Home Theater Forum and Systems banner

1 - 16 of 16 Posts

·
Registered
Joined
·
38 Posts
Discussion Starter #1
I am getting two of the LMS-Ultra 15" drivers. I have been messing around with WinISD and had some questions. First off, I have a 12' x 26' HT, completely sealed, with superchunk bass traps, OC703 on front and back walls, and at first reflection points. My current subs (Rythmiks and Mael-X) show an ample amount of room gain(12 db at 20Hz, even more lower). Now, for the questions.

A 3 cf sealed box(Qtc of .514) with a 3600W max input(CE4000 on 220) will have 26mm cone excursion at 10Hz, and 10-20mm from 50Hz down to 20Hz. Is that accptable margin of safety? SPL shows 118db at 70Hz, and 108db at 20Hz.

To contrast, a LMS 15" with 2 of the AE 18" PR's tuned to ~16 Hz will have the same max SPL output, but will be still cranking out 114db at 16Hz. The question is, is it worth it? The 1600g PR's are on sale for $100 each, and then I would need some kind of filter. Are room gain db's sonically equivalent to PR dbs? Does room gain apply in the same manner to the PR box, increasing my headroom even further?

Two of the "high profile" LMS builds(Jai and Robert's) went with PR's. I would love some opinions on this sealed vs. PR topic. Thanks!
 

·
Premium Member
Joined
·
1,941 Posts
A 3 cf sealed box(Qtc of .514) with a 3600W max input(CE4000 on 220) will have 26mm cone excursion at 10Hz, and 10-20mm from 50Hz down to 20Hz. Is that accptable margin of safety?
For these drivers yes.
To contrast, a LMS 15" with 2 of the AE 18" PR's tuned to ~16 Hz will have the same max SPL output, but will be still cranking out 114db at 16Hz. The question is, is it worth it?
It depends if you feel you need the extra output at 16Hz and up at the expense of say 10 Hz, which for me is perfectly acceptable. Nevertheless the LMS ultra models pretty good in a sealed enclosure... and that's its major strength (very linear even in a small enclosure)... so either option will be great.
The 1600g PR's are on sale for $100 each, and then I would need some kind of filter.
I wouldn't worry too much about that with such a driver, but you may use a 13 Hz high pass if you want.
Are room gain db's sonically equivalent to PR dbs? Does room gain apply in the same manner to the PR box, increasing my headroom even further?
I don't quite understand your question, but a PR acts like a port... A PR will add low frequency extension down to the tuning point.
Two of the "high profile" LMS builds(Jai and Robert's) went with PR's. I would love some opinions on this sealed vs. PR topic. Thanks!
For any other sub, I automatically recommend a ported design, but with such a capable driver, you can't go wrong with any design. Ilkka's measurement threads will help you decide, you must have a look!!
 

·
Registered
Joined
·
38 Posts
Discussion Starter #3 (Edited)
I don't quite understand your question, but a PR acts like a port... A PR will add low frequency extension down to the tuning point.
Let me ask that question about sound quality another way. Let's say a sealed sub in room has 12db of room gain at 20Hz, which takes its 100db output up to 112db. The same driver in a PR enclosure has an actual output of 112 db at 20Hz without the benefit of room gain. Would they sound exactly the same? The reason I ask is that those with PR subs comment about the extra "punch" or "slam" they get over a sealed sub, and I can't imagine there is any difference if the levels are the same.

Thank you for all the helpful responses.
 

·
Registered
Joined
·
2,431 Posts
Your room will affect the PR enclosure and sealed enclosure the same way. If you room has 12db of boost at 20 hz, both alignments will be affected by it.

Are you modeling both drivers off of the 3600w? I'm showing that one driver would be over 45mm excursion at 10hz in a 3ft box with that much power. The drivers are 4ohm so the CE4000 will be giving about 1200w to each if you run both off of one amp. Use a 3rd order Butterworth HPF at 8hz in your modeling. That's what's in the CE4000. If you reduce the box volume to 2.4ft per driver you should be ok throwing 3600w to each driver with no filter.
 

·
Registered
Joined
·
38 Posts
Discussion Starter #5
Ricci:

I had one parameter wrong--your model is correct. I have to shrink my box to be safe--closer to 2-2.5cu. ft. Thanks for the bit about the filter in the CE4000. I should have two of them, so it would be 3600W potentially to each driver.

Thanks!
 

·
Premium Member
Joined
·
1,941 Posts
Your room will affect the PR enclosure and sealed enclosure the same way. If you room has 12db of boost at 20 hz, both alignments will be affected by it.

Are you modeling both drivers off of the 3600w? I'm showing that one driver would be over 45mm excursion at 10hz in a 3ft box with that much power. The drivers are 4ohm so the CE4000 will be giving about 1200w to each if you run both off of one amp. Use a 3rd order Butterworth HPF at 8hz in your modeling. That's what's in the CE4000. If you reduce the box volume to 2.4ft per driver you should be ok throwing 3600w to each driver with no filter.
Hi Josh,

Are you using peak excursion while modeling? If so I don't think that is really representative of program material. I use RMS instead, moreover throwing 3600W at 10 Hz in a movie is not very likely to happen, so I guess the 45 mm won't happen in real life either. I believe peak values simulate sine waves more than anything else so I'd keep the 3 ft box to benefit from better efficiency down low :T
 

·
Premium Member
Joined
·
1,941 Posts
Mike, what do you mean??
RMS excursion is less than peak excursion at a fixed power input (check WinISD).
 

·
Premium Member
Joined
·
1,941 Posts
Yeah I see what you mean.... exactly. To represent program material, modeling should be using the RMS value of cone excursion regardless of peak excursion. That is IMO more realistic unless one plays sine waves...
 

·
Registered
Joined
·
2,431 Posts
All that I'm saying is that the LMS drivers will bottom out hard and damage themselves if driven too hard. He will have enough power on hand to do it in the 3 foot box. It might take a very rare event to do it, but I'd rather not take the chance that it ever does. The further you get out there into high excursion, high power combos, the less room for error that you have. The LMS drivers hard bottom at 44mm xmech and they sound clean all the way up until "whack!".
 

·
Registered
Joined
·
38 Posts
Discussion Starter #12
I got one done(except for painting that MDF edge black where the driver is recessed). It's sealed, 2.4 cu. ft. internal, with 3/4" baltic birch inside, laminated with 1/2" MDF(3/4" on baffle, which has a double BB thickness), and veneered in figured walnut.

 

·
Registered
Joined
·
38 Posts
Discussion Starter #15
That is very pretty. What do you think soundwise?
I have been moving it around the room to get a smooth response at my listening positions, so that has been ongoing before an extended listening comparison session. It can take the power for sure, and it's loud.

Noooice...:T

How is the damaged CE4000 issue going?
Thanks. UPS denied the seller's insurance claim, he is appealing that claim, and my credit card company is looking into my dispute. I wish you would have put your CE4000's up for sale before I got into this mess!
 

·
Registered
Joined
·
2,074 Posts
Woah, beautiful box, Fat!! Do you have any construction pics? I've always thought that mixing materials (ply and MDF) would be beneficial to the density of the walls, but some people had concerns about the different materials expanding and contracting at different rates. Either way, very, very nice work, and I'd love to see some more detail on the veneering.
 
1 - 16 of 16 Posts
Top