[Garbz]

OMG Alert not headphone related

I added a subwoofer to my system ages ago and since then have played with various ways of integrating it with my main speaker system and now I'm plain out of ideas.

- I've crossed it over really low, but my main speakers are weak in their bass,
- I've crossed it over at 100hz, but because my main speakers are ported there are loads of phase problems and bloating.
- I've blocked the ports of my main speakers but that gives a very nasty sound degredation in midrange, bass sounds wonderful though

So I need to somehow crossover the sub with the speakers. I'm using an integrated amp with pre-outs going to sub controller / amp. My options are now:

- Place some kind of high pass filter between amp and speakers.
- Modify speaker crossover to add high pass filter.
- Build an entirely separate preamp to handle the crossover and volume controls (don't want to do really).

So does anyone have any other ideas? Or can someone help me with the first 2? Is it even possible to add a highpass filter inline with the speaker cable, or is modifying crossovers the only way? I'd also rather not operate on my crossover so the first option would be best if possible.

 

[velmeran42]

This won't be a super helpful response in and of itself, but try posting this question on www.diyaudio.com . It's where I learned everything I know about speaker design and speaker amps. They're knowlegable and helpful there.

 

[Garbz]

I am not that desperate yet.

 

[velmeran42]

I'll throw in my 2 cents then, if you aren't posting over at diyaudio yet.

If there is any way to put a line level highpass infront of the amp with out effecting your sub pre-outs, I'd go that way if possible. It would be much cheaper, and you can afford to tweak the thing with out going broke. I added a high pass filter to an existing amp by cutting the traces on the board right before the chip-amp and air wiring the crossover there. I don't know if you can do so, but it's much easier than trying to tear into a speaker level crossover.

I'll also throw in that www.madisound.com has good components for good prices (Eagle resistors, Bennic capacitors, and Madisound air core inductors) should you decide to do any speaker level work.

One last thing, throwing a high pass in line with the speakers will only work well if the speaker doesn't have one internally already, otherwise your response gets all funny with the two interacting.

 

[Garbz]

Ok thanks. If I could have done it pre - amp then it would be easy

. Modifying an amplifier that expensive while it's still under warrenty is also out of the question.

I got some positive responses over at diyhifi (not to be confused with the idiots of a similar name) regarding changing the subwoofer crossover to a different curve which I'll try next week.

 

[regal]

I have found that a highpass filter on mains usually isn't needed.

Sounds like you're problem is that your mains have too small of a driver to integrate with a sub. Usually a minimum of 6" driver is needed to integrate with a sub.

 

[Garbz]

They are 6.5"s. The problems are definitely phase responses. When ports are used the phase of the sound bounces around rather widly at the tuning frequency. That is having problems integrating with an almost phase flat sub. I will try a different kind of filter for the sub though. Carlosfm on diyhifi suggested bringing the filter poles in at different frequencies. I'll play with that after exams.

 

[SHLim]

Have a look at Elliott's project 103- Subwoofer Phase Controller and Project 107- Phase/Polarity Inversion Switch.
http://sound.westhost.com/project103.htm
http://sound.westhost.com/project107.htm

The good thing is - the plan is free. The bad thing is, there no pcb for it and not sure how many have tried them.
He also has many project that relate to sub woofer that you might find interesting.


Have fun,
Sam

 

[Garbz]

lol PCBs are for wusses

I acutally previously looked at all the subwoofer articles on his site some 6 months ago. I incorported a lot of his ideas into my current controller. Including the phase switch which I already have.

If you read the article in detail and the ones liked from the phase controller you'll realise why it won't work though.

I did have another idea (funny enough before I had my morning coffee which doesn't happen to often). Suppose I filter the input to the integrated with a second order HP filter cornered at 100hz. Now at -12dB/octave that would be ~26dB down at 20Hz. Then I put a separate second order LP filter which gives a 26dB gain in before the subwoofer circuitry.

So basically I'm pre-emphasising the signal into the integrated, and then reversing it with a post-emphasis after the integrated but before the subwoofer's own controller. If my theory is right than at 20Hz the signal will be roughly 1:0.05 or 1/20th of the actual which, if I use low noise design techniques, should be quite manageable. I'll run the math through in detail next week as I need to study for my filtering exam anyway

 

[SHLim]

Have a look at this active crossover board. It might give you want you wanted. If you search a little deeper, you can find the pcb layout and mod for your own use.
http://www.diyaudio.com/forums/showt...0&pagenumber=1


Have fun,
Sam

 

[Garbz]

Nah still not what I'm after, although I will probably head in that direction anyway. I do not think there is a viable electrical solution to my integration problem. I think I'll just keep messing with the filter untill i get the least interactions, and then live with it.

 

[blaken]

Do you have an spl meter?

If you do I would recommend taking some measurements to see what is going on. If you head over here http://www.hometheatershack.com/foru...downloads.html

you can register and download a nice excel spread sheet and test tones to help you graph your room response. Or you can download room eq wizard and set it up if you want to go to the trouble of using a pc as a source to do your testing. Its worth the time.

I used a behringer feedback destroyer pro DSP-1124P to integrate my sub into my system. It worked great and I have a pretty stable house curve from 16Hz to 200Hz
You can read the bfd guide here http://www.hometheatershack.com/forums/bfdguide/

You can pick up a bfd at parts express for $99 its worth every penny.


Edit: Have you tried just moving the sub? If you want to find optimal placement the easiest thing to do is crawl for bass. Set the sub where you normally sit, play some test tones, and crawl around the edge of the room until you find a place where the sub sounds best and set it there. It sounds crazy but it does work. Helps if you have an spl meter too.

 

[Garbz]

Room interactions are not much of a problem. I've been using speakers with EQs for years and it doesn't take long to eliminate most room modes. The problem I have is that even after they are eliminated the bass is indistinct thanks mainly to the fact that there is some overlap in the frequencies the speakers and the sub play which is causing driver related phasing, not room related.

Thanks for the links though. I do use computer as source sometimes and I'll play around with it to see how it all works. Also moving my sub is somewhat out of the question. The sheer size of it makes it impossible. I designed it to be overkill from the start, and yeah it was. http://www.garbz.com/blog/projects/subwoofer.html

/EDIT: As a matter of interest do you EQ the total response of your system or just the sub?

 

[blaken]

Just the sub but I sweep past the cross over point and make adjustments so the overlap is smooth. If I were you I would head over to htguide.com The DIY there is the place to get information for DIY home audio.


Thats a nice sub but is in no way overkill.

You should look into infinite baffle if you want to see what overkill is. Cult of the infinitley baffled These guys are crazy.

Here this is what I am talking about.. and btw this is 1 of 2 the guy has in his attic

I have a sono-sub design myself its for my HT but does pretty darn well with music too.

Now if only I could get myself to stain the woodwork and put it up

 

[Garbz]

Why do you think the box is so big? Could it be that the driver was chosen for future infinite baffle in mind.

With my small room dimensions also applying gain below 40hz the sub had to be de-tuned. Otherwise an 17Hz sine wave caused my windows and picture frames to shake, lol. Overkill for my needs anyway.

Will check them out thanks.