Replacing a 4 ohm with 30 ohm sub driver - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 17 Old 04-30-2010, 04:56 PM - Thread Starter
Advanced Member
 
UofAZ1's Avatar
 
Join Date: Nov 2009
Posts: 713
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 51
I mentioned this in the Definitive Technology speaker thread, but a few years ago I bought a pair of BP7001s that come with a 10" 30 ohm powered driver attached to rwo 10" passive radiators and powered by a 1500 watt amp. Well one of the subs was bad so Chet at DT sent me a new driver and a new amp, it was the amp that was bad, so for two years, I have had this 40 pound driver sitting in a box collecting dust.

So last weekend I am shopping at Ultimate Electronics and they have a damaged Def Tech Prosub 1000 (driver was punctured) for literrally pennies, since I have this powerful driver at home, I figure I'll put that one in. Well the issue I have is the driver that was in the Prosub is a 10" 4 ohm driver and the amp is only 300 watts, while the driver I want to use is a 10" 30 (thirty) ohm driver (the 30 ohms was confirmed by Chet at DT) and was made to handle 1500 watts (especially made for peaks above 750 watts)

My main purpose of this sub is to use it as a sumpliment to my center channel speaker only, using the speaker level inputs (which means the crossover is fixed at 80hz and I'll have the center channel crossed to my seperate SVS sub at 40 Hz so this sub will only handle 40-80hz for center duty only. This way my center bass frequency can keep up with my 7001 mains.

A few more thoughts, the driver in the 7001 is the same exact one in the supercube 1 subs and those also come with a 1500 watt amp. The dimensions of the supercube 1 has a total cubic volume of 1.172 feet while the dimensions of the Prosub 1000 is a cubic feet volume of 1.31 feet (almost the same) my concern is because the amp is only 300 watts and only has one 10 " passive radaitor as compred to the two PR in the supercube ones, and the vast differences in ohms am I foolish to install the 40 pound 30 ohm driver in place of the 10 pound 4 ohm driver.

I understand that the 30 ohms driver will be easier to drive but require alot of power to reach the same levels as a 4 ohm driver with 300 watts. but since this is gonna be a mid bass driver I won't need that much power.

Sorry so long, I know very little about subs and would appreciate any help.
UofAZ1 is offline  
Sponsored Links
Advertisement
 
post #2 of 17 Old 04-30-2010, 05:27 PM
AVS Special Member
 
Drew Eckhardt's Avatar
 
Join Date: May 2001
Location: Sunnyvale, CA USA
Posts: 2,674
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
1. Forget it without measuring. You have no idea whether the Thiele-Small parameters are going to yield acceptable performance in the enclosure.

2. You're only going to get 42W out of the amplifier due to the impedance.
Drew Eckhardt is offline  
post #3 of 17 Old 04-30-2010, 05:39 PM - Thread Starter
Advanced Member
 
UofAZ1's Avatar
 
Join Date: Nov 2009
Posts: 713
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 51
wow Drew 42 watts, well that sucks thanks for the response.
UofAZ1 is offline  
post #4 of 17 Old 04-30-2010, 08:28 PM
AVS Special Member
 
Ivan Beaver's Avatar
 
Join Date: Dec 2005
Posts: 1,639
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 41
If you want to use an amp that is rated for 4 ohms, to produce 1500 watts into a 30 ohm driver, you will need to find an amp that will produce in the neighborhood of over 11,000 (yes eleven thousand) watts into a 4 ohm load.

That is to get the required 212V voltage swing.

It will take a LARGE pro amp-mono bridged to get that.

Danley Sound Labs

Physics-not fads
Ivan Beaver is offline  
post #5 of 17 Old 04-30-2010, 11:43 PM - Thread Starter
Advanced Member
 
UofAZ1's Avatar
 
Join Date: Nov 2009
Posts: 713
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 51
Ivan, I don't want to produce 1500 watts, I just wanted to use a 30 ohm driver which I already had with a amp powerful enough to produce 40-80Hz with enough gusto to keep up with my mains, I don't listen at outrageous levels, but it appears I will have to wait for the replacement driver to arrive from DT to make my sub "original" and use that as a MBM.
UofAZ1 is offline  
post #6 of 17 Old 05-01-2010, 04:47 AM
AVS Special Member
 
flyng_fool's Avatar
 
Join Date: Aug 2009
Location: Frisco, TX
Posts: 3,425
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Liked: 71
Quote:
Originally Posted by UofAZ1 View Post

Ivan, I don't want to produce 1500 watts, I just wanted to use a 30 ohm driver which I already had with a amp powerful enough to produce 40-80Hz with enough gusto to keep up with my mains, I don't listen at outrageous levels, but it appears I will have to wait for the replacement driver to arrive from DT to make my sub "original" and use that as a MBM.

