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In Reply to: RE: How many quads should I stack? posted by Mendel on February 02, 2016 at 10:43:26
IME most stats just need some reinforcement of the last octave. Quads as an example have mid/upper bass as good as it gets. Why use a sub to cover the mid/upper bass region when all that is needed is the bottom octave?
Given that all that is needed is bottom octave I don't see any advantage to a dipole. Get a standard self-powered sub and cross it over around 40Hz. Let the main speakers run full range. If set-up properly the integration will be quite good. I have heard this type of set-up many times using any number of self-powered subs, some quite inexpensive some really expensive.
Integration is much more of an issue when one tries to crossover high, 100Hz as an example. Even the Gradient is far from seamless given its 115Hz crossover point. It crosses over much to high and being a dipole does not help IMO. And the Gradient is really not all that great in the bottom octave.
If one want even more energy from the main speakers a series cap in front of the amp to roll off the bottom octave is all that is required. No crossover is truly neutral, they all leave a thumb print, but a series cap will be the least offensive type of crossover. The Gradient crossover for the high pass filter is.......well it pretty much sucks and that is being kind.
Follow Ups:
Although I hate to disagree with Kentaja, who did such a great job on my speakers and has given me excellent advice, here is a different perspective, based on my own (surely rather special) situation. I have Stax F83's, which in principle have decent bass down to 60 hz or so but with some resonance peaks around 80 hz. The bass has slam but not much bloom or pitch. But the killer was the following: Strangely for an ELS, the impedance goes down in the bass region instead of up, and my OTL amp can't deliver enough current and would distort, even at low levels. So I ended up getting a pair of subwoofers designed explicitly for ELS speakers, with a steep electronic crossover with (I think) the -3db point at 100 hz. (This was higher than I had originally thought, but was recommended by the manufacturer of the woofers and crossover.) Now I don't have to worry about overloading the speakers (panels or transformers), and have very satisfying tuneful bass, with what seems to me (and at least some experts) excellent integration between the subs and the main speakers. And actually getting the bass out of the panels (and amp) has, I think, improved the midrange too. (Is this possibly due partly to reduced doppler distortion?) My crossover goes between the preamp and the amplifiers, and I have a separate outboard amplifier for the woofers. Perhaps to get this to work one needs to be careful about the subs (mine are designed for electrostatics) and the crossover, but I am very happy at this point.
Stax are a bit different. While they have good extension given their limited panel size power in the bottom is not going to be great. The Quad has much better energy in the mid bass versus the Stax.
Adding a sub to the Stax will require a higher crossover point and since that point will be rather high the Stax will need a filter to roll off the bottom end. Removing the bass from the Stax will improve the midrange.
Thank you very much. This was my experience exactly.
Thanks for sharing your experience.
The Spectra 22 actually have a built in (highpass?) crossover that removes below 100Hz from the panels. There is a toggle switch on the interface for running the panels full range or only above 100Hz. This was for use with the Accoustat sub-woofer. 100hz does seem like a high point for bringing in the sub. I have run the speakers with this switch in the 100Hz position (but no sub hooked up) and the midrange did seem cleaner but the sound was thin. I tried to have my tech change this feature so the crossover would cut at 50 or 60Hz but he was unable to do this for some reason.
I could activate this and try to bring a pair of small nimble subs in at 100Hz. But sound is so good now would hate to spend the money and then ruin it.
One of the main reasons I am considering this is to free the panels from having to deal with low bass notes. But very concerned with a loss of transparency and coherence by introducing a crossover even at 40 or 50Hz.
I like the idea of using a cap to roll off the response to the Accoustats. What value of cap would provide the roll off below 50 hertz and what type would be best (most transparent)? I'm guessing a pricy film cap like a V-Cap. If the sub came in at 50Hz it probably would not need to be dipole. Would 2 be better than 1 or no difference this low? Thanks.
That is the dilemma. Any type of crossover even a simple series cap will cause some loss in terms of transparency not so much in terms of coherence.
The question becomes does this slight loss of transparency, and it will be slight with a series cap, out weight the increase in terms of dynamics by removing the bottom octave from the main speakers? That is a personal call. For some the answer will be yes others might say no.
Pretty simple to try both ways. Start with letting the main speakers run FR. Then try a series cap in front of the amp. See which way you like best.
The value of the cap is a simple calculation you can find any number of on-line crossover calculators. You need to know the input impedance of the amp, crossover point and slope. A series cap will be a 6dB slope.
The value of the cap will be several hundred pF. Exotics like polystyrene or even Teflon won't cost much. Polystyrene of this kind of value is in the $10 range that is what I would start with. Once you have everything tweaked you can try a Teflon but that may be closer to $50.
I have tried both ways. For me using Quads I am happy letting the Quad run FR and blending in the sub. In my younger days when I was more of a head banger and was after maximum dynamic slam I rolled off the bottom of the Quad.
Kentaja,
Your experiences and recommendations totally resonate with me. A 40HZ crossover point really eases the requirements of the sub to achieve a good integration. This is even more true in the situations wihere you can use a steeper crossover slope on both sides, though that is probably not desired here.
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