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EP500 Freq Response Help
#97580 06/03/05 04:02 PM
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mrnomas Offline OP
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First – Long time lurker, first time caller.

Background – I’ve been living with my all Axiom setup for a couple of months now and I’ve never been particularly thrilled with the frequency response of the EP500. I had the sub corner loaded and was experiencing a near 30db boost at 40hz followed by a 20hz lull at 70hz. Last night I finally broke down and moved that 70lbs monster to the prime listening area and did the “crawling for bass” thing again. As I feared, the best sub spot I could find was behind the couch (now I have to figure out how to run a wire back there).

Last night, I ran through the test tones provided by Real Traps and (since I can’t post a pic) I have reduced my peak and lull, but they are not completely gone. To summarize the table below, I’ve got a peak (+12db) at 39hz with an >+5db extension between 30hz and 48hz and a lull (-11db) at 71hz with an >-5db extension between 62hz and 76hz. So, my questions:

1) Should I worry too much about this?
2) Should I be looking into EQ? Perhaps the BFD?
3)I’m running a 3805 so I could boost the manual EQ at 63hz to bring up the lull. Is this a viable solution?

Here are my measurements (from my crossover point (80hz) down):
Freq db
19 59
20 80
21 84
22 80
23 78
24 77.5
25 76
26 78.5
27 80.5
28 82
29 83
30 86
31 86
32 84
33 84.5
34 86.5
35 88.5
36 90
37 91.5
38 92
39 92.5
40 92
41 92
42 92
43 91.5
44 90.5
45 89
46 88
47 86.5
48 86
49 85
50 84
51 84
52 83
53 83
54 82
55 81
56 80.5
57 79.5
58 78.5
59 78
60 77
61 76
62 75
63 73.5
64 72.5
65 72
66 71.5
67 71
68 70.5
69 70
70 69
71 69
72 70
73 71.5
74 73
75 74
76 75
77 76
78 76
79 76
80 76
81 76




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Re: EP500 Freq Response Help
#97581 06/03/05 04:31 PM
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axiomite
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A bit easier to read :



Bumping up nulls doesn't usually work very well; I would concentrate on taking down that 40 Hz peak a bit. IIRC the Denon's EQ is fixed frequency when you are adjusting manually but adjustable frequency for auto-EQ, is that correct ?

Do you have a 14 foot dimension in your room (maybe even 14x14-ish) ? That would explain the dips at 20/60 and the peaks at 40.


M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8
Re: EP500 Freq Response Help
#97582 06/03/05 04:38 PM
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mrnomas Offline OP
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In reply to:

the Denon's EQ is fixed frequency when you are adjusting manually but adjustable frequency for auto-EQ, is that correct ?




Yes.

In reply to:

Do you have a 14 foot dimension in your room




Yes again (14.5 by 12.5 by 8)

Maybe I should look into getting a mic and letting the auto eq do the work for me?


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Re: EP500 Freq Response Help
#97583 06/04/05 07:21 AM
Joined: May 2002
Posts: 10,654
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Welcome, no more. As John Bridgman suggested, that elevated area around 35-45Hz appears to be the result of the nearly square room dimensions causing two adjacent mode peaks(560 divided by 14.5 and 12.5 feet). Both of those modes would be minimized by placing the sub near the center of the room, but that's not likely to be practical.

The equalization on the 3805 has been reported to be helpful to some and not to others, but in any case it doesn't equalize the sub output, just the other speakers, so that wouldn't be helpful on the 500. Besides positioning, the BFD, which can be connected to equalize the sub output can likely smooth out the lowest bass.


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Enjoy the music, not the equipment.


Re: EP500 Freq Response Help
#97584 06/06/05 03:35 PM
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mrnomas Offline OP
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Thanks John and John,

Moving the 500 behind the couch definitely helped, I am looking into the BFD right now (got to convince my wife of the "need"). You've been very helpful.


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Re: EP500 Freq Response Help
#97585 06/09/05 04:49 PM
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Guys:

How exactly are you determining the dips/peaks of the spectrum vs the room size?? I know the formula for wavelenght, but I dont picture when a room dimension will cause a dip or a peak in the spectrum.

And why the 560...? is not the speed of sound in air around 1135ft/s (at 74degf, ie). I understand the physics, but I never use them before in acoustics. So I guess that the half-wavelenght and full-wavelenght dimensions have to do, but which one cause dips, and which one cause peaks?? It its a silly question I guess.

As soon as my preamp arrive, I will make the same spectra analisys in diferent positions, to help myself to place the sub (my room dimensions are 14x20x8, not 14x20x10 as I post wrongly before). The best place so far is just in the middle of the room, but if I walk behind it, towards the TV, man it sounds not good.

Thanks.

Re: EP500 Freq Response Help
#97586 06/09/05 06:31 PM
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axiomite
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Hopefully someone can post some good links, but the basic idea is that bass reinforcement is a result of standing waves between the walls or ceiling/floor of your room. A standing wave happens when the wavelength (or 2, 3, 4.. wavelengths) is equal to the round-trip distance between the surfaces.

You can see where this is going. Speed of sound is ~1130 feet per second (1120, 1135, whatever). Let's assume you have 14 feet between walls, 28 feet round trip. You get a peak at 1130/28 or 40.4 Hz, plus all the multiples of 40 hz (80, 120 etc...).

You can either divide 1130 by the round trip distance (there and back) or divide 565 by the one-way distance. Same thing.

You get dips when the round trip distance is half a wavelength or any multiple. Simple rule of thumb is :

1130 / twice distance gives you the frequency of the first peak, with subsequent peaks at 2x, 3x, 4x... the frequency, each peak being less of an issue. Same for each pair of walls. Angles are hard, ask a pro with a computer simulation

Half the frequency of the first peak gives you the frequency of the first dip, plus the ODD multiples of the first dip

14 feet between walls gives you peaks at 40, 80, 120, 160... and dips at 20, 60, 100, 140...

Do a search for "modecalc" and "download" or I'll post a link tonight.


M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8
Re: EP500 Freq Response Help
#97587 06/10/05 02:12 AM
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Alberto, John explained it very well(I often use 560/one length as being a bit easier mental calculation)and you can find all sorts of info, including calculators, by Googling a topic such as "room modes". An example is this article.

A factor totally separate from room modes leading to peaks are suckouts caused at 1/4 wavelength from a room surface or 1/2 wavelength between drivers of separate speakers playing the same frequency.

So, what we have are players and amplifiers(and even wires!) doing an essentially flawless job, and speakers such as Axiom which are quite accurate in their response, but then the room screws things up.


-----------------------------------

Enjoy the music, not the equipment.


Re: EP500 Freq Response Help
#97588 06/10/05 02:19 AM
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axiomite
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>>or 1/2 wavelength between drivers of separate speakers playing the same frequency

Whoops, I had forgotten about that one. Thanks !!


M60ti, VP180, QS8, M2ti, EP500, PC-Plus 20-39
M5HP, M40ti, Sierra-1
LFR1100 active, ADA1500-4 and -8

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