RS100P, TM or MTM? High crossover point... - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 30th April 2014, 01:09 PM   #1
diyAudio Member
 
Join Date: Apr 2014
Location: North of boston
Default RS100P, TM or MTM? High crossover point...

New here, and to speaker building. Signed up to ask about this...

So I'm building new speakers for my computer desk. They'll be mostly against the wall, at ear level, and not raised off the desk or anything. Listening distance is about 4ft.

I'd like to try out the new dayton RS 4" paper woofers, because they're frequency response is ridiculously flat out to like 8khz, which should make the crossover design super easy. I did some modeling using WinPCD and a simple second order filter crossed between 3.5 and 5khz depending on the tweeter looks like it would work really well. I like the idea of letting the drivers do the work, rather than coming up with a more complex crossover like I needed to do with a 2-way using aluminum drivers (DA175 and silkies).


Anyway, I have two options I'm considering.

2-way, RS100P and the vifa XT25SC, crossed at 4khz.

MTM, RS100P and the dayton ND16, crossed at 5khz.


The 2-way should be *really* easy, as the tweeter and woofer overlap by like 3 octaves, and both have super flat responses and easy to manage impedance curves. This would almost certainly be a naturally good speaker, with minimal effort.


But I like the looks of an MTM better, and I would learn more designing it. The narrow vertical dispersion is also interesting (though I'm not sure how much of a benefit that actually is?). I decided to switch to the ND16 so I can mount the drivers very close (2.6"CTC, about 5.5khz). Unfortunately, that's a very high crossover point for an MTM, and I don't understand enough to know if the close spacing will make up for it.

So, advice? Other configurations I should consider?

Last edited by sniper1rfa; 30th April 2014 at 01:32 PM.
  Reply With Quote
Old 30th April 2014, 04:08 PM   #2
diyAudio Member
 
Join Date: May 2010
Location: MN
Sounds like you've already set up everything you need to simulate the MTM lobe-null-lobe angles/frequencies/etc. yourself.
  Reply With Quote
Old 30th April 2014, 04:27 PM   #3
diyAudio Member
 
5th element's Avatar
 
Join Date: Oct 2002
Location: England
Unfortunately with an MTM the C-C spacing that one uses is the spacing between the mid/bass drivers as it's the interference pattern between the two that controls the vertical directivity.

If you want to make sure that the effects of this are minimised (a very good idea for a desk based project imo) then you need to cross over at at least the frequency that the wavelength the C-C spacing dictates. Preferably lower. Most MTMs aren't crossed over low enough imo. In thise case, with a C-C of around 13cm we're looking at an xover frequency of around 2.5kHz. You'd probably be better off using the Vifa_DQ25SC and crossing over around 2.2kHz.

The XT25SC + RS100P will have around 8.5cm C-C, which does allow for a 4kHz xover. The SC will handle 3kHz without issue though, so you might consider lowering the xover point for a wider primary listening lobe.

Out of your two design choices the first makes the most sense.

Going MTM doesn't net you anything over an TM except the ability to go louder. It's the same with a TMM. You don't get more bass extension, in fact a lot of the time you get less because people compromise on the cabinet volume and use less net volume per driver in the dual woofer systems. This inevitably loses you bass extension and raises low end group delay. Halving the load impedance, especially with how low it can dip once the crossover is introduced, does not make for an easy to drive pair of loudspeakers either. Then you've got the added cost and more constraining/difficult design decisions to work with around the more complex systems.


For a pair of near-field, wall reinforced, computer speakers, I would be very surprised if you needed the extra SPL capabilities of two drivers.

There is also the benefit that the XT25 has poorer off axis dispersion than a standard 25mm dome. This is a good thing as it will reduce the reflections from the desk that they are presumably going to be placed on.

I know that building a dual woofer system has a certain allure about it, but all things considered I'd go with the TM.
__________________
What the hell are you screamin' for? Every five minutes there's a bomb or somethin'! I'm leavin! bzzzz!
  Reply With Quote
Old 1st May 2014, 04:54 AM   #4
diyAudio Member
 
LineSource's Avatar
 
Join Date: Sep 2003
Location: SiliconValley
I would build the TM because:
-- it would sound more coherent at the short computer desk listening distance;
-- you are not concerned with high SPL/dynamics;
-- the extra box volume will support a round port, plus rear stuffing for a clear midrange.

An LR2 Xover acoustic slope should provide enough M--T overlap for a smooth vertical soundstage shift even at the short listening distance. The 4" RS100P will just start beaming above the quarter wavelengtht (13550 ips / (4*3.6" dia)) ~ 940Hz. A quick sim with XDIR suggests a 2.4K-2.8KHz xover keeps one large lobe, but a 3KHz+ Xover begins to generate side lobes. These lobes will bounce off the desk.

