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Thought I'd post this as it has some valuable lessons. At least in my opinion. It's not strictly about vintage, but does include it.
A while back I heard some PSB B15 speakers. Little guys with a 1" dome and 5.25" mid-woofer. Great sound, but lacking the low bass, of course. Might be good candidates for adding a sub, or better still a pair of woofers running in stereo. So after waffling for a year and a half, last week I bought a pair.
I used my Advents as the bass speakers, and also used them as stands for the PSBs. The stacked speakers are located right where the Advents had been on their 16" stands. (the Advents are now right on the floor)
I rewired the tweeter switch on the Advents to give me one position with theinput straight to the woofer with no series inductor, and one with the inductor in series. The third position is the full range setting with my last and best crossover.
The bass amp is a pair of Parts Express plate amps (150 W into 8 ohms). Currently they are sitting on the floor and connected to the Advents with long cables. The plate amps have level, phase and low pass frequency adjustments. These do not have a boosted low end.
The PSB's are driven by my NAD C320BEE integrated amp which has pre out and main in jacks. I soldered some 0.1 uF capacitors internally, between the pre out and main in jacks. This gives a rolloff of 6 dB per octave below 80 Hz, and is down 3 db at 80 Hz. If I want the NAD to work full range, i just put the jumpers back and bypass the caps. Since the caps come after the preamp out, the pre out jacks have a full range signal, and this is used to drive the plate amps.
I tried the Advents in the two woofer only modes and settled on the one with the inductor bypassed - it's tighter. The plate amps have a typically low Damping Factor (high source impedance) and the DCR of the inductor adds too much resistance for tight bass.
The plate amp setting were made with the aid of my Real Time Analyzer which has 1/6 octave bands, and a 1/2" condenser mike. The mike was located where my head normally is for listening. I could have made the system flatter, but listening tests showed I needed more bass to sound balanced. This is due to the lower sensitivity of human hearing at low frequencies and lower levels. I live in a condo and can't crank up the levels, and at my normal levels my hearing (and everyone else's) is less sensitive in the bass, so it needs a little boost to sound "normal". It's the reasoning effect behind the Loudness control.
Once the plate amp controls were set, the system was finished and the serious listening began. The sound is clear, open, transparent, natural and voices sound live. Without doubt, it is my best system, ever.
The use of stereo subs means there is no pulling of the image and no way to locate the sub. I am also of the opinion that you can't do this set up without instruments. Your ears just are not good enough.
I was also curious as to how this system compared to my JBL L-110's which are stock except for a pair of SEAS 25F-EW woofers. So, I set them up along side the PSB/Advent stacks with the JBLs on the 16" stands which got the JBL and PSB tweeters at the same height. To my very great surprise, the JBLs sounded almost exactly like the PSBs. A small adjustment to the JBL's L-pads on the mid and tweeter made them even closer (about "+1/2 hour" on each).
OK, a couple of points here. The PSB's are excellent, but in the mids and highs they are no better than a pair of 1978 JBL's. The Advents are providing better bass, but the Advent woofers are near the floor for better coupling to the room and the plate amp controls allow some EQ you can't easily do with a fullrange speaker. I'm pretty sure I can equal the PSB/Advent performance with the JBL's and a graphic EQ, but it might take a 1/3 octave EQ to do it. But older "vintage" speakers can do it too. The B15/Advent system sounds a lot like my memory of the Fried Model R III from the late 70's. That same openness and crystal clarity without being harsh or edgy.
The PSB/Advent system is better than what I can achieve with the Advents. I spent 7 years tinkering with them, and got them to Very Good; but I don't think I can get them to be any better with the stock tweeter. It just isn't as smooth as the PSB or JBL tweeters. However,there are not all that many modern speakers that are better than a tweaked Advent. Back in 2002, when I brought home a stock pair of Advents on trial, they absolutely blew away my B&W 602.2's with B&W ASW500 sub. Nautilus tweeter, Kevlar cone, and all, it was no contest.
The PSB B15's, like the JBL's have a very smooth midrange and treble. There is no sibilence or stridency in the mids and highs, but everything is there, and there is no boxiness or closed in sound. Add to that a clean and tight bass line. and it makes for a great system.
How good? I'll go out on a limb here and suggest it's better sounding than the PSB Synchrony One. When I first heard the B15's the same shop had the Synchrony One. My friend Tim was with me, and we both felt the B15 was cleaner, but of course, lacking in the bass. The Synchrony One was nice, but seemed too thick in the midbass. I think that's a consquence of fattening up the bass to sound balanced at normal levels (the old Loudness thing, again); but it's difficult with just speaker voicing to add some low bass without also fattening up the midbass and adding a bass edge to male voices. But with my bi-amped system, I can do that.
I hope this wasn't toooo long. but there's a lot to tell.
Jerry
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now that I know the crossover point you chose is to raise that by at least an octave. This I say for two reasons: added headroom for the five inchers since they are presently asked to handle some 40 hz content and more importantly, the ability to equalize the woofers to deal with room modes. In my 17 x 26 den, I've got some serious modes that took a fair amount of adjustment to neutralize. With my similar approach Polk RT35 monitors sitting atop 12" Eosone powerered woofers, I tried several high pass settings available on the NAD receiver: 50 hz, 100 hz, 120 hz, 150 hz and 200 hz. With my room, the highest setting allowed the woofers to fully "participate" in the correction since I use the EQ on the subs only. I tried running it full range just for grins and was not pleased with the results. Its sins are not evident on woofers alone.
