12" and 15" at same cabinet

[babagau]

Hello guys, two years ago I built a cab with 2 drivers: a 15" and I made a mistake placing also an 8" thinking that it 'd be cool for highs. But the power handling specs for the 8" were exaggerated(?), anyway it was not suitable at all as I could hear distortion, so I put it out. Now it is time to use the extra space. Another 15" would fit but it is too much low end for me. I think of using a 12". What would you do? Place it in the same enclosure or divide them? I'd like to achieve a good trade off between wide freq response, clarity and high SPL.

thank you.

[washburn_it]

Was it into its own enclosure (typically a closed box)? How did you wire that 8"? Through a passive crossover or directly with the 15" (in parallel)? If it sounded distorted probably it's because it was always (or often) exceeding its maximum excursion (the power handling spec doesn't mean nothing, it just tells you when the speaker's coil starts to melt).

Regards,

Roberto

[babagau]

it was wired in parallel, total 4Ω, no crossovers. Placing it back with highpass filter is not an option, it is used in another smaller cab now. It sounded distorted at loud levels, ah yes it surely exceeded maximum excursion, that's it, thanks!

[washburn_it]

You can't wire directly in parallel different speakers in the same cab for many reasons (if you search on this forum you will find a lot of threads that explane why).
I wonder how you didn't blow that 8" since it was getting the same power and frequencies of the 15" !
If you put two different speakers in parallel the result is unpredictable, also if they are in separated cabs (and most of the times the result is bad).
Building a cab is much more than simply put a speaker into a large or small box, there are so many things to know about cab building before proceeding with building one cab.
So my suggestion for you is to read everything about this matter or...buy an used cab

Regards,

Roberto

[steve_rolfeca]

Originally Posted by babagau

it was wired in parallel, total 4?, no crossovers. ...ah yes it surely exceeded maximum excursion, that's it, thanks!

Depending on what drivers you're using, you won't get much more clarity from simply adding a 12, and the dispersion will still be poor up high.

You'd do better to turn it into a proper 2-way cab by dividing the box and using a crossover, similar to a fEarful 12/6. If you set the x-over point correctly, a good 6 or an 8 in it's own mini-enclosure will handle the power just fine.

Done correctly, you'd still be taking enough load off the 15 to substantially increase the maximum output, and the improved dispersion and transient response would be pretty noticeable.

[babagau]

Originally Posted by steve_rolfeca

Depending on what drivers you're using, you won't get much more clarity from simply adding a 12, and the dispersion will still be poor up high.
You'd do better to turn it into a proper 2-way cab by dividing the box and using a crossover, similar to a fEarful 12/6.

why do they use 6" inch for bass, when the highs are audible with 10" even with 15" depending on the players' demands?

Originally Posted by steve_rolfeca

Done correctly, you'd still be taking enough load off the 15 to substantially increase the maximum output

what if I want the 15" to get all the sound and just use a highpass on the 8" just to protect it from reaching max excursion?

[billfitzmaurice]

Originally Posted by babagau

it was wired in parallel, total 4Ω, no crossovers.

That is why it didn't work.

why do they use 6" inch for bass, when the highs are audible with 10" even with 15" depending on the players' demands?

Dispersion. Highs that are only audible when standing directly in front of the speaker aren't particularly useful.

what if I want the 15" to get all the sound and just use a highpass on the 8" just to protect it from reaching max excursion?

You should not use two different drivers in the same bandwidth. There is nothing to be gained from doing so, and potentially much to be lost.

[MuzikMan]

^^^^^ I recommend taking the above advise very seriously. It is the key to your success.

[babagau]

Originally Posted by washburn_it

You can't wire directly in parallel different speakers in the same cab for many reasons (if you search on this forum you will find a lot of threads that explane why).
If you put two different speakers in parallel the result is unpredictable, also if they are in separated cabs (and most of the times the result is bad).

the result is bad when the cabinet is constructed bad, not taking into account thiele-small parameters. If you at least place the drivers into a cabinet emulator, and calculate properly, you can't go that bad.

Originally Posted by washburn_it

I wonder how you didn't blow that 8" since it was getting the same power and frequencies of the 15" !

because I did not play that loud, when I heard distortion, jamming with a louder band, I realised the situation.

Originally Posted by washburn_it

Building a cab is much more than simply put a speaker into a large or small box, there are so many things to know about cab building before proceeding with building one cab.So my suggestion for you is to read everything about this matter or...buy an used cab

We are not talking about cabinets for CERN here, we (I) just need sth that works happily for my home studio. I haven't gotten into all this diy audio area to end up buying cabs. The more we learn the more we can produce ourselves. :-)

[washburn_it]

Originally Posted by babagau

We are not talking about cabinets for CERN here, we (I) just need sth that works happily for my home studio. I haven't gotten into all this diy audio area to end up buying cabs.