Can you get the Theile-Small parameters for the driver that is bad, and perhaps find a much cheaper after-market solution? Maybe you can find an OEM one on eBay.

Dumb enough to spend lots of cash on this junk!
flyng_fool is offline  
post #7 of 17 Old 05-01-2010, 04:53 AM
AVS Special Member
 
Ivan Beaver's Avatar
 
Join Date: Dec 2005
Posts: 1,639
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 6 Post(s)
Liked: 41
Quote:
Originally Posted by UofAZ1 View Post

Ivan, I don't want to produce 1500 watts, I just wanted to use a 30 ohm driver which I already had with a amp powerful enough to produce 40-80Hz with enough gusto to keep up with my mains, I don't listen at outrageous levels, but it appears I will have to wait for the replacement driver to arrive from DT to make my sub "original" and use that as a MBM.

I was just pointing out that with a much higher impedacne driver it takes a lot more "equalivent" "watts" to get the same output.

Most pro amps will not deliver much power into a 30 ohm load.

Let's say your amp does 100 watts at 4 ohms. That is a 20Volt output.

That is only 13 watts into a 30 ohm load-so it will take a lot "larger" amp to produce the voltage swing you need.

Yes watts is watts-but it is the voltage swing on the output that mostly determines what "wattage" an amp can deliver.

Danley Sound Labs

Physics-not fads
Ivan Beaver is offline  
post #8 of 17 Old 05-01-2010, 06:51 AM
AVS Special Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 9,566
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1312
Quote:
Originally Posted by Ivan Beaver View Post

I was just pointing out that with a much higher impedacne driver it takes a lot more "equalivent" "watts" to get the same output.

Most pro amps will not deliver much power into a 30 ohm load.

Let's say your amp does 100 watts at 4 ohms. That is a 20Volt output.

That is only 13 watts into a 30 ohm load-so it will take a lot "larger" amp to produce the voltage swing you need.

Yes watts is watts-but it is the voltage swing on the output that mostly determines what "wattage" an amp can deliver.

+1. The only logical reason one would use a 30 ohm driver is related to current. 1500 watts into a 30 ohm load is 212 volts at 7 amperes, as opposed to an 8 ohm driver that would run at 109 volts and 14 amperes. Where the power handling of a voice coil is concerned the higher the current the more heat is created, so there is an advantage to the higher impedance driver in that respect. You'd be hard pressed to find a 14 ampere capable voice coil. The disadvantage is that amps with standard topology don't put out 212 volts, and for that matter those that can put out even 109 volts are rare, not to mention quite expensive.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #9 of 17 Old 05-01-2010, 08:33 AM
AVS Special Member
 
catapult's Avatar
 
Join Date: Sep 2001
Posts: 3,824
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 12
So do you have the damaged sub and the spare driver sitting there at home? If so, hook it up and see how it sounds. You won't damage anything. Worst case it won't play very loud or the frequency response won't be very flat. Give it a try, it may work fine.

Dennis H
catapult is offline  
post #10 of 17 Old 05-01-2010, 10:33 AM - Thread Starter
Advanced Member
 
UofAZ1's Avatar
 
Join Date: Nov 2009
Posts: 713
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 9 Post(s)
Liked: 51
Well after doing some research it turns out that Chet at DefTech may be in error on his numbers. After searching Google and Yahoo it turns out the only driver sthat are 30 ohms are used in headphones, so I think Chet may have been thinking of either 3 ohms or 30 Hertz (hard to tell which one he may have meant) I went to Parts Express and found the driver that closely matches my DT driver.

http://www.parts-express.com/pe/show...number=293-656

Both drivers look and weigh the same with same specs. What has me concerned is the fact that the Supercube driver I have uses an 8 amp 250 volt sloblo fuse, while the Prosub driver it's replacing is a 3.2 amp 250 sloblo fuse. According to the link I posted the 21 pound driver is a 3.72 ohm driver which is close enough for impendence to the OEM 4 ohm driver.

Catapult, I have already hooked it upand watched "Avatar" with it using the 3.2 amp fuse and it worked and sounded fantastic. I just don't want to use it till I know for sure that I have the right fuse in and am not risking blowing the driver or amp. It's hard when the manufactorer gives you info telling you it's a 30 ohm driver, oh and Chet at DefTech is already sending me a OEM driver, but if given the choice I would rather use this massive driver I have and put it to some good use.

