displacement and sensitivity - AVS Forum
Forum Jump: 
 
Thread Tools
post #1 of 21 Old 04-03-2010, 01:35 PM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
lets say, i want to build a mtm speakrs, my mids are zaph audio 5", rated at 87db/1w. If i use 2 in a mtm config, would the sensitivity of the system increase to 90 db/1w? I ask because i am hoping to use this w/ a ribbon cross at 2.5K. The ribbons at 96db/1w.
datranz is offline  
Sponsored Links
Advertisement
 
post #2 of 21 Old 04-03-2010, 01:38 PM
AVS Special Member
 
gooki's Avatar
 
Join Date: Apr 2002
Location: Queenstown, New Zealand
Posts: 3,812
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Yes at 1 watt input you would see an increase of 3db.

International HDDVD Screenshot Archive (Full 1080p Images): www.hdmovies.co.nz
gooki is offline  
post #3 of 21 Old 04-03-2010, 01:52 PM
AVS Special Member
 
Bill Fitzmaurice's Avatar
 
Join Date: Nov 2009
Location: New Hampshire
Posts: 9,478
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Liked: 1284
Quote:
Originally Posted by datranz View Post

use 2 in a mtm config, would the sensitivity of the system increase to 90 db/1w?

Yes and no. The half-space 1w sensitivity would go up by 3dB. But below the baffle step frequency you're not going to get 90dB, it will roll off down to 84dB.
One of the reasons for the MTM is baffle-step compensation. If you have an 8 ohm 87dB tweeter, for instance, and a pair of 8 ohm 87dB midbasses and you configure the crossover and baffle step correctly you can end up with 87dB/2.83v throughout the speaker bandwidth.
In your case if you want to get that 90dB/watt full bandwidth you'll need to find a way to keep the midbasses in half-space, such as wall mounting.

Bill Fitzmaurice Loudspeaker Design

The Laws of Physics aren't swayed by opinion.
Bill Fitzmaurice is online now  
post #4 of 21 Old 04-03-2010, 02:28 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,115
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 197 Post(s)
Liked: 912
speaker sensitivity is limited by the lowest sensitivity driver in the system (more or less). mating a high sensitivity ribbon to a pair of low sensitivity drivers might not be the best option. 18sound has a high sensitivity 8", 8nmb420 iirc...yes, here it is:
http://www.eighteensound.com/index.a...roduct&pid=256

that might come really close to a sensitivity match and that will have many other benefits that i won't argue here.

Listen. It's All Good.
LTD02 is offline  
post #5 of 21 Old 04-03-2010, 02:34 PM
AVS Special Member
 
Looneybomber's Avatar
 
Join Date: Sep 2006
Location: Lawrence, KS
Posts: 4,668
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Liked: 23
Quote:
Originally Posted by LTD02 View Post

speaker sensitivity is limited by the lowest sensitivity driver in the system (more or less). mating a high sensitivity ribbon to a pair of low sensitivity drivers might not be the best option. 18sound has a high sensitivity 8", 8nmb420 iirc...yes, here it is:
http://www.eighteensound.com/index.a...roduct&pid=256

that might come really close to a sensitivity match and that will have many other benefits that i won't argue here.

8" woofers in an MTM and a ribbon in the middle will likely have the CTC spacing of the woofers at 10-11". How do you make that work with a crossover point of 2500hz?

YID DIY
Looneybomber is offline  
post #6 of 21 Old 04-03-2010, 03:11 PM
AVS Addicted Member
 
LTD02's Avatar
 
Join Date: Oct 2003
Posts: 16,115
Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 197 Post(s)
Liked: 912
the 8" that i pointed to has about the same sensitivity as the ribbon, so no need for an mtm design...just a simple tm should be fine.

edit: but crossing a little lower would still be advised, as the 8" may be beaming more than the ribbon at 2.5khz.

Listen. It's All Good.
LTD02 is offline  
post #7 of 21 Old 04-03-2010, 04:34 PM
AVS Addicted Member
 
penngray's Avatar
 
Join Date: Feb 2006
Location: Florida
Posts: 26,779
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 29
Quote:
Originally Posted by datranz View Post

lets say, i want to build a mtm speakrs, my mids are zaph audio 5", rated at 87db/1w. If i use 2 in a mtm config, would the sensitivity of the system increase to 90 db/1w? I ask because i am hoping to use this w/ a ribbon cross at 2.5K. The ribbons at 96db/1w.

Is this your G3 ribbon project? Great price on those

If you want to stick with the comercial designs maybe the SB Acoustics drivers with their > 90 dB sensity.

