Help making design choices, large 2-way

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CoolJazz

CoolJazz

Member
Joined 2009
#1
After building several proven designs, it's now time to have a go at designing a speaker from scratch.

The basic goals are set (and don't try to convince me otherwise 😉

2 way, 15 inch (mid)bass and a compression driver on a horn/waveguide.
Crossover will be done with DSP.
SPL is not very important, these will be in my living room and will rarely play above 95-100dB

I've been modelling various drivers in boxes of different sizes in WinISD and now I feel stuck. I can model the same freq. response and SPL using very different approaches and I don't really know why I should choose one over the other.

Using a Linkwitz transform, I can do 110dB, f3@35hz with all of these:
Using the Faital 15FH500 in a closed 70L box, in a 120L closed box and in a 100L vented box.

DSP kind of ruins the usual decision making process, and I don't really care if the box will be 70 or 120L. Size is not that important. ~150L is the limit though.

So.... what would be valid reasons for choosing one over another here?
I'm leaning towards a closed box but don't really have a good reason for it. Some say they sound better, but some say vented sound more 'open' or 'natural'.

Are there general characteristics for sealed and ported designs that people agree on?
Is it somehow better if you need less of a boost in the bottom end?

I will have more questions when this is sorted, but first things first 🙂

Thanks
 
#2
Do you play, or listen to, acoustical instruments much? If so, you will likely prefer
a well designed closed box, or an aperiodic. The DSP should have to do as little as possible.
 
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#3
I'd say go for smaller since it would have its internal modes higher up in frequency and outer dimensions would also affect things greatly. If somehow there is not enough bass you can always add more subs. Same goes for the driver selection, choose midrange performance over bass, any 15" driver system has plenty compared to small shoeboxes. I think the 15fh500 is fine and I would concentrate other things on the system first before setting a volume for bass box, you can always come back to it later since it is the most trivial parameter on the whole system. As you have noticed, it almost doesn't matter. Have fun! 😉
 
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#4
I'd lean toward designing a bit of flexibility into the enclosure. Making it 130l will allow you to keep it sealed and experiment w/ported if you'd like. From a sealed stand point, the lower end will be more extended with less DSP input. Grouping enclosure resonances in the 300-450hz range won't hurt the overall frequency response too much judging by Faitals' response graphs. Sealed enclosures, especially with larger drivers in a home HI-FI setting, are my pick. If you feel you need even more -low bass- add in some subs as this would be more flexible.
 
#5
Thanks for the responses. I've been toying with the idea of doing a ~120L box with a port I can easily plug, so I can see what I like best and even switch between sealed and vented depending on needs.

Woofer is sorted I think. I initially wanted to use the 15PR400 but that's a no go in a sealed box and the 15FH500 also looks pretty good.
Still like to hear your opinions/suggestions otherwise.

Next choice to make is the compression driver & horn.
I'd like to xo around 700-800hz so I'm looking at 1.4 or 2 inch exit drivers. There are some 1" that will cross that low for home use which only adds more choices.
From what I read, I probably will like 'plastic' diaphragms better than metal/titanium ones, but I don't really know. Lots of community favourites are titanium. Behaviour above 15k is not the most important for me (I'm over 12 years old)
There are dozens available that fit my needs spec-wise, arrrggg...
 
#8
When it comes to sealed vs ported, the tradeoff is this:

- Ported will give you more LF output, down to the tuning frequency
- Sealed will give you less output compared to the ported box, but can be operated down to the <20Hz range.

The time domain performance of a typical room is a couple of orders of magnitude worse than either design, so IMO the higher group delay of a ported box becomes irrelevant.


FWIW, the 15FH520 might be worth consideration: that adds demodulation in the motor, which will lower distortion.


Chris
 
#9
markbakk said:
I'd prefer the HF500 above the PR400 just because the latter has a lowish Xmax. Even a 15" has it's limits in closed designs at 40Hz.
Click to expand...
On the face of it I have no argument with with what you say Mark. In a sealed design though, were the 15" is responsible for a portion of the mid range, trying to extract even lower bass frequencies tends to muddy the low-mid range response. At least this has been my experience.


