[FullRangeMan]

The Metronome also appeal to me, its a horn or a bassreflex?
What the inside Liters volume?
Its suited for the Omega 7A?

[MJK]

Agreed -which is why I made the point that they have a 1/4 wave fundamental, but as far as I am aware, like an open pipe they produce both odd and even order harmonics, not just odd.

A 1/4 wave pipe can only produce odd harmonics (3/4, 5/4, 7/4, ...), even harmonics (2/4, 4/4, 6/4, ...) are not possible. Look at the mode shapes in the link you provided to see examples of the first three mode shapes for a conical pipe.

[planet10]

The Metronome also appeal to me, its a horn or a bassreflex?

A mass loaded quadratic pipe… close enuff to just model a mass loaded voigt.

dave

[FullRangeMan]

A mass loaded quadratic pipe… close enuff to just model a mass loaded voigt.

dave

Do you would sell me the FHXL and Metronome plans?

[planet10]

FHXL plans can be had for a $10 donation to diyAudio … send me the paypal receipt.

Metronime plans are what they are … some examples and a table of start/finish area, a length, and an appropriate port size for various drivers. If your driver is not in the list there are helpfulpeople that will help you.

dave

[FullRangeMan]

How is the Metronome sound?
I suppose it have more bass because of the bigger litrage.
THe BSC is mandatory?

[planet10]

How is the Metronome sound?

It has been a long time since i heard a Met. They were bipole EL70 and sounded quite good.

I suppose it have more bass because of the bigger litrage.

Because they are mass-loaded quarter-wave pipes there is the potentialto get maximum bass out of them

THe BSC is mandatory?

Depends. What driver? Bipoles? Where in the room? How big the room?

dave

[FullRangeMan]

The driver is the Omage 7A 6,5'' alnico I mention earlier:
OMEGA 7A SPECS
Re - 7.2 ohm
Fs - 43.585 Hz
Sd - 134.782cm2
Md - 2 grams
BL - 4.971T-M
Qms - 2.030
Qes - 0.430
Qts - 0.355
No - 1.186%
SPL - 93dB
VAS - 63.770Liters
Cms - 2.47 2m M/N
Krm - 242.164 ohm
Erm - 0.979
Mms - 5.394 grams
Mmd - 4.494 grams
Kxm - 20.332 mH
Ekm - 0.585
Baffle Wood Hole 5 7/8

[planet10]

Numbers look pretty good for a Met, maybe a bit high Vas for an FHXL but i'd have to get Scott to model for it.

dave

[FullRangeMan]

Thanks. Its monopole.
PM me your email for the receipt.

[Scottmoose]

A 1/4 wave pipe can only produce odd harmonics (3/4, 5/4, 7/4, ...), even harmonics (2/4, 4/4, 6/4, ...) are not possible. Look at the mode shapes in the link you provided to see examples of the first three mode shapes for a conical pipe.

I stand corrected Martin. Perhaps you could help clear up one query though: every reference I have been able to find on pipe resonance that includes expanding pipes / conical bores (applying the latter term as a very loose synonym) states that they produce a full harmonic structure. For e.g. the hyperphysics site I linked to states 'A conical air column will produce the same fundamental frequency as an open cylinder of the same length and will also produce all harmonics.' From the above, I take it then that their various authors are mistaken?

[MJK]

Scott,

Count the number of quarter waves in the plots on that page. The frequency is just a number, the mode shapes characterize/define the air motions. All of those modes are quarter wave standing waves that have frequencies that hapen to be consecutive multiples of the fundamental frequency, this is not true for all expanding pipes. When you are looking to predict the SPL coming from that conical pipe the mode shapes are important and the building blocks for the internal air motions at any arbitrary frequency of interest.

Martin

[Scottmoose]

Why is it I have to refresh the Audiocircle page multiple times before it actually decides to do something? Happens on every PC I use. Most odd.

No doubt Martin; I wasn't going by the visuals / the drawing but the text of the different references on expansion etc. Thank you for clearing that up. My over-wide generalising comes back to bite me yet again.

As for a metronome, if anybody trusts anything I do in future (unlikely), you could try this:

L = 60in
St = 4 9/16in x 4 9/16in
Sl = 12in x 12in
Zd = 30in
Vd = 3in
Vl = 3/4in
Line pipe top, back & one sidewall with 1in acoustic fibreglass or desired equivalent

I don't have any modelling software loaded at present after changing HDDs, which has also taken out my old copy of MathCAD, so I can't run Martin's worksheets at present. However, going from the alignment table I knocked up a few years back, that should give you a ~max-flat alignment with an F3 around 40Hz. Adjust as required. That's anechoic; how much of a shelving filter would be required will depend on positioning etc. so YMMV as always.

[FullRangeMan]

Thanks Scott for these Metronome data.
For some reason I have missing this plan.

This is the same data in metric system
for non US members:
Length Internal High 152,4cm
Square Top              11,6cm x 11,6cm
Square internal bottom 30,5cm x 30,5cm
Zd = 76,2mm driver offset from the inside top.
The driver sits midway on the panel.
Vent diameter  76mm
Vent length       19mm

[FullRangeMan]

Metronome raw litrage is 67,2L