But my choice would be the new TD6M from John @ AE speakers. I believe they will be shipping at the end of April ($150/each initial "preorder" soon).

It is not "open-minded" to reject knowledge - Bob Lee
penngray is offline  
post #8 of 21 Old 04-05-2010, 05:36 AM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 944
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 19 Post(s)
Liked: 38
Quote:
Originally Posted by datranz View Post

lets say, i want to build a mtm speakrs, my mids are zaph audio 5", rated at 87db/1w. If i use 2 in a mtm config, would the sensitivity of the system increase to 90 db/1w? I ask because i am hoping to use this w/ a ribbon cross at 2.5K. The ribbons at 96db/1w.

Amplifiers are essentially voltage sourcing devices so when you put two speakers in parallel, the impedance halves and you get double the power for the same input voltage.

So, if your speakers are 8ohm nominal, then your sensitivity spec is for a 2.83V input. When you hook the speakers in parallel, your amplifier will put out 2W, and thus so you will end up with 93dB SPL. So if your ribbon is 96dB for a 2.83V input, then your woofers will only be 3dB down.

Ribbons tend to beam quite a bit as you go higher in frequency, so you might consider going with a gentle shelf filter to pad down the lower levels of the ribbon by ~3dB and leave the highs tipped up a bit (to get back to a flat power response in the room). If you're clever with the xover design, then you might be able to do this with just one additional cap...so not a huge cost. Worst case you'd need to add a capacitor and a resistor.

Another thing to keep in mind is that in order to get more sensitivity from another driver, either the cabinet needs to get larger, or you need to accept less low frequency extension...Hoffman's Iron Law.

-Mike Bentz
~It's all about compromise~
MBentz is offline  
post #9 of 21 Old 04-05-2010, 05:46 AM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 944
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 19 Post(s)
Liked: 38
Quote:
Originally Posted by Bill Fitzmaurice View Post

But below the baffle step frequency you're not going to get 90dB, it will roll off down to 84dB.

That doesn't tell the whole story...unless you're outside in an open field.

In a typical home setting, if your front baffle is relatively close to the front wall (as if often the case), then you don't have any baffle step issues to deal with. Flush mounting on an infinite baffle would be the extreme scenario of this behavior, and that's how the drivers are measured (in the engineering world at least).

In fact, anywhere the system polars are wide enough (and the boundaries are close enough to not comb-filter), then you could even see 93dB or even up to 99dB depending on speaker position. That's also assuming the walls are perfectly reflective, but that's never the case.

If you're going to pull the speakers way out into the room, then I would recommend choosing a wide Q porting alignment and turning a bit high...and then you don't need to pad anything down and waste precious amplifier power (or really, voltage swing in this case). But then you better sit really close so that the comb-filtering doesn't dominate. I'd say a rough rule of thumb would be about half the distance of the shortest reflection path...so maybe 3ft or so? So basically a studio monitor configuration.

-Mike Bentz
~It's all about compromise~
MBentz is offline  
post #10 of 21 Old 04-05-2010, 05:50 AM
Advanced Member
 
MBentz's Avatar
 
Join Date: Jun 2006
Location: Chicago
Posts: 944
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 19 Post(s)
Liked: 38
Quote:
Originally Posted by Looneybomber View Post

8" woofers in an MTM and a ribbon in the middle will likely have the CTC spacing of the woofers at 10-11". How do you make that work with a crossover point of 2500hz?

Technically that's too high for even a pair of 5" too if you want to match polars.

I suppose they could always be splayed to fire wider on the front baffle to help keep the DI down.

Bose Panaray?

-Mike Bentz
~It's all about compromise~
MBentz is offline  
post #11 of 21 Old 04-05-2010, 08:19 AM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
thanks everyone for replying with so much info. Its almost too overwheming. But i will find my way to comprehend everything since i like this hobby enough. Got to start somewhere.
datranz is offline  
post #12 of 21 Old 04-05-2010, 09:01 AM
AVS Special Member
 
kbgl's Avatar
 
Join Date: Mar 2005
Posts: 1,647
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by datranz View Post

thanks everyone for replying with so much info. Its almost too overwheming. But i will find my way to comprehend everything since i like this hobby enough. Got to start somewhere.

Two 5 ohm resistors will reduce the ribbon output to 87 dB. Different resistor values will let you adjust up or down from there if needed. The 96 dB sensitivity is not an issue at all. The required 2.5k x-over point is an issue, and will mean that the midbasses need to be very clean to 3k or higher for the best results.

