. If you can't control this and it's a manufactured speaker, an idea would be to connect the Modwright amp to the mid/high binding posts and not use an active crossover for this at all. For the woofer, you could use an active crossover to the Crown amp, but then wire the crown amp directly to the woofer (do not use the internal woofer crossover). All this will require some DIY work on the speaker to accomplish. Let me know if I haven't explained these ideas correctly. |
So can we assume you have bypassed the internal crossovers and replicated them in miniDSP? That's usually the easiest way to go. Test 1 driver with the passive crossover. Adjust miniDSP until your active filter looks the same. Repeat with next. Make sure your sensitivity matches before and after. Best, Erik |
Thanks for the additional info. I can’t say what the answer is at this point, but here are some thoughts and possibilities to consider: 1)You didn’t say which miniDSP model you are using as the crossover, but I see that the "2x4," which appears to be a likely possibility, has a maximum rated output of 0.9 volts. The sensitivity of the Crown amp is selectable as either 1.4 volts or 0.775 volts. If you have not set it to 0.775 volts that could certainly be a contributing factor. Also, my suspicion is that those two numbers apply to its balanced inputs, which could mean that the corresponding figures for the unbalanced inputs are twice those numbers. If so, it can be calculated that even if you are using the 0.775 volt setting an input of 0.9 volts would not drive the amp to more than about 72 watts into the 8 ohm nominal impedance of the woofer, which is about 1/3 of its rated power capability. 2)The miniDSP 2x4 has a very low input impedance of 6K. While your Modwright tube preamp has a specified output impedance of 300 ohms, I suspect that as with most tube preamps its output impedance rises to much higher values in the deep bass region, due to the coupling capacitor it most likely uses at its output. Many tube preamps having nominal output impedances of a few hundred ohms have output impedances in the area of 2K to 4K at 20 Hz. If that is the case with the LS100 (and you might check with Dan Wright on that), and if you are using the 2x4 or some other miniDSP model having a similar input impedance, it would certainly explain a weakness in the deep bass region. 3)Although you stated that "all the right adjustments" have been made, between the plethora of settings in the amp and in the miniDSP there is lots of opportunity to go wrong. So double and triple checking everything would seem to be in order. For starters, be sure of course that your settings result in the amps being properly gain matched. And be sure that the high pass, low pass, and bandpass filter functions the amp provides have been either turned off or set to values that would not contribute to the problem. 4)Regarding the comments by the others, the woofer you are using does not seem to be a particularly difficult load, and I would not expect it to require a particularly high current amp. See the impedance plot in this datasheet, which shows its impedance as being at or above 7 ohms at all frequencies, and not having particularly negative (capacitive) phase angles at most frequencies. Although it should be noted that the rise to as much as 30 ohms in the vicinity of 30 Hz means that at frequencies in that vicinity the amp’s power capability will be far less than the 215 watts it can supply into 8 ohms. Although a similar reduction in power capability into the high impedances at those frequencies would occur with nearly all solid state amps. Hope that helps. Regards, -- Al |
Something doesn't seem right here; the 225 wpc should drive the bass driver well. Is this an open baffle design, which might account for the disappointment in low end. More info needed. While the Crown may be poor quality there should be plenty of bass happening. I suspect something else wrong. I concur with Al that it may be in the setup. Even a poorer amp will not sound "horrible" or unlistenable when set up correctly. A profound lack of bass and horrible sound is evidence something is way off track. I suspect mis-wiring in the system. |
My guess is that the Crown amp is going to be really weak in regards to controlling the speaker (even though it’s rated at a higher power) -- Class D circuits can have a problem with weak bass when driving woofers. The Modwright amp is probably going to have a much better overall power supply and current delivery. One quick experiment you can try is to switch around the amps so that the Modwright is powering the woofer and the Crown is powering the mids/highs. If you get strong bass with the Modwright, you’ll know that the Crown is severely lacking. I’m going to guess that the Crown is going to sound weak when driving the mids/highs as well. If the Modwright does sound better than the Crown when driving the woofer and you still want to bi-amp, you will want to look for a really strong high-current amp. Some thoughts would be to look for a pair of Emotiva XPA-1 monoblocks. For slightly less, you could try a pair of XPA-1L monoblocks (smaller) and then run them in Class A mode. They will still give a smooth/full midbass but they won’t have quite as much weight in the bass (though this difference is very very small). If you want to spend more, I have heard that Parasound A21 has very strong bass. It may be sweeter/nicer sounding than the Emotiva’s. Anything less is likely not going to be able to match the Modwright. |
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More info is needed. What model is the other amp; what preamp are you driving the two amps with; is there an electronic crossover "ahead" of the amps; if there is no electronic crossover how is the preamp connected to each amp (e.g., XLR or RCA); what speaker is it; does "10 woofer" mean 10 ohms or 10 inches? Does the bass weakness seem to occur at any volume level, or just at high volume levels? Regards, -- Al |
