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I usually hang out on the Vintage Forum; but no help there; so here I am.
I'm quite experienced with speakers and mods; but this model is new to me; so I thought I'd ask first.
Definitely a pair of Monitor 7B; but apparently early as they have the Peerless tweeters and not the Polk Polydome.
Are there any highly recommended mods? The series cap on the Peerless is a 12 uF Mylar.
Any thoughts or opinions would be appreciated. Sound is very good with my NAD C350.
I've been on the lookout for a pair of these for some time, and these just fell into my lap yesterday.
Jerry
Follow Ups:
See Epicure 14 6 1/2 inch woofer, 8 inch passive radiator
http://humanspeakers.com/e/epicure-14.htm
It was a decent speaker but a brilliant design marketing wise, a 2 way speaker with a small woofer/mid and a large 'fluid coupled' passive radiator that made it look like it had to be a 3 way.
Yes,
I remember that. You had to look hard at the literature to find out the "woofer" was passive.
Sounds pretty darn good driven by my NAD C350.
Jerry
Polk speakers are good, but nothing special. I sold a bunch of them to people who had bought in to their hype, but I wouldn't buy them myself.
My advice? If you like them, leave them as is; or, sell them and buy something better.
Sorry to burst your bubble.
No bubble to burst. They sound very good to me.
One of the best reproductions of the "Jazz at the Pawnshop" LP set I ever heard was on Monitor 7's.
Jerry
You would be surprised at how much better these speakers sound with the proper crossover components!
That being said, I very much prefer late '70's to late '80's Infinity designs, as they are capable of even greater leaps of sound quality when properly tweaked!
The best mod components that I have found are Obbligato Gold Premium Caps and Mundorf Supreme Resistors.
Make sure that the poly-fill is folded so it fills the upper portion of the cabinet just to the upper half of the bass-midrange.
As long as the tweeters retain fluidity, these speakers do not require anything else. I do however get better results from extending the crossover frequency to 4K, using a 4th-order Bessel filter for the low-pass.
Thanks.
I couldn't find the crossover frequency in the specs on the Polk site. What is the factory frequency?
I did pull out the crossover/input cup and checked the filler - it's in place as you said it should be. There do not appear to be any mods to the crossovers, and they use fuses rather than the later polyswitch for tweeter protection.
Jerry
The specs I have on the 7A indicate 3K for the hi-pass, with the bass-midrange rolling off @ 60Hz to the passive radiator.
The frequency plot shows a clean, usable response from 40Hz-20Khz, with a measurable human-threshold response from 30Hz-25Khz!
It however lists a continuous handling rating of 50-watts (100 for the 10!). This may be inaccurate info, even though this series uses an older plasticized woofer design, which may account for the lack of power handling.
and from the Audio magazine equipment directory (1984) the 7c crossover point's the same as the 7a (3K) so it seems likely the 7B is the same...
Thank you.
I have an RTA, so I'll have to dig it out and see how reality compares to advertising. Just listening, the 30-40 Hz sounds pretty reasonable compared to my Advents and JBL L-110's.
Jerry
If you want info on Polks!
Thanks for the response. Yes, I went over there and signed up. Much less helpful than I expected.
Jerry
......what you are doing I'd leave them as is. You start changing crossover components and you'll get an "improvement" alright, albeit one that's prob got a wonky frequency response after the fact.
Thanks, that's generally good advice. However, I have a good idea of what I'm doing and a 61 band RTA and 1/2" condenser instrumentation microphone to help me. Not all the answers; but a big help. Biggest problem is a lack of specific knowledge about the Polks.
Jerry
I used to call on a Polk Audio dealer years ago and I'm familiar with the 7 and 10. The "B" designation - I'm not sure what the change may have been.
As you know, since you've been involved with audio a lot of years, at one time that Peerless and a similar (cosmetically) Audax dome with those metal rectangular shaped flanges were the most commonly used dome tweeters other than a manufacturer's proprietary tweeter. Perhaps you could add Philips domes to that list, of course. Anyway, if they're using 12 mfd to the tweeter - you don't mention a parallel inductor - they probably calculated the crossover by the DCR and not nominal impedance. Personally, if these were mine and I wanted to get a bit more SPL and have more reliability with the tweeter, I'd try a series 10 mfd cap and .45 mH inductor (18 AWG OK) parallel with the tweeter. This adds only about 15 degrees of phase (I believe) and if you think you need to add some capacitance stack a small value poly cap, like a .47 mfd. I like to use a mix of electrolytics and poly caps with vintage speakers. I believe I hear the difference but I might be convincing myself that I hear it. I did a similar thing with some EPI 100's. I re-built them to sell them but ended-up keeping them.
You said that you liked the sound with your NAD, so maybe the best thing to do is to leave them alone. Like the adage, "if it ain't broke..."
Thanks for the reply. My bad! I mentioned the series cap value, but there is a 0.23 mH parallel indusctor for a 2nd order high pass. Low pass is also 2nd order.
One thing I have yet to do is open 'em up and look at the crossover and make some measurements.
Jerry
My Polk 7b's always liked ample wattage.
Back in the late 70's I bought mine new (2 pairs) stacked them on their sides, tweeters to the outside, and eventually drove them with a Carver Cube (at a claimed 200w/ch). My best sound was with a room placement along a line diagonal, 2/3rds into a squarish room.
I never thought to mod them though, only add to the size of image (to make them more like Polk's 10b, which had twin 6 1/2" drivers per enclosure).
Enjoy your find!
I had one of those carver cubes for a while. Never seemed to have any low end though.
I've now tried the Polks with two different NAD integrated amps - the one with the huskier power supply (C350) has noticeably deeper and more solid low bass. There's that matching thing again.
Jerry
...Could very well be, but I wouldn't have noticed as I bought mine with an Audio Pro B250 Subwoofer.
Subwoofers were getting big when I wasted coin on mine. I say wasted because I just had no clue at the time that efficient speakers could deliver the goods - that was "so 60's" and 60's was "old".
How we learn.
I always thought that was a great subwoofer.
Jerry
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