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Old 5th January 2015, 06:00 AM   #1
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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?
Thanks!!
Rich
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Old 5th January 2015, 06:10 AM   #2
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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.
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Old 5th January 2015, 07:18 AM   #3
Lojzek is offline Lojzek  Croatia
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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.
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Old 5th January 2015, 07:30 AM   #4
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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.
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Old 5th January 2015, 07:41 AM   #5
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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?
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Old 5th January 2015, 07:43 AM   #6
Tytte71 is offline Tytte71  Norway
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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.

Cheers

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.
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Old 5th January 2015, 07:50 AM   #7
CLS is offline CLS  Taiwan
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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.
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Old 5th January 2015, 08:40 AM   #8
AndrewT is offline AndrewT  Scotland
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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).
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Old 5th January 2015, 10:31 AM   #9
Scott L is online now Scott L  United States
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Greetings,

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 ?
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Old 5th January 2015, 10:37 AM   #10
Tytte71 is offline Tytte71  Norway
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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.
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