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B652 Modifications- Upgrades?

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  • Pete Basel
    replied
    Re: B652 Modifications- Upgrades?

    Thanks, so I think this is correct now:
    Attached Files

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  • steveeboy
    replied
    Re: B652 Modifications- Upgrades?

    Originally posted by Pete Basel View Post
    Nice work comparing the different mods. I wasn't sure if I was following your description of the Dennis Murphy mod, is this correct below: Are the drivers wired in phase?
    Pete,

    you have the woofer correct.

    According to the schematic Dennis Murphy was kind enough to send me, the tweeter circuit is slightly different.

    You have it cap, then 2 ohm resistor, then the 1 ohm resistor and inductor paralleled from that point.

    Dennis Murphy had the cap and then the two resistors paralleled from it--the 1 ohm connected to the + pole of tweeter, and the 2 ohm connected to the .330mH inductor.

    The phase is not inverted.
    Attached Files

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  • Whitneyville1
    replied
    Re: B652 Modifications- Upgrades?

    On "projects" like these, you've got to know when to say "good 'nuff" and quit throwing money at them. J. Richards has cooked up several bookshelf speakers in the "bargain basement" price range using MCM drivers. Minus cabinets and such, better sounding speakers can be built for about $65 a pair. I'm assuming you have a saber-saw, electric drill (cordless is better) and some (bunch) of clamps.A router is a BIG bonus, but a "scrolling" (free-head) saber-saw and the narrow scrolling blades will do a 4" diameter cut-out. A "no-name" or reconditioned "Roto-Zip" type tool (get a heavier duty one than the 1.1 amp Dremel). You can buy surface mount drivers. While not "ideal", many very good designs have been built with them. Double the money, many, many times the performance.

    Leave a comment:


  • Pete Basel
    replied
    Re: B652 Modifications- Upgrades?

    Nice work comparing the different mods. I wasn't sure if I was following your description of the Dennis Murphy mod, is this correct below: Are the drivers wired in phase?
    EDIT: SCHEMATIC WAS WRONG - SEE LATER POST #22 FOR CORRECTION
    Last edited by Pete Basel; 07-13-2014, 02:02 PM.

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  • steveeboy
    replied
    Re: B652 Modifications- Upgrades?

    SO,

    I finally got a chance to do an A/B comparison with three sets of B652s all modified with bracing and polyfill as suggested by Zaph. Also replaced internal wiring with 16g speaker cable.

    1. Straight Zaph Crossover design

    2. b652 with GRS 8 ohm woofer upgrade and a slightly modified Zaph crossover with some ideas from the "cabrini" project found on here-johnny richards design. For woofer there I used a 1mH coil with a 6uF + 10ohm shunt circuit with tweeter circuit same as original Zaph

    3. A Dennis Murphy designed crossover for which he was kind enough to send me the schematics. That one is .8 mH coil in series with woofer with 3ohm resistor and 12uF cap paralleled across leads. And 10UF cap in series with tweeter,then 2 ohm resistor and .33mH coil parallel across leads AND 1 ohm resistor in series with tweeter. I used the more expensive Dayton polypropylene capacitors for the tweeter in these.


    Prior to this test, I had only used the modified speakers as part as my desktop near field set up. I power them there with a SURE tda7498 amp and run them with an optimus passive subwoofer.

    For the test, I set the modified b652s up on a yamaha 773 AVR feeding a vintage Sansui b2101 power amp as" set a" and "set b" and switched back and forth. I compared all three sets to each other and picked the best sounding ones for each round.

    I used a FLAC files of Pink Floyd "Dark Side of the Moon."


    I was astonished at how much power was needed to get any kind of volume out of the b652s. I would never be able to play the Sansui amp at that high a level with my main speakers--Cerwin-Vega PD-9s. I mean the neighbors would call the cops for sure. Crazy how inefficient the b652s are compared to the CVs. Crazy too how little bass there is from these bookshelves at any volume. I guess the sub under my desk REALLY helps them out.

    Of the three modded b652s, the Dennis Murphy crossover one had the best sound. They sounded the best during the test and they also sound the best in my near field desk set up. They had the nicest high end and mid range. The Zaph crossover set with original drivers was second. bass was not really that different from the straight Zaph modified speaker set, but the way the high end sounded just didn't seem as "shimmery" or clear. The B652s with the new woofers were a distant third for sure. The set with the GRS 8 ohm woofers aren't "right" with that slightly modified Zaph crossover. They just sounded weak. I am going to replace the GRS woofers with some of the PE original 4 ohm woofers and run a straight zaph crossover there.