As for the demodulation rings ... pretty sure I've read some literature recently that outlined their use in woofers as not being very effective when it came to distortion reduction. The rings have more effect in mid range drivers. I believe it was a paper done by Purifi if not mistaken.
Some Speaker Problems That Needed Solving - PURIFI
 
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#10
CoolJazz said:
After building several proven designs, it's now time to have a go at designing a speaker from scratch.

The basic goals are set (and don't try to convince me otherwise 😉

2 way, 15 inch (mid)bass and a compression driver on a horn/waveguide.
Crossover will be done with DSP.
SPL is not very important, these will be in my living room and will rarely play above 95-100dB

I've been modelling various drivers in boxes of different sizes in WinISD and now I feel stuck. I can model the same freq. response and SPL using very different approaches and I don't really know why I should choose one over the other.

Using a Linkwitz transform, I can do 110dB, f3@35hz with all of these:
Using the Faital 15FH500 in a closed 70L box, in a 120L closed box and in a 100L vented box.

DSP kind of ruins the usual decision making process, and I don't really care if the box will be 70 or 120L. Size is not that important. ~150L is the limit though.

So.... what would be valid reasons for choosing one over another here?
I'm leaning towards a closed box but don't really have a good reason for it. Some say they sound better, but some say vented sound more 'open' or 'natural'.

Are there general characteristics for sealed and ported designs that people agree on?
Is it somehow better if you need less of a boost in the bottom end?

I will have more questions when this is sorted, but first things first 🙂

Thanks
Click to expand...

Did not read any other comments.

I do not believe that any LF source is preferable by a large margin, but I have settled on closed box. That's because I use DSP to setup the entire room LF using several sources and compact is great. It's not what any one LF source is doing but what they are all doing. Individual "types" don't really matter much.

Make sure that you have a state-of-the-art waveguide for your system such as can be found over at "Acoustic Horn Design" thread.
 
#11
I'd like to run these without subs, at least to start with. I've never had speakers that go very low so I'll probably already be very happy with something that is flat to ~40hz. And as I'm going the DSP way, I can always add subs later easily.

gedlee said:
Make sure that you have a state-of-the-art waveguide for your system such as can be found over at "Acoustic Horn Design" thread.
Click to expand...

I've been following that thread with great interest. Although most of the science goes over my head, I very much like the idea of 'generating' and printing my own waveguide.

Any thoughts on HF driver materials? Let's say Faital HF140 vs HF146?
Are there other things to consider besides LF and HF extension?
 
#12
Compression drivers are a commodity to me - except for the pretty bad Chinese knockoffs. Stick a long time reputable company like B&C, or JBL and they are all pretty much the same to me. I do like to stay away from metal diaphragms as they can often ring too much.

Don't be swayed into using a bigger driver if this is for home use as it just isn't necessary. Smaller 1" drivers work best for broad range coverage. Larger drivers have more problems.

"No subs" is a mistake if it's for maximum listening perception. With DSP, even very small ones in closed boxes can be driven pretty hard. Good high power pro, like some 10" can make a pretty small sub, lots of power and DSP and you can achieve some very good results.

With the waveguides, even if you buy a commercial model, it should look a lot like the axisymmetric ones that ATH has come up with - nice mouth flare, none of this sharp termination stuff.

I don't deal in specific model recommendations, I have little interest in the current marketplace. If asked I'd say use B&C like I did. Very happy with there products.
 
#16
Thanks all
The purpose of this thread was always to understand how to make certain choices. What specs to look at and understanding the pros and cons of my choices.
Not so much getting specific model recommendations.

About picking a CD, the specs often mention a minimal xo point. I understand that you can cross lower if you don't need 120dB. Is there a way to guestimate how low you can cross a driver in a specific waveguide other then actually buying and measuring them?
 
#19
diyiggy said:
Alas not sourcable and not feasible w/o expensive machine or huge 3D printers
Click to expand...

Yes, that is unfortunate. Why manufacturers are not interested in making better waveguides is beyond my understanding. This may change and it may not. Manufacturers are very very NIH (Not Invented Here) and loath to "copy" the great designs that that thread has produced. All we can do is wait. And hope things change.
 
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