Advice requested for portable two way - 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 17th June 2013, 11:53 AM   #1
woytek is offline woytek  Netherlands
diyAudio Member
 
Join Date: Jun 2013
Default Advice requested for portable two way

Hello everybody! I am new here, have been reading for a while now. Next to the reading I have also been designing and now I think it is time to get my design and plans validated by some more experienced builders.

I am new to speaker building. The project I am working on is a portable speaker and is my first. This subject has been discussed plenty on these forums and more than once I stumbled upon the term "boominator". I do not intent to make my own boominator, it will be a design of my own with which I need some help from you!

The idea:
Let me start by showing the design, to make the idea clear from the start:
Click the image to open in full size.

This is a sketchup model of how I would like to build the two-way. Dimensions are WxHxD 40cm x 20cm x 25cm (16"x8"x10"). Internal volume around 10L (0.35ft3).

The idea behind this design is a small lightweight portable speaker that is loud enough for a small group (max 20 people) to listen to some music, both relaxed music and some heavy bass electronic music. Although some might think this application does not need a hifi-ish approach, I enjoy doing things properly and that is why I try to make a properly designed speaker.

Now of course the challenges are to combine efficiency with portability and bass...

The components:
Box: birch plywood (12 or 18mm, 1/2" and 7/10")
Woofer: Silver Flute W17RC38-4ohm (link)
Tweeter: Vifa XT25BG60-4ohm (link)
Amplifier: MaxAmp20 Class-D (link)
Filter and crossover: MiniDSP + UMIK-1 (link)

The design:
Since I do not have any experience in filter and crossover circuits, I think it is wise to do this with a DSP, the miniDSP in this case. This solution allows me to quickly measure and change the crossover/filters. On this forum I have read more than once about the difficulties in proper crossover design for beginners.

The woofer is selected based on very positive reviews, also on these forums, paired with reasonable efficiency and low Qts and Vas. Below you can find a plot from WinISD. The woofer can reach quite low although the box is fairly small, 10L (0.35ft3) tuned to 45Hz. As you can see in the plot, the response is not flat. I do this to let it run a bit further down allowing me to raise it a little bit with the miniDSP. Now the f3 is around 70Hz but with a filter it should easily reach 50Hz, as can be seen from the second plot where I applied a parEQ 50Hz, Q=0.8 and gain=2dB.

Click the image to open in full size.
Response with highpass @ 25Hz
Click the image to open in full size.
Response with highpass @ 25Hz and parEQ @ 50Hz (Q=0.8, gain=2dB)
Click the image to open in full size.
Amplifier apparent load with parEQ
Click the image to open in full size.
Cone excursion with parEQ

Since I am using a low power amplifier with:
full battery: 14W (1% THD), 18W (10% THD)
Empty battery: 10W (1% THD), 13W (10% THD)

I wonder if the higher apparent load due to the filter is going to cause problems. Or is this only related to passive filtering and is the effect different when I filter via the miniDSP?

The port is on the front since the speaker will be played outside and I do not want a part of the sound pressure to be radiated to the back. The drivers are mounted flush on the front panel to reduce diffraction. To further optimize this, the edges are rounded with a 3cm (1 1/6") radius and the tweeter is mounted asymmetrical.

I want the crossover low to allow the woofer to play low with ease. I hope it is possible to put it at 1800Hz but that might be a little low. Else I will shift it up towards 2500Hz. Advantage is that the miniDSP allows for very steep crossovers. The tweeter level might need some adjusting but this is not a problem with the DSP.

The stereo signal from for example a phone will be transformed to mono by using a simple passive summing circuit (link). This mono signal will go through the miniDSP which deals with the crossover and filters/gains. Two outputs will go to the 2ch. amplifier which powers the drivers.

I am anxious to hear what you think of my idea/design! Are there any concerns about hardware selection? Are there important factors I have not taken into account?
Attached Images
File Type: png winisd.png (27.1 KB, 160 views)
File Type: png winisd_filter.png (26.0 KB, 160 views)
File Type: png power.png (28.3 KB, 160 views)
File Type: png cone.png (24.8 KB, 160 views)
File Type: png boombox_v6.png (335.6 KB, 166 views)

Last edited by woytek; 17th June 2013 at 12:19 PM.
  Reply With Quote
Old 17th June 2013, 12:23 PM   #2
woytek is offline woytek  Netherlands
diyAudio Member
 
Join Date: Jun 2013
Something went wrong, I will try reposting...

Nevermind, it magically appeared again, yay!

Last edited by woytek; 17th June 2013 at 12:28 PM.
  Reply With Quote
Old 17th June 2013, 12:41 PM   #3
diyAudio Member
 
Join Date: Aug 2009
Location: North Texas, USA
One factor jumps to the top of my list.

Do you have any idea of how you will construct that box?

Not to mention the roundover. The port is almost certainly too small.
__________________
I was so much older then, I'm younger than that now.
  Reply With Quote
Old 17th June 2013, 01:00 PM   #4
woytek is offline woytek  Netherlands
diyAudio Member
 
Join Date: Jun 2013
Good point, the box is not easy to build. The roundover is large and routers that size are expensive. I was thinking of using three layers of plywood stacked and having a local woodworking company mill it down to the required radius. I should inquire about this!

The port is 3cm (1 1/6") in diameter so that it is not too long inside and so that I can make a nice rounded flare on the outside. Speed according to WinISD is 35m/s max.
  Reply With Quote
Old 17th June 2013, 01:10 PM   #5
diyAudio Member
 
chris661's Avatar
 
Join Date: Feb 2008
Location: Sheffield
Blog Entries: 8
I'd tune the port higher. You won't hear 50Hz from a 6" cone outside.

