Newb speaker questions about a subwoofer

micahwc

micahwc

May 14, 2012
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#1
I'm trying to understand this but it's all kind of new to me. I was looking at a lot of different speakers and I found this:

18" Subwoofer Driver Speaker / Sub Woofer / Raw Speakers

1: The speaker has a sensitivity of 102, so if I understand correctly this speaker measures 102db at 1 meter with a 1 watt input. My Acme Low B2 has a sensitivity of 93db, so assuming the same distance from the speaker, and the same wattage of amp, the New Madrid will be roughly 9db louder, so almost twice as loud as the B2. Is this correct?

2: The frequency graph is a little hard to read because it's blurry when you zoom in, but it appears that it stays above 90db from about 45hz to 2khz. My understanding is that bass guitar is primarily from about 30 to 400 for fundamentals (5 string with low B) and then of course overtones higher than that. This frequency graph appears to me that it would work well as a dedicated bass guitar speaker. Does this appear to be the case? (I guess assuming tone is decent, which can't really be determined by a graph can it?)

3: Putting numbers into the DIYaudio speaker box enclosure calculator seems to have left me at a dead end as the "QTC must be greater than the QTS". I don't know if I'm blind or if it's not listed, but I don't see a QTS measurement listed on the description of the subwoofer. What should I put for the QTS measurement in the calculator? I found the answer to this, I want to get as close to .707 as I can while keeping the QTC higher than QTS.


Thanks in advance for any help understanding this.
 
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#3
@BassmanPaul knows his stuff, so I'm not countering his recommendation, but if you ignore it, read on... Buying can be less expensive than building.

I'm going to discourage you from building a cab for that speaker. I don't see an Xmax spec and you can't really model it without. I hate to hate, but the cabs they sell don't have a great rep here. For a cheap driver, that's too much money to pay without full specs. MCM equivalent is $50 less with full specs and the dimensions you need to properly model in winISD.

http://www.mcmelectronics.com/content/ProductData/Spec Sheets/55-2984.pdf
MCM Audio Select 18'' Die Cast Professional Woofer - 700W RMS | 55-2984 (552984) | MCM Audio Select

I will bet Paul's next paycheck that the MCM is a good speaker, and the specs are probably mostly close. At least those involved in modeling it. I have its little brother in 15" in a sealed cab and the specs I measured were pretty close to published.

Add $20 and you can get an Eminance with not only good specs, but plans for several cabs with specs on those and free shipping form PE: "Eminence Sigma Pro-18A-2 18" Cast Frame Driver" from www.parts-express.com!

Plans: http://www.parts-express.com/pedocs/more-info/290-427-eminence-sigma-pro-18a-2-more-info-1309.pdf You're going to need this if you don't know or want to learn the specs and modeling. Count on months of learning.

Specs: www.parts-express.com/pedocs/specs/290-427--eminence-sigma-pro-18a-2-specifications.pdf

See the note on SPL, Eminance measures it right.

Shop around:
18'' Woofers within Woofers - MCM Electronics Category
Pro Woofers, Subwoofers & Midrange Speakers in the Speaker Components Department at Parts Express | 31
US SPEAKER - 18" Speakers - 18" speakers by Eminence Speaker, 21" woofers, JBL, EV, RCF, Beyma, Peavey, Celestion, P.Audio, Ampeg, Crate, Jensen, Fane and Pyle. 18" bass speakers & 21" bass speakers. Find the right 18" woofer here.

Others listed in the sticky below.




Other suggestions:

1. What Paul said
2. Check @basscooker to see what a custom sub would cost you.
3. Check Fender Rumble Club to see if a Rumble 15 has been paired and proven with a B2
4. Read the Bible! https://redirect.viglink.com/?forma...The Speaker Builders Bible from Parts Express
5. Read the rest of the links under "Build discussion links and tools" @ AMPS FAQ!! Info on OHMS, Allsize RIGS-OverUnderPowerCabs DIY TechTalk-Links (about 3/4 down the sticky thread 1st page).
 
#6
I can't view the parameters with my poopy phone lol

But Qts is the total Q or Quality of the driver which needs the electrical and mechanical qualitys of the driver. or electrical = Qes and Mechanical = Qms
so you can calculate Qts if you have the Qes and Qms

by the way your observation of sensitivity ratings is correct and using drivers with higher Db ratings
aabsolutely saves a lot of amplifier power

likewise the 102db rating is absolutely complete bull crap

large coils like 4inch voicecoils typically have much lower sensitivity and likewise takes a lot of wire to make such a large voicecoil which increases inductance of the coil. high inductance coils reduce the capability of the speaker to produce high frequency. so typically 4inch 18" speakers don't go much above 1k

and likewise this looks like a cheap ceramic 18" I doubt it goes over 93 to 94db and since you stated the frequency chart is showing 45hz at 90db it's definitely nowhere close to102db it wwould take a pair of very amazing 18s to touch 102db

anyway Qtc is total Q of the speaker
in a enclosure. and has to do with the response of the speaker in a certain volume so Qtc would not be included in ts parameters for a speaker.

basically the 98db sigma pro that was recommended is a excellent recommendation it has lower inductance or Mh and has good sensitivity. basically if you double speaker area you gain 3db so a pair of sigmas would be 101db

so yeah the 102db rating is bullcrap most 4" voicecoil 18" are low around 94/96 db
 
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