Multiple Small Subs - Geddes Approach

[ro9397]

Earl
What is the ideal recommended f3 bass cutoff for the main speakers with correctly setup multiple subwoofers?

The answer to the above question could save money & enlarge one's list of potential main speakers (& also assist w/ the speaker-to-amp interface).

Incorporating your advice has been as close as I expect to ever find to the proverbial free gourmet lunch.

[gedlee]

Originally posted by ro9397
Earl
What is the ideal recommended f3 bass cutoff for the main speakers with correctly setup multiple subwoofers?

The answer to the above question could save money & enlarge one's list of potential main speakers (& also assist w/ the speaker-to-amp interface).

Incorporating your advice has been as close as I expect to ever find to the proverbial free gourmet lunch.

There is no "ideal". You fit the subs to whatever response the mains provide. I've done this with several f3's and all of my speakers have f3's.

Yes, doing multiple subs the way that I suggest, seems to be a no-brainer. I remain unconvinced that doing anything more is required.

[gedlee]

Originally posted by cap'n todd

I hope you're not quibling about a theoretical mathematical issue which has no significant effect.

Whether it is or isn't, you will be forever open to criticism if you continue to do it wrong.

[cap'n todd]

Originally posted by gedlee


Whether it is or isn't, you will be forever open to criticism if you continue to do it wrong.

If there's another way thats more accurate that calculates as fast, I'm all ears.

[Bigun]

Originally posted by Patrick Bateman
If anyone reading this thread wants to give this a whirl, and do it cheaply, this might be an opportunity to do so.

Newegg has a $250 Polk subwoofer marked down to $100 at the moment. At that price, it's hard to go wrong.

This makes the idea of a DIY sub somewhat silly - if the quality of sound is good. Anybody heard this thing ? - makes me a bit nervous that it's BR when I was looking for a sealed unit to avoid the 'boom' box problem.

[gedlee]

Originally posted by cap'n todd


If there's another way thats more accurate that calculates as fast, I'm all ears.

Todd

Have you looked up the Morse reference that I am talking about? There is no speed of calculation penalty for doing it right. In fact, because the series converges faster, it is more efficient, fewer terms are required. If you stopped arguing that wrong was OK and looked into what I have been suggesting you would have seen that.

[gedlee]

Originally posted by Bigun

makes me a bit nervous that it's BR when I was looking for a sealed unit to avoid the 'boom' box problem.

Just seal the ports!! I've done this lots of times. Add some mass to the cone to lower the resonance, a slightly different mass for each one. You will loose efficiency with the greater mass, but if you have three or four you don't need efficiency.

[cap'n todd]

Originally posted by gedlee



Todd

Have you looked up the Morse reference that I am talking about? There is no speed of calculation penalty for doing it right. In fact, because the series converges faster, it is more efficient, fewer terms are required. If you stopped arguing that wrong was OK and looked into what I have been suggesting you would have seen that.

I'll check it out, though rewriting the code is prbably not in the works for me right now. I should rahter compare exising code to some known good FEM/BEM method and see how far off I am. I suspect its a very small error for the way I am using it.

[TRADERXFAN]

-Brought below over from another thread to which I posted by accident

Originally posted by TRADERXFAN
Since my listening room has one large opening to the rest of the house should I be thinking in terms of arranging multiple subs throughout the ground floor or can I just think about the main room?

I use what was designed to be a dining room for my listening room.
Its approx 13 x 14x9 feet high.

The rear wall is open, with a 8x8' opening, so most of that wall is this opening. Beyond this, the space opens into a 7.5' wide 2 story foyer/hallway, and then directly behind this is a mirror image of the room described -so the actual rear wall is about 35' back.

Also there is an open doorway on the left on the listening room.

The rest of the ground floor is almost entirely wide open. The house is "normal sized" I guess, not a huge house by most standards. So I assume I am still in the realm of the small room schroeder frequency, but not sure how much you can open up a room to a larger room before it clouds the way you set this up.

Going with the thinking that at bass frequencies the listener hears the room not the source, what would be the proper way to think of a situation like this?

Also, I currently use a dipole servo controlled sub, and it seems to work pretty well. However, as most things in audio, you never seem to realize deficiency until its in comparison to something better.

My first attempt to add subs:
I tried adding a 2nd, sealed, sub to this but I had a hard time getting them to sound well together. Maybe dipoles and monopoles shouldn't be mixed?

I didn't have the proper tools to measure or do spacial averaging. By ear, I did try several various setting of the phase and gain and locations in the room. Having little more than 3 walls with the mains along one, didn't leave me too many options for placement. I did build a tall stand and tried with it above the centerline, too.

I follow the Linkwitz suggestion to keep the dipole sub angled towards the listener, along the side wall, equidistant to the listener as the mains, which is also near a corner in this case.

Thanks for help.

Tony

Originally posted by gedlee
Tony

Highly couple spaces act like one room, but the subs should be kept closer to the listening space. Your coupled spaces act like one big space, but the energy can flow into one of the other spaces and then back again. This can be a negative effect if the nerby spaces are highly reverberant, but its generally not a problem.

Measurements are almost a must and they are not hard to get. I have even used a Creative Labs mic that was free with a sound card. Works fine at LFs. Software is free and any measurements are going to help.

I've used monopole and dipoles together. Its not an issue, but might be a little harder to set up.

Would you think a more enclosed room would be better for the bass performance? I chose this room mainly because I would have few issues with rear wall reflection. I wonder if it would be better to set up the listening room in a spare bedroom until I finish the basement.

Would damping still be important if it is this open? I assume so, but thought I would ask.

I do have a measurement mic, and a laptop connected up with that Room eq wizard program to do the measurments, but not sure how to go about spatial averaging. I can run a frequency sweep, that's about it. There is a real time analyzer but it doesn't capture -at least I don't think it does.

I must say that I am tempted to simplify my life and just get another dipole sub for the other side of the room to boost output and call it a day. It would be about $550 for 2 more drivers and amp. The H frame box construction is very simple. I think it would integrate well together.

Earl, I think you mentioned that dipole bass you heard was smooth like the multiple monopole sub setup but fell off 25-50 range. The negative was it costs more to do that, but maybe since I am already half way there I just get another one. Each sub uses two 12" drivers per side with the shelving circuit built in (and designed to accomodate 3 woofers per amp). The main reason I would desire to add to it is because I find that I can bottom them out with certain material.

-Tony

[john k...]

Todd,

Can you give me any information of where you specified the mic or listening position in you calculations? I can get results very similar to yours but only at very limited mic position. If I move the mic around I see wide, deep dips in the response.

I have checked my code against an FEM simulation and for similar setups I get very similar results. I do not include a term for the direct sound.