Can your amp handle a 4 ohm speaker load?
kbgl is offline  
post #13 of 21 Old 04-05-2010, 09:17 AM
AVS Special Member
 
kbgl's Avatar
 
Join Date: Mar 2005
Posts: 1,647
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
These Peerless 5.25" HDS drivers are about $29 each. A sealed .6 cu-ft box (.3 cu-ft per woofer) should have an f3 of 84 hz.

http://www.parts-express.com/pe/show...TOKEN=17686603
kbgl is offline  
post #14 of 21 Old 04-05-2010, 10:51 AM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
this will be my music only system. I am thinking of an emotiva upa 2 amp w/a sub crossed at 80hz. my reason with 2 mids is because i want it to be at least 100db at 9ft away.
datranz is offline  
post #15 of 21 Old 04-05-2010, 10:53 AM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
Quote:
Originally Posted by kbgl View Post

These Peerless 5.25" HDS drivers are about $29 each. A sealed .6 cu-ft box (.3 cu-ft per woofer) should have an f3 of 84 hz.

http://www.parts-express.com/pe/show...TOKEN=17686603

thats a great price, ordered 4. thanks man.
datranz is offline  
post #16 of 21 Old 04-05-2010, 11:33 AM
AVS Special Member
 
kbgl's Avatar
 
Join Date: Mar 2005
Posts: 1,647
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by datranz View Post

thats a great price, ordered 4. thanks man.

For the record, I haven't used those drivers, but they look good based on the specs. I've been very pleased with two other Peerless HDS drivers that I have used.

I think you will be happy with them, but dang that was a quick decision!

You might need more than two for that kind of SPL. Might be a good idea to port them. Box will need to be bigger though I think. Maybe someone can model the response for you.

Specifications: *Power handling: 110 watts RMS/155 watts max *VCdia: 1" *Le: 0.8 mH *Impedance: 8 ohms *Re: 5.36 ohms *Frequency response: 57-7,000 Hz *Fs: 58.5 Hz *SPL: 87 dB 1W/1m *Vas: 0.31 cu. ft. *Qms: 4.32 *Qes: 0.56 *Qts: 0.49 *Xmax: 3.5 mm
kbgl is offline  
post #17 of 21 Old 04-05-2010, 11:54 AM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
Quote:
Originally Posted by kbgl View Post

For the record, I haven't used those drivers, but they look good based on the specs. I've been very pleased with two other Peerless HDS drivers that I have used.

I think you will be happy with them, but dang that was a quick decision!

You might need more than two for that kind of SPL.

well, the spec looks pretty good up to 5k. i was also kinda looking at the zaph audio 5" but this has a higher power handling.
datranz is offline  
post #18 of 21 Old 04-05-2010, 12:03 PM
AVS Special Member
 
kbgl's Avatar
 
Join Date: Mar 2005
Posts: 1,647
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Liked: 10
Quote:
Originally Posted by datranz View Post

well, the spec looks pretty good up to 5k. i was also kinda looking at the zaph audio 5" but this has a higher power handling.

How big is your room? How much more than 100 dB are you after?

There's two kinds of power handling. One is thermal. I think these may be good there due to the copper voice coil, and venting. The other is excursion. These drivers should be pretty clean at 3mm excursion, but I don't know how loud that will be. Ported should get you a couple more dB than sealed at the same excursion.
kbgl is offline  
post #19 of 21 Old 04-05-2010, 12:33 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 datranz View Post

lets say, i want to build a mtm speakrs, my mids are zaph audio 5", rated at 87db/1w. If i use 2 in a mtm config, would the sensitivity of the system increase to 90 db/1w? I ask because i am hoping to use this w/ a ribbon cross at 2.5K. The ribbons at 96db/1w.

The sensitivity will increase 6dB if they're wired in parallel and 0dB for series.

The efficiency in both cases will increase 3dB.
Drew Eckhardt is offline  
post #20 of 21 Old 04-05-2010, 01:34 PM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
Quote:
Originally Posted by kbgl View Post

How big is your room? How much more than 100 dB are you after?

There's two kinds of power handling. One is thermal. I think these may be good there due to the copper voice coil, and venting. The other is excursion. These drivers should be pretty clean at 3mm excursion, but I don't know how loud that will be. Ported should get you a couple more dB than sealed at the same excursion.

well, i dont think i will listen that loud but its nice to know i can get there.
datranz is offline  
post #21 of 21 Old 04-05-2010, 01:35 PM - Thread Starter
Advanced Member
 
datranz's Avatar
 
Join Date: Feb 2008
Location: fontana, california
Posts: 955
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 11 Post(s)
Liked: 29
Quote:
Originally Posted by Drew Eckhardt View Post

The sensitivity will increase 6dB if they're wired in parallel and 0dB for series.

The efficiency in both cases will increase 3dB.

thanks.
datranz 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