Axiom Home Page Forums General Discussion Technical Questions m80's frequency response

Today I performed a frequency sweep on my m80's along with my av123 MFW-15 subwoofer. I ploted the frequecy response. I was shocked by the very uneven frequency response that was produced across the frequency range of 20hz up to 200hz.

There were peaks as high as 90db at 130hz and the lowest point was 57db at 97hz. That is an amazing 33db variation between maximum and minimum values.

Here I was thinking that my speakers were producing a very high quality smooth response across the frequency spectrum.

I have come to the conclusion that there are several possibilities as to why I have such a poor frequency response.

Either:
1. The audyssey calibration of my speakers is not doing the job properly. I have an Onkyo 875 amp, my front speakers are set to large, calibration resulted in my m80's being automatically set to full range.

or
2. The characteristics of my room have devasted the natural frequecy response of my m80's. I have solid timber floors (not ideal) and the room is large (20 ft x 45ft.) Is there anything I can do to correct any room related problems such as using bass traps?

or
3. My Onkyo 875 has a poor frequency response with the 4 ohm load of my m80's.

or
4. My speakers are faulty.

Can someone please shed some light as to what they believe is my most likely problem here??

Most of the problem is going to be your room. Room modes play hell with the frequency response from 20-200Hz. The first thing you can do is play with speaker/subwoofer and seat positioning. Just a few inches to a foot one way or another especially closer or farther from a room surface (including floors) can make a huge difference. Bass traps AFAIK are best for taming the FR between 100-200Hz loosing effectiveness the lower the frequency. Having multiple low frequency sources like more than one subwoofer and/or running your mains with “double bass” can also help even things out. Finally, EQ can help some though the EQ available is Audyssey is limited and has a hard time compensating for room modes across multiple seats since it has to come up with a compromise EQ solution. EQ for one seat especially with something purposed built to EQ low frequencies can have a profound effect. I’ve been testing SVS AS-EQ1 that Charles “CV” loaned me with fantastic results for a single seat but only marginal results across three seats but it only works for the LFE channel.

http://www.axiomaudio.com/boards/ubbthreads.php?ubb=showflat&Number=307389&fpart=1

Another possible issue you are having is with the crossover point between the M80s and the sub depending on how you have that set up.

Also, I’ve never seen a FR graph for the MFW-15 so it’s possible that’s also contributing but I‘m just speculating here.

There are several good articles here:

http://www.axiomaudio.com/newsletter_index.html

And much more info out on the internet that can help you with positioning and deciding if room treatments, multiple subs and EQ might help you.

Just wondering if you ever noticed any issues with the quality of the sound you’re hearing or is the first time you noticed something when you measured it.

Cheers,
Dean

What equipment, software, cd/dvd did you use for this test?

Thanks for your reply Dean. When listening to music I have sensed that I was lacking some mid bass possibly around 100Hz. My measurements confirmed this. I have just changed the receiver settings for the front speakers changing the setting from full range to 80hz and performed the test again. I have a dramatic improvement now.
Do my results below appear to be acceptable:
30 hz 88 db
31 hz 90 db
32 hz 91 db
33 hz 91 db
34 hz 92 db
35 hz 93 db
36 hz 92 db
37 hz 92 db
38 hz 92 db
39 hz 91 db
40 hz 91 db
41 hz 90 db
42 hz 90 db
43 hz 88 db
44 hz 86 db
45 hz 81 db
46 hz 77 db
47 hz 82 db
48 hz 85 db
49 hz 90 db
50 hz 94 db
51 hz 95 db
52 hz 95 db
53 hz 95 db
54 hz 94 db
55 hz 92 db
56 hz 91 db
57 hz 91 db
58 hz 92 db
59 hz 92 db
60 hz 93 db
61 hz 93 db
62 hz 92 db
63 hz 90 db
64 hz 88 db
65 hz 85 db
66 hz 80 db
67 hz 77 db
68 hz 80 db
69 hz 82 db
70 hz 86 db
71 hz 88 db
72 hz 89 db
73 hz 89 db
74 hz 89 db
75 hz 88 db
76 hz 86 db
77 hz 82 db
78 hz 78 db
79 hz 77 db
80 hz 78 db
81 hz 80 db
82 hz 81 db
83 hz 83 db
84 hz 83 db
85 hz 83 db
86 hz 83 db
87 hz 83 db
88 hz 83 db
89 hz 84 db
90 hz 84 db
91 hz 85 db
92 hz 85 db
93 hz 85 db
94 hz 85 db
95 hz 84 db
96 hz 84 db
97 hz 84 db
98 hz 82 db
99 hz 82 db
100 hz 81 db
101 hz 81 db
102 hz 80 db
103 hz 80 db
104 hz 81 db
105 hz 82 db
106 hz 82 db
107 hz 82 db
108 hz 82 db
109 hz 81 db
110 hz 79 db
111 hz 76 db
112 hz 78 db
113 hz 78 db
114 hz 83 db
115 hz 86 db
116 hz 88 db
117 hz 89 db
118 hz 90 db
119 hz 91 db
120 hz 90 db
121 hz 90 db
122 hz 89 db
123 hz 85 db
124 hz 84 db
125 hz 81 db
126 hz 83 db
127 hz 87 db
128 hz 89 db
129 hz 89 db
130 hz 89 db
131 hz 89 db
132 hz 88 db
133 hz 88 db
134 hz 88 db
135 hz 89 db
136 hz 89 db
137 hz 87 db
138 hz 81 db
139 hz 77 db
140 hz 81 db
141 hz 84 db
142 hz 84 db
143 hz 84 db
144 hz 83 db
145 hz 82 db
146 hz 81 db
147 hz 78 db
148 hz 79 db
149 hz 83 db
150 hz 85 db
151 hz 87 db
152 hz 89 db
153 hz 90 db
154 hz 91 db
155 hz 91 db
156 hz 91 db
157 hz 90 db
158 hz 89 db
159 hz 88 db
160 hz 87 db
161 hz 86 db
162 hz 85 db
163 hz 82 db
164 hz 80 db
165 hz 82 db
166 hz 86 db
167 hz 88 db
168 hz 88 db
169 hz 88 db
170 hz 88 db
171 hz 86 db
172 hz 84 db
173 hz 80 db
174 hz 76 db
175 hz 68 db
176 hz 70 db
177 hz 78 db
178 hz 80 db
179 hz 80 db
180 hz 78 db
181 hz 76 db
182 hz 77 db
183 hz 80 db
184 hz 82 db
185 hz 84 db
186 hz 85 db
187 hz 86 db
188 hz 86 db
189 hz 86 db
190 hz 84 db
191 hz 78 db
192 hz 75 db
193 hz 74 db
194 hz 70 db
195 hz 70 db
196 hz 77 db
197 hz 82 db
198 hz 87 db
199 hz 89 db
200 hz 90 db

