Active crossover info for S7 load (LE15A, LE85 w/ HL91 lens)?

[FoolForARadio]

That's what I have, in 5.25 cubic foot unported cabinets, although there is a rectangular adjustable slot in the front on each cabinet. I have been advised (here) to install ports, and I plan to. Anyway, I am daydreaming about active crossovers - any advice, or can you point me to where this has been covered, if it has? Are these speakers good candidates for active crossovers? What crossover system would you recommend? And what about amplification choices? Right now I'm using a Magnavox 8802 amplifier - could I still use it as one of the amps? Thanks...

[HCSGuy]

I've played with my S7 load with both an adjustable Rane (Forgot the model #) and a JBL M552 - they're both decent sounding, and adjustable enough. M552's are usually $125 or so on Ebay. It's been a couple years since I had mine up and running, so I don't remember what crossover point I liked best. If you do pursue this, make sure to put a protection capacitor on your LE85 to keep DC out of the driver - those diaphragms are expensive and hard to get! If your driver is 16ohm, I think JBL recommends a 20uF Non-polarized capacitor in line with the driver. If it's 8ohm, use 40uF. These are their recommendations for drivers with a lowest crossover point of 500hz, per their 5235 owner's manual.

[Lee in Montreal]

What crossover system would you recommend?

Hi

I don't think that your choice of active crossover depends on your speakers, but rather on what type of adjustments you expect from the crossover. I own a simple analog Behringer CX3400 and a bell&whistle DCX 2496. In all honesty, I still prefer the simple analog unit, and cost is perhaps only $120usd for a brand new one.

51647

[FoolForARadio]

I've played with my S7 load

So what did you think? Absolutely worth doing or not so much? Thanks for the advice about the protection capacitors...

[HCSGuy]

Was it worth it? Absolutely. I was forced into it by a LE15A that went out to the reconer as a 16ohm and came back 8ohm, and I didn't think to check the impedance upon receipt, but put them on the shelf for a couple of years in ignorant bliss. There's nothing noteworthy about the stock crossover - you can either build a better modern one, or go active and get some adjustability. Go with a basic analog crossover and you can't screw the sound up to bad. After changing to the active crossover, my S7's definitely sounded better than they ever had before. considering you can get the protection caps and a basic active crossover for less than $200, and reverse it all later, I'd go for it. Hopefully you have a good second power amplifier lying around, too.

[more10]

Absolutely worth it. You will get more detail.

But you need to figure out how to do baffle step compensation. You need to increase output with 6 db below ~300 Hz, depending on the size of your baffle. If you put a filter before the amp, the size of the components will be much smaller than if you put it after the amp.

I solved baffle step by dividing my bass unit (4530 with e145) from my midrange (2118h) at 300 Hz.

Get a 3-way filter, should be in the same price range as a 2-way. You will have use for it if you decide to go 3-way later. You can always wire it as 2-way.

Behringer I don't trust, I had one that broke the first night i used it. Put it next to my 4530, could't take the vibrations I guess.

DBX 234(XL) (Harman product), LAB ACN3C, JBL 553. Simple Linkwitz-Riley filters all of them. If you want to go digital, miniDSP 2x8 kit (http://www.minidsp.com/onlinestore/detail/7-minidsp-kits/flypage/73-minidsp-2x8-kit?sef=hcfp), but you will have a new hobby :-). With a digital filter you should be able to do baffle step filtering.

You don't need very much power for the amp driving the compression driver. About 1/10 of the amp driving the woofer. A class-A amp?

[FoolForARadio]

$99 for the Behringer CX3400 shipped plus some xlr-rca cables and some 20uF caps is cheap enough to find out if I like it. Do I need the caps to protect the tweeters if I'm using tube amp (Magnavox 8802?) For the LE15A's I've got a Fisher X-100 being fixed up right now, but I can use the amp section of a big Yamaha integrated I've got in the meantime.

[HCSGuy]

I've attached two pages from JBL's 5235 owner's manual; sorry for the poor quality. These cover the protection caps as well as adding power resistors to make the inductive part of the HF speakers load more manageable. If you're using a tube amp for HF, this seems more critical. (I added the red box)

[FoolForARadio]

Thanks for the info and the attachment. This is not as plug and play as I had hoped. It's amazing how quick I can get in over my head! So 20W 160 Ohm resistor across amplifier outputs for my 16 Ohm LE85's. Parts Express has 20 Watt 80 Ohm resistors - can I combine in some fashion? And would the resistor across the speaker terminals also be necessary? Thanks...

