Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Multi-Way Conventional loudspeakers with crossovers

Low Qts in Low Qtc sealed box?
Low Qts in Low Qtc sealed box?
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
Thread Tools Search this Thread
Old 5th January 2015, 06:00 AM   #1
Richidoo is offline Richidoo  United States
diyAudio Member
Join Date: Oct 2005
Location: Raleigh
Default Low Qts in Low Qtc sealed box?

I read that sealed Qtc .5 was the best transient response, many articles say this is the best for classical music, bass clarity.

I once had Eton 11-580 in a commercial ported speaker and I liked the bass sound, very detailed. But I read that sealed Qtc 0.5 is best for music, and ported has not as good transient response as sealed. A couple previous attempts at designing ported bass speakers were not encouraging. I used formulas and bass design apps and the results did not sound as good as commercial ported speakers, more like disco speakers with overbearing punchy bass, and not good detail. Drivers were DeltaLite2512 and TD12H. o I didn't have confidence that free web software can design good sounding musical vented speaker so I decided on sealed.

I saw a good deal on the Etons so I bought them for a 3 way. I built big sealed boxes for them Qtc .5 (3cu ft.) from what I read, EbP is 74 and between 50 and 100 could work sealed or vented.

Now I play them and the sound is not great. It is boomy and loose, not tight and clear, as I expected. Does not sound like good transient response.

Then I read some more. The Etons are Qts .30, that might be too low for sealed?

My question is why does the low Q speaker sound bad in sealed Qtc .5? I was under the illusion that any speaker would have best transient response, best damped, maximum clarity, with Qtc .5. But I am not hearing that.

I am using active crossover and electronic EQ to flatten the FR. I am using low source impedance SS amplifier with low resistance wires direct connected to the speaker, so it is not a electrical damping issue.

My crossover is 150Hz to the 6.5" sealed mid. Other commercial speakers, reflex, dipole, sealed did not have this problem in my room, so it is not room modes.

I experimented with stuffing. Started with 2" pink FG on 3 interior surfaces, boomy. I added 2.5 pounds of polyfill, packed completely full rather tightly. This seemed to reduce the boominess, but it sounded so terrible I couldn't tell much. I removed half of the stuffing, fluffed it up, still doesn't sound natural, it's stuffy and dead. I removed half again, only half the box volume filled with very fluffed up polyfill. that sounds better. The boom still persists, although it is lessened a bit, I think.

Do I need to make a smaller sealed box? Madisound suggests 0.7 cu ft (20 liters) for sealed, but says vented is better. Or should I just forget about sealed box for this driver, and convert the box to vented? I want ultimate clarity for solo piano, tenor vocals, etc. I don't listen too loud and I have enough amp power for EQ.

How do I get the maximum LF clarity from this driver?
  Reply With Quote
Old 5th January 2015, 06:10 AM   #2
Richidoo is offline Richidoo  United States
diyAudio Member
Join Date: Oct 2005
Location: Raleigh
I have Omnimic, WT3 and SPL meter. What parameter can I measure which will quantify what I am hearing?

The box is made of inner 3/4" MDF with outer layer of 3/4" hardwood ply, with Green glue layer between, and lots of corner and cross bracing beams, but not window bracing. I can feel only slight vibration when the speaker is playing loudly, knock test is pretty quiet.

Last edited by Richidoo; 5th January 2015 at 06:18 AM. Reason: Added box details.
  Reply With Quote
Old 5th January 2015, 07:18 AM   #3
Lojzek is offline Lojzek  Croatia
diyAudio Member
Lojzek's Avatar
Join Date: Feb 2012
Location: Croatia
Whatever theory of Qtc=0,5 says, it's crap.
I don't find thin sounding (fast transient = pressure not high enough)
speakers pleasing, never have and never will.

For optimal results you should measure TS parameters yourself,
work with them in a box simulation program to see how low
you would like to have it and what box size is acceptable.

My philosophy has always been to use the maximum a driver
can offer. In the end this means bigger boxes with F3/F6/F10
as low as possible.

Deltalite of yours has nothing to do in sealed boxes, according to
manufacturers parameters.
  Reply With Quote
Old 5th January 2015, 07:30 AM   #4
richie00boy is offline richie00boy  United Kingdom
Did it Himself
diyAudio Member
richie00boy's Avatar
Join Date: Nov 2003
Location: Gloucestershire, England, UK
Low Qts in Low Qtc sealed box?
If you are using EQ to flatten (boost) the response then you are undoing the advantage of the low Q. It's probably this that is causing the boomy sound. I reckon you are having to EQ quite a bit because if you don't the bass is really thin and shallow? Well that's the problem with sealed low Q boxes, early roll off.

Don't believe all you read on the internet, as you have found yourself there are great sounding ported speakers out there. And low Q sealed isn't all it's cracked up to be.

Fortunately as you have made oversized sealed boxes, there may be some scope for adding a port and getting a response without EQ that is more to your taste. Post up the driver specs and box volume and see what people can come up with.
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, modules and more.
  Reply With Quote
Old 5th January 2015, 07:41 AM   #5
Tattoo is offline Tattoo
diyAudio Member
Tattoo's Avatar
Join Date: Aug 2014
Location: Laniakea
The room itself is the dominant factor in the bass response of your speaker. Peaks and dips there will be orders of magnitude greater than the peaks and dips of your speaker, no matter what the configuration.