I know I'm preaching to choir with you, but for others - one of the greatest advantages to such a bi-amped arrangement is isolation of the bass channel from the rest of the system. Using demanding content that may push or clip the woofer amps has no effect on the quality of most of the sound. Space Shuttle launches and sonic booms from the Blu-Ray copy of NASA's film The Dream is Alive tend to gobble bass power. :) Have fun experimenting!
rw
I did consider the crossover point. If I were able to play the system loudly, that would be a major consideration. It was the reason the earlier Polk Advent system used a 175 Hz crossover. The Polks couldn't handle as much power and they also had a more peaked output in the 80-90 Hz region. But in the condo, with my current downstairs neighbors, I really can't play all that loud, and the 80 Hz high pass is OK. Putting the input to the PSB's down 3 db at 80 Hz and 9 dB (an 8:1 ratio)at 40 Hz.
Raising the crossover point by one octave to 160 Hz would be better for high power use; but it would also mean that I'd need to use a graphic EQ in the system to get the bass contour I want. At 80 Hz, the plate amp controls allow me to get what I want.
The required stroke of a given speaker varies inversely as the square of the frequency for constant output level. So doubling the crossover frequency cuts the stroke on the satellite speaker by 4:1. But once you get near the speaker's in-box resonance that changes - particularly if the speaker is ported as the stroke is at a minimum at the port tuning frequency. In this case, I left the ports open as the port tuning frequency is low enough to help prevent overstroke.
Years ago I helped a friend put together a similar system using AR3 woofers and Rogers LS3/5a. There was a first order roll off on the Rogers at 125 Hz and it survived quite well, even though the system was played at very high levels. The bass was driven by a Phase Linear 700 which produces over 450 W/ch into 4 ohms. The mid and highs were driven by a Van Alstine modified Stereo 120. But again, we had to use a Soundcraftsmen EQ to flatten the mid-bass.
One of the saving graces of my den is that the room modes don't cause a lot of problems for me; but it took me two years to come up with the speaker locations which are asymmetric to the long axis of the room.
Your comment on the benefits of active biamping are right on. You can clip the bass amps and the clipping distortion is masked by the clean energy from the satellites. Also, active biamping gives a lot more effective power. For example, if the crossover were at the half power point in the system and the woofers and the satellites had the same sensitivity, a 50 watt amp on the bass and a 50 watt amp on the mids and highs gives undistorted loudness equal to a single full range amp of 200 watts. But the smaller satellite speaker is still only driven by a 50 watt amp. Much easier on the speakers if you drop the tone arm. The higher effective power is one of the reasons why the speakers for rock concerts are biamped or triamped.
I picked some simplifying assumptions for my example, and for typical systems you need 2-3 times the power on the bass that you do on the mids and highs. In my system, I'm at 4:1.
Jerry
Is this not a variation on what you were doing with the little Polks, and had at Dayton DIY, some years back?
I suspect we will have a DIY again this year in Lexington, around Thanksgiving.
Maybe you should pack them up and bring them down. I'm sure the guys would be interested.
David
David,
Yes, exactly. Your memory serves you well, that was about 5 years ago.
There are three key differences besides the PSB B15's Vs the Polk RTi28's. First, the PSB's allow a lower crossover frequency; second, I bypassed the Advent's series inductor this time; and third, this time around I had the Behringer RTA and mike to help with the set up. Everything else is pretty much the same stuff.
I think that if I had the RTA back then it might have been more successful. I did have a Radio Shack meter, the Infinity RABOS kit, and some test CD's back then, but they really were not good enough. For one thing, after I got the RTA, I looked at the output from some 1/3 octave pink noise test CD's. The noise was on 1/3 octave frequency intervals; but the bandwidth of the noise was much greater than 1/3 octave - being nearly a full octave wide. So you think you're doing a narrow band measurement, but you're really not.
My son still has the Polks with the Dennis Murphy crossovers. Great little speakers, and a huge improvement over the stock crossover; but the PSB's are better in several respects.
Jerry
I second the praise of Fried Model Rs. I have series II improved from 1976 and they have a very natural sound especially good on classical with real bass. Work well with Cyrus Two integrated or B&K ST-140 amp but they were slow and muddy sounding with a 25 watt NAD 3225PE integrated.
Very interesting as always!,By the way your post are never to long.I as well as others seem to enjoy your never ending journey to what sounds near perfect to your ears and how you went about achiving that sound!Brian
... when he designed his Advent Loudspeakers, Jerry! It's been several years since Brown Soun re-coned the woofs & replaced the tweets in those Utility Advents. They still continue to amaze in direct wired woof & 13 uf non-polarized capped tweet configuration. Am currently usin' a Carver MXR-130 Receiver for amplification, & its' tighter bass delivery is loud-n-clear through those Advents. Even coaxes a bit of high-end sparkle from those fried egg tweets. Two combined audio mavericks' designs continue to create musical magic! ... BTW Jerry & David LD, if you're fans of vintage Jensen sound, you might enjoy Ted Weber's Signature Series speakers for future speaker projects. They're not as pricey as current Jensen/Recoton reissues, yet are faithful to vintage Jensen specs. Just ordered a 8" Alnico 8S 15 watter in hopes of converting an 80's era Fender Sidekick 10 into a solid-state Champ Amp!!!
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