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Old 27th March 2007, 03:26 PM   #1
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Default Cabinet for trumpet player

Hello,

After long searching/reading around, I decided to consult fellow experts here about my current cabinet making attempt

Here is the situation

I have a 300w (rms @ 4ohms) head (although it is sold as a bass amp it is a full range one), and a delta-15lfa (new version I guess) speaker in hand (an apt:80 tweeter and a proper crossover is on the way).

I'm hoping to use this combination for stage monitoring/PA purposes during gigs of our jazz band which I play trumpet in (it is a Bb trumpet but I usually add lower 12th harmonics on it with an effect processor).

I think delta will use only 150 watts max or so since it's 8ohms.

As you may guess I couldn't decide on cabinet dimensions and between vented/sealed choices since this speaker is something almost in the middle in terms of suitability (vented/sealed).

Another confusing point is in pdf documents available from eminence site, parameters stated like this:

Resonant Frequency (fs): 41Hz
Qts: 0.58
Compliance Equivalent Volume: 86.1 liters / 6.6 cu. ft.

But on their specific page for this model, it is stated as:

Resonant Frequency (fs): 39Hz
Qts: 0.48
Compliance Equivalent Volume: 241.0 liters / 8.51 cu. ft.

I guess differences come from the existence of two models (new and old??) with polymide and Kapton formers though I'm not sure.

Despite I can easily reach all necessary materials, I don't have enough time and motivation for multiple trial/error attempts (mmm bad for a diyer). Thus if something goes wrong the only possible modification after finishing a cabinet is to open some suitable vents (if I begin with sealed version of course).

So could you please recommend something as a start point? Should I try a sealed cab with a mediocre volume first, (average of their recommended sizes)?

Thanks in advance

Temporal
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Old 27th March 2007, 04:30 PM   #2
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Sorry if this isn't very helpful, but Kapton is a brand name for polyimide:

http://en.wikipedia.org/wiki/Polyimide

I'm not sure why they list different specs for the driver.

How low of a frequency do you wish to play with this? I've seen a number of guitar amps (maybe they were practice amps) with open backs. If you're playing just above 150 hz, this could be an option for you. I don't know the Bb trumpet, but this website lists the low end of a C trumpet's range as 150 hz:

http://www.listenhear.co.uk/general_acoustics.htm

I know you said you can't do trial and error, but if you whip together a box with an open back, it's not like it needs to be sealed or anything. Heck, it doesn't really need a bottom. Can you do four sides of a box?
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Old 27th March 2007, 05:12 PM   #3
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Thanks for reply

A real Bb trumpet is close to 140 cm long, and the pitch of its "fundamental" is Bb 2. But that note is essentially impossible to sound. So the lowest practical note (the "open" note) is the first harmonic, Bb3.

But I occasionally add lower harmonics via a processor. I forgot to mention that I also want to make this cabinet suitable for a 4 string bass. Because the amp is actually a bass amp so err...

I would like to use this delta-15lf to its limits at least to 40 hz (lowest note of a 4 string bass I think).

And "open back" you recommended... well actually I never thought about this option untill you mentioned So now it's a decision between three. Humm...

All ideas will be appreciated

PS: Sorry for any syntax errors, English is not my native language
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Old 27th March 2007, 05:37 PM   #4
rj45 is offline rj45  United States
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Default trumpet stage monitor - PA

Dude, (American term)

Lots to consider here.

For a pure trumpet monitor, something like a box with 4 10 inch
speakers should work really good. Consider an A 440 Hz, and
about the lowest note on the horn is an octave below, so you
won't need any output below about 220 Hz. Don't know anything about your effects processor and what it's doing....

300 watts should be very good for a jazz band.
For a 15 inch driver, I don't think a tweeter will match up to it
very good - you'll have a big hole from about 1K Hz to 3 Khz.

For a 4 string bass, a 15 inch is good for jazz. Not real happy about your plan to run both a trumpet and a bass through the same speaker.

Not sure I can really help, but what size clubs do you perform in, what kind of sound pressure levels do you need, and what are your thoughts about carrying around some big boxes to the gig?

HTH,
-Don
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Old 27th March 2007, 08:23 PM   #5
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Hi again

About bass guitar; I rarely play it at home and never on stage so you may disregard it for now.

For the woofer tweeter combination, I wrote eminence for a suitable tweeter and that apt-80 was the one they recommended.
"Usable frequency range" of delta-15lf is 42Hz-3.2kHz and it goes relatively flat between these limits.

http://www.eminence.com/proaudio_spe...5&SUB_CAT_ID=2

Apt:80's relatively flat area begins from 2k or so if I'm reading the chart correctly.

http://www.eminence.com/pdf/apt80.pdf

So there may not be a huge lost range between them.

Actually I have seen cabinets around utilizing only a woofer and a tweeter but it seems they are for bass amps like this BL-115 one in http://www.drbasscabs.com/ and I have no idea if it's suitable for trumpet.

We usually play in small clubs and small concert halls and I'm also not keen on shaking the room So hi-fi ish sound is more important than sound level to me.

Would you say that sealed cabinets are more hi-fi then vented ones?

The effect processor I used is a Korg Toneworks model. And resultant sound are not limited to a usual trumpet's. I sometimes even amplify weird whistling/buzzing sounds coming from the mouthpiece (somewhat Arve Henriksen'ish). They have considerably high pitch.

Combos and cabinets for keyboards (supposed to be full range as well) are usually sealed, aren't they? So should I go this way?

Finally the size; it should fit in a hatchback Opel

It's hard to decide, considering my occasional itch, to poke our nosiy drummer with an unexpected bass note from the tumpet

Cheers

Temporal
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Old 29th March 2007, 02:53 PM   #6
rj45 is offline rj45  United States
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Default trumpet PA stuff

Some of the drbass cabs look good for your use.