I don't know how much you are into the "DIY cab" matter, I didn't mean to offend you in any way (if I ever did it), but I thought you were not certainly an expert since you are asking basic things that should be known by someone who wants to build a good sounding cab.
And certainly to wire an 8" in parallel with a 15", with all respect, it is not an "expert thing" (CERN or not CERN).

Regards,

Roberto

[Dekker]

It was also not clear from your original post whether you separated the interior space of the cabinet for the individual drivers. If not, then the motion of one driver (say the 15") would affect the motion of the other drivers (like the 8"). This would also add considerable distortion.

In general, the basics of multi-driver passive speaker design is a science, refined by a bit of art (gained through some experience of what you can tweak to improve the design). I would strongly suggest you do as much research as you can (a good book is Loudspeaker Design Cookbook)

As stated, experimenting with drivers in a cabinet may get you something that works, but without understanding a bit of the science, it is doubtful that it will work well/efficiently or even sound good throughout its intended frequency range.

That said, when I first started out, I just threw speakers together, and had fun learning, even though it sounded like crap

[babagau]

Originally Posted by billfitzmaurice

That is why it didn't work.
Dispersion. Highs that are only audible when standing directly in front of the speaker aren't particularly useful.
You should not use two different drivers in the same bandwidth. There is nothing to be gained from doing so, and potentially much to be lost.

Ok, so I 'm thinking of not changing the dimensions, (they fit fine the 15" and adhere the golden ratio π, φ or whatever). I'll put the 8" or an equivalent back, but on it's own enclosure, probably sealed and without absorbers. The 15" will be with the ports, how much absorbers I don't know, will start with minimal. I'll recalculate diameter-length because now the dimensions change. Crossover around 2KHz maybe..? no... less, well, it's a different subject.
15": Visaton - Lautsprecher und Zubehör, Loudspeakers and Accessories
8": http://profesional.beyma.com/pdf/8MI100E.pdf

[babagau]

Originally Posted by Dekker

It was also not clear from your original post whether you separated the interior space of the cabinet for the individual drivers. If not, then the motion of one driver (say the 15") would affect the motion of the other drivers (like the 8"). This would also add considerable distortion.

I mentioned it at the title, forgetting to repeat it at the body.

Originally Posted by Dekker

In general, the basics of multi-driver passive speaker design is a science, refined by a bit of art (gained through some experience of what you can tweak to improve the design). I would strongly suggest you do as much research as you can (a good book is Loudspeaker Design Cookbook)
As stated, experimenting with drivers in a cabinet may get you something that works, but without understanding a bit of the science, it is doubtful that it will work well/efficiently or even sound good throughout its intended frequency range.
That said, when I first started out, I just threw speakers together, and had fun learning, even though it sounded like crap

The problem with me is that I gain disperse information from forums here and there and I haven't read any book although I have a few. This is because I want to do things fast because I am eager with the result. Hope someday I'll print it and read in my free time. It'll do me good. But going through all the knowledge will take about a year. You don' t do this unless you go profesionally. Anyway this cab sounded well as long as you didn't play heavy metal levels. Others (they were not sound engineers, just amateur musicians) liked it too. Now it's time to make it better.

[washburn_it]

If you can use one of the various software of simulation like WinISD (and you know the meaning of all the graphs) you can have an idea of how those speakers will "behave" inside their enclosures, especially if you are going to build a reflex cab.
If you didn't do it before, brace the cab internally, if you read the thread of the building of my 2x10", browse the pages and you will find a scheme for a good bracing, the same that I used for my cab, suggested by the guru BillFitzMaurice.
If you will follow all the advices of the experts, you will be surprised by how good the cab will sound (and how much you will have learnt).
Those are just some steps to start to "make it better".

Regards,

Roberto

[babagau]

Originally Posted by washburn_it

So my suggestion for you is to read everything about this matter or...buy an used cab

reading everything about this matter if you mean all the maths physics, waves, mechanics would take a year at least and you don't do it unless you go into this industry. If I ever dig speaker books I'll do it really slow and my head will become a soup cauldron from the logs. Three years ago I thought logs where only for the fireplace. Hopefully I am much better now. So the aim here is going through advises and practical / try-error-tryAgain-errorAgain and make two-three working cabs - monitors just for myself because I can do it at 1/3 of the price (per item), learn up to a point and have fun killing time coz we have no job, who am I man? Nothing. You help too Roberto, thanks!

[babagau]

from front to back: 1. general purpose monitor made from combo amp, taking off the amp and putting the 8" as second driver.
2. guitar. again combo with amp replaced by driver
I like amps separate to wire as I like.
3. the bass cab we are talking here