Question on replacing JBL woofers with Daytons - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 16 Old 05-02-2012, 09:20 AM - Thread Starter
Senior Member
 
below90hz's Avatar
 
Join Date: Aug 2009
Posts: 310
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
Question for the gurus:

My center channel is an old JBL SC305 with two 5.25" woofers. SPECS

I would like to extend its capabilities, so I was considering swapping out the oem drivers for these Dayton ND140's from partsexpress. SPECS

The only thing is, I don't know if the SC305 freq response only goes down to 100hz because the built-in circuitry has a high-pass filter limiting it, or if it's simply a driver limitation. If it's the former, then there's no point in dropping in beefier drivers, but if it's the latter I'd like to know so I can do a cheap upgrade.

Anyone know the answer to that?

Quit readin my signature ya stupid signature reader.
below90hz is offline  
Sponsored Links
Advertisement
 
post #2 of 16 Old 05-02-2012, 09:58 AM
AVS Special Member
 
beastaudio's Avatar
 
Join Date: Dec 2010
Location: Western NC
Posts: 6,947
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 223 Post(s)
Liked: 558
The crossover for that dayton replacement will not be optimal. If you have no other choice you could give it a shot, but more than likely your performance is going to be decreased over getting another of the same jbl drivers. anytime you just do a straight driver switch, the XO would have to be adjusted accordingly and that means measurement gear and expertise that only a few have around here...

that 100hz bottom is what is called the f3 point aka where the drivers response starts to fall off drastically. with JBL, their f3's are a little more realistic than other companies that grossly overrate their response characteristics. you wont get much further down from 100hz with just a pair of 5 1/4 daytons either (in that particular cabinet at least). so basically, I would say dont mess the speaker up, you wont need much under 100hz for a center channel anyways

(European models do not accept banana plugs.)

 

"If you done it, it ain't bragging." ~ Walt Whitman

 

AE TD12x SEOS12 Build

Beast's DIY Master Measurement Thread

DIY Emminence Coaxial Surround Thread

beastaudio is offline  
post #3 of 16 Old 05-02-2012, 10:12 AM - Thread Starter
Senior Member
 
below90hz's Avatar
 
Join Date: Aug 2009
Posts: 310
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
thx for the quick reply. I need a clarification though - when you say "performance will be decreased", what aspect(s) of the speaker's performance are you referring to?

Also curious as to why you say the Dayton's won't go much farther down than 100hz? Is that a enclosure or XO limitation? or are you assuming the specs are inflated?

Thx for the help, your answers will help me develop Plan B...

Quit readin my signature ya stupid signature reader.
below90hz is offline  
post #4 of 16 Old 05-02-2012, 12:24 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 15,951
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Liked: 850
the frequency response and the level matching with the tweeter could change dramatically. at worst, the net resistance could be below what your receiver can handle and cook it.

Listen. It's All Good.
LTD02 is online now  
post #5 of 16 Old 05-02-2012, 12:30 PM - Thread Starter
Senior Member
 
below90hz's Avatar
 
Join Date: Aug 2009
Posts: 310
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
ah. I see. So how do I get around that? Buy a different crossover?

Also re: impedance - I thought I'd be safe replacing a 4ohm driver with a 4ohm driver. What did I overlook?

Quit readin my signature ya stupid signature reader.
below90hz is offline  
post #6 of 16 Old 05-02-2012, 12:39 PM
AVS Special Member
 
beastaudio's Avatar
 
Join Date: Dec 2010
Location: Western NC
Posts: 6,947
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 223 Post(s)
Liked: 558
Quote:
Originally Posted by below90hz View Post

thx for the quick reply. I need a clarification though - when you say "performance will be decreased", what aspect(s) of the speaker's performance are you referring to?

Also curious as to why you say the Dayton's won't go much farther down than 100hz? Is that a enclosure or XO limitation? or are you assuming the specs are inflated?

Thx for the help, your answers will help me develop Plan B...

That crossover was designed specifically for that driver and tweeter combo. Changing the mid to another type of driver will require adjustments to the XO to help them blend the way they are supposed to. Just one little part like if the JBL mid is a decibel more sensitive on it's own, compared to the dayton, then it wont "blend" correctly with the tweeter. Crossovers are arguably the most important part of a 2 way system. A poorly designed crossover can make a $10,000 speaker sound like a tin can, and often, a well designed crossover with just a decent set of speakers can compete with the higher priced commercial offerings. I speak from experience using a "stock" emminence crossover from PE for a coaxial design I made for surrounds. After looking a little deeper, I found a custom made XO for the exact woofer/tweeter combo I was using and HOLY COW! It sounded like a completely new speaker. There wasnt even a comparison!!

