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Old 15th May 2006, 03:48 AM   #1
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Default Cheapy Passive Sub?

I am in the middle of building Zaph's Project #14

These are fairly small speakers (4" woofer), with power handling issues if driven in the lower frequency's... thus a sub is rather encouraged.

Also encouraged is a wife that doesn't crush me dead spending money ;-)

To that end, I have a theory

I am driving these speakers from a fairly cheap Sony receiver -- STR-DE598. 70w per channel (in theory ). It has a separate set of outputs "A" vs "B" (A does 6.1, B is just stereo).

So, I simply build a box out of the Dayton 8" sub, and add a passive cross over to it. I am not super sure what "dual voice coil" means, but I assume it means I hook up both "left" and "right" outputs to the same speaker? Does that mean its getting double the power?

I think I can lie to my receiver, and tell it I have a sub on the "A" set, and it will let me set the crossover value from 40-160hz, 160hz being best for power handling on the 4" woofers. Otherwise I can just add a pass xover to those as well, and maybe do it at 200hz to further help power handling.

One problem will be balancing the volumes of the sub vs mains, I guess I can just add a potentiometer to the sub (assuming its louder than the mains... which seems likely if its getting double power, and has a higher SPL @ 89db vs 85db on the 4" woofers).

Anyway... thanks for any input you guys have. Trying to avoid having to buy/build an amp for the sub... and thus save some duckets and some wife aggro
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Old 15th May 2006, 04:22 AM   #2
owdi is offline owdi  United States
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If the A and B outputs are driven by the same channels on the receiver, then having both on is like wiring them in parallel. In that case you will present too low of an impedance to the receiver.

It is a surround receiver, why not just use the rear channels.

Dan
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Old 15th May 2006, 05:03 AM   #3
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So... basically, you are saying "your receiver is happy w/ an 8 ohm speaker, if you do that madness... it will look like 4 ohm's, and mr. receiver may get quite cranky".

Sadness.

re: using rear channel... not sure how that would work. I don't think there is a mode where it is sending the same signal to the rear speakers as the fronts.

Still, even if the dual coil madness doesn't work, couldn't I sent just the left (or right) to my passive sub?
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Old 15th May 2006, 06:06 AM   #4
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I think in A+B mode, these will be in series, since I doubt if the amp maufacturer will allow for the amp to be overdriven.
All my amps have the series set up, I can notice the volume levels on A to reduce when the set B is also switched on.
Also, I doubt if there are so kind manufacturers who provide an extra set of amplifiers to power another set of speakers.

Now for setting the crossover frequency on your receiver, you cannot do it only for one set(A or B).

In case you really want to use a passive sub through set B, a low pass filter is all you need. But it needs careful tailoring to match up with the mains. In other words, it would be similar to using 3-way loudspeaker if your present mains is 2-way.
Lots of effort required.. May not be worth the effort afterall.

BTW, dual voice coils can be connected as you say, but take care of polarity.
"Does that mean its getting double the power?" - Yes

Regards,
Francis
P.S: I hate to call your by name, you are not
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Old 15th May 2006, 04:39 PM   #5
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Quote:
Originally posted by francis varkey
Now for setting the crossover frequency on your receiver, you cannot do it only for one set(A or B).
LOL. I am so dumb

Okay, so xover from the receiver is totally out (else I am only gonna send high freq's to not only the mains... but my sub... not savory).

So, I am thinking passive 4th order xover (at say... 175hz) for both my two way Zaph 14's, and my hypothetical sub (which will be that dual voice coil Dayton, hooked up to the "B" mode)
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Old 15th May 2006, 04:55 PM   #6
sreten is offline sreten  United Kingdom
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Hi,

There is no way round doing this properly.

A passive sub will cause you untold grief, unless you get the right
specification driver you will never get it right, even if you do I doubt
you'll ever get the crossover to work properly. The crossover parts
wil likely cost you more than the plate amplifier below.

http://www.partsexpress.com/pe/showd...number=300-784

Is the sort of thing you need. Note that you should use something
like WinISDPro to match the limited maximum levels of your speakers
to the subwoofer level. There is no point building a sub far too loud
for the main speakers, a less loud sub gives deeper bass. That is
choose a bass driver of the correct sensitivity for the application.

/sreten.
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Old 15th May 2006, 05:25 PM   #7
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You are a party pooper, and you get to tell my wife

Probably go with this one I guess:
http://www.mcminone.com/product.asp?...Fid=50%2D6266A

My receiver can cross over between 40 and 160hz... obviously higher the better in my scenrio. I suspect 160hz will allow me to get loud enough for my tastes, else I am still gonna need to add a passive xover to my main speakers.

btw, how do I know if I have gone "too loud"? (ie, exceeded Xmax...)
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Old 16th May 2006, 06:24 AM   #8
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Quote:
Probably go with this one I guess:
Can't make out if this one has a built in power supply, whereas the one suggested by sreten does indeed have one.

If you're going to feed the sub amp from the speaker outputs, you shouldn't set the crossover in your receiver.
Since you'll then deprive the sub's amp of a significant amount of bass info.
If you use the receivers sub-out, then you can.

My advice is to set the gain(of plate amp) starting off from its minimum upto the point where you can clearly hear the low bass.
Note that the mains should be playing as well. Try not to go much beyond that.

Hope this helps,
Francis
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Old 16th May 2006, 12:45 PM   #9
sreten is offline sreten  United Kingdom
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Hi,

I really don't understand what you think is going on.

AFAIK (i don't have HT stuff, just pure Stereo) an AV amplifier that
allows you to set the main speakers high pass c/o frequency will
route bass below that frequency to the 0.1 channel.

For the subwoofer you only set its level, you use a bypass input
so the AV amplifier can implement the subwoofer low pass.

Adding a further passive high pass to the speakers will upset this.
(And require expensive components to do properly. If 160Hz ends
up being too low, basically you should have used the 5" driver)

For max levels etc model speakers and sub in WinISD Pro.

/sreten.
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Old 16th May 2006, 04:17 PM   #10
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My n00b'ness is probably confusing you, I will restate how things are layed out in my head

Say I set the active xover on my receiver to 160hz, and all is pretty well... until I turn the volume up too loud (and excede the Xmax of the woofer on my main).

Two questions:
a) How do I know that happened?
b) What are my options at that point?

I actually have no idea if this is a reasonable concern, since I don't have any concept of how many decibels it takes to get on the loud side, nor whether my HT receiver can reach those levels.

But if it does happen (all hell breaks loose at a volume I want to listen at)... I am just wondering what I can do about it

So, say I want it louder... seems to me the only option would be to xover a bit higher to keep the lows out of the mains... say, xover at 200hz.

For the sub, the dayton plate amp can xover as high at 200hz (the other plate amp I listed only goes to 160). I suppose I won't be able to use the "sub out" out my receiver at that point (since I am sure its always crossover, and won't go higher than 160)... so I would have to use speaker input's to the plate amp for the sub, and set it for 200hz. Fine.

For the mains... I would need to add a high pass filter at 200hz.

Okay, all that was to answer "I really don't understand what you think is going on."

btw, you can see http://www.zaphaudio.com/audio-speaker14.html for Zaph's page on these speakers, and you can look at the power handling chart "Power vs excursion 1-128 watts" to get a feel for the xover values I am talking about.

Hopefully this is is all strictly acedemic, I don't suspect I will want to play these loud, ... I am just concerned since I have no idea what "loud" is
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