    I do think the tweaks are worthwhile, and I want to let people know that with the new sets of b652s, to my ear the Dennis Murphy crossover sounds better than the Zaph one.

    So, while I really appreciate all that I have learned working with these B652s, I think I am pretty much at the end of my tweaks.

    Leave a comment:


  • Whitneyville1
    replied
    Re: B652 Modifications- Upgrades?

    For ~ $12 worth of XO parts and some "sweat equity" in modding the enclosures I have learned a lot of what's "worthwhile" and "what you gain" from this laboratory of a pair of off the shelf speakers. I considered changing drivers "cheating" for me. Using the B652's tweeter and an MCM mid-woofer ( a 5 1/4" would work), for ~$40-45 a pair, I'm pretty darn sure I can build a better speaker, if using one of the B652's drivers was a requirement. It surprised me what I learned from a pair of $33 speakers.

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  • steveeboy
    replied
    Re: B652 Modifications- Upgrades?

    I had a bad woofer in a 652 so I bought some buyout woofers from PE and threw them in there. They were the GRS 9s PE had on close out back in Spring.

    I also did the Zaph mods too (xover, bracing, polyfill, and upgraded internal wiring with heavier gauge speaker wire)...

    I asked on here for some tweaks to the Xover based on the GRS9 specs. You can search for that, the experts here just gave me some adjusted values for the woofer.

    I think the upgraded woofer did sound better, but as others suggest it is not cost effective unless you get a steal on the new parts. Since my b652s were bad and PE sent me a new pair, I considered the woofer upgrade "cheap" since it was being done to a "Free" pair of b-652s.

    Currently, I am running the b-652s with a passive old optimus passive subwoofer powered with a Sure tda7498 amp and it sounds great on my desk. I think the b652s are fun to mod if you just want to get into it. And PE has great customer service and the people on this forum are very helpful.

    Leave a comment:


  • Tin_Ears
    replied
    Re: B652 Modifications- Upgrades?

    Originally posted by johnastockman View Post
    Sure, spending even $20 more for a couple new tweeters defeats the price-point purpose. For the same price as the stock '652s, you could get a raw knock-down kit and start with a solid foundation...which will offer much more improvements and benefits regarding SQ than using the stock boxes. Those "mods" I incorporated did not cost hardly anything. Most have scrap left over and laying around, plus some extra chunks of acoustic damping. I wouldn't go out and buy some dowels and poly/Dacron fill for these speakers, but I have a lot of that stuff accumulated over the years. It took about 15 minutes, I got to show my nephew how to do it, and he noticed a bit better SQ by just doing those 2 things. So I mainly do it to show skeptical sorts how much is left on the table just by the omission of those two simple things. I never thought about spending more on tweeters and/or XO parts after I examined the cabinets. But fiddling around with them could lead to learning a little, so that part has value. Fine for two braces and some Dacron batting, but anything beyond that would be better used & spent with a solid foundation/cabinet to begin with.


    John A.
    Good points, John. I'm sure I can talk my buddy into the dowel rod reinforcement and extra poly fill mods... especially if I provide the materials. BTW, I'm just a novice but I'd guess those two mods are the best time/money spent on these.

    Leave a comment:


  • Whitneyville1
    replied
    Re: B652 Modifications- Upgrades?

    The tweeter isn't really a total pig, it's just crossed to too high as built. It's a single 5.6 uf cap going to a 4 ohm tweeter so by P-E's own calculator, that's about 7KHz. The woofer can't play half that high without hurting your ears, and the tweeter can play 3.5 KHz or a little lower fine. Soooo, just going with cheesy 1st order "textbook" cross-over, L1~.6uH for some BSC and C1~11mF will be better than nothing. You really can't do much harm. Here, a small (20 gauge) inductor is your friend.

    Leave a comment:


  • johnastockman
    replied
    Re: B652 Modifications- Upgrades?

    Sure, spending even $20 more for a couple new tweeters defeats the price-point purpose. For the same price as the stock '652s, you could get a raw knock-down kit and start with a solid foundation...which will offer much more improvements and benefits regarding SQ than using the stock boxes. Those "mods" I incorporated did not cost hardly anything. Most have scrap left over and laying around, plus some extra chunks of acoustic damping. I wouldn't go out and buy some dowels and poly/Dacron fill for these speakers, but I have a lot of that stuff accumulated over the years. It took about 15 minutes, I got to show my nephew how to do it, and he noticed a bit better SQ by just doing those 2 things. So I mainly do it to show skeptical sorts how much is left on the table just by the omission of those two simple things. I never thought about spending more on tweeters and/or XO parts after I examined the cabinets. But fiddling around with them could lead to learning a little, so that part has value. Fine for two braces and some Dacron batting, but anything beyond that would be better used & spent with a solid foundation/cabinet to begin with.