What im saying is for that speaker, with just 2 5.25 mids, you arent going to get much below 100hz. Dont get me wrong, that speaker will play lower than 100hz, it just wont be able to play below 100hz as loud as it is able to the rest of the spectrum. Once again, many speaker companies will tell you their speakers go from 40hz-20khz, when in actuality, their speaker wont come close to producing 40hz with enough OOMPH as it can the rest. the bottom number stated by JBL basically says the speaker is down 3 decibels at 100hz and will continue to drop the further down the frequency response you get. The average human can only tell volume fluctuations around 3 db's apart, so that is why the "f3" is commonly used to spec speakers. Sometimes the speaker co's will fudge and use the f5 or f6 number so their specs look better (5 or 6 db's down).

(European models do not accept banana plugs.)

 

"If you done it, it ain't bragging." ~ Walt Whitman

 

AE TD12x SEOS12 Build

Beast's DIY Master Measurement Thread

DIY Emminence Coaxial Surround Thread

beastaudio is offline  
post #7 of 16 Old 05-02-2012, 12:47 PM
AVS Special Member
 
fbov's Avatar
 
Join Date: Nov 2006
Location: Bushnell's Basin, NY
Posts: 1,014
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 28
Beast +1... What aspects of the speaker are you trying to improve?

Let's start with tonal balance. If the replacement drivers are more or less sensitive than the original drivers, the result will be bass- or treble-heavy respectively. Granted, a resistor fixes the latter, but that's an XO change. This is a big issue for my ears, second only to...

If the replacement driver Qtc is differrent, you'd expect low bass to either be boomy or lacking. That could be fixed by a port change, made difficult by use of an oval port, or by blocking off the port.

If the replacment driver frequency response is different, the XO filters will not correct the response back to flat, so there will be more linear distortion. If the replacement driver impedence response is different, crossover frequency can shift resulting in more linear distortion.

What will not happen is no sound. The change will result in a functional speaker, but it may not be any better and could be much worse. Which brings be back to your goal; you want to extend it's capabilities, but you don't say what aspect?

If we assume bass, you'd be better off with a lower Qtc replacement than this. As Curt says on his Aviatrix page, "the high driver Qts of the ND140 precludes use in a traditional vented design." Sealed is an option, but not one that extends bass capabilities.

Does this make sense?

HAve fun,
Frank
fbov is offline  
post #8 of 16 Old 05-02-2012, 01:51 PM - Thread Starter
Senior Member
 
below90hz's Avatar
 
Join Date: Aug 2009
Posts: 310
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
ltd02, beast, frank - thank you guys. your responses are exactly why i felt i should ask the gurus before I just swapped out drivers.

My next question - ok wait fbov has a point, I guess I should provide a little more insight into what I'm looking for before i go any farther.

I bought a pair of Polk Monitor 70's off newegg a couple weeks ago, which are a vast improvement over my JBL CM52's. I've owned those JBL's for about 17 years and have always been quite content with their performance, even after hearing friend's speakers that cost well into the 5-digit range. But after hearing superior speakers in my own room, I've realized I've been missing a lot.

So now I want a center channel that can dig deeper, go louder below 90hz (that's ma name don't wear it out ha HA) without sounding bright and without breaking my pockets since I am a cheap bassturd. I also need an enclosure that has the angled top because my center channel sits on the floor below my 130" screen. I was looking at the Polk CS2 which seems to be a perfect fit, but I thought if I could use my existing center channel enclosure that might help me keep cost under $100 and maybe I'd learn a few things about speaker building along the way.

So my question is...what do you guys recommend would be the best path to reach my goals?

Quit readin my signature ya stupid signature reader.
below90hz is offline  
post #9 of 16 Old 05-02-2012, 02:07 PM
AVS Special Member
 
beastaudio's Avatar
 
Join Date: Dec 2010
Location: Western NC
Posts: 6,947
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 223 Post(s)
Liked: 558
bottom line is the matching center that polk suggests to go with the monitor 70's will be your best bet. It will be the closest timbre matched to your L/R's and will show the closest performance-wise. My main question to you is: WHY would you want your center to get down into where a competent sub could easily outperform it anyways? with a center channel, it is primarily used for vocals where 80-100hz is more than low enough to take care of all of that. IMHO a decent sub is going to do what you want, and be a whole heck of a lot better at it than trying to reinvent the wheel with a powerful center and asking it to reproduce bass frequencies that it will inherently struggle with.