I would use the Vifa XT25SC for its superior SPL/freq, either naked or with the small mounting plate to minimize T-M distance.

Let us know if the Dayton RS100P is really flat out to 8khz. How does it sound full range... no tweeter?

Don't forget to add a small woofer.
Attached Images
File Type: jpg 4kHz.JPG (83.6 KB, 177 views)
File Type: jpg Small Woofer.jpg (102.2 KB, 176 views)
  Reply With Quote
Old 1st May 2014, 11:48 AM   #5
diyAudio Member
 
Join Date: Apr 2014
Location: North of boston
Quote:
Originally Posted by dumptruck View Post
Sounds like you've already set up everything you need to simulate the MTM lobe-null-lobe angles/frequencies/etc. yourself.
Everything except the know-how.

Where should I start? Reading, software? I just downloaded XDir, anything else I should be looking into?

Quote:
Don't forget to add a small woofer.
I'm not sure I can fit that under my desk and also my legs. One or the other. Maybe sacrifices could be made. :-)

It's being backed up by an RSS210 in a sealed enclosure on the underside of my desk, which is working great. F3 is about 54hz and it sounds good and is unobtrusive. Not ideally situated by SWMBO friendly.


Anyway, thanks for the advice. I'll build the TM. I kinda knew it was the right choice, but needed to be talked into it.

Will report back on the RS100P, but a couple other people have measured them and they apparently match the factory specs surprisingly well. Flat to 8k with a small rise to 10k, and falling off rapidly after that. Not sure they would go as a full range driver but it's a close run thing.
  Reply With Quote
Old 29th May 2014, 03:49 PM   #6
diyAudio Member
 
Join Date: Apr 2014
Location: North of boston
Got the drivers in, finishing the box this weekend probably.


Doing a 4.5L box ported at ~75Hz.

Click the image to open in full size.

Last edited by sniper1rfa; 29th May 2014 at 04:09 PM.
  Reply With Quote
Old 2nd June 2014, 03:23 PM   #7
diyAudio Member
 
Join Date: Apr 2014
Location: North of boston
Finished building this weekend, and put them together with an initial crossover based purely on the factory data. Definitely sound good, so I think the factory data is pretty close.

I did end up keeping the 4khz xo - actually ended up more like 4.2khz in order to keep the phasing good. Nothing but a second order electrical on each driver, and a massive L-pad for the tweeter obviously. I like it so far - vocals image really well. Not so awesome for cymbals but I don't really know what tracks I should use for that.

Did some quick measurements yesterday. Bass extension is good - down to 60Hz or so. No data on the high end - was having some kind of feedback problem where I would get a sharp rise in response after about 6khz even with the amplifier off.

Box is 5L. port is 1" x 1.6"L

EDIT: oh, incidentally the sensitivity is super low. Definitely not the claimed 85db.





Click the image to open in full size.

Last edited by sniper1rfa; 2nd June 2014 at 03:37 PM.
  Reply With Quote
Old 2nd June 2014, 03:32 PM   #8
diyAudio Member
 
5th element's Avatar
 
Join Date: Oct 2002
Location: England
Well those do look nice

The RS100Ps also look very well made, just like their non paper versions really.
__________________
What the hell are you screamin' for? Every five minutes there's a bomb or somethin'! I'm leavin! bzzzz!
  Reply With Quote
Old 2nd June 2014, 03:36 PM   #9
diyAudio Member
 
Join Date: Apr 2014
Location: North of boston
Thank you. Poplar sides, maple front and top.

The one on the right has pretty bland figuring in the maple but nice bits of poplar, The left has nice maple and bland poplar. That's what you get when buying wood at the depot.

Hopefully I can get some measurements today or tomorrow, but no idea how good they'll be since I'm new at this. If anybody north of boston wants to take a crack, that would be cool too.
  Reply With Quote
Old 2nd June 2014, 04:03 PM   #10
PKI is offline PKI  United States
diyAudio Member
 
PKI's Avatar
 
Join Date: Aug 2011
Nice looking speakers! What is the actual sensitivity, 80-83db? These 100p drivers are really nice on the paper, except sensitivity :-(
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

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


Similar Threads
Thread Thread Starter Forum Replies Last Post
Dayton Audio ND105-4 ( Aura NS4 ) for computer monitors - MTM or TMM or TM ? Jimmy154 Multi-Way 16 21st August 2013 03:29 AM
An old argument: TM vs. MTM sqlkev Multi-Way 15 28th August 2006 05:50 PM
modifying TM into MTM or TMM ultrachrome Multi-Way 3 12th May 2004 05:01 PM
TM vs MT vs MTM vs TMM vs MMT Bricolo Multi-Way 37 10th January 2004 02:16 PM
high crossover point.... plasmodium Multi-Way 3 13th December 2002 09:33 PM


New To Site? Need Help?

All times are GMT. The time now is 02:11 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2