The Dahlquist DQ-LP1 provides an 18dB/octave (3rd order) active low-pass filter, and a 6dB/octave (1st order) passive high-pass filter. So no, the DQ-LP1 will not give you the 6dB/octave boost you need to counteract the dipole cancellation in your subs (I know because I have dipole subs and speakers, and a DQ-LP1).
However, Rythmik Audio, in conjunction with GR Research, has designed an OB/Dipole sub, and the plate amp included in the sub kit DOES include a 6dB/octave "shelving" boost circuit---specifically to compensate for dipole cancellation. The plate amp is available separately, a mono 370 watter with a lot of great features and controls specifically designed for subwoofers. The x/o frequency is adjustable from 40Hz all the way up to around 300Hz---very versatile. Look on the Rythmik website for more info.
I used a modded DQ-LP1 for better than two decades and wish I hadn’t sold it. I’m not certain if a 5dB boost at 20Hz is enough for what you need, but the DQ-LP1 does offer that, via it’s EQ setting. Mentioned under, "controls and adjustments" on page 3 of the manual. If you need the entire Bass level increased, you could adjust in favor of the bottom, via the Level settings, which offer 15dB of gain. Manual here: (https://sites.google.com/site/mpbarney/home/dahlquist-dq-lp1)
Good thought, rodman, but what f456gt is in need of is not a set boost of 5dB at 20Hz (or any other single frequency), but rather a 6dB/octave slope to counteract the dipole cancellation of his subs, adjustable for different x/o frequencies. THAT is exactly what the dipole "shelving" circuit in the Rythmik plate amp provides. The only separate x/o I know of that provides that is the special version of the First Watt B4, made especially for open baffle speakers, which also of course exhibit dipole cancellation with decreasing frequency.
Got it now. Kinda like a Bose 901 EQ does(at both ends of the spectrum), but- not at as high an order. Then again: I've seen Tympani Bass panels, used with different mains(ie: QRS) and a DQ-LP1, with great results. WHEW(that's been a few decades)!
I was planning to buy one to use with a pair of Gradient W-63 OB clones using two 12" Peerless 830500 drivers per side, it is very similar to the prototype built by Sigfried Linkwitz.
The problem with the crossover is that the sub needs a 6dB/octave boost because it is a dipole and
I would guess most off-the-shelf solutions don't offer this.
The subs will be connected to my pair of QUAD ESL-63. I would also like to use my spare QUAD 405-2 for the subs.
I considered the Rythmik OB kit using two GR SW12-8FR and one A370PEQ Servo amplifier) but the dual driver configuration costs $1,200. I am retired, with a fixed income and the price is a little bit stiff.
The price of the Gradient project would cost $252 for the drivers, plus the price for a crossover. I will build the enclosure myself, I have plenty of baltic plywood left from other projects.
Yeah Horacio, the GR Research/Rythmik OB/Dipole Sub isn't exactly cheap, though it is worth what it costs. And the First Watt B4 x/o for dipole subs is about the same price as a pair of those subs, $1500 list, discounted to about $1200.
Rodman, the Dahlquist is actually perfect for use with Tympani IV and IVa bass panels, as they require exactly what the DQ-LP1 provides---a 250Hz, 18dB/octave electronic filter. But that is in addition to the acoustic roll-off of the speaker, which is not textbook dipole (for some reason).
Horacio, I just looked it up on the First Watt website, to refresh my memory. The B4 is a regular x/o, but there is a special version of it---the B5, made especially and specifically for full-range drivers with woofers in open baffles. Go to the First Watt site for all the details.
Regarding the Dahlquist DQ-LP1 and the Magneplanar Tympani-IV and IVa loudspeakers, I remember why the Tympani requires the 3rd order (18dB/octave) low-pass filter that the DQ-LP1 provides rather than the 1st order required to compensate for the 6dB/octave roll-off caused by the dipole cancellation found in all open baffle woofers: It is to create the correct relationship between the Tympani’s woofer panels and it’s midrange/tweeter drivers, in terms of phasing.
By the way, the T-IV requires a 1st order-6dB/octave high-pass filter at 500Hz, but the T-IVa a 2nd order-12dB/octave h-p filter at 400Hz. The Dahlquist provides the former, but not the latter. That’s one reason I got the First Watt B4---it provides 1st-2nd-3rd-4th order filters, both high-pass and low-pass, from 25Hz to 3200Hz, in 25Hz increments. Incredible!
I have just received an email from a First Watt dealer.
He said that the
B-4 is a two-way crossover. If you want to have three-way active
crossover system, you will need two B-4’s and connect them in a
cascading fashion. A “6 dB boost” of sorts can be achieved by
attenuating the top-end(s) and having a linestage preamp with more gain
(if needed) or power amps with more sensitive inputs (if needed).
B-4 and set up is complex. I agree with Nelson Pass who has said that
with active crossover a person “needs to know where they are, where they
are going, and when they’ve arrived.” Crossovers with millions of
combinations are not for everyone. I agree with him after reading the owners manual.
Good decision. You get not only the Rythmik dipole-cancellation compensation shelving circuit, but a great sub power amp, x/o, and other controls (phase, damping). The Rythmik plate amp is available in a couple of iterations: 370 watt, 600 watt, and dual-channel 400 watt. It is also available in both single-ended/RCA and balanced/XLR form.