Infinite baffle Sub? Is it for me?

[Octavia]

+1 on the Eminent Tech rotary woofer. Just give Bruce Thigpen a phone call and see if he can help you with designing the right manifold space. He's really helpful, easy to talk to and I'm sure if it can work he'll be the one who can figure it out and if not he'll be honest and tell you so.

 

[JapanDave]

Now we are getting somewhere about your purposes, albeit way out of my competence as mega-buck home theater. You are right to visit this forum just like somebody with money in the stock market (even with a financial adviser) needs to read lots about investing and has to start somewhere. For sure, your issues aren't the minutiae of driver parameters so beloved at this forum. You need to have system design addressed first.

Best is to read Floyd Toole's book because it deals with the whole world of reproducing sound in real rooms, not just the short strokes of driver selection just as you would read books on investing.

Returning to your question about bass, and I'm just guessing, I suspect you need an earthquake sub and then a bottom octave of music sub, then good speakers in pairs above. I say this because system design (and final acceptance testing and tuning) becomes immeasurably simpler as you break up the frequency compass and use separate amps. BTW, separating the speaker ranges substantially reduces amp power requirements (which is based on the statistics of sound and goes haywire as the range gets bigger) and restores some sanity to the balance-of-power problem you've run head-first into.

There is no defensible criterion called objectively "flat" and ultimate setting is by feel, guided by microphone snapshots of performance. Start early in setting up a measurement system and your baseline snapshots.

Nice that you have the help of these Erskine people, I guess. But there is no practical way to shape super-low freq room response or to anticipate room boost. So another reason to separate out earthquake sounds* and organ music and bass... so you can wrangle them separately.

I buy my amps at the Salvation Army and feel any dollar spent on gussied-up or high-power amps wasted money that is better spent elsewhere (except for driving electrostatics).

Ben
*Ooops, I mean recorded earthquake sounds if you have the heart in Japan to watch those disaster movies about tsunamis and earthquakes.

Thanks for the comments.
When I say flat, I meant to the house curve flat, but I do have a few room modes that cause some problems.

Hey Dave,
The IB is generally speaking the most fragile alignment when such high power is available as the lack of a restoring force the "box" normally provides is missing. The driver is totally reliant on it's suspension for protection from mechanical dammage. A very large IB array of many drivers could possibly work if wired to limit power.

I think what happened was sort of a rookie mistake. I thought you had four LMS drivers when I "helped" in the bridging... The image of the Sony SACD advert with the rusty sledge hammer and the butterfly comes to mind... I know of another LMS user that crashed 6 at one shot but never really came out on the forum to tell the story. The LMS really needs additional clearance beyond X-max in the motor... 30mm X-max / 48mm X-$$$ as you now know. The thing has 1/2kg mms and a powerful motor 60mm X-mech might not have been sufficient... What's another slice of magnet and a longer pole piece cost on that driver ~$10. But is there 60mm under the bottom spider in the basket??? This would likely lead to another mode of failure the stretched/torn spider. If it's not one thing...

I can say that the end table box I designed long long ago looks like it could help get you into the low teens with some headroom. Looking at the LG web it seems the amp would be capable of 350V p-p bridged 175V per channel, any way you look at it, single driver stereo or bridged into four drivers series parallel the driver is at it's limit. Some feeling out of the system and it's setup/limiters could give you stable results. The amps huge dynamic headroom is uncommon and must be managed with care/respect.

Not to worry, I do/did have 4 subs, I just did not have the boxes built so I wirred the bridge amp into the one sub. I replaced the damaged sub and wired into one channel, cut gain in half and applied the HPF. I watched WOTW last night and on rather moderate volume I could sometimes hear a very small aluminum sound which suggests at that volume it was at its limits. Not quite the max output I would ultimately like.

After much thought and research (I don't know why I did not consider this first) the IB approach seems the best for me. As I understand it with an IB you get better efficiency the lower the frequencies go. It would be very simple to add an IB sub my theater and at the same time I think I could probably be safer as well.

What I mean is that the IB designed woofer seems to be much more predictable. Something that I would be able to deal with and not only that all the consensus is that it gives a far better sound as well.

Anyway, I am still open to thoughts and criticisms.

 

[bentoronto]

You are right to favor a "house curve" over ruler-flat. But flat or a bit curved, I think you'll find them no better than suggestions. (Unless you are building a commercial movie theater... but maybe even then.)

Ben

 

[Octavia]

Dave given that your room is a concrete chamber you might consider using DSPeaker Antimode unit with whatever subwoofer system you end up with.