So how does your speaker sound outdoor, where room effects are zero?

Maybe give us some measurements of your speaker.
Measure really close to the woofer and measure at the listening position. What are the differences?
If you search for X, than eventually you'll find X. Hopefully X is the truth.
  Reply With Quote
Old 5th January 2015, 07:43 AM   #6
Tytte71 is offline Tytte71  Norway
diyAudio Member
Join Date: Oct 2010
Hi Rich and happy new year.

There are loads of general rubish rules out there that don't apply to the real world. One thing is whatever Qts/Qtc to use. We can simply not speak of bass reproduction without including the room into the equation. A proper designed BR may very well be preferred over sealed one for your application, while for others it may be the opposite.

What you have made is a pretty predictable cabinet design for measurement and for optimizing towards your final design. You know the net cabinet volume and you know the driver parameters. Since I do not have a clue what your in-room response is, it comes in convenient that you are able to measure the response.

I take for granted that you are not using any DSP, but plain passive crossover design, maybe with separate amp for the bass. If however you are using DSP, tuning the response would be obvious.

My suggestion would be to measure the bass frequency response in sweet spot and by e.g. four-six other points around sweet spot within a range of +/- two feet from sweet spot. Then you can average the measured responses to get an image of how the bass is perceived in the listening position.

Complete by doing a separate near-field measurement with the mic as close as possible to he dust cap.

Based on your known design and now, your known responses, it would be easier to give you hint on how to proceed revising your bass system.


Edit: I also presume that you have positioned your woofer to the best location

Last edited by Tytte71; 5th January 2015 at 07:50 AM.
  Reply With Quote
Old 5th January 2015, 07:50 AM   #7
CLS is offline CLS  Taiwan
diyAudio Member
Join Date: Jun 2005
Location: Taiwan
I had similar experiences in stuffing the port(s) of vented boxes. The bass sound changed from boomy/flooding to dead/muffled. It's far from punchy and tight.

Many factors join in the game as stated above.

I just quit trying and turned to OB.
  Reply With Quote
Old 5th January 2015, 08:40 AM   #8
AndrewT is offline AndrewT  Scotland
Join Date: Jul 2004
Location: Scottish Borders
I started modifying a big PA speaker a few years ago and during my researching, a few Members that I trusted advised aiming for a Q quite a bit lower than the normal Butterworth type response.
It was suggested going as low as Q=0.5 ( Bessel is just a little bit above 0.5).

I tuned my B950 to have a roll off curve that resembled a Q of around 0.55, before the vented loading then made it tumble towards the 3pole roll-off inherent to the vented design.

Listening to it is a pleasure. No bass hump. Goes very deep. No exaggeration of voice. Reproduces film sound effects well.
No regrets.

I'm going to look at modifying my Leopards to match the same roll-off, as I repair each one. (surrounds torn due to excessive PA duty).
regards Andrew T.
  Reply With Quote
Old 5th January 2015, 10:31 AM   #9
Scott L is offline Scott L  United States
diyAudio Member
Join Date: Dec 2008
Location: Knoxville, TN
Low Qts in Low Qtc sealed box?
Default Enclosure


What are the dimensions of your enclosure, and what is it made out of ?
What method of bracing technique?
How did you affix the driver to the cabinet ?
  Reply With Quote
Old 5th January 2015, 10:37 AM   #10
Tytte71 is offline Tytte71  Norway
diyAudio Member
Join Date: Oct 2010
AndewT; First of all I am glad you hit the nail and are satisfied with your system.
But your experience really can't be used as a general design guide, nor fasit to Richidoo without knowing his environment (not to be rude).

Just to illustrate; In my current setup I use sealed cabinets with almost exact the same Q as yours. With some limitations the 4 pcs. 18" woofers is carefully located by measurements to achieve the most even response with as few peaks and dips as possible at listening position. Still the uncorrected system shows a 16dB linear falling response from 125z to 22Hz. Below 22Hz the response raises. If I would implement a 6dB boost at 20Hz linear rising from e.g. 150Hz, it would imply a 22dB boost to achieve the target. Close to the backwall however the compensation needed is limited to 6-8dB. In my case I would be better off with huge BR tuned ruler flat to the sub octaves.
Fortunately I was aware of this room issue prior to making the cabs.

Like CLS mentioned, he gave up and went OB. He does not say that this is the medicine to cure all pain, but it might seem like dipole/cardiode sometime can be easier to integrate. This is also the case in my living room. I've tested a small U-baffel with great results. Therefore I will also switch to a cabinet free system. But it very soon becomes expensive when sacrificing on capacity is not an option.
  Reply With Quote


Low Qts in Low Qtc sealed box?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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Faking an extended sealed box response with a low-tuned damped vent IG81 Multi-Way 20 24th June 2014 09:12 PM
Would it be okay to mix Low qts and high qts of the same sub? icecreamxd Subwoofers 7 4th December 2013 08:00 PM
Sealed with low Qts owenhamburg Multi-Way 48 25th August 2012 09:10 AM
Need 8" sub - low Qts, low Fs??? geolemon Subwoofers 14 19th June 2005 12:38 AM
Question about Qtc and sealed woofer box sizes mazeroth Multi-Way 12 3rd December 2004 08:49 AM

New To Site? Need Help?

All times are GMT. The time now is 05:08 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio