500uf? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 17 Old 08-11-2018, 09:56 PM - Thread Starter
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500uf?

I'd like to try running my F15s as low as I can. Since they are ported to 50hz they need a HPF. My avr will only allow them to either be full range or crossed over to a sub.

I can use LFE+main to get full range L&R and still pick a xo to the sub. But that is too much LF for the F15s.

My idea is to use LFE+main and put a 500uf cap on the F15s to passively high pass them around 50hz.

The high pass would be 1st order but models show safe excursion with avr power. The F15s are around 6 ohms at 50hz and 500uf would be around a 53hz high pass.

Other than extra strain on the avr wasting power into the cap, does anyone see any problems with this?

I would run the xo at 120hz, so I would have overlap between 50 and 120hz plus the roll offs on either side of that. If everything is time aligned correctly it should all sum constructively.

It just seems like a shame to have speakers that can do so well at 60-120hz and then chop off that capability.

I'm not sure if it's better to add the cap before the xo, or on the woofer positive wire after the xo.

PE has the caps for $5, so there's not much risk in the experiment.
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post #2 of 17 Old 08-11-2018, 10:28 PM
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I run my new towers lfe+mains at 80hz
I set them at large and it still digs deep. I would try that also take some sweeps and see if 40hz. Looks and sounds good to. I think as long as there set to large with a crossover on your avr like mine are you will dig deep with the F-15’s.
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post #3 of 17 Old 08-12-2018, 04:45 AM - Thread Starter
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LFE+mains does sound good with the F15s, but that sends full range power to the F15s. At moderate levels everything is fine. But at high volume the 15s get out of control with low frequency. Even just 50 watts can get past xmax at 30hz.

I need at least a shallow HPF on the 15s to be safe.
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post #4 of 17 Old 08-12-2018, 06:30 AM
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I don't understand, isn't high passing them passively and using lfe + main the same as using bass management except you are only redirecting bass to the subs for all other channels besides the LCR?
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post #5 of 17 Old 08-12-2018, 07:52 AM - Thread Starter
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It's difficult to explain but actually pretty simple.

Normally bass management is at a set point between a speaker and the sub. But I don't want that. I want everything below 120hz to go to the sub. But I also want my mains to play down to 50hz. So there is some overlap. I'm not sure if any avr will let you set things up this way.

Pre outs would work since I could just set a HPF for the mains in the amp, but my avr doesn't have pre outs.

A passive HPF for the mains is my best idea.
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post #6 of 17 Old 08-12-2018, 09:44 AM
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I'm sure I'm missing something, but if your avr doesn't have pre-outs, then how are you getting the LFE to the subs?

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post #7 of 17 Old 08-12-2018, 09:55 AM - Thread Starter
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LFE+mains sends a full range signal to any speaker set to large. It also allows you to pick a xo point where anything below that point goes to the sub along with the LFE. It's just like regular bass management, but it just sends the large speakers a full range signal instead of high passing them.
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post #8 of 17 Old 08-12-2018, 10:08 AM
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Yeah I get that, but how are you connecting the amp used for the sub to the avr without a sub-out from your avr?

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post #9 of 17 Old 08-12-2018, 10:13 AM
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Quote:
Originally Posted by johnson636 View Post
Yeah I get that, but how are you connecting the amp used for the sub to the avr without a sub-out from your avr?
Has pre-out(s) for sub, but not for Front L/R.
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post #10 of 17 Old 08-12-2018, 10:15 AM
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Quote:
Originally Posted by smcmillan2 View Post
Has pre-out(s) for sub, but not for Front L/R.
See I told you it was something I was missing Thanks for clearing that up

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post #11 of 17 Old 08-12-2018, 10:26 AM - Thread Starter
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Here's an example: say you have JTR 215RTs, and a sub. Normally most would suggest using an 80hz crossover. That will just waste all the potential you paid good money for with the 215s. Instead you could run the 215s full range and still send everything below 80hz to the sub (along with the LFE). That gets you 80hz and below output from all the speakers, not just the sub. The JTRs can handle anything an avr can send to them, but the diysg kits may not be able to handle 100 watts at 20hz so they need some form of high pass.

The diysg kits that have capable woofers can play pretty darn good down to 40-50hz. To demonstrate this, setup your system with an 80hz crossover and unplug the sub. So only the mains are playing with the 80hz crossover still on. You will not hear much of any bass out of them. Now, with the sub still unplugged, turn the crossover down to 40hz. I bet you enjoy the sound of them more with the 40hz xo. But with a 40hz xo, the sub is now wasted since it isn't playing anything above that.

Instead I'm suggesting we let the mains play down to whatever range they can safely handle, and use the sub up to whatever range works best. I'm not aware of any avr that has this type of feature, probably because they assume we want a flat response and the crossover as designed is ideal for that. But we like our bass hot, and just turning up the sub level creates a huge cliff between the mains and sub. Letting the mains and sub overlap in the 40-100hz range can soften that transition and add some additional midbass.

With pre-outs, you can send the mains the full range signal via LFE+mains, and then just use the outboard amp to set the high pass. When using only an avr you need some other form of high pass to protect the woofers, which is what I'm after.
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post #12 of 17 Old 08-12-2018, 10:28 AM - Thread Starter
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No pre-outs on my avr, just the sub out, unless you consider that a pre-out. I guess it is, but not what most mean when they say pre-outs.
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post #13 of 17 Old 08-12-2018, 11:48 AM
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Quote:
Originally Posted by Samps View Post
It's difficult to explain but actually pretty simple.



Normally bass management is at a set point between a speaker and the sub. But I don't want that. I want everything below 120hz to go to the sub. But I also want my mains to play down to 50hz. So there is some overlap. I'm not sure if any avr will let you set things up this way.



Pre outs would work since I could just set a HPF for the mains in the amp, but my avr doesn't have pre outs.



A passive HPF for the mains is my best idea.


Got it. Thanks for explaining.
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post #14 of 17 Old 08-12-2018, 01:08 PM
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Passive high pass with just a capacitor won't work for most speakers due to the impedance profile of the woofers at low frequencies.

Here is what happens to the electrical transfer function when you add a 500uF cap added to the F-15 woofer:


Have you tried just running them full range off the avr? Most of the time there isn't a strong enough 30hz signal on the mains channel to drive the woofer into excursion issues on AVR power unless you are listening to heavily bass boosted dub step or something. I've played lots of bass heavy music on the F15 without a highpass using a 400w amp and without using EQ to boost the bottom end it hardly even reaches xmax before you end up clipping due to content that's in the midbass or midrange.

Another point I would like to make is that it takes 50-100w with the driver free air using low frequency sine waves to get the woofer to start sounding distressed. It is a pro woofer and the suspension does a pretty decent job controlling cone motion.
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post #15 of 17 Old 08-12-2018, 02:07 PM - Thread Starter
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@mtg90

Thanks. I was only going by the model. I had read that the eminence 8" woofers were tight and hard to bottom, but the 15" seems a lot looser in comparison.

If they can handle avr power then I guess my problem is easily solved by just running LFE+mains.

I'll still high pass the center and surrounds, but the extra midbass from the F15 L&R is a nice bonus. With only one sub I can certainly use some additional sources of midbass. The 15-40hz range seems well covered everywhere by the single sub.
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post #16 of 17 Old 08-13-2018, 04:15 AM
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That's a good idea to make maximum use of whatever bass you have from the mains, a bit like adding two more subs.

If your worried about excursion limits on the mains and have eq available in the AVR, then you could eq the 40Hz and below down by 10 or 15dB. I have Dirac in my AVR and can put in any target curve I like, I might try running the mains (ELX-115P's) full range and see if I can get more tactile midbass.
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post #17 of 17 Old 08-13-2018, 04:29 AM - Thread Starter
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I will try that. My eq only goes down to 60hz, and it only works if you turn audyssey off, so it may not work.
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