I used some mp3 files from
http://www.realtraps.com/test-cd.htm

The equipment I used was a radio shack SPL meter. I Set the weighting to 'C' and used 'fast' response mode. I Sat the SPL meter at my seated ear height and measured the readings at each frequency.

I'd definitely try it with Audyssey off, at least for comparison purposes.

If you look at the 20Hz to 100Hz range your variation is 77dB to 95dB or about 18dB which is the same swing (different frequencies) that I’m getting on the “before curve” measured by the SVS AS-EQ1 for just the subwoofer in my room. Also, unless I missed a reading it looks like the largest swing from 20Hz to 200Hz is about 25dB from 70dB to 95dB which IMO looks similar in magnitude to what I’m seeing in my room. So I would say that your room is already looking better than mine.

As for what’s acceptable to you only your ears can determine that and now that you are measuring the FR the numbers are also going to start playing tricks on your head. I suggest doing some serious listening along with the measurements while continuing to tweak the existing setup you have. If you have some headphones that are reasonably flat from 200Hz to down below 100Hz that might be a better way to gauge how the FR of your speaker should sound w/o the room in the equation since I’ve noticed using both Audyssey and the AS-EQ1 that a few (+/- say 3) dB improvement here and there is hard to make out under real listening conditions.

Eventually you may want to consider room treatments to take care of the 100Hz to 200Hz range if tweaking speaker/seating placement doesn’t help enough. For the below 100Hz range multiple subwoofers is probably your best bet, and you’ve got a pretty big room so a little extra dB there might also help. Only after tweaking placement and using room treatments and multiple subs would I consider going beyond the EQ already available in your receivers Audyssey. IMO even a dedicated subwoofer EQ system like the AS-EQ1 can’t tame the low frequencies across multiple seats very well. Should know more today on how it performs with multiple subs as Sean is coming over with two of his for some testing.

Like Ken said try measuring with Audyssey off. When tweaking placement turn Audyssey off since it’s applying correction for that last setup it measured. Also, it’s better to find the best placement for you speakers and subwoofer and then run Audyssey. While Audyssey can help some people a lot it works best if you give it as much help as possible.

Hopefully some of our experts on this subject will chime in soon as most of my knowledge on this is still theoretical and several people here have done much more practical application in this area than I have.

Cheers,
Dean

Once you start measuring the tweaking will never end. Stop measuring and worrying about it and just enjoy the sounds eminating from your speakers.

It is definately the room. For bass trapping to be effective, you need to apply a fair bit, all 4 corners floor to ceiling if you can.

It's the room.

Yeah, just ask Mark.

Because references to Mark's room never get old. Not like Jack.

Because references to Jack's age are always as welcome as a hello from Amie.

Drew, 3. is a no and 4. was a "highly unlikely" that changed to a no with the results of your second test with an appropriate crossover for the M80s. 2. is more on target, although "devastated" is a bit strong. Good room EQ, such as Audyssey MultEQ, can help significantly. Re 1., Audyssey was doing the job that the settings in the 875 required. Specifically, for that model, as long as good response to 80Hz was measured, Onkyo required that the setting be "Full Range". Dr. Kyriakakis has pointed out that this is unrealistically high and suggested that the manufacturers use a 40Hz criterion(which Onkyo now does)or even better, delete any provision for "Full Range" or "Large" settings when a sub is in use.

The results from above 80Hz in your second test look pretty acceptable, considering how difficult room modes can be. So, change the setting from Full Range to the 80Hz crossover following running Audyssey.

does anyone know where I can get blank templates I can print off to plot frequency/response measurements ?

I've made some.

I can send you a .PDF if you PM me your email address!

Click on the RABOS graoh worksheet link here:

http://www.infinitysystems.com/home/products/product_detail.aspx?prod=IL60BLKL

or, just make your own in Excel.

I have an excel spreadsheet that I enter the data on one tab and a graph is created from that data, now where did I place that spreadsheet. hhhhmmm

Mark's has Buffy The Vampire watermarks on it, just so you know.

Those are Buffy The Vampire SLAYER watermarks... She's a slayer, not a vamp!

Well, I heard she was in Cruel Intentions...

Eh, most of the time.

Must have been subliminal.
My nephew describes her as "Vampolicious". He has a thing for Goth chicks and says she doesn't look goth but is deserving of the title by association.