    John A.

    Leave a comment:


  • Whitneyville1
    replied
    Re: B652 Modifications- Upgrades?

    I didn't address the woofer. The buy-out woofer and the OEM woofer in the B652's are just about the same beast. To get much improvement from a better woofer, you need a bigger enclosure, so for ~$150 in parts, you can build Paul Carmody's ClassixII's. I think it's my favorite "get you feet wet" in DIY design. It's easy to build, and it has the eye-opening sound that store speakers don't have until the "listening room" price range.

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  • Tin_Ears
    replied
    Re: B652 Modifications- Upgrades?

    I don't intend to burst the OP's bubble but... building new enclosures plus redesigning and replacing the crossovers seems inappropriate for these drivers. I'll just restate that I think these should be left alone and used as inexpensive systems for very casual listening. I can't see going to all that trouble and expense for these. I dunno... maybe just lower the crossover to 5KHz with a single coil on the woofer and change the cap value on the tweeter?

    The above stated, I do intend to build arrays with these same buy-out woofers, 3" buyout mids and cheap 50 cent tweeters. But those will be 8 feet tall and mounted on unfinished open back 4x8 plywood sheets. I already have some MCM bi-amp plates with built-in crossovers for the 3's and tweets and Yung SW plate amps to run the 6.5's. It's play... but hoping the great multitude of drivers used will compensate for the low limited excursion abilities of the drivers. We'll see...

    Again, I don't intend to burst the OP's bubble but if one is going to put so much time and money into making some nice MT speakers I think spending a bit more on drivers makes sense because the single drivers will be pushed much harder than in arrays. Arrays are a different animal because so many drivers are needed that the cost could run up to thousands and excursion is kept to a minimum so maybe these will be fine.

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  • Whitneyville1
    replied
    Re: B652 Modifications- Upgrades?

    Zaph's mod put's some BSC on the woofer and some woofer shaping (Zobel-like), moves the XO from a 1st order at about 7Khz (!!!) to a 2nd order @ closer to 2.5Khz, which the tweeter can handle. A non-resonate enclosure bigger than the about 6.2 net stock tightly stuffed above the woofer with loose fiberglas (I used nearly 2 lbs.) and some very very thin fiberglas behind the woofer (mattress topper would be fine) in either a 15 or 12 Liter enclosure (net volume) with the stock drivers make a big SQ improvement at the cost of "power handling". A 11-12L enclosure gains you nearly 10 Hz lower F5, about 5Hz lower F3. The 15 liter enclosure nets you a full 10Hz lower F0, F3, and ~12-14 Hz F10. It also helps tame that nasty 100-200+ Hz hump in a small box. With everything I've done to them, they're just passable audio speakers. They make decent side and upper front "surround" speakers, and a pair of them can pass for a center channel.

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  • SirNickity
    replied
    Re: B652 Modifications- Upgrades?

    You already have them so that's something to consider, but in general, I don't see the point of buying cheap speakers and then spending 2x the price trying to make them sound like better speakers. Just buy better speakers. If you have the itch to modify things, buy a kit or build your own instead.

    The B652 is what it is, and to be substantially more apparently requires a larger box, bracing, a better crossover, and a better tweeter. But hey, you can keep the woofer and terminal cup. ;)

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  • johnastockman
    replied
    Re: B652 Modifications- Upgrades?

    If you try to use textbook formulas, you're using a fixed number like 4 or 8 ohms, for a number that varies. No driver is ever a constant impedance across its useable freq. range, so if you use say, 8 ohms in your "formula", it will not cross where you "assumed" it was going to. It could be 10, 12 15 or maybe 20 ohms at your chosen cross-point. You might be able to get a marginal result if you can find the impedance plot/graph and take note of what the impedance is at the crossover frequency. That will get you closer. I think PE has those simple textbook calculators on the site here, so find the impedance at whatever freq. you're using and use that number in the formula. I just got a pair of those speakers for my nephew for some background tunes in his kitchen. There was a tweeter recommendation, but I can't recall right now. The best improvement (without changing drivers and XO) came from adding in a couple of internal braces, side-to-side and front-to-back and some correct acoustic damping material in the right amounts. I just used some 1" thick Dacron quilt batting to line the inside. We listened before and after, I took my usual evaluation notes, and we both agreed that bracing and acoustic damping made a noticeable improvement. Not night/day, but you could hear it with the bass and midrange being a little more defined and less fatiguing. If you do make any mods, let us know what you think...more opinions/impressions are always good.


    John A.

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