The Boominator (which I'd consider the reference for outdoor boombox design) uses a too-small cabinet, tuned quite high. The result is a bump in the response around 80-120Hz, with very little output below that. That bump will make the speaker hit you in the chest, whereas trying to get the same trick at 50Hz will need a lot of speakers and power.

IIRC, the tweeter you've chosen is very sturdy, and shouldn't have any problems going to 1800Hz. Be sure to keep the crossover steep though - I like 4th order Linkwitz Riley.

Chris
  Reply With Quote
Old 17th June 2013, 01:52 PM   #6
woytek is offline woytek  Netherlands
diyAudio Member
 
Join Date: Jun 2013
Thank you for the confirmation about the tweeter!

Could you possibly elaborate on the advantages of a bump at 80Hz compared to a slightly sloping response to 50Hz? I get the way it works I am just trying to figure out why the first option is better.

I've read about this in the boominator thread as well, what exactly is the reason behind choosing the bump if you play in free field? Does it have something to do with the baffle step which reduces the bass in free field more than in a room since there are no reflections?
  Reply With Quote
Old 17th June 2013, 02:13 PM   #7
diyAudio Member
 
Join Date: Nov 2009
Location: Birmingham, UK
For an outdoors/party type speaker I'm a bit worried about that tweeter with its protruding phase plug nipple. Seems it might easily be damaged.
I'd go for a tweeter with a more recessed dome like these:
http://www.scan-speak.dk/datasheet/pdf/d2606-922000.pdf

http://www.tymphany.com/files/D27TG-35-06%20Rev1_0.pdf

Or use a waveguide.


PS: While googling these I noticed that according to the heading in google Tymphany is the manufacturer of Scan-Peek (sic) drivers!
  Reply With Quote
Old 17th June 2013, 03:55 PM   #8
diyAudio Member
 
chris661's Avatar
 
Join Date: Feb 2008
Location: Sheffield
Blog Entries: 8
The bump in the bass response, as well as upping your maximum SPL, has a psychological effect: a bump ~100Hz will make a speaker system sound (to the untrained ear) like there's plenty of bass, when in fact there is no "real" bass present. These little portable wireless speakers do much the same thing, making a fairly hefty sound from a couple of 2" drivers.

Indoors, a sloping response to 50Hz would be quite listenable, as you get boundry gain and room pressure mode to boost those frequencies, giving (in room) a ~flat response to 50Hz.
Outdoors, its an entirely different game: forget about going low, just make what the woofer can do as loud as possible (or at least, audible). I'd aim for 80Hz with a 6" - I'm using a couple of 8"s to go to 63Hz (-3dB point). In a "normal" ported alignment they'd hit around 35Hz.

Its very hard to explain the effect, but it definitely does work, and you can try it quite easily:
When you build your speaker, get one of those ports where you can change the length (and therefore the tuning) and see what happens to the sound when you're outdoors. I'd bet you go for a higher tuning than 50Hz

Chris
  Reply With Quote
Old 17th June 2013, 05:38 PM   #9
woytek is offline woytek  Netherlands
diyAudio Member
 
Join Date: Jun 2013
Thanks Chris, that's a very good explanation. And you are right, I can easily test this when I have all the materials. Here is the plot for a 10L box with tuning at 70Hz. Is something like this okay? I can also tune it to 93Hz and I would get a 6dB bump around 100Hz and an f3 slightly below 80Hz.

Click the image to open in full size.

Now you also made a fair point about this: "just make what the woofer can do as loud as possible"

The woofers I am using right now are in my opinion quite good. They allow a small cabinet size and offer decent sensitivity. However, comparing them to the 10" boominator PA woofers, they are a bit of a let down.

Current woofer is 4ohm with sensitivity of 89db (1W/1m) and with 14W I can achieve SPL of 101dB at 1m.

The PA woofers usually are 8ohm and 96dB (1W/1m) and would go quite a bit louder. Difference would be even bigger if two of these are used in parallel for a 4ohm combined load.

The problem is that there is no step between, using two 10" woofers greatly increases the size and decreases the portability. Are my woofers a solid choice nevertheless?

Also, since I am not using woofers on both sides, I will lose some bass response due to baffle step. Is this something I should take into account or is it easily fixed by using the miniDSP?
Attached Images
File Type: png response_high_tuning.png (27.1 KB, 140 views)

Last edited by woytek; 17th June 2013 at 05:47 PM.
  Reply With Quote
Old 17th June 2013, 09:26 PM   #10
woytek is offline woytek  Netherlands
diyAudio Member
 
Join Date: Jun 2013
Since I cannot seem to edit my previous post, i made a new one. I made a quick comparison between the 6.5" silver flute and the 8" faital 8FE200 (link)

Click the image to open in full size.
Response
Click the image to open in full size.
SPL
Click the image to open in full size.
Power
Attached Images
File Type: png faital_vs_silver_flute_response.PNG (25.2 KB, 139 views)
File Type: png faital_vs_silver_flute_SPL.PNG (25.4 KB, 135 views)
File Type: png faital_vs_silver_flute_power.PNG (27.8 KB, 136 views)
  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
Advice on 6418 design requested skajam66 Tubes / Valves 0 6th July 2011 12:17 PM
New idea in the construction of amps-advice requested fenderjazz Construction Tips 10 18th December 2010 12:37 PM
Advice on Greenlee Punches Requested SRMcGee Parts 2 15th November 2005 12:37 AM
Simple high school project - advice requested mountaingoat Full Range 29 12th November 2005 04:48 AM
Unique(?) Portable Sound Requirement -- Advice Requested lydanynom Everything Else 7 21st July 2005 05:52 AM


New To Site? Need Help?

All times are GMT. The time now is 01:40 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