I'd advise to just go with something like the BL210 and
be done with it. Saves lots of time and money.

You can try to build your own, but I can't believe that a 15 inch can go up to 3.2K, then you have the hassle of creating a crossover and mating with the amplifier.

HTH,
-Don
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Old 29th March 2007, 04:42 PM   #7
Variac is offline Variac  United States
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We have lots of members that know about PA type speakers, and value good sound. I'm sure if we keep discussing this, some of them will start to appear..

There are various drivers by Eminence and others that use neodymium magnets. These drivers tend to weigh about 8 pounds vs. about 20 for conventional magnets. Their specs are different though, but I think for a trumpet they might work out.

Could you mention the frequency of Bb3? and how low the processor goes? Even if we make the speaker not going as low as your lowest note of the processor, the bass doesn't disappear altogether. You could boost the processed bass a bit as I would suspect the processor has a volume control.

You might get by fine with a 12" driver, which will integrate better with a tweeter. (For open baffle, the 15 is probably right..With a trumpet, you are going to need a crossover and tweeter for sure to get the high harmonics. IF we can do this well, I think that will be the way it will be better than most commercial gear. An option that might be easiest to work with would be a coaxial driver. This is a bass driver with a tweeter mounted in the center. IT still requires a crossover filter, but that's something we could work out..

I realize you already have the drivers, so some of these are sugggestions for maybe a future build. What is your budget?

As far as cabinets go, and open backed cabinet is called an "open Baffle" to the hifi folks.

I've knom some gigging musicians, and I've always seen how they suffer with lugging their amps and cabinets around. That's why I suggested a neodymium driver. For the cabinet proper, possibly you could just have a baffle that is made up of three panels hinged together so it folds flat. Then you could set it up like a decorative screen that people use to divide rooms, either a bit zig zigged or with the 2 side panels folded back somewhat. The "screen would only have to be 4'x4' I would guess, so it would fold down
to 48"x 15" or 45x 18 with a 15" driver You could keep the driver in a box and attach it to the baffle with wing nuts.

Or: have the driver permanantly mounted in the center panel with walls around it as deep as the driver, an then have "wings" on each side which fold when it isn't in use to create a top and bottom, protecting the driver.

This would result in a box 48x18 by maybe 8 inches when folded.

You would use high grade plywood for the final one, as it is a LOT lighter and a LOT more durable than MDF.

If you don't need tone adjustability, a Class D amp module or commercial Class D amp would be small and light, and have the same power.

Do you have a mic preamp that is separate?

I'm interested in what the more knowlegable members think about my ideas!
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Old 30th March 2007, 10:48 AM   #8
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Don't worry about the bottom end, it would need a huge box and amp, and wouldn't carry that well in a room anyway without possible feedback problems. I'd look for a self powered commercial 15+horn box, something like the JBL active EONs. Should be pretty reasonable S/H and will give you what you want cheaper than building it yourself. They're also pretty small and robust, ideal for gigging, and don't sound half bad.
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Old 30th March 2007, 11:12 AM   #9
Pano is offline Pano  United States
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And the 10" EONs are way, way better for vocals. I've used them on 100s of gigs.

So they might be better for trumpet, too.
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Old 31st March 2007, 04:27 PM   #10
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Hello again and thanks for ideas.

Firstly, yes a 2x10 like BL210 or even a 4x10 could produce tighter (from a view point... or should I say ear point ) sound that may be more suitable for trumpet compared to a single 15 inch. Indeed, I would go for a 2x10 or a 4x10 if I already don't have this 15 inch driver at hand.

And this foldable "open baffle" idea is brilliant. It led to many interesting others in my mind. Like even using this 15inch naked i.e., putting it on a rod like stand without any cover or panels. This may also have some fun factor. Like I walk through the stage with my trumpet in my hand as usual, but this time also with an 15 inch speaker in my other hand, I put my trumpet on trumpet stand and put the speaker on its stand then start playing .

Well, if I leave the fiction part there and come to real (technical) stuff (which is very well known by fellow audio diyers here, but let me repeat), speakers start to suffer due to some limitations when used in open baffle and/or vented configurations. This is xmax/Xmech issue. Open baffle guitar cabinets utilize drivers supposed to have considerably higher xmech values. And most of these guitar amps/combos use the advantage of having limited frequency ranges that do not cause over excursion and cone displacement, as they don't reach very low frequencies. Although my driver (delta-15lfa) has a Maximum Mechanical Limit of 16.5mm (one of the highest I have seen around), it should be used in a relatively small sealed cabinet even with a high pass filter if one wants to use it to its power/volume limits. Details and examples are here:

http://www.eminence.com/pdf/cab-delta-15lfa.pdf

Actually I find this somewhat confusing. This driver is rated as 500 watts rms but you have to limit it like this

"Displacement Limited to 325 Watts; F3 of 56 Hz. Use a steep High Pass filter set to 50 Hz" in a small vented cabinet

or

"Displacement Limited to 350 Watts. Use a steep High Pass filter set to 100 Hz" in a small sealed cabinet.

If you want to hear some lower frequencies power handling drops even more and you should limit the power to 130 watts or so if you donít want over excursion till approx 40 Hz.

Probably this is "the nature of entities" (a local idiom translated literally and I donít know if it makes sense in English ) and I shouldn't complain

In summary, thanks for the recommendations about other driver options and I'll certainly consider them for future projects but for now I have to stick with this driver, and I'll really appreciate your comments about making a decision between vented (not open baffle) and sealed configurations with this driver.

Regards

Temporal
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