(European models do not accept banana plugs.)

 

"If you done it, it ain't bragging." ~ Walt Whitman

 

AE TD12x SEOS12 Build

Beast's DIY Master Measurement Thread

DIY Emminence Coaxial Surround Thread

beastaudio is offline  
post #10 of 16 Old 05-02-2012, 02:11 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 15,951
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Liked: 850
well, if you really like the polks, try using one for your center and see what happens. it seems like that is what you are looking for, an mtm horizontal, but with more bass. there are some reasons why you might not want to do that, but in your case, why not experiment and see how you like it. :-)~

Listen. It's All Good.
LTD02 is online now  
post #11 of 16 Old 05-02-2012, 02:50 PM - Thread Starter
Senior Member
 
below90hz's Avatar
 
Join Date: Aug 2009
Posts: 310
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
beast - well I used to think all I needed was a decent sub and I wouldn't worry about what my speakers could do down low, but a while ago I heard a full range center-channel in my room and was really impressed with the new dynamic it brought to my listening experience. The problem is I can't afford that particular center channel (my bro let me borrow it). I had kinda forgotten about it until I bought those full-range Polks for my mains, which made me more certain I want a center that can handle bass too, at least down to 50hz or so.

anywho, thank you both for the help. You guys' advice makes sense, sounds like I'm going to get the Polk CS2.

...when it goes on sale.

Quit readin my signature ya stupid signature reader.
below90hz is offline  
post #12 of 16 Old 05-02-2012, 06:37 PM
AVS Special Member
 
beastaudio's Avatar
 
Join Date: Dec 2010
Location: Western NC
Posts: 6,947
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 223 Post(s)
Liked: 558
The cs2 with cherry finish is on newegg right now for 129.99. Not too shabby really but I don't know msrp.

(European models do not accept banana plugs.)

 

"If you done it, it ain't bragging." ~ Walt Whitman

 

AE TD12x SEOS12 Build

Beast's DIY Master Measurement Thread

DIY Emminence Coaxial Surround Thread

beastaudio is offline  
post #13 of 16 Old 05-02-2012, 07:08 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 15,951
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Liked: 850
"Quit readin my signature ya stupid signature reader."

that is a really good one.

$130 - time, effort, frustration, and money saved by asking good questions and not building the wrong thing = free. :-)

Listen. It's All Good.
LTD02 is online now  
post #14 of 16 Old 05-02-2012, 07:46 PM - Thread Starter
Senior Member
 
below90hz's Avatar
 
Join Date: Aug 2009
Posts: 310
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 15
when I said "when it goes on sale", I meant "when it goes on even more sale", cuz i think it might hit $100 at some point. That's when ole below90hzy pulls the proverbial trigger.

Quit readin my signature ya stupid signature reader.
below90hz is offline  
post #15 of 16 Old 05-03-2012, 07:04 AM
AVS Special Member
 
beastaudio's Avatar
 
Join Date: Dec 2010
Location: Western NC
Posts: 6,947
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 223 Post(s)
Liked: 558
Quote:
Originally Posted by below90hz View Post

when I said "when it goes on sale", I meant "when it goes on even more sale", cuz i think it might hit $100 at some point. That's when ole below90hzy pulls the proverbial trigger.

Eh, just buy two less cases of beer in a month, then you got your 30 bucks

(European models do not accept banana plugs.)

 

"If you done it, it ain't bragging." ~ Walt Whitman

 

AE TD12x SEOS12 Build

Beast's DIY Master Measurement Thread

DIY Emminence Coaxial Surround Thread

beastaudio is offline  
post #16 of 16 Old 05-03-2012, 04:50 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 15,951
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 122 Post(s)
Liked: 850
another approach is to just put a quarter in the jar every time that he checks the prices and when the jar exceeds the discount, buy it. :-)

Listen. It's All Good.
LTD02 is online now  
Reply DIY Speakers and Subs

User Tag List

Thread Tools
Show Printable Version Show Printable Version
Email this Page Email this Page


Forum Jump: 

Posting Rules  
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off