Thanks for the responses guys.
UofAZ1 is offline  
post #11 of 17 Old 05-01-2010, 04:22 PM
AVS Special Member
 
Drew Eckhardt's Avatar
 
Join Date: May 2001
Location: Sunnyvale, CA USA
Posts: 2,674
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 14
Quote:
Originally Posted by Bill Fitzmaurice View Post

+1. The only logical reason one would use a 30 ohm driver is related to current. 1500 watts into a 30 ohm load is 212 volts at 7 amperes, as opposed to an 8 ohm driver that would run at 109 volts and 14 amperes.

Good engineers reduce the cost of goods sold to the minimum.

The high impedance lets Definitive run a pair of 106 VRMS amplifiers in a bridged configuration straight off line voltage without an expensive power transformer.

At least one of Definitive's small high-output sub-woofers was built this way, although I couldn't tell the original poster whether it's the sub they have.
Drew Eckhardt is offline  
post #12 of 17 Old 05-01-2010, 04:39 PM
AVS Special Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 9,566
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1312
Quote:
Originally Posted by Drew Eckhardt View Post

Good engineers reduce the cost of goods sold to the minimum.

The high impedance lets Definitive run a pair of 106 VRMS amplifiers in a bridged configuration straight off line voltage without an expensive power transformer.

At least one of Definitive's small high-output sub-woofers was built this way, although I couldn't tell the original poster whether it's the sub they have.

Eliminating the power transformer has its obvious benefits, but output devices capable of that voltage are quite expensive. That's the reason why the trend has long been to higher current capacity amps driving lower impedance loads, rather than higher voltage capacity amps driving higher impedance loads. If the reverse was the less expensive option that's what would dominate the market.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #13 of 17 Old 05-09-2010, 07:23 AM
AVS Special Member
 
Servicetech571's Avatar
 
Join Date: Apr 2008
Posts: 4,691
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
You can thank the automotive industry for promoting low ohm speakers. Traditionally they only had 12V to power the amps before DC-DC converters became popular in the 80's.
Servicetech571 is offline  
post #14 of 17 Old 05-10-2010, 01:08 PM
AVS Special Member
 
Jim Hef's Avatar
 
Join Date: Sep 2003
Location: Yardley, PA
Posts: 4,340
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Can't the OP simply put an ohm meter across the terminals to see what it reads?
Jim Hef is offline  
post #15 of 17 Old 05-10-2010, 02:25 PM
AVS Special Member
 
Stereodude's Avatar
 
Join Date: Jan 2002
Location: Detroit Metro Area
Posts: 9,907
Mentioned: 2 Post(s)
Tagged: 0 Thread(s)
Quoted: 494 Post(s)
Liked: 534
Quote:
Originally Posted by Jim Hef View Post

Can't the OP simply put an ohm meter across the terminals to see what it reads?

Well, that will only measure the DC resistance, which isn't really the important characteristic.
Stereodude is offline  
post #16 of 17 Old 05-10-2010, 04:04 PM
Advanced Member
 
Aaron Gilbert's Avatar
 
Join Date: Jan 2002
Location: Bonney Lake, WA
Posts: 819
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
I have worked with Chet at Definitive Technology for many years, and he was not in error. The BP7001SC subwoofer driver is indeed a nominally 30 ohm driver, and will be exceedingly underwhelming when driven by the ProSub1000 amplifier, which is designed for a four ohm woofer.

If your intent is to use the ProSub1000 cabinet and amplifier, then your best solution is to purchase the ProSub1000 driver. Given that the cabinet is passive radiator design, I would not advise just throwing any woofer in there which seems like it might be close. Manufacturers are not in the habit of providing T/S parameters for any product, much less currently selling product, and who can blame them? So, the only chance you have to find a match would be if you already had a working ProSub1000 driver and the equipment to measure the T/S parameters yourself.

Alternatively, you could build a cabinet for your BP7001SC woofer and amplifiers - though it may end up somewhat larger than the ProSub1000.
Aaron Gilbert is offline  
post #17 of 17 Old 05-10-2010, 04:11 PM
Advanced Member
 
Aaron Gilbert's Avatar
 
Join Date: Jan 2002
Location: Bonney Lake, WA
Posts: 819
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 11
Quote:
Originally Posted by Stereodude View Post

Well, that will only measure the DC resistance, which isn't really the important characteristic.

True, but the DC resistance measurement is closely related to a woofer's nominal impedance. A 30 ohm nominal woofer measures about 26 ohms DCR, an 8 ohm woofer measures around 6.5 ohms, a 4 ohm woofer around 3.2 ohms, etc. So while the DCR indeed will not tell you the impedance at a specific frequency or set of frequencies, it will at least allow you to determine the nominal impedance of your driver. Obviously, a 4 or 8 ohm woofer is never going to measure 26 ohms unless the coil is defective.
Aaron Gilbert is offline  
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