[HCSGuy]

If you put two 20w 80ohm resistors in series, you'll have the equivalent of a 20w 160ohm resistor. I have zero experience with tube amplifiers, but the Magnavox seems like a pretty simple vintage design. For this reason, I'd go with both sets of resistors, just to be safe, unless someone chimes in with experience with your amp (or ask on AudioKarma for more info). You'll lose a couple DB of sensitivity, which should be fine as this is for home use. My builds are usually with Bryson or Parasound SS amps, which are extremely stable, so I skip the resistors and just put the capacitor in series with the HF Driver.

[Eaulive]

If you put two 20w 80ohm resistors in series, you'll have the equivalent of a 20w 160ohm resistor.
Actually you will have a 40W, 160ohms resistor.

[FoolForARadio]

So, across the amplifier output posts a 10W 10 Ohm + a 10W 150 Ohm should be equivalent to 20W 10 X Resistance (16 Ohms), that is 20W 160 Ohm, and 5 10W 7.5 Ohm resistors should get me 50W 2 to 3 X resistance (50W 37.5 Ohms) across the LE85 terminals.

Any problems doing it that way? Those are values Parts Express has. And if I chicken out, how about one of those T-amps from PE for the high end? Does the fact that they have a volume control compromise anything?

[Eaulive]

So, across the amplifier output posts a 10W 10 Ohm + a 10W 150 Ohm should be equivalent to 20W 10 X Resistance (16 Ohms), that is 20W 160 Ohm, and 5 10W 7.5 Ohm resistors should get me 50W 2 to 3 X resistance (50W 37.5 Ohms) across the LE85 terminals.

Any problems doing it that way? Those are values Parts Express has. And if I chicken out, how about one of those T-amps from PE for the high end? Does the fact that they have a volume control compromise anything?

If you put two different resistors in series, their power rating won't add up since the dissipation will not be equally split between the two.
In the case of a 150ohms and a 10ohms, the first one will dissipate 15 times as much power than the latter.
I.E. when the current going through them create a 10W dissipation (250mA), the 150ohms dissipates 9.375W, the 10ohms only 625mW

[HCSGuy]

Eaulive's right, I'm wrong on the power handling - thanks for busting out the voltage divider rule, Eaulive!

[Jonis]

Actually you will have a 40W, 160ohms resistor.

Are you sure? I'm not at all.... but intuitively I would guess that power capability is only doubled when the resistors are in parallel. It's been a long time since I had the simple circuits class that are thrust on ME's. I stand by nothing I've said.:D

[grumpy]

Power capability is a function of each device. If both are the same value,
the power dissipation is split evenly between them, regardless of series or parallel.
If they are not the same value, they still can dissipate their rated capacity in watts,
but one may well blow (reach its maximum capacity) before the other.

[Jonis]

Thanks Grumpy. It always nice to have people around who know (and remember). Eaulive, my apologies.:)

[FoolForARadio]

So to comply with the pages attached by HSCGuy it appears to me I need a 20 Watt 160 Ohm resistor for the amp and 50 Watt 32-48 Ohms for the tweeter. If I want to use a tube amp with output transformers, which is the case. I can't find these values but I can find 10W 75 Ohm or 10W 68 Ohm and I have read that the actual impedance on the driver is more like 12 Ohm anyway, so 10X resistance might be less than 160.

So what combination of resistors will give me what I need? Is it the case that I can sum both watts and ohms if the resistors are of equal values and in series?

And thanks for entertaining what are dumb questions for most of you. I know some of you do for a living what I am bumbling around trying to do. I promise I'm not going to sell this stuff, I just want to hear it.I actually am reading Electronics for Dummies but trying to proceed with this project in the meantime.

[grumpy]

Is it the case that I can sum both watts and ohms if the resistors are of equal values and in series?

Yes... and I seriously doubt you'll need resistors with that much power rating...
3-10W would probably be plenty unless you're planning on sustained deafening
levels (that such drivers are capable of). The recommendations are for what I'd
call industrial usage (e.g., cinema or hard P.A. use).

[FoolForARadio]

Thanks - I was getting around to wondering if the power handling was as important as the resistance, and these are just for garage use and fooling around with.

[grumpy]

They are suggested to keep your tube amp alive and happy.